X=Y−ZH compounds as potential 1,3-dipoles. Part 43. Metal ion catalysed asymmetric 1,3-dipolar cycloaddition reactions of imines and menthyl acrylate

Abstract

Metallo-azomethine ylides, generated from imines by the action of amine bases in combination with LiBr or AgOAc, undergo cycloaddition with both 1R, 2S, 5R- and 1S, 2R, 5S-menthyl acrylate at room temperature to give homochiral pyrrolidines in excellent yield. The stronger the base the faster the cycloaddition and the greater the yield with: 2- 2-t-butyl-1,1,3,3-tetramethylguanidine > DBU > NEt 3. X-Ray crystal structures of representative cycloadducts establish that the absolute configuration of the newly established pyrrolidine stereocentres is independent of the metal salt and the size of the pyrrolidineC(2)-substituent for a series of aryl and aliphatic imines.