Metal‐Free Arylations of Oxygen and Nitrogen Nucleophiles : Applications of Diaryliodonium Salts
Sammanfattning: This thesis concerns development of new methods for metal‐free arylations in organic synthesis. The protocols discussed in the thesis are based on a class of hypervalent iodine compounds called diaryliodonium salts. These reagents are known to transfer aryl moieties to suitable nucleophiles.The first part describes O‐arylation of ethyl acetohydroxamate, which serves as a hydroxylamine equivalent. Electron‐rich as well as electron‐poor aryl groups could be transferred from the diaryliodonium salts. The arylation products could then be used as intermediates in a straightforward meta‐free one‐pot synthesis of benzofurans. Using this procedure, various substituted benzofurans were obtained in good yields. Furthermore, this methodology was used to synthesise the natural product Stemofuran A in one single step, starting from commercially available compounds. Three formal syntheses of other bioactive benzofurans were included.The second part describes N‐arylation of secondary acyclic amides. The chemoselectivity was explored with unsymmetric diaryliodonium salts, and aryl moieties with ortho‐substituents were preferably transferred. The protocol was suitable for electron‐deficient as well as highly sterically congested diaryliodonium salts. The transfer of electron‐rich aryl moieties was problematic. However, the reactivity for the amide was complementary to that of the salts and electron‐rich amides were phenylated in high yields. Furthermore, the protocol was compatible with benzamides and amides having sterically hindered acyl groups.Both arylation protocols discussed in this thesis work at ambient temperature and a variety of counter‐ions of the diaryliodonium salts were tolerated.
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