Asymmetric Catalytic Epoxidation of Terminal Enones for the Synthesis of Triazole Antifungal Agents
Qianwen He, Dong Zhang, Fengcai Zhang, Xiaohua Liu* and Xiaoming Feng*
*Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu 610064, China, Email: liuxhscu.edu.cn, xmfengscu.edu.cn
Q. He, D. Zhang, F. Zhang, X. Liu, X. Feng, Org. Lett., 2021, 23, 6795-6800.
DOI: 10.1021/acs.orglett.1c02588 (free Supporting Information)
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A chiral N,N'-dioxide/ScIII complex catalyzes an enantioselective epoxidation of α-substituted vinyl ketones in the presence of H2O2 as the oxidant to provide key epoxide intermediates for the synthesis of various triazole antifungal agents. The reaction proceeded efficiently in high yields and with good enantioselectivities.
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proposed working modes
General procedure for the catalytic asymmetric synthesis
Enone (0.2 mmol, 1.0 equiv.), Sc(OTf)3 (5 mol%) and ligand (5 mol%) were weighted into a dry reaction tube, followed by i-PrOH (1.0 mL). The mixture was stirred at 30°C for 30 min, and then hydrogen peroxide (50 μL, 0.6 mmol, 35% w/w in H2O, 3.0 equiv.) was added under stirring. The reaction mixture was stirred at 30°C for 24 hours. The residue was purified by flash chromatography on silica gel (eluent: petroleum ether/ethyl acetate, from 50/1 to 19/1) to afford the desired product (the silica gel was buffered with 3‰ triethylamine solution in petroleum ether). Unstable epoxides were purified by flash filtration with a thin silica gel to avoid decomposition.