Phosphorus-Bearing Axially Chiral Biaryls by Catalytic Asymmetric Cross-Cyclotrimerization and a First Application in Asymmetric Hydrosilylation

A novel and efficient, two‐step route to axially chiral biaryls is demonstrated. In a direct asymmetric cross‐cyclotrimerization in the presence of a chiral cobalt(I) catalyst, axially chiral biaryls bearing phosphoryl moieties have been prepared, and through indirect evidence the authors have been able to clarify the origin of the stereochemical induction and the nature of the central intermediate in the catalytic cycle. By subsequent reduction of the phosphoryl moiety to the corresponding phosphine, a very efficient and atom‐economical approach to chiral systems has been developed. These chiral systems clearly have great potential use as axially chiral monodentate P‐ or bidentate P,O‐ligands, as has been demonstrated by the employment of the novel NAPHEP as a new monodentate acting ligand in an asymmetric hydrosilylation reaction. Chiral atropisomers of phosphorus‐bearing biaryls have been prepared through cross‐cyclotrimerization of alkynes in the presence of chiral CoI catalysts, followed by recrystallization and simple reduction to the corresponding phosphines (see scheme). Mechanistic investigations and the results of the employment of the novel monodentate ligand “NAPHEP” in asymmetric hydrosilylation are also presented.