Bagutski, Viktor published the artcileMechanistic studies into amine-mediated electrophilic arene borylation and its application in MIDA boronate synthesis, Application of 5,5′-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,2′-bithiophene, the publication is Journal of the American Chemical Society (2013), 135(1), 474-487, database is CAplus and MEDLINE.
Direct electrophilic borylation using Y2BCl (Y2 = Cl2 or o-catecholato) with equimolar AlCl3 and a tertiary amine has been applied to a wide range of arenes and heteroarenes, yielding aryl and heterocyclic boronates in a regioselective way. In situ functionalization of the ArBCl2 products is possible with Me3SiOCOCH2NMeCH2CO2SiMe3 (TMS2MIDA), to afford bench-stable and easily isolable MIDA-boronates in moderate to good yields; pinacol and neopentylglycol esters were also prepared According to a combined exptl. and computational study, the borylation of activated arenes at 20° proceeds through an SEAr mechanism with borenium cations, [Y2B(amine)]+, the key electrophiles. For catecholato-borocations, two amine dependent reaction pathways were identified: with [CatB(NEt3)]+, an addnl. base is necessary to accomplish rapid borylation by deprotonation of the borylated arenium cation (σ complex), which otherwise would rather decompose to the starting materials than liberate the free amine to effect deprotonation. Apart from amines, the addnl. base may also be the arene itself when it is sufficiently basic (e.g., N-Me-indole). When the amine component of the borocation is less nucleophilic (e.g., 2,6-lutidine), no addnl. base is required due to more facile amine dissociation from the boron center in the borylated arenium cation intermediate. Borenium cations do not borylate poorly activated arenes (e.g., toluene) even at high temperatures; instead, the key electrophile in this case involves the product from interaction of AlCl3 with Y2BCl. When an extremely bulky amine is used, borylation again does not proceed via a borenium cation; instead, a number of mechanisms are feasible including via a boron electrophile generated by coordination of AlCl3 to Y2BCl, or by initial (heteroarene)AlCl3 adduct formation followed by deprotonation and transmetalation.
Journal of the American Chemical Society published new progress about 239075-02-6. 239075-02-6 belongs to alcohols-buliding-blocks, auxiliary class Thiophene,Boronic acid and ester,Boronate Esters, name is 5,5′-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,2′-bithiophene, and the molecular formula is C20H28B2O4S2, Application of 5,5′-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,2′-bithiophene.
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