Cyclization reactions of some o-acylphenylhydrazones

Abstract

The hydrazones Ia-Id and IIa-IId have been prepared by azo coupling of ethyl cyanacetylcarbamate and cyanacetamide, respectively, with diazotized o-aminoacetophenone, o-aminobenzophenone, 2-(2-aminobenzoyl)benzoic acid and 1-amino-9,10-anthraquinone. The hydrazones Ia-Id have been alkaline or thermally cyclized to 2-aryl-4,5-dioxo-2,3,4,5-tetrahydro-1,2,4-triazine-6-carbonitriles IIIa-IIId. On boiling in strongly acidic medium the hydrazones I and II are cyclized to the corresponding 3-substituted indazoles Va-Vc and 2,6-dihydronaphtho[1,2,3-c,d]indazol-6-one (Vd). Three hours boiling in 20% hydrochloric acid does not affect the 1,2,4-triazine cycle of nitriles IIIa-IIId, the nitrile groups being only hydrolyzed to give the corresponding carboxylic acids IVa-IVd. On the contrary, boiling in aqueous pyridine causes splitting of the 1,2,4-triazine cycle and formation of arylhydrazonocyanacetamides IIa-IId. IR and NMR spectroscopy has been used to study the possibility of simultaneous hydrogen bond to the both carbonyl groups in hydrazones I and II.