Photocycloaddition of 2-Morpholinopropenenitrile to 8-Acetylquinoline

Upon broad-band UV-irradiation in benzene solution, the title compounds 2 and 5 form rel-(2R,2aR,8bS)-8b-acetyl-2- morpholino-1,2,2a,8b-tetrahydrocyclobuta[h]quinoline-2-carbonitrile (6) in a [2+2]- and rel-(5R,8R,10R)-8-acetyl-10- morpholino-5,8-ethano-5,8-dihydroquinoline-10-carbonitrile (7) in a [4+2]-photocycloaddition. The latter compound may be thermally cleaved into the starting materials 2 and 5 (AH≠= 130.5 ± 8 kJ mol–1 and AS≠= 46 ± 3 J mol–1 K–1) and hydrolyzed to the tricyclic diketone rel-(5R,8R)-8-acetyl-5,8-ethano-5,5-dihydroquinolin-10-one (8).