Synthesis of castasterone and its 22S,23S-isomer : two plant growth promoting ketones

Abstract

Castasterone (22R,23R,24S)-2α,3α,22,23-tetrahydroxy-5α-ergostan-6-one (1) and its (22S,23S)-isomer have been synthesized from (20S)-6β-acetoxy-3α,5-cyclo-5α-pregnane-20-carbaldehyde. The side chain with the correct stereochemistry was constructed via a Claisen rearrangement and the nuclear functionalities were introduced by osmilation of the intermediate obtained by opening of the cyclopropane ring with hydrochloric acid and dehydrohalogenation.