Annelation of a pyrimidine ring

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. 

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... 

B. Annelation of a Pyrimidine Ring on to an Existing Triazole Ring. 160... 

Annelation of a pyrimidine ring to an existing ring , Albert, A., Adv. Heterocycl Chem., 1982, 32, 1. 

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