Desulfurization/α-alkylation of β-keto sulfones

A one-pot procedure for the reductive alkylation of β-keto sulfones is described. The method proceeds by a lithium in liquid ammonia desulfurization of the starting β-keto sulfone, resulting in regiospecific generation of an intermediate enolate. Subsequent admixture of tributyltin chloride followed by addition of the alkylating agent in HMPA generates the C(α)-alkylated product in good yield and with excellent regiocontrol. Thus, 2-(phenylsulfonyl)-5-(2-propenyl)cyclopentanone gives 2,5-di(2-propenyl)cyclopentanone in 71% isolated yield with <1% of 2,2-di(2-propenyl)cyclopentanone detected in the crude reaction mixture. Experiments are presented which underscore the advantages of this procedure over traditional α-alkylation/desulfurization protocols.