A HYDRIDE TRANSFER-REACTION FROM SALTS OF CARBANIONS TO ACTIVATED OLEFINS

A novel reaction - a beta-elimination of a hydride ion from carbanion salts RM (R = Li, MgBr) and R2N(-)Li(+), and its transfer to tetra-sub stituted activated olefins of the type Ar2C=C(CN)CO2R (R=Me,Et), was s tudied. Yields of the reduced H--acceptor were used to follow the exte nt of the H--transfer reaction. A competing Michael addition reaction of RM to the activated olefin also took place, The effects of the solv ation properties of the solvent, the reaction temperature, the positiv e 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 bimolecula rity of the reaction. A benzyl substituent at C-beta of RM, a methine- type beta-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 pre sently studied beta-elimination of a hydride ion takes place by a bimo lecular E(2)cB-type mechanism.