The heterodiquinane derivative was prepared from the photochemical reaction of 7-methoxy-3-[1-(methoxyimino) ethyl]-N-phenyl-1, 2-dihydrocinnoline 1, 2-dicarboximide with diethyl 1, 3-acetonedicarboxylate in acetonitrile. The structure and the stereochemistry were determined by X-ray diffraction. The compound crystallizes in triclinic, space group P1 with cell parameters of a = 12.171(5) A゜, b = 12.372(5) A゜, c = 10.431(2) A゜, α= 92.21(2)°, β= 109.75(2)°, γ= 89.19(3)°, and Z = 2 ; the final residual factor is R1 = 0.043 for 2489 reflections.