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.