In recent years the chemistry of cyclic iodonium salts has experienced ever‐growing development. The advantages of using cyclic iodonium salts over acyclic iodonium salts are that the reactions between cyclic iodonium salts and various nucleophiles lead, under suitable reaction conditions, to dual arylations in a one‐pot manner and to the formation of new heterocycles. Variously functionalized thiophenes, carbazoles, fluorenes, phenanthrenes and triazolophenanthridines have been synthesized by utilizing cyclic diaryliodonium salts. Various new ladder‐type π‐conjugated systems have also been synthesized by employing cyclic iodonium salts. In this microreview, the recent advancements in the synthesis and application of cyclic diaryliodonium salts are discussed in a systematic and concise manner.
A mild, convenient and transition metal free methodology for oxidative ipso nitration of diversely functionalized organoboronic acids, including heteroaryl- and alkylboronic acids, has been developed at ambient temperature using a combination of [bis-(trifluoroacetoxy)]iodobenzene (PIFA) - N-bromosuccinimide (NBS) and sodium nitrite as the nitro source. It is anticipated that the reaction proceeds through in situ generation of NO2 and O-centred organoboronic acid radicals followed by the formation of an O-N bond via combination of the said radicals. Finally transfer of the NO2 group to the aryl moiety occurs through 1,3-aryl migration to provide the nitroarenes.
An efficient, metal and base-free, chemoselective synthesis of aryl-, heteroaryl-, and alkyl primary amines from the corresponding boronic acids has been achieved at ambient temperature mediated by [bis(trifluoroacetoxy)iodo]benzene (PIFA) and N-bromosuccinimide (NBS) using cyanamidyl/arylcyanamidyl radicals as the aminating species. The primary amine compounds were initially obtained as their corresponding ammonium trifluoroacetate salts which, on treatment with aq NaOH, provide the free amines. Finally, the primary amines were isolated through column chromatography over silica-gel using hexane-EtOAc solvent system as the eluent. The reactions are sufficiently fast, completing within 1 h. Quantum chemical calculations in combination with experimental observations validate that the ipso amination of substituted boronic acids involves the formation of cyanamidyl/arylcyanamidyl radical, followed by regiospecific interaction of its nitrile-N center with boron atom of the boronic acids, leading to chemoselective primary amination.
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