The Wolff rearrangement is one of the most characteristic transformations of diazo ketones [1]. Diazo ketones of the tetrahydrofuran series are thus converted into oxetane derivatives. Using tetramethylsubstituted diazotetrahydrofuranone as an example, we previously showed [2] that its photolytic Wolff rearrangement was the most efficient [2]. Photoinduced reactions of aryl-substituted diazotetrahydrofuranones are characterized by lower selectivity, and they give rise to a number of products [3, 4]. The goal of the present work was to study thermal and acid-catalyzed decomposition of 2,2,5,5-tetrasubstituted 4-diazotetrahydrofuran-3-ones, compare the results with those obtained by photolysis, and estimate synthetic potential of these processes. As substrates we selected 4-diazo-2,2,5,5-tetramethyltetrahydrofuran-3one (I), 4-diazo-2,2-dimethyl-5,5-diphenyltetrahydrofuran-3-one (IIa), 4-diazo-5,5-bis(4-fluorophenyl)-2,2dimethyltetrahydrofuran-3-one (IIb), 4-diazo-5,5-dimethyl-2,2-diphenyltetrahydrofuran-3-one (IIIa), and 4-diazo-2,2-bis(4-fluorophenyl)-5,5-dimethyltetrahydrofuran-3-one (IIIb). in the absence of solvent (in melt), and the progress of reactions was monitored by TLC and H NMR.