The tetrahydrofuran-nitrile (CH(3)CN, n-C(4)H(9)CN, C(6)H(5)CN)-zeolite (faujasites, mordenite, beta, pentasils) system and its transformations under supercritical conditions were studied. The feasibility of direct synthesis of the corresponding N-acylpyrrolidines from THF and nitriles of aliphatic and aromatic acids was shown for the first time. The dependence of the THF reaction with nitriles on the temperature, the reaction time, the nature of the exchanged cations in zeolite, the type of zeolite, and the catalyst pretreatment conditions was revealed. Acid zeolites were shown to exhibit a high catalytic activity. The yield of N-acylpyrrolidines at 350A degrees C in the presence of the most active catalysts (HNaY and HCaLnY) was 10-40% at a selectivity of up to 80%. The key role of H(2)O was found, and a two-step scheme of the process, including the hydrolysis of nitrile to amide and the reaction of the latter with tetrahydrofuran resulting in the formation of N-acylpyrrolidine, was proposed.