B(C₆F₅)₃-Catalyzed Diastereoselective Formal (4 + 1)-Cycloaddition of Vinylcyclopropanes and Et₂SiH₂

Abstract

A formal (4 + 1)-cycloaddition of vinylcyclopropanes and Et 2 SiH 2 to afford 3,4-disubstituted silolanes is reported. The reaction sequence commences with the known B(C 6 F 5 ) 3catalyzed alkene hydrosilylation with dihydrosilanes. Cleavage of the remaining Si−H bond in the hydrosilylation product assisted by B(C 6 F 5 ) 3 leads to formation of a cyclopropane-stabilized silylium ion. The activated cyclopropane ring is then opened by the in situ-generated borohydride accompanied by ring closure to the silolane. The diastereoselectivity is rationalized by a mechanistic model.

Skeletal Rearrangements Involving Cyclopropyl- and Alkene-Stabilized Silylium Ions

“…In 2021, we reported a B(C 6 F 5 ) 3catalyzed diastereoselective (4+1) cycloaddition of alkylsubstituted VCPs 18 and Et 2 SiH 2 (6a) to afford trans-3,4disubstituted silolanes 19 (Scheme 6). 30 This reaction bears similarities to the above (5+1) cycloaddition in that a -silicon-stabilized carbenium ion 13 + with [HB(C 6 F 5 ) 3 ]as the counteranion is generated. Unlike the scenario with the [B(C 6 F 5 ) 4 ]counteranion, initial reduction occurs to furnish the hydrosilylation product.…”

Controllable Si–C Bond Formation from Trihydrosilanes En Route to Synthesis of 1,4-Azasilinanes with Diverse Silyl Functionalities

“…The three-component reaction was initially performed by mixing equimolar amounts of trihydrophenylsilane 1a , dienamide 2a , and 1-( tert -butyl)-4-vinylbenzene 3a in CH 2 Cl 2 , followed by addition of 10 mol % of B­(C 6 F 5 ) 3 (Table , Method A). After the reaction was stirred for 12 h at 25 °C, the desired 1,4-azasilinane 5a was obtained in 32% yield via (5 + 1)-annulation, followed by hydrosilylation with 3a (entry 1) . Switching the solvent from CH 2 Cl 2 to toluene provided a comparable yield of 39% (entry 2), while benzotrifluoride improved to 49% (entry 3).…”

Silylium-Ion-Promoted Skeletal Reorganization of β-Silylated Cyclopropanes Bearing an Allyl Group at the Silicon Atom Coupled with Intermolecular Formation of a Quaternary Carbon Atom

“…Vinylcyclopropanes (VCPs) are multifaceted synthetic building blocks . Our laboratory recently reported a diverse set of formal cycloaddition reactions between VCPs I and dihydrosilanes with either a silylium ion as a promoter , or B­(C 6 F 5 ) 3 as a catalyst (Scheme ). Deceptively simple variations of the R group in VCPs I and generation of the silicon electrophile led to dramatically different reaction outcomes (eqs 1–3 in Scheme ).…”

“…Despite the complexity of the underlying reaction mechanisms, these three processes share diastereomeric cyclopropane-stabilized silylium ion II as a common intermediate (gray box). The resulting reaction cascades end with hydride transfer from a hydrosilane or borohydride to a carbenium ion (as in the cases of III and V ) or loss of a proton from a Wheland complex (as in the case of IV ).…”

“…In summary, we developed another fascinating bond reorganization starting from a cyclopropane-stabilized silylium ion. Unlike previous formal cycloaddition reactions of VCPs and dihydrosilanes, , the reaction cascade is not terminated by C–H but instead C–C bond formation. This added complexity to the overall process.…”