Synthesis of Multifunctional 2,3‐Dihydroquinolin‐4(1 H )‐one Building Blocks via Permanganate‐Promoted Oxidation of 1,2,3,4‐Tetrahydroquinolines

A practical and scalable method for the preparation of 2,3-dihydroquinolin-4(1H)-one derivatives has been developed via selective benzylic oxidation of N-acyl-protected 1,2,3,4-tetrahydroquinolines using aqueous KMnO₄. The optimized oxidation protocol demonstrates excellent functional-group tolerance toward halogen, nitro, and methoxy substituents and proceeds efficiently on multi-gram scale (up to 20 g) without erosion in yield. The synthetic versatility of the obtained quinolinones was further demonstrated through their transformation into diverse bifunctional building blocks, including mono-N-Boc diamines bearing either exocyclic or endocyclic protected nitrogen atoms, aryl- and vinylboronates.