Hydrogen bonding in three anticonvulsant enaminones

The crystal structures of three anticonvulsant enaminones: methyl 4-[(p-chl orophenyl)amino]-6-methyl-2-oxo-3-cyclohexen-1-carboxylate (1), methyl 4-[( p-ethylphenyl)amino]-6-methyl-2-oxo-cyclohexen-1-carboxylate (2), and methy l 4-[(4'-chloro-2'-pyridinyl)amino]-6-methyl -2-oxo-3-cyclohexen-1-carboxyl ate (3) have been determined. The cyclohexene rings adopt sofa conformation s, with the methyl substituent at the out-of-plane carbon atom in equatoria l position. The dihedral angle between the mean planes of cyclohexene and a romatic ring is significantly smaller for pyridinyl derivative as compared with phenyl ones; for the former an intramolecular C-H...N(pyridinyl) hydro gen bond closes nearly planar six-membered ring. For all compounds, the int ermolecular N-H...O=C hydrogen bonds form infinite chains of molecules. Bot h the graph-set notation and resonance-assisted hydrogen bond approach have been used for description of hydrogen bond networks. For 1 and 2, there is a significant disorder of the carbomethoxy groups, caused by a rotation of 180 degrees around the C-C(OOC) single bond. (C) 2000 Elsevier Science B.V . All rights reserved.