Syntheses of di- and tetrahydropyrroles

The constants and thermodynamic parameters of the ring-chain tautomeric equilibrium of p-substituted (benzene ring) 2,3,3-trimethyl-1-aryl-2-hydroxy-5-pyrrolidones in aqueous pyridine solution were determined by PMR spectroscopy. Conversion of the ring tautomer to the open form is accompanied by an increase in the enthalpy and entropy. The AH value decreases by a factor of 2.8 kcal/mole on passing from electron-donor substituents to electron-acceptor substituants, whereas the AS value remains approximately constant and decreases by 2–4 eu only for strong electron acceptors (COOCH₃, CN, and NO₂). The correlation between the free energies and the a substituent constants in the benzene ring is discussed.See 1] for communication XII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 634–638, May, 1977.