The Use of 2‐Chloro‐4H‐4‐oxo‐pyrido[1,2‐a]pyrimidine as a Building Block in the Synthesis of Some New Heterocyclic Compounds

New approaches for the synthesis of some heterocyclic compounds, such as the pyridopyrimidodiazepine derivative 3 , pyrazolopyrido1,2‐a]pyrimidine derivative 4 , tetrazolo1.5‐a]1,8]naphthyridine derivative 9 , pyrazolylpyrido1,2‐a]pyrimidine derivatives 10a , 10b , 12 , pyrrolopyrido1,2‐a]pyrimidine derivatives 14a , 14b , 14c , 14d , and 16a , 16b , starting from 2‐chloro‐4H‐4‐oxo‐pyrido1,2‐a]pyrimidine ( 1 ), are described.