Thermal and photoinduced reduction of some benzyl bromides by an NAD(P)H model: the effect of electron withdrawing groups on mechanism and reactivity

A series of compounds, o-bromomethylbenzylidene-malononitrile (1), dimethyl o-bromomethyl-benzylidenemalonate (2) and methyl α-cyano-o-bromomethylcinnamate (3) were reduced in the dark and under irradiation by an NAD(P)H model, 1-benzyl-1,4-dihydronicotinamide (BNAH). Two different mechanisms were found, i.e. one-step hydride transfer (polar pathway) and multi-step sequence initiated by single electron transfer (SET pathway). The effect of electron-withdrawing groups on the reactivity of the substrates were discussed in terms of Hammett substituent constants, 13C NMR chemical shift values and cyclic voltammetric redox potentials, and their correlations.