Mitsunobu reactions with methanesulfonic acid; The replacement of equatorial hydroxyl groups by azide with net retention of configuration

Treatment of equatorial cyclohexanols with Ph3P/DEAD/MsOH gives clean conversion to the axial mesylates. Subsequent reaction with NaN3 gives the equatorial azides in overall yields of 74-87%. Axial hydroxyl groups are not affected, allowing the regioselective conversion of methyl cholate into a 3 alpha-azidodiol intermediate for steroid-based synthetic receptors. (C) 1997 Elsevier Science Ltd.