Synthesis and photoisomerization of provitamin D analog with 11β,19-oxide bridge

Abstract

Triol diester 1 was converted into the B-ring 5,7-diene 6 representing the first example of the provitamin D analog where the 10β angular methyl group is connected to ring C by a C11/C19 ether linkage. Ultraviolet light irradiation of 6 resulted in the formation of stereoisomeric 9β,10α-compound 8a. The structure of the photoproduct was established by analysis of vicinal 1H-1H coupling constants and by molecular mechanics.