Pyrimidine ring annellation

Pyrimidine bases, aza analogs of, 1, 189 Pyrimidine ring annelation to an existing ring, 32, 1... 

Examination of the pyrazino[2,3-rf]pyrimidine structure of pteridines reveals two principal pathways for the synthesis of this ring system, namely fusion of a pyrazine ring to a pyrimidine derivative, and annelation of a pyrimidine ring to a suitably substituted pyrazine derivative (equation 76). Since pyrimidines are more easily accessible the former pathway is of major importance. Less important methods include degradations of more complex substances and ring transformations of structurally related bicyclic nitrogen heterocycles. 

Albert, A., 4-Amino-1,2,3-triazoles, 40, 129 The Chemistry of 8-Azapurines( 1,2,3-Triazolo[4,5-d]pyrimidines), 39, 117 Annelation of a Pyrimidine Ring to an Existing Ring, 32, 1 Covalent Hydration in Nitrogen Heterocycles, 20, 117. 

In general, benzoselenadiazole is stable to oxidizing agents such as 30% hydrogen peroxide in acetic acid <1957JOC503>. However, 1,2,5-selenadiazoles annelated with pyrimidine rings 151a-c are less stable (Scheme 10)... 

In the series of N-alkyl-1,4-diazinium salts 36-40, great attention was paid to the abilities of these compounds to form either mono- or diadducts. The stabilities of the c-adducts formed were varied to a great extent either by the introduction of an aza group and/or substituents into the pyrazine ring or annelation of the latter with a benzene, pyridine, or pyrimidine ring (86KGS1380). 

Aminochromes, 5, 205 Aminomethylenemalonates and their use in heterocyclic synthesis, 54 4-Amino-1,2,3-triazoles, 40, 129 Anils, olefin synthesis with, 23, 171 Anionic cr-adducts of heterocycles, 34, 305 Anions, ring-opening of five-membered heteroaromatic, 41, 41 Annelation of a pyrimidine ring to an existing ring, 32, 1... 

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