Palladium(I)-Iodide-Catalyzed Deoxygenative Heck Reaction of Vinyl Triflates: A Formate-Mediated Cross-Electrophile Reductive Coupling with cine -Substitution.

The first deoxygenative Heck reactions are described, as illustrated by formate-mediated cine -substitutions of vinyl triflates with aryl iodides. The collective data corroborate a mechanism in which Pd(OAc) 2 and Bu 4 NI form the dianionic iodide-bridged dimer [Pd 2 I 6 ][NBu 4 ] 2 , which, under reducing conditions, serves as a precursor to the palladium(I) complex [Pd 2 I 4 ][NBu 4 ] 2 . Dinculear oxidative addition of aryl iodide forms [Pd 2 I 5 (Ar)][NBu 4 ] 2 , which dissociates to the monometallic complex [PdI 2 (Ar)][NBu 4 ]. Vinyl triflate migratory insertion-sulfonate elimination delivers a palladium(IV) carbene, which upon β-hydride elimination/C-H reductive elimination gives the product of cine -substitution. These processes are the first efficient formate-mediated cross-electrophile reductive couplings beyond carbonyl addition.