Lithium-halogen exchange alkyl iodides

Lithium-Halogen Exchange of Primary Alkyl Iodides.213... 

LITHIUM-HALOGEN EXCHANGE OF PRIMARY ALKYL IODIDES... 

Reactivity and yields are greatly enhanced by the presence of 0.5-1% Na in the Li. The reaction is also generally available for the preparation of metal alkyls of the heavier Group 1 metals. Lithium aryls are best prepared by metal-halogen exchange using LiBu" and an aryl iodide, and transmetalation is the most convenient route to vinyl, allyl and other unsaturated derivatives ... 

Even if not impaired by side reactions, the condensation of lithium, sodium, or potassium acetylides with alkyl halides is only moderately fast in ethereal media unless alkyl iodides or sulfonates are applied. Good results can be obtained in liquid ammonia. To speed up the reaction with primary alkyl bromides in THF, they may be performed in the presence of 10% of sodium iodide, in other words, under halogen/halogen exchange conditions. Polar solvents such as dimethylformamide (DMF) are mandatory with alkyl bromides and, a fortiori, chlorides. ... 

Buchachenko (1974) has advanced another theory. He based his reasoning on the absence of the CIDNP signals for the reaction of //-butyl iodide with t-butyl lithium conducted in ether at -70°C. The halogen and metal quickly exchange under these conditions, but the C—C bond does not form. In contrast to the preceding scheme, Buchachenko s theory assumes that the radicals produced form complexes with the alkyl lithium associates. Alkyl... 

Diphenylarsinomethyllithium (16) can be prepared by transmetallation of bis(diphenylarsino)methane (Scheme 17), or by halogen-lithium exchange of diphenylarsinomethyl iodide. The anion derived by the former method can be alkylated. 

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