Synthesis of rigidly linked donor–acceptor systems designed to test the effect of orbital symmetry on the dynamics of long-range intramolecular electron transfer processes

Abstract

The synthesis of the novel rigid bichromophoric systems, 3, 4, 6, together with the monochromophoric system, 5, is described. Such systems are characterized in terms of each possessing a polynorbornyl bridge, one end of which is terminally fused to a bicyclo[2.2.2]octene unit. Deacetalization of the dimethoxyacetal, 7, with formic acid gave the ketone, 9, which readily underwent thermal decarbonylation to give the diene 11. Diels–Alder reaction of 11 with dicyanoacetylene or dimethylacetylene dicarboxylate readily gave the adducts, 13 and 15, respectively, resulting from endo-attack by the dienophile on the diene. Catalytic hydrogenation of 13 and 15 gave 3 and 6 respectively. In a similar manner, 4 and 5 were synthesized starting from the dimethoxyacetals, 8 and 19a, respectively. Single crystal X-ray structures of 3 and 6 were determined and are consistent with the structures shown.