Photochemical nucleophilic substitution of 5,8-dimethoxy-1,2-dimethylnaphth[2,3-d]imidazole-4,9-dione. An unusual long-range directing effect in the photoexcited state
Abstract
Photochemical substitution of 5,8-dimethoxy-1,2-dimethylnaphth[2,3-d]imidazole-4,9-dione (1a) with primary alkylamines gives mixtures of the 5-alkylamino-8-methoxy- and 8-methylamino-5-methoxy-isomers in high yield; the predominance of the 5-alkylamino-isomers, which is not observed in the thermal substitution reaction, can be explained in terms of the predicted π-electron densities at the 5- and 8-positions in the first excited state.