(Stranger)
07-15-03 09:09
No 447353
(Rated as: excellent)
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 Reaction
Klapars, 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.
(Chief Bee)
07-15-03 15:53
No 447454
That's a very nice article, but you got the DOI all wrong (both the markup and the actual DOI). Here's the correct one, as well as the full article.
Copper-Catalyzed Halogen Exchange in Aryl Halides: An Aromatic Finkelstein Reaction
Klapars, A.; Buchwald, S. L.
J. Am. Chem. Soc. 124, 14844-14845 (2002) (../rhodium/pdf /aromatic.fin
DOI:10.1021/ja028865v - Supporting Information (Experimental) (../rhodium/pdf /aromatic.fin
(Hive Bee)
07-21-03 21:44
No 448866
(Rated as: excellent)
ORGANIC LETTERS 2002 Vol. 4, No. 6 973-976.pdf (http://www.angelfire.lycos.com/scifi2/l
DOI:10.1021/ol025548k
Abstract: A simple and mild method for the coupling of aryl iodides and aliphatic alcohols that does not require the use of alkoxide bases is described. The reactions can be performed in neat alcohol. For more precious alcohols, the etherification was carried out in toluene as solvent using 2 equiv of alcohol. Additionally, the cross-coupling of an optically active benzylic alcohol with an unactivated aryl halide was demonstrated to proceed with complete retention of configuration.
Typical Experimental Procedure
A test tube was charged with CuI (10 mol %), 1,10-phenanthroline (20% mol), Cs2CO3 (1.4-2.0 mmol), aryl iodide (1.0 mmol), and either (a) the alcohol (1 mL) or (b) the alcohol (2 mmol) and toluene (0.5 mL). The test tube was sealed, and the reaction mixture was stirred at 110 °C for ~24 h. The resulting suspension was cooled to room temperature and filtered through a 0.5 x 1 cm pad of silica gel, eluting with diethyl ether. The filtrate was concentrated. Purification of the residue by flash chromatography on silica gel gave the desired product.
Lego's voice: Usually the corresponding alkoxide are used for the alcoholysis of aryl iodides. These alkoxides are moisture sensitive and strong corrosive bases. The disadvantage of this method is, although the authors do not mention it, is that the reaction is carried at a higher temperature than the boiling point of the alcohol. Methanol and ethanol boil at 65 °C resp. 78 °C, allyl alcohol which might bee of interest for the synthesis of allylbenzenes has a boiling point of 97 °C. Therefore the reaction vessel and its environment has to bee protected against overpressure.
The candle that burns twice as bright burns half as long
(Chief Bee)
08-13-04 06:35
No 525185
(Rated as: excellent)
Novel and Simple Solvent-Free Method for Nucleophilic Aromatic Substitution of Inactive Aryl Halides
M. M. Hashemi, M. Akhbari
Synth. Commun. 34(15), 2783-2787 (2004) (../rhodium /nas.so
Abstract
A simple, high yield, and short time method for nucleophilic displacement reaction of inactive aryl halides is reported. The reaction is performed in microwave oven under thermal condition with montmorillonite supported AgNO3.
The Hive - Clandestine Chemists Without Borders
(arrogant bee of the day)
08-13-04 10:52
No 525221
At the risk of sounding dumb and not caring, but trying to learn. Can someone please explain to us what implications/relevance this has to us in simple chemistry terms? This isn't the novel or serious forum after all. Can we kind of make it a general rule, because I read everything here ever the last 6 years and heaps of shit sounds exciting but I don't see the relevance because stated patents are for other substances and I can't correlate them to relevant ones we know.
I'm not fat, I'm just too short for my weight.
http://www.whatreallyhappened.com
(Hive Bee)
08-15-04 22:16
No 525574
Halogenated aromatics are useful substrates for the synthesis of several drug precursors, e.g. vaniline via bromination, hydroxylation and methylation is a precursor for mescaline or methylenation and bromination of catechol gives a precursor for safrole.
The article posted by Ziqquratu is of interest because aryl iodides are much more reactive than aryl bromides and sometimes essentiell for certain reactions. Aryl bromides can bee easily prepared (often more easily than iodides) and then converted to aryl iodides.
Why Lego posted this article was to show another way of performing these reactions. The classical introduction of a methoxy group either needs methoxides (for some bees they are hard to get) or a methylating agent (in general unhealthy), so the article posted above would show an alternative to this reaction.
Reaction of 4-iodo-anisole with allyl alcohol would give after claisen rearrangement an exellent precursor for the 2,5-dimethoxysubstituted compounds.
Rhodiums articles offer another possibility to converte halogenated aryls to phenols and the exchange of a halogen to a cyano group is another possibility to get a benzaldehyde after partial reduction.
This is why Lego thinks that these articles might bee relevant for clandestine chemistry, perhaps not a break-through like the Wacker reaction but they might show novel ways to the desired compounds.
The tendency is to push it as far as you can