Synthesis of 6-deoxohomodolichosterone, a new plant-growth-promoting steroid

Abstract

6-Deoxohomodolichosterone (1), a new member of the brassinosteroid family, was synthesized in twelve steps from stigmasterol (4). Birch reduction of the dienone (5) gave directly 5α-stigmast- 22-en-3β-ol (6), the mesylate of which was treated with lithium bromide in refluxing dimethylformamide. Selective oxidation of the 2-ene function of the resulting 2,22-diene (7), followed by acetonide formation, provided the acetonide 22-alkene (8). Epoxide-ring opening of the (22R,23R)-epoxide (9), derived from (8), with phenylselenolate anion, treatment with 30 % hydrogen peroxide, and epoxidation with peracid afforded the 22-hydroxy-23,24-epoxide (15). Ready cleavage of the epoxide ring of compound (15) with aluminium isopropoxide and deprotection yielded 6-deoxohomodolichosterone (1).