Copper‐Catalyzed Isomerization and Cyclization of E/Z‐o‐Haloaryl N‐Sulfonylhydrazones: Convenient Access to 1H‐Indazoles

Abstract The isomerization of the C=N double bond in hydrazones has drawn considerable attention because of its potential for application in a broad range of chemical transformations. Generally, this isomerization can be realized either photochemically or thermally. A new isomerization approach is presented, namely a copper‐catalyzed C=N double bond isomerization of hydrazones, which is followed by an efficient intramolecular C−N coupling reaction, providing an unprecedented catalytic approach for the synthesis of 1 H ‐indazoles from readily accessible Z / E mixture of o ‐haloaryl N ‐sulfonylhydrazones.