Alkylation of 4-pteridones in dimethylformamide

Abstract

4-Pteridone (II) and its 6,7-dimethyl or -diphenyl derivatives are alkylated by methyl iodide in dimethylformamide to give the corresponding 1,3-dimethyl-4-oxopteridinium salts (V). Both 1-methyl and 3-methyl-4-pteridone give the same dimethyl derivative (V). The preferential attack in the pyrimidine ring is related to the charge distribution in (V). Calculations by the HMO and SCF-PPP method show that the negative charge at N-1 or N-3 in (II) is much larger than the charge at N-5 or N-8.