PHOTOINDUCED REACTION OF DIETHYL 2-BROMO-1-PHENYLETHYLIDENEMALONATE WITH 1-BENZYL-1,4-DIHYDRONICOTINAMIDE AND THE EFFECT OF MAGNESIUM(II) ION ON THE REACTION

2-Bromo-1-phenylethylidenemalonic ester reacts with 1-benzyl-1,4-dihyd ronicotinamide (BNAH) in acetonitrile under illumination at lambda > 3 20 nm to give three debrominated products: an alpha,beta-unsaturated e ster, alpha beta,gamma-unsaturated ester and a dimer. In the presence of magnesium ion, the beta,gamma-unsaturated ester is formed exclusive ly. Using deuterated BNAH-4,4-d(2) as reagent and spin-trapping techni que for monitoring reactive intermediate, it has been shown that the r eaction proceeds via two different mechanistic pathways: e(-) transfer -debromination-H abstraction or dimerization for the formation of the alpha,beta-unsaturated ester and the dimer, and e(-) transfer-debromin ation-e(-) transfer-H+ transfer for the formation of the beta,gamma-un saturated ester. (C) 1997 Elsevier Science S.A.