Au(I)-Catalyzed Formal Intermolecular Carbene Insertion into Vinylic C(sp2)–H Bonds and Allylic C(sp3)–H Bonds

We report a metal-catalyzed formal intermolecular carbene insertion into the vinylic C(sp2)–H bond of alkenes, wherein Au(I) proved to be more efficient than the other metal catalysts screened. This provides facile access to C4-alkenyl isochromanones and isoquinolinones from the corresponding diazo reagents and α-methylstyrenes in moderate to good yields and excellent chemoselectivity. Mechanistic studies suggested two possible reaction pathways simultaneously exist, the gold-carbenoid participating nucleophilic attack-selective elimination and a cyclopropanation–ring-opening–olefin isomerization process. The structure of diazo reagents has a great impact, as diazo(thio)oxindoles react with α-methylstyrenes via the formal allylic C(sp3)–H insertion to afford 3-allyl(thio)oxindoles.