Lewis acid-mediated isomerisation of (25R)-3β-acetoxy-5α-spirostan-23-one, a C-22 spiroacetal: an approach to the synthesis of C-23 spiroacetal steroidal sapogenins
Abstract
Treatment of (25R)-3β-acetoxy-5α-spirostan-23-one (23-oxo-tigogenin acetate)3 with titanium tetrachloride afforded the 22-oxo-23-spiroacetal isomer 4 in excellent yield.