Synthesis of 5-(pyrazol-4-yl) pentanoic acids and 4-(pyrazol-4-yl) butanoic acids via a cascade
Kalinga H Nayak1, Robert K Jijin1, Beneesh P Babu1
1Department of Chemistry, National Institute of Technology Karnataka Surathkal Mangalore 575025 India pbbeneesh@nitk.edu.in.
Abstract:
Herein, we report an interesting [3 + 2] annulation/ring-opening cascade reaction between hydrazones and exocyclic dienones via an aerobic, copper(ii) catalysis to synthesize 5-(pyrazol-4-yl) pentanoic acid and 4-(pyrazol-4-yl) butanoic acid derivatives. The annulation first affords a spiro pyrazoline with unprecedented regiochemistry, followed by a cascade nucleophilic ring opening by water to yield pyrazolyl pentanoic and butanoic acid derivatives in good yield. Broad substrate scope, inexpensive and green catalyst and oxidant, and relatively mild reaction conditions enhance the versatility of this protocol.
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