Mechanochemically Activated Oxidative Coupling of Indoles with Acrylates through C-H Activation: Synthesis of 3-Vinylindoles and β,β-Diindolyl Propionates and Study of the Mechanism.

Construction of 3-vinylindoles (3) and β,β-diindolyl propionates (4) through solvent-free C-H functionalization has been explored under high-speed ball-milling conditions. The reaction selectivity is influenced by the catalyst dramatically: Pd(OAc)2 provides 3 in moderate to good yields, whereas PdX2 (X = Cl, I) affords 4 as the major products. The reaction mechanism has been further studied by using electrospray ionization mass spectrometry, implicating the dimeric palladium complex A as the key intermediate in an explanation of the selectivity.