Organic Reaction Mechanisms 1985

619 Pages·1987·21.162 MB·English

ORGANIC REACTION MECHANISMS 1984
*
ORGANIC REACTION
MECHANISMS 1985
An annual survey covering the literature
dated December 1984 through November 1985
Edited by
A. C. KNIPE and W. E. WATTS,
University of Ulster,
Northern Ireland
An Interscience@ Publication
JOHN WILEY & SONS
- - - -
Chichester New York Brisbane Toronto Singapore
Copyright @ by John Wiley & Ltd.
1987 Sons
All rights reserved.
No part of this book may be reproduced by any means,
or transmitted, or translated into a machine language
without the written permission of the publisher.
Library of Congress Catalog Card Number
66-23143
British Libmry Cataloguing in Publicalion Data:
Organic reaction mechanisms.-1
985
Chemistry, Physical organic-
1.
Periodicals Chemical reactions-
2.
Periodicals
547.1'394'05 QD476
ISBN 0 5
471 91127
Phototypeset by Macmillan India Ltd.
Printed and bound in Great Britain by the Bath Press, Bath, Avon
Contributors
A. ALBERT1 Istituto dei composti del carbonio, Con-
tenenti eteroatomi e loro applicazioni,
Consiglio Nationale delle Ricerche.
Bologna, Italy
C. CHATGILIALOGLU Istituto dei composti del carbonio, Con-
tenenti eteroatomi e lor0 applicazioni,
Consiglio Nationale delle Ricerche,
Bologna, Italy
D. J. COWLEY Department of Chemistry, University of
Ulster at Coleraine, Londonderry,
Northern Ireland
R. A. COX Department of Chemistry, University of
Toronto, Canada
M. R. CRAMPTON Department of Chemistry, Durham Uni-
versity
G. W. J. FLEET Dyson Perrins Laboratory, Oxford Uni-
versity
A. C. KNIPE Department of Chemistry, University of
Ulster at Coleraine, Londonderry,
Northern Ireland
R. B. MOODIE Department of Chemistry, University of
Exeter
C. J. MOODY Department of Chemistry, Imperial Col-
lege of Science and Technology,
London
R. A. MORE O’FERRALL Department of Chemistry, University
College, Dublin, Ireland
A. W. MURRAY Department of Chemistry, University of
Dundee
M. I. PAGE Department of Chemical Sciences,
Huddersfield Polytechnic
R. M. PATON Department of Chemistry, University of
Edinburgh
J. SHORTER Department of Chemistry, University of
Hull
W. J. SPILLANE Chemistry Department, University Col-
lege, Galway, Ireland
C. I. F. WATT Department of Chemistry, University of
Manchester
V
Preface
The present volume, the twenty-first in the series, surveys research on organic
reaction mechanisms described in the literature dated December 1984 to
November 1985. In order to limit the size of the volume, we must necessarily
exclude or restrict overlap with other publications which review specialist areas
(e.g. photochemical reactions, biosynthesis, electrochemistry, organometallic
chemistry, surface chemistry and heterogeneous catalysis). In order to minimize
duplication, while ensuring a comprehensive coverage, the editors conduct a
survey of all relevant literature and allocate publications to appropriate chapters.
While a particular reference may be allocated to more than one chapter, we do
assume that readers will be aware of the alternative chapters to which a border-
line topic of interest may have been preferentially assigned.
There has been only one change of author since last year. Dr Billington, who
had written the Polar Addition chapter since 1982 found it necessary to with-
draw, through conflict of interest, and the chapter has reverted to the previous
author, Dr Knipe. We acknowledge the expert contribution which Dr Billington
made to Organic Reaction Mechanisms during his period as a contributor.
Once again we wish to thank the publication and production staff of John
Wiley & Sons and our team of experienced contributors for their efforts to
ensure that the standards of this series are sustained. We are also indebted to
Dr N. Cully who compiled the subject index.
A.C.K.
W.E.W.
vii
Contents
1 . Reactions of Aldehydes and Ketones by M . 1. Page ............... 1
.
2 Reactions of Acids and their Derivatives by W . J . Spillane ......... 29
.
3 Radical Reactions: Part 1 by A . Alberti and C . Chatgilialoglu ..... 85
.
4 Radical Reactions: Part 2 by D . J . Cowley ...................... 129
5 . Oxidation and Reduction by G . W . J . Fleet ...................... 169
6 . Carbenes and Nitrenes by C . J . Moody ......................... 223
.
7 Nucleophilic Aromatic Substitution by M . R. Crampton ............ 245
.
8 Electrophilic Aromatic Substitution by R . B . Moodie ............. 265
.
9 Carbocations by R . A . Cox ................................... 281
.
10 Nucleophilic Aliphatic Substitution by J . Shorter ................. 299
11. Carbanions and Electrophilic Aliphatic Substitution by C . I . F . Watt 329
12 . Elimination Reactions by R . A . More O'Ferrall .................. 357
13 . Addition Reactions-1 . Polar Addition by A . C. Knipe ........... 381
14 . Addition Reactions-2 . Cycloaddition by R . M . Paton ............ 407
.
15 Molecular Rearrangements by A . W . Murray .................... 445
Author index. 1985 .............................................. 543
Subject Index. 1985 ............................................... 595
ix
Organic Reaction Mechanisms 1985
Edited by A. C. Knipe, W. E. Watts
Copyright © 1987 by John Wiley & Sons, Ltd.
CHAPTER 1
Reactions of Aldehydes and Ketones and Their Derivatives
M. I.
PAGE
Department of Chemical & Physical Sciences, Huddersfeld Polytechnic
Formation and Reactions of Acetals, Ketals and Orthoesters . . . . . . . . . . . 1
Hydrolysis and Formation of Glucosides ......................... 5
Non-enzymic Reactions .................................. 5
Enzymic Reactions. .................................... 5
Reactions and Formation of Nitrogen Derivatives, Schiff Hydrazones,
Oximes and Related Species ......................B.as.e.s., ......
6
C-C Bond Formation and Fission, Aldol and Related Reactions. . . . . . . . . . 10
Other Addition Reactions. ................................. 17
Enolization and Related Reactions. ............................ 19
Other Reactions. ....................................... 22
References ........................................... 23
Formation and Reactions of Acetals, Ketals and Orthoesters
a- and 8-Secondary deuterium kinetic isotope effects on the acid-catalysed
hydrolysis of acetaldehyde diethyl acetal and ethyl vinyl ether are consistent with
both reactions forming the same intermediate carbonium ion (1). The rates of
hydrolysis of the acetal become slower with increasing concentration of dioxan and
the isotope effects decrease, apparently as the mechanism changes to a concerted S,2
m1
type
The relative rates of the acid-catalysed hydrolysis of diethyl acetal and those of
ethyl vinyl ether as a function of the molar fraction of organic solvent in mixtures of
trifluoroethanol and water show identical patterns of behaviour. This solvent
mixture cannot therefore be used to distinguish between A1 and 4 2me chanisms.’
The hydrolysis of the acetal (3)i n aqueous dioxan is said to involve nucleophilic
participation by the ~olvent.~
The ketal function nearest the neighbouring methoxy group is preferentially
hydrolysed in the acid-catalysed hydrolysis of the quinone bisketal(4). Although this
is attributed to intramolecular general acid catalysis by the adjacent protonated
methoxy group many other factors could be responsible?
The general base-catalysed formation of the hemiacetal(5) from cischalcone C is
reversible and proceeds by a stepwise mechanism. There are apparently two breaks
1
2 Organic Reaction Mechanisms 1985
H H
+
CH 3-CH-OEt
Me
H
,CHz-OPh
"'"'-0
9
I
NO2
(3)
in the buffer-rate plot. The changeover from the normally concerted reaction is
attributed to the stability of the phenoxide ion compared with common alkoxide
ions.5
Oxygen-exchange, in aqueous solution, of the pyrylium cation (6) is hydroxide-
ion- and buffercatalysed. It is thought that the intermediate pseudo-base (7), a
hemiketal, reversibly ring-opens to give the ketone-en01 and the diketone.6
The acid-catalysed hydrolysis of 2-hydroxymethylfuran and 5-
to give levulinic acid proceeds by intermediate
hydroxymethylfuran-2-carbaldehyde
formation of a hemiacetal.'
Bromination of the vinyl ether, a-methoxystyrene, proceeds by rate-limiting
breakdown of the hemi-acetal (8). Rate constants for this latter process may be
directly measured and, as expected, show hydroxide-ion, acid, buffer and water
catalysis.8
Thermodynamic activation parameters for the hydrolysis of vinyldioxanes and
vinyldioxolanes (9) have been correlated with ~tructure.~
The reaction of o-phthaldehyde with primary amines in the presence of thiols
produces a thio-indole which is intensely fluorescent. The mechanism probably
involves initial imine formation which is then attacked by the thiol to give the
intermediate (10) which ring-closes to product. Hemi-thioacetal formation inhibits
the reaction."
The previously reported rate constant for the hydroxide-ion-catalysed break-
down of the cyclic hemiorthoester (ll),w hich was above the diffusion controlled
I Reactions of Aldehydes and Ketones and Their Derivatives 3
(7)
H
SR
limit, is in error because the rate of reaction shows a non-linear dependence on buffer
concentration. In the absence of buffer the rate-limiting step is deprotonation of the
hydroxy group of (11 ). In more concentrated buffer deprotonation becomes
reversible and the breakdown of the anion is rate-limiting.’ Similar observations
have been made with the sulphur analogue (12).”
The acid-catalysed hydrolysis of proceeds by rate-
2-methylene-1,3-dithiolane
limiting formation of the carbonium ion (13) above pH 3 but by hydration of (13) at
high buffer concentration. Below pH 2, breakdown of the hydrogen orrho-ester (14)
becomes rate-1imiti11g.I~T hese observations are in contrast to the behaviour of
ketene acetals which show rate-limiting non-reversible protonation of carbon.
The pseudophase model for the acid-catalysed hydrolysis of acetals and oximes in
the presence of anionic micelles of sodium dodecyl sulphate fails at high acid
concentrations. This discrepancy has been attributed to an additional catalytic
pathway across the interfacial b0~ndary.I~
The Page-Jencks theory of intramolecular and enzymatic reactions has been
’
criticized.’ Although the examples of relative rates of intramolecular reactions used
can be explained by a combination of entropy and strain energy effects it has now
been proposed that a time-critical distance parameter is more useful.
The evaluation of the effect of strain energy changes on reactivity has been
reviewed;I6 this includes additions to the carbonyl group and the hydrolysis of
acetals and orthoesters.
The stereochemistry of spiroacetals formed in cyclization reactions has been
established.”
Acid-catalysed benzy lidenation of gives exo-phenyl
l-t-butylcyclohexane-1,2-diol
benzylidene acetal under kinetic control whereas other alkyl-substituted derivatives
give the endo-isomer. This has been attributed to unfavourable steric interactions in
the intermediate carbonium ion (15) leading to the endo-phenyl product.”.
The reaction of camphor with trifluoromethanesulphonic anhydride in the
absence of base gives a mixture of triflate ketals and rearranged di-triflates. Similar
products can be generated from camphenyl triflates, indicative of common
*
intermediates.
O
4 Organic Reaction Mechanisms 1985
'YI
HO 0
The acid-catalysed cleavage of unsymmetrically substituted cyclic formals with
acetic anhydride occurs by preferential rupture of the less congested C - 0 bond (16)
and is totally regiospecific for 1,3-dioxanes. It is assumed that ring-opening is
irreversible and the selectivity is due to differences in energies of the oxocarbonium
ion intermediate.21
The bicyclic ketal(17), is resistant to hydrolysis but is specifically cleaved by acetyl
iodide.22
Dimethyl ketals can be hydrolysed during the hydroboration and basic peroxide
oxidation of alkenes if the methoxy group can coordinate to the organoboron
intermediate.23
Dimethylboron bromide and diphenylboran bromide are very efficient reagents
for the cleavage of cyclic and acylic acetals and ketals. Coordination of the boron to
the least hindered oxygen of cyclic ketals and subsequent ring opening (18) have
been used to explain chemoselectivity and reacti~ity.~~
The highly chemo- and stereoselective cleavage of acetals with organoaluminium
and organotitanium reagents has been attributed to a combination of steric and
anomeric effects. Unfortunately, it is not clear whether the model suggested for the
aluminium reagent is applicable to titanium cases.2s
In addition to the usual tertiary alcohol, the reaction of methylmagnesium iodide
with the acetal(l9) gives products arising from regioselective carbon-oxygen bond
fission and intermolecular transfer of the Grignard methyl group to the intermediate
oxocarbonium ion.26