Tandem Acyl Substitution/Michael Addition of Thioesters with Vinylmagnesium Bromide.

A tandem reaction of thioesters with vinylmagnesium bromide is reported. The initial acyl substitution provides an α,β-unsaturated ketone which further reacts with the liberated thiolate. This transition-metal-free synthesis of β-sulfanyl ketones takes place under mild reaction conditions, whereas the addition of a second Grignard molecule is almost completely suppressed. The carefully chosen parameters enabled the transformation of different substrates in moderate to good yields.