Kinetic study on the anelation of heterocycles. 3 . Pyrazino[2,3- d ]pyrimidine derivatives synthesized by the hinsberg reaction

A kinetic study on the obtainment of pyrazinopyrimidine derivatives (pteridines) was performed. The regioselective synthesis of compounds 6-methylpyrazino[2,3-a]pyrimidin-7(8H)-one (5a) and 7-methylpyrazino[2,3-d]pyrimidin-6(5H)-one (5b), in good yields, was expected by the Hinsberg reaction because the synthesis of both isomers analytically pure was never reported to date. This Hinsberg reaction gave good results to obtain compound 5a, regioselectively and in good yields, either in pH 5 aqueous buffer solution or in methylene chloride, among several organic solvents. However, structural and solvation factors prevented the synthesis of the isomer 5b, which was regioselectively formed in very acid solutions (Ho = -0.89), but in very poor yield.