摘要
Several new classes of hybrid catalysts have been synthesized by tethering heterocyclic metal (Lewis acid) chelating scaffolds to several different amines capable of facilitating enamine catalysis. Oxazole, thiazole, and imidazole-based chiral precatalysts were prepared in several steps from amino acid starting materials, and these were combined with a variety of metal Lewis acids for potential use as catalysts for various carbon carbon bond formations. Air- and moisture-tolerant catalysts for enantioselective direct aldol reactions with activated benzaldehyde acceptors were identified, with optimal results obtained with proline-derived oxazole carboxamide precatalysts combined with Zn(OTf)(2) or lanthanide (III) salts. Control studies support the hypothesis that these act as unimolecular hybrid catalysts for the aldol reaction of propionaldehyde and 4-nitrobenzaldehyde.
- 出版日期2016-7-7