Acetolytic cleavage of 2β,19-Epoxy-5α-cholestane involving a 1,2-Hydride shift to C2

Acetolytic cleavage of 2β,19-epoxy-5α-cholestane (1a) with boron trifluoride and acetic anhydride followed by hydrolysis gave the 2α,19- diol (2b), the only rearrangement product the 1α,19-diol (3b) and a mixture of olefins (4b). Deuterium exchange studies and the use of a paramagnetic shift reagent have shown that the reaction leading to the rearranged diol(3b) is not concerted and appears to involve an intermediate carbonium ion since hydride shift from both C 1 and C 3 occur. The formation of the 1α,19-diol (3b) as the only rearranged product can be rationalized as nucleophilic attack on the acetoxonium ion (8).