Axial and Equatorial Hydrogen Shifts in Methyl Substituted Cyclohexylidenes. Stereochemically-dependent Isotope Effects and Bystander Assistance

Article abstract of DOI:10.1016/0040-4039(94)88352-1

Carbenes were generated from 4-t-butyl-cis-2-methylcyclohexanone (4a) and from 4-t-butyl-cis-2-trans-6-dimethylcyclohexanone (8a, and its corresponding 2,6-d₂ analog 8b) by conventional Bamford-Stevens reactions.Product analysis revealed that an equatorial CH3 assists migration of a geminal H more efficiently than does an axial CH3 by a factor of about 4.6.The primary deuterium isotope effect (k_H/k_D) for axial shift (I_ax) is ca. 1.5 times greater than for equatorial shift (I_eq) in the anchored dimethyl substituted carbene 9.