Photochemical Cobalt-Catalyzed Hydroalkynylation To Form 1,3-Enynes

A photochemical hydroalkynylation is reported employing a metallaphotoredox approach using cobalt catalysis and an organic dye, 4CzIPN. The protocol enables catalysis without the need for stoichiometric metal reductants, normally needed to convert higher oxidation state cobalt complexes to their more active lower oxidation states. The hydroalkynylation provides 1,3-enynes in good to high yields and E-selectivity (25-99% yield, 17 -> 99:1 E:Z, 27 examples). Importantly, cross-dimerizations of terminal alkynes that are typically rare are also possible and occur with unusually high levels of stereoselection. In addition, macrocyclic hydroalkynylations are reported in good to high yields, affording macrocyclic enyne motifs, which are found in numerous bioactive natural products