Organic Reaction Mechanisms 1988

744 Pages·1990·21.223 MB·English

ORGANIC REACTION MECHANISMS 1988
ORGANIC REACTION
MECHANISMS 1988
An annual survey covering the literature
dated December 1987 to November 1988
Edited by
A. Knipe and W. E. Watts
C.
University of Ulster,
Northern Ireland
An Interscience' Publication
JOHN WILEY & SONS
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Organic reaction mechanisms.
I. Organic compounds. Chemical reactions.
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Contributors
R. A. AITKEN Department of Chemistry, University of St.
Andrews, Purdie Building, St. Andrews,
Fife KY 16 9ST, Scotland
R. A. COX Department of Chemistry, University of
Toronto, 80 George Street, Toronto,
Ontario M5S 1A1, Canada
M. R. CRAMPTON Department of Chemistry, Durham Uni-
versity, Durham DHI 3LE, UK
G. W. J. FLEET Dyson Perrins Laboratory, Oxford Uni-
versity, South Parks Road, Oxford
3QT, UK
OX1
P. HANSON Department of Chemistry, University of
York, Heslington, York YO1 5DD, UK
C. D. JOHNSON School of Chemical Sciences, University of
East Anglia, Norwich, UK
A. C. KNIPE Department of Chemistry, University of
Ulster at Coleraine, Coleraine, Co. Lon-
donderry BT52 lSA, Northern Ireland
P. KOCOVSKP Czechoslovak Academy of Sciences, In-
stitute of Organic Chemistry and Bioche-
mistry, 166 10 Praha 6, Czechoslovakia
R. B. MOODIE Department of Chemistry, The University,
Exeter EX4 4QD, UK
R. A. MORE O’FERRALL Department of Chemistry, University
College, Belfield, Dublin 4, Ireland
A. W. MURRAY Department of Chemistry, The University,
Dundee DD1 4HN, Scotland
D. C. NONHEBEL Department of Pure and Applied Chemis-
try, University of Strathclyde, Thomas
Graham Building, Glasgow G1 IXL,
Scotland
M. I. PAGE Department of Chemical Sciences, The
Polytechnic, Queensgate, Huddersfield,
West Yorkshire HDl 3DH, UK
J. SHORTER Department of Chemistry, The University,
Hull HU6 7RX, UK
W. J. SPILLANE Department of Chemistry, University
College, Galway, Ireland
Contents
.
1 Reactions of Aldehydes and Ketones and their Derivatives by 1
M . I . Page . . . . . . . . . . . . . . . . . . . . . . . . .
.
2 Reactions of Acids and their Derivatives by . J . Spillane . . . . . 23
W
.
3 Radical Reactions: Part 1 by P . Hanson . . . . . . . . . . . . 95
.
4 Radical Reactions: Part 2 by D . C. Nonhebel . . . . . . . . . . 157
5. Oxidation and Reduction by G . . J . Fleet . . . . . . . . . . . 223
W
6. Carbenes and Nitrenes by R . A . Aitken . . . . . . . . . . . . 285
7. Nucleophilic Aromatic Substitution by M . R . Crampton . . . . . . 305
.
8 Electrophilic Aromatic Substitution by R . B . Moodie . . . . . . . 323
.
9 Carhations by R . A . Cox . . . . . . . . . . . . . . . . . . 335
10 . Nucleophilic Aliphatic Substitution by J . Shorter . . . . . . . . . 357
.
11 Carbanions and Electrophilic Aliphatic Substitution by A . C . Knipe 387
.
12 Elimination Reactions by R . A . More O’Ferrall . . . . . . . . . 411
.
13 Addition Reactions: Polar Addition by P . Kdovskjl . . . . . . . 435
.
14 Addition Reactions: Cycloaddition by C . D . Johnson . . . . . . . 479
.
15 Molecular Rearrangements by A . . Murray . . . . . . . . . . 525
W
Author Index. 1988 . . . . . . . . . . . . . . . . . . . . . . . . 663
Subject Index. 1988 . . . . . . . . . . . . . . . . . . . . . . . . 719
Preface
The present volume, the twenty-fourth in the series, surveys research on organic
reaction mechanisms described in the literature dated December 1987 to November
1988. 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 che-
mistry 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 have been two changes of author since last year and we welcome Professor
Pave1 KoEovsky (Czechoslovak Academy of Sciences) and Dr David Johnson
(University of East Anglia) who have contributed reviews of Polar Addition and
Cycloaddition, respectively. They replace Professor Arthur Fry and Dr Michael
Paton whose expert contributions to this continuing series are gratefully acknow-
ledged.
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.
Organic Reaction Mechanisms 1988
Edited by A. C. Knipe and W. E. Watts
0 1990 John Wiley 8c Sons Ltd
CHAPTER 1
Reactions of Aldehydes and Ketones and their Derivatives
M.I. PAGE
Department of Chemical and Physical Sciences, Huddersfield Polytechnic
Formation and Reactions of Acetals, Ketals, and Orthoesters . . . . . . . .. .. .. 1
Hydrolysis and Formation of Glucosides, Nucleosides, Oxazines, a dR elated
Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Non-enzymic Reactions . . . . . . . . . . . . . . . . . . . . . . . . 3
Enzymic Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Reactions and Formation of Nitrogen Derivatives, Schiff Bases, Hydrazones, Oxhes, 4
and Related . . . . . . . . . . . . . . . . . . . . . . . . . . .
Species
C-C Bond Formation and Fission: Aldol and Related Reactions . . . . . . . . 6
Other Addition Reactions. . . . . . . . . . . . . . . . . . . . . . . . . 11
Enolization and Related Reactions . . . . . . . . . . . . . . . . . . . . . 12
Hydrolysisand ReactionsofVinylEthersand Related Compounds . . . . . . . 16
Other Reactions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Formation and Reactions of Acetals, Ketals, and Orthoesters
Geminal oxygen atoms in acetals, hydrates, and orthoesters have a mutual stabiliz-
ing interaction which has a stereochemical component manifested in the anomeric
effect. This interaction is not confined to oxygen and appears to be a general
phenomenon with electronegative elements. A nice example has been demonstrat-
ed with the iodination of methoxyacetone which kinetically yields the methyl-
substituted product but thermodynamically gives 1-iodo-1- methoxypropanone (1).
The favourable geminal interaction is thought to stabilize the product by about
.'
7 kcal mol-'
NMR analysis of solutions of trifluoropropan-Zone in the strong acid system
HBr-CBr,F, shows the formation of the HBr adduct, a novel stable a-bromo-
alcohol (2).*
Structure-reactivity correlations, including imbalances between estimates of
reaction progress from the effect of substituents in different parts of the molecule,
have been re~iewed.~
There is no detectable trapping of the oxocarbocation (3) by azide ion which
indicates that the lifetime for this putative intermediate in aqueous solution is less
than 5 x lo-" s. It is concluded that the hydrolysis of acetals cannot proceed
through diffusionally equilibrated ions such as (3). The apparent slower rate of
1
2 Organic Reaction Mechanisms 1988
OMe OH
I I
MeCO-C-H F,C-C-R
I I + +
I Br RCH=OMe RCH=OH
(1) (2) (3) (4)
OR
n
addition of water to protonated acetaldehyde (4) may be the result of using an
erroneous pK, for the latter: The measurement of the acidity constants of the
conjugate acids of very weak bases is usually based on acidity functions which are
not very reliable. The pK, values of protonated carbonyl compounds may be
estimated from keto-enol equilibria and their carbon acidity constants. This
method calculates pK, values which are more negative than usually assumed; for
example, that for acetone is - 7.1 and that for acetaldehyde is - 8.8.5
Protonation of 1,3dione gives an intramolec-
1,3-diphenyl-2-methylpropane-
ularly hydrogen-bonded conjugate acid (5) which shows a 'H NMR signal at 621,
A negative deuterium isotope effect is observed on the shift which is compatible
with a very strong hydrogen bond!
The pathways of the breakdown of methyl hemiacetals of a-bromoacetophenone
involve an acid, base, and pH-independent pathway similar to those observed for
aldehyde derivatives. The Hammett p-values are reported for each step and are
similar to those for hemiacetals of benzaldehyde. It is suggested that there may be
some imbalance in the acid-catalysed reaction between deprotonation and C-0
bond-breaking so that the transition state is developing some protonated carbonyl
character (6).'
A macromolecule containing basic and acidic residues is an effective catalyst for
the dissociation of a glycoaldehyde dimer. Hemiacetal cleavage is suggested to be
facilitated by complexation and general acid-base catalysis.*
Saturated acetals react up to 105-foldm ore slowly than a,p-unsaturated acetals
with methyl vinyl ether, catalysed by boron trifluoride etherate. The Hammett
p-value for substituted benaldehyde acetals is - 4.6 and the rates of reaction of the
acetals correlate with the corresponding rates of acid-catalysed hydrolysis. It is
assumed that the rate-limiting step is the addition of the reversibly formed alkoxy-
carbocation to the vinyl ether.9
1 Reactions of Aldehydes and Ketones and their Derivatives 3
The rate of the acid-catalysed hydrolysis of benzaldehyde diethyl acetals in
reverse micelles shows a non-linear dependence on acid concentration. It is suggest-
ed that the reaction takes place in the polar head-group region of the micelle but
there is no satisfactory explanation for the acidity dependence.''
Tropone acetals complexed with tricarbonylchromium (7) undergo acid-
catalysed hydrolysis to generate intermediate cations which are more stable than
the uncomplexed alkoxytropylium ions. The heterolysis reactions are exo-stereo-
specific.'
I
There has been a report on further studies of the hydrolysis of 1,3-dio~olanes.'~
The cyclization of 2-cyanobenzaldehyde with alcohols to give isoindoles is both
acid- and basecatalysed. The most likely mechanism involves ring-closure of the
intermediate hemiacetal
@).I3
RCH7, +7
OR'
0 0-
H'
(9)
CH,OAc
A&- cJA-oOc
OAc
The reactions of acetals with halogenosilanes leading to halogenoalkoxysilanes
have been re~iewed.'~
Hydrolysis and Formation of Glucosides, Nucleosides, Oxazines, and Related
Compounds
Non-enzymic Reactions
The mechanism of the hydroxide ion-catalysed hydrolysis of the glycosyl bond of
/?-NAD+ has been reinvestigated. It is suggested that dissociative cleavage is
facilitated by the ionized ribose diol anion stabilizing the oxocarbocation inter-
mediate (9) but this does not involve epoxide formation."
4 Organic Reaction Mechanisms 1988
The “0 kinetic isotope effect for the acidcatalysed hydrolysis of 4-
is temperature-dependent and is attributed
nitropheny1[1-’*0]-~-g1ucopyranoside
to a change from specific to general acid catalysis as the temperature is lowered.
At low temperature the reaction is general acidcatalysed by trifluoroacetate
buffers and shows a temperature-dependent solvent deuterium isotope effect
which, however, is lower than generally observed for acetal hydrolysis.16
The anomerization of methyl-D-glucofuranoside, but not the pyranoside, in
acidic methanol is accompanied by the formation of the dimethyl acetal of D-
glucose (10) and it is suggested that this is an intermediate during anomerization.”
The base-catalysed anomerization of 2,4-dinitrophenyl b-D-glucopyranoside is
suggested to proceed by nucleophilic aromatic substitution displacing the glycosyl
oxyanion intermediate (11) which ring-opens and closes and then recombines with
the aromatic residue.’*
The kinetics of the mutarotation of a-D-glucose catalysed by alumina with
surface basicities are explained by a surface reaction mechanism. The adsorption
of b-glucose is greater than that of the a-anorner~.’~
Diazomethane cleaves oligoglycosides at the sugar-aglycone linkage if the
aglycone contains a suitably placed aldehyde group. The mechanism is thought to
involve initial epoxide formation at the aldehyde centre followed by aglycone
oxygen nucleophilic attack (12).M
Enzymic Reactions
The application of FAB mass spectrometry to biochemical reactions, including
oligosaccharide processing, has been reviewed?’
Reactions and Formation of Nitrogen Derivatives, Schiff Bases, Hydrazones,
Oxima, and Related
Species
As expected, the inclusion of one or two water molecules in the calculations for the
energetics of the addition of ammonia to formaldehyde dramatically decreases the
activation energy. Linear rate-equilibrium relationships are found for substituted
nucleophiles which are compared with experimental structure-activity correla-
tiomZ2
The cyclization of a-alkylaminonitriles with trichloroacetaldehyde occurs from
the carbinolamine adduct (13) to give novel 5-iminoo~azolidines.~~
NMR studies of the acid-catalysed hydrolysis of 2-substituted-3-methyl-1 ,2-
‘H
oxazolidines show the presence of both the E and the 2 forms of the Schiff base
intermediate (14). The carbinolamine intermediate may also be detected, the
breakdown of which is rate-limiting.”
Aromatic aziridines add to aldehydes to give intermediate carbinolamines
which lose hydroxide to generate iminium ions (15) which, in turn, undergo
ring-opening by nucleophilic addition of another molecule of aziridine.’’
Schiff base formation between pyridoxal derivatives and n-hexylamine is sug-