- Efficient synthetic method of β-fluorocinnamate by arylboronic acids and ethyl 3,3,3-trifluoropropionate under palladium-catalyzed conditions
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A convenient and efficient method for synthesizing β-fluorocinnamate and derivatives is reported. Palladium (II) catalysis was employed in β-F elimination and coupling reaction of phenylboronic acid and ethyl 3,3,3-trifluoropropionate with a high yield and E-selectivity. The reaction was conducted under mild conditions and could be widely adapted to boronic acid substrates.
- Chen, Wei-Hao,Pei, Xiao-Jun,Li, Xiao-Xuan,Feng, Yi-Si
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- Stereodivergent Alkyne Hydrofluorination Using Protic Tetrafluoroborates as Tunable Reagents
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The discovery of safe, general, and practical procedures to prepare vinyl fluorides from readily available precursors remains a synthetic challenge. The metal-free hydrofluorination of alkynes constitutes an attractive though elusive strategy for their preparation. Introduced here is an inexpensive and easily handled reagent that enables the development of simple and scalable protocols for the regioselective hydrofluorination of alkynes to access both the E and Z isomers of vinyl fluorides. These reaction conditions were suitable for a diverse collection of alkynes, including several highly functionalized pharmaceutical derivatives. Computational and experimental mechanistic studies support C?F bond formation through vinyl cation intermediates, with the E- and Z-hydrofluorination products forming under kinetic and thermodynamic control, respectively.
- Geaneotes, Paul,Guo, Rui,Liu, Peng,Qi, Xiaotian,Wang, Ruihan,Wang, Yi-Ming,Xiang, Hengye
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supporting information
p. 16651 - 16660
(2020/07/16)
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- A Bio-Inspired, Catalytic e → Z Isomerization of Activated Olefins
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Herein, Natures flavin-mediated activation of complex (poly)enes has been translated to a small molecule paradigm culminating in a highly (Z)-selective, catalytic isomerization of activated olefins using (-)-riboflavin (up to 99:1 Z/E). In contrast to the prominent Z → E isomerization of the natural system, it was possible to invert the directionality of the isomerization (E → Z) by simultaneously truncating the retinal scaffold, and introducing a third olefin substituent to augment A1,3-strain upon isomerization. Consequently, conjugation is reduced in the product chromophore leading to a substrate/product combination with discrete photophysical signatures. The operationally simple isomerization protocol has been applied to a variety of enone-derived substrates and showcased in the preparation of the medically relevant 4-substituted coumarin scaffold. A correlation of sensitizer triplet energy (ET) and reaction efficiency, together with the study of additive effects and mechanistic probes, is consistent with a triplet energy transfer mechanism.
- Metternich, Jan B.,Gilmour, Ryan
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p. 11254 - 11257
(2015/09/21)
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- Palladium(0)/copper(I)-cocatalyzed cross-coupling of the zinc reagent of ethyl 3-bromo-3,3-difluoropropionate with aryl (alkenyl) halides: An efficient stereoselective synthesis of β-fluoro-α,β-unsaturated esters
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Ethyl 3-bromo-3, 3-difluoropropionate was prepared in an overall yield of 75% from the radical addition of dibromodifluoromethane to ethyl vinyl ether under Na2S2O4 initiation, followed by oxidation of the acetal with Caro acid. The treatment of 1 with active zinc dust in anhydrous DMF at room temperature produced the zinc reagent ZnBrCF2CH2CO2C2H5 (2). The cross coupling of the zinc reagent 2 with aryl (alkenyl) halides (R-X) in DMF using Pd(0)-Cu(I) as cocatalyst stereoselectively provided the β-fluoro-α,β- unsaturated esters (RCF=CHCO2C2H5 4) directly and in moderate yields. An E/Z ratio ranging from 3:2 to 1:0 was observed. This is the first example that Cu(I) can improve the selectivity of the cross-coupling reaction. Mechanistic studies revealed that zinc reagent 2 underwent stereoselective elimination to produce (Z)-1-fluoro-2-(ethoxycarbonyl)ethenylzinc reagent 6, and then the cross-coupling of 6 with aryl(alkenyl) halides under palladium(O) catalysis afforded the β-fluoro-α,β-unsaturated esters 4.
- Peng, Sheng,Qing, Feng-Ling,Li, Yi-Qun,Hu, Chang-Ming
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p. 694 - 700
(2007/10/03)
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