The sensitized photoexcitation of 2-diazocyclopentane-1,3-diones in the presence of THF leads to the insertion of the terminal N-atom of the diazo group into the α-С–Н bond of THF, producing the associated N-alkylhydrazones in yields of up to 63–71%. Further irradiation of hydrazones derived from furan-fused tricyclic diazocyclopentanediones culminates in the cycloelimination of furans to yield 2-N-(alkyl)hydrazone of cyclopentene-1,2,3-trione. By contrast, the direct photolysis of carbocyclic diazodiketones gives only Wolff rearrangement products with up to 90–97% yield.

acid O O R 1 R 2 R 3 R 4 acids: TFA, TfOH, TsOH, etc.; R 1 , R 2 , R 3 , R 4 = alkyl, aryl R 1 -R 2 , R 3 -R 4 = cycloalkyl, cycloaryl 4,5-alkyl(aryl) 3(2H)-furanones up to 99% -N 2 O R 1 R 2 O R 3 R 4 -N 2 ring-fused spiro-3(2H)-furanones 75-91% acid 3 examples 19 examplesAbstract The interaction of 5,5-dialkyl(diaryl)-substituted 4-diazo-3(2H)furanones with Brønsted acids (TFA, TsOH, etc.) causes elimination of nitrogen accompanied by 1,2-nucleophilic rearrangement, giving rise to exclusive formation of 4,5-dialkyl(diaryl)-substituted 3(2Н)-furanones, ring-fused 3(2H)-furanones, and phenanthro[9,10-b]furan-3(2H)-ones in yields of up to 99%. The reaction is a new highly efficient way for the synthesis of multisubstituted 3(2Н)furanones.