Regioselectivity and Kinetics of Hydride Transfer in Substituted 1-Benzyl-3-quinolinecarboxamide Redox Reactions

Article abstract of DOI:10.1021/jo00229a005

A systematic study on the factors that affect the regioselectivity and rate of hydride transfer in systems involving 1-benzyl-4-methyl-3-quinolinecarboxamides as donors or acceptors is reported.The study reports two major findings: (1) Hydride transfers from borohydride or 1-propyl-1,4-dihydronicotinamide to 1-benzyl-4-methyl-3-quinolinecarboxamide cation display distinct regioselective patterns-borohydride results in hydride transfer to the 2-position of the acceptor and dihydronicotinamide results in hydride transfer to the 4-position of the acceptor. (2) Substitution of the 4-hydrogen by a methyl group on either the oxidant or reductant quinoline lowers the rate constants for hydride transfer by a factor of over 2000.When methyl replaces hydrogen in both the oxidant and reductant, the rate constant for hydride transfer is lowered by a factor of over 5 000 000.These observations are interpreted in terms of a two-step mechanism: (1) formation of a ?-complex between the oxidant and reductant stabilized by charge-transfer interactions and (2) rate-determining hydride transfer within the complex.