ChemInform Abstract: Synthesis of Pyrazolo[3,4‐d]‐4,5‐dihydropyrimidin‐6‐ones.

A small library of hitherto unprepared pyrazolo[3,4-d]-4,5-dihydropyrimidin-6-ones was synthesized on a preparative scale. The synthesis starts with a substituted 5-aminopyrazole that reacts with an isocyanate to give the corresponding urea. The latter undergoes a chlorotrimethylsilane-promoted [5+1] cyclocondensation with an aldehyde yielding the title pyrazolo[3,4-d]-4,5-dihydropyrimidin-6-one. Both synthetic steps are high-yielding (74-94%). The intermediates and the target compounds were isolated by simple crystallization. Ketones with the exception of isatin do not react with the open-chain urea intermediates. (C) 2014 Elsevier Ltd. All rights reserved.