Hydrogen migration and lithium iodide alpha-elimination in 1-iodo-1-lithioethene. Concerted vs stepwise mechanism.

1-Iodo-1-lithioethene is prepared from 1-iodoethene and LDA in THF. The lit hiated derivative can be trapped by electrophiles, but it readily decompose s to acetylene; the decomposition process cannot be analyzed by experimenta l techniques. Ab initio calculations indicate that 1-ioda-1-lithioethene sh ould be a monomer in a THF solution. Furthermore, hydrogen migration and li thium iodide alpha-elimination procedures should occur through a concerted mechanism. The activation barrier for the cis and trans hydrogen migration should be almost identical.