Direct Access to Benzofurans and Indoles from Ethylene with 2-Methylphenols/Anilines through Iridium-Catalyzed Dehydrogenative Annulation

The direct conversion of o-cresol and 2-methylphenols to 2-methylbenzofurans was achieved by an Ir/DTBE-DPPE-catalyzed reaction under an atmosphere of ethylene (1 atm). The reaction involves the initial selective formation of a C-C bond at the benzylic C(sp³)-H bond of 2-methylphenols with ethylene without the accommodation of the C(sp²)-H bonds at the 6-positions, which is followed by subsequent C-O bond-forming annulation along with associated dehydrogenation and double bond migration steps. The reaction conditions also allowed for the direct conversion of o-toluidine and 2-methylanilines into 2-methylindoles.