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The reaction of 2-chlorobicyclo[2.2.1]heptene with methyllithium
TetrahedronLettereRo. 35, pp 3035 - 3038, 1975.
hr@mon
THE REACTION OF 2-CHLOROBICYCLO[2.2.l]HEPTENE
Pre~ee. R+.nted in Great &i-i+
WITH METHYLLITHIUM
Paul G. Gassman and Thomas J. Atkins Department of Chemistry, The Ohio State University, Columbus, Ohio
43210
and
Department of Chemistry,' University of Minnesota, Minneapolis, Minnesota 55455
(Receivedin USA 4 April 1975; received in UK for publication15 July 1975) The reaction of methyllithium with 2-chlorobicyclo[2.2.1]heptene produce P-methylbicyclo[2.2.l]heptene
(x) in 73% yield.2
(j,)has been reported to
This appeared to be a unique example
of a substitution of a vinylic chloride by an alkyl group through reaction with an organolithium reagent.
Whereas, alkyllithium reagents were not noted for such substitution reac-
tions, the replacement of vinylic halides through reaction with aryllithium had ample precedent.3'"
This substitution of halide by aryl was established to proceed via dehydrohalo-
genation of the vinylic halide to an alkyne and subsequent addition of the aryllithium to the acetylenic linkage.3
In view of this background, we deemed it of interest to determine
whether bicyclo[2.2.1]heptyne
(2) was an intermediate in the conversion of 1 into &.
We now
wish to report the results of this mechanistic study. If the reaction of 2-chlorobicyclo[2.2.l]heptene
(I) with methyllithium
proceeded via 2,
the first part of the process would involve removal of the vinylic proton followed by loss of
chloride.
Addition of methyllithiumto
2 should then produce 1, which on hydrolysis should Jo35
3036
%io. 35
The simplest test of this process would be a work-up with deuterium oxide which
yield 2.
would be expected to give 2-methyl-3-deuteriobicyclo[2.2.1]heptene. five equivalents of ethereal methyllithium
When J, was stirred with
for 8 days, followed by the addition of deuterium
oxide, no deuterium incorporation was observed.
Since it could be argued that inadvertent
hydrolysis of 1 had occurred during the course of this relatively slow reaction, we prepared 2-chloro-3-deuteriobicyclo[2.2.l]heptene
&
Treatment of 2 with methyllithium
/&
Cl D
5
(2) .5
6a
-1
as described
CH3 D
-t
above, followed by aqueous work-up, resulted in no loss of deuterium in the product.
Within
experimental error & was labelled to the same extent as 2, which ruled out the intermediacy of 2 (and of any other symmetrical intermediate).
On the basis of the results discussed thus far,
it could be suggested that methyllithium added to 2 to produce 2, which on a-elimination gave ,Q. In principle, 0 could serve as a precursor of either & (by deuterium migration). over methyl migration,6 &.
Unfortunately,
(by methyl migration) or of @
On the basis of the established preference for hydrogen migration
it would appear that the mechanism described would lead primarily to
the labelling experiment carried out with 2 dws
to be made between &
not permit a distinction
and &.
In order to determine whether inversion or retention of configuration had occurred in the reaction of 2 with methyllithium, we prepared (+)-(lS)-2-chlorobicyclo[2.2.l)heptene
cd;” +
1.3 + 0.1' (c 9.72, CHCls) according to the method of McDonald and Steppel.7
ment of w!
[m], Treat-
under the standard conditions described above gave 2-methylbicyclo[2.2.1]-
heptene [J,+&?], [a];' + 2.0 f 0.1'
(C
10.2, CHCls).
In order to determine the absolute
3038
1.
Correspondence concerning this work should be addressed to P. G. Gassman at the University of Minnesota.
2.
P. G. Gassman, J. P. Andrews, Jr., and D. S. Patton, J. C. s., 437 (1969).
3.
L. K. Montgomery and L. E. Applegate, J. Amer. &em. Sot., 8 , 2952 (1967); L. K. Montgomery, A. 0. Clouse, A. M. Ct-elier, and L. E. App 4 egate, ibid., 89, 3453 (1967); L. K. Montgomery, F. Scardiglia, and J. D. Roberts, ibid., 87, 19171/)(1965); L. K. Montgomery, and J. 0. Roberts, ibid., a, 4750 (1960); F. Scamiglia and J. D. Roberts, !l’eetr&e&ua, 1, 343 (1957); G. Wittig and G. Harborth, C&m. Ber., 306 (T944); see also 6. $ittig, J. Weinlich, and E. R. Wilson, Chem. Ber., , ii i (1965); G. Wittig and P. Fritz, Angew. &em. Intern. Ed. Engl., 2, 846 (196 ; A. T. Eottini, F. P. Corson, R. Fitzgerald and K. A. Frost, III, Tetrahedron, 50, 4883 (1972); G. Wittig and J. Heyn, Justua Liebigs Ann. &em., m, 1 (1972); G. Kobrich, Angew. &em. Intern&. Ed. Engl., Q, 473 (1972).
4.
For a general review see R. W. Hoffmann, "Dehydrobenzene Press, New York, N. Y., 1967, Chapter 8.
5.
The details of the preparation of 2 will be presented in a full paper on this subject.
6.
&em. conmnm.,
and Cycloalkynes", Academic
H. Shechter and A. R. Kraska, private communication; A. R. Kraska, 2%~. 3855b (1972).
Abstmcts,
3,
!3$, 5664 (1970).
7.
R. N. McDonald and R. N. Steppel, J.
8.
The exact nature of this "coupling" reaction cannot be elucidated on the basis of the data currently available.
hr.
C’hem. Sot.,
hr@mon
THE REACTION OF 2-CHLOROBICYCLO[2.2.l]HEPTENE
Pre~ee. R+.nted in Great &i-i+
WITH METHYLLITHIUM
Paul G. Gassman and Thomas J. Atkins Department of Chemistry, The Ohio State University, Columbus, Ohio
43210
and
Department of Chemistry,' University of Minnesota, Minneapolis, Minnesota 55455
(Receivedin USA 4 April 1975; received in UK for publication15 July 1975) The reaction of methyllithium with 2-chlorobicyclo[2.2.1]heptene produce P-methylbicyclo[2.2.l]heptene
(x) in 73% yield.2
(j,)has been reported to
This appeared to be a unique example
of a substitution of a vinylic chloride by an alkyl group through reaction with an organolithium reagent.
Whereas, alkyllithium reagents were not noted for such substitution reac-
tions, the replacement of vinylic halides through reaction with aryllithium had ample precedent.3'"
This substitution of halide by aryl was established to proceed via dehydrohalo-
genation of the vinylic halide to an alkyne and subsequent addition of the aryllithium to the acetylenic linkage.3
In view of this background, we deemed it of interest to determine
whether bicyclo[2.2.1]heptyne
(2) was an intermediate in the conversion of 1 into &.
We now
wish to report the results of this mechanistic study. If the reaction of 2-chlorobicyclo[2.2.l]heptene
(I) with methyllithium
proceeded via 2,
the first part of the process would involve removal of the vinylic proton followed by loss of
chloride.
Addition of methyllithiumto
2 should then produce 1, which on hydrolysis should Jo35
3036
%io. 35
The simplest test of this process would be a work-up with deuterium oxide which
yield 2.
would be expected to give 2-methyl-3-deuteriobicyclo[2.2.1]heptene. five equivalents of ethereal methyllithium
When J, was stirred with
for 8 days, followed by the addition of deuterium
oxide, no deuterium incorporation was observed.
Since it could be argued that inadvertent
hydrolysis of 1 had occurred during the course of this relatively slow reaction, we prepared 2-chloro-3-deuteriobicyclo[2.2.l]heptene
&
Treatment of 2 with methyllithium
/&
Cl D
5
(2) .5
6a
-1
as described
CH3 D
-t
above, followed by aqueous work-up, resulted in no loss of deuterium in the product.
Within
experimental error & was labelled to the same extent as 2, which ruled out the intermediacy of 2 (and of any other symmetrical intermediate).
On the basis of the results discussed thus far,
it could be suggested that methyllithium added to 2 to produce 2, which on a-elimination gave ,Q. In principle, 0 could serve as a precursor of either & (by deuterium migration). over methyl migration,6 &.
Unfortunately,
(by methyl migration) or of @
On the basis of the established preference for hydrogen migration
it would appear that the mechanism described would lead primarily to
the labelling experiment carried out with 2 dws
to be made between &
not permit a distinction
and &.
In order to determine whether inversion or retention of configuration had occurred in the reaction of 2 with methyllithium, we prepared (+)-(lS)-2-chlorobicyclo[2.2.l)heptene
cd;” +
1.3 + 0.1' (c 9.72, CHCls) according to the method of McDonald and Steppel.7
ment of w!
[m], Treat-
under the standard conditions described above gave 2-methylbicyclo[2.2.1]-
heptene [J,+&?], [a];' + 2.0 f 0.1'
(C
10.2, CHCls).
In order to determine the absolute
3038
1.
Correspondence concerning this work should be addressed to P. G. Gassman at the University of Minnesota.
2.
P. G. Gassman, J. P. Andrews, Jr., and D. S. Patton, J. C. s., 437 (1969).
3.
L. K. Montgomery and L. E. Applegate, J. Amer. &em. Sot., 8 , 2952 (1967); L. K. Montgomery, A. 0. Clouse, A. M. Ct-elier, and L. E. App 4 egate, ibid., 89, 3453 (1967); L. K. Montgomery, F. Scardiglia, and J. D. Roberts, ibid., 87, 19171/)(1965); L. K. Montgomery, and J. 0. Roberts, ibid., a, 4750 (1960); F. Scamiglia and J. D. Roberts, !l’eetr&e&ua, 1, 343 (1957); G. Wittig and G. Harborth, C&m. Ber., 306 (T944); see also 6. $ittig, J. Weinlich, and E. R. Wilson, Chem. Ber., , ii i (1965); G. Wittig and P. Fritz, Angew. &em. Intern. Ed. Engl., 2, 846 (196 ; A. T. Eottini, F. P. Corson, R. Fitzgerald and K. A. Frost, III, Tetrahedron, 50, 4883 (1972); G. Wittig and J. Heyn, Justua Liebigs Ann. &em., m, 1 (1972); G. Kobrich, Angew. &em. Intern&. Ed. Engl., Q, 473 (1972).
4.
For a general review see R. W. Hoffmann, "Dehydrobenzene Press, New York, N. Y., 1967, Chapter 8.
5.
The details of the preparation of 2 will be presented in a full paper on this subject.
6.
&em. conmnm.,
and Cycloalkynes", Academic
H. Shechter and A. R. Kraska, private communication; A. R. Kraska, 2%~. 3855b (1972).
Abstmcts,
3,
!3$, 5664 (1970).
7.
R. N. McDonald and R. N. Steppel, J.
8.
The exact nature of this "coupling" reaction cannot be elucidated on the basis of the data currently available.
hr.
C’hem. Sot.,