Enantioselective organocatalytic direct Michael addition of nitroalkanes to nitroalkenes promoted by a unique bifunctional DMAP-thiourea.
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 %.
Rabalakos
Constantinos
C
Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA.
Wulff
William D
WD
D000473:Alkanes / Q000138:chemical synthesis* / Q000737:chemistry; D000475:Alkenes / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D015394:Molecular Structure; D009574:Nitro Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D055601:Organic Chemistry Phenomena; D011725:Pyridines / Q000737:chemistry*; D013237:Stereoisomerism; D013890:Thiourea / Q000737:chemistry*
C417980:4-(dimethylamine)pyridine; D000473:Alkanes; D000475:Alkenes; D009574:Nitro Compounds; D011725:Pyridines; D013890:Thiourea