Ligand‐Controlled Diastereoselective Cobalt‐Catalysed Hydroalkynylation of Terminal Alkynes to E ‐ or Z ‐1,3‐Enynes

A diastereoselective hydroalkynylation of terminal alkynes to form the head‐to‐head dimerization products by two different cobalt‐phosphine catalyst system is reported. The use of the bidentate ligand dppp and additional triphenylphosphine led to the selective formation of the (E)‐1,3‐enynes (E:Z>99:1) in good to excellent yields, while the tridentate ligand TriPhos led to the corresponding (Z)‐1,3‐enynes in moderate to good yields with excellent stereoselectivities (up to E:Z=1:99). Both pre‐catalysts are easy to handle, because of their stability under atmospheric conditions. The optimized reaction conditions were identified by the Design of Experiments (DoE) approach, which has not been used before in cobalt‐catalysed reaction optimisation. DoE decreased the number of required reactions to a minimum.
Cobalt catalysis at a crossroad: The choice of the ligands in a cobalt‐catalysed hydroalkynylation of terminal alkynes is decisive to form the dimerization products in a diastereoselective fashion. The (E)‐1,3‐enynes are formed in good to excellent yields and outstanding selectivities (E:Z>99:1), while the corresponding (Z)‐1,3‐enynes were isolated in moderate to good yields with excellent stereoselectivities (up to E:Z=1:99).