X-Y-ZH Systems as potential 1,3-dipoles. Part 15¹ 1 Part 14. R. Grigg, H.Q.N. Gunaratne and V. Sridharan, Tetrahedron, 1987, 43, 5887.. Amine generated azaallyl anios versus metallo-1,3-dipoles in cycloadditions of α-amino acid esters. Facile regio- and stereo-specific formation of pyrrolidines

Kinetic studies of the deprotonation of arylidene imines of alanine and phenylglycine esters by tertiary amines and pyridine and cycloaddition of the resultant 4π-azaallyl anions to N-phenylmaleimide show the expected dependance on the p-substituent in the aryl ring. e.g. p-NO₂ > H > OMe >fs NMe₂. A combination of metal salt (silver, lithium. or zinc) and triethylamine in THF, dipolar aprotic solvents (MeCN, DMSO, DMF) or N-methylacetamide effects regio- and stereo-specific or highly stereo-selective inter- and intra-molecular cycloaddition of imines of phenylglycine. alanine and glycine esters to a range of dipolarophiles probably via metallo-1,3-dipole formation at room temperature. Silver acetate is a more efficient and selective catalyst than lithium bromide and reactions in acetonitrile, DMSO or N-methylacetamide, are especially rapid (O.1-3.5h).