Organic Reaction Mechanisms 1994

655 Pages·1996·20.018 MB·English

ORGANIC REACTION MECHANISMS 1994
*
ORGANIC REACTION
MECHANISMS 1994
An annual survey covering the literature
dated December 1993 to November 1994
Edited by
A. C. Knipe and W. E. Watts
University of Ulster
Northern Ireland
An Interscience" Publication
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Contributors
W. R. BOWMAN Department of Chemistry, Loughborough University,
Loughborough, Leicestershire, UK
D. R. COGHLAN Department of Chemistry, Loughborough University,
Loughborough, Leicestershire, UK
R. G. COOMBES Department of Chemistry, Brunel University, Uxbridge,
Middlesex, UB8 3PH, UK
R. A. COX Department of Chemistry, University of Toronto, 80 St.
George Street, Toronto, Ontario M5S 1A1, Canada
M. R. CRAMPTON Department of Chemistry, University of Durham, Durham
DH1 3LE, UK
N. DENNIS Australian Commercial Research and Development Ltd, GPO
Box 248 1, Brisbane, Queensland 4001, Australia
G. W. J. FLEET Dyson Perrins Laboratory, University of Oxford, South Parks
Road, Oxford, OX1 3QY, UK
S. G. W. GINN School of Applied Biological and Chemical Sciences,
University of Ulster Newtownabbey, Co. Antrim
BT37 OQB, UK
J. G. KNIGHT Department of Chemistry, University of Newcastle upon Tyne,
Newcastle upon Tyne NE1 7RU, UK
A. KNIPE School of Applied Biological and Chemical Sciences,
C.
University of Ulster, Coleraine, Co Londonderry,
BT52 lSA, UK
P. KO~OVSKY Department of Chemistry, University of Leicester, Leicester
LE1 7RH, UK
A. W. MURRAY Department of Chemistry, University of Dundee, Dundee
DDI 4HN, UK
M. I. PAGE Department of Chemical and Biological Sciences, University
of Huddersfield, Huddersfield, W. Yorkshire, UK
J. SHORTER School of Chemistry, University of Hull, Hull HU6 7RX, UK
W. J. SPILLANE Department of Chemistry, University College, Galway, Ireland
J. H. STEWART School of Applied Biological and Chemical Sciences,
University of Ulster, Newtownabbey, Co. Antrim
BT37 OQB, UK
V
Preface
The present volume, the thirtieth in the series, surveys research on organic reaction
mechanisms described in the literature dated December 1993 to November 1994. 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 borderline topic of interest may have been preferentially
assigned.
There has been only one change of authorship since last year. We say farewell to Dr
H. Maskill, who has for several years contributed expert comment on carbocations, and
welcome the return of Dr R. Cox, who has enjoyed a productive time-out. Once again
we wish to thank the publishing 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 increasingly aware of the conflicting pressures experienced
by university academics as they attempt to meet publication deadlines, often in vain, but
remain optimistic that there will be some improvement in due course. 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 and their Derivatives
by M . I . Page ..................................... 1
.
2 Reactions of Acids and their Derivatives by W. J . Spillane ..... 19
.
3 Radical Reactions: Part 1 by W. R . Bowman and D . R . Coghlan . 73
.
4 Radical Reactions: Part 2 by S . W. Ginn and J . H . Stewart ..... 107
.
5 Oxidation and Reduction by G . W. J . Fleet ................ 147
.
6 Carbenes and Nitrenes by J. G . Knight .................. 175
.
7 Nucleophilic Aromatic Substitution by M . R . Crampton ....... 195
.
8 Electrophilic Aromatic Substitution by R . G . Coombes . . . . . . . 211
.
9 Carbocations by R . A . Cox .......................... 223
.
10 Nucleophilic Aliphatic Substitution by J. Shorter . . . . . . . . . . . . 243
.
11 Carbanions and Electrophilic Aliphatic Substitution
by A . C . Knipe ................................... 275
.
12 Elimination Reactions by A . C . Knipe ................... 305
.
13 Addition Reactions: Polar Addition by P. KoEovslj ......... 331
.
14 Addition Reactions: Cycloaddition by N . Dennis . . . . . . . . . . . 373
.
15 Molecular Rearrangements by A . W. Murray .............. 405
Author Index 1994. ................................... 53 I
Subject Index 1990-1994 ................................ 57 1
ix
CHAPTER I
Reactions of Aldehydes and Ketones and their Derivatives
M. I. PAGE
Department of Chemical and Biological Sciences, University of HuddersJield
Formation and Reactions of Acetals and Orthoesters . . . . . . . . . . . . . . . . . 1
Hydrolysis and Formation of Glucosides, Nucleosides, Oxazines, and
Related Compounds ...................................... 2
Reactions and Formation of Nitrogen Derivatives, Schiff Bases, Hydrazones,
Oximes, and Related Species ................................. 4
C-C Bond Formation and Fission: Aldol and Related Reactions . . . . . . . . . 7
Other Addition Reactions ................................... 9
Enolization and Related Reactions ............................. 11
Hydrolysis and Reactions of Vinyl Ethers and Related Compounds ........ 12
Other Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
References. ............................................ 14
Formation and Reactions of Acetals and Orthoesters
The breakdown of the unstable methyl hemiacetals of aryl-substituted acetophenones
(1) has been studied following their build-up in the acid-catalysed hydrolysis of the
corresponding dimethyl acetals. Substituent effects suggest that the general base-
catalysed reaction involves an imbalance in the transition state (2) with considerable
C-0 bond cleavage (as measured by p) but little change in hybridization at C (as
measured by p).
The hydrolysis of the acetal (3) occurs with intramolecular general acid catalysis and
the kinetically equivalent acid-catalysed reaction of the carboxylate anion is about 300-
fold faster than that of the corresponding methyl ester. This is attributed to the strong
intramolecular hydrogen bond formed in the hydrolysis product (4).2
The Lewis acid-mediated addition of carbon nucleophiles to acyclic acetals occurs
through oxocarbenium ion intermediates rather than by the previously claimed SN2-type
process. 3
There have been kinetic studies on the hydrolysis of bicyclic acetals4 and cyclic
aceta~s.~
Based more on assertion than on fact or logical deduction, the contribution of
stereoelectronic effects to the hydrolysis of acetals has been reviewed. Circular
arguments are used to suggest that acid-catalysed hydrolysis of acetals derived from
aldehydes have a late oxocarbocation-like transition state whereas that for acetals
derived from ketones resembles the conjugate acid.6
Organic Reaction Mechanisms 1994 Edited by A. C Knipe and W E. Watts
1996 John Wiley & Sons Ltd
1
2 Organic Reaction Mechanisms 1994
From thermochemical data, some very useful equilibrium constants for acetal
formation and hydration have been calculated. For example, the equilibrium constant
for acetal formation from methyl formate is only 150-fold less than that for
acetophenone.?
The lithium perchlorate-catalysed formation of dithioacetals from aldehydes and
acetals in diethyl ether occurs by the intermediate formation of oxocarbenium ions.'
Glyoxalase enzymes catalyse the transformation of a-keto-aldehydes into the
corresponding a-hydroxy-carboxylic acids by an initial formation of a thiohemiacetal
followed by deprotonation to form the enediol A 8-cyclodextrin modified with
(5). an
aminothiol side-arm favours hemithioacetal formation with 2-naphthylglyoxal but
decelerates the subsequent rearrangement.'
OH, ,OMe
Ar/'\Me
(1)
Hydrolysis and Formation of Glucosides, Nucleosides, Oxazines, and Related
Compounds
The neighbouring 2-phosphate dianion in (6) catalyses the hydrolysis of the glucoside
by intermediate formation of a 1,2-cyclic phosphate diester. The pH-independent rate of
hydrolysis of (6) is about 100 times faster than that of 4-nitrophenyl 8-D-glucoside.l o
The hydrolysis of 0-isopropenyl a-glucopyranoside occurs by irreversible C-
protonation (7) followed by alkenyl ether cleavage, and not by glycosidic bond
I Reactions of Aldehydes and Ketones and their Derivatives 3
cleavage. The p-anomer reacts five times more slowly and also does not involve
'
glucosyl-oxygen fission.'
The hydrolysis of aryl glycosides of N-acetylneuraminic acid occurs by four pH-
dependent pathways. "0 kinetic isotope effects on the leaving group are in line with the
expectation from leaving-group effects. l2
Cyclitol (8) formation from the treatment of 5-enopyranosides (9) with Hg(I1) salts is
non-stereoselective with respect to C(6) and is thought to occur by initial addition of Hg
to the alkene followed by ring-opening and -closing to give (8).13
The intramolecular trapping of the intermediate oxocarbenium ion formed during the
acetolysis of caged sugar acetals can generate ticyclic ~ystems.'~
The acid-catalysed hydrolysis of the cyclic nucleosides (10: X = 0, S, NH) occurs
with exclusive cleavage of the N-glycosidic bond for the S- and N-bridged derivatives
whereas the 0-bridged cyclonucleoside also undergoes fission of the 5',8-cyclo
linkage.
l5
HO
\
z-03p0\
*OR Ro OR OH
(8)
I 1
OH OH
4 Organic Reaction Mechanisms 1994
Reactions and Formation of Nitrogen Derivatives, Schiff Bases, Hydrazones,
Oximes, and Related Species
The aniline adducts of a-nitrostilbenes undergo a unimolecular decomposition into the
corresponding iminium ion and the nitroalkene carbanion (11). The rate of
decomposition has a strong dependence on the aniline substituent (p = - 2.2) and
the pK, of the arylnitromethane (PIg= - 1.28). There is a substantial transition-state
imbalance similar to that in the deprotonation of arylnitromethanes.l 6
Linear free energy treatment of the equilibrium and rate constants for the methoxide
ion-catalysed addition of methanol to substituted N-benzylideneanilines indicates that
resonance-induced polar effects and direct resonance contributions need to be separated
and their individual effects are, in fact, of opposite signs.I7 A similar treatment for
Schiff base formation concludes that the Young-Jencks equation is the best way to deal
with the rate and equilibrium constants."
The hydrolysis of the 0-alkoxy-substituted imines (12) is catalysed by alkaline earth
metal ions, which is attributed to coordination involving the ether side-chain."
The hydrolysis of benzoquinone imines has been studied in acid solution.20
Kinetics and activation parameters have been determined for the hydrolysis of Schiff
bases formed from 2-hydroxy- 1- naphthaldehyde and hydroxyanilines.21
The acid-catalysed formation of benzylideneanilines has been studied.22
The pH dependence of the rate of hydrolysis of the Schiff base, N-salicylidene-m-
methylaniline has been reported.23
The reaction of propeniminiurn ions with imines leads to the formation of
heterocyclic iminium salts by intramolecular enamine addition to the initially formed
iminium ion add~ct.~~
The reaction of ammonia with gives variable
benzenesulfonamide-p-benzoquinone
products controlled by the solvent-dependent equilibrium with charge-transfer
complexes.2 5
A theoretical study of the imine-enamine tautomeric equilibrium indicates that anti-
acetaldimine is favoured over vinylamine.26
Linear free energy studies on the dehydration mechanism of the carbinolamine
intermediate formed from substituted benzaldehydes and N-methylhydroxylamine to
give nitrones suggest an imbalanced transition state. Complexation of 2-hydroxyben-
zaldehyde with borate facilitated the reaction.27
A theoretical study of the addition of ammonia to formaldehyde has been reported.28
The mechanism for formaldehyde reacting with the endocyclic imino groups of
nucleic acid bases giving hydroxymethylated adducts is calculated to involve a
concerted process assisted by water.29
The reaction of methoxide ion with the (2)-oxime ether (13) gives substitution of the
cyanide with retention of stereochemistry and the corresponding amide from hydration
of the nitrile. The E-isomer undergoes methoxide ion-catalysed isomerization faster
than substitution. Addition of methoxide ion generates a tetrahedral intermediate (14),
which expels cyanide ion to give the thermodynamically most stable isomer.30
Oxime formation from pyridinecarboxaldehydes occurs with rate-limiting carbino-
lamine (1 dehydration under both acidic and neutral conditions. The acid-catalysed
5)