Efficient synthesis of 8-substituted pyrazolo[1,5-a]-1,3,5-triazines by regioselective acylation

An efficient two-step synthesis of 8-acylated pyrazolo[1,5-a]-1,3,5-triazines has been accomplished. The key strategic elements of this novel synthetic approach involve the use of the N-methyl-N-phenylamino activating group, which was easily obtained in high yield by treatment of the pyrazolotriazin-4-one with phosphorus oxychloride and dimethylaniline through high pressure reaction coupled with a regioselective acylation at position 8 followed by the subsequent displacement of the N-methyl-N-phenylamino group upon treatment with various amines.