Approaches to Fused Pyrimidine Derivatives by the Pyrimidine Ring Construction and Their Application to Synthesis of Purines

Fused pyrimidines can be easily synthesized from the corresponding ortho-aminobenzylamine derivatives or their heteroanalogues. ortho-Nitrobenzaldehydes, ortho-aminobenzaldehydes, anthranilic acid derivatives, ortho-isocyanatobenzoates, ortho-aminobenzonitriles, ortho-isocyanatobenzonitriles, N-substituted anilines, ortho-halobenzoates, benzenediazonium salts, (2-nitroaryl)methylisocyanides, and derivatives of the all above compounds were also used for this purpose. Often the limiting factor for the above syntheses is the difficulty encountered in obtaining the key intermediates or their precursors. Recently, this problem was successfully solved in several ways by the use ofVicarious Nucleophilic Substitution of Hydrogen (VNS). As a result, many quinazolines and new bicyclic and tricyclic heteroaromatic compounds and their mono-N-oxides were obtained, when starting from aromatic nitro compounds. These approaches were also successfully applied to the synthesis of purines with the use of 4-nitroimidazole derivatives.