S. Peng, F. Qing, and Yi-Zhi Li
Jan 20, 2000
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0
Influential Citations
29
Citations
Journal
Journal of Organic Chemistry
Abstract
Ethyl 3-bromo-3, 3-difluoropropionate (1) 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 (RCFCHCO2C2H5 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(0) catalysis afforded the β-fluoro-α,β-unsaturated esters 4.