Iodine as oxidant

Nucleophilic Trapping of Radical Cations. To investigate some of the properties of Mh radical cations these intermediates have been generated in two one-electron oxidant systems. The first contains iodine as oxidant and pyridine as nucleophile and solvent (8-10), while the second contains Mn(0Ac) in acetic acid (10,11). Studies with a number of PAH indicate that the formation of pyridinium-PAH or acetoxy-PAH by one-electron oxidation with Mn(0Ac)3 or iodine, respectively, is related to the ionization potential (IP) of the PAH. For PAH with relatively high IP, such as phenanthrene, chrysene, 5-methyl chrysene and dibenz[a,h]anthracene, no reaction occurs with these two oxidant systems. Another important factor influencing the specific reactivity of PAH radical cations with nucleophiles is localization of the positive charge at one or a few carbon atoms in the radical cation. 

Diphenyl ether undergoes cleavage on ultraviolet irradiation in alcoholic solvents,but irradiation of dilute solutions in cyclohexane in the presence of an equimolar amount of iodine as oxidant produces dibenzo-furan As in heteroatom-directed photoarylations, a conrotatory elec-trocyclization producing the carbonyl ylide intermediate 40 (Scheme 1) is... 

As oxidation reactions may often be complicated by further attack on the product by the oxidant, the choice of both oxidant and reaction conditions is critical. Ferric chloride under CO is the oxidant of choice, but even this sometimes causes cluster breakdown or buildup (see Section II,B.3). Mercuric salts have been used in the oxidation of [Co6(CO)i4] and [Cog(CO)i5] to give Cog(CO)i6 (138,389), but condensation of two cluster species incorporating atomic Hg may occur, as in the oxidation of [OsiqC(CO)24] to [Os2oHg(C)2(CO)48] (338). Iodine has been used successfully in a few cases, for example in the one-electron oxidation of [Fe3Pt3(CO)i5] to the monoanion [Fe3Pt3(CO)u] (283), as well as in the two-electron oxidation of [Os6(CO),g] to Os6(CO),g (88). As discussed in Section III,A,2, however, the use of iodine as oxidant often results in the addition of I to the anionic cluster. 

Development of novel oxidation reactions in water using /,(9-heterocycles with hypervalent iodine as oxidants 04YGK116. 

Laarhoven has examined the fate of the dihydrophenanthrene intermediate (148) formed by photocyclisation of the styryl benzo-phenanthrenes (149). When the reaction is performed in the presence of iodine as oxidant the expected arene (150) is obtained but in the absence of the oxidant compound (148) rearranges to the more stable, isolable dlhydroarenes (151) and (152). This rearrangement is base catalysed and the proportions of (151) and (152) isolated depend upon the nature of the base and the solvent. 

Oxidative doping enhances conductivity in conjugated polymers. Using iodine as oxidant in the case of methylacetylene/HZSM-5 gave UV-VIS spectra that essentially look hke a superposition of the separate spectra of I2 and methy-lacetylene in HZSM-5 (Fig. 39) and confirm that, as electron-deficient entities, the cationic species will not be readily oxidized further. 

Thiophen Analogues of Helicenes.— The photocyclization with iodine as oxidant of 1,2-di(diheteroaryl)ethenes, in which the heteroaryl group is derived from benzo[fe]thienyl or from tricyclic systems such as (434) or (440), is the key step in the synthesis of heterohelicenes. The ethylenes in turn are prepared from the aldehydes and the chloromethyl derivatives via phos-phonium salts or phosphonates through the Wittig reaction. The Bestmann method was also used for the synthesis of symmetrically substituted ethylenes from phosphonium periodates. Thus from (443) the heterohexahelicene (444) was obtained, (445) gave (446), and the hetero-heptahelicene (448) was obtained from (447). The undecahelicene (450) was prepared from (449). - These syntheses illustrate the fact that heterohelicenes are more easily available than helicenes, as the necessary aldehyde is prepared by metalation of (448) with butyl-lithium followed by reaction with iV-methylformanilide. The heptahelicene (452) was obtained by a double photocyclization of (451). 

Dixanthogen can also be produced from xanthate by adopting ammonium sulfate, high electrovalent metal ion, or iodine as oxidizer. The oxidation reactions of xanthate can be expressed as follows ... 

The bis(thienoquinolyl)ethene derivatives 24a—c are photocycUzed with iodine as oxidant and furnish diazadithia[7]helicenes 25a—c in good yields (Scheme 10) (2013CEJ12077). In this case, the ring closure occurs between the two y carbons of pyridine rings. 

Stoichiometric intermolecular amination reactions of arenes have been explored to a larger extent recently. Of major interest had been the investigation on the behavior of phthalimide in the presence of hypervalent iodine as oxidation promoter, which was simultaneously reported by DeBoef and Chang (Scheme 6) [20, 21], The respective reactions of p-xylene 26 to 2-phthaloyl xylene 27 and arenes 28 to... 

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