Unique reactivity of a 1,4-dilithiobutadiene with methyl iodide

Reactions of 1,4-dilithiobutadiene 5 with MeI in THF gave predominantly methyl iododiene 6. Monolithio monoiodo intermediate 8 was shown not to be involved in the formation of 6, but the results were consistent with the involvement of monolithio monomethyl intermediate 11, which could lead to 6 by metal-halogen exchange. Several other lithioalkenes also reacted with MeI to give alkenyl iodides.