Substituted pyridopyrimidinones, Part IV: 2-chloro-4h-pyrido[1,2-a]pyrimidin-4-one as a synthone of some new heterotricycles

Chloro-4H-pyrido(1,2-a)pyrimidin-4-one (1) was utilized as a syn- thone precursor to prepare novel heterotricyclic systems. 2-Azido and 2-hyd- razino derivatives (2 and 3) were obtained by nucleophilic replacement evolving compound 1. The hydrazine derivative 3 was transformed into the azido deriva- tive 2 by nitrosation. Treatment of compound 3 with (bis(methylthio)methyl- ene)malononitrile afforded 2-pyrazolylpyridopyrimidine 4. When compound 1 was reacted with 5-amino-3-(methylthio)-1H-pyrazole-4-carbonitrile, the same compound 4 was obtained with no evidence for the production of (pyrazolyl- amino)pyridopyrimidine 5 or pyrazolodipyridopyrimidine 6. Poly-functionalized dipyridopyrimidine 8 was obtained by reaction of compound 1 with 2-((me- thylthio)-(phenylamino)methylene)propanedinitrile. Cyanoguanidine was reacted with compound 1 to afford N-pyridopyrimidinylguanidine 9, which was subjected to cyclization reaction, in presence of piperidinium acetate, to give pyridopyrimidopyrimidine 10.