Novel photochemical reactions of carbocyclic diazodiketones without elimination of nitrogen - a suitable way to N-hydrazonation of C-H-bonds.

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.

Light-Induced Reactions of Diazotetrahydrofuranone without Elimination of Nitrogen: Experimental and Mechanistic Study.

The energies and lifetimes of the excited states (S1, S2, S5, T1) of a diazotetrahydrofuranone were determined using experimental and computational methods. It was shown that direction of the diazoketone photochemical transformations without elimination of nitrogen is determined by multiplicity and energy of the excited state, generated by UV irradiation of diazo compound: isomerization to α-ketodiazirine proceeds from the singlet S1 state, whereas the alternative process of C-H insertion with hydrazone formation occurs through the triplet T1 state. The most probable excited state that leads to elimination of nitrogen and Wolff rearrangement is one of the highest singlet excited states of diazotetrahydrofuranone.