ALKENYLZINC-MEDIATED APPROACH TO THE VITAMIN-D SKELETON - APPLICATIONTO THE SYNTHESIS OF 6-METHYL ANALOGS OF VITAMIN AND PREVITAMIN-D

Palladium-catalyzed cross-coupling of alkenylzine reagents, bearing th e C,D-ring/side chain portion, and (Z)-1-iodo-1,3-bis-exocyclic dienes (as A-ring precursors), provides a mild, convergent entry to the vita min D skeleton, that is suitable for the synthesis of thermally labile derivatives such as those bearing substituents on the triene system.