Cobalt(III)-Catalyzed Fast and Solvent-Free C-H Allylation of Indoles Using Mechanochemistry.

Mechanochemical conditions have been applied to a highly efficient cobalt(III)-catalyzed C-H bond activation for the first time. In a subsequent step to the olefin insertion and β-oxygen elimination, N-pyrimidinylindoles were allylated with vinylethylene carbonates in the absence of organic solvent under high-speed ball-milling condition. As the reaction afforded the desired products in up to 98% yields within a short time, this method constitutes an environmentally friendly and powerful alternative to the common solution-based approaches.