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

Add time:08/02/2019    Source:sciencedirect.com

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 the imines to imidazolidines. In the latter case cycloaddition to other imines also occurs. Use of Mg(II) salts can lead to either pyrrolidines or imidazolidines depending on the salt used. A correlation with metal cation hydration enthalpies is noted. Heating imidazolidines in the presence of dipolarophiles effects a tandem cyclo-reversion-cycloaddition process leading to new cycloadducts.

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