Rhodium-Catalyzed Pauson–Khand Reaction Using a Small-Bite-Angle <i>P</i>‑Stereogenic <i>C</i>₁‑Diphosphine Ligand

The asymmetric Pauson–Khand reaction catalyzed 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.