19641-58-8Relevant academic research and scientific papers
Mechanism and scope of salen bifunctional catalysts in asymmetric aldehyde and α-ketoester alkylation
Fennie, Michael W.,DiMauro, Erin F.,O'Brien, Erin M.,Annamalai, Venkatachalam,Kozlowski, Marisa C.
, p. 6249 - 6265 (2005)
Metal complexes of C2-symmetric Lewis acid/Lewis base salen ligands provide bifunctional activation resulting in rapid rates in the enantioselective addition of diethylzinc to aldehydes (up to 92% ee). Further experiments probed the reactivity of the individual Lewis acid and Lewis base components of the catalyst and established that both moieties are essential for asymmetric catalysis. These catalysts are also effective in the asymmetric addition of diethylzinc to α-ketoesters. This finding is significant because α-ketoesters alone serve as their own ligands to accelerate racemic 1,2-carbonyl addition of Et2Zn and racemic carbonyl reduction. The latter proceeds via a metalloene pathway, and often accounts for the predominant product. Singular Lewis acid catalysts do not accelerate enantioselective 1,2-addition over these two competing paths. The bifunctional amino salen catalysts, however, rapidly provide enantioenriched 1,2-addition products in excellent yield, complete chemoselectivity, and good enantioselectivity (up to 88% ee). A library of the bifunctional amino salens was synthesized and evaluated in this reaction. The utility of the α-ketoester method has been demonstrated in the synthesis of an opiate antagonist.
The First Catalytic Asymmetric Addition of Dialkylzincs to α-Ketoesters
DiMauro, Erin F.,Kozlowski, Marisa C.
, p. 3781 - 3784 (2002)
(Matrix Presented) The first catalytic, enantioselective addition of organozinc reagents to α-ketoesters is described. Modular bifunctional salen catalysts that contain Lewis acid and Lewis base activating groups accelerate the carbonyl addition to a much greater extent than the competing carbonyl reduction. α-Hydroxyesters containing new quaternary stereogenic centers are obtained in high yield and moderate enantiomeric excess. Enrichment to 98% ee can be effected by recrystallization of the corresponding α-hydroxy acid.
