期刊
CRYSTALS
卷 11, 期 4, 页码 -出版社
MDPI
DOI: 10.3390/cryst11040404
关键词
Claisen– Schmidt reaction; Michael reaction; Robinson annulation reaction; half-curcuminoids; (E)-but-3-en-2-ones; 3-methylcyclohex-2-enones
资金
- DGAPA (PAPIIT), UNAM [IT200720]
- CONACYT [FOINS-307152]
Expected (E)-but-3-en-2-ones and unexpected 3-methylcyclohex-2-enones were synthesized via Claisen-Schmidt reaction, showing their configuration and conformational characteristics. Compound III presents a rare case of racemic solid solution, where crystal packing is mainly stabilized by weak intermolecular interactions.
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 compounds III and IV arose from an unexpected reaction of but-3-en-2-ones in the cascade reaction of a Michael-type addition of a second molecule of acetone followed by Robinson annulation under strong basic conditions. Both enones exhibit the (E)-configuration, compound I displays s-trans conformation, whereas compound II exhibits conformational disorder as solid solution of s-cis and s-trans conformations. The related 3-methylcyclohex-2-enones exhibit envelope conformation. Compound III constitutes an example of the rarest case of racemic solid solution (pseudoracemate), where a lack of chiral discrimination with respect to the two enantiomers leads to an enantiomeric disorder of a racemic mixture with different occupancies at the reference site. Due to the lack of strong hydrogen-bond donors in all compounds, the crystal packing is mainly stabilized by weak intermolecular C-H center dot center dot center dot O interactions between the molecules. The present work provides a new perspective on the search for by-products normally overlooked in Claisen-Schmidt condensations.
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