Addition of dichlorocarbene to steroidal olefins. Preparation of a stereoisomer of demethylgorgosterol, a cyclopropane-containing marine sterol

Abstract

Dichlorocarbene generated by pyrolysis of sodium trichloroacetate added to the 24,28-double bond of 5α-stigmast-24(28)-ene [Δ²⁴⁽²⁸⁾-fucostene](6) but failed to add to either the 5,6- or 22,23-double bond of ergosta-5,22-dien-3β-ol (brassicasterol)(19). However, dichlorocarbene generated by reaction of sodium hydroxide with chloroform in the presence of benzyltriethylammonium bromide added from the β side to the 5,6-double bond of cholesteryl (9), stigmasteryl (12), and brassicasteryl (18) acetates, to the 7,8-double bond (from the α side) of cholest-7-en-3β-yl (10) and 5α-ergosta-7,22-dien-3β-yl (17) acetates, and to the 22,23-double bond of 5α-ergost-22-en-6β-yl (11) and brassicasteryl (18) acetates.