Mechanism of the boron trifluoride etherate-catalysed rearrangement of an acyclic trisubstituted epoxide to a carbonyl compound

Abstract

The mechanism of the BF₃-catalysed rearrangement of an acyclic trisubstituted epoxide to a carbonyl compound has been studied using (24S,25S)-[26-¹³C] and (24R,25R)-[26-¹³C]-desmosterol benzoate 24,25-epoxides (2) and (3), demonstrating that C-24 hydrogen migration leading to the 24-oxo compound (4) occurs with retention of configuration at the migration terminus (C-25), whereas C-23 alkyl group migration leading to aldehyde (5) proceeds with inversion of configuration at C-25.