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 compounds III and IV arose from an unexpected reaction of bu...

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Bibliographic Details
Published in:Crystals (Basel) 2021-04, Vol.11 (4), p.404
Main Authors: Obregón-Mendoza, Marco A., Arias-Olguín, Imilla I., Meza-Morales, William, Alvarez-Ricardo, Yair, Chávez, María Isabel, Toscano, Rubén A., Cassani, Julia, Enríquez, Raúl G.
Format: Article
Language:English
Subjects:
(E)-but-3-en-2-ones
3-methylcyclohex-2-enones
Acetone
Aldehydes
Cascade chemical reactions
Chemical reactions
Chromatography
Claisen-Schmidt reaction
Crystal structure
Crystals
Enantiomers
half-curcuminoids
Michael reaction
Potash
Potassium
Robinson annulation reaction
Software
Solid solutions
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Summary: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···O interactions between the molecules. The present work provides a new perspective on the search for by-products normally overlooked in Claisen–Schmidt condensations.
ISSN:2073-4352
2073-4352
DOI:10.3390/cryst11040404