Chem 450—Advanced Organic Chemistry Exam 4

Chem 450—Advanced Organic Chemistry
Exam 4
Fall 2008
90
Name________________________ 100 points
1. Give the major product of the following reactions, including stereochemistry where
required. Give only one answer. (28 pts).
O 1. LDA
O OH
THF/HMPA
Br
O
O
O
O
2
O
+
O
O
Ph
N
N
O
N
O
O
O
O
O
O
2. iPrCHO (1 eq)
3. dil. HCl
1. LTMP
2. nC 4H 9Br
1. LDA/THF
2.
H
1. LDA/THF
2. CH 3CH 2I
KOH
O
EtOH
1. KOtBu
2. CH 3I
H 2SO 4
Br
O
2
O
O
O
N
N
O
O
OH
Ph
O
O
O
O
O
O
N
O

2. Give the structure major enolate formed under the following conditions. Give only
one answer. (12 pts).
O
O
O
O
N
O
O
O
LDA
THF/HMPA
LDA
THF
KHMDS
THF
LTMP
THF
OLi
Li
O O
3. Give the reagents required for the following transformations (9 pts).
O
O
O
O
H
O
Et 3N
THF
1. LDA/HMPA
2. PhCH 2CHO
3. Dilute H 3O +
KOH
EtOH, ∆
O
O
OLi
O
OH
N
OK
NO 2
O OH
racemate
4. What is a “directed” aldol reaction (3 points)?
An aldol in which the enolate is preformed. Thus only the preformed enolate is able
to react with the carbonyl compound, forcing condensation to occur in only one
direction.
O
O

5. Give all possible products of the following reaction and indicate the major product (10
pts).
2
O NaOH
CF 3
EtOH, reflux
F 3C
6. Give a transition state explaining the stereochemistry of the enolate below (4 points).
O
O
LDA
THF
OH
N
H
O
Li
O
O
THF
CF 3
CF 3
THF
7. Explain the stereochemical outcome of the following reaction (4 points).
H
O
O
H
O
1. LDA/THF
2. BnBr
The enolate is attacked from the convex face opposite the aromatic ring as the H is
smaller. (The approach will also depend on the configuration next to the oxygen,
though this was not specified.)
+
and
+
Bn
H
OLi
F 3C
O
O
O
OH
O
O
CF 3
CF 3

8. Give structures illustrating why LDA alone promotes formation of the E-enolate, while
addition of HMPA promotes the formation of Z-enolates (8 points)?
Open TS Li does not bridge
Closed TS - Cyclic
H
O
H
N
O Li
THF
THF
9. Explain why the following reaction does not produce the desired product and suggest a
likely structure for the major product obtained (6 points).
O
+
O
NaOH
CH3 O
H3C CH3 H3C H
EtOH H3C H
O
H
OH O
OH O
H3C H
or
H3C CH3 Aldehyde is much more reactive. Also, no heat so no elimination.
10. The following compound was prepared using a Robinson annulation. Give the
structures of the starting materials (6 points).
O
+
O
KOH
EtOH
O
N
H
O

Extra Credit 5 points: Give a step by step mechanism for the product below.
O
H
H
O
+ CH 3NO 2
NaOH + CH3NO2 H2C
O
N
O
HO
O
N
H
O
O
H2C N
O
NO 2
HO O
H
Na +
O
O
H
HO
H
cat. NaOH
O
O
N H
O
EtOH
+ Na +
H
O
H2C N
O
O
NO 2
HO OH
O
H2C O
N
+ Na
O
+ + H2O O
N H
H
O
HO
Na +
O
N
H
O
NO2 + H2O HO OH
+ NaOH
H
H
O
O