cis-[4a]-cisoid-[4a,4b]-cis-[4b]-8a,8b-Diethyl-1,3,6,8-tetramethylperhydro-1,3,6,8-tetraazabiphenylene-2,4,5,7-tetraone

The title compound, C16H24N4O4, was prepared by [2+2]-photocycloaddition of 1,3-dimethyl-6-ethyluracil in acetone. The structure determination was undertaken in order to determine the stereoconfiguration of the product which could not be extracted from NMR data. Single-crystal X-ray analysis revealed that the methyl groups are located on the same side of the cyclobutane ring (cis) and that the monomers are oriented head-to-head (syn). There are two crystallographically independent molecules in the asymmetric unit; these differ only slightly in geometry. [GRAPHICS]