Iridium-catalyzed direct borylation of five-membered heteroarenes by bis(pinacolato)diboron: Regioselective, stoichiometric, and room temperature reactions

An iridium(I) complex generated from 1/2[Ir(OMe)(COD)](2) and 4,4'-di-tert-butyl-2,2'-bipyridine catalyzed the direct borylation of 2-substituted thiophenes, furans and pyrroles in stoichiometric amounts relative to bis(pinacolato)diboron in hexane at room temperature. The heteroarylboronates from regioselective C-H activation at the 5-position were formed in high yields. Similar borylations of unsubstituted heteroarenes with an equimolar amount of the diboron regioselectively provided 2,5-bis(boryl)heteroarenes.