Cooperative Rh(II)/Pd(0) Dual Catalysis: Synthesis of Highly Substituted 3(2H)-Furanones with a C2-Quaternary Center via a Cyclization/Allylic Alkylation Cascade of α-Diazo-δ-keto-esters
Qian-Qian Zhou, Ming Cheng, Qing Liu, Bing-Qian Qu, Xiao-Yan Huang, Fang Yang, 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: chenzshnwsuaf.edu.cn
Q.-Q. Zhou, M. Cheng, Q.-Liu, B.-Q. Qu, X.-Y. Huang, F. Yang, K. Ji, Z.-S. Chen, Org. Lett., 2021, 23, 9151-9156.
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The combination of Rh(II)/Pd(0) catalysts promotes a cyclization/allylic alkylation cascade of stable α-diazo-δ-keto-esters to efficiently provide highly substituted 3(2H)-furanones with a C2-quaternary center under mild conditions. Remarkably, this binary catalytic system shows high chemo-, regio-, and stereoselectivity and excellent functional group tolerance.
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General procedure for reaction of α-diazo-δ-keto-esters with allyl tert-butyl carbonate
In an oven-dried 10 mL Schlenk flask equipped with a stir bar, Rh2(OAc)4 (0.9 mg, 2.0x10-3 mmol, 1.0 mol %), [PdCl(allyl)]2 (1.5 mg, 4.0x10-3 mmol, 2.0 mol %) and Xantphos(2.6 mg, 4.4x10-3 mmol, 2.2 mol %) were stirred in anhydrous toluene (0.5 mL) at room temperature (20°C) for 5 min under an argon atmosphere. Allyl tert-butyl carbonate (0.24 mmol, 1.2 equiv) was introduced by syringe. Then, a solution of α-diazo-δ-keto-ester 1 (0.20 mmol, 1.0 equiv) in toluene (1.5 mL) was added dropwise for 15 min. The reaction was stirred at 30°C. 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.