Palladium‐Catalyzed Synthesis of 1‐Alkyl‐5‐Arylpyrazoles: The Auto‐Tandem Catalysis for C−C Bond Cleavage/Heck Arylation

Abstract

The regioselective synthesis of 1‐alkyl‐5‐arylpyrazoles, which are potential drug candidates, has been difficult to achieve thus far. In this study, we developed an auto‐tandem Pd‐catalyzed C–C bond cleavage/Heck arylation of N‐cyclopropylhydrazones followed by cycloisomerization to afford diverse 1‐alkyl‐5‐arylpyrazoles. This step‐economical synthesis involves the cleavage of two C–H bonds and one C–C bond as well as the incorporation of directing groups. The identification of the reaction intermediates indicated an auto‐tandem catalytic pathway. The further transformation of products to 1,4,5‐substituted pyrazole and functional group transformations were carried out.