Reductive Cross-Coupling of Alkynes with Aryl Bromides via Zr/Pd Synergistic Catalysis

The cocatalytic reductive cross-coupling of unactivated alkynes with aryl bromides is reported, using 2 mol % Pd(PPh3)4 and 10 mol % Cp2ZrCl2 in combination with a hydrosilane reductant. Hydroarylated products are furnished in upward of 91% yield across 25 elaborated substrates, including those containing unprotected alcohols, esters, amides, and terminal alkenes. Syn-selective hydrozirconation of alkyne substrates prior to transmetalation ensures exceptional (>20:1) (E)-selectivity across all alkene products. Further, this protocol was successfully implemented on gram scale without loss of efficiency or selectivity.