INTERMEDIATES AND REARRANGEMENTS

Transcription

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2 INTERMEDIATES AND REARRANGEMENTS IN ORGANIC SYNTHESIS Bapusaheb S. Jagdale M.Sc., Ph.D. Thansing B. Pawar M.Sc., Ph.D. Vishnu A. Adole M.Sc., CSIR-NET (JRF), UGC- SET, GATE MUMBAI NEW DELHI NAGPUR BENGALURU HYDERABAD CHENNAI PUNE LUCKNOW AHMEDABAD ERNAKULAM BHUBANESWAR KOLKATA

3 Authors 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 and/or otherwise without the prior written permission of the publisher. First Edition : 2016 Published by : Mrs. Meena Pandey for Himalaya Publishing House Pvt. Ltd., Ramdoot, Dr. Bhalerao Marg, Girgaon, Mumbai Phone: / , Fax: himpub@vsnl.com; Website: Branch Offices : New Delhi : Pooja Apartments, 4-B, Murari Lal Street, Ansari Road, Darya Ganj, New Delhi Phone: , ; Fax: Nagpur : Kundanlal Chandak Industrial Estate, Ghat Road, Nagpur Phone: , ; Telefax: Bengaluru : Plot No , 2nd Main Road Seshadripuram, Behind Nataraja Theatre, Bengaluru Phone: , , Phone: , , , Hyderabad : No , Lingampally, Besides Raghavendra Swamy Matham, Kachiguda, Hyderabad Phone: , Chennai : New-20, Old-59, Thirumalai Pillai Road, T. Nagar, Chennai Mobile: Pune : First Floor, "Laksha" Apartment, No. 527, Mehunpura, Shaniwarpeth (Near Prabhat Theatre), Pune Phone: / ; Mobile: Lucknow : House No 731, Shekhupura Colony, Near B.D. Convent School, Aliganj, Lucknow Phone: ; Mobile: Ahmedabad : 114, SHAIL, 1st Floor, Opp. Madhu Sudan House, C.G. Road, Navrang Pura, Ahmedabad Phone: ; Mobile: Ernakulam : 39/176 (New No: 60/251) 1 st Floor, Karikkamuri Road, Ernakulam, Kochi Phone: , Mobile: Bhubaneswar : 5 Station Square, Bhubaneswar (Odisha). Phone: , Mobile: Kolkata : 108/4, Beliaghata Main Road, Near ID Hospital, Opp. SBI Bank, Kolkata , Phone: , Mobile: DTP by : Rajani Tambe Printed at : Geetanjali Press Pvt. Ltd., Kundanlal Chandak Industrial Estate, Ghat Road, Nagpur On Behalf of HPH.

4 We Dedicate This Book To Our Students

5 Preface We are very much happy to present this book titled Intermediates and Rearrangements in Organic Synthesis in the hands of students and teachers. The main purpose of writing this book is to create more interest in the subject of organic chemistry. This book provides the deeper understanding of organic reaction mechanism. The special thing about this book is it is written by keeping in mind various competitive exams. The book consists of main topics of organic chemistry which are very useful for the preparation of different exams based on chemistry. The topics included are intermediates and rearrangement reactions. Intermediates and rearrangements are very important parts of organic chemistry without which students cannot get good understanding of organic chemistry. The topics are explained in simple way which will give clear ideas to the students. Each concept is explained by giving ample number of examples to help a detailed understanding. The examples from various competitive exams are also included and thus, this will provide easy platform for the students who are preparing for different exams. So we hope that this book shall be received by the students and teachers with great excitement. Suggestions for next edition will be accepted with warm welcome. Authors

6 ACKNOWLEDGMENT To write a book not only requires hard work of the authors but also the support of well-wishers. Our special thanks goes to Hon. Dr. Apoorbhau Prashantdada Hiray who always motivates us for undertaking challenging academic works. We would like to extend our thanks to the staff and students of the Department of Chemistry, Loknete Vyankarao Hiray College, Nashik, who made our work easier. We would like to thank Prof. Kishore R. Nikam, Department of English, Loknete Vyankarao Hiray College, Nashik, who helped us in drafting the language. Mr. V.A. Adole would like to thank the teachers who developed excitement in the subject of organic chemistry. We authors would also like to thank all the people who helped directly and indirectly during our project. Last but not the least, we are very much thankful to our publishers who showed interest in our work. Authors

7 Contents Sr. No. Name Page No. 1 Reaction Intermediates 1.1 Carbocation 1.2 Carbanion 1.3 Free radicals 1.4 Carbenes 1.5 Nitrenes 1.6 Benzyne 2 Molecular Rearrangements 2.1 Introduction 2.2 Pinacol-pinacolone rearrangement 2.3 Beckmann rearrangement 2.4 Baeyer-Villiger rearrangement 2.5 Dienone-Phenol rearrangement 2.6 Wagner-Meerwein rearrangement 2.7 Favorskii rearrangement 2.8 Benzil-Benzillic acid rearrangement 2.9 Wolff rearrangement 2.10 Hofmann rearrangement 2.11 Schmidt rearrangement 2.12 Curtius rearrangement 2.13 Lossen rearrangement 2.14 Fries rearrangement 2.15 Claisen rearrangement 2.16 Cope rearrangement 2.17 Sommelet-Hauser rearrangement 2.18 Stevens rearrangement 2.19 Dakin rearrangement 2.20 Lumiketone rearrangement 2.21 Di- -methane rearrangement 2.22 Transannular rearrangements 2.23 Eschenmoser-Tanabe fragmentation

8 2.24 Grob fragmentation 2.25 Wharton olefin synthesis 2.26 Baker-Venkataraman rearrangement 2.27 Benzidine rearrangement 2.28 Ciamician-Dennstedt rearrangement 2.29 Neber rearrangement 2.30 Payne rearrangement 2.31 Pummerer rearrangement 2.32 Smiles rearrangement 2.33 Bamberger rearrangement 2.34 Brook rearrangement 2.35 Meyer-Schuster rearrangement 2.36 Mislow-Evans rearrangement 2.37 Carroll rearrangement 2.38 Orton rearrangement 2.39 Hofmann-Martius rearrangement 2.40 Hydroperoxide rearrangement Practice Problems Bibliography 156

9 3 Chapter Practice Problems A. Explain each of the following observations. 1. Cyclopentadiene is more acidic than cycloheptatriene Bromotrypticine is inert towards SN1 reaction. 3. Benzene on reaction with neopentyl chloride/alcl 3 gives following compound as a major product. 4. Addition of HBr to styrene in presence of H 2O 2 forms (2-Bromoethyl)benzene. 5. How will you account for given variation in pka value? 6. In the following reaction, compound A is formed and not compound B. 7. The compound given below is less acidic. 8. Cis- and trans-1,2- dimethylcyclohexane-1,2-diol give different products on treatment with concentrated sulfuric acid. 9. The dehydration of 3,3-dimethylbutan-2-ol gives tetramethylene.

10 144 Intermediates and Rearrangements in Organic Synthesis 10. In the pinacol rearrangements of PhMeC(OH)-C(OH)PhMe and Ph 2C(OH)-C(OH)Me 2, a phenyl group migrates in the former case but a methyl group migrates in the latter. 11. Compound X reacts faster than Y in Pinacol-Pinacolone rearrangement. 12. The reaction given below does not proceed via normal Favorskii rearrangement pathway. 13. Both compound A and B gives same product C when treated with NaOMe/MeOH. 14. Compound given below does not undergo Pinacol-Pinacolone rearrangement. 15. Wolff rearrangement is used to prepare higher homologue of starting acid. 16. Pinacol rearrangement is used to prepare spiroketone. 17. Aldoximes are not suitable substrates for the Beckman rearrangement. 18. Fries rearrangement of Phenyl acetate gives o-hydroxy acetophenone at high temperature and p-hydroxy acetophenone at low temperature. 19. Ortho tolyl group is having less migratory aptitude than phenyl group in Benzil-Benzillicacid rearrangement. 20. N-Methyl benzamide does not give N-Methyl aniline when treated with Br 2/NaOH whereas benzamide gives aniline under similar reaction conditions. 21. Beckman rearrangement is used prepare synthetic polymer. 22. In the Claisen rearrangement of β-phenyl allyl ether, the allyl group migrates to the 1 position and not to the 3 position.

11 Practice Problems The reaction of compound A with conc. H 2SO 4 forms compound B and C with 57% and 43% respectively. 24. In the Baeyer-Villiger rearrangement of compound 1 with PhCO3H, compound 2 is obtained and not compound In Baeyer-Villiger rearrangement, t-butyl group migrates in preference to phenyl group. B. Provide suitable reaction pathways for following transformations and justify your answer. 1 2

12 146 Intermediates and Rearrangements in Organic Synthesis H H N H Cl O Ba(OH) 2 H H N H O OH

13 Practice Problems 147 O 12 NaOH Br COOH

14 148 Intermediates and Rearrangements in Organic Synthesis

15 Practice Problems O 1.NH 2 OH 2. PCl 5 H N O

16 150 Intermediates and Rearrangements in Organic Synthesis

17 Practice Problems O 48 O CH3 CO 3 H, NaOAc AcOH O 49 50

18 152 Intermediates and Rearrangements in Organic Synthesis C. Predict the products of following O 7 O CH 3 AlCl 3 Low Temperature?

19 Practice Problems

20 154 Intermediates and Rearrangements in Organic Synthesis OH Cl AgNO 3 H 2 O? R

21 Practice Problems