Catalytic Enantioselective Construction of Silicon-Stereogenic Silacarbocycles†

Abstract

Comprehensive Summary

Silicon-stereogenic silacarbocycles constitute a privileged class of organosilicon compounds with wide-ranging applications in asymmetric synthesis, functional materials, and medicinal chemistry. This review provides a systematic overview of recent advances in catalytic enantioselective synthetic methods, organized by catalytic systems, and traces the evolution of key strategies—with particular emphasis on desymmetrization of prochiral precursors, alongside kinetic resolution (KR) and dynamic kinetic asymmetric transformation (DYKAT). The field was initially established through pioneering Pd-catalyzed transformations, notably the asymmetric ring-expansion of strained silacyclobutanes with alkynes—a fundamental methodology for constructing cyclic tetraorganosilicon stereocenters. Subsequently, Rh-catalyzed systems have emerged as highly versatile platforms, enabling diverse transformations including dehydrogenative C–H silylation for accessing monohydrosilanes and heterocycles, intramolecular hydrosilylation toward cyclic monohydrosilanes and spirosilabiindanes, and formal [2+2+2] cycloadditions for synthesizing dibenzosiloles and silaspiranes. Driven by economic and sustainability considerations, research has fruitfully expanded to encompass earth-abundant base metal catalysis. Ni-catalyzed systems facilitate efficient intramolecular aryl transfer and ring-expansion reactions, while Co- and Cu-catalyzed approaches enable sequential hydrosilylation cascades that construct silacycles bearing consecutive Si and C stereocenters. Concurrently, metal-free organocatalysis has emerged as a powerful sustainable alternative, with chiral N-heterocyclic carbenes (NHCs), chiral phosphoric acids (CPAs), enamine catalysts, and confined imidodiphosphorimidates (IDPi) demonstrating remarkable efficacy in enantioselective desymmetrization processes. Despite substantial progress, we also offer a critical perspective on current methodologies, outline existing challenges and limitations, and highlight promising directions for future research. Current limitations include reliance on elaborate prochiral substrates and historical dependence on precious metals. Future efforts should focus on developing more efficient and atom-economical substrate synthesis, expanding sustainable catalytic systems including base-metal, organo-, and biocatalysis, integrating emerging technologies such as photocatalysis and electrocatalysis, and deepening mechanistic understanding to enable the rational design of advanced strategies such as DYKAT.

Key Scientists

In 2011, Hayashi and Shintani reported a pioneering Pd-catalyzed asymmetric ring expansion of silacyclobutanes with alkynes, enabling the construction of cyclic tetraorganosilicon stereocenters and marking the inception of this field. Subsequently, Takai and coworkers developed a Rh-catalyzed asymmetric synthesis of chiral spirosilabifluorene through sequential Si–H and C–H bond activations. In 2015, Nozaki and Shintani developed an efficient Rh-catalyzed [2+2+2] cycloaddition for the highly enantioselective synthesis of Si-stereogenic dibenzosiloles. In 2018, Xu and colleagues established a Pt-catalyzed tandem hydrosilylation/cyclization, and in 2022, the same group made further breakthroughs in the Rh-catalyzed dynamic kinetic asymmetric hydrosilylation to access Si-stereogenic benzosiloles. Meanwhile, the Song group developed a Rh-catalyzed ring expansion of silacyclobutanes with alkynes, expanding the methodologies for synthesizing axially chiral spirosilanes. In 2021, He et al. made an important contribution through Rh-catalyzed C–H silylation, enabling the enantioselective synthesis of Si-stereogenic monohydrosilanes and various heterocycles. Concurrently, the group of Wang conducted impressive studies on Rh-catalyzed asymmetric hydrosilylation and established a kinetic resolution strategy for the efficient synthesis of Si-stereogenic cyclic monohydrosilanes. More recently, Zhao reported a base-metal-catalyzed intramolecular ring expansion and an Ir-catalyzed enantioselective C–H silylation for constructing Si-stereogenic silacarbocycles, thereby further broadening the catalyst scope in this area. Numerous other researchers have also made important contributions; however, due to space constraints, a comprehensive acknowledgment of all achievements is not feasible within this review.