Catalysis iodine

Waters, H. D. C., A. R. Caverhill and P. W. Robertson The Kinetics of Halogen Addition to Unsaturated Compounds, Part XII. Iodine Catalysis of Chlorine and Bromine Addition to Ethyl Cinnamate. J. chem. Soc. (London) 1947, 1168. 

While only two geometrical isomers exist in simple unsaturated molecules, a number of cis-trans isomers can exist in polyenes (e.g. carotenoids ). Normally, the alI-/ra/w-isomer is preponderant in carotenoids. Isomerization of the all-ftms-carotenoids by acid- or iodine-catalysis yield the so-called neo-carotenoids. The neo-carotenoids are believed to possess one c/s-ethylenic bond in the central position of the conjugated chain9. The neo-carotenoids exhibit not only a weaker long wavelength band 470 nyx) than the all... 

The key step of the synthesis is the rearrangement of the a-acetylenic alcohol 97 into the unsaturated carbonyl compound 124. This rearrangement was carried out with tris(triphenylsilyl)vanadate, triphenylsilanol and benzoic acid to give a mixture of the isomers 124 and 125. The latter was converted by iodine catalysis into the desired isomer 124. This key intermediate was afterwards transformed into the Cis-phosphonium salt 123 by standard procedures. The Wittig olefination of the Cio-dial 45 first with the fucoxanthin end group 123 and then with the peridinin end group 122 gave, in five steps, the C4o-carotenoid 126. Finally the epoxidation of this compound resulted in optically active fucoxanthin (121) and its (5S,6R)-isomer (Scheme 28). 

Iodine catalysis can also promote full (thermal) cis-to-trans conversion of enclathrated cfa-stilbene. The absence of any sign of partial conversion supports the idea that the overall process is not biased by the presence of particular sites... 

Oxazolidiaones. Under iodine catalysis, carbon dioxide reacts with aziridines to form 2-oxazolidinones (equation I). In the case of aziridine itself the yield is somewhat low (21.5%) because of polymerization. ... 

Since the beginning of the twenty-first century, the organic chemistry of hypervalent iodine compounds has experienced an unprecedented, explosive development. Hypervalent iodine reagents are now commonly used in organic synthesis as efficient multipurpose reagents whose chemical properties are similar to derivatives of mercury, thallium, lead, osmium, chromium and other metals, but without the toxicity and environmental problems of these heavy metal congeners. One of the most impressive recent achievements in the field of iodine chemistry has been the discovery of hypervalent iodine catalysis. 

Thus, at the moment it is difficult to say whether (or to which extent) the type of activation depicted in Fig. 4 is indeed relevant for the reported cases of iodine catalysis. Although no conclusive mechanistic studies have been published, in a few cases it could be shown by comparison experiments that hydrogen iodide is less active than iodine in the respective reaction (for an example, see Scheme 7) [89, 90]. While this rules out hidden acid catalysis, there is clearly a need for further detailed mechanistic investigations of iodine-catalyzed reactions. 

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