Chiral Bis-pyridinium Salts as Novel Stereoselective Catalysts for the Metal-Free Diels-Alder Cycloaddition of alpha,beta-Unsaturated Aldehydes

摘要

The synthesis of enantiomerically pure C_2-symmetric bis-pyridinium salts was realized through a simple condensation of 2-pyridyl-carboxyaldehydes with a chiral diamine. The catalytic properties of such novel compounds were preliminarily studied and the trifluoracetate salts of chiral bis-imines of 2-picolinaldehydes derived from 1,1'-binaphthyl-2,2'-diamine were shown to catalyze the Diels-Alder reaction between cyclopentadiene and alpha,beta-unsatur-ated aldehydes. Modest exo stereoselectivities and enantioselectiv-ities of up to 55% were obtained.