Boryl substitution of functionalized aryl-, heteroaryl- and alkenyl halides with silylborane and an alkoxy base: expanded scope and mechanistic studies

Abstract

A transition-metal-free method has been developed for the boryl substitution of functionalized aryl-, heteroaryl- and alkenyl halides using a silylborane/alkoxy-base reagent. Borylation of (Z)-alkenyl halides proceeded in a stereoretentive manner.

Catalytic Borylation using an Air‐Stable Zinc Boryl Reagent: Systematic Access to Elusive Acylboranes

“…[1] Boronic acids/esters and related derivatives represent the most widely used class of such compounds,w ith diboron(4) esters,B 2 (OR) 4 ,t ypically being employed to access such species by borylation of C À halogen (and even C À H) bonds. [3] Tr ansient masked boryl anions are frequently postulated as key intermediates in these transformations, [4] and af ew examples of anionic sp 2 -sp 3 tetraalkoxy diboron compounds have been successfully isolated and proved to be catalytically relevant. [3] Tr ansient masked boryl anions are frequently postulated as key intermediates in these transformations, [4] and af ew examples of anionic sp 2 -sp 3 tetraalkoxy diboron compounds have been successfully isolated and proved to be catalytically relevant.…”

Formation of C(sp2)Boronate Esters by Borylative Cyclization of Alkynes Using BCl3

“…Recent advances in transition-metal-free borylation include benzannulations, [3] radical mediated borylation, [4] electrophilic borylation, [5] and carbanion-mediated borylation. [6] One underexplored approach to metal-free C(sp 2 )ÀB bond formation proceeding from simple hydrocarbon precursors is the borylative cyclization of alkynes,w herein ab oron electrophile activates an alkyne for intramolecular electrophilic cyclization with as econd p-system. This approach represents as tep-economical reaction which would simultaneously create new C(sp 2 )ÀBa nd CÀCb onds to generate new polycyclicf rameworks such as borylated dihydroquinolines,dihydronaphthalenes, and phenanthrenes, which are prevalent in (or are key precursors to) biologically active molecules,p harmaceuticals (e.g.…”

Direct Introduction of a Dimesitylboryl Group Using Base‐Mediated Substitution of Aryl Halides with Silyldimesitylborane

“…This reaction allows the directb oryl substitution of aryl, alkyl, alkenyl, and heteroaryl halides withoutu sing organometallic reagents. [12] We expected that the use of as ilyl borane [13] with ad iaryl borylg roup instead of B(pin) could provideapotent complementary method for the synthesis of triarylb oranes. Herein, we report the first direct dimesitylboryl substitution of aryl halidesu sing (diphenylmethylsilyl)dimesitylborane (Ph 2 MeSiÀBMes 2 ) [14] and Na(OtBu), which provides the corresponding aryl dimesitylboranes in good to high yield with high borylation/silylation( B/Si)r atios (Scheme 1b).…”

“…[12,18] Ph 2 MeSiÀBMes 2 initially reacts with Na(OtBu)t og ive the corresponding ate complex A.T he nucleophilic Ph 2 MeSi group of A attacks the bromine atom in the aryl bromidet og ive the aryl anion intermediate B.S ubsequent nucleophilic attack of the carbanion species to the boron atom in the Mes 2 B(OtBu) affords triaryl borane 3.T hisp roposed mechanism followst he same process as the mechanism for boryl substitution with PhMe 2 SiÀB(pin) and an alkoxyb ase. [12] However,t he optimized conditions for dimesityl borylation are slightly different from those for the previously reportedb oryla-Scheme2.Diaryl borylation of dihaloarenes with Ph 2 MeSiÀBMes 2 and Na(OtBu). Reactions were carried out at 50 8Cf or 24 h. Yield is based on 1 HNMR analysis of the crude products.Y ield of the isolatedborylated product is showninparentheses.…”