Unsaturated steroids. Part 3. Synthesis of steroidal 22,24(28)-dienes, ergosta-5,7,22,24(28)-tetraen-3β-ol, and cholesta-5,7,22-trien-3β-ol

Abstract

Dehydrobromination of 22,23-dibromo-5β-ergostane with 1,5-diazabicyclo[3.4.0]non-5-ene (DBN) gives 5β-ergosta-22,24(28)-diene (3). This structure has been confirmed by partial synthesis.

Ergosteryl acetate is readily regenerated from its adduct (8) with 4-phenyl-1,2,4-triazoline-3,5-dione by the action of warm DBN. The adduct reacts with bromine to yield the 22,23-dibromo-derivative, which forms ergosta-5,7,22,24(28)-tetraen-3β-ol (7) directly, in high yield, when heated with DBN.

The structure (9)(cholesta-5,7,22-trien-3β-ol) assigned to a metabolite of the protozoan, Tetrahymena pyriformis, has been confirmed by partial synthesis from stigmasterol.