One-Pot (3 + 2) Cycloaddition-Isomerization-Oxidation of 2,2,2-Trifluorodiazoethane and Styryl Derivatives

Synthesis of Fully Substituted Difluoromethylpyrazoles by Cyclization of Difluoroacetohydrazonoyl Bromides with 2-Acylacetonitriles or Malononitrile

A concise and efficient method for the construction of fully substituted difluoromethylpyrazoles is achieved by a cyclization reaction between difluoroacetohydrazonoyl bromides and 2-acylacetonitrile or malononitrile. The method features advantages such as mild reaction conditions, broad substrate scope, good product yields, and high regioselectivity.

Iodobenzene-Catalyzed Synthesis of Fully Functionalized NH-Pyrazoles and Isoxazoles from α,β-Unsaturated Hydrazones and Oximes via 1,2-Aryl Shift

An iodine(III)-catalyzed general method for the synthesis of fully functionalized NH-pyrazoles and isoxazoles from α,β-unsaturated hydrazones and oximes, respectively, via cyclization/1,2-aryl shift/aromatization/detosylation, has been developed. The reaction progresses through an anti-Baldwin 5-endo-trig cyclization. It gives direct access to an advanced intermediate for the preparation of valdecoxib and parecoxib, drugs used for COX-inhibition. In addition, a method for N-alkynylation of pyrazoles has also been developed in the presence of TIPS-EBX.