We report an unprecedented multicomponent reaction of acetoacetanilide with malononitrile leading to a structurally novel bicyclic product (9) in a high yield. The structure has been confirmed by X-ray crystallography and comparative Hirshfeld surface analysis of 5-cyano-2-hydroxy-2-methyl-N-phenyl-4-(yridine-4-yl)-6-(thiophen-2-yl)-3,4-dihydro-2H-pyran-3-carboxamide 2, 5-cyano-2-hydroxy-2-methyl-6-oxo-N-phenyl-4-(thiophen-2-yl)piperidine-3-carboxamide 4 and 2-(8-amino-7,8a-dicyano-1-imino-4a-methyl-3-oxo-2-phenyl-1,3,4,4a,5,8a-hexahydroisoquinolin-6(2H)-ylidene)-N-phenylacetamide 9.

In the molecular structure of the title compound, C₁₆H₁₃Cl₂N₅, the 1,4-dihydropyridine ring of the 1,3,4,8-tetrahydro-2H-pyrido[1,2-a]pyrimidine ring system adopts a screw-boat conformation, while the 1,3-diazinane ring is puckered. In the crystal, intermolecular N—H...N and C—H...N hydrogen bonds form molecular sheets parallel to the (110) and (\overline{1}10) planes, crossing each other. Adjacent molecules are further linked by C—H...π interactions, which form zigzag chains propagating parallel to [100]. A Hirshfeld surface analysis indicates that the most significant contributions to the crystal packing are from N...H/H...N (28.4%), H...H (24.5%), C...H/H...C (21.4%) and Cl...H/H...Cl (16.1%) contacts.

In the title compound, C₁₆H₁₁BrN₆O·2C₂H₆OS, the 1,2,3,7-tetrahydroimidazo[1,2-a]pyridine ring system and the oxindole moiety are both nearly planar [maximum deviations = 0.042 (2) and 0.115 (2) Å, respectively] and their planes form a dihedral angle of 86.04 (5)° with each other. Intermolecular N—H...O, C—H...O and C—H...N hydrogen bonds link molecules in the crystal through the O atoms of the solvent molecules, generating a three-dimensional network. A Hirshfeld surface analysis was performed to further analyse the intermolecular interactions.

New tetrahydroisoquinoline-5,7-dicarbonitrile derivatives have been synthesized by piperazine hydrate-catalyzed reaction of acetoacetanilide with 2-(1-arylethylidene)malononitriles (Knoevenagel condensation products of acetophenones and malononitrile) in aqueous ethanol at room temperature. The product structure was confirmed by NMR spectra and X-ray analysis of 1,6-diamino-4a-methyl-3-oxo-2,8-diphenyl-2,3,4,4a-tetrahydroisoquinoline-5,7-dicarbonitrile.

In the title compound, C₂₀H₁₇BrO₅S, molecules are connected by intermolecular C—H...S hydrogen bonds with R ² ₂(10) ring motifs, forming ribbons along the b-axis direction. C—H...π interactions consolidate the ribbon structure while van der Waals forces between the ribbons ensure the cohesion of the crystal structure. According to a Hirshfeld surface analysis, H...H (40.5%), O...H/H...O (27.0%), C...H/H...C (13.9%) and Br...H/H...Br (11.7%) interactions are the most significant contributors to the crystal packing. The thiophene ring and its adjacent dicarboxylate group and the three adjacent carbon atoms of the central hexene ring to which they are attached were refined as disordered over two sets of sites having occupancies of 0.8378 (15) and 0.1622 (15). The thiophene group is disordered by a rotation of 180° around one bond.

Michael addition of various substituted benzylidene- and thiophen-2-ylmethylidenemalononitriles with acetoacetanilide gave the corresponding...