Rh(II)-Catalyzed Transannulation of
1,2,3-Triazoles with Nitriles

Significance

Reported is the efficient two-step synthesis of N-sulfonylimidazoles 5 starting from alkynes 1, sulfonyl azides 2 and nitriles 4. The formation of the required 1,2,3-triazole intermediates 3 was achieved under Cu(I) catalysis using conditions recently developed by the authors (J. Org. Chem. 2008, 73, 5520). Treatment of 3 with Rh(II) complexes generates the ring-opened rhodium α-iminocarbenoid which, upon reaction with nitriles 4, gives imidazoles 5 in modest to excellent yield. A range of catalysts and conditions were screened, and two sets of conditions were identified under both microwave and conventional heating. The scope of the reaction was well studied and tolerates alkyl, alkenyl and aryl nitriles. The nature of the C-4 substituent also has a significant effect on the reaction, with aromatic groups preferred over aliphatic groups. The two-step reaction was further telescoped into a one-pot process in one instance. Removal of the sulfonyl group from imidazoles 5 is easily achieved on treatment with HOBt.