Sequential 1,3-Dipole Cycloaddition of Nitrile Imines with Alkenyl Isoxazoles and Aromatization: A One-Pot Access to 1,3,4-Triarylpyrazoles

Abstract

A novel one-pot two-step process for the preparation of 1,3,4-triarylpyrazoles was disclosed. This process involved a sequential 1,3-dipole cycloaddition reaction of in situ generated nitrile imines with alkenyl isoxazoles and SnCl2-promoted aromatization/elimination reaction, offering a collection of 1,3,4-triarylpyrazoles in a fully regioselective manner. This protocol featured mild reaction conditions, easily available raw materials and excellent regioselectivity.

Advances in the Synthesis of Heterocycles with Two and Three Heteroatoms using Hydrazonoyl Halides

“…In other reactions, the yields reach 70–99 % [91] . The subsequent reaction of aromatization/elimination of the oxazole fragment under the influence of SnCl 2 when heated in DMF at 100 “C leads to 1,3,4‐triarylpyrazoles [92] …”

“…[91] The subsequent reaction of aromatization/elimination of the oxazole fragment under the influence of SnCl 2 when heated in DMF at 100 "C leads to 1,3,4-triarylpyrazoles. [92] Of the many similar syntheses in this direction, as an example, we can also mention the preparation of biologically significant pyrazoles 111 by condensation of enaminone 112 with hydrazonoyl chloride 113 by boiling in xylene in the presence of triethylamine. In these examples, the removal of the dimethylamino group during the synthesis promotes aromatization to pyrazole (Scheme 37).…”