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

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.