Advanced Organic Synthesis METHODS AND TECHNIQUES RICHARD S. MONSON DEPARTMENT OF CHEMISTRY CALIFORNIA STATE COLLEGE, HAYWARD HAYWARD, CALIFORNIA ACADEMIC PRESS New York and London COPYRIGHT © 1971, BY ACADEMIC PRESS, INC. ALL RIGHTS RESERVED NO PART OF THIS BOOK MAY BE REPRODUCED IN ANY FORN BY PHOTOSTAT, MICROFILM, RETRIEVAL SYSTEM, OR ANY OTHER MEANS, WITHOUT WRITTEN PERMISSION FROM THE PUBLISHERS. ACADEMIC PRESS, INC. Ill Fifth Avenue, New York, New York 10003 United Kingdom Edition published by ACADEMIC PRESS, INC. (LONDON) LTD. Berkeley Square House, London WlX 6BA LIBRARY OF CONGRESS CATALOG CARD NUMBER: 75-165531 PRINTED IN THE UNITED STATES OF AMERICA Contents Preface xi I. FUNCTIONAL GROUP MODIFICATIONS 1. Chemical Oxidations I. Chromium Trioxide Oxidation 3 II. Periodate-Permanganate Cleavage of Olefins 5 III. Free Radical Oxidation of an Allylic Position 7 IV. Epoxidation of Olefins 8 V. Baeyer-Villiger Oxidation of Ketones 9 VI. Lead Tetraacetate Oxidation of Cycloalkanols 11 VII. Photolytic Conversion of Cyclohexane to Cyclohexanone Oxime 11 VIII. Oxidation of Ethers to Esters 12 IX. Partial Oxidation of an Aliphatic Side Chain 13 X. Bisdecarboxylation with Lead Tetraacetate 14 XI. Oxidation with Selenium Dioxide 15 References 16 2. Hydride and Related Reductions I. Reduction by Lithium Aluminum Hydride 18 II. Mixed Hydride Reduction 20 III. Reduction with Iridium-Containing Catalysts 22 IV. Reduction of Conjugated Alkenes with Chromium (H) Sulfate 23 References 24 3. Dissolving Metal Reductions I. Reduction by Lithium-Amine 25 II. Reduction by Lithium-Ethylenediamine 26 III. Reduction of a,/MJnsaturated Ketones by Lithium-Ammonia 27 IV. Reduction of a,/9-Unsaturated Ketones in Hexamethylphosphoric Triamide .... 28 V. Reduction of an a,/?-Unsaturated y-Diketone with Zinc 29 References 30 VI CONTENTS 4. Hydroboration I. Hydroboration of Olefins as a Route to Alcohols 32 II. Selective Hydroborations Using Bis(3-methyl-2-butyl)borane (BMB) 35 III. Purification of a Mixture of J9-10- and J1(9)-Octalins 37 References 38 5. Catalytic Hydrogenation I. Hydrogenation over Platinum Catalyst 39 II. Low-Pressure Hydrogenation of Phenols over Rhodium Catalysts 40 III. c/j-4-Hydroxycyclohexanecarboxylic Acid from /?-Hydroxybenzoic Acid 41 IV. 3-Isoquinuclidone from/7-Aminobenzoic Acid 42 V. Homogeneous Catalytic Hydrogenation 43 References 44 6. The Introduction of Halogen I. Halides from Alcohols by Triphenylphosphine—Carbon Tetrahalide 45 II. Halides from Alcohols and Phenols by Triphenylphosphine Dihalide 46 III. Allylic and Benzylic Bromination with W-Bromosuccinimide 48 IV. a-Bromination of Ketones and Dehydrobromination 49 V. Stereospecific Synthesis of /ra/w-4-Halocyclohexanols 51 References 52 7. Miscellaneous Elimination, Substitution, and Addition Reactions I. Methylenecyclohexane by Pyrolysis of an Amine Oxide 54 II. The Wolff-Kishner Reduction 55 III. Dehydration of 2-Decalol 56 IV. Boron Trifluoride Catalyzed Hydrolysis of Nitriles 56 V. Bridged Sulfides by Addition of Sulfur Dichloride to Dienes 57 VI. Methylation by Diazomethane 58 VII. Oxymercuration: A Convenient Route to Markovnikov Hydration of Olefins . ... 60 VIII. Esterification of Tertiary Alcohols 62 IX. Ketalization 63 X. Half-EsterificationofaDiol 64 XI. Substitution on Ferrocene 65 XII. Demethylation of Aryl Methyl Ethers by Boron Tribromide 66 References 67 CONTENTS VlI II. SKELETAL MODIFICATIONS 8. The Diels-Alder Reaction I. 3,6-Diphenyl-4,5-cyclohexenedicarboxylic Anhydride ........... 71 II. Reactions with Butadiene .................. 72 III. Catalysis by Aluminum Chloride ................ 74 IV. Generation of Dienes from Diones ................ 75 V. Reactions with Cyclopentadiene ................. 77 References ....................... 79 9. Enamines as Intermediates I. Preparation of the Morpholine Enamine of Cyclohexanone ......... 80 II. Acylation of Enamines ................... 81 III. Enamines as Michael Addition Reagents .............. 82 IV. Reactions of Enamines with j3-Propiolactone ............. 83 V. Reactions of Enamines with Acrolein ............... 84 References ....................... 86 10. Enolate Ions as Intermediates I. Ketones as Enolates: Car bethoxylation of Cyclic Ketones ......... 87 II. Esters as Enolates: 1,4-Cyclohexanedione and Meerwein's Ester ....... 90 III. Methylsulfinyl Carbanion as a Route to Methyl Ketones .......... 92 IV. Cyclization with Diethyl Malonate ................ 96 V. Carboxylations with Magnesium Methyl Carbonate (MMC) ......... 97 VI. Alkylation of j3-Ketoesters .................. 99 VII. The Robinson Annelation Reaction ................ 101 References ....................... 103 1 1 . The Wittig Reaction I. Benzyl-Containing Ylides .................. 104 II. Alkyl Ylides Requiring «-Butyl Lithium .............. 105 III. Methylsulfinyl Carbanion in the Generation of Ylides .......... 106 IV. The Wittig Reaction Catalyzed by Ethylene Oxide ........... 107 V. Cyclopropylidene Derivatives via the Wittig Reaction .......... 108 References ....................... 110 1 2 . Reactions of Trialkylbor anes I. Trialkylcarbinols from Trialkylboranes and Carbon Monoxide ........ Ill II. Dialkylketones from Trialkylboranes and Carbon Monoxide- Water ...... 112 III. The Reaction of Trialkylboranes with Methyl Vinyl Ketone and Acrolein ..... 114 IV. The Reaction of Trialkylboranes with Ethyl Bromoacetate ......... 115 References ....................... 115 Viil CONTENTS 13. Carbenes as Intermediates I. Carbene Addition by the Zinc-Copper Couple 116 II. Dibromocarbenes 117 III. Dihalocarbenes from Phenyl(trihalomethyl)mercury Compounds 119 References 120 14. Ethynylation I. Generation of Sodium Acetylide in Liquid Ammonia 121 II. The Generation of Sodium Acetylide in Tetrahydrofuran 123 III. The Generation of Sodium Acetylide via Dimsylsodium 124 References 125 15. Structural Isomerizations I. Acid Catalyzed Rearrangement of Saturated Hydrocarbons 126 II. Photolytic Ring Contraction 127 III. Isomerization of 1-Ethynylcylohexanol: Three Methods 129 IV. Photolytic Isomerization of 1,5-Cyclooctadiene 130 V. Oxidative Rearrangement of /3-Diketones 130 VI. Base Catalyzed Rearrangement of 4-Benzoyloxycyclohexanone 131 VII. Allenes from 1,1-Dihalocyclopropanes by Methyllithium 132 References 133 16. Elimination, Substitution, and Addition Reactions Resulting in Carbon-Carbon Bond Formation I. Carboxylation of Carbonium Ions 134 II. Paracyclophane via a 1,6-Hofmann Elimination 136 III. Diphenylcyclopropenone from Commercial Dibenzyl Ketone 137 IV. Phenylcyclopropane from Cinnamaldehyde 139 V. Conversion of Alkyl Chlorides to Nitriles in DMSO 140 VI. Photolytic Addition of Formamide to Olefins 141 VII. Intermolecular Dehydrohalogenation 142 VIII. Ring Enlargement with Diazomethane 143 IX. Conjugate Addition of Grignard Reagents 144 X. Dimethyloxosulfonium Methylide in Methylene Insertions 145 Xl. Acylation of a Cycloalkane: Remote Functionalization 147 XII. The Modified Hunsdiecker Reaction 149 References 150 CONTENTS IX 17. Miscellaneous Preparations I. Derivatives of Adamantane 151 II. Percarboxylic Acids 153 III. Diazomethane 155 IV. Trichloroisocyanuric Acid 156 References 157 Appendix 1. Examples of Multistep Syntheses 158 Appendix 2. Sources of Organic Reagents 161 Appendix 3. Introduction to the Techniques of Synthesis I. The Reaction 166 II. TheWorkup 175 III. Purification of the Product 178 References 188 Subject Index 189 Preface The developments in organic synthesis in recent years have been as dramatic as any that have occurred in laboratory sciences. One need only mention a few terms to under- stand that chemical systems that did not exist twenty years ago have become as much a part of the repertoire of the synthetic organic chemist as borosilicate glassware. The list of such terms would include the Wittig reaction, enamines, carbenes, hydride reductions, the Birch reduction, hydroboration, and so on. Surprisingly, an introduc- tion to the manipulations of these reaction techniques for the undergraduate or grad- uate student has failed to materialize, and it is often necessary for students interested in organic synthesis to approach modern synthetic reactions in a haphazard manner. The purpose of this text is to provide a survey, and systematic introduction to, the modern techniques of organic synthesis for the advanced undergraduate student or the beginning graduate student. An attempt has been made to acquaint the student with a variety of laboratory techniques as well as to introduce him to chemical reagents that require deftness and care in handling. Experiments have been drawn from the standard literature of organic synthesis including suitable modifications of several of the reliable and useful preparations that have appeared in "Organic Synthesis." Other examples have been drawn from the original literature. Where ever possible, the experiments have been adapted to the locker complement commonly found in the advanced synthesis course employing intermediate scale standard taper glassware. Special equipment for the performance of some of the syntheses would include low-pressure hydrogenation apparatus, ultraviolet lamps and reaction vessels, Dry Ice (cold finger) condensers, vacuum sublimation and distillation apparatus, and spectroscopic and chromato- graphic instruments. In general, an attempt has been made to employ as substrates materials that are available commercially at reasonable cost, although several of the experiments require precursor materials whose preparation is detailed in the text.