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Updated: May 12, 2026

Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
Published on: June 10, 2021
Selective synthesis of 1-substituted 4-chloropyrazolo[3,4-d]pyrimidines
Suresh Babu1, Christie Morrill, Neil G Almstead
1PTC Therapeutics, Inc., 100 Corporate Court, South Plainfield, New Jersey 07080, United States.
Abstract:
Strategies for carrying out the reaction of 4,6-dichloropyrimidine-5-carboxaldehyde with various hydrazines to generate 1-substituted 4-chloropyrazolo[3,4-d]pyrimidines in a selective and high-yielding manner are presented. For aromatic hydrazines, the reaction is performed in the absence of an external base, which promotes exclusive hydrazone formation. The hydrazones subsequently cyclize at an elevated temperature to form the desired pyrazolo[3,4-d]pyrimidine products. For aliphatic hydrazines, the reaction sequence proceeds as a single step in the presence of an external base.
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