KEY
Massachusetts Institute of Technology
Dr. Kimberly L. Berkowski
5.13, Fall 2006
Organic Chemistry II
PRACTICE EXAM #4
Hour exam #4 will be held on Wednesday, December 6, from 12:0512:55.
Books, notes, and calculators will not be allowed during the exam.
Molecular model kits will be allowed during the exam. You will be
given a periodic table and blank pages.
Material Covered on Exam #4:
• Everything presented in lecture related to Enols and Enolates and
Carbocations
• Recitation and Drill Problems
• Problem Sets 7 & 8
• McMurry Chapters 22 & 23
• All 5.12 materials.
The answer key will be posted on Monday
1
(1) (1 point each, 7 points total) Please provide the pKa value for the indicated “H”.
O O
Me
H
O O
O O
Me
Me
9
H
OMe MeO
13
11
O
MeCO2H
Me3NH
4-6
9-11
OMe
H
O
H
Me
H
EtO
16-23
23-27
2
Figure by MIT OCW.
(2) (2 points for each box; 20 points total) Please provide the indicated
information. If you use a base or an acid, please specify whether a “catalytic
amount”, “1 equivalent”, etc. is required.
(a)
(a)
O
CH3
Ph
(b)
O
Ph
1eq.
LDA
O
CHI3
O
O
Ph
CH3
Ph
(b)
excess I2
4 eq. NaOH
also acceptable:
l eq. LDA; H workup
cat. OH
(c)
O
Ph
or H
O
CH3
H
O
H
OH
Ph
cat. OH
(c)
O
(d)
Ph
OH
or H
∆
O
Ph
H2O
Figure by MIT OCW.
1 eq. LDA
also accepted
1 eq.
OMe
O
(e)
H+
O
CH
2 H3CO
O
H3CO
cat.
OMe
CH3
CH3
(f)
O
O
O
CH3
CH3
CH3
CO2CH3
also accepted:
O
(g)
CH3
MeS
MeS
O
Ph
CO2CH3
O
O
O
CH3
O
cat.
OMe
H3CO
O
1 eq. LDA; H workup
Ph
Ph
O
O
(h)
(i)
O
CH3
Ph
cat.
OMe
O
1 equiv. of base
CH3
O
MeS
Me
also accepted:
O O
MeS
Me
Figure by MIT OCW.
3
(3) (12 points) Please provide an efficient synthesis of the indicated target
compound. All of the carbons of the target compound must come from ethyl
acetate and 1, 5-dibromopentane.
O
Me
Br
O
Br
EtO
Me
target compound
O
2 EtO
Me
1 equv
EtO
Br
O OEtO
Br
EtO
Br
Me
OO
Me
1 equiv. LDA
O
OO
H2O EtO
+
cat H or HO
D
-
Figure by MIT OCW.
4
(4) (12 points) Please provide an efficient synthesis of the indicated target
compound. All of the carbons of the target compound must come from the three
illustrated alcohols.
O
Me
OH
O
OH
Me
Me
Me Me
OH
target compound
SYNTHESIS:
(1)
OH
OH
(2)
OH
(3)
PCC
PCC
PCC
O
O
O
}
O
O
1. LDA(1.1 eq.)
OLi
1.
H
OH, ∆
2.
O
O
O
O
O
cat. NaOMe
Figure by MIT OCW.
5
(5) (12 points) Please provide an efficient synthesis of the indicated target
compound. All of the carbons of the target compound must come from acetone and
diethyl malonate.
O
O
Me
O
Me
O
O
Me EtO
Me
OEt
target compound
O
1 eq. EtO
O
O
cat H+
O
O
EtO
1 eq. EtO
OEt
EtO2C
H+, H2O
∆
O
O
EtO
O
O
O
EtO ,
OEt
EtO
∆
(-H2O)
O
O
Mechanism
not
necessary
O
XS
∆ ,-H2O
O
O
EtO
OEt
O-
O
O
O-
O
OEt
EtO
O
O
H+
H2O ∆
EtO2C
O
EtO2C
O
6
OEt
EtO
O
O
O
O
H
H
O
OEt
Figure by MIT OCW.
(6) (12 points) Provide a mechanism for the conversion of A to B and B to C.
Please show all arrow pushing.
O
O
Me
H
OH cat.
O
O H
CH2
H
OH
OH
O
O
OH
O
O
H
O
OH
OH
C
O
H2O
O
OH
O
O
B
H
O
A
OH cat.
OH
A
O
H OH
OH
O
H OH
HO
OH
H OH
O
HO
OH
OH
O
OH
OH
B
O
OH
H OH
O
O
C
Figure by MIT OCW.
7
(7) (12 points) Provide the best mechanism for the illustrated transformation.
Please show all arrow pushing.
O
OH
catalyst
OH
+ OH
H
O
OH
OH
O
O
OH
O
O
HO
H
O
O
O
O
H
O
OH
O
Figure by MIT OCW.
8
(8) (13 points) Provide the best mechanism for the illustrated reaction. Please show
all arrow pushing. Hint: RSθ can serve as a nucleophile and add to the β carbon of
Michael acceptors.
O
Ph
O
H
OH
Me
catalytic RS
Me
Me
O
O
O
Ph
O
H
Me
O
Ph
O
Ph
Me
SR
RS
RS
OH
OH
O
Ph
O
Ph
Me
Me
SR
A
Tautomerization mech. (not necessary)
O
Ph
RSH O
O
Me
H
O-
Ph
OH
Me
SR
SR
Ph
A
O
Me
RS
RS
Keto
Enol
Protonated enol
Figure by MIT OCW.
9
(9) BONUS question (10 points) The process shown below is an example of a
“Mannich reaction”. Nature uses this reaction to synthesize alkaloids (natural
product that contain a basic nitrogen). Suggest the best mechanism for this process.
Please show all arrow-pushing.
O
Ph
O
Me Ph
H+
O
H
Me2NH
OH
Ph
Ph
H Cat.
Ph
OH
H
O
Ph
O
H
+
OH
N
Ph
Ph
A
OH2
NMe2
Ph
Me2NH
Ph
H
HO
OH
Ph
Ph
A
B (H2O or Me2NH)
H+
NMe2
O
Ph
Ph
N
NMe2
N
Ph
Ph
B
B
O
Ph
NMe2
Ph
+
H
Figure by MIT OCW.
10