A hydride transfer reaction from salts of carbanions to activated olefins

A novel reaction - a β-elimination of a hydride ion from carbanion salts RM (R = Li, MgBr) and R₂N^-Li⁺, and its transfer to tetra-substituted activated olefins of the type Ar₂C=C(CN)CO₂R (R=Me,Et), was studied. Yields of the reduced H^--acceptor were used to follow the extent of the H^--transfer reaction. A competing Michael addition reaction of RM to the activated olefin also took place. The effects of the solvation properties of the solvent, the reaction temperature, the positive counter-ion, and of various structural features of the H^--donor and the H^--acceptor, were studied. Structural factors associated with both reactants, played a critically significant role due to the bimolecularity of the reaction. A benzyl substituent at C β of RM, a methine-type β-carbon, or a small size of R of RM, resulted in a relatively high extent of the H^--transfer reaction. It is suggested that the presently studied β-elimination of a hydride ion takes piace by a bimolecular E₂cB-type mechanism.