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(1 H )‐one derivatives has been developed via selective benzylic oxidation of N ‐acyl‐protected 1,2,3,4‐tetrahydroquinolines using aqueous KMnO 4 . The optimized oxidation protocol demonstrates excellent functional‐group tolerance toward halogen, nitro, and methoxy substituents and proceeds efficiently on multigram 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.