Mechanistic studies of direct and sensitized photolysis of methyl (4-nitrophenyl)diazoacetate in the presence of an electron-donating amine: photochemical generation of the diazoalkane radical anion

Abstract

The direct and perylene-sensitized photolysis of methyl (4-nitrophenyl)diazoacetate (1) in the presence of an electron-donating amine was investigated by the characterization of reaction products and by the direct observation of reactive species using a laser flash photolysis technique. In the direct photolysis of 1 in the presence of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD), electron transfer from TMPD occurs and the photoproducts are obtained through an intermediate other than the carbene 3, which we suppose to be the carbene radical anion 3⁻˙. In the perylene-sensitized photolysis of 1 in the presence of an amine having a large electron-donating ability such as N,N-dimethylaniline and TMPD, the radical anion of 1 can be generated by perylene-mediated electron transfer from the amine to 1. The resulting 1⁻˙ appears to undergo extrusion of dinitrogen to give 3⁻˙ smoothly, the behavior of which is dependent on the amine employed as an additive. The product studies revealed that 3⁻˙ reacts readily with O₂ to give the ketoester 5 or abstracts hydrogen atoms to give the ester 7, which is not inconsistent with the theoretical prediction that 3⁻˙ has a σ radical character in its electronic structure.