Synthesis of Ring-Fused, N-Substituted 4-Quinolinones Using pKa-Guided, Base-Promoted Annulations with Isatoic Anhydrides: Total Synthesis of Penicinotam.

An anionic annulation strategy employing isatoic anhydrides and a wide assortment of enolizable partners was developed to afford over 80 novel ring-fused, N-substituted 4-quinolinones, an underrepresented privileged template. Multiple factors governing the efficiency of the transformation were determined, resulting in a reliable and tunable synthetic platform applicable for a broad range of substrates with variable deprotonation susceptibility, such as tetramic and tetronic acids, cyclic 1,3-diketones, and cycloalkanones. Application to the synthesis of bioactive, pyrrolizine-fused 4-quinolinone, penicinotam 3, resulted in the most brief and highest yielding total synthesis of the alkaloid in three steps and a 36% overall yield.