Influence of remote substituents on the equatorial/axial selectivity in the monooxygenation of methylene C-H bonds of substituted cyclohexanes

The reactivity of individual C-H bonds in the methyl(trifluoromethyl)dioxir ane TFDO oxygenation of stereogenic methylene groups in conformationally ho mogeneous monosubstituted cyclohexanes (2) has been determined. The unexpec tedly high occurrence of O-atom insertion into C-H-ax bonds suggests an in plane trajectory attack in the oxygenation while the diastereoselectivity o f the reaction is qualitatively interpreted on the basis of the distinct hy perconjugative stabilization by the substituent of diastereomeric transitio n states due to long-range through bond interactions.