ChemInform Abstract: C2-Symmetric Copper(II) Complexes as Chiral Lewis Acids. Scope and Mechanism of the Catalytic Enantioselective Aldol Additions of Enolsilanes to Pyruvate Esters

Autor: Christopher S. Burgey, David A. Evans, Steven W. Tregay, Marisa C. Kozlowski
Rok vydání: 2010
Předmět:
Zdroj: ChemInform. 30
ISSN: 1522-2667
0931-7597
Popis: The C2-symmetric (S,S)-tert-butyl-bis(oxazolinyl)Cu(OTf)2 complex (1a) has been shown to catalyze the enantioselective aldol reaction between α-keto esters and silylketene acetals or enolsilanes with enantioselectivities ranging from 93 to 99%. With substituted silylketene acetals, syn reaction diastereoselection ranging from 90:10 to 98:2 and enantioselectivities ranging from 93 to 98% are observed. High levels of carbonyl regioselectivity (98:2), diastereoselectivity (93:7), and enantioselectivity (97% ee) are also observed in the aldol addition to 2,3-pentanedione. In all instances, the aldol adducts are generated in high yield and in excellent enantiomeric excess using as little as 1 mol % of the chiral complex 1a. Mechanistic insight into the pyruvate aldol reaction has also been gained. Silyl crossover experiments demonstrate that the silyl-transfer step is intermolecular. Based upon these results, TMSOTf has been identified as an addend to accelerate these reactions. Furthermore, solvent was shown ...
Databáze: OpenAIRE
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