Photocyclisation of 1-styrylimidazoles. A novel route to N-bridgehead compounds

Abstract

The photoisomerisation of trans-1-styrylimidazole and derivatives to the cis-isomers is described. The cis-compounds undergo a stereospecific photodehydrocyclisation involving the 2-position of the imidazole ring to give imidazo[2,1-a]isoquinoline, benzimidazo[2,1-a]isoquinoline, and derivatives. The reverse mode of cyclisation, involving 2-styrylbenzimidazoles in C–N bond formation, is also demonstrated; benzimidazo[1,2-a]quinoline and its 2,3,10-trimethyl derivative have been obtained from the corresponding 2-styryl compounds.