Initials______________
Chemistry 634, Fall 2009
Midterm Exam
300 points (3 hours)
•
•
•
You may use model sets and hand-written note cards (no larger than 4X6
inches).
Answers should be written in boxes provided, other markings will not be
considered. Scratch paper can be found at the back of the exam packet.
Points will only be awarded for clearly communicated answers.
Name _______________________________________
Question 1: ________/60
Question 2: ________/40
Question 3: ________/45
Question 4: ________/9
Question 5: ________/46
Question 6: ________/25
Question 7: ________/25
Question 8: ________/25
Question 9: ________/25
_____________________
Total:_______/300
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Initials______________
1) (60 points) Predict the expected major product for each reaction sequence.
Denote stereochemistry where needed. If no reaction is expected, state so.
OH
LDA (2 equiv.)
then CH2=CHCH2Br
O
Me
OEt
Me
5 pts
OTBS
HO
(COCl)2, DMSO
Et3N, -78°C
OMe
5 pts
Me
N
O
O
Me
Me
Me
Et3N
5 pts
PR3, Pd(OAc)2
Bu3SnCH=CH2
tol, 110 °C, 15 h
I
N
Ts
10 pts
1) Boc2O (I equiv)
2) TBDPSCl, imid.
NH2
OH
5 pts
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Initials______________
Problem 1 continued)
O
O
Me
N
O
1) LDA, then BnBr
2) LiAlH4
Me
Me
5 pts
O
F
OH
N
O
N
Me
Me
Pr4N+ RuO4–
5 pts
ZnCl
O
OTf
Pd(PPh3)4, LiCl
5 pts
BnO
EtO
B
Cl
Pd(OAc)2
PCy3
OEt
5 pts
O
Me
Bn
N
Me
Br
NH
5 mol% Pd(OAc)2
10 mol% PPh3
MeCN, 80 °C
O
10 pts
____/60 points
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Initials______________
2) (40 points total) Provide the necessary reagent(s) to provide high yielding
transformations. Write answers in box provided. Be mindful of stereochemistry, if
specified. Note, for each scheme more than one step may be required (unless
otherwise noted). If more than one step is proposed, please indicate clearly.
O
O
Me
Me
Br
10 pts
O
O
Me
Br
Me
10 pts
Bn
Me
O
MeMe
H
O
O
Me
O
Me
Me
10 pts
H
MeMe
H
Me
O
O
H
Me
Me
OH
CO2H
Me
Single Step
10 pts
O
O
Me
Me
Me
Me
Me
______/40 points
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Initials______________
3) (45 points) Illustrated below is part of the route from Overman’s total synthesis
of (–)-idiospermuline (Tetrahedron, 2003, 59, 6905). Using the given information
provided, give the missing reagents, intermediates, and final product. For the
reagents, please put the reagents for each step in a different box.
MeH Me
N
N
5 pts
N
N
H H Me
5 pts
5 pts
5 pts
5 pts
5 pts
OTf
Me
N
O
MeH Me
N
N
SnBu3
NMeTs
OTf
5 pts
N
N
H H Me
Me
N
O
NMeTs
5 pts
Pd(OAc)2
(S)-Tol-BINAP
PMP, MeCN
80 °C
PMP =
Me
Me
N
Me
Me
Me
Ignore Stereochemistry
5 pts
______/45 points
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Initials______________
4) (9 points) Paramethoxybenzyl trichloroacetimidate (PMBTCA) is a reagent that
allows formation of PMB ethers under Bronsted or Lewis acidic (such as
Yb(OTf)3) conditions. In the space provided, provide a mechanism for this
transformation.
NH
Cl3C
O
OMe
(PMBTCA)
ROH
ROPMB
Yb(OTf)3
9 pts
______/9 points
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Initials______________
5) (46 points) Bressy and Pons have shown (Org. Lett. ASAP) that simply by
varying the order of the same four steps (A-D, shown below), either enantiomer
of 2 can be prepared from 1. Using the spaces provided, show the correct
sequence of steps that leads to each product (letters in small boxes) and show
the intermediates that are formed along the way (structures in big boxes).
OMe
Me
2 pts
Me
AcO
H
O
2 pts
OH
H
1
5 pts
5 pts
2 pts
2 pts
5 pts
5 pts
2 pts
2 pts
5 pts
2 pts
Me
OMe
5 pts
Conditions A: PMBTCA, Yb(OTf)3, tol, rt
Conditions B: Zn, EtOH, heat
Conditions C: I2, PPh3, Imidazole, tol, heat
Conditions D: K2CO3, MeOH
2 pts
OMe Me
PMBO
OPMB
Me
2
Me
Me
Me
ent-2
______/46 points
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Initials______________
6) (25 points) Propose a synthesis of 3 from the given starting materials.
Br
Br
Me Me
OH
+
EtOAc
3
25 pts
______/25 points
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Initials______________
7) (25 points) Propose a synthesis of 4 from the given starting materials.
OH
Me
Me
Me
Me
Me
O
4
25 pts
______/25 points
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Initials______________
8) (25 points) Propose a synthesis of 5 from the given starting materials.
OMe
HO
Me
+
O
I
Me
iPr
Bn
CN
O
5, enantiomerically enriched
25 pts
______/25 points
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Initials______________
9) (25 points) Propose a synthesis of 6 from the given starting materials.
EtO2C
TBSO
Ph
OH
6
25 pts
______/25 points
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Initials______________
This page provided for scratch paper. No answers on this paper will be graded.
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Initials______________
This page provided for scratch paper. No answers on this paper will be graded.
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Initials______________
This page provided for scratch paper. No answers on this paper will be graded.
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Initials______________
This page provided for scratch paper. No answers on this paper will be graded.
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