Massachusetts Institute of Technology
Organic Chemistry 5.13
October 13, 2006
Prof. Timothy F. Jamison
Problem Set #4
Due Friday, October 20, 12:05 p.m., in lecture (before lecture)
1. Treatment of compound 1 below with a strong base (e.g., n-BuLi) gives a heterocycle with a 5
membered ring treatment with a weak acid (work-up). Account for the relative stereochemistry
observed in the product.
1
n-BuLi
HN
N
N
N
2. Propose a mechanism for the reaction below that involves a thermal 4π electrocyclic ring
closure. Clearly indicate the relative stereochemistry in all intermediates.
O
O
catalytic H+
Me
Me
3. Based on the photochemical and thermal electrocyclic reactions of compound 2 below,
comment on the nature of the π system in its 9-membered ring. Account for the relative
stereochemistry observed in each of the two reactions.
4. Heating compound 3 below at reflux in toluene in the presence of methyl acrylate affords two
products, A and B in a 1:1 ratio of diastereomers. With a catalytic amount of base, A is
converted to B. What are the structures of A and B? Clearly indicate the relative
stereochemistry in each. Hint: A Diels-Alder reaction is involved in part of the mechanism.
O
CN
+
3
!
OMe
1
A
+
B
5. Using retrosynthetic analysis, propose a synthesis of the five molecules below using a DielsAlder reaction in each case. Starting with the Diels-Alder reaction you decide to use, write your
synthesis in the “forward” direction, showing all steps and reagents necessary.
(a)
(b)
H
H
O
(c)
CH3 O
O
H
O
(d)
CH2CH3
OH
CH2CH3
Ph
H
O
HO
OH
OH
HO
O
(e)
CH3
CH3
O
CH3
H3CO
H3CO
O
6. Compound A undergoes a ring-opening reaction when heated at 100 °C, but no reaction occurs
when C is subjected to the same conditions. Suggest a mechanism for the conversion of A to
B, identify the type of reaction involved, and explain why C does not undergo a similar
transformation.
100 °C
H H
A
B
100 °C
No reaction
H H
C
2
Practice Problems for Exam 2. (You do not need to turn these in with your problem set.) Some of
the following problems cover material that we will not have covered by the time Problem Set 4 is due.
Not all of the problems on the exam will be like this, but they are representative of some of the ones you
might encounter.
For each of the following problems:
i. Fill in the boxes with the predicted product or necessary starting material. Indicate
relative stereochemistry and/or double bond geometry, where appropriate. If no reaction
occurs, write “no reaction” and skip parts ii. and iii.
ii. Classify each pericyclic reaction according to the Woodward-Hoffmann rules ([π4s + π2s]
cycloaddition, e.g.).
a.
!
C10H16
H3C
H
H3C
H
h"
C10H16
b.
!
H
h"
H
!
H
h"
H
c.
N
O
!
N
CH3
d.
O
O
O
O
O
CH3
h"
!
O
!
!
CH3
O
O
O
O
O
CH3
h"
!
CH3
3
O
!
!
e.
!
CH3
O
f.
H3C
H
g.
!
Hint: A 1H NMR spectrum of the product indicates
2 CH3 singlets,1 CH3 doublet, and 3 alkene protons.
CH3
C7H12
D
O
D
CH3
!
Note: D = deuterium (2H).
CH3
h.
O
CH2
C
+
1.
H
h!
MgBr
CH2
H
(allene)
KH
2. HCl, H2O
O
H+
"
H
C11H16O
Note: A 13C NMR spectrum of this
compound shows 11 signals: one
at 208.2 ppm, 4 between 100 and
150 ppm, and 6 between 10 and 50
ppm.
Note: The brackets indicate that
the product of the reaction with
potassium hydride is not isolated,
but rather rapidly converted to the
next structure after treatment with acid.
4