Sugar-based organocatalyst for the diastereoselective desymmetrization of dibenzylideneacetones

Abstract

A Brønsted acid catalyzed highly regio- and diastereoselective desymmetrization of dibenzylideneacetones in the presence of azlactones is described (only 1,4 addition, > 20:1 dr). A novel organocatalyst based on D-galactose was synthesized and applied in this reaction. In terms of product, a new C-C σ-bond and two stereogenic centers are created, one of which is quaternary. The relative stereochemistry was assigned by comparison of both chiral HPLC traces and 13C NMR spectroscopic data as being 1,2-anti. One of the final Michael-type adducts could be converted into an N-protected α-functionalized amino acid in good yield and with no loss of diastereoselectivity. A sweet organocatalyst based on D-galactose was designed and applied in a highly regio- and diastereoselective desymmetrization of dibenzylideneacetones in the presence of azlactones (only 1,4 addition, > 20:1 dr). The final Michael-type product contains two stereogenic centers, one of them quaternary.