Benzindazoles based on triketones of the indan series

With phenylhydrazine, 2-acetonyl- and 2-phenacyl-2-phenylindan-1,3-diones form phenylhydrazones at the carbonyl group of the side chain. On prolonged heating, a reaction takes place with the expansion of the five-membered ring into a six-membered ring and the formation of the corresponding 5-hydroxy-1-phenylbenzg]indazoles. A reaction mechanism is proposed. The structure of the compounds obtained has been confirmed by their IR and UV spectra.