Application of chiral ligands: carbohydrates, alkaloids–lanthanides and other Lewis acid complexes to control regio- and stereoselectivity of the dipolar cycloaddition reactions of nitrile oxides and crotonamides and cinnamides

Abstract

Chiral Lewis acid mediated 1,3-dipolar cycloaddition reactions of aryl nitrile oxides and secondary α- or β-substituted acrylamides and cinnamides were examined. Excellent enantioselectivities with moderate to good regioselectivities were achieved for crotonamides with complexes of carbohydrates with Yb(OTf)3, TiCl4, Mg(OTf)2, and CsF as well as with the (−)-sparteine–Yb(OTf)3 system. High enantiomeric excess and high regioselectivity were observed for cinnamides in reactions mediated by Yb(OTf)3 complexes with carbohydrate, R-BINOL, and (−)-sparteine.