Diversity-oriented synthesis of substituted pyrazolo〔4,3-d〕〔1,2,3〕triazin-4-ones

An efficient synthesis of 3,7-disubstituted 3,5-dihydro-4H-pyrazolo-[4,3-d][1,2,3]triazin-4-ones (2), especially suited for late-stage decoration, is described. Diverse 3-benzyl analogs were obtained by amidation-cyclization in one pot and various pyrazolotriazinone-7-bromides were employed in Suzuki and Sonogashira cross-coupling reactions.