Phototransposition chemistry of pyridine and substituted pyridines in the vapor phase (original) (raw)

Irradiation of the six isomeric dimethylpyridines or six isomeric trideuteropyridines in the vapor phase at 254 nm leads to two triads of three interconverting compounds. Monosubstituted pyridines undergo phototransposition in the vapor phase at 254 nm to yield one triad of the three interconverting compounds. Thus the three isomeric methylpyridines, the three isomeric cyanopyridines, and the three isomeric tetradeuteropyridines each undergo phototransposition to three interconverting compounds. These ring transposition reaction take place by photo-ring closure followed by N-migration around the five sides of the cyclopentadienyl and rearomatization. This mechanism allows nitrogen to insert between each pair of ring atoms. The mechanism predicts the observe regioselectivity of the transposition reactions.