2, 13-Diaza [5] helicene: synthesis, theoretical calculations and spectroscopic properties

An easy approach to the synthesis of azahelicenes is based on the photochemical cyclisation of symmetrically or asymmetrically 1,2-aryl-substituted double bonds. In the synthesis of 2,13-diaza[5]helicene, irradiation of 9-(2-pyridin-4-yl-vinyl)-benzo[h]isoquinoline yielded 2,9-diaza-dibenzo[a.h]anthracene together with the desired helicene, and the ratio of the two products depends on the solvent. In this paper we suggest that the ratio between the two products should not be ascribed to different transitions induced by the solvent but to different populations of the two Z conformers