1,4-Malonate addition, asymmetric protonation

SCHEME 31.30. 1,4-Malonate addition followed by asymmetric protonation of chiral calcium... 

Poisson T, Yamashita Y, Kobayashi S. Catalytic asymmetric protonation of chiral calcium enolates via 1,4-addition of malonates. 7. Am. Chem. Soc. 2010 132 7890-7892. 

The epi-quinine urea 81b was also found by Wennemers to promote an asymmetric decarboxylation/Michael addition between thioester 143 and 124 to afford the product 144 in good yield and high enantioselectivity (up to 90% ee) (Scheme 9.49). Here, malonic acid half-thioesters serve as a thioester enolate (i.e., enolate Michael donors). This reaction mimics the polyketide synthase-catalyzed decarboxylative acylation reactions of CoA-bound malonic acid half-thiesters in the biosynthesis of fatty adds and polyketides. The authors suggested, analogously with the enzyme system, that the urea moiety is responsible for activating the deprotonated malonic add half-thioesters that, upon decarboxylation, read with the nitroolefin electrophile simultaneously activated by the protonated quinuclidine moiety (Figure 9.5) [42]. 

Carbon-carbon bond formation by using metal enolates as synthons in organic chemistry and the protonation, alkylation, arylation, and vinylation of enolates have been reviewed. " The stereoselective carbon-carbon formation of bond through Mannich reaction has been detailed according to the type of Mannich base produced. Phosphine-catalysed asymmetric additions of malonate esters to y-substituted allenoates and aUenamides have been reported. ... 

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