Cobalt catalyzed electrochemical [4 + 2] annulation for the synthesis of sultams†
Cobalt catalyzed electrochemical [4 + 2] annulation of sulfonamides with alkynes is demonstrated in this work, which provided a practical and environmentally friendly way to synthesize structurally diverse sultams. Notably, by employing anodic oxidation in an undivided cell to recycle the cobalt catalyst, this electrochemical method avoided the utilization of stoichiometric amount of metallic oxidant, delivering H2 as the sole by-product. Moreover, this cobalt catalyzed electrochemical protocol proved to be practical and scalable. When the model reaction was scaled up to 5.0 mmol, 86% yield of product could still be obtained.