Mechanically Induced Fe(III) Catalysis at Room Temperature: Solvent-Free Cross-Dehydrogenative Coupling of 3-Benzylic Indoles with Methylenes/Indoles.

An Fe(III)-catalyzed solvent-free cross-dehydrogenative coupling of 3-benzylic indoles and compounds with acidic methylene groups has been achieved under high-speed ball-milling (HSBM) conditions at room temperature. The reactions afford desired 3-arylmethylindole derivatives in moderate to high yields within 21 min of grinding. Besides, both N-substituted and N-free indoles can take part in this mechanochemical reaction as efficient nucleophiles to give bisindoles with satisfactory results. Remarkably, this protocol displays the possibility to induce high activity when using iron catalysts under HSBM conditions.