A new monoclinic polymorph of 3-diethylamino-4-(4-methoxyphenyl)-1,1-dioxo-4H-1 lambda 6,2-thiazete-4-carbonitrile

A new monoclinic form of the title compound, C14H17N3O3S, has been found upon slow crystallization from water. Another monoclinic form of the compound was obtained previously from a mixture of dichloromethane and diethyl ether[Clerici, F.; Gelmi, M. L.; Soave, R.; Lo Presti, L. Tetrahedron 2002, 58, 5173-5178.]. Both phases crystallize in space group P21/n with one molecule in the asymmetric unit. The formally single exocyclic C-N bond that connects the -NEt2 unit with the thiazete ring is considerably shorter than the adjacent, formally double, endocyclic C=N bond. This is likely to be due to the extended conjugated system between the electron-donor diethylammine fragment and the electron-withdrawing sulfonyl group. In the newly discovered polymorph, the methoxy group is rotated by almost 180° around the phenyl-OCH3 bond, resulting in a different molecular conformation.