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Molecular Rearrangements in Organic Synthesis MOLECULAR REARRANGEMENTS IN ORGANIC SYNTHESIS MOLECULAR REARRANGEMENTS IN ORGANIC SYNTHESIS Edited by CHRISTIAN M. ROJAS Barnard College, New York, NY, USA Copyright © 2015 by John Wiley & Sons, Inc. All rights reserved Published by John Wiley & Sons, Inc., Hoboken, New Jersey Published simultaneously in Canada No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4470, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, or online at http://www.wiley.com/go/permissions. Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended bysales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. For general information on our other products and services or for technical support, please contact our Customer Care Department within the United States at (800) 762-2974, outside the United States at (317) 572-3993 or fax (317) 572-4002. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic formats. For more information about Wiley products, visit our web site at www.wiley.com. Library of Congress Cataloging-in-Publication Data: Molecular rearrangements in organic synthesis / Edited by Christian M. Rojas. pages cm Includes bibliographical references and index. ISBN 978-1-118-34796-6 (cloth) 1. Rearrangements (Chemistry) 2. Organic compounds–Synthesis. I. Rojas, Christian Miguel, editor. QD281.R35M65 2015 547′.2–dc23 2015013578 Typeset in 10/12pt Times by SPi Global, Chennai, India. Printed in the United States of America 10987654321 1 2015 CONTENTS LIST OF CONTRIBUTORS xvii PREFACE xxi PART 1 1,2-MIGRATIONS 1 1 Pinacol and Semipinacol Rearrangements in Total Synthesis 3 1.1 Introduction, 3 1.2 Pinacol Reaction, 4 1.2.1 Background and Introduction, 4 1.2.2 Stereochemistry of the Pinacol Rearrangement, 6 1.2.3 Preparation of Substrates for the Pinacol Rearrangement, 7 1.2.4 Applications of the Pinacol Reaction in Complex Molecule Synthesis, 7 1.3 Semipinacol Rearrangement, 15 1.3.1 Background and Introduction, 15 1.3.2 Mechanism of the Semipinacol Rearrangement, 17 1.3.3 Selected Variants of Semipinacol Rearrangements, 17 1.3.4 Key Features of the Semipinacol Rearrangement, 18 1.3.5 Examples of Semipinacol Rearrangements in Total Synthesis, 19 1.4 Conclusion, 30 References, 32 vi CONTENTS 2 Baeyer–Villiger (BV) Oxidation/Rearrangement in Organic Synthesis 35 2.1 Introduction, 35 2.2 Mechanism, 35 2.3 Synthetic Applications, 37 2.3.1 Oxidation of Linear Ketones to Esters, 37 2.3.2 Oxidation of Aldehydes to Esters, 42 2.3.3 Oxidation of Cyclic Ketones to Lactones, 42 2.3.4 Asymmetric BV Oxidation/Rearrangement, 48 2.3.5 Oxidation of -Diketones to Anhydrides, 53 2.4 Summary and Outlook, 55 References, 55 3 The Wolff Rearrangement: Tactics, Strategies and Recent Applications in Organic Synthesis 59 3.1 Introduction, 59 3.2 Tactics and Strategies via the Wolff Rearrangement, 60 3.2.1 Methylene Carboxylic Acid Derivatives (Arndt–Eistert Reaction), 60 3.2.2 One-Carbon Ring Contraction of Cyclic -Diazoketones, 61 3.2.3 Reactions of Ketenes and -Oxo-Ketenes, 61 3.3 Mechanistic Features and Selectivity Issues of the Wolff Rearrangement, 63 3.4 Preparation of -Diazocarbonyl Compounds, 64 3.4.1 Acylation of Diazoalkanes, 65 3.4.2 Diazo-Transfer Reactions, 65 3.4.3 Alkyne Cycloaddition, 66 3.5 Recent Synthetic Applications of the Wolff Rearrangement, 67 3.5.1 Wolff Rearrangements Leading to Ketene Intermediates, 67 3.5.2 Wolff Rearrangements Leading to -Oxo-Ketene Intermediates, 73 3.6 Conclusion and Outlook, 80 References, 81 4 Alkyl and Acyl Azide Rearrangements 85 4.1 Introduction, 85 4.2 Alkyl Azide Rearrangements, 86 4.3 Acyl Azide Rearrangements, 98 4.4 Hofmann Rearrangement, 102 4.5 Lossen Rearrangement, 104 4.6 Conclusion, 107 References, 108 CONTENTS vii 5 Beckmann Rearrangements and Fragmentations in Organic Synthesis 111 5.1 Introduction, 111 5.1.1 Beckmann Rearrangement, 112 5.1.2 Beckmann Fragmentation, 115 5.1.3 Photo-Beckmann Rearrangement, 117 5.2 Strategic Planning: A Historical Perspective, 118 5.3 Recent Applications Toward the Synthesis of Natural Products, 121 5.3.1 Toward the Total Synthesis of Pinnaic Acid and Halichlorine, 121 5.3.2 Access to the Core of Mersicarpine, 123 5.3.3 Formal Synthesis of Gephyrotoxin 287C, 124 5.3.4 First Asymmetric Total Synthesis of (+)-Sparteine, 126 5.3.5 Synthesis of the Chloropentane Core of Palau’amine, 128 5.3.6 The Total Synthesis of (−)-Elegansidiol, 128 5.4 Access to Diverse Scaffolds via the Beckmann Reaction, 129 5.4.1 Diterpene Hydrocarbons, 129 5.4.2 Monoterpene-Related Synthesis, 133 5.4.3 Furopyran Synthesis, 133 5.4.4 Synthesis of a Pyrazine Imide, 134 5.5 Formation of Heterocyclic Scaffolds, 136 5.5.1 Oxadiazoles, 136 5.5.2 Synthesis of Benzisoxazoles and Benzoxazoles, 138 5.5.3 Isatins, 138 5.5.4 N-Imidoylbenzotriazoles, 139 5.6 Synthesis of Functional Groups, 140 5.6.1 Amidines, 140 5.6.2 Thioamides, 141 5.6.3 Synthesis of DNA-Photocleaving Agents, 142 5.7 Summary and Outlook, 144 References, 145 6 Brook Rearrangement 151 6.1 Introduction, 151 6.2 Mechanism, 152 6.3 Methods for Generation of -Silyl Alkoxides, 153 6.4 Synthetic Reactions Using Brook Rearrangements in the Reactions of Acylsilanes with Nucleophiles, 154 6.4.1 Preparation of Acylsilanes, 154 6.4.2 Reaction of Acylsilanes with Nucleophiles, Either of Which Contains an -Leaving Group, 155 viii CONTENTS 6.4.3 Reaction of Acylsilanes with Nucleophiles, in Which Generated Carbanions Can Be Stabilized by Conjugating Groups, 157 6.4.4 Use of Ketone Enolates as Nucleophiles Containing an Electron-Accepting Moiety, 163 6.5 Synthetic Reactions Using Brook Rearrangements Triggered by Deprotonation of -Silyl Alcohols, 166 6.6 Synthetic Reactions Using Brook Rearrangements Triggered by Addition of Silylmetallic Reagents, 169 6.7 Synthetic Reactions Using Brook Rearrangements in -Silyl Alkoxides Generated via Regioselective -Ring-Opening of ,-Epoxysilanes by a Nucleophile, 172 6.8 Synthetic Reactions Using Brook Rearrangements in -Silyl Alkoxides Generated by a Base-Induced Ring-Opening of ,-Epoxysilanes, 173 6.9 Conclusion, 176 References, 178 PART II 1,2-MIGRATIONS VIA THREE-MEMBERED RINGS 183 7 The Quasi-Favorskii Rearrangement 185 7.1 Introduction, 185 7.1.1 The Favorskii Rearrangement, 185 7.1.2 The Quasi-Favorskii Rearrangement, 189 7.2 Retrons of the Quasi-Favorskii Rearrangement, 191 7.3 Mechanistic Considerations in the Quasi-Favorskii Rearrangement, 192 7.4 The Preparation of Substrates for the Quasi-Favorskii Rearrangement, 193 7.5 Applications of the Quasi-Favorskii Rearrangement in Synthesis, 199 7.5.1 Methodology, 199 7.5.2 Natural Products, 205 7.5.3 Unnatural Products, 215 7.6 Conclusions and Prospects, 220 Acknowledgments, 222 References, 222 8 The Ramberg–Bäcklund Reaction 227 8.1 Introduction, 227 8.2 Methods to Synthesize Sulfones as RBR Precursors, 229 8.3 Variations of the RBR, 231 8.4 Mechanistic Evaluation of the RBR, 233 CONTENTS ix 8.5 Strategic Considerations Relevant to the Use of the RBR in Synthesis, 234 8.6 Utility, Scope, and Limitations of the RBR, 236 8.6.1 (Sterically Crowded) Acyclic Alkenes, 236 8.6.2 Acyclic Trisubstituted Alkenes, 239 8.6.3 Polyunsaturation, 240 8.6.4 Strained Cyclic Alkenes, 242 8.7 Recent Applications of the RBR in the Synthesis of Complex Target Structures, 246 8.7.1 Fawcettidine, 246 8.7.2 Cylindrocyclophanes A and F, 247 8.7.3 Hirsutellones A–C, 249 8.7.4 Aigialomycin D, 251 8.8 Concluding Remarks, 254 Acknowledgments, 256 References, 256 9 Applications of Di--Methane and Related Rearrangement Reactions in Chemical Synthesis 261 9.1 Introduction: The Basic Process and its Variants, 261 9.2 Mechanistic Features and Competing Reactions, 265 9.3 Structural Requirements of Substrates and Matters of Regio- and Stereochemistry, 271 9.3.1 Basic Structural Requirements, 271 9.3.2 Matters of Regioselectivity, 273 9.3.3 Matters of Stereoselectivity, 275 9.4 Synthetic Routes to Substrates and Applications in Synthesis, 277 9.5 Outlook, 284 References, 285 PART III 1,3-TRANSPOSITIONS 289 10 Payne Rearrangement 291 10.1 Background on the Payne Rearrangement, 291 10.1.1 Payne Rearrangement, 291 10.1.2 Aza-Payne Rearrangement, 293 10.1.3 Thia-Payne Rearrangement, 295 10.2 Synthetic Applications of 2,3-Epoxy Alcohols, 295 10.2.1 Construction
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