X=Y-ZH compounds as potential 1,3-dipoles. Part 24. Preparation and thermal fragmentation of imidazolidines. Influence of metal salts on pyrrolidine versus imidazolidine formation
Imines of diethyl aminomalonate slowly dimerise imidazolidines in ethanol or methylene chloride at 40°C, but cycloaddition to other imines does not occur. Imines of glycine, alanine and phenylglycine methyl esters undergo rapid regio- and stereo-specific cycloaddition to methyl acrylate (MeCN, 25°C) in the presence of Ag(I) or Mn(II) salts, and triethylamine, whilst Zn(II)-or Co(II) salts dimerise