Syntheses and Crystal Structures of Four Novel Thiophene/Phenyl-Piperidine Hybrid Chalcones

Abstract

Four closely related novel chalcones, (2E)-1-(4-methylthiophen-2-yl)-3-[4-(piperidin-1-yl)phenyl]prop-2-en-1-one, C₁₉H₂₁NOS, I, (2E)-3-[4-(piperidin-1-yl)phenyl]-1-(thiophen-2-yl)prop-2-en-1-one, C₁₈H₁₉NOS, II, (2E)-3-[4-(piperidin-1-yl)phenyl]-1-(thiophen-3-yl)prop-2-en-1-one, C₁₈H₁₉NOS, III, and (2E)-1-(5-chlorothiophen-2-yl)-3-[4-(piperidin-1-yl)phenyl]prop-2-en-1-one, C₁₈H₁₈ClNOS, IV, have been prepared by the reaction of 4-(piperidin-1-yl)benzaldehyde with different aromatic ketones in alkaline media. All the compounds have been characterized by IR and E.I.M.S. In all structures, the piperidine rings are in chair conformations, thiophene rings are essentially planar and the C=C bonds in the prop-2-en-1-one fragment adopt E-conformation. All crystal structures are devoid of any classical hydrogen bonds. However, non-classical hydrogen bonding interactions of the type C–H···O in compounds I, III and IV link the molecules into chains extended along the b-axis. Moreover, C–H···Cg interactions [involving thiophene rings in I and II and benzene ring in IV] and π···π interactions between benzene rings lying about inversion centers are present in I and III.

Graphical Abstract

The syntheses and crystal structures of four novel thiophene/phenyl-piperidine hybrid chalcones have been determined which are presented in this article.