XY–ZH systems as potential 1,3-dipoles. Part 6. Metallo-1,3-dipoles. Cycloadditions of divalent metal complexes of glycine and alanine imines to electronegative olefins

Abstract

Copper(II), zinc(II), and cadmium(II) complexes of imines derived from α-oxo acids and glycine or alanine undergo stereospecific cycloaddition at room temperature to 1,2-disubstituted electronegative olefins in the presence of weak base. Corresponding reactions of lead(II) complexes give insoluble cycloadducts. In contrast, the reactions of the same metallo imines with methyl acrylate, phenyl vinyl sulphone, and acrylonitrile frequently give mixtures of regio- and stereo-isomers. These mixtures are shown to arise by stereoisomerisation of initial cycloadducts formed by a 4π+ 2π concerted cycloaddition of intermediate metallo-1,3-dipoles.