Catalyst-free carbosilylation of alkenes using silyl boronates and organic fluorides via selective C-F bond activation

Abstract

A regioselective carbosilylation of alkenes has emerged as a powerful strategy to access molecules with functionalized silylated alkanes, by incorporating silyl and carbon groups across an alkene double bond. However, to the best of our knowledge, organic fluorides have never been used in this protocol. Here we disclose the catalyst-free carbosilylation of alkenes using silyl boronates and organic fluorides mediated by tBuOK. The main feature of this transformation is the selective activation of the C-F bond of an organic fluoride by the silyl boronate without undergoing potential side-reactions involving C-O, C-Cl, heteroaryl-CH, and even CF3 groups. Various silylated alkanes with tertiary or quaternary carbon centers that have aromatic, hetero-aromatic, and/or aliphatic groups at the β-position are synthesized in a single step from substituted or non-substituted aryl alkenes. An intramolecular variant of this carbosilylation is also achieved via the reaction of a fluoroarene with a ω-alkenyl side chain and a silyl boronate.

Organic Photoredox-Catalyzed Silyl Radical Generation from Silylboronate

“…Shibata et al . illustrated the silyl radical-mediated carbosilylation of alkenes via C–F bond cleavage . Nonetheless, these protocols required transition metals with a unique ligand or an excess amount of strong base.…”

Etherification of Fluoroarenes with Alkoxyboronic Acid Pinacol Esters via C–F Bond Cleavage

“…Because of the rapid growth in availability of fluorine-containing pharmaceuticals and agrochemicals in the market in the 21st century, C–F cleavage protocols have recently garnered substantial attention as they can offer dependable and convenient strategies for molecular modification in drug discovery . However, it is significantly difficult to cleave the C–F bond, which is the strongest interaction among organic compounds, owing to its high bond dissociation energy .…”

Silylboronate-Mediated Defluorosilylation of Aryl Fluorides with or without Ni-Catalyst

“…The substrate-scope showed slightly better yields when the reaction was performed in the presence of an Ni-catalyst, although we noticed that the effect of Ni-catalyst was not significant (Scheme 1E). While the results of Uchiyama and co-workers (Scheme 1D); (Kojima et al, 2019) and our recent results (Scheme 1E); (Zhou et al, 2021) indicate that Ni-catalyst is not necessary for their transformations, the conditions are not precisely the same such as bases, solvents and reaction times, which is difficult to conclude the Ni-effect. We thus decided to carefully re-examine our original work of defluorosilylation of aryl fluorides in 2018 (Scheme 1A); (Cui et al, 2018) by the same conditions, R 3 SiBPin in the presence of KOtBu, with or without an Ni-catalyst.…”

“…A schematic reaction of the catalyst-free defluorosilylation process is presented in Scheme 2 by considering our previous work and Uchiyama’s elegant DFT calculations ( Kojima et al, 2019 ). First, R 3 SiBPin 2 reacts with t BuOK to provide potassium silyl anion species C complexed with t BuO-BPin via A and B ( Cui et al, 2018 ; Jain et al, 2018 ; Zhou et al, 2021 ). C approaches the aryl fluoride 1 to form the intermediate I .…”

“…In situ generated silyl anion species enabled the direct defluorosilylation of fluoroarenes ( Scheme 1D ). In 2021, we have continuously reported the catalyst-free carbosilylation of alkenes using R 3 SiBPin and organic fluorides, including aryl and alkyl fluorides, via selective C–F bond activation ( Zhou et al, 2021 ). The substrate-scope showed slightly better yields when the reaction was performed in the presence of an Ni-catalyst, although we noticed that the effect of Ni-catalyst was not significant ( Scheme 1E ).…”