Flipping the Switch on Palladium-Catalyzed Carboiodination: Accessing Kinetic and Thermodynamic Products

Abstract

A palladium-catalyzed epimerization reaction of stereogenic alkyl iodides is reported. This transformation involves use of an air-stable precatalyst that efficiently epimerizes the C−I bond from the exo to the endo face of [2.2.1] bicyclic compounds. Mechanistic experiments support the stereoinversion of the C−I bond via reversible bond formation to generate the antiproduct bearing an endo iodide. Density functional theory studies were conducted to support a thermodynamically driven epimerization. Stoichiometric experiments suggested that irradiation of isolable alkyl−Pd(II) complexes promoted the C−I reductive elimination, which could even be applied to C−Br bond formation.

Photoexcited Nickel-Catalyzed Carbohalogenation

“…The underlying role of this functionality was unclear, but substrates lacking this element failed to react. Subsequently, palladium and visible light proved an effective method to afford similar compounds. , These studies revealed that analogous halogenated heterocycles could be prepared under increasingly mild conditions using readily available precatalysts. The C–X bond was proposed to undergo reversible bond formation via a Pd­(I) radical pair, − whereas reversible addition with C–Br was known to be more difficult. − Palladium/blue light broadens the scope; however, a precious metal catalyst was still needed.…”