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Author
Núñez Bendinelli, Alberto
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Abstract
Iodine is a characteristic halogen in terms of its reactivity. Due to its position in the Periodic Table, where the elements acquire a greater metallic character, iodine has a greater capacity to assume the oxidation states of +3 and +5, forming relatively stable species. Molecules that have iodine atoms in these unusually high valences are known as hypervalent iodine species. The present work focuses on trivalent iodine compounds, called λ3-iodans, and aims on the one hand to explain their fundamental chemistry, and on the other to develop a proposal regarding the use of these species in CH al·lilation reactions.
Due to their high oxidation state, hypervalent iodine species, as a whole, are often involved in oxidation reactions, including oxidative functionalization reactions of substrates. A new example of this last class of reactivity is the coupling of carbonate fragments in an arc that some types of aryl-λ3-IODA carry out. In these, the hypervalent iodine centers act as directing groups in the C-H functionalization of their aryl fragments. This characteristic reactivity was baptized as the iodonium Claisen reaction, due to its parallels with the classic rearrangement reaction discovered by Ludwig Claisen in 1912. Until today, al·lilació, propargylation and benzylation reactions have been described through the reaction iodonium-Claisen. In them, an allyl, propargyl and benzyl fragment, respectively, is coupled to the C-H bond of the ARE, without the need to use a metal catalyst. In recent years, our research group has focused on studying the pattern of reactivity defined by this reaction and exploring new methodologies within its scope. Along the same lines, this work also includes a set of proposals focused on the iodonium-Claisen alkylation reaction. In some of them the use of potential cyclic substrates of allyl silanes is proposed to carry out this coupling, the use of which is largely unexplored. Additionally, by way of illustrating the versatility offered by this kind of coupling of the hypervalent iodine species, a possible synthetic route of hopanoic acid is proposed via the iodonium-Claisen allylation reaction. This drug is widely used as a contrast agent to oral cholecystography tests, in addition to being marketed as a medication to treat hyperthyroidism.
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