J. Am. Chem. Soc. 1983,105, 3716-3717
3716
tively little C,-C, double-bond character. The higher value of the "C than the @Cisotope effect is readily interpreted in terms of extensive delocalization of the developing negative charge at C, into the aromatic ring (added C,ring bond formation). Further experiments are planned to study the variation of the *C and @Cisotope effects with ring substituents and as the solvent is charged to the diglyme system, for which Kwart's group proposes a changeover from a linear (large ring-Me2S0 involved) @-proton transfer to a nonlinear transfer. Model calculations comparing syn and anti mechanisms and linear (Me,SO involved) vs. nonlinear proton transfers are also planned. The carbon isotope effect data place stringent constraints on the structures and geometries of the acceptable transition-state models.
Scheme I
Me3Si
Acknowledgment. We are indebted to Drs.John R. I. Eubanks and M. Kanska for preparation of some of the labeled compounds. Registry No. (2-@-Methoxyphenyl)ethyl)dimethylamine N-oxide, 34875-26-8; (2-(p-methylphenyl)ethyl)dimethylamine N-oxide, 8566227-7; (2-@-chloropheny1)ethyl)dimethylamine N-oxide, 34875-27-9; (2phenylethy1)dimethylamine N-oxide, 19270- 13-4; (2-@-nitrophenyl)-
3 Scheme I1
1 Ye
ethy1)dimethylamino N-oxide, 85662-28-8; carbon-14, 14762-75-5. Me3Si0
H. RCHO
05%
I
C O C 1 3 , r l ( 2 4 - 4 8 hr)
MeSSi
?O
