1,2‐Bis(boronate) Arenes by Borylation Directed Borylation

ABSTRACT Aryl boronate esters are ubiquitous in synthesis and are efficiently produced by C–H borylation. However, there are no reported methods to date that convert arenes into vicinal bis‐boronate ester derivatives by double C–H borylation. Instead, all current routes require pre‐functionalized arene precursors. Vicinal bis‐boronate esters are highly desirable, as arenes with this substitution pattern are pervasive in biologically active compounds and organic materials. Herein we show that boron electrophiles derived from tetrahalo‐pyrazaboles (X 2 B(μ‐pyrazole) 2 BX 2 ) and AlX 3 (X = Cl or Br) affect the regioselective vicinal double C–H borylation of arenes and polycyclic aromatic hydrocarbons (PAHs). This afforded diborylated products that were notable in their own right, representing novel cationic PAHs containing an unusual cyclic C 2 B 2 N 2 unit. A subsequent pinacol installation step then affords the vicinal bis‐boronate ester‐substituted arene/PAH. A wide range of arenes and PAHs were shown to undergo highly regioselective one‐pot conversion to the vicinal bis‐boronate ester‐substituted products, of which multiple were unprecedented before this work. Overall, this work is the first, to our knowledge, double C–H borylation methodology to form vicinal bis‐boronate ester‐substituted arenes/PAHs and therefore is a useful addition to the synthetic chemist's toolbox given the considerable utility of organoboranes.