Synthesis of Polysubstituted Furans via Rh(II)-Catalyzed [2 + 3] Annulation of N‑Sulfonyl-1,2,3-triazoles with Enaminones

An unprecedented [2 + 3] annulation of N-sulfonyl-1,2,3-triazoles with enaminones is reported for the access of polysubstituted furans. The key to the success of the transformations lies in the use of Rh­(II)–Brønsted acid as cooperative catalysts. Unlike the conventional annulations of N-sulfony-l-1,2,3-triazoles, the Rh­(II)-azavinyl carbenes species play dual functions in this work, enabled by the cleavage of the C­(sp2)−N bond. The mechanism studies suggested that an intermolecular rearrangement of the TsNH– group is crucial to the annulation process.