Cyclization of some Δ7-22-hydroxy-steroids to 14β,22-ethers

Abstract

Treatment of 3β-benzoyloxy-23,24-bisnor-5α-chol-7-en-22-ol (2) and its 3α,5β-analogue (9) with phosphorus tribromide in chloroform gives the 14,22-epoxy-23,24-bisnor-5α-cholan-3β-yl benzoate (3) and its 3α,5β-analogue (10), respectively. The structures have been proven by oxidation with ruthenium tetroxide to the corresponding lactones (4) and (11). The utility of the cyclization process in the synthesis of a 14β-hydroxy-steroid has been demonstrated. In contrast, under analogous conditions, 3α,5-cyclo-23,24-bisnor-5α-chola-6,8(14)-dien-22-ol (17) failed to cycliz, but gave a rearranged bromide. Similarly, (22RS)-5α-cholest-7-en-3β,22-diol (19) failed to cyclize, and instead gave isomerized Δ⁸⁽¹⁴⁾- and Δ¹⁴-3,22-diols (22) and (23). The biogenetic implications of the cyclization process are discussed.