Ag-Catalyzed Diastereo- and Enantioselective Vinylogous Mannich Reactions of α-Ketoimine Esters. Development of a Method and Investigation of its Mechanism
- 4 November 2008
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 131 (2) , 570-576
- https://doi.org/10.1021/ja8062315
Abstract
An efficient diastereo- and enantioselective Ag-catalyzed method for additions of a commercially available siloxyfuran to α-ketoimine esters is disclosed. Catalytic transformations require an inexpensive metal salt (AgOAc) and an air stable chiral ligand that is prepared in three steps from commercially available materials in 42% overall yield. Aryl- as well as heterocyclic substituted ketoimines can be used effectively in the Ag-catalyzed process. Additionally, two examples regarding reactions of alkyl-substituted ketoimines are presented. An electronically modified N-aryl group is introduced that is responsible for high reaction efficiency (>98% conversion, 72−95% yields after purification) as well as diastereo- (up to >98:2 dr) and enantioselectivity (up to 97:3 er or 94% ee). The new N-aryl unit is crucial for conversion of the asymmetric vinylogous Mannich (AVM) products to the unprotected amines in high yields. Spectroscopic and X-ray data are among the physical evidence provided that shed light on the identity of the Ag-based chiral catalysts and some of the mechanistic subtleties of this class of enantioselective C−C bond forming processes.Keywords
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