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CHEM 330 Final Exam, Exams of Organic Chemistry

University of Dallas (UD)Organic Chemistry

Complete this diagram by indicating all missing reagents / products. Each box corresponds to one reagent / product. Note: aqueous workup steps ...

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CHEM 330
Final Exam
December 4, 2008
Your name:
This a closed-notes, closed-book exam
The use of molecular models is allowed
This exam contains 12 pages
Time: 2h 30 min
1. ________ / 20
2. ________ / 20
3. ________ / 20
4. ________ / 30
5. ________ / 40
6. ________ / 40
7. ________ / 40
8. ________ / 40
TOTAL ________ / 250 = ________ / 100
This exam counts for 45% of your CHEM 330 final grade
ANSWERS
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Download CHEM 330 Final Exam and more Exams Organic Chemistry in PDF only on Docsity!

CHEM 330

Final Exam

December 4, 2008

Your name:

This a closed-notes, closed-book exam

The use of molecular models is allowed

This exam contains 12 pages

Time: 2h 30 min

1. ________ / 20

2. ________ / 20

3. ________ / 20

4. ________ / 30

5. ________ / 40

6. ________ / 40

7. ________ / 40

8. ________ / 40

TOTAL ________ / 250 = ________ / 100

This exam counts for 45% of your CHEM 330 final grade

ANSWERS

1. (20 pts.) Write a chemical equation to show an example of the following reactions ( do not

write mechanisms – just the reactions).

a. Barton-McCombie deoxygenation:

b. Yonemitsu reaction:

c. Cannizzaro reaction:

d. A sigmatropic reaction:

e. Parekh-Doering oxidation:

R

2

R

1 OH

PhO

S

Cl

Et 2

N

R

2

R

1 O

S

OPh

Bu 3

SnH

AIBN

R

2

R

1

R

O

Cl

Et 2

N

EtOH

reflux

O

O O

O

R

O

O

O

O

O

R

O

OEt

O

O

H

(or any non-enolizable aldehyde)

NaOH

OH O

OH

O

heat

O

R

2

R

1 OH

R

2

R

1

N S

O

O

O

DMSO,

then Et 3

N

O

primary or

secondary

aldehyde

or ketone

3. (20 pts.) Seychellene, C , is a component of patchouli extract, an essential oil of interest in

perfumery. A synthesis of seychellene involved heating compound A to 450°C for a few

seconds, whereupon B was obtained. Intermediate B was then converted into C in two steps.

a. Write the missing reagents required to advance B to C in the appropriate boxes

b. Write a mechanism for the conversion of A into B

c. Advance a succinct explanation as to why such a high temperature was necessary to

effect this transformation (write in the box below).

O

H

H

C

seychellene

O

Se

Ph O

450 °C

A

B

H

H

2

, Pd

Ph 3

P=CH

2

The reaction required such a high temperature probably because :

The dienophile, a simple vinyl group, is not sufficiently activated

O

Se

Ph O

A

H

H

O

H

O

H

DA

B

4. (30 pts.) A synthesis of the antitumor agent, coriolin, proceeded as outlined in the reaction

scheme below. Complete this diagram by indicating all missing reagents / products. Each

box corresponds to one reagent / product.

Note : aqueous workup steps are understood and are not to be included in your answers.

O O

together with

A

Krapcho

reaction

O

MeO OMe

O

Me

Me

Me

O

( 120 °C)

2. TBAF

O

Me

Me

O

Me

O

H

Me

steps

O

Me

Me

O

H

Me

O

H

Me

Me

B

1. LDA

  1. aq. HCl

O

Me

Me

H

H

O

Me

Me

steps

OH

Me

Me

H

H

O

Me

O

HO

O

coriolin

COOMe

O

MeO OMe

DBU

O

O

MeO

OMe COOMe

aq. acid

(ketal hydrolysis)

NaOMe

(aldol-dehydration)

OTMS

NaOMe

(aldol-dehydration)

O

Me

Me

H

H

O

Me

Me

NOTE: OTHER ANSWERS ARE POSSIBLE

6. (40 pts.) Predict the structure of the major product expected from the following reactions.

Note: It is not necessary to draw mechanisms.

Note : aqueous workups at the end of each step are understood

O

O

200 ° C

a.

H

H

(or enantiomer)

N O

O

O

Bn

1. LDA

3. K

2

CO

3

MeOH

b.

Br

OMe

O

H

( R-config.)

1. CH

2

=CHCu(PBu 3

2

  1. TMS-Cl, Et 3

N

c.

O

OTMS

  1. Cy 2

BCl

Et 3

N

d.

Ph

O

CHO

OTBS

TBSO OH O

Ph

  1. 9 - BBN-OTf

Et 3

N

  1. PhCHO

  2. Et 2

BOMe

NaBH 4

O

e.

OH OH

H

H

H

(or enantiomer)

COOMe

OH

H

H

O

OMe

1. LDA, THF

CHO

Ph

f. then aq.

wrkp. H

O

  1. excess NaH,

cat.EtOH, 1 eq.

(EtO) 2

CO

  1. Ph-CH 2

Br

  1. Aq. wrkp.

g. OEt

Ph

O O

OMe

CHO

N O

O

O

Bn

  1. Bu 2

BOTf,

Et 3

N

h.

then aq.

wrkp.

OMe

OH O

N O

Bn

O

O

O

OMe

OMe

c. O

O

O

H

H

tBuOK

CH

3

I

OMe

OMe

O

3

, then

H

2

O

2

, H

+

OMe

OMe

COOH

COOH

EtOH

H

2

SO

4

OMe

OMe

COOEt

COOEt

NaH,

cat. EtOH

aq. NaCl

DMSO

heat

OMe

OMe

O

COOEt

O

1. TBSCl

imid.

2. DIBAL

3. DMSO,

(COCl) 2

then Et 3

N

TBSO

d.

Me

H

OH

Me

OH

H

H

(this enantiomer)

Me

OH

O

CHO

TBSO

N O

O

O

B

Bu Bu

Bn

TBSO

OH

COX

c

TBSO

OTBS

CHO

O

B

Cy Cy

Me

H

OH

Me

O

H

H

Me

TBSO

TBSO

NaBH(OAc) 3

Me

H

OH

Me

OH

H

H

Me

TBSO

TBSO

TBAF

NOTE: OTHER ANSWERS ARE POSSIBLE

8. (40 pts) Propose a method to achieve the enantioselective synthesis of the molecules shown

below starting with the indicated building blocks. Be careful about protecting groups and

configurations of stereocenters. Assume the availability of all needed reagents, auxiliaries,

etc. Present your answer as a flowchart. It is not necessary to draw mechanisms.

a. starting with

O

Cl

O

Me

O

OH

Me

O

Cl

HN O

Ph

O

Et 3

N

N O

Ph

O

O

LDA, then

PhCH 2

Br

O

X

c

1. DIBAL

2. DMSO,

(COCl) 2

then

Et 3

N

O

H

N O

Bn

O

O

B

Bu Bu

OH

Me

CO-X

c

1. TBSCl, imid.

2. DIBAL

3. DMSO, (COCl) 2

then Et 3

N

OTBS

Me

CHO

N O

Me

O

O

B

Bu Bu

Ph

TBSO

Me

X

c

OH O

TBSO

Me

OH

Me

X

c

OC

TBAF

O

Me

O

OH

Me