An Efficient Synthesis of Substituted Pyrazoles from One-Pot Reaction of Ketones, Aldehydes, and Hydrazine Monohydrochloride
Vit Lellek*, Cheng-yi Chen, Wanggui Yang, Jie Liu, Xuebao Ji, Roger Faessler
*Janssen R&D, Pharmaceutical Development and Manufacturing Sciences, Small Molecule API Switzerland, Cilag AG, Hochstrasse 201, 8205 Schaffhausen, Switzerland, Email: vlellekits.jnj.com
V. Lellek, C.-y. Chen, W. Yang, J. Liu, X. Ji, R. Faessler, Synlett, 2018, 29, 1071-1075.
DOI: 10.1055/s-0036-1591941 (free Supporting Information)
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One-pot condensations of ketones, aldehydes and hydrazine monohydrochloride readily formed pyrazoline intermediates under mild conditions. In situ oxidation employing bromine afforded a wide variety of pyrazoles in very good yields. Alternatively, a more benign oxidation protocol affords 3,5-disubstituted or 3,4,5-trisubstituted pyrazoles by simply heating pyrazolines in DMSO under oxygen.
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