CHEM 345 Problem Set 16 Key 1.) One way to make 1,3-dicarbonyls is the Claisen condensation

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CHEM 345 Problem Set 16 Key
1.) One way to make 1,3-dicarbonyls is the Claisen condensation.
The Claisen condensation is base mediated only. Acid does not work.
Draw the mechanism for the following reaction. Why is the Claisen
condensation base mediated rather than base catalyzed? What
base and solvent should be used?

O O O
base H O+
3
solvent
OMe O
The base and solvent should match the ester, otherwise a trans-
esterification gives a different product. The reaction is base mediated,
because the 1,3-dicarbonyl has a pKa of ~ 10, which consumes the
strong base during the reaction.

2.)Why does the following reaction not work?

O NaOH O O
H O H O+
2 3
OMe OH
A saponification would occur before the Claisen condensation occurs.
The resulting carboxylate would be unlikely to undergo nucleophilic
attack.
3.) Predict the product and provide a mechanism for the following
reactions:

O O
NaOMe
C H O
7 10
MeOH
C H O
7 12 2
3.) Predict the product and provide a mechanism for the following
reactions:

NaOMe
C H O
10 14
MeOH
O O
C H O
10 16 2
4.) Fill in the Boxes:
MgBr
FeBr
3 Br
Br2 Mg
O
Compound A
CH2O H3O+ PCC O
Compound A
CH Cl
2 2
O
Compound B
AlCl
3
O
LDA
Cl O
O
O
Compound C
O OH
H O+
3
Compound B Compound C
O
racemic
5.) Breakdown the following molecules into the starting materials that
made them. Write the reaction (Aldol and Claisen) that was used.
2
O O
Claisen O
a. 1 3
OMe
O
O O Aldol
b. 3 O O O
1
2
O O O
c.
O
2
1 3 Claisen
MeO
O O O O
O O
O O
c.
2
1 Claisen
O
O 3 O
O OMe
O O
c.
O O O
Claisen
1
O 3 O
2
O OMe
d. O Aldol O
3
H H
2 N N
HO 1 O
6.) The following molecule does not exist. Or if it did, it would not
exist for long. Draw the molecule that this would rapidly and I mean
rapidly rearrange to if formed. (Hint: carbonyls are in equilibrium
with what other functional group)?
O O OH O
tautomerization
O O HO OH
7.) Fill in the boxes to provide a synthesis of the following sets of
diastereomers.
A.)
O
LDA
O
H O
H
O
O OH
H O+
3 O O
H
H

B.)
O O
LDA
H H
O
O
O OH
H O+
3
O O
H
H
8.) Draw the mechanisms of the following reactions.

a. O NaOH O OH
H O
2

b. O NaOH O
H O
2
c. O NaOH O O
H O
2
O
d. O NaOH
H O
2