Mn-Catalyzed Aromatic C–H Alkenylation with Terminal Alkynes

The first <i>manganese-catalyzed</i> aromatic C–H alkenylation with terminal alkynes is described. The procedure features an operationally simple catalyst system containing commercially available MnBr­(CO)₅ and dicyclohexylamine (Cy₂NH). The reaction occurs readily in a highly chemo-, regio-, and stereoselective manner delivering <i>anti</i>-Markovnikov <i>E</i>-configured olefins in high yields. Experimental study and DFT calculations reveal that (1) the reaction is initiated by a C–H activation step via the cooperation of manganese and base; (2) manganacycle and alkynylmanganese species are the key reaction intermediates; and (3) the ligand-to-ligand H-transfer and alkynyl-assisted C–H activation are the key steps rendering the reaction catalytic in manganese