Expedient Synthesis of Dihaloalkenynes via Pd‐Catalyzed Haloalkynylation Reaction

Herein, the PdII‐catalyzed construction of functionalized dihaloalkenynes from haloalkynes via a self‐haloalkynylation reaction, without specialized ligands or oxidizing additives, is reported. The method tolerates a diverse range of haloalkynes, including electron‐donating and electron‐withdrawing functional groups, such as macrocyclic alkynols, spiro‐oxy ring alkynols, and even carbazole‐containing, pyrrolidine‐2,5‐dione‐containing and silyl‐protected bromoalkynes. Using an opposite lithium halide (LiX) to the haloalkyne starting material, remarkably high regio‐ and stereoselectivity of the haloalkynylation reaction is possible, yielding 1‐bromo‐2‐chloroalkenyne or 2‐bromo‐1‐chloroalkenyne products as desired. A robust and regioselective PdII‐catalyzed haloalkynylation of haloalkynes has been established under ligand‐free and oxidant‐free conditions. Careful selection of the haloalkyne starting material, with respect to electron densities of the alkyne, allows for strong control of the order and selectivity of the halide atoms in the coupled product.