A highly stereospecific synthesis of (E)- or (Z)-alpha-fluoro-alpha,beta-unsaturated ketones 4, via a kinetically controlled Negishi palladium-catalyzed coupling reaction, was developed, providing an easy and general access to valuable fluorinated intermediates (pharmaceutical, peptide mimic, and so on). The synthesis involved a reaction between E/Z gem-bromofluoroolefins 2 and alkoxyvinylzinc species 6 under controlled reaction temperature. At 10 degrees C, (Z)-4 (70 to 99% yields) was obtained along with unreacted (Z)-2 (66 to 99% yields). At THF reflux, the recovered olefin was transformed into (E)-4 (up to 98% yield).
2006
Halogen compounds Q 0090First Stereospecific Synthesis of (E)-or (Z)-α-Fluoroenones via a Kinetically Controlled Negishi Coupling Reaction. -Treatment of a mixture of (E)-and (Z)-bromofluoroalkenes with vinylzinc chlorides at 10°C results in selective formation of (Z)-α-fluoroenones. At this temperature only the (E)-isomers are converted. The (Z)-isomers do not react and can easily be separated from the products. At 55-70°C the (Z)-isomers also undergo Negishi coupling to give (E)-α-fluoroenones which sometimes undergo isomerization. -(DUTHEUIL, G.; PATUREL, C.; LEI, X.; COUVE-BONNAIRE, S.; PANNECOUCKE*, X.; J. Org. Chem. 71 (2006) 11, 4316-4319; Inst. Rech. Chim. Org. Fine Heterocycl., CNRS, Inst. Natl. Sci. Appl. Rouen, F-76131 Mont-Saint-Aignan, Fr.; Eng.) -Jannicke 43-070
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