Desymmetrization‐Oriented Enantioselective Synthesis of Silicon‐Stereogenic Silanes by Palladium‐Catalyzed C−H Olefinations

Abstract

A palladium‐catalyzed chelation‐assisted enantioselective C−H olefination of symmetrically diaryl‐substituted tetraorganosilicon derivatives was developed, enabling the generation of nitrogen‐containing silicon‐stereogenic tetraorganosilicon compounds with modest to good yields and good to excellent enantioselectivities (up to 95.5:4.5 e.r.). The Thorpe–Ingold effect exerted by the substituents on silicon was observed to have a profound influence on formation of olefinated products which were further converted into other relevant chiral organosilanes without the loss of enantiomeric purity, thus demonstrating the synthetic utility of the developed enantioselective olefination.

Enantioselective Construction of Si‐Stereogenic Center via Rhodium‐Catalyzed Intermolecular Hydrosilylation of Alkene

“…Among the catalytic methods, desymmetrization of prochiral tetraorganosilanes (Si−C bonds) and dihydrosilanes (Si−H bonds) represents the forefronts of stereogenic silicon chemistry [5] . In terms of Si−C bond desymmetrization, Shintani's group [6] and others have made great progresses, including Si−C activation of silacyclobutanes [6a, b, 7] stereoselective C−H bond activation, [8] stereoselective benzoylation of 2‐sila‐1,3‐propanediol, [9] stereoselective diborylation of ethynylsilanes [10] and protoboration of vinylsilanes [11] . Desymmetrization of Si−H bonds has found an even larger arena.…”

Enantioselective C–H Functionalization toward Silicon-Stereogenic Silanes

“…14 In 2019, Xu and co-workers developed a Pd-catalyzed enantioselective C-H olefination of prochiral diarylsubstituted tetra-organosilane 36 by employing pyridine as the directing group (Scheme 6). 15 This intermolecular enantioselective C-H olefination was enabled by the use of the protected amino acid ligand Fmoc-Phe-OH. Various functionalized olefin derivatives, such as acrylates (37a, 37d), acrylamide (37e) and styrenes (37f, 37g) were found to be competent reaction partners in this transformation.…”

Construction of Si‐Stereogenic Silanes through C−H Activation Approach

“…Inspiring by the pyridine or pyrimidine directed C−H functionalizations of arylsilanes developed by Gevorgyan, [30] Xu and coworkers reported the first example of asymmetric desymmetrization of tetraorganosilanes via Pd‐catalyzed azine‐directed intermolecular C−H alkenylation (Scheme 18). [31] With chiral mono N ‐protected amino acid ligand (MPAA) [32] L16 and pyridine as the directing group, the azine‐tethered Si‐stereogenic silanes were obtained in 37–71 % yields and 74–91 % ee. It is noteworthy that the replacement of pyridine with quinoline led to better yields and enantioselectivities.…”