mol thf 2 7 l and triethylamine 125 ml was added anhydrous hydrazine 25 5 ml in 600 ml of water drop wise over 25 min alternatively hydrazine monohydrate can be used instead of anhydrous hydrazine the mixture was stirred for 1 h the solids were filtered off and the filtrate was evaporated to remove about 80 of the thf water was added and the resulting precipitate was filtered and dried under vacuum the solid was then dissolved in a minimum volume of hot dmf and precipitate by addition of water to provide 112 g 85 yield of 4 chloro 6 aminopyrazolo 3 4 d pyrimidine 3 compound 3 70 4 g 0 416 mol was refluxed in methanolic sodium methoxide solution 25 g sodium dissolved in 1 l methanol for 2 h the reaction mixture was cooled to room temperature and neutralized by addition of acetic acid 75 ml the mixture was evaporated to dryness and the solid was triturated in 600 ml of water filtered and dried to provide 67 5 g 99 yield of 4 methoxy 6 aminopyrazolo 3 4 d pyrimidine 4 a mixture of compound 4 105 g 0 636 mol sodium acetate 263 g and iodine monochloride 140 g was mechanically stirred in 1 3.