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

Article abstract of DOI:10.1016/S0040-4020(96)01075-7

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.