Devi L, Sharma G, Kant R, Shukla SK, Rastogi N. Regioselective synthesis of functionalized pyrazole-chalcones
via a base mediated reaction of diazo compounds with pyrylium salts.
Org Biomol Chem 2021;
19:4132-4136. [PMID:
33870359 DOI:
10.1039/d1ob00274k]
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Abstract
A base-mediated reaction of triaryl/alkyl pyrylium tetrafluoroborate salts with α-diazo-phosphonates, sulfones and trifluoromethyl compounds affords the corresponding functionalized pyrazole-chalcones as 5-P-5 and 3-P-3 tautomeric mixture. The reaction proceeds through an initial nucleophilic addition of diazo substrates to pyrylium salts followed by a base-mediated pyrylium ring-opening and intramolecular 1,5-cyclization to afford formal 1,3-dipolar cycloaddition products. The products underwent a Nazarov-type cyclization upon hydride reduction followed by acidic-workup, furnishing the corresponding indenyl-pyrazoles in high yields.
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