Enantioselective Silicon-Directed Nazarov Cyclization
Jin Cao, Meng-Yang Hu, Si-Yuan Liu, Xin-Yu Zhang, Shou-Fei Zhu* and Qi-Lin Zhou
*The State Key Laboratory and Institute of Elemento-Organic Chemistry, College of Chemistry, Nankai University, Tianjin 300071, China, Email: sfzhunankai.edu.cn
J. Cao, M.-Y. Hu, S.-Y. Liu, X.-Y. Zhang, S.-F. Zhu, Q.-L. Zhou, J. Am. Chem. Soc., 2021, 143, 6962-6968.
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A highly enantioselective silicon-directed Nazarov reaction is cooperatively catalyzed by a Lewis acid and a chiral Brønsted acid. The silicon group in the dienone substrate stabilized the β-carbocation of the intermediate, thereby determining the position of the double bond in the product.
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Enantioselective Silicon-Directed Nazarov Cyclization - Typical Procedure
Zn(OTf)2 (3.6 mg, 0.01 mmol, 5 mol %), (S)-3d (8.6 mg, 0.012 mmol, 6 mol %) and PhOH (20.7 mg, 0.22 mmol, 1.1 equiv) were introduced into an oven-dried Schlenk tube in an argon-filled glovebox. After 3 mL DCE was injected into the Schlenk tube, the mixture was stirred at 40°C. The substrate 1aa (48.8 mg, 0.2 mmol) was introduced into the mixture in one portion and stirred at 40°C for 12 h (the reaction progress was monitored by TLC). Then the reaction mixture was concentrated and purified by a flash chromatography on silica gel (PE/EA = 20:1, v/v) to give 2aa as a white solid.
Nazarov cyclization, cyclopentenones