The presence of a p-nitrophenyl group converts acetone into an excellent and versatile nucleophile in organocatalytic processes, able to react with α,β-unsaturated aldehydes affording β-substituted α-arylcyclohexenones via a Michael reaction/aldol reaction/dehydration sequence, which occurs in good yields, ee up to 96% and complete diastereoselectivity. The resulting compounds are excellent synthons for the diastereoselective preparation of a variety of synthetically useful polysubstituted cyclohexanones and derivatives.
Keywords: Asymmetric catalysis / Organocatalysis / Michael additionAlthough several nucleophiles derived from arylacetic acids have been described in catalysis via iminium activation, none have presented good enantioselectivity and reactivity with both β-alkyl and β-aryl enals. This study on the Michael addition of p-nitrophenylacetic thioesters suggests that this behavior is due to the different reactivity and distinct tendency
An Organocatalytic Approach to Enantiomerically Enriched α-Arylcyclohexenones and Cyclohexanones. -α,β-Disubstituted cyclohexenones are easily obtained by simple organocatalytic Michael addition of commercially available ketone (I) to α,β-unsaturated aldehydes, followed by aldol reaction and a dehydration sequence. The resulting compounds are excellent synthons for a variety of synthetically useful compounds. Their preparation by other ways is nontrivial and usually requires umpolung strategies or long reaction sequences. -(DUCE, S.; JORGE, M.; ALONSO, I.; GARCIA RUANO, J. L.; CID*, M. B.; Org. Biomol. Chem. 9 (2011) 24, 8253-8260, http://dx.
The differences in the reactivity of the thioesters (I) with β‐alkyl and β‐aryl‐substituted enals (II) are overcome by optimization allowing the synthesis of diastereomeric mixtures of Michael adducts (III) and (IV).
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