Substituent Effects on the Product Distribution in Diazo Amide Photochemistry. Role of Ground-State Conformational Populations

Article abstract of DOI:10.1021/jo00319a010

Effects of substituents on the photochemical processes of several α-diazo amides (1a-f) have been studied .Irradiation of 1b in ethyl ether and acetone afforded, in addition to a β-lactam, the reaction products with the solvents, ie., EtOCH2CONMe2 and 1,3-dioxolane, respectively, whereas similar irradiation of 1a in these solvents gave only intramolecular reaction products, ie., β- and γ-lactams.Displacement of oneof the alkyl groups on the amide nitrogen with a Ph group markedly changed its photochemical processes.Thus irradiations of 1c and 1d in MeOH gave oxindole almost exclusively.Introduction of an acetyl group on the diazo carbon also caused a change in the product distributions.Photolysis of 1e in methanol gave, for exaple, the Wolff rearrangement (WR) product of Me migration and a β-lactam, whereas similar irradiation of 1f afforded WR product and oxindole.The results are interpreted as indicating that the β-lactam, the oxindole, and the WR product are derived from the excited singlet state of s-Z form of the diazo amide itself, whereas that of s-E form dissociates nitrogen to generate singlet carbene, and that populations of each conformers in the ground state are important in determining the photochemical processes of the α-diazo amide.