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  • Title: Enantioselective organocatalytic direct Michael addition of nitroalkanes to nitroalkenes promoted by a unique bifunctional DMAP-thiourea.
    Author: Rabalakos C, Wulff WD.
    Journal: J Am Chem Soc; 2008 Oct 15; 130(41):13524-5. PubMed ID: 18808117.
    Abstract:
    A new catalyst is designed, synthesized, and evaluated for the asymmetric Michael addition of nitroalkanes to nitroalkenes. The obdurate nature of this reaction has made this a formidable challenge to subdue by asymmetric catalysis. The catalyst design includes a thiourea function to activate the nitroalkene by a double H-bond and a 4-dimethylaminopyridine unit to deprotonate the nitroalkane and to bind the resulting nitronate anion also by a double H-bond. The chiral scaffold for the catalyst is 2,2'-diamino-1,1'-binaphthalene (BINAM), and a bis-conjugate is prepared by the attachment of the thiourea unit and the dimethylaminopyridine moiety (DMAP) via the two amino groups. The resulting catalyst will effect the reaction of nitroalkanes to a variety of nitrostyrenes and gives excellent asymmetric inductions (91-95% ee) over a range of 10 substrates. Remarkably, the asymmetric induction increases with decreasing catalyst loading with the optimal compromise between rate and induction at a loading of 2 mol %.
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