Synthesis, characterization and biological activity of new cyclization products of 3-(4-substituted benzylidene)-2H-pyrido[1,2-a]pyrimidine 2,4-(3H)-diones

A method is presented for the synthesis of 4-(substituted phenyl)-3-(3-substituted phenyl)4 H -spiro[isoxazole-5,3′-pyrido[1,2- a ]pyrimidine]-2′,4′-dione (3) , 3-(4-substituted phenyl)-3 H -isoxazole[3, 4- d ]pyrido[1,2- a ]pyrimidin-4-(3a H )-one (4) and 3-(4-substituted phenyl) 3,3a-dihydropyrazolo[3,4- d ]pyrido[1,2- a ]pyrimidin-4-(2 H )-one (5) which consists of the conversion of 2 H -pyrido[1,2- a ]pyrimidine-2,4(3 H )-dione (1) to chalcones (2) and their 1,3-dipolar cycloaddition with appropriate aldoximes to give spiro compounds and heterocyclization using amines to yield isoxazolines and pyrazolines. All the compounds were screened for their antimicrobial and antitubercular activity. Graphical Abstract 1,3-Dipolar cycloaddition of pyrido-pyrimidine chalcones with appropriate aldoximes give spiro compounds; heterocyclization using hydroxylamine or hydrazine to yield isoxazolines or pyrazolines, respectively. All the compounds were then screened for their biological (antimicrobial and antitubercular) activity.