Synthesis of indazole derivatives from a N,N-disubstituted 2-halobenzoic hydrazide. Crystal structure of 1,2-pentamethylene-5-nitro-1,2-dihydro-3H-indazol-3-one

Thermal cyclization of the N,N-disubstituted 2-chlorobenzoic hydrazide 1 yields the 1,2-pentamethylene indazolone 5 , which structure is confirmed by X-ray crystallography. We suggest that the reaction proceeds through an N,N-alkyl shift in an initially formed indazolinium salt 2 . An intermediate 1-(5-chloropentyl)indazolol 4 has been isolated.