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.