Regio‐ and Stereoselective 1,2‐Oxyhalogenation of Non‐Conjugated Alkynes via Directed Nucleopalladation: Catalytic Access to Tetrasubstituted Alkenes

A catalytic 1,2‐oxyhalogenation method that converts non‐conjugated internal alkynes into tetrasubstituted alkenes with high regio‐ and stereoselectivity is described. Mechanistically, the reaction involves a Pd(II)/Pd(IV) catalytic cycle that begins with a directed oxypalladation step. The origin of regioselectivity is the preference for formation of a six‐membered palladacycle intermediate, which is facilitated by an N,N‐bidentate 2‐(pyridin‐2‐yl)isopropyl (PIP) amide directing group. Selectivity for C(alkenyl)−X versus −N (X=halide) reductive elimination from the Pd(IV) center depends on the identity of the halide anion; bromide and iodide engage in C(alkenyl)−X formation, while intramolecular C(alkenyl)−N reductive elimination occurs with chloride to furnish a lactam product. DFT calculations shed light on the origins of this phenomenon.