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(sp 2 ) - N bond. The mechanism studies suggested that an intermolecular rearrangement of the TsNH - group is crucial to the annulation process.