Selectivity of Oxidizing Agents toward Axial and Equatorial Hydroxyl Groups.

A total of 16 oxidizing reagents were screened to compare their oxidation selectivities for axial and equatorial hydroxyl moieties using steroidal methyl chenodeoxycholate, methyl deoxycholate, and 4- tert -butylcyclohexanol ( cis / trans 1:1 mixture). These compounds were selected for their stable chair conformations. The results of our study demonstrated that, for the oxidation of a scaffold bearing both axial and equatorial hydroxyl groups, nitroxide-radical-based reagents should be the first choice if oxidation of the equatorial hydroxyl group is needed and Stevens or Dess-Martin reagents should be the first choice for the preferential oxidation of the axial hydroxyl group.