Pd-Catalyzed Perfluoroalkylative Aryloxycarbonylation of Alkynes with Formates as CO Surrogates

The highly toxic,
inflammable, and odorless nature of CO causes
problematic handling on laboratory-scale experiments. Replacement
of CO cylinders by CO surrogates is particularly attractive, especially
in the case of multicomponent reactions leading to valuable fluorinated
products. We report a Pd-catalyzed three-component protocol for the
direct synthesis of perfluoroalkyl-substituted α,β-unsaturated
esters from acetylenes and perfluoroalkyl iodides, applying formates
as convenient CO sources. The tandem reaction proceeds under mild
conditions with excellent regio- and stereoselectivities toward the E-isomer (>95:5, E:Z).
Detailed mechanistic investigations revealed that the process proceeds
through an off-cycle, base-induced decomposition of formate to CO
and phenoxide, which are reassembled on the Pd-center into an aryloxycarbonyl
moiety, which is ultimately installed on the alkene scaffold. To complete
the mechanistic picture of the reaction, the experimental study was
supported by DFT calculations.