2-Ethoxyvinyllithiums and diethoxyvinyllithiums: what makes them stable or fragile?

The elusive (E)-2-ethoxyvinyllithium can be readily generated in THF at -75 Deg 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 decomps. rapidly at -50 Deg whereas its (Z)-isomer, which lacks the possibility to eliminate LiOEt in a favorable antiperiplanar process, is stable under the same conditions. (E)-1,2-Diethoxyvinyllithium even sustains reflux temps. (.apprx.75 Deg). 2,2-Diethoxyvinyllithium and (Z)-1,2-diethoxyvinyllithium can be conserved at 0 Deg 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. [on SciFinder (R)]