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

Abstract

Abstract:The first Dimesitylboryl substitution of aryl halides with a silylborane bearing a dimesitylboryl group in the presence of alkalimetal alkoxides is described. The reactions of aryl bromides or iodides with Ph2MeSi-BMes2 and Na(OtBu) afforded the desired aryldimesitylboranes in good to high yields and with high borylation:silylation ratios. Selective reaction of the sterically lesshindered C−Br bond of dibromoarenes provided monoborylated products. This reaction was used to rapidly construct a D-π-A dimesitylarylborane with a non-symmetrical biphenyl spacer.Boron-containing π-conjugated compounds have received considerable attention as an important class of organic materials [1] with uses such as emissive materials, [2] two-photon absorption materials, [3] ion sensors, [4] electron-transporting materials, [5] and nonlinear optical materials.[6] The unique optical properties of these compounds arise from the pπ-π* conjugation between the vacant p-orbital of the boron atom and the π* orbital of the attached carbon π-conjugated moieties. A dimesitylboryl (BMes2) group has been employed in most of these compounds because of its strong π-electron accepting ability and air stability. The routes to access aryldimesitylborane are highly limited despite considerable efforts to develop methods to synthesis organoboron compounds. [7][8][9][10] The most popular synthesis of aryldimesitylboranes involves nucleophilic substitution of dimesitylboryl electrophiles (Mes2BX, X = halogen or OR) with organometallic compounds (ArM, M = Li, Mg). Aryldimesitylboranes are also synthesized by reaction of aryl boronic acid esters and MesLi.[11] These reactions are laborious and must be individualized for each aryldimesitylborane prepared. The use of organometallic reagents limits reaction scope and these reagents require multi-step syntheses, with low total yields (Scheme 1a). There are no direct methods to synthesize ArBMes2 from ArX. We recently reported a transitionmetal-free boryl substitution of organohalides using (phenyldimethylsilyl)pinacolborane [PhMe2Si-B(pin)] and an alkoxy base. This reaction allows the direct boryl substitution of aryl, alkyl, alkenyl and heteroaryl halides without using organometallic reagents. [12] We expected that the use of a silyl borane [13] with a diarylboryl group instead of B(pin) could provide a potent complementary method for the synthesis of triarylboranes. Herein, we report the first direct dimesitylboryl substitution of aryl halides using (diphenylmethylsilyl)dimesitylborane (Ph2MeSi-BMes2) [14] and Na(OtBu), which provides the corresponding aryldimesitylboranes in good to high yield with high borylation:silylation (B:Si) ratios (Scheme 1b). Boryl substitution of the less sterically hindered bromo group of dibromoarene substrates was highly selective and gave monoborylated products. We demonstrate the utility of this method by rapidly constructing a D-π-A dimesitylarylborane containing a nonsymmetrical biphenyl spacer.

Direct Dimesitylborylation of Benzofuran Derivatives by an Iridium‐Catalyzed C−H Activation with Silyldimesitylborane

“…BMes 2 groups can also be introduced into aromatic compounds by the reaction of aryl boronic acid esters with MesLi (Scheme a, B) . Recently, our group has reported the direct dimesitylborylation of aryl halides with silyldimesitylborane Ph 2 MeSi‐BMes 2 and Na(O t Bu), that is, a base‐mediated borylation with silylborane (BBS reaction) (Scheme a, C) . Although the corresponding dimesitylborylation products are obtained in good yield using both methods, a stoichiometric amount of base or organometallic reagent is needed.…”

“…We initially investigated the optimizationo ft he reaction conditions for the Ir-catalyzed CÀHd imesitylborylation of benzofuran (2a)w ith 1 (Table1), [15] startingb ys creening as eries of different ligands ( Table 1, entries [1][2][3][4][5][6]. For that purpose, a 1,4-dioxane solution of 1 and 2a was heated to 120 8Ci nt he presenceo f[ Ir(OMe)(cod)] 2 (2.5 mol %; cod:1 ,5-cyclooctadiene) and av ariety of different ligands.…”

“…[2,4] Recently,o ur group has reported the direct dimesitylborylation of aryl halides with silyldimesitylboraneP h 2 MeSi-BMes 2 and Na(OtBu), that is, ab ase-mediated borylation with silylborane (BBS reaction) (Scheme 1a,C ). [5,6] Although the corresponding dimesitylborylation products are obtained in good yield using both methods, as toichiometric amount of base or organometallic reagent is needed. Furthermore, in both reactions, the availability of the BMes 2 compounds relies on the availability of the preceding organohalide precursors, which are often difficult to access, especially in the case of highly functionalized organic halides.…”

Synthetic Approaches to Triarylboranes from 1885 to 2020

“…Ito and co‐workers reported the direct dimesitylborylation of various aryl halides [115] by reaction of (diphenylmethylsilyl)dimesitylborane with aryl halides in the presence of a base (Scheme 23 A). The halide was replaced by boron or silicon in a ratio of ca.…”

“… A) Dimesitylborylation of aryl halides [115] . B) Dimesitylborylation of benzofuran derivatives [116] …”