Reactions of 1,4,5-trisubstituted 3-hydroxy-3-pyrrolin-2-ones with diphenyldiazomethane yield the O-alkylation products. Thermolysis of 1,5-diaryl-4-heteroyl-3-hydroxy-3-pyrrolin-2-ones is accompanied with suprafacial [1,5]-sigmatropic rearrangement.