Expected and Unexpected Products in Half Curcuminoid Synthesis: Crystal Structures of But-3-en-2-ones and 3-Methylcyclohex-2-enones

The expected (E)-but-3-en-2-ones compounds I and II (half curcuminoids) were obtained by the Claisen–Schmidt reaction between aldehydes 3,4-dimethoxybenzaldehyde or 4-nitrobenzaldehyde with acetone. Concomitantly, 3-methylcyclohex-2-enones III IV arose from an unexpected of but-3-en-2-ones in cascade a Michael-type addition second molecule acetone followed Robinson annulation under strong basic conditions. Both enones exhibit (E)-configuration, compound displays s-trans conformation, whereas exhibits conformational disorder as solid solution s-cis conformations. related envelope conformation. Compound constitutes example rarest case racemic (pseudoracemate), where lack chiral discrimination respect to two enantiomers leads enantiomeric mixture different occupancies at reference site. Due hydrogen-bond donors all compounds, crystal packing is mainly stabilized weak intermolecular C-H···O interactions molecules. present work provides new perspective on search for by-products normally overlooked condensations.