Protecting Group-Controlled Regioselective Synthesis for Unsymmetrical 3,5-Disubstituted Pyridones

Protecting group-controlled regioselective functionalization of 3,5-dibromo-2-pyridones has been studied for preparation of unsymmetrical 3,5-disubstituted 2-pyridones. A bulky di-tert-butyl(isobutyl)silyl (BIBS) group was utilized for C5 regioselective arylation in Suzuki-Miyaura reactions. Meanwhile, the p-toluenesulfonyl (Ts) group was used to maximize C3 selective halogen-lithium exchange employing flow chemistry. Most of the reactions proceeded well, with yields of 76 to 95% and excellent regioselectivity. A one-pot synthesis of unsymmetrical 3,5-diaryl-2-pyridones starting from 3,5-dibromo-2-silyloxypyridine was conducted to demonstrate the practical convenience. Further functionalization onto the remaining bromine group, such as transition metal-catalyzed C−C and C−N bond-forming reactions and retro-Brook rearrangement for C−Si bond formation, was accomplished for synthesis of biologically relevant 3,5-disubstituted 2-pyridones. Finally, amrinone and milrinone, commonly used for congestive heart failure, were synthesized in three steps from 3,5-dibromo-2-pyridones in 41% and 56% overall yields, respectively. (Figure presented.).