The First General and Selective Palladium(II)-Catalyzed Alkoxycarbonylation of Arylboronates: Interplay among Benzoquinone-Ligated Palladium(0) Complex, Organoboron, and Alcohol Solvent

Methoxycarbonylation of aryl- and alkenyylboron Compounds was performed using the palladium(II) acetate/triphenylphosphine [Pd(OAc)(2)/PPh3] catalyst with p-benzoquinone as a stoichiometric oxidant in methanol at ambient temperature to obtain the corresponding methyl esters in good yields. A wide variety of functional groups including various carbonyl functionalities, nitrile, nitro. sulfone, and unprotected pyrrole rings were tolerated in the methoxycarbonlation, while the use of higher alcohols except for tert-butanol afforded various p-chlorobenzoates in moderate to high yields. The catalytic alkoxycarbonylation proceeded without any acid or base additive, and an oxidative transmetalation step is proposed to explain the exceptional efficacy of this protocol. DFT and MP2 calculations support the proposed mechanism.