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Mini-Reviews in Organic Chemistry, 2013, 10, 281-301 281
1570-193X/13 $58.00+.00 © 2013 Bentham Science Publishers
Application Progress of Recent Advances in Some Copper Catalyzed Coupling Reactions
Sunil U. Tekalea*, Vivekanand B. Jadhav
a, Vijay P. Pagore
a, Sushma S. Kauthale
b, Digambar D.
Gaikwadb and Rajendra P. Pawar
b
aDepartment of Chemistry, Shri Muktanand College, Gangapur - 431 109 (MS) India
bDepartment of Chemistry, Deogiri College, Station Road, Aurangabad - 431 005 (MS) India
Abstract: Different cross-coupling reactions for the formation of biologically important motifs and intermediates in or-
ganic synthesis using various suitable copper catalysts are reviewed. These include C-C, C-N, C-O, C-S heteroatom bond
forming, cyclization and other miscellaneous reactions catalyzed by elemental copper, copper salts, CuI, Cu (OTf)2, CuBr,
Cu2O etc. The use of copper reagents instead of palladium catalysts and ligands seems to be advantageous from the com-
mercial point of view. The methods described herein afford the products in excellent yield without using expensive and
moisture/air sensitive palladium catalysts, ligands and reagents.
Keywords: Copper catalysts, Cross coupling reactions, Ligands.
1. INTRODUCTION
The metal copper and its alloys are extensively used by
mankind since thousands of years. Copper (derived from the
Latin word cuprum) is a first-row transition metal that exists
mainly in (I) and (II) oxidation states. The Cu (II) (Cu2+
) ions
are soluble in water. In sufficient amounts, copper salts can
be poisonous to bacteria, fungi and higher living organisms
too. However, despite universal toxicity at higher
concentrations, the copper (II) ion at lower concentrations is
an essential trace nutrient to all higher plants and animal life.
In animals it is widely dispersed in tissues, liver, muscle and
bone. It serves as a co-factor in various enzymes and copper-
based pigments.
Copper is a coinage transition metal in the field of co-
ordination chemistry and catalysis that constitutes the heart
of organometallic chemistry. One of the most important
striking features of transition metals is the variable oxidation
states due to which they show efficient catalytic activity.
Many copper reagents are widely utilized as catalysts for
numerous organic reactions. Transition metal catalyzed
coupling reactions are the important tools in synthetic
organic chemistry to construct C-O, C-N, C-C and C-S
bonds and several other miscellaneous reactions.
Recently the copper reagents are replacing the palladium
catalysts which are limited for industrial applications mainly
due to high costs. The Pd catalyst and ligands have restricted
applicability due to their expensiveness, air and moisture
sensitiveness [1].
Nowadays, the copper mediated organic reactions have
become a significant and interesting area of research in the
scientific community due to versatile nature of the copper
*Address correspondence to this author at the Department of Chemistry,
Shri Muktanand College, Gangapur - 431 109 (MS) India; Tel: +91
(02433)221342; Fax: +91 (02433) 221342;
E-mail: [email protected]
catalysts. They are mainly employed in the Ullmann and
Buchwald type of protocols.
The classical Ullmann reaction which encompasses the
synthesis of diphenyl amines, diphenyl ethers and diphenyls
normally requires the conditions of high temperature under
which many functional groups are not tolerated hence has
limited utility. It also requires stoichiometric amounts of the
copper catalysts which on scale up process poses the
disposal problem. Further DMF is the conventional solvent
for this reaction whose removal from the reaction mass is
tedious. So attempts are being made by the scientific
community to use catalytic quantities of copper reagents
instead of stoichiometric amounts. Studies are directed
towards the investigation to develop novel protocols using
copper catalysts along with a combination of suitable base
and ligand under relatively mild reaction conditions. The
commonly used solvents in the copper catalyzed
transformations include THF, DMF, DMSO, acetonitrile,
toluene while DIPEA (N,N-Diisopropylethylamine), Et3N
(triethylamine), Cs2CO3, K2CO3, K3PO4 etc. are the
frequently used bases. The ligands employed also play a
crucial role in such reactions, normally labile i.e. those
which can be displaced easily are used. Though the ligand
plays no direct role in the reaction its presence is essential
for the reaction to occur. It protects the Cu ion from
interactions which may degrade the reactants or form side
products and also prevents the oxidation of the Cu (I) species
to the Cu (II). The ligand may act as a proton acceptor and
hence eliminating the requirement of a base.
2. COPPER CATALYZED ORGANIC TRANSFOR-MATIONS
In the present review we would like to focus attention on
certain synthetic strategies using copper catalysts. Herein we
have categorized the copper catalyzed reactions into six
classes:
282 Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 Tekale et al.
i. C-Arylation (Ullmann protocol: C-C bond forming
reactions)
ii. N-Arylations/alkylation (Buchwald protocol: C-N
bond forming reactions)
iii. S-Arylation (C-S bond forming reactions)
iv. O-Arylation (C-O bond forming reactions)
v. Cyclization reactions and
vi. Miscellaneous reactions
2.1. C-Arylation (C-C Bond Forming Reactions)
Organic chemistry is the chemistry of carbon
compounds. Consequently; C-C bond forming reactions are
of much significance in synthetic organic chemistry. This
part of the present review concerns with different C-C bond
forming reactions catalyzed by various copper catalysts.
Dawei Ma et al. [2] developed an efficient method for the
arylation of active methylene compounds such as diethyl
malonate, ethyl acetoacetate etc using CuI/L-proline catalyst
(scheme 1). Among the various bases (Cs2CO3, K2CO3, NaH,
K3PO4) and solvents (toluene, dioxane and DMSO) used
for the optimization of reaction conditions; the base
Cs2CO3 in DMSO at 50 oC was highly useful. This protocol
was successful with aryl iodides as well as aryl bromides.
R
O
OEt
O
ArX CuI/L-proline
Cs2CO3, DMSO, 40-50oC
Ar
O R
O
OEt
X = I, Br,
R = Me, Ph, OEt
Scheme 1.
R X
-MgBr+
1) Cu(OTf)2
iPr2O, 25OC, 3h
2) H2, PtO2
R -
Scheme 2.
OAc n-BuMgI
14 mol% of (S)-1
Bu
S
Me
NMe2
Cu
(S)-1
*
(R)
Scheme 3.
Cu(OTf)2 was reported as a convenient catalyst for the
reaction between aryl halides and cyclopentadieny-
lmagnesium bromide reagent in isopropyl ether [3]. This
constitutes a method for the synthesis of substituted
cyclopentane ring systems (scheme 2). Allylic substrates are
important for many addition reactions. G. J. Meuzelaar et al. [4]
catalyzed asymmetric allylic substitution reaction with
Grignard reagent by a chiral arenethiolatocopper (I) complex
(scheme 3).
The cross coupling reaction between aryl iodides and
bromides with ethyl acetoacetate using CuI catalyst in the
presence of N-methyl glycine ligand is documented in
literature [5]. The various solvents (THF, toluene, dioxane)
and ligands (L-cystein, glycine, sacrocine etc) were tried for
the reaction (scheme 4). Jin-Heng Li et al. reported an
efficient protocol using Cu2O nanoparticles/ ionic liquid [6]
as a novel combination for the Stille coupling reaction. They
used various catalysts, ligands and ionic liquids for
optimizing the reaction and demonstrated Cu2O
nanoparticles/P(o-tol)3/TBAB system as the efficient and
reusable system for Stille coupling (scheme 5). The reagent
required for the present protocol being readily available and
inexpensive, the Cu2O nanoparticles/P(o-tol)3/TBAB system
is superior over the application of palladium catalysts in
Stille coupling. Regioselective and enantioselective allylic
alkylation using a catalytic amount of copper bromide (1 mol
%) and dialkylzinc in the presence of phosphoramidite
ligand was successfully developed by Ben L. Feringa and
coworkers [7] (scheme 6). The catalyst CuBr was generated
in situ during the reaction from CuBr·Me2S source. F. Y.
Kwong et al. [8] reported -arylation of malonate esters
using aryl iodides or bromides, a catalytic amount of CuI (5
mol%) in the presence of 2- picolinic acid as the ligand and
Cs2CO3 base at room temperature (scheme 7).
R
X
R'Sn(n-Bu)3
Cu2O, P(o-tol)3
KF,TBAB, 125-130 oC
R
R'
Scheme 5.
The effect of ligand was also studied during optimization
of the reaction conditions. Since mild reaction conditions
were used many functional groups such as methoxy, nitrile,
fluoro were found to be tolerated.
K. A. Jorgensen et al. [9] demonstrated an enantio-
selective and efficient nitro-aldol (Henry) reaction using a
catalytic amount of Cu(OTf)2 and triethyl amine base to form
the corresponding -nitro- -hydroxy esters in excellent yield
(scheme 8). Benzoxazoles can be arylated at the C-2 position
using CuI in DMF as a solvent in the presence of lithium or
potassium t-butoxide base [10]. Although it requires higher
temperature, the reaction is rapid for the arylation purpose
(scheme 9). Iron salt/ CuI catalyzed reaction of aryl iodides
with terminal alkynes was reported [11] (scheme 10). CuI
I O
O
O
RR
O
O
K2CO3, CuI
N-methyl glycine,
reflux, 48h
dioxane
Scheme 4.
Recent Advances in Some Copper Catalyzed Coupling Reactions Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 283
was used as an efficient catalyst for the stereospecific
synthesis of ethyl (2Z)- 2, 3-difluoro-4-oxo-substituted 2-
butenoates from (E)-2,3-difluoro-3-stannylacrylic ester and
acid chlorides by D. Burton [12]. This was the first synthetic
route for cis-difluoro-substituted analogues of 4-oxo-2-
butenoates (scheme 11). G. Sekar reported the arylation of
alkynes from aryl halides and terminal alkynes using the
Sonogashira type cross-coupling reaction (scheme 12) [13].
2.2. N-Arylations/alkylation (Buchwald Protocol: C-N
Bond Forming Reactions)
N-aryl amines including many nitrogen containing
heterocycles such as imidazole, pyrazole etc motifs are
biologically and pharmaceutically interested compounds
[14]. Buchwald and others have reported several protocols
for the formation of C-N bonds [15, 16]. The C-N cross
coupling between aryl iodides and amines using the Buchwald
Br
Et2Zn
2 mol% L
1 mol % CuBr.Me2S
diglyme,
-40 oC, 18 h
Et
77% ee
L =
O
O
P
Ph
Ph
Scheme 6.
X
REtO
O
OEt
O
R
O OEt
O
OEt
5 mol % CuI
10 mol % L
Cs2CO3, dioxane
r.t.
X = I, Br
N
O
OH
L = 2-picolinic acid
Scheme 7.
R COOEt
O
R COOEt
OH
NO2
MeNO2
20 mol% Cu(OTf)2, L
20 mol % Et3N
N
OO
N
t-But-Bu
L =
Scheme 8.
O
N10 mol% CuI
PhX, DMF, base
140 oC,10 minO
N
Ph
Scheme 9.
I
Fe salt/CuI
Cs2CO3 (2 eq)
NMP, 140 oC
Scheme 10.
284 Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 Tekale et al.
protocol under ligand free condition in the presence of
copper oxide nano particles is documented in literature [17].
The reaction can also be carried out in the atmosphere of air.
An important feature of this method is reusability of the
catalyst which is significant from economic point of view.
The catalyst showed remarkable activity without any much
loss of activity (scheme 13). CuBr was used as a catalyst for
the one pot synthesis of propargyl amines from aldehydes,
secondary amines and terminal alkynes using chiral (R)
Qinap ligand in toluene at room temperature [18]. However
the reactions required prolong time (scheme 14).
Anilinoanthraquinones can be obtained from the Cu (0)
catalyzed and microwave assisted synthesis from
bromaminic acid with aniline derivatives [19]. During the
reaction pH has to be maintained between 6-7 using
phosphate buffers. Initially the reaction was tried under two
conditions: i) CuCl, Na2CO3 and Na2SO3 in H2O at room
temperature for 8-24 h, or under reflux at 120 °C for 8-10 h
and ii) CuSO4 and Na2CO3 in H2O at 120 °C for 12-48 h. It
was observed that no products or only poor yields could be
obtained by these strategies. Further there was formation of
1-amino-4-hydroxy-9, 10-dioxo-9, 10-dihydroanthracene 2-
sulfonate as the undesirable product (scheme 15).
F. Y. Kwong and coworkers [20] reported N-arylation of
hydrazides using copper (I)-picolinic acid as an effective
catalytic system (scheme 16). Among the several solvents
(dioxane, THF, tert-amyl alcohol, toluene, DMF) and bases
(Na2CO3, K2CO3, LiCO3, NaOt-Bu etc.); the combination of
Cs2CO3/DMF provided the highest yield of the products.
Stephen L. Buchwald [21] described a highly efficient and
selective route for the N-arylation of amines using aryl
bromides. N, N-diethylsalicylamide was used as the effective
ligand and potassium phosphate as the base in this reaction
(scheme 17). Usually the cross coupling reactions carried out
by conventional methods require more reaction time which
can be reduced to few minutes using microwave irradiation.
Such a microwave promoted C-N cross coupling reaction of
aryl halides with amino acids was investigated by Sivan
Velmathi [22] using copper catalyst (scheme 18). The N-
arylation of azaheterocycles like benzimidazole with aryl
SnBu3
F
COOEt
FF
COOEt
F
O
RRCOCl
10 mol % CuI
DMF, r.t.
Scheme 11.
R R'I
R R'
Ligand-CuI (20 mol%)
K2CO3, DMF, 140 oC
NHBn
NHBn
Ligand
Scheme 12.
XN
R'
R1.26 mol% CuO nanoparticles
1.12 eq RR'NH
1 eq KOH, DMSO,
80-110 oC, air,1.2-29 h
Scheme 13.
R H
O R"
HNR2'5 mol % CuBr, MS 4A
5.5 mol % (R)-Quinap
toluene, r.t.1-6 days
R
NR'2
R"
N
PPh2
(R)-Qinap
Scheme 14.
Recent Advances in Some Copper Catalyzed Coupling Reactions Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 285
halides can be performed with copper catalysts such as
Cu(I)I and Cu(II)(OAc)2·H2O using K2CO3 base and 4,7-
dichloro-1,10-phenanthroline as the ligand in NMP solvent
(scheme 19) [23].
The reductive amination of bromonaphthyridines can be
carried out at room temperature in the presence of copper-
catalysts in aqueous ammonia [24]. The effective method for
preparation of alkyl 2, 7-diaminonaphthyridine mono-amides
can be carried out by performing the amination in ethylene
glycol/aqueous ammonia solution at room temperature in the
presence of Cu2O. This provides an important access to the
synthesis of nonsymmetrical 2, 7-diamido-1, 8-
naphthyridines (scheme 20). A C-N cross coupling reaction
between aryl halides and amines using Cu (I) catalyst and
pyridine based ligand in DMF as the solvent was carried out
by Wanzhi Chen et al. [25]. Among the various ligands and
copper catalysts; the combination of CuI and 1,3-di(pyridine-
2-yl)propane-1,3-dione was found to be efficient for C–N
coupling reactions to afford various N-arylated products in
good to excellent yields (scheme 21).
O
O
NH2
Br
SO3NaNH2
R
O
O
NH2
HN
SO3Na
R
Cu(0), pH 6-7
MW, 2-20 min
Scheme 15.
Me
Me I
HN
Boc
NH2
Me
Me N
Boc
NH2
CuI (5 mol%)
2-picolinic acid (10 mol%)
Cs2CO3( 3 mol %)
N2, DMF, 80 oC,
24 h
Scheme 16.
Br
R HN
R'
R''
R
NR''
R'
NEt2
O
OH
CuI, L
K3PO4
L =
Scheme 17.
X
Y
R OH
OH2N
Y
HN COOH
R
CuI/K2CO3, DMF
MW, 15-25 min, 140 oC
Scheme 18.
NH
N
Br
NN
ClCl
Cu(I)I or Cu(II)(OAc)2·H2O
K2CO3, 125 oC, NMP
N
N
Scheme 19.
N N NH2NH
R
O
N NH
ONH
R
Oi) PBr3, 110 oC
ii) Cu2O
amination, r.t.
10-87%
Scheme 20.
286 Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 Tekale et al.
ArX NuH ArNuCuI (10 mol %), L (10 mol%)
K2CO3, DMF, 110 oC
N
O O
N
L =
X = Br, Cl
Ar = aryl, heteroaryl
NuH = N- heterocycles
Scheme 21.
N
Br
HN
S
R2
OO
R1
CuI/L, K2CO3, DMF
110-120 oC, 40h
N
N
S
R1
R2O
O
N
O O
N
L =
Scheme 22.
HN O
YX
N O
Y
X
I
20 mol % CuI
40 mol % L
2 eq K3PO4
1,4-Dioxane, 110°C
16-24 h
Scheme 23.
S
IH NHR1R2
S
NR1R2
N,N-dimethyl ethanolamine
10 mol % Cu metal
2 eq K3PO4.H2O
Scheme 24.
Different bromopyridines were successfully coupled with
sulfonamides by using CuI (20 mol %) and 1, 3-di (pyridin-
2-yl) propane-1, 3-dione (20 mol %) with K2CO3 (2 eq). The
proper solvent used was DMF and the reactions were carried
out at 110–120 °C [26]. The reactions required prolong time
for completion, nearly 36–40 h (scheme 22). C. S. Li [27]
demonstrated an efficient protocol for the Buchwald
coupling reaction of pyridine-2-ones with aryl iodides. N,
N’-dimethyl ethylene diamine ligand and K3PO4 base were
conveniently used for the reactions (scheme 23). The
presence of substituent affects reactivity of the halides. It
was observed that aryl iodides having electron withdrawing
groups react readily than the substrate without substituent
which in turn reacts faster than the iodides possessing
electron-donating groups. Thiophene ring is the central core
of many optoelectronic materials. Halothiophenes can be
aminated using copper metal catalyst, N, N-dimethylethanol-
amine ligand and potassium phosphate base [28] (scheme
24). Different amines including cyclic, acyclic, aromatic
reacted smoothly with halothiophenes.
Ar I HNR1R2
CuI(10 mol %)
Ligand (10 mol %)
K3PO4 or Cs2CO3
Ar NR1R2
Scheme 26.
Ar X HNR1R2
CuI (5 mol %)
2 eq HO(CH2)2OH
2 eq K3PO4
Ar NR1R2
80 oC, i-PrOH
Scheme 27.
R1
N
EWG
HKHMDS, CuI
R2Br
pyr, r.t.
R1
N
EWG
R2
Scheme 28.
COOR
Ar
2-NsNCl2/2-NsNHNa(2:1)
CuOTf (10 mol %)
Ar
COORCl
NH S
O
O
O2N
Scheme 29.
Cu(PPh3)3Br complex was used as a catalyst for the cross
coupling reaction of amines and aryl iodides in toluene at
100 oC by D. Venkataraman and coworkers [29] (scheme
25). The complex was stable to air and is soluble in many
organic solvents. The coupling of aryl iodides with amines,
amide and various nitrogen heterocycles using CuI catalyst,
K3PO4 or Cs2CO3 base in dioxane solvent at 110 o
C
temperature was reported by S.-K. Kang et al. [30]. The
reaction was complete within around 24 h to afford the
NH
R2
R1
I
R3
Cu-complex
base, toluene
110-120 oC
N
R1
R2
R3
N N
RRCu
Ph3P Br
R = H Cu(phen)(PPh3)Br
R = Me Cu(neocup)(PPh3)Br
Cu- complex
Scheme 25.
Recent Advances in Some Copper Catalyzed Coupling Reactions Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 287
products in 41-95% yield (scheme 26). The cross coupling of
alkyl amines and aryl halides utilizing CuI (5 mol %) in the
presence of ethylene glycol as the additive and potassium
phosphate base at 80 oC in isopropyl alcohol was reported by
Buchwald S. L. [31] (scheme 27). A common process for the
N-alkynylation of carbamates, ureas and sulfonamides using
copper iodide catalyst was reported by R. L. Danheiser [32].
Initially the amides were deprotonated with KHMDS and
then treated with CuI and an alkynyl bromide to afford the
corresponding alkynes in excellent yields (scheme 28). A
regioselective and stereo selective aminohalogenation of
cinnamates was successfully carried out [33]. The reactions
were carried out using 2-NsNCl2/2-NsNHNa as the nitrogen
and chlorine sources and copper (I) triflate as the catalyst
(scheme 29). The synthesis of 1, 2, 3-triazole derivatives of
2-indolones can be accomplished using a catalytic amount of
CuI (scheme 30) [34].
CuO/AB i.e. CuO nanospheres immobilized on acetylene
black (AB) was demonstrated as a versatile catalyst for the
N-arylation of different amines in excellent yield by Park
and coworkers [35] (scheme 31). Boshun Wan [36]
synthesized oxime-phosphine oxide ligand which was found
to be highly active in the copper-catalyzed N-arylation of
alkyl amines and various N–H heterocycles under mild
N
HOZ
O
R1
R2
N
HOZ
O
X
R2
N N
NBn
NaN3, BnBr, CuI, Et3N
tBuOH:H2O, 6 h
R1 = CH2CCH, CH2OCH2CCH
R2 = H, CH3, Br, F
Z = CN, CO2Me, CO2Et, CO2Bu
X= CH2, CHOCH3
Scheme 30.
X
R1HN
R2
R3
5 mol% CuO/AB
KOtBu, toluene
180 oC, 18 h
N
R1
R2
R3
Scheme 31.
I
R1
R2NH2
5 mol% Cu2O
20 mol% ligand
Cs2CO3
NHR2
R1
N
OH
P
O
PhPh
Ligand
Scheme 32.
Z
NH
X
Y
B(OH)2
Cu(OAc)2, Bipy
Na2CO3, DCM
70 oC, 2-6 hZ
N
X
Y
Scheme 33.
Br
R
N
HN
N
HN
NH
N
CuI, KF/Al2O3, 130-140 oC
1, 10-phenanthroline
N
RN
N
N
N
N
R
R
Scheme 34.
288 Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 Tekale et al.
conditions (scheme 32). The ligand was stable and the
reaction was successful under solvent free conditions. The
construction of cyclopropyl ring is an important and much
difficult task. The N-alkylation of several nitrogen
containing heterocycles such as azoles, amides,
sulfonamides, pyrroles etc was carried out with cyclopropyl
boronic acids in excellent yield (scheme 33) [37].
R. Hosseinzadeh et al. [38] reported KF/Al2O3 as an
efficient base for the N-arylation of pyrazole, imidazole etc
with aryl bromides using 1, 10-phenanthroline ligand and
CuI catalyst (scheme 34). Mild reaction conditions, simple
and inexpensive catalyst and air insensitiveness of the
catalyst are the striking features of the catalyst. Further
strong basic character of the system makes this protocol
attractive to replace organic bases in synthesis. The
amidation of allylic and benzylic C-H bonds using copper
triflate catalyst can be carried out successfully [39] (scheme
35). The amidation was successful with both primary and
secondary amides in excellent yields. O-Acyl ketoximes can
be converted into N-substituted imines by treating them with
boronic acids or organostannanes in the presence of copper
catalysts [40] (scheme 36).
2.3. S-Arylation (C-S Bond Forming Reactions)
Diaryl sulfides constitute an important class of structural
units present in many valuable intermediates for organic
synthesis and biologically active compounds [41]. Aromatic
compounds with a C-S bond constitute a privileged class
those have attracted the attention of chemists in
pharmaceutical and medicinal chemistry. The cross coupling
reaction between aryl halides and thiols is a simple way for
C-S bond formation. Among the several approaches
suggested, transition metal catalyzed reactions are the
important routes for the synthesis of diaryl sulfides [42].
From literature survey; many copper catalysts are useful for
such reactions.
Synthesis of thioethers by the cross- coupling of
thiophenols with aryl halides using CuI catalyst,
benzotriazole ligand and potassium t-butoxide base was
reported by A. K. Verma and coworkers [43] (scheme 37).
The advantages of this method are tolerance of several
functional groups, simple work up and readily available low
cost catalyst. Jin-Heng Li et al. [44] reported the first silicon
reagent employed solvent-free protocol for the conversion of
disulfides into sulfides with aryltrimethoxysilanes in the
presence of CuI/TBAF/2-(di-tert-butylphosphino) biphenyl
(scheme 38). The reaction can be carried out even in the
presence of O2 atmosphere and moderate to good yields were
obtained by this method.
Ar S
S Ar
Ar'Si(OMe)3
CuI, L, air
TBAF, 100 oC
Ar S
Ar'
PtBu2
L =
Scheme 38.
The conversion of aryl boronic acids into alkyl-hetero
aryl sulfones using copper acetate can be easily carried out
[45]. Sulfinate salts were utilized as the coupling partners in
these reactions. Among the various ligands tried for
optimizing the reaction conditions, 1-benzyl-imidazole was
found to be the best ligand under these conditions (scheme
39).
The combination of copper iodide/ cis-1, 2-
cyclohexanediol was used as an effective system for the
cross-coupling of alkyl or aryl halides with thiols in
R2
R1
NH
SR3
R4
O O Cu(OTf)2
1,10-phenanthroline
t-BuOOAc
4A MS, DCE
R2
R1
NSR3
R4
O O
Scheme 35.
R1 R2
N
R1 R2
N
R3OR' R3B(OH)2
R3Sn(n-Bu)3
or
Cu(I) or Cu(II)
DMF, Ar or air
50-70 oC
R' = Ac, COC6F5
R1, R2 = aryl, heteroaromatic, alkyl
R3 = aryl, alkenyl
Scheme 36.
SH
R1
R2
Br S
R1 R2
CuI (0.5 mol %) / L (1 mol %)
KO-tBu, DMSO, 100 oC
10-18 h
NH
N
N
L =
Scheme 37.
Recent Advances in Some Copper Catalyzed Coupling Reactions Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 289
excellent yield. The coupling was carried out using K3PO4
base and DMF solvent at 30 or 60 oC
(scheme 40) [46]. A
ligand-free synthesis of thioethers was carried out [47] using
a catalytic amount of Cu2O in DMSO/H2O solvent system.
Using this protocol, a number of diaryl sulfides and alkylaryl
sulfides were obtained in excellent yields (scheme 41). The
coupling reaction of disulfides and boronic acids was used
for an efficient synthesis of thioethers by N. Taniguchi [48]
using Cu metal catalyst and bipyridyl ligand. A major
disadvantage of this protocol is the requirement of excess of
boronic acid (3 eq) (scheme 42).
The synthesis of vinyl sulfides using the homogeneous
catalyst [Cu(phen)(PPh3)2]NO3 was described by D.
Venkataraman (scheme 43) [49]. The reactions proceeded
with retention of stereochemistry in good yield. The
synthesis of aryl sulfides from thiols and iodides was
reported [50] using 10 mol % CuI, 10 mol-% neocuproine
and NaOt-Bu base (scheme 44). Raul Martin et al. [51]
reported a method describing the S-arylation of arenethiols
with activated aryl chlorides using copper chloride catalyst
in the presence of ethylene diamine ligand as well as base.
The reaction required excess of ethylene diamine (4 eq).
Since the reactions were performed in water, it constitutes a
green and environment-friendly synthesis. This protocol also
allowed the coupling of sterically hindered aryl chlorides
(scheme 45).
The selective S-arylation of mercaptobenzimidazoles
using Cu(I) iodide catalyst and 1, 10-phenathroline ligand
was reported by Anandan Sambandam et al. (scheme 46)
[52]. A mild approach can be applied for the synthesis of
diaryl thioethers by the cross coupling reaction between aryl
halides and thiophenols catalyzed by CuI/L-proline in
biphasic system [53]. The reaction was carried out in the
presence of ATPS at 80 o
C to afford the corresponding
thioethers in excellent yields (scheme 47). An efficient
copper-catalyzed protocol was documented in literature for
the S-Arylation of thiols with aryl bromides and chloride
(scheme 48) [54].
A two step method for the synthesis of diaryl ethers
utilizing xanthate precursor instead of thiols was developed
by G. Sekar [55]. The strategy involves treatment of aryl
iodides and potassium ethyl xanthogenate in the presence of
copper acetate and ligand in DMF at 105 o
C followed by
reaction with another halide using KOH base (scheme 49).
The synthesis of alkyl-aryl thioethers through the copper
triflate catalyzed cross coupling reaction using BINAM
ligand and Cs2CO3 base (scheme 50) is reported in literature
[56].
A simple and novel method for the methylthiolation of
aryl halides was developed using DMSO as the source of
sulfur and suitable copper catalyst (scheme 51) [57]. For aryl
iodides 10 mol % CuBr and for bromides, 10 mol % CuI
were used. During the reactions many functional groups
including formyl, nitro, chloro, fluoro, methoxycarbonyl etc
remained intact.
The S-arylation of thiophenols can be carried out in the
presence of strong basic condition such as KOH/DMSO
(scheme 52) [58]. Thioethers were also obtained under base
free conditions from the cross-coupling reaction between
boronic acids and N-thioimides in tetrahydrofuran at 45-50
oC (scheme 53) by Lanny Liebeskind et al. [59]. Palomo and
co-workers [60] described CuBr catalyzed efficient synthesis
Y
SH
R
Cl
EWG
NH2H2N
10 mol % CuCl
H2O, 1200C
Y = C, N
R
S
Y
EWG
Scheme 45.
Ar B(OH)2S
O
ONaR
Cu(OAc)2 (20 mol %)
1-Bn-imidazole (40 mol %)
4 A MS, DMSO
60oC, 22 h
R S Ar
O
O
Scheme 39.
R I HS-R'
0.1 eq CuI
0.2 eq L
1.5 eq K3PO4
DMF 30 or 60 oC
0.5-8 h
SR R'
OH
OH
L =
Scheme 40.
Ar I HS R
1.1 eq
5 mol % Cu2O
2 eq KOH
DMSO/H2O(4:1)
80 oC, 24 h
Ar S R
Scheme 41.
S
S
ArAr (OH)2B-R
5 mol % Cu
5 mol % bipyridine
air, DMSO/H2O (2:1)
100 oC, 12-48 h
S
Ar R
Scheme 42.
R SH I
R'
5 mol % [Cu(phen)(PPh3)2]NO3
1.5 eq K3PO4
toluene, 110 oC
4-24 h
S
R'R
Scheme 43.
10 mol % CuI
10 mol % neocuproine
1.5 eq NaOt-Bu
24 h
S
Ar RAr-I HS-R
toluene, 110 oC,
Scheme 44.
290 Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 Tekale et al.
of diaryl ethers with phosphazene base in toluene under
reflux condition within 1-4 hours (scheme 54).
2.4. O-Arylation Reactions
The copper catalyzed Ullmann types of reactions are
traditional routes for the synthesis of diaryl ethers [61].
These normally require harsh conditions and stoichiometric
amount of the copper reagents. Here is a summary of certain
attempts conducted by different research groups to develop
mild reaction protocols using catalytic amounts of the copper
catalysts.
Dawei Ma [62] reported a simple CuI catalyzed and N,
N-dimethyl glycine promoted synthesis of diaryl ethers from
the Ullmann coupling of aryl halides and phenols as the
R N
HN
SH
R N
HN
S
R N
N
SH
i) CuI
ii) 1,10-phenanthroline
NR
R = H, OCHF2
X
(X = Br, Cl)
Scheme 46.
R1
XHS
R2 R1
S
R2
X = Br,Cl
CuI/L-Proline
ATPS, 80 oC
Scheme 47.
X
R1
HS
R2
20 mol % CuBr
20 mol % L
2 eq Cs2CO3
DMF, 130 oC, 48 h
S
R1 R2
Scheme 48.
R
I
KS
S
OEt
S OEt
S
R
S
Ar
NH2
NH2L =
Cu(OAc)2, L
DMF, 105 oC
KOH
ArXR
Scheme 49.
R
X
R
S
R'
NH2
NH2
BINAM, Cu(OAc)2,
Cs2CO3, DMF, 110 oCR'SH
BINAM
Scheme 50.
Recent Advances in Some Copper Catalyzed Coupling Reactions Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 291
synthons. The reactions were carried out by using Cs2CO3
base and dioxane as the solvent under relatively mild
conditions (scheme 55). This protocol is applicable to a wide
range of compounds bearing different functional groups.
Cu(I)/1-butylimidazole was found to be an efficient catalytic
system for the practical synthesis of diaryl ethers through the
coupling reaction of aryl bromides and suitable phenols [63]
(scheme 56). Diaryl ethers were obtained in excellent yield
[64] from aryl iodides and phenols using copper iodide and
Cs2CO3 under microwave irradiation (scheme 57).
The utility of copper nano-particles for the Ullmann
protocol involving the synthesis of diaryl ethers in excellent
yields was made by Mazaahir Kidwai et al. [65]. This
protocol avoids the use of a heavy metal co-catalyst. The
copper nano-particles being reusable, it is an economic
process. Further the reactions were carried out without the
use of additives, the method needs low catalyst loading and
the conversions take short reaction-times (scheme 58).
Aryl iodides and phenols were cross-coupled through
Ullmann type coupling reactions using BINAM–Cu(OTf)2
complex [66] in catalytic amount under mild reaction
conditions (scheme 59).
2.5. Cyclization Reactions
Miquel A. Pericas et al. [67] described the synthesis of
1,2,3-triazoles using a copper catalyst based on Tris
(triazolyl)methanol-Cu(I) structure (scheme 60). 1,2,3-
triazoles can be synthesized from the 1,3-dipolar cycloaddition
reaction between aryl azides and calcium carbide by using
copper iodide as the catalyst. Calcium carbide was employed
as a source of acetylene in this reaction. The reaction was
carried out in acetonitrile-water solvent mixture (scheme 61)
[68]. Triazoles can be synthesized using Cu/AlO(OH) as an
efficient heterogeneous catalyst at room temperature [69].
The reaction can be performed even in the absence of any
additive (scheme 62). Copper nanoparticles supported on
activated charcoal were used as a novel heterogeneous
catalyst for the same purpose (scheme 63) [70].
The utility of heterogeneous catalysts predominates over
the homogeneous ones due to several advantages such as
simple recovery, their reusability etc. 1,2,3-Triazoles were
X
Y Y
HO
Z
O
Z
X= I, Br
CuI/ N,N-dimethyl glycine
Cs2CO3, dioxane, 90 oC
Scheme 55.
BrHO
O
Cu(I)/N-alkyl imidazole
Scheme 56.
OH I
But
CuI, Cs2CO3
MW
O
But
Scheme 57.
OH I
10 mol % Cu-np
Cs2CO3, CH3CN
50-60 oC, N2, 1 atm
O
Scheme 58.
R
X
Me
S
Me
O[Cu]
ZnF, 150 oC
R
SMe
Scheme 51.
XSH S
R KOH/DMSOR
130 oC
Scheme 52.
R1B(OH)2 N
O
O
R2S R1-SR2cat. Cu(I)
THF, 45-50 oC
R1 = aryl, alkenyl
R2 = alkyl, aryl, heteroaryl
Scheme 53.
Ar I
R1
SNa
CuBr ( 20 mol %)
R1
S
Ar
B ( 2eq), toluene
reflux,1-4 h
P
N
P
NMe2
NEt
Me2N
NMe2
Me2N NMe2
B =
Scheme 54.
292 Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 Tekale et al.
regioselectivley synthesized from alkyl or benzyl halides,
sodium azide and terminal alkynes using silica supported
copper catalysts [71] (scheme 64). An important advantage
of the catalyst is the ease of separation by simple filtration
which can be studied for its catalytic reusability. Aromatic
amines can be efficiently converted into azides using t-butyl
nitrite and trimethyl silyl azide which on treatment with
terminal acetylene in the presence of CuSO4 and sodium
ascorbate cyclizes to yield the corresponding 1,4-
disubstituted-1,2,3-triazoles at room temperature [72]
(scheme 65). Kimberly D. Grimes [73] developed a method
for the synthesis of 1-heteroaryl substituted -1,2,3-triazole
derivatives from boronic acids and boronates or
trifluoroborate esters by converting them into azides as the
good leaving groups followed by cyclization to afford the
corresponding triazoles at room temperature (scheme 66). A
drawback of the present protocol is excess quantity of the
acetylene carboxylate ester required during the reaction. A
two step method was developed for the synthesis of several
heterocyclic compounds from Aza-Michael reaction based
on pyrazolone-triazole skeleton (scheme 67) [74]. The
thermal cyclization of azide and terminal alkynes results in
the formation of a regioisomeric mixture of anti and syn
1,2,3-triazoles which poses a separation problem whereas the
application for Cu(I) catalyst for the reaction gives
exclusively the anti isomer (scheme 68) [75, 76]. Stephen L.
Buchwald et al. [77] carried out the CuI catalyzed
conversion of 1, 4-dihalo-1, 3-dienes into pyrroles and
heteroaryl pyrroles using N,N’-dimethylethylenediamine
(DMEDA) at 80-100 oC (scheme 69). The reactions were
performed using K2CO3 or Cs2CO3 base. Under these
conditions several functional groups including esters, ethers, Boc-protected hydrazines, alkenes, heterocycles etc were
observed to remain intact.
Copper bromide was used as a catalyst for synthesis of
indoles and benzofurans by the cyclization reaction between
N-tosylhydrazones and terminal alkynes under ligand free
conditions [78] (scheme 70). X. Liu and coworkers [79]
reported heterocyclization of substituted ortho bromo/iodo
anilines with secondary amine, CS2 and CuCl2 as the
catalyst. With bromo substrates, the reaction required
slightly higher temperature as compared to the iodo (scheme
71). Different cyclic sulphonamides were synthesized by
copper-catalyzed intramolecular reaction of unsaturated
iminoiodinanes [80]. An important advantage of this method
is that the aziridines may be opened by various nucleophiles
such as methanol, thiophenol, allylmagnesium bromide,
benzylamine etc to give the corresponding substituted cyclic
sulfonamides (scheme 72). The first successful metal-
R X R'NaN3
catalyst
5 mol% Cu(I)
EtOH, reflux, 24h
N
N
N
R
R'
O
O
O
O
O
O
Si
Si
NH2
NH2
2g
1 mmole CuI, DMF, r.t., 4hX= Br,Cl
Catalyst preparation
Scheme 64.
Ar NH2
1.5 eq t-BuONO
1.2 eq TMSN3
CH3CN, r.t., 2 h
Ar N3
1 eq Ph
7 mol% CuSO4
14 mol % sodium ascorbate
CH3CN/H2O(10:1), r.t.
N
N
N
Ph
Ar
Scheme 65.
X OH
R R' R
O
R'
BINAM-Cu(OTf)2
(20 mol %)
Cs2CO3,
dioxane, 110 oC
X = I, Br
Scheme 59.
R N3 R'
N
N
NR
R'
0.25-.5 mol % catalyst
H2O, r.t., 4-18 h
R: Ar, alkyl, COOEt
R': Ph, Bn, C8H17
Scheme 60.
Ar N3 CaC2
0.3 eq CuI
0.3 eq Na ascorbate
MeCN/H2O (2:1)
r.t., 2-20 h
N
N
N
Ar
Scheme 61.
R N3R'Cu/ AlO(OH)
hexane,r.t.
1-24 h
N
N
N
R
R'
Scheme 62.
R N3 R'
N
N
N0.1 eq Cu/C
1.1 eq Et3N
dioxane 60 oC
10-120 minR'
R
Scheme 63.
Recent Advances in Some Copper Catalyzed Coupling Reactions Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 293
catalyzed cyclization of heterocyclic system with
alkenyldiazo compounds was made by M. Tomas et al. [81].
NH2
X
Z
S
N
NRR'Z
CS2, HNRR', CuCl2.2H2O
K2CO3, DMF
X = I, 110 oC
X = Br, 140 oC
Scheme 71.
S
N
O
OIPh
n
n = 0,1, 2.....
CuI or II, CH3CN
S
N
O
O
n
Scheme 72.
Copper bromide was used as a catalyst for the synthesis
of indolizines via the [3+2] cycloaddition of alkylidene
diazoacetate over the pyridine ring (scheme 73). (Fig. 1)
illustrates mechanism for the copper (I)-catalyzed regio-
selective synthesis of indolizines form alkenyldiazoacetates
and pyridine involving the [3 + 2] cyclization. The diazo
compound (1a) interacts with copper bromide to form the
copper (I) alkenylcarbene (1b) which reacts with pyridine
(1c) resulting in the species (1d). The intermediate (1d)
undergoes cyclization to the desired indolizine product (1g)
via the formation of intermediate (1f).
R = H, Me
N
R
COOEt
N2
N
COOEt
RCuBr (5 mol%)
DCM, r.t.
Scheme 73.
Ar B(OH)2
1.5 eq NaN3
0.1 eq Cu(OAc)2
MeOH, 50 oC,1-3 h
Ar N3
3 eq COOMe
10 mol % sodium ascorbate
25 oC, 16 h
N
N
N
Ph
Ar
Scheme 66.
R1
N
N
R2
COR
ROC
R2 N
HN
R1
NN
N
R3
N
HN
N
O
R1
R2
NN
R3
3.CH3OH
K2CO3
4. Dowex
HCRS(E)
1. CH2Cl2
TMSN3
Cu(OAc)2.H2O
2. H2O
Na-ascorbate
R3
Scheme 67.
R1-N3 R2
Cu (I)
neat, 80 oC
N
N
N
N
N
N N
N
N
R1
R2
R1
R2
R2
R1
antisyn
Scheme 68.
X
R1
X
R4
R2 R3
NBoc
R3R2
R1 R4
X = Br, I
NH2Boc
CuI (5mol%)
DMEDA
solvent, base
80-100 oC
Scheme 69.
XH
NNHTsR
R'
X R'
X = O, NH, NAc
CuBr (10 mol%)
Cs2CO3 (3 eq)
MeCN, 100 oC
R
Scheme 70.
294 Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 Tekale et al.
R
O
SO2Ph
N2
O
SO2Ph
R
CuCl, ligand,
NaBARF
CH2Cl2
Scheme 74.
The enantioselective (ee 82%) synthesis of
cyclopentanone derivatives can be carried out from -diazo-
-keto sulfones using copper catalyst (scheme 74) [82].
Benzoxazoles constitute an important class of organic
ring skeletons commonly observed in a number of
biologically active natural products and medicinally
significant compounds [83]. 2-Arylbenzoxazoles were
obtained from bisaryloxime ethers using copper triflate as a
catalyst in the presence of molecular oxygen (Scheme 75)
[84].
The plausible mechanism for the copper (II)-catalyzed
transformation of bisaryloxime ethers into 2-
arylbenzoxazoles is depicted in (Fig. 2). Initially the
bisaryloxime ether (2a) undergoes chelation with the copper
(II) catalyst to form the intermediate (2c) which rearranges to
(2d) followed by reductive elimination of copper to afford
the 2-arylbenzoxazoles (2e).
S. Cacchi et al. reported a novel synthetic route for the
synthesis of 2-aryl and 2-heteroaryl indole moieties from
NN+
N CuBr
N
N
Me
CO2Et
CuBr
Me
CO2Et
N2
Me
Cu-Br
CO2Et
Me
CO2Et
CO2Et
Me
CuBr
CO2Et
Me
CuBr
(1a)
(1b)
(1c)
(1d)
(1e)
(1f)
(1g)
Fig. (1). Mechanism for the Cu(I)-catalyzed synthesis of indolizines (Scheme 73).
H
NO
R1
R1
H
N
O
CuH
O
R2
CuL2
R2
L2Cu -LH
L
N
R2R1
-LH
R2
O
N
Cu
O R1
R2
R1, R2 = EWG, EDG
L = OTf
-Cu
R1
(2a) (2b)
(2c)
(2d)(2e)
Fig. (2). Mechanism for copper (II)-catalyzed synthesis of 2-arylbenzoxazoles from bisaryloxime (scheme 75).
Recent Advances in Some Copper Catalyzed Coupling Reactions Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 295
1-alkynes and o-iodotrifluoroacetanilide using the catalyst
[Cu(phen)(PPh3)2]NO3 in the presence of potassium
phosphate base (scheme 76) [85]. A one pot synthesis of 2,
3-disubstituted indoles via the intermolecular cyclization
between ortho-iodoanilines and -keto esters was reported
under mild conditions [86]. The reaction proceeds smoothly
at 50 oC in the presence of Cs2CO3 base and BINOL ligand
(scheme 77). Additives and base played important role
during the reaction.
Quinazolines are present in many biologically important
heterocyclic compounds [87]. An important method for the
synthesis of quinazolines from benzamidines and
monosubstituted arenes was developed [88]. The synthesis
was carried out in the presence of CuBr catalyst and K2CO3
base (scheme 78). The synthesis of benzodiazepine was
carried out by M. Nayaka and S. Batra [89] from 4-iodo-1,5-
diphenyl-1H-pyrazole-3- carbaldehyde and ortho-phenylene
diamine using a catalytic amount of CuI (10 mol %) and
potassium phosphate base in DMSO solvent under nitrogen
atmosphere at 90 oC (scheme 79). Stoichiometric amounts of
copper bromide was used for the construction of indole ring
[90] from N-tosylated 2-ethynylaniline, paraformaldehyde
and diisopropylamine in dioxane in 92 % yield (scheme 80).
S. Chang et al. [91] reported the use of copper catalyst for
the cycloaddition reaction of - aryldiazoesters and terminal
alkynes for the efficient synthesis of indenes in excellent
yield (scheme 81).
2-Boryl- and silylindoles were synthesized by copper-
catalyzed cyclization of 2-alkenylaryl isocyanides in high
yields [92] (scheme 82). Enantioselective synthesis of trans-
aryl and heteroaryl-substituted cyclopropyl boronates can be
achieved using CuCl catalyst [93] (scheme 83).
R2
O
N
R1
O
N
R1
R2Cu(OTf)2 (20 mol %)
Toluene, O2, 80 0C
1.5-4 h
Scheme 75.
I
NH
COCF3
R
NH
R[Cu(phen)(PPh3)2]NO3
K3PO4
toluene, 110 oC
Scheme 76.
I
NH2
R
O
OR'
O
NH
COOR'
R
10 mol % CuI
20 mol % BINOL
Cs2CO3 (1 eq)
DMSO
Scheme 77.
NH
Ph
NHO2N
O
I
O
TIPS
N
N
Ph
TIPS
CuBr, K2CO3
benzene, 80 oC
Scheme 78.
N
N
CHO
I
Ph
Ph
NH2
NH2
N
N
Ph
Ph
NH
N
10 mol % CuI
3 eq K3PO4, N2 atm
DMSO, 90 oC, 36 h
Scheme 79.
NHTs
(HCHO)n (i-Pr)2NH
NTs
N(i-Pr)2CuBr (1 eq)
dioxane
80 oC
Scheme 80.
296 Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 Tekale et al.
Ar Br Ar I5 mol% CuI, 10 mol% L
2 eq NaI, Dioxane
110 oC, 22-24 hNHMe
NHMe
L =
Scheme 85.
O
R1 R3
R2 R4
Cu(OTf)2
acetone, r.t.O
O
R1
R2
R3
R4
O
R4(R3)
R3R4
R2
R1
Scheme 86.
2.6. Miscellaneous Reactions
Finally in this last part of the present review many
miscellaneous reactions catalyzed by different copper
catalysts; particularly oxidation reactions are described.
A versatile method for the synthesis of allylboronates
from allylic carbonates and bis(pinacolato)diboron involving
-substitution in the presence of achiral Cu(I) catalyst in
excellent optical purity was described by M. Sawamura et al.
[94] (scheme 84). Tolerance of different functional groups,
good selectivity, high yields etc are the advantages
associated with this protocol.
Aryl iodides are synthetically important substrates for
many cross coupling reactions such as Heck, Suzuki,
Ullmann etc. S. L. Buchwald [95] demonstrated that aryl
bromides can be converted into aryl iodides by using a
catalytic amount of CuI and suitable ligand (Scheme 85).
The copper(II)-catalyzed conversion of oxiranes into 1,3-
dioxolanes using copper (II) catalyst can be carried at
ambient temperature [96]. During these transformations, the
copper catalysts act as the Lewis acids (scheme 86).
T. Punniyamurthy and coworkers reported a method for
the conversion of sulfides to sulfoxides [97]
and alkyl
benzenes into the corresponding ketones using 30% H2O2 in
the presence of a recyclable copper complex (scheme 87 and
88). It was observed that yield of the transformation was
increased with the addition of TEMPO.
Normally the reductive deprotection of benzyl ethers
requires rigorous conditions. A regioselective and specific
oxidative cleavage of benzyl ethers in the presence of
diacetoxyiodobenzene and p-toluene sulfonamide using
copper (II) trifluoromethane sulfonate under mild conditions
was reported in literature [98] (scheme 89). A. J. Phillips
R1
N2
OR2
O
Ar H
R1
Ar
OR2
O
10 mol % Cu(Pr)Cl
12 mol % AgSbF6
12 mol % NaB(ArF)4
CH2Cl2, 25 oC, 30 min
Scheme 81.
COOMe
N
C:
cat.Cu(I)PPh3
B2(pin)2
MeOH
THF, 25 oCNH
COOMe
B(pin)
Scheme 82.
Ph OP(O)(OR)2 (pin)B-B(pin)
10 mol % CuCl
12 mol % Ligand
1 eq K(O-t-Bu)
toluene/THF
Ph
B(pin)
trans/cis 99:1
Scheme 83.
Ph
OCOOMe
Me
PhMe
B(pin)
Ph
Me
B(pin)
(pin = pinacolato)
B B
O
OO
O
MeMe
Me
Me
MeMe
Me
Me O
PPh2 PPh2
Me Me
Cu(O-t-Bu) (5 mol%)
Xantphos (5 mol%)
r.t., 3h
Bispinacolato diborane
Bispinacolato diborane
Xantphos
Scheme 84.
Recent Advances in Some Copper Catalyzed Coupling Reactions Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 297
et al. [99] synthesized the precursor ketone from natural
trans-kumausyne, a marine natural product, using
stoichiometric amounts of Stryker’s reagent and phenylsilane
(scheme 90).
J. Xu [100] studied the selective synthesis of 4-hydroxy
benzaldehyde from p-cresol via the oxidation of methyl
group using carbon supported copper and magnesium
bimetallic oxide, CuMn/C (scheme 91). The catalyst worked
without loss of activity for subsequent runs. The
combination of Cu(NO3)2.5H2O and CuBr2 catalytic system
for the oxidation of sulfides into sulfoxides under mild
reaction conditions was made applicable by S. E. Martin
[101] (scheme 92). A copper acetate catalyzed asymmetric
sulfoxidation of aryl alkyl and aryl benzyl sulfides with
aqueous H2O2 is also reported (Scheme 93) [102]. Recently;
O
O
H
H
(Ph3P)CuH
PhSiH3
toluene, r.t. O
O
H
H
Scheme 90.
CH3
OH
CHO
OH
COOH
OH
7.4 % CuMn(5:1)
NaOH, MeOH, O2
75 oC, 3h
98.5%
Scheme 91.
S
O
SCu(NO3)2.5H2O-CuBr2
CH3CN , O2, r.t.
3 h
Scheme 92.
S R' S+
O-
R'
RRCu(acac)2 (2 mol%)
Ligand (4 mol%)
30% H2O2, r.t.
Scheme 93.
O OHN
Ts
PhI(OAc)2/TsNH2
CH2Cl2, 40 oC
Cu(CF3SO3)2
Scheme 89.
CuIIPhCH2OH
100 oC
Cu(OCH2Ph)2
H2O2
PhCH2OH
CuII
O
O
OH
C
H
H
PhH2O
CuII
H2O
O-
CuII
H2O
OH
O OH
H2O2
PhCH2OHH2O
(3a)
(3b)
(3c)
O
Ph
H
H2O
Fig. (3). Catalytic cycle for CuSO4 catalyzed oxidation of benzylic alcohols into carbonyl compounds (Scheme 95).
1 mol % Complex
5 mol % TEMPO
2 eq 30 % H2O2
4.5-24 h, 20 oC
ACN
R
S
O
R'R
S
R'
Cu
N N
OO
H H
Cu-complex
Scheme 87.
0.1 mol % Complex
10 eq 30 % H2O2
80 oC, 5-10 h
ACN
R
O
R'R R'
Cu
N N
OO
HH
Cu-complex
H2O
Scheme 88.
298 Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 Tekale et al.
HNS
O
R2R1R3
R3 N
S
O
R1 R2
CuCl2 (10 mol%), O2 (1 atm)
pyridine, Na2CO3,
1,4-dioxane, 30 oC
Scheme 94.
OH
R
R'
O
R
R'
O
R
R'
CuSO4, H2O
H2O2, 100 oC
CuSO4, H2O
H2O2, 60 oC, Ligand
TEMPO, K2CO3
Ligand = 2-N-(p-fluorophenyl)-pyrrolecarbaldimine
Scheme 95.
ArCHO ArCN
Cu2+/ NH3 (aq.) /O2
ArCH2OH
Cu2+/TEMPO/NH3 (aq.) /O2
MeCH=NOH
one pot
Ar-CONH2
Scheme 96.
R
OH
R'
R
O
R'
nano CuO (10 mol%)
bipyridine, t-BOOH (70%)
CH2Cl2, r.t., 2-24 h
Scheme 97.
OH
Ph
R R
O
Ph
CuCl, K2CO3
DMF, 60 oC, air
Scheme 98.
R
B
OH
OHR
OHCuSO4 (10 mol%), Phen. (20 mol%)
KOH, H2O, r.t., 1-10 h
Scheme 99.
N N
H
H
R1R2
H
HR1
N
N
R2
[Cu] cat.,air or O2
H2O
Scheme 100.
an efficient synthesis of N-alkynylated sulfoximines from
sulfoximines and alkynes using copper chloride was reported
by Carsten Bolm et al. (scheme 94) [103]. CuSO4 can be
effectively used a catalyst for the oxidation of benzylic
alcohols into carbonyl compounds using 30% H2O2 as the
oxidant in the presence of 2-N-(p-fluorophenyl)-
pyrrolecarbaldimine ligand in combination with
TEMPO/K2CO3 (scheme 95). The reaction can be performed
under base free and ligand free conditions at 100 oC. Under
these conditions; primary benzylic alcohols were oxidized
into aldehydes (70–90%); remaining being the corresponding
carboxylic acids as the side products [104]. The mechanism
for the copper catalyzed oxidation is shown in (Fig. 3). A
direct oxidation of alcohols into amides via nitriles is
possible using NH3 as the nitrogen source, O2 oxidant and
TEMPO as the co-catalyst (scheme 96) [105]. Propargylic
alcohols can be oxidized to ynones by copper oxide
nanoparticles using TBHP or air as the oxidant (scheme 97)
[106]. It was observed that use of bipyridine ligand
significantly enhanced the reaction rate. The combination of
CuCl and K2CO3 can be effectively used for the ligand free
conversion of benzylic alcohols into ketones (scheme 98)
[107]. The reactions occur in the atmosphere of air. Y. Hu et
al. reported a room temperature method for the direct
oxidative hydroxylation of arylboronic acids in aqueous
medium (scheme 99) [108]. Aromatic azo compounds can be
obtained by the oxidative coupling of anilines using CuBr as
the simple catalyst. The reaction can be carried out by air or
oxygen as the oxidant (scheme 100) [109].
Recent Advances in Some Copper Catalyzed Coupling Reactions Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 299
CONCLUSION
The copper reagents have low cost and are not
air/moisture sensitive in contrast to the palladium catalysts.
Hence they provide a broad platform for the cross coupling
reactions in synthetic organic chemistry using low cost and
readily available copper catalysts. The reactions discussed
herein indicate the application of copper catalysts in
numerous chemical processes. Improvements in activity and
scope of these catalysts will assist to reduce the
environmental impact and increase the sustainability of
synthetically useful catalytic transformations. Challenges for
future developments in this area will be to develop novel and
reusable heterogeneous copper catalysts with scope and
activity. Copper-catalyzed cross-coupling reactions and the
synthesis of various heterocyclic compounds are useful in
synthetic organic chemistry. We hope this review will be
helpful for the researchers in the field of copper chemistry to
develop novel reusable heterogeneous copper catalysts and
their utility in the exploration of new routes for different
organic transformations.
CONFLICT OF INTEREST
The author(s) confirm that this article content has no
conflict of interest.
ACKNOWLEDGEMENTS
The authors are thankful to the Principal, Shri.
Muktanand College, Gangapur (MS) India for encouraging
them.
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Received: January 02, 2013 Revised: May 06, 2013 Accepted: May 09, 2013