Catalyst-Controlled Regiodivergent CH Borylation of Multifunctionalized Heteroarenes by Using Iridium Complexes

• Published in: Chemistry : a European journal 2015-06, Vol.21 (25), p.9236-9241
• Main Authors: Sasaki, Ikuo, Taguchi, Jumpei, Hiraki, Shotaro, Ito, Hajime, Ishiyama, Tatsuo
• Format: Article
• Language: English
• Subjects: Adjustment; Biocompatibility; borylation; Catalysis; Catalysts; CH activation; heterocycles; Iridium; Iridium compounds; Ligands; regioselectivity
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201500658

The regiodivergent CH borylation of 2,5‐disubstituted heteroarenes with bis(pinacolato)diboron was achieved by using iridium catalysts formed in situ from [Ir(OMe)(cod)]2/dtbpy (cod=1,5‐cyclooctadiene, dtbpy: 4,4′‐di‐tert‐butyl‐2,2′‐bipyridine) or [Ir(OMe)(cod)]2/2 AsPh3. When [Ir(OMe)(cod)]2/dtbpy was used as the catalyst, borylation at the 4‐position proceeded selectively to afford 4‐borylated products in high yields (dtbpy system A). The regioselectivity changed when the [Ir(OMe)(cod)]2/2 AsPh3 catalyst was used; 3‐borylated products were obtained in high yields with high regioselectivity (AsPh3 system B). The regioselectivity of borylation was easily controlled by changing the ligands. This reaction was used in the syntheses of two different bioactive compound analogues by using the same starting material. Minor adjustments, major differences: The regiodivergent CH borylation of 2,5‐disubstituted heteroarenes with bis(pinacolato)diboron was achieved by using iridium catalysts formed in situ from [Ir(OMe)(cod)]2/dtbpy (cod=1,5‐cyclooctadiene, dtbpy: 4,4′‐di‐tert‐butyl‐2,2′‐bipyridine) or [Ir(OMe)(cod)]2/2 AsPh3 (see scheme).