Fluoride-Mediated Elimination of Allyl Sulfones: Application to the Synthesis of a 2,4-Dimethyl-A-ring Vitamin D3 Analogue

A coupling strategy for the synthesis of 2,4-dimethyl-1 alpha,25(OH)(2)D-3 is achieved which involves methylation of a pro-A ring vinyl sulfone and in situ traping of the allyl sulfonyl anion with a CD ring allyl chloride. TBAF-promoted 1,2-eliminative desulfonylation and concomitant silyl ether deprotection gives the vitamin D-3 analogue.