Reactions of Enals with NHCs under Oxidation

Based on the elegant work from the group of Studer on redox activation of a,p-unsaturated aldehydes/ the You group realized enantioselective NHC-catalyzed Michael addition reactions to a,p-unsaturated aldehydes by redox oxidation. With 10 mol% of camphor-derived triazolium salt, developed by the authors group, the reactions of various dicarbonyl compounds 

The Studer group presented a new cascade for the highly enantioselec-tive synthesis of substituted indane derivatives. Three stereocenters are formed in the NHC-catalyzed cascade reaction of enals with various p-dike-tones to give the corresponding indane derivatives with excellent stereoselectivity (up to 74% yield, 99% ee). It is predicted that the reaction occurs via a catalytic cycle using oxidative NHC catalysis. Reaction of the enal with NHC in the presence of an oxidant generates an o,p-unsaturated acylazolium ion. Conjugate addition of the likely deprotonated 1,3-dicarbonyl compound 

The Chi group disclosed the first oxidative y-addition of enals to trifluo-romethyl ketones and enantioselective control via Lewis acid/NHC cooperative catalysis to give unsaturated 5-lactones. Enantioselective control involving the relatively remote enal y-carbon was achieved via Lewis acid and NHC cooperative catalysis (up to 81% yield and 94% ee). A reaction pathway 

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