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Updated: Jul 19, 2026

Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of α-Imino γ-Lactones and Alkylidene Pyrazolones
Published on: February 7, 2019
In Situ Generation and [3 + 2] Annulation Reactions of Propiolaldehyde─A Metal-Free, Cascade Route to Pyrazole and
Mariswamy K Sreelekha1, Ali Shamnad1, Rasmi P Bhaskaran1
1Department of Chemistry, National Institute of Technology Karnataka (NITK), Surathkal, Mangalore-575025, Karnataka, India.
Abstract:
Propiolaldehyde, the most reactive yet less explored electrophilic acetylene, was generated in situ via a base-free Kornblum oxidation from propargyl tosylate and successfully intercepted with hydrazones affording pyrazole-4-carboxaldehyde in one-pot by a [3 + 2] annulation reaction. Further, the pyrazole-4-carboxaldehyde endured a unique cascade reaction with phenylhydrazine and propargyl tosylate, yielding synthetically challenging bipyrazole carboxaldehydes. The method is free of any metal catalyst, base, or additives and offers a convenient protocol to handle the reactive and volatile propiolaldehyde under ambient conditions.
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