EXAM #3 EXTRA PROBLEMS - MIT OpenCourseWare

[Pages:14]Massachusetts Institute of Technology Dr. Kimberly L. Berkowski

5.13, Fall 2006 Organic Chemistry II

EXAM #3 EXTRA PROBLEMS

KEY

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

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.

(a)

1. KCN 2. H3O+

i-Pr

Br

1. Mg ,ether

or

2. CO2

3. H3O+/workup

(b)

1. SOCl2

2. LiAl(OtBu)3H

or

3. workup

O

i-Pr OH

1. LiAlH4 (XS) 2. H2O 3. PCC

O i-Pr

OH

O

i-Pr

H

Figure by MIT OCW.

2. (2 points each, 8 points total) Please provide the products of the following reactions. If no reaction is expected, write "NR".

(a) O

Et Cl

(b)

O

Et OH

(c)

O

Et OMe

1. Excess Na BH4 2. Workup

1. Excess MeMgBr 2. Workup

1. Excess MeLi 2. Workup

Et OH

NR or O Et O

HO Me

Et Me

(d)

O

Et NMe2

1. Excess LiAlH4 2. Workup

Et

NMe2

NAME____________________________

Figure by MIT OCW.

1

3. (2 points each, 16 points total) Please provide the requested products or reagents. If no reaction is expected, write "NR".

(a)

O Me

NH2 Me

Br2, NaOH

Me NH2 H2O2, Me

(b)

O

H2N OH

N-OH

1. LiAlH4

NH2

Me Me cat. H+

2. workup

(c) POCl3

O n-Bu NH2

n-Bu CN

H3O+ H2O

O nBu OH

(d)

NH2

NaNO2

N2

CuBr

Br

HCl

Name_________________________

Figure by MIT OCW.

2

4. (11 points) Please provide a detailed mechanism for the illustrated conversion of acetic acid (A) to acetyl chloride (B).

O

O

Me

+ OH

Cl S Cl

A

O S Cl O Cl

Me OH

O O S Cl

Me OH + Cl

O + SO2 + HCl

Me Cl

B

O S Cl O OH Me Cl

O H Me Cl

Cl + SO2

Figure by MIT OCW.

Name_______________________

3

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.

Allowed Starting Materials:

Me

Me

Me CO2 Me

OH

Me

A

Pick Two:

Me

N C

Me

Synthesis # 1:

A

KMnO4 D

2

B

HO Me

Me

Me

OH O

1.O3 2.MeS

3.Na2Cr2O7 H2SO4

O Cl NH3

SOCl2

O NH2

POCl3

N C

Me OH

C H N Me

B

1.BH3, THF

2. H2O2,-OH

or H3O+/H2O

OH 1.PBr3 2.Mg

MgBr

1.CO2 2. H+

OH (excess) 1.MeMgBr

2.H2O

O OH

SOCl2 O Cl

Name__________________________

Figure by MIT OCW.

4

5. (Continued)

Allowed Starting Materials:

Me

Me

Me CO2 Me

OH

Me

Me-OH

Pick Two:

A Me C N

Me

B HO Me Me

C Me

H N

Me

Synthesis #2:

C

OH

PBr3 or

TsCl, Pyridine

O

1.

NK

O Br 2. H2NNH2

or 1. NaN3

2. LiAlH4 3. H3O+ or XS NH3

PCC MeOH

O HH

NH2 Cat H

1. LiAlH4 N 2. H2O

NH2

H N

Figure by MIT OCW.

Name________________________________

5

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.

O Me

O Me

A

HNO3 O2N H2SO4

H2N

N2

O HO

Me

B O

Me

H2, Pd

O Me

NaNO2, HCl O

Me

H2SO4, H2O

O

HO

Me

Figure by MIT OCW.

Name________________________________

6

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.

NH

HO-

O

+ MeOH

(1)

Me OMe

H2O

A

Me

NH2

N-H

PT

Me

OMe

OH

NH2

Me

OMe

O

O + MeO

Me NH2

H OH MeOH + OH

Figure by MIT OCW.

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

HH N

Me OMe H2O

NH Me OMe

excess H+ H2O

O + NH4

Me OMe

(2)

A

NH2

PT

Me OMe

OH2

NH3 Me OMe

OH

H O Me OMe + NH3

O Me OMe + NH4

Figure by MIT OCW.

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

Basic conditions: NH2 worse L.G. than OMe . Elimination favors amide Acidic conditions: Acid/base equilibrium favors protonation of ntrogen making it a good

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

Figure by MIT OCW.

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