✦ LIBER ✦

A modified, economical and efficient synthesis of variably substituted pyrazolo[4,3-d]pyrimidin-7-ones

✍ Scribed by Khalid Mohammed Khan; Ghulam Murtaza Maharvi; Muhammad Iqbal Choudhary; Atta-ur- Rahman; Shahnaz Perveen

Publisher: Journal of Heterocyclic Chemistry
Year: 2005
Tongue: English
Weight: 161 KB
Volume: 42
Category: Article
ISSN: 0022-152X
DOI: 10.1002/jhet.5570420608

No coin nor oath required. For personal study only.

✦ Synopsis

1-Methyl-3-propyl-1H-pyrazole-5-carboxylic acid (3) was exclusively brominated at the 4-position by bromine in the dark. Brominated product 8 was then converted into 1-methyl-3-propyl-1H-pyrazole-5-carboxamide 9 by successive treatment with thionyl chloride and ammonium hydroxide. Carboxamide 9 was treated with various aroyl amides under microwave (MW) irradiation to afford 4-aroylamino-1-methyl-3propyl-1H-pyrazole-5-carboxamides 10-22 and 5-aryl-1-methyl-3-propyl-1,6-dihydro-1H-pyrazolo[4,3d]pyrimidin-7-ones 23-35. The 1H-pyrazole-5-carboxamides 10-22 were also converted to pyrimidinones 23-35 either by conventional heating or by MW irradiation. However, MW irradiation method gives excellent yields in very short time.

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## Abstract Pyrazolo‐[3,4‐__d__]pyrimidine‐4,6‐diones **5** and pyrazolo[4,3‐__d__]pyrimidine‐5,7‐diones **7** were synthesized by Curtius rearrangement of pyrazolic mono‐esters **2** and **3** followed by hetero‐cyclization __via__ the ureas derivatives **4** and **6** under alkaline conditions.