Synthesis, NMR analysis and X-ray crystal structure of 6,12-bis(4-fluorophenyl)-3,9-dioxatetraasterane

Tetraethyl 2,4,8,10-tetramethyl-6,12-bis(4-fluorophenyl)-3,9-dioxapentacyclo[6.4.0.02,7.04,11.05,10]dodecane-1,5,7,11-tetracarboxylate (1, simplified as 6,12-bis(4-fluorophenyl)-3,9-dioxatetraasterane) was synthesized by [2 + 2] photocyclization of diethyl 2,6-dimethyl-4-(4-fluorophenyl)-4H-pyran-3,5-dicarboxylate (2) in solution. The NMR analysis of 1 is discussed in detail by the splittings and assignments of signals according to the three-dimensional structure. Single-crystal X-ray diffraction shows that 1 is situated on an inversion center. The molecular symmetry is close to C2h except for the terminal ethyl groups.