Dithioacetals as geminal dication synthons

Abstract

The NiCl2(PPh3)2-catalyzed cross coupling reactions of benzylic and allylic dithioacetals with alkyl Grignard reagents give the corresponding olefination products. The reactions of the dithioacetal with cyclopropyl Grignard reagent under the same conditions provide a stereoselective synthesis of substituted butadienes. The applications of this methodology lead to a unified synthesis of vinylsilanes and silyl-substituted butadienes. The aliphatic dithioacetals can undergo the coupling reaction when there exists a proximal heteroatom which, in combination with the sulfur moeity, can form a chelation complex with the nickel catalyst. Trithioorthoesters and tetrathioorthocarbonate behave similarly to yield the corresponding alkylative olefination products. The nickel catalyst having a bidentate phosphine ligand can promote geminal dimethylation of allyiic dithioacetals under similar conditions. These reactions can be considered as using dithioacetals as C2+ synthons.