Vinyl halides or triflates are well known to undergo conventional transition-metal-catalyzed cross-coupling with premetallated reagents to afford ipso-substitution products. However, the use of stoichiometric premetallated reagents also raises waste and safety issues. One of the solutions to circumvent these issues is transition-metal-catalyzed cross-electrophile coupling reaction, which utilizes two electrophiles directly in the presence of a terminal reductant. While metallic reductants such as zinc or manganese are the most common terminal reductants, it would be more ideal to develop methods using inexpensive organic reductants. Herein, we discovered the first formate-mediated deoxygenative Heck reactions by cine-substitution of vinyl triflates with a variety of aryl iodides. Mechanistic studies corroborate a mechanism involving the formation of a dianionic iodide-bridged dimer [Pd₂I₆][NBu₄]₂, which under reducing conditions can in situ generate a palladium(I) complex [Pd₂I₄][NBu₄]₂. Dinculear oxidative addition of aryl iodide to this palladium(I) complex forms [Pd₂I₅(Ar)][NBu₄]₂, followed by dissociation to give the monometallic complex [PdI₂(Ar)][NBu₄]. Carbopalladation followed by triflate elimination leads to a palladium(IV) carbene, which then undergoes β-hydride elimination-C-H reductive elimination to furnish the product with cine-substitution. This method allows rapid access to products that could not be easily prepared, which could be a useful tool for medicinal chemists.

Michael Krische

Univ Texas at Austin

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