Direct Access for the Regio- and Stereoselective Synthesis of <i>N</i>-Alkenylpyrazoles and Chromenopyrazoles

Abstract

A highly regio- and stereoselective method was developed for the preparation of <i>N</i>-alkenylpyrazoles and chromenopyrazoles by the reaction of <i>N</i>-tosylhydrazones and salicyl <i>N</i>-tosylhydrazones with alkynes under neat conditions in the presence of La(OTf)₃. The present study was found to be efficient and convenient for direct access to <i>N</i>-alkenylpyrazoles and chromenopyrazoles through C-C, C-N, and C-O bond forming reactions. Structure assignment of <i>N</i>-alkenylpyrazole compound <b>5c</b> was confirmed by X-ray analysis.