Novel 2α-methyl-, 2α-(3-hydroxypropyl)- and 2α-(3-hydroxypropoxy)-substituted 25-dehydro-1α-hydroxyvitamin D3-26,23-lactone derivatives were efficiently synthesized via Reformatsky type allylation and palladium-catalyzed alkenylative cyclization processes, and their biological activities were evaluated. Introducing functional groups into the 2α-position of the vitamin D3-26,23-lactones resulted in remarkable enhancement of their antagonistic activity on vitamin D receptor (VDR).