Abstract
2,2-Disubstituted 1,2-dihydro-3H-indol-3-ones are useful synthetic intermediates for natural products. Therefore, its preparation in a concise manner is highly desirable. Recently, we reported a methodology for the preparation of 2,2-disubstituted 1,2-dihydro-3H-indol-3-ones through the successive oxidation of indoles and Mannich-type reaction of 2-hydroxy-1,2-dihydro-3H-indol-3-ones with various carbon nucleophiles. Using this method, we accomplished the total synthesis of (±)-hinckdentine A. The synthesis featured seven-membered lactam formation by Murahashi’s Ru catalyst and the selective tri-bromination of aromatic ring. Also, we performed the synthesis of isatisine A framework. In this research, we found an intriguing reaction in which nucleophiles are introduced at the C-2 position of 3H-indol-3-one via activation with TFAA. Towards the total synthesis of leuconoxine, ring construction steps featuring the N-acyliminium mediated intramolecular piperidine cyclization and the one-step pyrrolidone formation using Bestmann’s ylide are achieved successfully. Utilization of a chiral phosphoric acid catalyst (VAPOL PA), the asymmetric desymmetrization of prochiral diester produced highly-enantioenriched lactam in excellent yield. Using this strategy, we accomplished the asymmetric total synthesis of (−)-leuconoxine.
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