Preparation and reactions of long-chain alkyllithiums bearing a remote carbon-carbon $\pi$-bond

The cyclization of 5-hexenyl- and 6-heptenyllithiums provides a convenient route to a variety of functionalized five- and six-membered carbocyclic systems. The facile ring-closure of such unsaturated alkyllithiums is a consequence of energetically favorable coordination of the lithium atom with the $\pi$-system in both the ground state of the molecule and in the transition state for the cyclization. Attempts have been made to extend this methodology for the construction of large rings. To this end, a variety of long-chain iodides bearing a remote carbon-carbon $\pi$-bond activated by an anion-stabilizing substituent or an allylic leaving group were prepared using standard synthetic procedures. These substrates were found to undergo lithium-iodine exchange to give the corresponding alkyllithiums in quantitative yields. However, attempts to cyclize these long-chain alkyllithiums, under a variety of experimental conditions, failed.