A convenient synthesis of 1,2-dihydro-1,2,4-triazolo[3,2-b]quinazolin-9(1H)-ones and their 1,2,4-triazolo derivatives

A range of 1,2-dihydro-1,2,4-triazolo[3,2-b]quinazolin-9(1H)-ones (3) has been synthesized in very good yields by the reaction of 3-amino-2-anilino-4(3H)-quinazolinone (1) with aromatics aldehydes in the presence of excess piperidine as a base. The 1,2,4-triazolo[3,2-b]quinazolin-9(1H)-ones could be obtained in very good yields by dehydrogenation of compounds 3 with thionyl chloride. Reaction of 1 with active methylene compounds (diethyl malonate and acetylacetone) resulted in the production of condensed products. These condensed products could be cyclized to 1,2,4-triazolo[3,2-b]quinazolin-9(1H)-one by heating above the melting point. Acetylation of 1 by acetic anhydride was found to be dependent on the reaction conditions. The acetyl derivative 3-acetamido-2-anilino-4(3H)-quinazolinone formed under mild conditions, while dimerization took place under strong conditions to give a pentacyclic compound in very good yield.