Synthesis of spiro-fused (C5)-pyrazolino-(C6)-triazinones, a new heterocyclic system

Reaction of 4-hydrazinoquinazoline with 2,4-diketoesters gives the corresponding 3-acylmethyl-2H-[1,2,4]triazino[2,3-c]quinazolin-2-ones in a one-step procedure via cyclocondensation–Dimroth-like rearrangement. Spectroscopic studies as well as X-ray analysis reveal that the obtained triazinoquinazolines exist in their ketoimine tautomeric form. Treatment of these compounds with hydrazine hydrate affords 3′-(2-aminophenyl)-3-(het)aryl-spiro[pyrazoline-5,6′(1′H)-1,2,4-triazin]-5′(4′H)-ones or 5-(het)arylpyrazole-3-carboxylic acid hydrazides depending on the reaction conditions. The structure of the spiro-heterocycles was elucidated by means of single-crystal X-ray analysis and confirmed by spectroscopic investigations.