Synthetic Organic Photochemistry

542 Pages·1984·15.374 MB·English

by  Andrew Gilbert (auth.), William M. Horspool (eds.)

Synthetic Organic
Photochemistry
Synthetic Organic
Photochemistry
Edited by
William M. Horspool
The University of Dundee
Dundee, United Kingdon
Plenum Press • New York and London
Library of Congress Cataloging in Publication Data
Main entry under tille:
Synthetic organic photochemistry.
Includes bibliographical references and index.
Contents: Photo-addition and -cydisalion processes of aromatic compounds / An
drew Gilbert-Enone photochemical cycloaddition and organic synthesis / Alan C.
Weedon- Synthetic aspects of photochemical electron transfer reaction I Patrick S.
Mariano and Jerome L. Stavinoha - (etc.]
I. Photochemistry. 2. Chemistry, Organic-Synthesis. I. HorspooJ, William M.
QD71S.s96 1984 547'.2 84-10480
ISBN-13: 978-1-46\2-9668-3 e-ISBN-] 3: 978-]-4613-2681-6
DOl; 10.1007/978-1-4613-2681-6
©1984 Plenum Press, New York
Soflcovcr reprint of the hardcover I sl edition 1984
A Division of Plenum Publishing Corporation
233 Spring Street, New York, N. Y. lOOi3
All rights reserved
No part of this book may be reproduced, stored in a retrieval system, or transmilted
in any form or by any means, electronic, mechanical, photocopying, microfilming,
recording, or otherwise, without written pennission from the Publisher
To Una, Linda, and Andrew
Contributors
Roger W. Binkley, Department of Chemistry, Cleveland State University,
Cleveland, Ohio 44115
Howard A. J. Cariess, Department of Chemistry, Birkbeck College, University
of London, London, WC1E 7HX, U.K.
John D. Coyle, Department of Chemistry, The Open University, Milton
Keynes, MK7 6AA, U.K.
Thomas W. Flechtner, Department of Chemistry, Cleveland State University,
Cleveland, Ohio 44115
Andrew Gilbert, Department of Chemistry, University of Reading, White
knights, Reading, Berkshire, RG6 2AD, U.K.
William M. Horspool, Department of Chemistry, The University, Dundee
DD1 4HN, U.K.
Patrick S. Mariano, Department of Chemistry, University of Maryland, Col
lege Park, Maryland 20742
Douglas C. Neckers, Department of Chemistry, Bowling Green State Uni
versity, Bowling Green, Ohio 43403
Albert Padwa, Department of Chemistry, Emory University, Atlanta, Georgia
30322
Jerome L. Stavinoha, Texas Eastman Company, P.O. Box 7444, Longview,
Texas 75607
Alois H. IA. Tinnemans, Department of Chemistry, Bowling Green State Uni·
versity, Bowling Green, Ohio 43403
Alan C. Weedon, Department of Chemistry, The University of Western On
tario, London, Ontario, Canada N6A 5B7
vii
Foreword
Of all major branches of organic chemistry, I think none has undergone such
a rapid, even explosive, development during the past twenty-five years as
organic photochemistry. Prior to about 1960, photochemistry was still widely
regarded as a branch of physical chemistry which might perhaps have oc
casional applications in the generation of free radicals. Strangely enough, this
attitude to the subject had developed despite such early signs of promise as
the photodimerization of anthracene first observed by Fritzsche in 1866, and
some strikingly original pioneering work by Ciamician and Silber in the early
years of this century. These latter workers first reported such varied photo
reactions as the photoisomerization of carvenone to carvone camphor, the
photodimerization of stilbene, and the photoisomerization of o-nitrobenzal
dehyde to o-nitrosobenzoic acid; yet organic chemists continued for another
fifty years or so to rely almost wholly on thermal rather than photochemical
methods of activation in organic synthesis-truly a dark age. When my
colleagues and I first began in the 1950s to study the synthetic possibilities
of photoexcitation in the chemistry of benzene and its derivatives, virtually
all the prior reports had indicated that benzene was stable to ultraviolet
radiation. Yet I think it fair to say that more different types of photoreactions
than thermal reactions of the benzene ring are now known.
Comparable growth of knowledge has occurred in other branches of
organic photochemistry, and photochemical techniques have in particular
made possible or simplified the synthesis of numerous highly strained organic
molecules.
Developments in organic photochemistry have been greatly stimulated
by a growing understanding of the underlying mechanisms. In particular, the
rules formulated by Woodward and Hoffmann have proved to have consid
erable predictive value despite the potentially complicating fact that most
organic photoreactions are diabatic, i.e., the products are formed in their
electronic ground states.
The development in Japan of a photochemical process for the manufac-
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x Foreword
ture of caprolactam by photo-oximation of cyclohexane encouraged many
workers to believe that further large-scale applications in organic synthesis
lay just over the horizon. In fairness, it must be said that these expectations
remain as yet unfulfilled, though there have been some useful applications
within the pharmaceutical and insecticide industries. Although future larger
scale devel<?pments remain a definite possibility, especially for those numerous
photoreactions that proceed readily under the influence of solar radiation,
the main future applications of synthetic photochemistry probably lie in the
production of relatively small quantities of products having high intrinsic
value, for example pharmaceutical intermediates. The situation could, how
ever, be transformed by the introduction of improved radiation sources and,
as noted above, use of the freely available quanta in solar radiation, especially
in desert areas of the world unsuitable for agriculture. This latter approach
was pioneered by Schonberg and Mustafa, but has not yet taken hold. For
example, some twenty years ago a major chemical company seriously con
sidered manufacturing the benzene/maleic anhydride photoadduct (a poten
tially valuable polymer intermediate which is also interesting in having bio
logical activity as an analgesic) by a sensitized solar irradiation method in a
desert area; but the idea seems to have been abandoned as involving a too
unorthodox type of technology.
Despite the substantial failure of industry to capitalize on the exciting
laboratory developments in organic photochemistry (often for good reasons,
it must be said), the potential for successful exploitation is still undoubtedly
very great. The worker in synthetic organic photochemistry soon finds himself
or herself in a whole new world of chemistry where he must put aside most
of his preconceptions about reactivity based upon the more conventional
thermal chemistry, which still dominates most chemistry textbooks and teach
ing courses. I strongly support the objective of the present book to provide
for synthetic chemists, both academic and applied, an up-to-date and broadly
based account of the exciting opportunities available to those prepared to
forsake the bunsen burner for the ultraviolet lamp, or even natural sunlight.
D. Bryce-Smith
Professor of Organic Chemistry
Preface
Organic photochemistry has in the last 30 years reached the full maturity of
a scientific discipline. From its early beginnings the subject has continued to
grow rapidly and hardly a month passes without the scientific literature
announcing a novel photo-reaction or a new natural product synthesis using
a photo-reaction as a key step. The steady development of the subject has
seen its application to the synthesis of many compounds which could not
have been synthesized by conventional routes and where often the photo
chemical path can be superior to existing ground-state steps. There is, however,
a reluctance for the synthetic chemist to embrace the technique wholeheartedly
regardless of the synthetic usefulness and the detailed understanding of many
of the photochemical processes.
This textbook is aimed at the chemist who is looking for newer and
superior methods. Sadly it is difficult to make a single volume totally com
prehensive. However the contents have been selected with an eye for areas
where there is currently active interest and where there is undoubted synthetic
potential. The topics covered are aromatic compounds, enones, electron
transfer reactions, phthalimides, heterocycles, azirines, photo-protecting
groups, oxetan formation, and a brief outline of equipment and techniques.
Where possible the authors have highlighted the synthetic value of the
reactions under discussion. It is hoped, by this approach, that more inves
tigators in academic life and, more importantly, in industry will be attracted
to this exciting and worthwhile area.
xi
Contents
1. Photoaddition and Photocyclization Processes of Aromatic
Compounds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Andrew Gilbert
I. Introduction .......................................................... . 1
2. Intermolecular Reactions ............................................... . 2
2.1. Arenes and Ethenes .............................................. . 2
2.2. Arenes and Acetylenes ............................................ . 9
2.3. Arenes and 1,3-Dienes ............................................ . 12
2.4. Acyclic Additions to Arenes and Reduction Processes ................. . 14
2.5. Arene Photodimerizations ................... . 18
3. Intramolecular Cyclization Processes ..................................... . 21
3.1. Arene-Ethene and Arene-Ethyne Systems ............. . 21
3.1.1. Hydrocarbon Systems. . . . . . . . . . . . . . . . . . . . . . . ............ . 21
3.1.2. Aryl Enones .............................................. . 25
3.1.3. Aryl Ethenyl Ethers, Thioethers, and N-Aryl Enamines. 27
3.1.4. Cyclizations of N-Arylanilides and N-Benzoylenamines ..... . 29
3.2. Aryl Butadiene and Butenyne Systems ............................... . 33
3.3. Intramolecular Photocoupling of Arenes ............................. . 37
3.3.1. Stilbene-Phenanthrene-Type Cyclizations ...................... . 37
3.3.2. Photocoupling of Arenes with Intervening Units Other Than
Ethylene. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.3.3. Coupling of Arenes as a Result of Halogen Acid Photoelimination 46
3.4. Photocyclizations of o-Substituted Arenes . . . . . . . . . . . . . . . . . . . . . 49
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
2. Enone Photochemical Cycloaddition in Organic Synthesis...... 61
Alan C Weedon
I. Introduction ...................................................... . 61
2. The Reaction Mechanism ......................... . 62
3. Regiochemistry of Enone Cycloaddition ................... . 70
4. Stereochemistry of Enone Cycloaddition ............... . 91
xiii