Photo-induced transformations. Part 57. The formation of bridged oxabicyclic compounds by intramolecular radical addition of oxyl radicals generated from some A-homo-4a-cholesten-3-ol hypoiodites

Abstract

Photoinduced reaction of the hypoiodites of A-homo-4a-cholesten-3α- and -3β-ol resulted in the formation of 3α,5-epoxy-4aβ-iodo-A-homo-5β-cholestane and 3β,5-epoxy-4aα-iodo-A-homo-5α-cholestane, respectively. 3α-Methyl-A-homo-4a-cholesten-3β-ol and the 3α isomer likewise gave 3β,5-epoxy-3α-methyl-4aβ-iodo-A-homo-5α-cholestane and 3α,5-epoxy-3β-methyl-4aα-iodo-A-homo-5β-cholestane, respectively, in good yield. Thus, unlike the corresponding reaction of 5-cholesten-3-ols, the intramolecular radical addition is a faster process than the β-cleavage in the oxyl radical derived from A-homo-4a-cholesten-3-ols.