Organic Reaction Mechanisms 1966

486 Pages·1967·19.95 MB·English

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ORGANIC REACTION MECHANISMS 1966
ORGANIC REACTION
MECHANISMS 1966
An annual survey covering the literature
dated December 1965 through November 1966
B. CAPON University of Leicester
M. J. PERKINS King’s College, University of London
C. W. REES University of Leicester
INTERSCIENCE PUBLISHERS a division of
- -
John Wiley & Sons London New York Sydney
Copyright @ 1967 by John Wiley & Ltd.
Sons
All rights reserved
Library of Congress Catalog Card Number
66-23143
Made and printed in Great Britain by
Spottiswoode, Ballantyne & Co. Ltd., London and Colchester
Preface to the 1965 Volume
This book is a survey of the work on organic reaction mechanisms published
in 1965. E’or convenience, the literature dated from December 1964 to
November 1965, inclusive, was actually covered. The principal aim has been
to scan all the chemical literature and to summarize the progress of work on
organic reaction mechanism generally and fairly uniformly, and not just on
selected topics. Therefore, certain of the sections are somewhat fragmentary
and all are concise. Of the 2000 or so papers which have been reported, those
which seemed at the time to be the more significant are normally described
and discussed, and the remainder are listed.
Our other major aim, second only to comprehensive coverage, has been
early publication since we felt that the immediate value of such a survey as
this, that of “current awareness”, would diminish rapidly with time. In
this we have been fortunate to have the expert cooperation of the London
office of John Wiley and Sons.
If this book proves to be generally useful, we will continue these annual
surveys, and then hope that the series will have some lasting value; some
form of cumulative reporting or indexing may even be desirable.
It is not easy to deal rigidly and comprehensively with so ubiquitous and
fundamental a subject as reaction mechanism. Any subdivision is a necessary
encumbrance and our system, exemplified by the chapter headings, has been
supplemented by cross-references and by the form of the subject index. We
should welcome suggestions for improvements in future volumes.
February 1966 B.C.
M.J.P.
C.W.R.
Contents
1. Classical and Non-classical Carbonium Ions . . 1
Bicyclic Systems . . 1
Phenonium Ions . . 19
Participation by Double and Triple Bonds. . . 24
Cyclopropyl Carbonium Ions . . 31
Cationic Opening of Cyclopropane and Cyclobutane Rings . 37
Other Stable Carbonium Ions and Their Reactions . . 40
2. Nucleophilic Aliphatic Substitution . . 44
Borderline Mechanisms and Ion-pair Phenomena . . 44
Solvent Effects . . 50
Neighbouring-group Participation . . 53
Isotope Effects . . 69
Deaminations and Related Reactions . . 70
Fragmentation Reactions . . 72
Displacement Reactions at Elements other than Carbon . 75
Ambident Nucleophiles . . 81
Other Reactions . . 82
3. Electrophilic Aliphatic Substitution . . 91
4. Elimination Reactions . . 103
5. Addition Reactions . . 124
Electrophilic Additions . . 124
Additions of halogens and related reactions . . 124
Addition of sulphenyl halides . . 130
Hydrations and related additions . . 132
Epoxidations . . 136
Nucleophilic Additions . . 137
Radical Additions . . 140
Diels-Alder Reactions . . 148
Other Cycloaddition Reactions. . , 152
6. Nucleophilic-aromatic Substitution . . 160
Meisenheimer and Related Complexes . . 168
Substitution in Polyfiuoro-aromatic Compounds . . 171
Heterocyclic Systems . . 172
Diazonium Decomposition . . 176
Other Reactions . . 178
Benzyne and Related Intermediates . . . 181
...
Vlll ’ Contelzts
7. Radical and Electrophilic Aromatic Substitution . %1* 48
,
Radical Substitution . . 188
Electrophilic Substitution . . 193
8. Molecular Rearrangements . . 209
Aromatic Rearrangements . . 209
Cope and Related Rearrangements : Valence-bond Isomerization . 217
Intramolecular Hydrogen Migrations and Related Reactions . ,225
Radical Rearrangements. . . 229
Heterocyclic Rearrangements . . 233
Other Rearrangements . . 239
9. Radical Reactions. . 246
Radical-formingR eactions . . 246
Reactions of Free Radicals . . 256
Radical abstraction and displacement processes . . 256
Oxygen radicals . . 263
Nitrogen radicals . . 264
Nitroxide radicals . . 265
Radical anions and cations . . 268
Miscellaneous data on free radicals . . 270
Electron-spin Resonance Data. . . 276
10. Carbenes and Nitrenes . . 279
11. Reactions of Aldehydes and Ketones and Their Derivatives . 307
Formation and Reactions of Acetals and Ketals . . 307
Reactions with Nitrogen Bases. . . 316
Enolization and Related Reactions . . 321
Other Reactions . . 334
12. Reactions of Acids and Their Derivatives . . 339
Carboxylic Acids . . 339
Non-carboxylic Acids . . 360
13. Photochemistry . . 369
14. Oxidations and Reductions . . 399
.
Ozonolysis . 399
Oxidations by Metallic Ions . . 402
Other Oxidations . . 406
Reductions . . 412
Hydrogenations . . 417
.
Author Index . 421
Subject Index . . 469
Errata for Organic Reaction Mechanisms, 1965 . . 481
Errata for Organic Reaction Mechanisms, 1966
P. 1 : Formula (3)s hould have a methyl group at position 1.
P. line For potential diagram read potential energy diagram
14, 6:
P. line 2: For acetate read
41, endobicyclo[3.3.l]nonan-l-yl endo-bicyclo[3.3.l]nonan-2-yl
acetate
P. 42: The first block is incorrect. It should be:
Me
Me \c ,Me
I
/Me
CHZ=CH-C-CMIH e ~OBS __f +CIHz-CHCH‘’ 2 +C H2=CH-CI Hs-C +‘Me
CHn\ ,Me /Me
I ,CH-C CH*=CH-CH=C
CHz +‘Jle + ‘Me
/Me
CH2=CH-CH2-C I
‘Me
J.
OAc
/Me
AcO-CHZ-CH~-CH=C
‘Me
P. 60,e quation :F or HOOCC6H~0r1e ad HOOCC6Hfl02
(1)
P. 70: The sulphur atom at the front of formula (64) should be doubly bonded to an
=NTs pup.
lines from bottom: For rate read range
P. 96,6
P. line For Freidel-Crafts read Friedel-Crafts
163, 16:
P. line Fur than read rather than
234, 8:
P. line 12 :D elete the
278,
P. lines and For phosphonate read phostonate
280, 13 16:
481
Organic Reaction Mechanisms 1966
Edited by B. Capon, M. J. Perkins, C. W. Rees
Copyright © 1967 by John Wiley & Sons, Ltd.
CHAPTER
1
Classical and Non-classical Carbonium Ions
Bicyclic Systems
This year there have been published three re~iewsl-a~n d a “collection of
reprints with ~ommentary)d’e~al ing with non-classicalions. All three reviewers
and the commentator support the view that exo-norbornyl compounds react
via a non-classical ion. Brown, on the other hand, has restated’his arguments
for believing that they do not.5
As a result of the discussion by Goering and Schewene6 and Brown and
Tritle’ of the 2-norbornyl system reported last year,s it is now clear that just
as the exo:endo rate ratio measures the difference only in free energy of
activation for ionization of the exo- and endo-isomers, the exo :endo product
ratio measures the difference only in free energy of the transition states for
capture of the 2-norbornyl ion(s) in the exo- and the endo-direction and that
these two differences are closely related. In the strictest sense, then, it is only
valid to draw conclusions about the structures of the transition states from
these kinds of result. One may then extrapolate to the structure of the inter-
mediate ion(s), but this involves an assumption that this structure is closely
related to that of the transition states. This is undoubtedly frequently valid
but it should be remembered that it is an assumption and need not always
be valid.
In our opinion the question that should now be asked about solvolysis
reactions of 2-norbornyl systems is not “does the exo-compound react via a
non-classical ion!” but “are the high exo:endo rate and product ratios the
result of delocalization of the 1,6-bonding electrons in the transition state for
ionisation of the exo-isomer and for capture of the intermediate ion! )’
Sargent in his review1 accepts Brown’s view that the high exo:endo rate
ratios observed in the solvolyses of tertiary 2-norbornyl derivativesg are not
G. D. Sargent, Quart. Rev. (London),2 0,301 (1966).
1
2 G. E. Gream, Rev. Pure. AppZ. Chem., 16,25 (1966).
3 C. A. Bunton in “Studies on Chemical Structure and Reactivity”, J. H. Ridd, ed., Methuen,
London, 1966, p. 73.
4 P. D. Bartlett, “Non-classicalI ons: Reprints and Commentary,”W . A. Benjamin, New York,
N.Y. 1966.
5 H. C. Brown, Chem. Brit., 2, 199 (1966).
6 H. L. Goering and C. B. Schewene, J. Am. Chem. Soc., 87,3516 (1965).
7 H. C. Brown and G. L. Tritle, J. Am. Chem. L~OC.,8 8,1320 (1966).
*
See Organic Reaction Xechanism, 1965, 13.
9 See Organic Reaction Mechanisms, 1965,s.
1
2 Organic Reaction Mechanisms 1966
the result of participation in the reactions of the exo-isomers, but he rejects
Brown's explanation that they result because the rates for the endo-isomers
are low owing to steric hindrance to ionisation. Instead he prefers the explana-
tion that they are caused by the release of steric strain in the transition states
for the reactions of the exo-isomers arising from the movement away of the
2-methyl or 2-phenyl substituent from the 6-hydrogen atom, and he calculates
the strain relieved (-3 kcal mole-l) to be in good quantitative agreement
with the observed exo:endo rate ratios. On this view, then, the difference in
activation energy for the solvolyses of secondary exo- and endo-derivatives,
caused by participation in the reaction of the exo-isomer, is, by chance, almost
identical with the difference for tertiary derivatives, which results from a quite
different factor, namely, release of steric strain.
As pointed out by Rei and Brown,lo however, equilibration studies (Table 1)
indicate that steric strain in exo- and endo-isomers must be approximately the
same as, or at most only slightly greater than, in the 1-norbornyl isomer which
they considered to be strain-free as far as the substituents are concerned. It is,
therefore, difficult to see how relief of steric strain as envisaged by Sargent
could be the cause of the rate differences between tertiary exo- and endo-
isomers.
Rei and Brownlo also studied the kinetics of the acid-catalysed conversion
of 2-methyl-exo-norbornan-2-01 into 2-methyl-endo-norbornan-2-01 and
and report that the former is formed twice as
1-methyl-exo-norborbornan-2-01
rapidly as the latter.
Brown and Takeuchill report that the rates of ethanolysis of 2-aryl-exo-
norbornyl chlorides can be correlated by the u+ constants to yield a p-value
(-4.3) similar to that observed with 1-arylcyclopentyl (-4.5) and 2-aryl-2-
propyl chlorides (-4.9). It was thought that if there were participation of the
1,6-bonding electrons in the reactions of the exo-norbornyl chlorides the
proportion of this should increase on going from the p-methoxyphenyl
(extrapolated k = 2.5 x lo2s ec-l) to the p-nitrophenyl compound (k = 7.08 x
sec-l) and that this would lead to a curved Hammett plot. Apparently
this does not occur and it seems reasonable to suppose that there is no par-
ticipation.
Brown and Muzzio12 have attempted to correlate the solvolysis rates of
bicyclic arenesulphonates with rates of borohydride reduction of the corre-
sponding ketones. Although a fast borohydride reduction tended to accompany
a slow arenesulphonate solvolysis the plot of log (partial rate factor) for
ketone reduction against log krel.f or toluene-p-sulphonate solvolysis was not
a straight line even when compounds believed to undergo solvolysis with
M-H. Rei and H. C. Brown, J. Am. Chem. SOC.8, 8,5335 (1966).
10
H. C. Brown and K. Takeuchi, J. Am. Chem. Soc., 88,5336 (1966).
11
H. C. Brown and J. Muzzio, J. Am. Chem. Soc., 88, 2811 (1966).
12
Classical and Non-classical Carboniurn Ions 3
Table 1. Percentages of exo- and endo-2-norbornyl and 1 -norbornyl derivatives present
at equilibrium.
Conditions Ref.
I Me
Me
5 70
Acetone at 100-137" 14
OH
20
60% Aqueous dioxan
A M e h O H at 25" 10
I Me
OH
17 61
AcOH at 6
48.9'
OAc
16
participation were excluded. In particular, the rate constants for endo-
derivatives were very poorly correlated. Thus the solvolysis of endo-norbornyl
toluene-p-sulphonate is slower than that of cyclopentyl toluene-p-sulphonate
and the reduction of 2-norbonanone from the endo-direction is also slower than
the reduction of cyclopentanone. This breakdown in the quantitative correla-
tion was attributed to unusual slowness of both attack from, and departure in,
the endo-direction.
N. A. Belikova, A. F. Plat6, and Kh. 3.S terin, J. Gen. Chem. U.S.S.R., 34, 125 (1964).
13
14 C. F. Wilcox, M. Sexton, and M. F. Wilcox, J. Org. Chem., 28, 1079 (1963); E. L. Eliel,
S. H. Schroeter, T. J. Brett, F. J. Biros, and J. C. Richer, J. Am. Chem. SOC.8, 8,3327 (1966).