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We describe a method to synthesize a new class of hetarylaminomethylidene derivatives of furan-2(3 H )-ones. The method uses 5-(4-chlorophenyl)furan-2(3 H )-one, triethyl orthoformate, and heterocyclic amines with different ring sizes and heteroatoms under refluxing in absolute isopropyl alcohol. The obtained enamines exist in an equilibrium of E - and Z -isomers, whose configurations relative to the double exocyclic C=C bond were confirmed with a set of NMR spectroscopy data. The E -/ Z -equilibrium of the synthesized compounds is affected by the configuration of the intermediate, the volume of its substituents, the site of enolate attack, the presence of intramolecular interactions of amino components, the time of the transformation, the order of mixing of the initial reagents, and the use of polar solvents in the NMR experiment. The advantages of the method are that the reaction time is short, the product yield is high, and product purification is easy.

3-(2-Chlorobenzylidene)-5-( p -tolyl)furan-2(3 H )-one ( 1 ), C 18 H 13 ClO 2 , crystallizes with Z = 8 and Z' = 2, and the structure at 100 K has orthorhombic ( Pna 2 1 ) symmetry. Each kind of molecule takes part in π-π stacking interactions to form infinite chains parallel to the c axis. We believe that the existence of two forms can be explained by the probable rotation around a single C-C bond. The quantum chemical modeling reveals that these molecules are almost equivalent energetically, and they can be described as the two most stable conformers (rotamers) with a minor rotational barrier of about 0.67 kcal/mol.

The title compound, C 17 H 10 BrCl 2 NO 2 , crystallizes in the monoclinic space group C 2/ c with a large cell volume of 6207 (3) Å 3 . The asymmetric unit of the title compound investigated at 120 K contains two crystallographically independent mol-ecules ( Z ' = 2). Each mol-ecule demonstrates slight non-planarity in the solid state and a Z -configuration for the exocyclic C=C bond. The crystal packing reveals the presence of π-π stacking inter-actions between the substituted benzene rings [centroid-centroid distances of 3.836 (5) Å, shift distances in the range 1.272-1.843 Å]., (© Mayorova et al. 2020.)

In the title compound, C 12 H 13 NO 2 , the pyrrolidinone moiety is almost flat while the oxazole ring adopts an envelope conformation with the carbon atom bearing the phenyl substituent as the flap: the angle between the mean planes of the fused heterocyclic rings is 45.47 (19)°. In the crystal, C-H⋯O and C-H⋯π contacts link the mol-ecules into infinite [010] chains., (© Linkova et al. 2020.)

The crystal structures and packing features of two homologous Meyer's bicyclic lactams with fused pyrrolidone and medium-sized perhydropyrimidine rings, namely, 8a-phenyl-2,3,4,7,8,8a-hexahydropyrrolo[1,2-a]pyrimidin-6(1H)-one, C 13 H 16 N 2 O (1), and 8a-(4-methylphenyl)-2,3,4,7,8,8a-hexahydropyrrolo[1,2-a]pyrimidin-6(1H)-one, C 14 H 18 N 2 O (2), were elucidated, and Hirshfeld surface plots were calculated and drawn for visualization and a deeper analysis of the intermolecular noncovalent interactions. Molecules of 1 and 2 are weakly linked by intermolecular C=O...H-N hydrogen bonds into chains, which are in turn weakly linked by other C=O...H-C ar interactions. The steric volume of the substituent significantly affects the crystal packing pattern.

In the crystal structure of the title compound, C 23 H 19 N 5 O 3 ·0.58C 2 H 6 OS·0.42C 2 H 3 N, prepared by the azo coupling of the 4-nitro-phenyl-diazo-nium salt with 3a-( p -tol-yl)-2,3,3a,4-tetra-hydro-1 H -benzo[ d ]pyrrolo-[1,2- a ]imidazol-1-one, the azo mol-ecules are linked by N-H⋯O hydrogen bonds into chains along the a -axis direction, and by the π-π inter-action into [101] chains. The dimethyl sulfoxide and aceto-nitrile solvent mol-ecules occupy the same positions, with populations of 0.585 (3) and 0.415 (3), respectively. These mol-ecules take part in C-H⋯O(N) and C-H⋯π contacts. The energy of the π-π inter-actions was estimated using DFT calculations. The Hirshfeld mol-ecular surface analysis revealed the positions of the most important inter-molecular contacts, such as hydrogen bonds and π-π inter-actions.