Regioselective acylation of aminoresorcinarenes Minna Luostarinen, a Maija Nissinen, a Martin Nieger, b Alexander Shivanyuk c, * and Kari Rissanen a, * a Nanoscience Center, Department of Chemistry, University of Jyv € askyl € a, PO Box 35, FIN-40014 JYU, Jyv € askyl € a, Finland b Department of Inorganic Chemistry, University of Bonn, Gerhard Domagk Str. 1, D-53121 Bonn, Germany c The Institute of Organic Chemistry, The National Academy of Sciences of Ukraine,Murmanska Str. 5, 02660, Kyiv-94, Ukraine Received 4 July 2006; revised 7 November 2006; accepted 16 November 2006 Available online 15 December 2006 Abstract—The acid catalyzed hydrolytic cleavage of the oxazine rings in the readily available tetraoxazine derivatives of resorcinarenes re- sults in tetraaminoresorcinarenes. A similar process applied to C 2 -symmetrical bisoxazine resorcinarene tetratosylates affords C 2v -symmet- rical resorcinarenediamines. The mild acylation of these resorcinareneamines with BOC-anhydride or para-nitrophenyl ester proceeds selectively at the nitrogen atoms without affecting the hydroxyl groups. Most of the resulting resorcinareneamides are thus obtained in pre- parative yields and can be easily purified by simple crystallizations. In the crystalline state the compounds obtained are found to bind chloride anions through hydrogen bonds and electrostatic interactions and to display a chiral arrangement of hydrogen bonded functional groups at the wide rim of the macrocycle. Ó 2006 Published by Elsevier Ltd. 1. Introduction Preorganization of multiple functional groups on a molecular platform is an efficient methodology for the design of func- tional supramolecular systems, nanoscale species, and crys- tal structures. 1 Calixarenes 2 and resorcinarenes 3 1 (Scheme 1) are very popular molecular scaffolds widely useful as building blocks for the synthesis of cation, anion and bifunc- tional receptors, 4 container molecules, 5 and self-assembling systems. 6 Scheme 1. Methods for the complete and selective functionalization of calixarenes at the wide and narrow rim of the macrocycle have been developed in order to preorganize multiple binding and/or catalytic subunits in close spatial proximity. Espe- cially efficient is the use of calixarenes bearing several amino groups, 7 which can be readily transformed into various hydrogen bonding and metal coordinating fragments. This methodology has furnished efficient and selective cation, 8 anion, 9 and polytopic receptors 10 as well as highly stable self-assembling capsules 11 and functional nanostructures. 12 Different types of aminoresorcinarenes have also been synthesized. For example, resorcinarene-based cavitands bearing amino or aminomethyl groups at the wide rim of the macrocycle were obtained in preparative yields. These compounds were used in the rational design of cation 13 and anion 14 receptors, nanoscale container molecules, 15 and molecular capsules. 16 A sequence of protection/deprotec- tion procedures afforded cavitands bearing four propylene- amino groups at the narrow rim of the macrocycle. These receptors were shown to bind various guests in polar protic media. 17 Several research groups have demonstrated the regioselec- tive aminomethylation of octaols 1 with primary amines and formaldehyde to afford C 4 -symmetrical tetraoxazine de- rivatives, 18 which can be transformed into resorcinarenes bearing four amino and eight hydroxy groups at the wide rim of the macrocycle. Similar transformations of C 2v - symmetrical resorcinarene tetratosylates 19 resulted in com- pounds bearing two oxazine rings and, after subsequent Keywords: Resorcinarenes; Selective functionalization; Hydrogen bonds. * Corresponding authors. Tel.: +380 44 5510628 (A.S.); tel.: +358 14 2602672 (K.R.); e-mail addresses: [email protected]; [email protected].fi 0040–4020/$ - see front matter Ó 2006 Published by Elsevier Ltd. doi:10.1016/j.tet.2006.11.044 Tetrahedron 63 (2007) 1254–1263
Transcript
Tetrahedron 63 (2007) 1254–1263
Regioselective acylation of aminoresorcinarenes
Minna Luostarinen,a Maija Nissinen,a Martin Nieger,b
Alexander Shivanyukc,* and Kari Rissanena,*
aNanoscience Center, Department of Chemistry, University of Jyv€askyl€a, PO Box 35, FIN-40014 JYU, Jyv€askyl€a, FinlandbDepartment of Inorganic Chemistry, University of Bonn, Gerhard Domagk Str. 1, D-53121 Bonn, Germany
cThe Institute of Organic Chemistry, The National Academy of Sciences of Ukraine, Murmanska Str. 5, 02660, Kyiv-94, Ukraine
Received 4 July 2006; revised 7 November 2006; accepted 16 November 2006
Available online 15 December 2006
Abstract—The acid catalyzed hydrolytic cleavage of the oxazine rings in the readily available tetraoxazine derivatives of resorcinarenes re-sults in tetraaminoresorcinarenes. A similar process applied to C2-symmetrical bisoxazine resorcinarene tetratosylates affords C2v-symmet-rical resorcinarenediamines. The mild acylation of these resorcinareneamines with BOC-anhydride or para-nitrophenyl ester proceedsselectively at the nitrogen atoms without affecting the hydroxyl groups. Most of the resulting resorcinareneamides are thus obtained in pre-parative yields and can be easily purified by simple crystallizations. In the crystalline state the compounds obtained are found to bind chlorideanions through hydrogen bonds and electrostatic interactions and to display a chiral arrangement of hydrogen bonded functional groups at thewide rim of the macrocycle.� 2006 Published by Elsevier Ltd.
1. Introduction
Preorganization of multiple functional groups on a molecularplatform is an efficient methodology for the design of func-tional supramolecular systems, nanoscale species, and crys-tal structures.1 Calixarenes2 and resorcinarenes3 1 (Scheme1) are very popular molecular scaffolds widely useful asbuilding blocks for the synthesis of cation, anion and bifunc-tional receptors,4 container molecules,5 and self-assemblingsystems.6
0040–4020/$ - see front matter � 2006 Published by Elsevier Ltd.doi:10.1016/j.tet.2006.11.044
Methods for the complete and selective functionalization ofcalixarenes at the wide and narrow rim of the macrocyclehave been developed in order to preorganize multiple bindingand/or catalytic subunits in close spatial proximity. Espe-cially efficient is the use of calixarenes bearing several aminogroups,7 which can be readily transformed into varioushydrogen bonding and metal coordinating fragments. Thismethodology has furnished efficient and selective cation,8
anion,9 and polytopic receptors10 as well as highly stableself-assembling capsules11 and functional nanostructures.12
Different types of aminoresorcinarenes have also beensynthesized. For example, resorcinarene-based cavitandsbearing amino or aminomethyl groups at the wide rim ofthe macrocycle were obtained in preparative yields. Thesecompounds were used in the rational design of cation13
and anion14 receptors, nanoscale container molecules,15 andmolecular capsules.16 A sequence of protection/deprotec-tion procedures afforded cavitands bearing four propylene-amino groups at the narrow rim of the macrocycle. Thesereceptors were shown to bind various guests in polar proticmedia.17
Several research groups have demonstrated the regioselec-tive aminomethylation of octaols 1 with primary aminesand formaldehyde to afford C4-symmetrical tetraoxazine de-rivatives,18 which can be transformed into resorcinarenesbearing four amino and eight hydroxy groups at the widerim of the macrocycle. Similar transformations of C2v-symmetrical resorcinarene tetratosylates19 resulted in com-pounds bearing two oxazine rings and, after subsequent
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hydrolysis, two amino groups.20 The reaction of two resor-cinarene tetraoxazines with acetic anhydride resulted inthe N-acylation and cleavage of the oxazine rings andafforded in 17–18% yield the parent resorcinarenes bearingfour acetamido and eight hydroxyl groups at the wide rim ofthe macrocycle.21
The present investigation seeks to evaluate the reactivity oftetra- and diamino-resorcinarenes with mild acylating agentsin order to provide a versatile means for the selective modi-fication of the amino groups in the presence of severalhydroxyls. Herein we report preparative methods for theregioselective BOC-protection and N-acylation of such re-sorcinarene amines as well as the structural characterizationand supramolecular properties of the compounds thusobtained.
2. Results and discussion
The regioselective Mannich type condensation of resorcin-arenes 1 with primary amine and CH2O affords C4-symmet-rical tetraoxazines 3a–h (Scheme 2) in 34–99% yields.Compounds 3 precipitate from the reaction mixtures andcan be obtained in high purity by simple crystallizations.
S
The acid catalyzed cleavage of the oxazine rings (HCl,n-BuOH, H2O) readily transforms tetraoxazines 3 intotetraammonium salts 4 (55–96% yield).
The reaction of compounds 4 with BOC-anhydride in thepresence of Et3N as a base (CH2Cl2, 20 �C) leads to the regio-selective acylation of the more nucleophilic nitrogen atomswhereas the OH groups remain intact. In this way, BOC-pro-tected resorcinarenes 5a–g are obtained in 50–90% yields.
The mild acylation of tetraammonium salts 4 with para-ni-trophenyl esters (Et3N, CH2Cl2) provides the correspondingtetraamides in 19–72% yield, including the chiral compound5i bearing four (R)-a-cyclohexylethyl fragments at the widerim of the macrocycle. The acylation of compounds 4 withfour moles of the relatively more reactive acetic anhydride(Et3N, CH2Cl2, 20 �C) leads to inseparable complex mix-tures of unidentified products.
The complete acylation of compounds 5 with acetic anhy-dride in pyridine at ambient temperature afforded octaace-tates 6a–d in 40–90% yields. In contrast the alkylation ofresorcinarenes 5 with ethylbromoacetate (K2CO3, MeCN,reflux) resulted in complex mixtures, likely the result ofthe side reactions of the aminomethyl resorcinol fragments.
cheme 2.
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The 1H NMR spectra of compounds 3 contain one set of sig-nals for the protons of the resorcinol rings and the methineprotons of the bridges. The methylene protons of the oxazinerings emerge as two pairs of AB doublets whose separationdisplays a marked dependence on the nature of the R substit-uent at the nitrogen atom. This pattern is consistent with thecrown conformation produced by the C4-symmetrical ar-rangement of the oxazine rings atop the crown conformationof the resorcinarene framework.
The 1H NMR spectra of tetraammonium salts 4 in CDCl3 con-tain one set of signals for the protons of the resorcinol ringsand the methine protons of the bridges, which is in keepingwith the C4v-symmetrical crown conformation. The 1H–14NSGQC-NMR experiment indicates that the signals positionedat 7.7 and 9.3 ppm correspond to the NH- and OH- protons,respectively. Previously, we have reported22 that in the crys-talline state and in CDCl3 the crown conformation of 4 isstabilized by hydrogen bonds between the neighboring OHgroups and a cyclic hydrogen bonded array formed by thefour ammonium fragments and chloride anions.
Compounds 4a and b bearing short aliphatic residues at thenitrogen atoms and on the carbon atoms of the methinebridges are readily soluble in water at neutral pH. Their 1HNMR spectra in D2O contain one set of signals for the pro-tons of the resorcinol rings and methine protons of thebridges, however, no signals emerge for the NH and OHgroups, apparently, due to the fast H–D exchange.
The 1H NMR spectra of tetraamides 5 measured in CDCl3 at295 K are sharp and contain one set of signals for the protonsof the resorcinol rings and the methine protons of the bridges,which are typical for the crown conformation (Fig. 1a). Twobroadened singlets for the OH protons are centered at 8.6 and11.1 ppm indicating that the amide groups of compounds 5
Figure 1. A section of the 1H NMR spectrum of tetraamide 5d (500 MHz,CD2Cl2) at 295 K (a) and at 223 K (b).
are arranged in a C4-symmetrical manner forming hydrogenbonds with the neighboring OH groups. It should be notedthat such an arrangement has been previously observed inthe crystal structure of a resorcinarene tetraacetamide oftype 5.21
Decreasing the temperature to 223 K results in a complicatedsplitting of all the signals (Fig. 1b) likely produced by dif-ferent combinations in the arrangements of the hydrogenbonded amide groups at the wide rim of the macrocycle.
The 1H NMR spectra of octaesters 6 in DMSO-d6 at 295 Kcontain broad and featureless signals, an apparent result ofthe fast pseudorotation of the boat conformations with twoquasiparallel and quasicoplanar resorcinol rings.23 This in-terconversion becomes fast at 378 K and the sharp spectrumobserved corresponds to a time averaged C4v-symmetricalstructure.
C2-Symmetrical bisoxazine derivatives 7 are obtained in 30–88% yields via the regio- and stereoselective Mannich typecondensation of C2v-symmetrical resorcinarene tetratosylate2 (Scheme 1) with primary amines and formaldehyde. Sub-sequent cleavage of the heterocyclic rings (HCl, n-BuOH,H2O) readily gives hydrochlorides 8 (58–74% yield), whichare readily purified by simple re-crystallizations.
The amino groups of compounds 8 are regioselectivelyacylated with BOC-anhydride (Et3N, CH2Cl2, rt) to give di-amides 9 in 52–61% yield. Complete O-acylation of diamide9a with acetic anhydride (pyridine, at room temperature)affords octaester 10 in 80% yield (Scheme 3).
The slow crystallization of compound 8a from CHCl3 af-forded diffraction quality crystals. In the crystalline statethe molecule of 8a adopts a boat conformation (Fig. 2a) inwhich the aminomethylated resorcinol rings are nearly par-allel (dihedral angle 2.5�) whereas the ditosylated ones arequasicoplanar (dihedral angle 139.9�). It should be notedthat an analogous conformation is adopted in the crystallinestate by resorcinarene tetrasulfonates 2 and their bisoxazinederivatives 7.19c,d,20
Two chloride anions are positioned above the tosylated resor-cinol rings and form hydrogen bonds to four OH groups andone ammonium fragment.24 The other ammonium group ishydrogen bonded to the OH and the SO2 fragments of a neigh-boring molecule of 8a. This results in the formation of hydro-gen bonded molecular chains. Since all the OH groups arehydrogen bonded to the chloride anions, they do not formintramolecular hydrogen bonds with the sulfonyl fragments.
Slow crystallization of diamide 9a from CH2Cl2/hexane gavecrystals suitable for single crystal X-ray analysis. In the crys-talline state the molecule of 9a adopts a boat conformation(Fig. 3) in which the ditosylated resorcinol rings are quasico-planar and the aminomethylated ones are quasiparallel.
The BOC fragments are arranged in a C2-symmetrical man-ner forming intramolecular hydrogen bonds to the closestOH groups, resulting in two eight-membered hydrogenbonded rings. The other two hydroxyls are hydrogen bondedto the sulfonyl groups of the neighboring tosyl fragments.
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Scheme 3.
Figure 2. (a) Molecular structure of 8a; (b) intermolecular hydrogen bonding contact between neighboring molecules of 8a. Hydrogen bonds are shown indotted lines, hydrogen atoms are omitted for clarity.
Figure 3. Molecular structure of 9a. Hydrogen bonds are shown in dotted lines. Hydrogen atoms are omitted for clarity.
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Apparently, the conformation of compound 9a is chiral, thecrystal containing both enantiomers in a centrosymmetricaldisposition (C2/c).
The 1H NMR spectra of bisammonium salts 8a and b mea-sured in CDCl3 at 295 K correspond to the C2v-symmetricalstructure, since they display three singlets for the protons ofthe resorcinol rings, a quartet for the methine protons of thebridges and a singlet for the protons of the OH groups.
The 1H NMR spectrum of diamide 9a (CDCl3, 295 K)contains one set of signals for the methine and methyleneprotons of the bridges and the protons of the tosyl fragmentswhereas the OH groups emerge as a broadened singlet at7.5 ppm. This pattern corresponds to a C2v-symmetricalstructure, which is likely the time averaged combination oftwo C2-symmetrical conformations similar to those foundin the crystalline state.
The 1H NMR spectrum of compound 9a measured at 295 K inCDCl3 and DMSO-d6 contains broad signals, most probablydue to the hindered interconversion of two boat conformers.The sharp spectrum measured in DMSO-d6 at 378 K corre-sponds to the time averaged C2v-symmetrical structure.
3. Conclusions
Readily available resorcinarene tetra- and diamines can beselectively acylated by BOC-anhydride or para-nitrophenolesters to give resorcinarene derivatives bearing OH andamido groups at the wide rim of the macrocycle. This simpleand accessible preparative methodology allows the construc-tion of novel resorcinarenes with widely variable solubilityand extremely diverse structural and functional properties.On the other hand, unique arrangement of positively chargedand hydrogen bonding groups at the wide rim of the resor-cinarene diammonium salts may be utilized for design ofnovel macrocyclic anion receptors.
4. Experimental section
4.1. Reagents and methods
The NMR spectra were recorded on Bruker Avance DRX 500(500 MHz) and Bruker DPX 250 (250 MHz) spectrometersusing the residual solvent signals as an internal reference.Melting points were determined with a MEL TEMP2capillary melting point apparatus and are uncorrected. ESIMass-spectra were recorded on a Micromass LCT ESI-TOF instrument equipped with a Z geometry electrosprayion source. MALDI-TOF Mass-spectra were recorded ona Micromass MicrobeLynx MALDI-TOF. Known proce-dures have been used for the preparation of compounds 1,25
2,19 3h,18c 7, and 8.20 The purity of all new compounds wasdetermined to be >95% by 1H NMR spectroscopy.
4.1.1. Synthesis of tetraoxazines 3. To a solution of resor-cinarene in ethanol, formaldehyde (37%) and amine wereadded. The mixture was stirred at room temperature for8 h. The precipitate was filtered off, washed with ethanol,and dried in vacuo. Amounts of reagents and solvents areindicated below for each specific compound.
4.1.2. General procedure for the synthesis of compounds4. To a solution of oxazine 3 in butanol, concd HCl and H2Owere added. The mixture was heated to reflux for 4 h. Afterthe removal of water and formaldehyde by azeotropic distil-lation, the remaining butanol was evaporated, ethanol andtoluene were added and solvents were evaporated in vacuo.The crude product was treated with acetonitrile, filteredoff, washed with acetonitrile, and dried in vacuo. Theamounts of reagents and solvents are indicated below foreach specific compound.
4.1.3. General procedure for selective BOC-protection oftetraamines 4. To a solution of compound 4 in dry THF,Et3N and BOC-anhydride were added. The reaction mixturewas stirred under nitrogen at room temperature overnight,the volatiles removed at reduced pressure. The solid residuewas dissolved in CH2Cl2 and precipitated with MeCN. Theprecipitate was filtered off, washed with MeCN, and driedin vacuo. The amounts of reagents and solvent are indicatedbelow for each specific compound.
4.1.3.8. Compound 5h. To a solution of compound 4b(0.3 g, 0.3 mmol) in 10 ml of CH2Cl2, Et3N (0.23 ml,1.6 mmol) and a solution of para-nitrophenylacetate(0.38 g, 2.1 mmol) in 5 ml of CH2Cl2 were added. The mix-ture was stirred overnight. The solution was evaporated, thesolid residue was dissolved in 5 ml of CH2Cl2 and extractedwith 1 M K2CO3 until the yellow color of the aqueous layerdisappeared. The organic layer was separated and evapo-rated in vacuo. The product was triturated with methanol,the precipitate formed was filtered off and washed withmethanol. Yield 220 mg (72%). Mp >300 �C. 1H NMR(CDCl3) d 1.26–1.33 (m, 12H), 2.19 (br s, 40H), 3.56–3.67(m, 4H), 4.40–4.52 (m, 8H), 4.61 (q, J¼7.2 Hz, 4H), 7.22(s, 4H), 8.85 (s, 8H). MS (ESI-TOF) 1179.76 [M+Na,100%]+. Anal. Calcd for C68H92O12N4$2H2O: C, 68.42; H,8.04; N, 4.69. Found: C, 67.92; H, 7.91; N, 4.60.
4.1.3.9. Compound 5i. Compound 5i was obtained as 5hfrom compound 4d (0.5 g, 0.4 mmol) and para-nitrophenyl-acetate (0.56 g, 3.1 mmol). Yield 0.35 g (69%). Mp>300 �C.1H NMR (toluene-d8) d 0.88–1.37 (m, 48H), 3.19 (s, 4H),4.53–4.61 (m, 12H), 7.42 (s, 4H), 9.27 (s, 4H), 12.31 (s,4H). MS (ESI-TOF) 1346.94 [M+Na, 100%]+. Anal. Calcd
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for C80H116O12N4$4H2O: C, 68.76; H, 8.30; N, 4.01. FoundC, 69.08; H, 8.52; N, 4.08.
4.1.3.11. Compound 6a. To a solution of compound 5a(1.0 g, 0.8 mmol) in pyridine (25 ml) acetic acid anhydride(12.6 ml, 0.13 mol) was added in one portion and the reactionmixture was stirred overnight under nitrogen at room temper-ature. The solution was evaporated to dryness in vacuo, theresidue was dissolved in toluene and the solvent was evapo-rated. The crude product was triturated with ether, filtered off,and washed with ether. Yield 1.04 g (82%). Mp 244–245 �C.1H NMR (DMSO-d6) d 0.82 (t, J¼7.6 Hz, 12H), 1.16–1.54(m, 64H), 2.26 (s, 24H), 2.71 (s, 8H), 4.02–4.16 (m, 12H),7.18 (s, 4H). 13C NMR (CDCl3) d 14.10, 14.28, 19.96,20.07, 20.87, 28.64, 28.71, 29.55, 29.74, 29.89, 30.13, 32.48,39.25, 44.35, 76.71, 79.37, 79.73, 123.06, 125.13, 134.01,146.13, 148.10, 155.59, 155.74, 169.03. MS (ESI-TOF)1644.29 [M+Na, 100%]+. Anal. Calcd for C88H124O24N4:C, 65.17; H, 7.71; N, 3.45. Found C, 65.43; H, 7.98; N, 3.54.
4.1.3.14. Compound 6d. To a solution of compound 5h(0.5 g, 0.4 mmol) in CH2Cl2 (30 ml), Et3N (0.3 ml,2.1 mmol) and acetic acid anhydride (15 ml, 0.13 mol)were added. The mixture was stirred for five days at roomtemperature. The solution was evaporated in vacuo, the crudeproduct was triturated with CH2Cl2 and hexane, filtered off,and washed with hexane. Yield 0.26 g (40%). Mp 214–215 �C. 1H NMR (DMSO-d6) d 0.80 (t, J¼7.3 Hz, 12H),1.07–1.19 (m, 16H), 1.22–1.34 (m, 16H), 1.91 (s, 24H),2.80 (s, 4H), 2.93 (s, 12H), 3.84 (t, J¼7.3 Hz, 4H), 4.31 (s,
8H), 7.22 (s, 4H). 13C NMR (CDCl3) d 11.67, 12.76, 18.66,19.66, 20.26, 26.59, 28.98, 38.43, 44.61, 122.32, 125.76,132.79, 146.26, 167.69, 168.59. MS (ESI-TOF) 1549.59[M+H, 100%]+. Anal. Calcd for C88H116O20N4$3H2O: C,65.89; H, 7.60; N, 3.49. Found C, 65.27; H, 7.55; N, 3.22.
Compounds 8 were obtained as compound 4a from corre-sponding bisoxazines 7. The amounts of reagents and sol-vent are indicated below for each specific compound.
Compounds 9 were obtained as compound 5a from corre-sponding salts 8. The amounts of reagents and solvent areindicated below for each specific compound.
4.2. X-ray data collection and crystal structuredeterminations
X-ray data were collected at 173.0 K on a Nonius KappaCCD diffractometer using graphite-monochromatizedMo Ka radiation. Structures were solved by SHELXS-97and refined on F2 by full-matrix least-squares techniques(SHELXL-97).26 Hydrogen atoms were calculated to theiridealized positions and refined as riding atoms (temperaturefactor 1.2 or 1.5 times C temperature factor). Crystallo-graphic data (excluding structure factors) for the structuresin this paper have been deposited with the Cambridge Crys-tallographic Data Centre as supplementary publicationnumbers CCDC-606116 and 606117. Copies of the datacan be obtained, free of charge on application to CCDC,12 Union Road, Cambridge CB2 1EZ, UK (fax: +44 123336033 or e-mail: [email protected]) (Table 1).
Acknowledgements
This research was financially supported by Finnish Acad-emy (project 63018) K.R. and A.S. and National TechnologyAgency of Finland (TEKES, project 40476/01) M.L. Wethank Mr. Rejo Kauppinen for his assistance in variabletemperature NMR measurements and Dr. Adel Rafai Farfor correcting the manuscript.
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