OK, I once again ran a search, but couldnt find this article listed on here. Thanks have to go to Organikum from another board (
www.sciencemadness.org) - I dont know if this is the same Organikum that we have here, although I would have assumed that if it were then he would have posted this by now... anyways...
Copper Catalyzed Halogen Exchange in Aryl Halides: An Aromatic Finkelstein ReactionKlapars, A. and Buchwald, S. L. (2002) JACS 124(50) 14844-14845 DOI:
DOI: 10.1021/ja027493n
ABSTRACT:
A mild and general method for the conversion of aryl, heteroaryl, and vinyl bromides into the corresponding iodides was developed utilizing a catalyst system comprising 5 mol % of CuI and 10 mol % of a 1,2- or 1,3-diamine ligand. A variety of polar functional groups are tolerated, and even N-H containing substrates such as sulfonamides, amides, and indoles are compatible with the reaction conditions. Both the reaction rate and the equilibrium conversion of the aryl bromide depend on the choice of the halide salt and the solvent. The best results were obtained using NaI as the halide salt and dioxane, n-butanol, or n-pentanol as the solvents.
The catalysts tested included, for example, trans-1,2-dimethylaminocyclohexane (which was effective at relatively low temperature), while something like 1,3-diaminopropane required higher temperatures. It may even be possible to use something as simple as ethylene diamine (VERY common, espescially when it comes to transition metal complex chemistry) as a catalyst. For aryl halides, yeilds on all tested samples were in excess of 90%, no yeilds given for the vinyl substitutions (according to the suporting information, they are lower than for aryl substitutiions - one example gave a 77% yeild). Also, it seems that when using chlorides, the yeilds suffer - 4-chlorotoluene gave a mere 33% yeild of 4-iodotoluene.
Reading the supporting information (available with the article), the process is somewhat oxygen and water sensitive. The reactions were carried out in a dried Schlenk tube under an argon atmosphere, with solids being added through the lid, then a septum being placed in the tube and liquid reagents added via syringe. Also, the procedure seems very selective - in the given examples, it did not in any way touch carbonyl derivitaves, nitriles, amines or sulfonamides.