Enantioselective Silylation of Aliphatic C−H Bonds for the Synthesis of Silicon‐Stereogenic Dihydrobenzosiloles

Abstract

Ar hodium(I)-catalyzed enantioselective silylation of aliphatic C À Hbonds for the synthesis of silicon-stereogenic dihydrobenzosiloles is demonstrated. This reaction involves ahighly enantioselective intramolecular C(sp 3)ÀHsilylation of dihydrosilanes,f ollowed by as tereospecific intermolecular alkene hydrosilylation leading to the asymmetrically tetrasubstituted silanes.Awide range of dihydrosilanes and alkenes displaying various functional groups are compatible with this process,g iving access to av ariety of highly functionalized silicon-stereogenic dihydrobenzosiloles in good to excellent yields and enantioselectivities. Scheme 1. Enantioselective silylation of aliphaticC ÀHbonds.

Catalytic Asymmetric Synthesis of Silicon‐Stereogenic Dihydrodibenzosilines: Silicon Central‐to‐Axial Chirality Relay

“…Among various approaches, transition‐metal‐catalyzed enantioselective C−H silylation recently has emerged as a powerful strategy for the synthesis of silicon‐stereogenic silanes [8] . On the basis of our previous work for the enantioselective C(sp 3 )−H silylation strategy, [8i] herein, we report a Rh‐catalyzed asymmetric synthesis of silicon‐stereogenic dihydrodibenzosilines featuring axially chiral 6‐member‐bridged biaryls (Scheme 1 c). In the presence of [Rh(cod)Cl] 2 catalyst with chiral diphosphine ligand Josiphos, a wide range of biaryl substituted dihydrosilanes can undergo enantioselective dehydrogenative benzylic C−H silylation to form the cyclized 6‐membered‐ring silicon‐stereogenic silanes in good yields with excellent enantioselectivities.…”

Enantioselective construction of six- and seven-membered triorgano-substituted silicon-stereogenic heterocycles

“…With the continued interest in silicon-stereogenic chemistry, we questioned whether we could utilize asymmetric dehydrogenative C–H silylation toolbox 57 , 58 for the construction of six- or seven-membered silicon-stereogenic silanes. To achieve this target, three major obstacles are expected: (1) the intramolecular C–H silylation must proceed through a disfavoured seven- or eight-membered-ring cyclometallated intermediate, which would be rather challenging; (2) the competing dehydrogenative homo-coupling of dihydrosilanes is plausible 59 , 60 ; (3) the control of high enantioselectivity is elusive.…”

Rhodium‐Catalyzed Synthesis of Chiral Monohydrosilanes by Intramolecular C−H Functionalization of Dihydrosilanes

“…The reaction involving unactivated C−H bonds are however much more demanding, since it requires harsher reaction conditions [9, 2u,v] due to the inert nature of the C−H bonds. This means that the monohydrosilanes could suffer a second C−H silylation, resulting in the undesired tetraorganosilanes as the thermodynamically favored products.…”

“…They very likely underwent an in situ Si−C bond formation in a stereospecific manner to afford the final tetraorganosilanes products. Very recently, He group reported two examples of intercepting the presumptive monohydrosilanes with alkenes [2u,v] . Again, only one monohydrosilane was reported in a low yield in the mechanistic study.…”