Synthesis of pyrrolidine-2,4-diones(tetramic acids) and some derivatives

Pyrrolidine-2,4-dione (tetramic acid) has been obtained by heating its 3-ethoxycarbonyl derivative with water or nitromethane. Prolonged heating with water yields 4-hydroxy-3,4′-bi-Δ³-pyrrolinyl-2,2′-dione, the anhydro-derivative of the dione. 1- and 5-Methylpyrrolidine-2,4-diones and their anhydro-derivatives have been obtained similarly. Previously reported syntheses of these pyrrolidine-2,4-diones are shown to be in error; the products obtained appear to have been the corresponding anhydro-derivatives, or their hydrates. Other derivatives of the diones are described. Condensation of ethyl-4-hydroxy-2-oxo-Δ³-pyrroline-3-carboxylate with aromatic aldehydes yields mainly the (E)-5-arylmethylene derivatives.