Inter- and intramolecular trapping reactions of photochemically generated diarylnitrilimines
Photolysis of 2,5-diphenyltetrazole (2a) in an ether/pentane/ethanol glass at 77 K in the presence of a 10fold excess of propionic acid yields diphenylnitrilimine (1b). Warming up the solution to 130 K leads to the formation of the ethanol adduct 5 (scheme 1 and fig. 1). Irradiation of 2a and propionic acid in a hydrocarbon glass at 77 K and raising the temperature to 135 K gives the adduct 3, which at 200 K undergoes a rearrangement to the N’-phenyl-N’-propionyl-benzohydrazide (4, scheme 1 and fig. 2). In the case of the tetrazole 6, the primarily formed nitrilimine 7 leads to the heterocyclic system 8 via intramolecular 1,3-dipolar cycloaddition (scheme 2 and fig. 3). The intermediate 7 can be trapped with propionic acid in the photolysis of 6 in a dioxane solution at room temperature.