Functionalization of substituted 2(1 H )‐pyridones. V. The synthesis of 1,2‐dihydro‐2‐oxo‐3,5‐pyridinedicarboxylic acid derivatives through a novel dianion route

A new pyridone dianion was prepared by halogen‐metal exchange from 5‐bromo‐1,2‐dihydro‐2‐oxo‐3‐pyrid‐inecarboxylic acid, t ‐butyl ester and two equivalents of n ‐butyllithium. This 1,5‐dianion readily reacted at C 5 with electrophiles. Quenching with carbon dioxide gave the previously unreported 1,2‐dihydro‐2‐oxo‐3,5‐pyridine dicarboxylic acid, 3‐ t ‐butyl ester. The 5‐carboxyl groups were selectively converted to the ethyl ester and the ethyl amide through the 5‐imidazolide. The 3‐ t ‐butyl ester was easily removed from all derivatives with acid hydrolysis.