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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.

DOI: 10.1021/acs.orglett.1c03469



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Abstract

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 (20C) 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 30C. 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

3(2H)-Furanones


ID: J54-Y2021