SYNTHESIS OF A NEW HETEROCYCLIC RING SYSTEMS VIA NUCLEOPHILIC SUBSTITUTION OF PYRIMIDOPYRIDAZINES

Article abstract of DOI:10.1016/S0040-4020(01)89084-0

Hydroxy groups at positions C⁵ and C⁸ were replaced in 2-phenyl- and 2-aminopyrimido<4,5-d>pyridazines by better leaving groups (Cl, OSiMe3, and SMe, OSiMe3 respectively), and the 5,8-disubstituted compounds were substituted by aminoalkanols.The 5- and 8-mono(ω-hydroxyalkylamino) derivatives obtained in regioselective reactions were cyclized into imidazo<1,2-b>pyrimido<5,4-d>pyridazine, imidazo<1,2-b>pyrimido<4,5-d>pyridazine, dipyrimido<1,2-b:5',4'-d>pyridazine and dipyrimido<1,2-b:4',5'-d>pyridazine derivatives containing new heterocyclic ring systems.Kinetic measurments and MNDO calculations showed that C⁸ site at the pyridazine ring is more reactive than C⁵, and aminolysis follows by usual two-step S_NAr mechanism.