Preparation of 1,10-dimethyl-benzo[c]cinnolines by photochemical cyclodehydrogenation of azobenzenes

Photocyclodehydrogenation of methylated azobenzene derivatives to the corre sponding benzo[c]cinnolines was utilized for the synthesis of a number of c ompounds featuring sterically hindered methyl groups with different degrees of sterical hindrance including close mutual methyl-methyl interaction. Su ch compounds are of special theoretical interest in the context of intramol ecular dynamics, spectroscopy, and quantum (tunneling) effects. Factors det ermining synthetic accessibility and product distribution are discussed.