- 2-Ethoxyvinyllithiums and diethoxyvinyllithiums: What makes them stable or fragile?
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The elusive (E)-2-ethoxyvinyllithium can be readily generated in tetrahydrofuran at -75 °C from (E)-1-bromo-2-ethoxyethylene by halogen/metal exchange and subsequently trapped with electrophiles. Alkylation opens a convenient entry to (E)-configurated enethers. (E)-2-Ethoxyvinyllithium decomposes rapidly at -50 °C whereas its (Z)-isomer, which lacks the possibility to eliminate lithium ethoxide in a favorable anti-periplanar process, is stable under the same conditions. (E)-1,2-Diethoxyvinyllithium even sustains reflux temperatures (approximately 75 °C). 2,2-Diethoxyvinyllithium and (Z)-1,2-diethoxyvinyllithium can be conserved at 0 °C although this time loss of alcoholate can occur in the anti-mode. Obviously it matters whether the energy-rich ethoxyacetylene is formed as the elimination product or simple acetylene, as in the case of (E)-2-ethoxyvinyllithium.
- Schlosser, Manfred,Wei, Heng-Xu
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p. 1735 - 1742
(2007/10/03)
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- 2,2-Di(ethoxy)vinyllithium: A synthetic equivalent of the ethyl acetate anion
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2,2-Diethoxyvinyllithium can be readily generated from 2-bromo-1,1,-diethoxyethylene by treatment with butyllithium. When dissolved in tetrahydrofuran, it can be stored at -25°C for hours, but decomposes rapidly at 0°C.
- Wei,Schlosser
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p. 2771 - 2772
(2007/10/03)
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