Torsional, rotor, and electronic effects in 4-tert-butylmethylenecyclohexane epoxidations and osmylations

The axial epoxidation preference for 2-substituted 4-tert-butylmethylenecyclohexanes is attributed to a combination of small effects, including existing bond torsion and rotor effects. Contributions from developing bond torsion are smaller and may be negligible. Cieplak (sigma-sigma*) effects are too small to identify in most of the epoxidations, but a marginal effect could be present according to comparisons of isosteric systems 11a and 15a or 19a and 19b. Dimethyldioxirane epoxidations and osmylations are more sensitive to steric factors, resulting in a trend for equatorial attack.