Synthesis of polyhydroxysterols (I): synthesis of 24-methylenecholest-4-en-3beta,6beta-diol, a cytotoxic natural hydroxylated sterol.

Starting from stigmasterol (2), 24-methylenecholest-4-en-3beta, 6beta-diol (1), a cytotoxic natural dihydroxylated sterol, was synthesized via 10 steps in 20% overall yield. The introduction of a side-chain of sterol was achieved by solid-liquid phase-transfer Wittig reaction using (3-methyl-2-oxo)butyltriphenylarsonium bromide (12) and K(2)CO(3). Construction of the steroidal nucleus was finished by the addition of 3beta-acetoxycholest-5,6-en-24-one (7) with NBA in dioxane under ambient temperature and by the elimination of 3beta, 6beta-diacetoxy-5a-bromocholestane-24-one (9). The spectral data of the synthetic product (1) are completely consistent with those of the natural compound (1).