Midterm Key - UCLA

CHEMISTRY 144
UCLA, FALL 2004
MIDTERM EXAM
On my honor, I have neither given nor received any aid on this exam.
________KEY_____________ __________________________
Signature I. D. Number
__________KEY____________ _____________________________
Name (Print) TA
Question Points
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1 (20)
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2 (14)
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3 (18)
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4 (18)
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5 (18)
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6 (20)
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Total

Chemistry 144, Fall 2004 Name: KEY
Page 2
1A. (3) Label the prochiral faces of the ketone below as Re and Si.
O
Re
Si
OH
B. (4) Label the indicated pairs of substituents as Homotopic, Enantiotopic, or Diastereotopic.
OMe
OMe
C. (3) List the pKa values for the following.
Homotopic Br
Enantiotopic
Acetylene Acetone Benzene
25 20 40
D. (5) Define the term Chemoselectivity. Use a drawing to illustrate your definition.
Selective reaction at one functional group in a molecule containing two or more functional
groups without using protecting groups.
MeO
O
O OH
NaBH4
MeOH
MeO
C. (5) Define the term Stereospecific. Use a drawing to illustrate your definition.
A reaction where the stereochemistry of the starting material determines the
stereochemistry of the product.
OsO 4
OH
OH
O
Cl
Cl
OsO 4
OH
OH

Chemistry 144, Fall 2004 Name: KEY
Page 3
2. (14) Draw the transition state models and products predicted for the following reactions.
O
O
OBn
H
OSiEt 3
EtMgBr MgBr 2
Et2O
NaBH 4 EtOH
Nu -
Br2
Mg
BnO O
H Et
H
Et
O
H
Me
OR
Chelation
OSiEt 3
Nu - Felkin-Anh
Br2Mg
BnO
O
H
Nu -
OH
OSiEt 3
OBn
OH

Chemistry 144, Fall 2004 Name: KEY
Page 4
3. (18) Draw the product or products, if any, expected from the following reactions.
Pay Attention to Stereochemistry.
A.
B.
C.
D.
E.
F.
O
O
O
NEt 2
a)
b)
1) Li NH 3
THF
2) OsO 4
L-Selectride
1a) s-BuLi TMEDA THF
O
2) Dibal THF
CuCNMgBr
Br
1a) Sia2BH THF
b) H 2O 2 NaOH H 2O
2) H 2 Pd/BaSO 4 Quinoline
OH
OH
OH
O
O
H
OH
O
H

HOOC
1) SOCl2
2) HNMe(OMe) Et3N
3) BuLi THF
4) H3O +
OEt
O
O

Chemistry 144, Fall 2004 Name: KEY
Page 5
4. (18) Propose reactions for the following transformations.
Pay Attention to Stereochemistry.
A.
B.
C.
O
O
O
COOH
O
NMe2
1a) BuLi THF
O
b)
NMe2 2) Ph2CuLi THF
1) SOCl 2
2) i-BuCuMgBr Et 2 O
1) NH 2-NHTs NaBH 3CN
2) LiBH4 EtOH
3) Dibal THF
3) BH3 CBs cat. THF
O
HO
OH
One En antiomer
O
H

Chemistry 144, Fall 2004 Name: KEY
Page 6
5. (18) Propose reactions for the following transformations.
Pay Attention to Stereochemistry.
A.
B.
C.
O
OH
HOOC COOH
O
OMe
OH
Several Possible Answers
1) HNMe(OMe) DCC CH 2Cl 2
2)
3)
BrMg
Li
1) SOCl2
2) Et 2CuLi
Et2O
THF
3) iPrNH2 NaBH3CN pH 5
1) HNMe(OMe) DCC CH 2 Cl 2
2) Dibal THF
3) MgBr2
4) Ac2O Et3N DMAP CH2Cl2
5) MeCuCNLi
MgBr
OH
OMe
Two ways to solve problem:
A) Make aldehyde and add vinyl group via chelation.
b) Make ketone and then reduce via Felkin-Anh control.
N

Chemistry 144, Fall 2004 Name: KEY
Page 7
6. (20) Propose detailed mechanisms for the following reactions.
Li
OMe
OMe Li NH3
OMe
H
NH2
OMe NH2
OMe
Li
OMe OMe
H 2O
OMe
H +
OMe
Me
O
O
H
H
H 3O +
Net Tautomerization
(1,5 Hydroden shift)
Me
O H
O
H
H
H
O
H
O
O H
H +
O H
H
O
H
O