Activated Metals in Organic Synthesis PDF
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ACTIVATED METALS in ORGANIC SYNTHESIS NEW DIRECTIONS in ORGANIC and BIOLOGICAL CHEMISTRY Series Editor C.W. Rees, FRS Imperial College of Science, Technology and Medicine London, UK Activated Metals in Organic Synthesis Pedro Cintas Capillary Electrophoresis: Theory and Practice Patrick Camilleri Cyclization Reactions C. Thebtaranonth and Y. Thebtaranonth Mannich Bases: Chemistry and Uses Maurilio Tramontini and Luigi Angiolini Vicarious Nucleophilic Substitution and Related Processes in Organic Synthesis Mieczyslaw Makosza Radical Cations and Anions M. Chanon, S. Fukuzumi, and F. Chanon Chlorosulfonic Acid: A Versatile Reagent R J. Cremlyn and J. P. Bassin Aromatic Fluorination James H. Clark and Tony W. Bastock Selectivity in Lewis Acid Promoted Reactions M. Santelli and J.-M. Pons Dianion Chemistry Charles M. Thompson Asymmetric Methodology in Organic Synthesis David J. Ager and Michael B. East Chemistry of Pyridoxal Dependent Enzymes David Gani The Anomeric Effect Eusebio Juaristi Chiral Sulfur Reagents M. Mikolajczyk, J. Drabowicz, and P. Kidbasihski ACTIVATED METALS in ORGANIC SYNTHESIS Pedro Cintas DepartmentofOrganic Chemistry UniversityofExtremadura Badajoz,Spain CRC Press TaylorSiFrancisGroup Boca Raton London New York CRC Press is an imprint of the Taylor & Francis Group, an informa business CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 1993 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works ISBN 13: 978-0-8493-7863-8 (hbk) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright.com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com Library of Congress Cataloging-in-Publication Data Cintas, Pedro Activated metals in organic synthesis/Pedro Cintas. p. cm. Includes bibliographical references and index. ISBN 0-8493-7863-X — 1. Organic compounds Synthesis. 2. Metals. I. Title QD262.C525 1993 — 547'.2 dc20 93-3570 CIP Library of Congress Card Number 93-3570 CONTENTS PART ONE: METAL ACTIVATION 1 I. BASIC FORMS OF METALS 3 A. MASSIVE METALS 3 B. DISPERSED METALS 5 1. Metal Films 5 2. Metal Powders 5 3. Organometallic Powders 7 4. Other Dispersed Forms 8 II. METAL VAPOR CHEMISTRY 12 A. GENERAL CONSIDERATIONS 12 B. ALKALI AND ALKALINE-EARTH METAL VAPORS 17 C. TRANSITION METAL VAPORS 19 D. METAL ATOM-SOLVENT CONDENSATIONS 32 E. OTHER APPLICATIONS 34 IB. DEPASSIVATING METHODS 45 A. ACTIVATION BY REAGENTS AND SOLVENTS 46 B. RIEKE METALS 47 C. METAL ANTHRACENE/NAPHTHALENIDE 50 D. OTHER REDUCING METHODS 55 E. INTERMETALLIC COUPLES 59 F. ULTRASONIC IRRADIATION 61 1. Sonochemistry. Basic Principles 61 2. Reactions on Metal Surfaces 62 3. Reactive Metal Powders 63 4. Organometallic Compounds 65 G. METAL GRAPHITES 70 1. Introduction 70 2. Structural Considerations 70 3. Graphite Intercalation Compounds 72 4. Metal Dispersions on Graphite Surfaces 77 5. Other Metallic Graphite Compounds 79 - PART TWO: METAL MEDIATED REACTIONS 93 IV. REDUCTIONS 95 A. UNSATURATED SYSTEMS 95 1. Alkenes, Alkynes, and Aromatic Systems 95 2. Carbonyl Substrates 105 3. Conjugated Reduction 108 B. ORGANIC HALIDES AND RELATED SYSTEMS 110 (v) C. DEOXYGENATION REACTIONS 116 D. REDUCTION OF NITROGEN AND SULFUR FUNCTIONAL GROUPS 119 V. REDUCTIVE CARBONYL COUPLING REACTIONS 130 A. PINACOL REACTION 130 1. Classical Methods 130 2. Low-Valent Metal Reagents 134 3. Other Metal-mediated Pinacolic Reactions 137 B. McMURRY-TYPE REACTIONS 140 1. Titanium Reagents 140 2. Scope and Limitations 143 3. McMurry Coupling with Metals other than Titanium 147 VI. ADDITION REACTIONS TO CARBONYL COMPOUNDS 154 A. BARBIER-TYPE REACTIONS 154 1. Introduction 154 2. Activated Metals 156 3. Reactions in Aqueous Media 166 B. REFORMATSKY-TYPE REACTIONS 172 1. Introduction 172 2. The Reformatsky Reagent 173 3. The Role of Zinc Activation 175 4. Metals other than Zinc 179 5. Stereoselective Reformatsky Reactions 181 VII. CYCLIZATIONS 190 A. SIMMONS-SMITH-TYPE REACTIONS 190 1. Introduction 190 2. Simmons-Smith Reagents 192 3. Metals other than Zinc 194 B. CYCLOADDITIONS 196 C. REFORMATSKY-TYPE CYCLIZATIONS 200 1. Dreiding-Schmidt Reactions 200 2. Intramolecular Reactions 202 3. Other Zinc-mediated Cyclizations 204 D. MISCELLANEOUS CYCLIZATIONS 207 VIII. THE BERNET-VASELLA REACTION 220 A. INTRODUCTION 220 B. ZINC REAGENTS 221 C. SYNTHETIC APPLICATIONS 224 Index 229 (vi) PREFACE Although the achievements of the past thirty years in pure organic chemistry have been quite remarkable, many chemists are convinced that only in the area of organometallic chemistry are there truly new reactions or novel processes waiting to be discovered. The importance of this discipline is clearly demonstrated by the increasing number of books, reviews, and articles dealing with specific reactions of particular metal derivatives, and their application in organic synthesis. The preparation of organometallic reagents represents therefore, an extremely important area of chemistry. Unfortunately, the high price, toxicity, and extreme sensitivity of many organometallic compounds constitute severe limitations and have added urgency to the search for other alternatives. An approach which has received considerable attention involves the use of activated metals. Thus, the reaction of a substrate at a metal surface, either in a catalytic fashion or in a stoichiometric reaction with consumption of the metal is a field that is receiving much current attention. Exceptional reactivity of the physically or chemically activated metal powders has been demonstrated by many reactions, including those of industrial importance. Several methods have been developed to increase the reactivity of the metal, in order to allow an easier access to some organometallic intermediates. Most metals, with the exception of a few alkali and alkaline-earth elements, are relatively too inert to afford the desired organometallic species by direct metallation. Thus, reaction of an organic halide with a transition metal is known to be difficult. Transmetallation, which is a two-step process from organolithium or organomagnesium precursors and the corresponding metal halide is the next preference. Activation methods have made transmetallation possible in a single step. In some cases, this methodology proceeds with increased yields, under milder conditions, and in shorter times, and contrasts with classical transmetallation. Interestingly, some metal-mediated organic transformations are conducted in aqueous media and in the absence of an inert atmosphere. Frequently a metal may not react, even if it is one of those known to be in principle highly reactive. The source of this absence of reactivity is often referred to as passivation, and the initial step in most organometallic preparations is metal activation or depassivation. The first part of this book provides a general account of the generation of activated metals by means of well-established procedures, and discusses how these highly reactive species can be used in the synthesis of some organometallic reagents. The concept of activation or depassivation may appear ambiguous and complex, and intricate phenomena of a physical or chemical nature may take place on the metal. In general, activation of the metal occurs by removing surface contaminants, usually a film of metal oxide, or more generally, increasing the reactive area. Importantly, this activation can be complemented in some instances by the transformation of the bulk solid to a dispersion, which greatly increases the surface area. For this reason, I have included a preliminary section on the basic forms of metals, from commercially available bulk solids usually referred to as massive metals, to those containing very small or fine particles and denoted as dispersed (vii) forms. This section is based mainly on reports by Klabunde, Bond, and others who have contributed significantly to this area. Emphasis has been placed on these dispersed metals, particularly on finely divided metal powders and metal slurries which are indeed organometallic species, since they are clusters of naked atoms stabilized by organic ligands. The second chapter analyzes the principles and applications of a rather physical activation, the vaporization and subsequent co-condensation of metal atoms. Part one concludes with a description of the depassivating methods employed commonly in . laboratory syntheses Part two describes some important metal-mediated organic reactions. These include representative reactions in which the activation of the metal plays a crucial role. In addition to metal-induced reductive methods and pinacolic, Reformatsky-, and Barbier-type reactions, I have added two relatively modem organic reactions: the McMurry ketone-olefin coupling and the Bernet-Vasella reaction. With a few exceptions, mechanisms are not generally discussed. The reader should not expect full information on these topics because that is not the purpose of this book. My aim has been to bring out the synthetic uselfuness of this approach in some relevant organic transformations rather than to provide a comprehensive account; and it is obviously not possible to cover each topic in great depth. Nor would this be desirable, even if possible. Nevertheless, the sections will be a source of general information and will stimulate the further pursuit of individual topics. In undertaking a task of this magnitude, particularly with regard to the large number of structural formulae, equations, and schemes, errors will be inevitable. I do hope, however, that serious as these may be, they will not detract from the essential interest of the book. Also, I apologize for any omissions or citations that have received less emphasis than deserved. I am indebted to all my talented colleagues for their fruitful discussions and continuous help, and particularly to Professors Martin Avalos and Jose L. Jimenez for their advice and assistance. I am also grateful to my good friends Dr. Alois Fiirstner (Graz, Austria) and Prof. Jean-Louis Luche (Grenoble) for their comments and valuable information on this subject. In addition, I would like to thank Professors Kenneth J. Klabunde (Manhattan, Kansas), Reuben D. Rieke (Lincoln, Nebraska), Andrea Vasella (Zürich), Helmut Bönnemann (Mülheim, Germany), and Dr. Bruno Bernet (Zürich) for their interest and gratifying encouragement in this project. Special thanks are due to Mr. Navin Sullivan (CRC Press Inc.) for his patience, advice, and assistance. Finally but not least, it is the sacrifice and understanding of my family that have made my writing possible. It is hoped that the reader will find this contribution worth while and will not hesitate to suggest ways in which this material may be improved. Criticisms are always welcome. PedroCintas Badajoz,Spain (viii) ABBREVIATIONS Ac Acetyl, acetate ATON 2,2’-azobisisobutyronitrile Ar Aryl Bn Benzyl Boc /m-Butyloxycarbonyl Bz Benzoyl Bu Butyl Cat Catalytic Cbz Carbobenzyloxy (Benzyloxycarbonyl) COD cisfcis-1,5-Cyclooctadiene Cp Cyclopentadienyl DABCO 1,4-Diazabicyclo[2.2.2]octane DBA Dibenzylideneacetone DBN l,5-Diazabicyclo[4.3.0]non-5-ene DBU l,8-Diazabicyclo[5.4.0]undec-7-ene DCC N -Dicyclohexylcarbodiimide DDQ 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone DEAD Diethylazodicarboxylate de Diastereomeric excess DIBAH Diisobutylaluminum hydride Diglyme Diethyleneglycol dimethyl ether DMA Af ,N-Dimethylacetamide DMAP 4-Dimethylaminopyridine DME 1,2-Dimethoxyethane DMF 7V,iV-Dimethylformamide DMSO Dimethylsulfoxide ee Enantiomeric excess EDA Ethylendiamine (1,2-Diaminoethane) Et Ethyl GIC Graphite intercalation compound Glyme 1,2-Dimethoxyethane Gr Graphite HMPA Hexamethylphosphoramide LAH Lithium aluminum hydride EDA Lithium diisopropylamide M Metal M* Activated metal (ix)
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