A concise and stereoselective synthesis of the brassinolide and related compounds’ side chains

A stereoselective synthesis of brassinolide, which involves construction of the side chain by highly stereoselective aldol reaction of 20S-6β-methoxy-3α,5-cyclo-5α-pregnane-20-carboxadehyde 5 with the anion of α-silyloxy ketone 6 is described.