Iridium-catalyzed borylation of thiophenes: versatile, synthetic elaboration founded on selective C-H functionalization

Iridium-catalyzed borylation has been applied to various substituted thiophenes to synthesize poly-functionalized thiophenes in good to excellent yields. Apart from common functionalities compatible with iridium-catalyzed borylations, additional functional group tolerance to acyl (COMe) and trimethylsilyl (TMS) groups was also observed. High regioselectivities were observed in borylation of 3- and 2,5-di-substituted thiophenes. Electrophilic aromatic C-H/C-Si bromination on thiophene boronate esters is shown to take place without breaking the C-B bond, and one-pot C-H borylation/Suzuki-Miyaura cross-coupling has been accomplished on 2- and 3-borylated thiophenes. (C) 2008 Elsevier Ltd. All rights reserved.