INTERMEDIATESAND

REARRANGEMENTSIN ORGANIC SYNTHESIS

Bapusaheb S. JagdaleM.Sc., Ph.D.

Thansing B. PawarM.Sc., Ph.D.

Vishnu A. AdoleM.Sc., CSIR-NET (JRF), UGC- SET, GATE

MUMBAI NEW DELHI NAGPUR BENGALURU HYDERABAD CHENNAI PUNE LUCKNOW AHMEDABAD ERNAKULAM BHUBANESWAR KOLKATA

© AuthorsNo part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by anymeans, electronic, mechanical, photocopying, recording and/or otherwise without the prior written permission of thepublisher.

First Edition : 2016

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We Dedicate This BookTo Our Students

Preface

We are very much happy to present this book titled “Intermediates and Rearrangements inOrganic Synthesis” in the hands of students and teachers. The main purpose of writing this book is tocreate more interest in the subject of organic chemistry. This book provides the deeper understandingof organic reaction mechanism. The special thing about this book is it is written by keeping in mindvarious competitive exams. The book consists of main topics of organic chemistry which are veryuseful for the preparation of different exams based on chemistry. The topics included are intermediatesand rearrangement reactions. Intermediates and rearrangements are very important parts of organicchemistry without which students cannot get good understanding of organic chemistry. The topics areexplained in simple way which will give clear ideas to the students. Each concept is explained bygiving ample number of examples to help a detailed understanding. The examples from variouscompetitive exams are also included and thus, this will provide easy platform for the students who arepreparing for different exams. So we hope that this book shall be received by the students and teacherswith great excitement.

Suggestions for next edition will be accepted with warm welcome.

Authors

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 forundertaking challenging academic works.

We would like to extend our thanks to the staff and students of the Department ofChemistry, Loknete Vyankarao Hiray College, Nashik, who made our work easier. We wouldlike to thank Prof. Kishore R. Nikam, Department of English, Loknete Vyankarao HirayCollege, Nashik, who helped us in drafting the language.

Mr. V.A. Adole would like to thank the teachers who developed excitement in the subject oforganic chemistry.

We authors would also like to thank all the people who helped directly and indirectly during ourproject. Last but not the least, we are very much thankful to our publishers who showed interest in ourwork.

Authors

ContentsSr. No. Name Page No.

1 Reaction Intermediates1.1 Carbocation1.2 Carbanion1.3 Free radicals1.4 Carbenes1.5 Nitrenes1.6 Benzyne

1 – 3229

16222829

2 Molecular Rearrangements2.1 Introduction2.2 Pinacol-pinacolone rearrangement2.3 Beckmann rearrangement2.4 Baeyer-Villiger rearrangement2.5 Dienone-Phenol rearrangement2.6 Wagner-Meerwein rearrangement2.7 Favorskii rearrangement2.8 Benzil-Benzillic acid rearrangement2.9 Wolff rearrangement2.10 Hofmann rearrangement2.11 Schmidt rearrangement2.12 Curtius rearrangement2.13 Lossen rearrangement2.14 Fries rearrangement2.15 Claisen rearrangement2.16 Cope rearrangement2.17 Sommelet-Hauser rearrangement2.18 Stevens rearrangement2.19 Dakin rearrangement2.20 Lumiketone rearrangement2.21 Di--methane rearrangement2.22 Transannular rearrangements2.23 Eschenmoser-Tanabe fragmentation

33 – 14233364651586065717478818588899299

102105106108112118122

2.24 Grob fragmentation2.25 Wharton olefin synthesis2.26 Baker-Venkataraman rearrangement2.27 Benzidine rearrangement2.28 Ciamician-Dennstedt rearrangement2.29 Neber rearrangement2.30 Payne rearrangement2.31 Pummerer rearrangement2.32 Smiles rearrangement2.33 Bamberger rearrangement2.34 Brook rearrangement2.35 Meyer-Schuster rearrangement2.36 Mislow-Evans rearrangement2.37 Carroll rearrangement2.38 Orton rearrangement2.39 Hofmann-Martius rearrangement2.40 Hydroperoxide rearrangement

125128129130131132133134134135136137138138139140141

3 Practice Problems 143 – 155

Bibliography 156

A. Explain each of the following observations.1. Cyclopentadiene is more acidic than cycloheptatriene.2. 1-Bromotrypticine is inert towards SN1 reaction.3. Benzene on reaction with neopentyl chloride/AlCl3 gives following compound as a major

product.

4. Addition of HBr to styrene in presence of H2O2 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 withconcentrated sulfuric acid.

9. The dehydration of 3,3-dimethylbutan-2-ol gives tetramethylene.

3Chapter

Practice Problems

Intermediates and Rearrangements in Organic Synthesis144

10. In the pinacol rearrangements of PhMeC(OH)-C(OH)PhMe and Ph2C(OH)-C(OH)Me2, aphenyl 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 Br2/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.

Practice Problems 145

23. The reaction of compound A with conc. H2SO4 forms compound B and C with 57% and 43%respectively.

24. In the Baeyer-Villiger rearrangement of compound 1 with PhCO3H, compound 2 is obtainedand not compound 3.

25. In Baeyer-Villiger rearrangement, t-butyl group migrates in preference to phenyl group.

B. Provide suitable reaction pathways for following transformations andjustify your answer.

1

2

Intermediates and Rearrangements in Organic Synthesis146

3

4

5

6

NH

H

H

Cl

O

Ba(OH)2

H

HNH OH

O

7

8

9

10

11

Practice Problems 147

12

Br

O

NaOH

COOH

13

14

15

16

17

18

Intermediates and Rearrangements in Organic Synthesis148

19

20

21

22

23

24

25

26

27

Practice Problems 149

28

O

1.NH2OH

2. PCl5

HN

O

29

30

31

32

33

34

35

Intermediates and Rearrangements in Organic Synthesis150

36

37

38

39

40

41

42

43

Practice Problems 151

44

45.

46

47

48O

CH3CO3H, NaOAc

AcOH

O

O

49

50

Intermediates and Rearrangements in Organic Synthesis152

C. Predict the products of following.

1

2

3

4

5

6

7

O

O

CH3

AlCl3

Low Temperature?

Practice Problems 153

8

9

10

11

12

13

14

15

16

Intermediates and Rearrangements in Organic Synthesis154

17

18AgNO3

H2O

OH

Cl

R

?

19

20

21

22

23

24

25

Practice Problems 155

26

27

28

29

30

31