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  • Title: Stereospecific asymmetric N-heterocyclic carbene (NHC)-catalyzed redox synthesis of trifluoromethyl dihydropyranones and mechanistic insights.
    Author: Davies AT, Taylor JE, Douglas J, Collett CJ, Morrill LC, Fallan C, Slawin AM, Churchill G, Smith AD.
    Journal: J Org Chem; 2013 Sep 20; 78(18):9243-57. PubMed ID: 23957790.
    Abstract:
    N-heterocyclic carbene (NHC)-catalyzed redox asymmetric hetero-Diels-Alder reactions of α-aroyloxyaldehydes with β-trifluoromethyl enones generates synthetically useful dihydropyranones containing a stereogenic trifluoromethyl substituent in good yields (up to 81%) and excellent diastereoselectivity and enantioselectivity (up to >95:5 dr and >99% ee). The process is stereospecific, with use of either (E)- or (Z)-β-trifluoromethyl enones forming syn- or anti-dihydropyranone products, respectively. Mechanistic studies through in situ kinetic analysis of the reaction reveal key differences in reactivity between chiral NHC precursor 1 and an achiral NHC precursor.
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