Copper-Catalyzed C-P Cross-Coupling of (Cyclo)alkenyl/Aryl Bromides and Secondary Phosphine Oxides with in situ Halogen Exchange

An efficient protocol for concurrent tandem halogen exchange/C-P cross-coupling of cycloalkenyl bromides and secondary phosphine oxides has been developed. The catalytic system is based on cheap and air-stable copper(I) iodide as the precatalyst, commercially available N,N'-dimethylethylenediamine as the ligand, and Cs2CO3 or K2CO3 as the base. The use of sodium iodide as an additive reduces the excessive use of organic bromides to near-stoichiometric by promoting the in situ transformation to the corresponding iodides. Diarylphosphine oxides undergo cycloalkenylation with 35-99 % yields and dicyclohexylphosphine oxide with 30-53 % yields. In the case of acyclic alkenyl bromides the cross-coupling products undergo conjugate addition of diphenylphosphine oxide and satisfying yields are observed only for internal olefins. In the case of aryl bromides satisfying yields (43-72 %) are observed only for sterically unhindered arenes or arenes possessing an ortho-directing group. Cycloalkenylphosphine oxides prepared in the cross-coupling reaction undergo base-catalyzed and base-promoted conjugate addition to give bis(phosphinoyl)cycloalkanes.