Table Of ContentACADEMIC PRESS RAPID MANUSCRIPT REPRODUCTION
Challenging Problems
in Organic Reaction
Mechansims
Darshan Ranganathan
Subramania Ranganathan
Department of Chemistry
Indian Institute of Technology
Kanpur, India
with a foreword by
Michael J. S. Dewar
Academic Press New York and London 1972
COPYRIGHT © 1972, BY ACADEMIC PRESS, INC.
ALL RIGHTS RESERVED.
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ACADEMIC PRESS, INC.
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United Kingdom Edition published by
ACADEMIC PRESS, INC. (LONDON) LTD.
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LIBRARY OF CONGRESS CATALOG CARD NUMBER: 72-9337
PRINTED IN THE UNITED STATES OF AMERICA
This work is gratefully dedicated to our teachers
S. Swaminathan, H. Shechter, R. B. Woodward
and
T. R. SeshadrU D. H. R. Barton
for their invaluable encouragement and guidance
FOREWORD
Much of the intellectual appeal of organic chemistry lies in the scope it gives for pure logical deduction, the
same kind of appeal indeed that holds chess players and readers of detective novels. However, the organic chemist
has the advantage in two respects. First, his problems are set by Nature, not man, and we are not told the solutions;
it is therefore impossible to cheat. And second, organic chemistry has practical value, so that the organic chemist
can enjoy his intellectual pastimes under the justifiable conviction that he is benefitting mankind by doing so.
In this context Dr. Ranganathan's work (there is an earlier volume "Fascinating Problems in Organic Reaction
Mechanisms"), can be regarded as compendia of chemical problems. Each of these books lists a series of reactions
leading to unexpected products as described in the current literature; the reader's task is to devise some reasonable
mechanism for them. In each case one is told only the reactants, reaction conditions, and products; further
information and the mechanism suggested by the discoverers of the reaction can of course be found in the original
papers to which references are given. There are no official solutions in the sense that chess problems have solutions;
for Nature has not divulged them to us. One can be certain that the original authors' suggestions are by no means
always correct!
In an age when scientific publishers are scraping the chemical barrel for new authors and new ideas, it is some
thing of an achievement to produce a book which is not only original but highly entertaining and instructive as well.
It is even more of an achievement to follow such a book with a successor that is not merely not an anticlimax but
fully as good as the first. This volume, as the first, will provide any organic chemist worthy of the name with end
less enjoyment, and also do much to sharpen his wits and extend his experience of the strange ways in which
Nature often behaves. The problems in it are searching ones; none are trivial, and many are very hard indeed.
I said of the first volume that, apart from its entertainment value, it seemed likely to prove an important
contribution to the chemical literature. Time has certainly confirmed this prediction, and the new volume will
undoubtedly prove equally valuable. Between them they form a chemical gold mine that will be an inspiration to
students and will stimulate much valuable research. It is a long time since anyone has compressed so much produc
tive chemical enjoyment into two such small and handy volumes, and I am sure that many like myself will now look
forward eagerly to Volume Three.
Michael J. S. Dewar
Department of Chemistry
The University of Texas
Austin, Texas
ix
PREFACE
The warm reception accorded our earlier book in this field has encouraged us to prepare the present work
reviewing the literature of organic reaction mechanisms from 1966 through 1971. We have found the task most
enjoyable and hope that the new book will lead to an even deeper appreciation on the part of the reader of the
intricate pathways that are possible in chemical transformations. The examples presented here not only reflect some
of the most subtle and delightful facets of organic chemistry, but also bring into focus many novel aspects of
syntheses, reactions, reagents, and reaction mechanisms, to say nothing of the whimsical proclivities of chemists in
naming compounds. Each problem describes the starting material, the conditions of the reaction, and the product,
followed by the reference to the original publication. This permits the reader to solve the problem independently
and then compare the results with those presented in the literature. The advantages of this method of presentation
are manifold. By way of example, for most of the rearrangements, more than one mechanism could be written. The
mechanism suggested in the reference need not be the original, the best one, or even a good one. Indeed, a highly
sophisticated mind will find a goodly number of suggestions lacking some measure of elegance or accuracy. The ex
amples are arranged in such a manner that each page is balanced. The utility of this collection has been enhanced by
inclusion of, first, a "compound index," which allows rapid identification of rearrangements associated with a
specific substrate; second, a "reaction-type index," which unifies reactions associated with a particular transition
state and brings into focus, for the first time, the usefulness of Woodward-Hoffman notations in understanding
bond formation and cleavage; and, finally, a "problem classification index," which grades each problem as a func
tion of its difficulty in terms of *, **, ***.
Professor M. J. S. Dewar's generous encouragements have been one of the chief motivating factors that led us
to take up this task, and we are indeed most grateful for his patronage. The entire manuscript was produced at
Kanpur by Mr. N. J. Tripathi and Mr. J. K. Misra, and we are proud of the excellent job these colleagues have done.
The tremendous encouragement that is essential for book writing was provided in abundant measure by members
of this department and, by Dr. M. S. Muthana, our Director.
D. Ranganathan
S. Ranganathan
xi
CHALLENGING ORGANIC MECHANISMS
L.A. Paquette, G.V. Meehan and S. J. Marshall,
J. Am. Chem. S o c, 91, 6779 (1969)
R.C. Fort, J r ., and W.L. Semon,
J. Org. Chem., 32 , 3685 (1967)
C0 Me CO Me
2 z
W.G. Dauben, M. G. Buzzolini, C.H. Schallhorn , D.L. Whalen
and K. J. Palmer, Tetrahedron Letters, 787 (1970).
1
D. RANGANATHAN AND S. RANGANATHAN
AcOH
4. -L
H 0
2
OMs
W. G. Dauben and D. L. Whaien,
J. Am. Chem. Soc, 88, 4739 (1966)
a
s Me Me
Ccc_.
J ^ f f-
T.F. Spande, A. Fontana and B. Witkop,
Η —Η ° Η
6 91 91 9 6
J. Am. Chem.Soc, 9J_, ( 9)
H.E. Zimmerman, R. W. Binkley, R.S. Givens,
G.L. Grunewald and M.A. Sherwin ,
J. Am. Chem. Soc, 91, 3316 (1969)
2
CHALLENGING ORGANIC MECHANISMS
Ο
R.L. Gargill and J.W. Crawford,
J. Org. Chem., 35, 356 (1970)
Me
R. B. Woodward and R. A. Olofson,
Tetrahedron {Stephen Spl.). 415 (1966)
COOMe
E.Vogel, W. Grimme, W. Meckel, H.J. Riebel
and J.F. M. Oth, Angew. Chem. (Int.), 5», 590 (1966)
3
D. RANGANATHAN AND S. RANGANATHAN
E. Wenkert and Z. Kumazawa,
Chem. Comm., 140 (1968)
HN-CN
11.
A.G. Anastassiou and S. W. Eachus,
Chem. Comm., 429 (1970)
heat
12.
W. D. Crow and C. Wentrup,
Tetrahedron Letters, 3115 (1968)
4
