A key intermediate for the convenient synthesis of series of vitamin D3 analogues with modified side chains

Tosylate 1, which features the vitamin D triene unit, was stereoselectively synthesized from commercially available starting materials. This key intermediate undergoes a very efficient one-pot, two-step reaction with tetrabutyl ammonium fluoride to afford vitamin D analogue 2, which bears a cyclic side chain. Reaction of 1 with lithium aluminium hydride and removal of the silyl protecting groups affords the 22-methylated vitamin D analogue 3.