Rh(II)-Catalyzed Chemoselective Oxy-alkynylation of Acceptor-Acceptor Carbenes: Synthesis of C2-Quaternary Alkyne-Substituted 3(2H)-Furanones
Qing Liu, Yang-Ting Ma, Xiao-Yan Huang, Yan-Zhen Li, Fang Yang, Shaukat Ali, Kegong Ji and Zi-Sheng Chen*
*Shaanxi Key Laboratory of Natural Products & Chemical
Biology, College of Chemistry and Pharmacy, Northwest A&F University, Yangling
712100, Shaanxi, P. R. China, Email: chenzsh
nwsuaf.edu.cn
Q. Liu, Y.-T. Ma, X.-Y. Huang, Y.-Z. Li, F. Yang, S. Ali, K. Ji, Z.-S. Chen, Org. Lett., 2023, 25, 4044-4049.
DOI: 10.1021/acs.orglett.3c01196
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Abstract
A Rh(II)-catalyzed oxy-alkynylation of acceptor-acceptor carbenes using EBX reagents provides diverse C2-quaternary alkyne-substituted benzofuran-3-ones and 2,2,4,5-tetrasubstituted 3(2H)-furanones under mild conditions with high functional group compatibility. The key alkyne-transfer step is likely to occur through a tandem process involving a β-addition, an α-elimination, and a 1,2-shift.
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proposed mechanism
General procedure for the synthesis of benzofuran-3-ones
In an oven-dried 10 mL Schlenk flask equipped with a stir bar, Rh2(tBuCO2)4 (2.4 mg, 4.0x10-3 mmol, 2.0 mol %) was stirred in anhydrous toluene (0.5 mL) at room temperature for 5 min under an N2 atmosphere. Then, a solution of α-diazo-β-ketoester (0.22 mmol, 1.1 equiv) and Hypervalent Iodine Reagent (0.20 mmol, 1.0 equiv) in toluene (1.5 mL) was added dropwise for 15 min. The reaction was stirred at 30~50 °C (oil bath). When the reaction was considered complete, as determined by TLC analysis, the product was directly isolated by chromatography on silica-gel using a mixture of petroleum ether/ethyl acetate as eluent.
General procedure for the synthesis of 3(2H)-furanones
In an oven-dried 10 mL Schlenk flask equipped with a stir bar, α-diazo-δ-keto-ester (0.24 mmol, 1.2 equiv), Rh2(tBuCO2)4 (2.4 mg, 4.0x10-3 mmol, 2.0 mol %), Cs2CO3 (65.2 mg, 0.20 mmol, 1.0 equiv), 5 Å MS (100 mg), and Hypervalent Iodine Reagent (0.20 mmol, 1.0 equiv) were added. Then the flask was sealed and was evacuated and back-filled with nitrogen. Anhydrous toluene (2.0 mL) was added by syringe. The mixture was stirred at 30 °C (oil bath). When the reaction was considered complete, as determined by TLC analysis, the product was directly isolated by chromatography on silica-gel using a mixture of petroleum ether/ethyl acetate as eluent.
Key Words
benzofuran-3-ones, 3(2H)-furanones
ID: J54-Y2023
