Exam 3 Probs Key

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Massachusetts Institute of Technology 5.13, Fall 2006

Dr. Kimberly L. Berkowski Organic Chemistry II

EXAM #3 EXTRA PROBLEMS

What to expect on Exam #3:1.

~1 Labeling experiment

2.

~2 Mechanisms

3. ~2 Syntheses

4.

~5 transformations – supply missing product

5. ~5 transformations – supply missing reagents

6.

~3 General questions

KEY



1. (4 points each, 8 points total) In the boxes, please provide the reagents for the illustrated

transformations. More than one step may be required.

2.

(2 points each, 8 points total) Please provide the products of the following reactions. If no

reaction is expected, write “NR”.

NAME____________________________

1

Figure by MIT OCW.

Figure by MIT OCW.

O

OHi-Pr

O

Hi-Pr

O

OHi-Pr

i-Pr Br

(a)

(b)

1. KCN

2. H3O+

or

or

1. Mg ,ether

2. CO2

3. H3O

+/workup

1. SOCl22. LiAl(OtBu)3H

3. workup

1. LiAlH4 (XS)

2. H2O

3. PCC

Et

O

Et Cl

O

OEt OH

O

Et OMe

O

(a)

(b)

(c)

(d)

Et NMe2

O

1. Excess Na BH4

2. Workup

2. Workup

1. Excess MeMgBr

2. Workup

1. Excess MeLi

2. Workup

1. Excess LiAlH4

OH

NR

or

HO Me

MeEt

Et NMe2

Et



3. (2 points each, 16 points total) Please provide the requested products or reagents. If no

reaction is expected, write “NR”.

Name_________________________

2

Figure by MIT OCW.

NH2 N2 Br

(d)

(c)

NH2

O

O

n-BuH2O

H3O

+

Me Me

H2 N

cat. H+

(b)

1. LiAlH4

2. workup

Me

MeMe

Me NH2 NH2

H2O2, ∆

(a)

Br 2,

NaOH

N-OH

POCl3

NaNO2

HCl

CuBr

O

n-Bu

NH2

O

OHnBuCN

OH



4. (11 points) Please provide a detailed mechanism for the illustrated conversion of acetic acid

(A) to acetyl chloride (B).

Name_______________________

3

Figure by MIT O

OHMe

O

OHMe Me

O

O

OHMe

O

Me

O

ClMe

OO

+S

Cl Cl

OSCl

Cl

O

S Cl

OS C l

C l

+ +

+

+

SO2

SO2

HCl

BA

Cl

Cl

H

Cl

OH



5. (11 points each, 22 points total) Please provide syntheses for only two of the three indicated

compounds. All the carbon atoms should be derived from the allowed starting materials. You

may use any common reagents.

Name__________________________

4

Figure by MIT OC

Allowed Starting Materials:

Me

MeMe Me

Me

Me CO2 OH OH

Me

Me

C N

C N

Me

Me

HO

MeMe N

H

A

A

B

B C

Pick Two:

Synthesis # 1:1.O3

2.MeS

3.Na2Cr 2O7

H2SO4

OH

O

2KMnO4

D

Cl

O

O

NH2 NH3

SOCl2

POCl3

1.BH3, THF

2. H2O2,−OH

or

H3O+/H2O

OH 1.PBr 3

2.Mg

MgBr 1.CO2

2. H

O

OH

O

Cl

SOCl2

1.MeMgBr

2.H2O

(excess)OH

+



5. (Continued)

Name________________________________

5

Figure by MIT OCW.

Allowed Starting Materials: Me

Me

Me

Me Me

Me

Me Me

CO2 OH

Me

Me-OH

NH2Br OH

PBr 3

or

or

or TsCl, Pyridine

Me

Me

C N

HO

NH

Pick Two:

Synthesis #2:

O

O

N K

2. H2 NNH2

1. NaN3

2. LiAlH4

3. H3O+

1.

NH2

N N

H

H

H

O

MeOHPCC

Cat H

1. LiAlH4

2. H2O

XS NH3

A B C

C



6. (11 points) Provide a synthesis that will selectively convert A to B. Show all the key

intermediates and furnish all the important reagents. This is not a one-step process.

Me

O

Me

O

Me

O

A

HO

Me

O

B

H2 N

HNO3

H2SO4

Me

O

Me

O

H2, Pd

NaNO2, HCl

O2 N

N2

Me

O

H2SO4, H2O

HO

Name________________________________

6

Figure by MIT OCW.



7. Methyl acetimidate (A) is hydrolyzed in aqueous sodium hydroxide to give mainly acetamide

and methanol (eq 1). In aqueous acid, A hydrolyzes to give primarily methyl acetate and

ammonium ion (eq 2).

a) Provide a detailed mechanism for the illustrated process. Please show all arrow

pushing.

b)

Provide a detailed mechanism for the illustrated process. Please show all arrow

pushing.

c) Briefly explain why the two reactions provide different products.

7

Figure by MIT OCW.

Figure by MIT OCW.

Figure by MIT OCW.

OMe NH2

OMe

Me

Me

A

H2O

NH

Me

NH2

O

O

NH2Me

O

+

OMeMe

N-H

OH

PT

(1) MeOH

MeOH + OH+ MeO H

HO-

OH

Basic conditions: NH2 worse L.G. than OMe . Elimination favor s amide

Acidic conditions:

L.G. Also, NH4 is not nucleophilic + formation of ester is reversible

Acid/base equilibrium favors protonation of ntrogen making it a good

OMe OMe

OMe

Me

Me

A

H2O

NH

OMeMe

N

Me

NH2

OH2

O

OMeMe

NH4+

OMeMe

NH3

OMeMe

O

NH4+

OH

PT O

(2)

H H

H2O

NH3

excess H+

+

H



Massachusetts Institute of Technology

5.13: Organic Chemistry II

8. Synthesize the indicated compounds from the allowed starting materials shown below. All ofthe carbons of the target compounds should be derived from the allowed starting materials.

8

Figure by MIT OCW.

Me OH

Me OH

Me OH

Me

Me OH

KMnO4, H+

O

H

H

O

Me H

O

Me

O

SOCl2Cl

Me

O

Cl

Me

O

PBr 3Br

Me Br Me Me

Me

Me

Me

PCC

C N NH2

O

N

Me

Me NH

H

HLiAlH4

LiAlH4

CN

T

3

1

2

3

2

4

1

T

N

MeOH MeOTs MeCN1) LAH

2) H2O

NaCN NH28.

EtOHEtBr EtMgBr

EtNH2, H+PCC

OHOMgHBr

TsCl

H O

1)

2)

O O

c)

b)

O

,

3+

Na2Cr 2O7

N





9

Figure by MIT OCW.

Cl Me

Me

AlCl3

O

Me

O

H-CN Me

CNOH

OH

LiAlH4

NH2

NH2

Br Br

Br NH2 NO2

Br Br

Br

N N

Br Br

Br

C N

H2SO4

HNO3

H2/Ni cat Br 2(excess)

FeBr 3

NaNO2

HCl

CaCNH2O, H

Br Br

Br O

OH

(d)

(e)

1 from part c

Br Br

Br O

Cl + H2 N Me

Br Br

Br O

N Me

H

4 from part c

SOCl2





9. Provide the best stepwise mechanism for the illustrated process. Please show all arrow

pushing.

10

Figure by MIT OCW.

O O O OH H

H H

H

H

NH2 NH2

H2O

H2O

+

H

H

+H

O

H

H HHH N OH

H

H N

HO

O

O

H

HH

H N

O

H

H

N

H

O

H

H

H

N

H

H

H

H

H NOH

N NaBH3CN

HH N " "

O

H

HH N

H

NaBH3CN

" "

NTarget

(9)





10. (a) Provide the best mechanism. Please show all arrow pushing.

O O

OH

OH

OH

OH

N C

C C

C

O H

H

HH

CH3

N

O

CH3

CH3

N

N

N Me

etc

OH

benzylic cation

Me

Target

or workup

(a)

11

Figure by MIT OCW.





(b) Provide the best mechanism. Please show all arrow pushing.

N

O

Me N

O

Me

H2O

H

H

H

OH2

NO

O

MeH

H

H N

OO

O

Me

Me

NH2

O

H H

H

HO

Me

NH3

O

H

O

Me

NH3

O

H NH3

O

O

OOH2

OH2

OH

H

H

H

NH3

O

O

H

H

H

H

Me

Me

Me

O H NH3

OH

NH2

O

O

H

H

workup

+

12

Figure by MIT OCW.





11. Consider the labeling experiments outlined below:

Name_______________

Figure by MIT OCW.

HO

NHMek 1

k 1

k 2

NHMeHO

NHMe

H2O

NHMe

PT H

OMe

OMeOMe OMe OMe

O

OH

NH2Me

H

OH

HO

O

HO

PT PT

k 2HO

PT PT

H

OH

OH

H

H

O

H

Proton transfer are very fast.Acid/base equilibria favor the protonated

N (not O). Therefore, once the tetrahedral

intermediate forms, loss of NH2Me (k 2) is

faster than loss of OH (k 1 .Very little is

incorporated into the unreacted starting

material.

All of the oxygens in the tetrahedral

intermediate are roughly equally basic.

Therefore, each protonated form 13

present in the same concentration ,and

k 2 =~ k 1. as a result, you would expect

more

incorporation into the ester startingmaterial than you would into the corresponding

amide.

11.Start with the mechanisms:

H2O H2O

O

O

O

O

HO

O

HO

k 1

k 1HOH2OPT

HH2O H2O

O

O

O

O

HO

HO

HO

HO

HO

HO

)

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