Propargylic Dithioacetal as an Allene 1,3-Dication Synthon. Nickel-Catalyzed Cross-Coupling Reactions of Propargylic Dithioacetals with Grignard Reagents

摘要

The synthesis of allenes from propargylic derivatives is well documented. In general, a good leaving group is required to facilitate the S_N2′ reaction leading to the formation of allenes. A series of the nickel-catalyzed cross-coupling reactions of dithioacetals with Grignard reagents was recently reported. To illustrate, the reactions of allylic compound under these conditions give the corresponding geminal dimethylation or the olefination products. The reaction can formally be considered as using the dithioacetal functionality as a geminal dication synthon. Interestingly, the NiCl_2(dppe)-catalyzed cross couplings of allylic trithioorthoesters with MeMgI afford the corresponding 1,1,3-trimethylation products, the first methyl group being introduced at the γ-position.