SYNTHESIS AND PHOTOISOMERIZATION OF PROVITAMIN-D ANALOG WITH 11-BETA,19-OXIDE BRIDGE

Triol diester 1 was converted into the B-ring 5,7-diene 6 representing the first example of the provitamin D analog where the 10 beta angula r methyl group is connected to ring C by a C11/C19 ether linkage. Ultr aviolet light irradiation of 6 resulted in the formation of stereoisom eric 9 beta, 10 alpha-compound 8a. The structure of the photoproduct w as established by analysis of vicinal H-1-H-1 coupling constants and b y molecular mechanics.