Rhodium-Catalyzed Pauson–Khand Reaction Using a Small-Bite-Angle P-Stereogenic C1-Diphosphine Ligand

The asymmetric Pauson−Khand reaction cata- lyzed by (Rh(COD)(MaxPHOS))BF4 is described. Several 1,6- enynes have been chosen as model substrates affording moderate yields and selectivities of up to 86% ee. Besides binap-type ligands, we have demonstrated that the P- stereogenic C1-symmetry small-bite-angle ligand MaxPHOS is a viable ligand in this process. The formation of (2+2+2) cycloaddition compounds has shown to be a competitive process. A mechanism is proposed to account for the observed results. The intermediate rhodium dicarbonyl complex 6 was synthesized, and its solid-state structure was elucidated by X-ray crystallography.