(E)- and (Z)-enamine Dewar pyrimidinones

The structures of (E)- and (Z)-methyl 1,6-dimethyl-5-oxo-2,6-diazabicyclo[2.2.0]hex-3-ylideneacetate, C 9 H 12 N 2 O 3 , have been established by X-ray diffraction analyses. The 2-azetidinone ring, azetidine ring and enamine moiety in both isomers are quite planar. The dihedral angles between the least-squares planes of the 2-azetidinone and azetidine rings in the two Dewar isomers are almost 112°.