Rh(II)-Catalyzed Ring Expansion of Cyclopropyl N-Tosylhydrazones to 1-Substituted Cyclobutenes

Abstract Cyclobutenes are highly useful synthetic intermediates as well as important motifs in functional molecules. Herein, we report a straightforward access toward monosubstituted cyclobutenes from cyclopropyl N-tosylhydrazone. 1,2-Aryl or -alkyl shift of the Rh(II) carbene intermediate plays the key role in this transformation.