Synthesis of Dimethyl 1-Aryl-4-ethoxy-5-oxo-2,5- dihydro-1H-pyrrole-2,3-dicarboxylates Mediated by Triphenylphosphine

Ethyl 2-arylamino-2-oxo-acetates undergo a complex reaction with dimethyl acetylendicarboxylate in the presence of triphenylphosphine to produce dimethyl 1-aryl-4-ethoxy-5-oxo-2,5-dihydro-1H-pyrrole-2,3-dicarboxylates in good yields. Dynamic NMR study of dimethyl 1-(2-methyl-6-nitrophenyl)-4-ethoxy-5-oxo-2,5-dihydro-1H-pyrrole-2,3-dicarboxylate shows a fairly high energy barrier (ΔG # = 95 ± 2 kJ mol− 1) for rotation around the N-aryl single bond, which leads to an observable atropisomerism.