TOPICS IN STEREOCHEMISTRY VOLUME 10

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1 TOPICS IN STEREOCHEMISTRY VOLUME 10

2 ADVISORY BOARD STEPHEN J. ANGYAL, University of New South Wales, Sydney, Australia JOHN C. BAILAR, Jr., University of Illinois, Urbana, Illinois GIANCARLO BERTI, University of Pisa, Pisa, Ztuly JOHANNES DALE, University of Oslo, Oslo, Norway DAVID GINSBURG, Technion, Israel Institute of Technology, Haifa, lsroel KURT MISLOW, Princeton University, Princeton, New Jersey SAN-ICHIRO MIZUSHIMA, Japan Academy, Tokyo, Jupan GUY OURISSON, University of Strusbourg, Strusbourg, France VLADIMIR PRELOG, Eidgenzssische Technische Hochschule, Zurich, Switzerland HANS WYNBERG, University of Groningen, Groningen, The Netherlands

3 TOPICS IN STEREOCHEMISTRY EDITORS ERNEST L. ELIEL Professor of Chemistry University of North Carolina Chapel Hill, North Carolina NORMAN L. ALLINGER Professor of Chemistry University of Georgia Athens, Georgia VOLUME 10 AN PUBLICATION JOHN WILEY & SONS NewYork Chichester Brisbane Toronto

4 An Intersciencea Publication 1978 by John Wiley & Sons, Inc. All rights reserved. Published simultaneously in Canada. Reproduction or translation of any part of this work beyond that permitted by Sections 107 or 108 of the 1976 United States Copyright Act without the permission of the copyright owner is unlawful. Requests for permission or further information should be addressed to the Permissions Department, John Wiley & Sons, Inc. Library of Congress Catalog Card Number: ISBN Printed in the United States of America

5 To the memory of William Klyne

INTRODUCTION TO THE SERIES During the last fifteen years several texts in the areas of stereochemistry and conformational analysis have been published, including Stereochemistry of Carbon Compounds

6 INTRODUCTION TO THE SERIES During the last fifteen years several texts in the areas of stereochemistry and conformational analysis have been published, including Stereochemistry of Carbon Compounds (Eliel, McGraw-Hill, 1962) and Conformational Analysis (Eliel, Allinger, Angyal, and Morrison, Interscience, 1965). While the writing of these books was stimulated by the high level of research activity in the area of stereochemistry, it has, in turn, spurred further activity. As a result, many of the details found in these texts are already inadequate or out of date, although the student of stereochemistry and conformational analysis may still learn the basic concepts of the subject from them. For both human and economic reasons, standard textbooks can be revised only at infrequent intervals. Yet the spate of periodical publications in the field of stereochemistry is such that it is an almost hopeless task for anyone to update himself by reading all the original literature. The present series is designed to bridge the resulting gap. If that were its only purpose, this series would have been called Advances (or Recent Advances ) in Stereochemistry. It must be remembered, however, that the above-mentioned texts were themselves not treatises and did not aim at an exhaustive treatment of the field. Thus the present series has a second purpose, namely to deal in greater detail with some of the topics summarized in the standard texts. It is for this reason that we have selected the title Topics in Stereochemistry. The series is intended for the advanced student, the teacher, and the active researcher. A background for the basic knowledge in the field of stereochemistry is assumed. Each chapter is written by an expert in the field and, hopefully, covers its subject in depth. We have tried to choose topics of fundamental import aimed primarily at an audience of organic chemists but involved frequently with fundamental principles of physical chemistry and molecular physics, and dealing also with certain stereochemical aspects of inorganic chemistry and biochemistry. It is our intention to bring out future volumes at intervals of one to two years. The Editors will welcome suggestions as to suitable topics. vii

7 viii Introduction We are fortunate in having been able to secure the help of an international board of Editorial Advisors who have been of great assistance by suggesting topics and authors for several articles and by helping us avoid duplication of topics appearing in other, related monograph series. We are grateful to the Editorial Advisors for this assistance, but the Editors and Authors alone must assume the responsibility for any shortcomings of Topics in Stereochemistry. E. L. Eliel N. L. Allinger June 1978

8 PREFACE The first of the four chapers in Volume 10, by Benzion Fuchs, is about the stereochemistry, and, in particular, the conformation of fivemembered rings, both carbocyclic and heterocyclic. In contrast to the cyclohexane ring and its heterocyclic analogs, which lie in deep energy wells represented by the chair conformations, five-membered rings are known to be highly mobile, conformationally speaking. It was recognized early that cyclopentanes are puckered and that there are two nonplanar conformations more symmetrical than the others: the half-chair or Cz and the envelope or C, conformation; it was also recognized that cyclopentane rapidly pseudorotates between these conformations and an infinity of other, less symmetrical ones. Nevertheless there arose a tendency to overinterpret the behavior of substituted cyclopentanes or heterocyclopentanes in terms of the two symmetrical conformations of the parent compound. In his chapter, Fuchs has critically examined the conformational behavior of a number of such compounds both on a theoretical and on an experimental basis, with the emphasis of the experimental work being on spectroscopic and diffractional behavior. While the chapter does not purport to be exhaustive, it hopefully deals with enough systems to allow workers in the field to generalize the findings to whatever saturated five-member ring they may have encountered. Topics in Stereochemistry has sometimes been criticized for its paucity of coverage of the extensive field of inorganic stereochemistry. This has largely not been by choice of the editors, but has resulted from the difficulty we have encountered in interesting inorganic chemists to contribute to a stereochemistry series in which the emphasis has been on the organic side. We are constantly endeavoring to correct this situation and are pleased that, in the present volume, there is a purely inorganicstereochemical chapter by Y. Saito concerned with the absolute stereochemistry of chelate complexes. Determining the absolute configuration of a representative series of chiral compounds is basic to the understanding of any area of stereochemistry; the emphasis in Saito s chapter is on the ix

X Preface determination of configuration of inorganic complexes, in most cases by the Bijvoet method (X-ray fluorescence), Saito proceeds to discuss the correlation of absolute configuration and

9 X Preface determination of configuration of inorganic complexes, in most cases by the Bijvoet method (X-ray fluorescence), Saito proceeds to discuss the correlation of absolute configuration and optical rotatory dispersion (or circular dichroism), the hope being that the much simpler and quicker technique of ORD-CD may take the place of the relatively tedious crystallographic determinations of configuration, at least when complexes of similar structure are compared. This correlation is so much the more important, since chemical interconversion-so popular in the determination of configuration of organic compounds-is generally not an available option for inorganic species which may differ in the nature of the metal as well as that of the ligand. The third chapter in this volume, by H. B. Kagan and J. C. Fiaud, deals with asymmetric synthesis. The topic of asymmetric synthesis was COVered exhaustively in Asymmetric Organic Reactions by J. D. Morrison and H. S. Mosher in (The hardback edition of this text is now out of print, but fortunately, the book has been reprinted as a paperback by the American Chemical Society.) However, much has happened since indeed, the subject of asymmetric synthesis has been a very popular one in recent years, with one or more articles or communications appearing in nearly every issue of the major organic journals today. The practical importance of synthesizing chiral compounds directly (avoiding the need for resolution) is self-evident and several efficient methods, both chemical and catalytic, have been developed in recent years (though the literature also abounds with cases which are clearly of no practical utility). Kagan and Fiaud have reviewed and organized the various types of syntheses developed or refined since the appearance of the Morrison-Mosher book in a chapter containing over 300 references. The fourth chapter, by G. Sullivan, deals with the determination of optical purity by chiral shift reagents. In Volume 2 of Topics in Stereochemistry we published a chapter by Raban and Mislow dealing with the general topic of determination of optical purity; this chapter has now become the classic in the field. The one important method which it does not include-because the method had not yet been discovered when the chapter appeared in 1967-is that involving chiral lanthanide complexes. Sullivan has discussed this method with special emphasis on the practical aspects, with the thought that the method will be much used in the future even by investigators who have little prior experience with the use of lanthanide shift reagents and that these investigators will appreciate any help they can get in planning their experiments with maximum opportunity for success.

10 Preface We are saddened to have to report the death, on November 13, 1977, of William Klyne, one of our advisors and one of the world s experts in the area of stereochemistry. We shall miss his sage advice and his loyal friendship. This volume is dedicated to his memory. Chapel Hill, Norih Carolina Aihens, Georgia June 1978 xi ERNEST L. ELIEL NORMAN L. ALLINGER

11 CONTENTS CONFORMATIONS OF FIVE-MEMBERED RINGS by Benzion Fuchs, Department of Chemistry, Tel-Aviv University, Tel-Aviv, Israel... 1 ABSOLUTE STEREOCHEMISTRY OF CHELATE COMPLEXES by Yoshihiko Saito, The Institute for Solid State Physics, University of Tokyo, Tokyo, Japan NEW APPROACHES IN ASYMMETRIC SYNTHESIS by H. B. Kagan and J. C. Fiaud, Universite' Paris Sud, Laboratoire de Synthbe Asyme'trique, Orsay, France CHIRAL LANTHANIDE SHIFT REAGENTS by Glenn R. Sullivan, Department of Chemistry, California Institute of Technology, Pasadena, California Subject Index Cumulative Index, Volumes xiii

12 TOPICS IN STEREOCHEMISTRY VOLUME 10

TOPICS IN STEREOCHEMISTRY EDITORS. ERNEST L. ELIEL Professor of Chemistry University of North Carolina Chapel Hill, North Carolina SAMUEL H.

TOPICS IN STEREOCHEMISTRY EDITORS ERNEST L. ELIEL Professor of Chemistry University of North Carolina Chapel Hill, North Carolina SAMUEL H. WILEN Professor of Chemistry Ciry College, City University of