Study on the syntheses of brassinolide and related compounds. Part 14. Highly stereoselective construction of the side-chain of brassinosteroids utilizing the β-alkylative 1,3-carbonyl transposition of the steroidal 22-En-24-one
Abstract
A stereoselective synthesis of the side-chain of brassinolide which involves β-alkylative 1,3-carbonyl transposition of the α,β-unsaturated ketone 3,6-diacetoxycholest-22-en-24-one is described. The overall yield of (22R,23R,24S)-22,23-isopropylidenedioxy-24-methyl-5β-cholestane-3α,6α-diol from 3α,6α-diacetoxy-5β-pregnane-20-carbaldehyde in six steps is 47%.