Asymmetric organosilicon compounds are widely applied in fields such as material science, pesticide science, biomedicine and organic synthesis. The development of novel methods for the synthesis of divergent organosilanes is crucial in promoting further applications of these molecules. Recent years have shown advances in asymmetric hydrosilylation, desymmetrization of silanes and asymmetric conjugate addition of silyl groups. However, these methods are still limited in accessing structurally divergent orgnaosilanes. Transition metal catalyzed asymmetric carbene insertion of Si-H bonds is another efficient methods towards organosilanes, yet the carbene precursors of these reactions are restricted to electron withdrawing group stabilized diazo compounds, thus narrowing the variety of possible organosilanes products.
Recently, Prof. Shoufei Zhu and co-workers demonstrated for the first time an asymmetric Si-H insertion reaction using alkynes as carbene precursors. This reaction utilizes chiral dirhodium tetracarboxylates as catalysts. The catalyst first promotes cyclization of the carbonyl-ene-yne to form a metal carbene intermediate, which then undergoes Si-H insertion with high enantioselectivity to afford the organosilane products. The reaction features mild conditions and broad substrate scope. Most products can be prepared with >90% ee. The enantioenriched allylsilanes are prone to further conversion. Acylation occurs without erosion of chirality. Kinetic experiments indicates a first order kinetic behavior with respected to the dirhodium catalyst and silane, and zero order kinetics in regard to the substrate. This shows that the rater determining step is the rhodium carbene insertion of the Si-H bonds. This is further confirmed by a KIE experiment using deuterated silanes (KIE=1.5). This study reveals that alkynes are able to serve as carbene precursors for highly enantioselective Si-H insertions. Alkynes being relatively easy to construct, this method provides a new direction for synthesizing novel organosilanes.
This work is published on ACS Catal. (ACS Catal. 2019, 9, 5353−5357). Mingyao Huang and Jimin Yang contributed equally. This work is funded by the National Natural Science Foundation of China, the Ministry of Education of China and the National Program for Special Supportof Eminent Professionals.
Ming-Yao Huang#, Ji-Min Yang#, Yu-Tao Zhao, Shou-Fei Zhu*, Rhodium-Catalyzed Si−H Bond Insertion Reactions Using Functionalized Alkynes as Carbene Precursors. ACS Catal. 2019, 9, 5353−5357.
