1924
i n s t e a d of the cyano group. The major s t r u c t u r a l d i f f e r e n c e between the eyano group and
s u b s t i t u e n t s with s i m i l a r electron-withdrawing c h a r a c t e r which are known to migrate
well 4,5, such as e s t e r s and ketones, is the h y b r i d i z a t i o n at the carbon atom. We b e l i e v e
that the major reason that cyano does not migrate is because of its SP hybridization,
which would give t r a n s i t i o n s t a t e that has v i n y l c a t i o n c h a r a c t e r . Experiments are
a
underway to compare the cyano with the ethynyl s u b s t i t u e n t (which has SP h y b r i d i z a t i o n but
lacks the tmfavorable p o l a r i t y ) in such rearrangements.
Comparison of the cyano group with another electron-withdrawing s u b s t i t u e n t which
also
group has tmfavorable p o l a r i t y , and has no compensating resonance s t a b i l i z a t i o n of the
carbocation p o s s i b l e . The CC13 group shows no tendency to migrate, but also has dra-
matic rate r e t a r d a t i o n (ca~ 108 times for methyl migration in methyl-trichloromethyl
does not migrate, the trichloromethyl group, is i n s t r u c t i v e 4c. The trichloromethyl
a
a
s u b s t i t u t e d dienone compored to a dimethyl s u b s t i t u t e d dienone). The rate r e t a r d a t i o n of
methyl migration in an a-cyano s u b s t i t u t e d c a t i o n is much l e s s , which we b e l i e v e r e f l e c t s
some s t a b i l i z a t i o n of the adjacent charge by resonance,
A c k n o w l e d g m e n t .
Financial support of this work by the Robert A. Welch Foundation
(grant D-326) is g r a t e f u l l y acknowledged.
R E F E R E N C E S
{
Present address: Department of Chemistry, Kyung Hee Univ. , South Korea.
1. Review: Gassman, P. G.; Tidwell, T. T. A c c t s . Chem. R e s . , 1983, 16, 279-285.
2. Kirmse, W.; Doer, B. J. Am. Chem. S o c . , 1990, 112, 4556-4557.
3.
4.
Gassman, P. G.; S a i t o , K.; Talley, J. J. i b i d . , 1 9 8 0 , 102, 7613-7615.
(a) Marx, J. N.; Argyle, J. C.; Norman, L. R. i b i d . , 1974, 96, 2121-2129. (b)
Marx. J. N.; Bombach, E. J. Tetrahedron L e t t . , 1977, 2391-2394. (c) V i t u l l o , V. P.;
Cashen, M. J. ; Marx, J. N.; Caudle, L. J. ; F r i t z , J. AM. Chem. S o c . , 1978, 1205-1210.
5. Review: Shubin, V. G. in Rees, C., ed. "Topics in Current Chemistry**, Springer
Verlag, B e r l i n , 1984, Vol 117, pp 267-341.
6.
V i t u l l o , V. P.; 6rossman, N. J. Am. Chem. S o c . , 1972, 94, 3844-3848.
7. McDonald, R. N.; D i l l , D. C. J. Org. Chem. 1970, 35, 2942-2948.
8. M i l l e r , T. G. J. Org. Chem., 1 9 6 9 , 34, 3710-3713.
9.
Danishefsky, S.; Kitahara, T. i b i d . , 1974, 96, 7807-7808.
10. Deshieldin6 of the ~ and fl v i n y l p r o t o n s i g n a l s in the PMR from 6.38 and 6.90 (CDC13)
r e s p e c t i v e l y to 7.43 and 8.26 (H2S04) corresponds to ca. 100% p r o t o n a t i o n in D2S044a.
11. Synthesis of an a u t h e n t i c sample of 8 (R=H) was accomplished via a Gatterman r e a c t i o n
on m-cresol, followed by oxime formation and dehydration. (Gross, H.; Reiche, A.;
Mattey, G. Chem. B e r . , 1963, 308-313; Van Es, T. J. Chem. S o e . , 1965, 1564-1568.
12. Ion
6 can not be d e t e c t e d by NMR s p e c t r a , s i n c e its i r r e v e r s i b l e formation from 4 is
f o l l o w e d by a r a p i d deprotonation to the phenol. 6
(Received in USA 2 January 1991 )