Fused Systems containing Two Six-Membered Rings

Two modes of cyclization have been observed when the 6-(r alkylhydra-zino)isocytosines (193) are treated with a-keto-acids (R CHjCOCOaH) in refluxing water. Pyruvic acid yields a pyrimidopyridazine (194 = H) 

The reaction of bromoacetic acid, ATV-dimethylformamide, and phos-phoryl chloride yields a triformylmethane derivative, which was condensed (in water) with 2,4-diaminopyrimidn-6(l/f)-one to give the pyridopyrimidine-6-carbaldehyde (202). The latter compound was used as an intermediate for the synthesis of 5-deazapterin.  

Yoneda, F. Takayama, and A. Koshiro, Chem. Pharm. Bull, 1979, 27, 2507. 

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Fused Systems containing Two Six-Membered Rings (6,6) Treatment of 6-amino-5-arylazo-uracils (187) with either urea or NN -carbonyldi-imidazole gave pyrimidotriazines (188). The latter compounds were hydrolysed with alkali to triazinecarboxylic acids (189) (6-azauracil-5-carboxylic acids) (Scheme 1) ... 

Fused Systems containing One Five- and One Six- or Two Six-Membered Rings. - R. C. 

Six-Membered Heterocyclic Compounds with a Single Nitrogen Atom in the Ring to which are Fused Two or More Carbocyclic Ring Systems, and Six-Membered Ring Compounds where the Hetero-Atom is Phosphorus, Arsenic, Antimony or Bismuth. Alkaloids Containing a Six-Membered Heterocyclic Ring System... 

A large number of polycyclic heterocycles containing two or more six-membered rings that share two or more carbon atoms are known. For the majority of these systems, only one of the six-membered rings contains the heteroatoms and the other rings are fused carbocyclic rings such as cyclohexane, benzene, naphthalene, and in rare examples, anthracene. Systems in which more than one of the six-membered rings contain heteroatoms are also briefly discussed these include spiro-cyclic compounds and substituted naphthalenes. 

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