Steric factors in the hydrogenolysis of some steroidal allylic alcohols by mixed hydrides

Abstract

The allylic steroidal alcohols 3β,7β- and 3β,7α-dihydroxycholest-5-ene [(5) and (7)], the corresponding 7-deuterio-compounds [(6) and (8)], and 3α- and 3β-hydroxycholest-4-ene [(12) and (13)] have been hydrogenolysed with dichloroaluminium deuteride or hydride and the α : β ratio of allylic duterium has been determined for each product. The results are intelligible in terms of hydride capture via reactant-like transition states resembling the initially formed allylic carbonium ions.