Synthesis and Photochemical Trasformations of 19-Phenylsulfonyl Provitamin D Analogue

Abstract

The synthesis of provitamin D analogue 19-(phenylsulfonyl)androsta-5,7-diene-3β,17β-diyl 3-acetate 17-pivalate (20) has been accomplished from 19-hydroxyandrost-5-ene-3β,17β-diyl 3-acetate 17-pivalate. 19-(Phenylsulfonyl)androst-5-ene-3β,17β-diyl 3-acetate 17-pivalate (10), a precursor of 20, was first obtained in low yield in the nucleophilic displacement reactions of 19-halogenated-5-ene steroids with sodium benzenesulfinate. Then a more efficient method has been used, which involves protection of the double bond as an epoxide. Introduction of the C(7)-C(8) double bond into olefin 10 has been also achieved in two ways. The first involved bromination-dehydrobromination and the other consisted of an allylic oxidation of olefin 10 leading to enone and the Bamford-Stevens reaction of its tosylhydrazone. UV irradiation of 5,7-diene 20 resulted in formation of a complex mixture of products. The structures of five isolated compounds were established on the basis of their 1H NMR spectra and mechanistic rationale.