Stereoselective cobalt-catalyzed halofluoroalkylation of alkynes

Stereoselective additions of highly functionalized reagents to available unsaturated hydrocarbons are an
attractive synthetic tool due to their high atom economy, modularity, and rapid generation of
complexity. We report efficient cobalt-catalyzed (E)-halofluoroalkylations of alkynes/alkenes that enable
the construction of densely functionalized, stereodefined fluorinated hydrocarbons. The mild conditions
(2 mol% cat., 20 C, acetone/water, 3 h) tolerate various functional groups, i.e. halides, alcohols,
aldehydes, nitriles, esters, and heteroarenes. This reaction is the first example of a highly stereoselective
cobalt-catalyzed halo-fluoroalkylation. Unlike related cobalt-catalyzed reductive couplings and Hecktype
reactions, it operates via a radical chain mechanism involving terminal halogen atom transfer which
obviates the need for a stoichiometric sacrificial reductant.