Regioselective Iridium‐Catalyzed C8‐H Borylation of 4‐Quinolones via Transient O‐Borylated Quinolines

Abstract

AbstractThe quinolone–quinoline tautomerization is harnessed to effect the regioselective C8‐borylation of biologically important 4‐quinolones by using [Ir(OMe)(cod)]2 as the catalyst precursor, the silica‐supported monodentate phosphine Si‐SMAP as the ligand, and B2pin2 as the boron source. Initially, O‐borylation of the quinoline tautomer takes place. Critically, the newly formed 4‐(pinBO)‐quinolines then undergo N‐directed selective Ir‐catalyzed borylation at C8. Hydrolysis of the OBpin moiety on workup returns the system to the quinolone tautomer. The C8‐borylated quinolines were converted to their corresponding potassium trifluoroborate (BF3K) salts and to their C8‐chlorinated quinolone derivatives. The two‐step C‐H borylation‐chlorination reaction sequence resulted in various C8‐Cl quinolones in good yields. Conversion to C8‐OH‐, C8‐NH2‐, and C8‐Ar‐substituted quinolones was also feasible by using this methodology.