Photochemical Electrocyclic Reactions of Aromatic Enamides for the Generation of Zwitterionic Intermediates

The 2-(methyl(l-phenylvinyl)carbamoyl)phenyl acetate molecule, upon irradiation, releases the acetate leaving group to give a six membered cyclic lactam as the major product. The molecule thus cyclizes regioselectively with release of the ortho leaving group. The minor process is cyclization at the alternate ortho position, which results in formation of a lactam retaining the leaving group. A zwitterionic intermediate is thought be responsible for product formation and would result from a conrotatory 6- electron photochemically-allowed, electrocyclic ring closure process. An minor oxidation product that retains the leaving group also formed, likely from loss of a proton and protonation/tautomerization of an enol. N-methyl-N-(2-methyl-l-phenylprop-l-enyl)benzamide and N-benzyl-N-(2- methyl-l-pheny)prop-l-enyl)benzamide iso\u27merize upon irradiation to lactams as the major photochemical process. 2-(benzyl(2-methyl-l-phenylprop-lenyl) carbamoyl)phenyl acetate undergoes regiospecific reaction that does not result in elimination of the leaving group. Attempts have also been made to increase the absorption wavelengths that effect the photochemical reaction by incorporating 2-naphthyl, pyrenyl and carbazoyl groups at the double bond. The quantum yields of the photochemical reactions have been measured and a plausible mechanism has been proposed to explain each photoproduct