Novel, radical cations

Imakubo T, Sawa H, Kato R (1995) Novel radical cation salts of organic )t-donors containing iodine atom(s) the first application of strong intermolecular-I -X-(X=CN, halogen atom) interaction to molecular conductors. Synth Metals 73 117-122... 

Zimmerman, H.E. and Hoffacker, K.D. Novel radical cation reactions of bichromophoric systems. Transannular aryl migrations mechanistic and exploratory organic photochemistry, /. Org. Chem., 61, 6526-6534, 1996. 

Chiral 2-imidazoline dianions undergo one-electron oxidation in the presence of TEMPO (2,2,6,6-tetramethyl-l-piperidinyloxy) to form a radical anion that is either trapped stereoselectively by TEMPO or undergoes dimerization. Oxidation of bis-diazene oxides leads to novel (9-stabilized 4N/3e radical cations and 4N/2e dications. These were detected by ESR spectroscopy and cyclic voltammetry. B3LYR/6-31G calculations confirmed the nature of the 4N/3e and 4N/2e systems. ... 

The one-electron oxidation of iV-benzylphenothiazine by nitric acid occurs in the presence of /i-cyclodextrin, which stabilizes the radical cation by incorporation into its cavity. The reaction is inhibited by adamantane, which preferentially occupies the cavity. Novel Pummerer-type rearrangements of / -sulfinylphenyl derivatives, yielding /7-quinones and protected dihydroquinones, and highly enantioselective Pummerer-type rearrangements of chiral, non-racemic sulfoxides have been reviewed. A comprehensive study has demonstrated that the redox potential for 7- and 8-substituted flavins is linearly correlated with Hammett a values. DFT calculations in [3.3.n]pro-pellanes highlight low ionization potentials that favour SET oxidative cleavage of the strained central C-C bond rather than direct C-H or C-C bond attack. Oxidations and reductions in water have been reviewed. ... 

Additional examples of these novel SET-promoted photorearrangement reactions were uncovered in our investigations with the 2-azadienes 78 and 82. These substances yield the corresponding A-vinylaziridines 93 and 94, respectively, upon DCA-sensitized irradiation (Structures 93-99). The study was extended to azadiene 73. The DCA-sensitized irradiation of 73 yields the aziridine 95 and the dihydroisoindole 96 [65]. However, under these conditions, 2-azadiene 97 affords, in addition to the expected aziridine 98, the dihydroisoquinoline 99. The formation of the isoindole 96 can be explain by a pathway in which a radical-cation centered on the C—double bond attacks the phenyl ring at C-3, as shown in Scheme 15. The formation of the dihydroisoquinoline 99 can be justified by... 

Recently, Kochi et al. described a novel photochemical synthesis for a-nitration of ketones via enol silyl ethers. Despite the already well-known classical methods, this one uses the photochemical excitation of the intermolecular electron-donor-acceptor complexes between enol silyl ethers and tetranitrometh-ane. In addition to high yields of nitration products, the authors also provided new insights into the mechanism on this nitration reaction via time-resolved spectroscopy, thus providing, for instance, an explanation of the disparate behavior of a- and (3-tetralone enol silyl ethers [75], In contrast to the more reactive cross-conjugated a-isomer, the radical cation of (3-tetralone enol silyl ether is stabilized owing to extensive Tr-delocalization (Scheme 50). 

Kodani M, Takamori A, Takimiya K, Aso Y, Otsubo T (2002) Novel conductive radical cation salts based on methylenediselenotetraselenafulvalene (MDSe-TSF) a sign of superconductivity in K-(MDSe-TSE)2Br below 4 K. J Solid State Chem 168 582-589... 

Some of the materials highlighted in this review offer novel redox-active cavities, which are candidates for studies on chemistry within cavities, especially processes which involve molecular recognition by donor-acceptor ii-Jt interactions, or by electron transfer mechanisms, e.g. coordination of a lone pair to a metal center, or formation of radical cation/radical anion pairs by charge transfer. The attachment of redox-active dendrimers to electrode surfaces (by chemical bonding, physical deposition, or screen printing) to form modified electrodes should provide interesting novel electron relay systems. 

The novel delocalized X -phosphorin radical cation 58 is unusually stable and quite insensitive to air. 

A novel synthesis of 5,6-dihydro-4//-1,2-oxazines (20) is presented via the photo-induced cyclization of y. d-unsaturated oximes (21) see Scheme 4. Irradiation of (21) in the presence of 9,10-dicyanoanthraccnc (DCA) led to the heterocycle (20) only. The proposed mechanism proceeds via the radical cation (22), generated by single-electron transfer (SET) from the oxime (21) to the excited sensitizer (DCA. Cyclization of (22) affords the oxazine (20) after proton transfer to the DCA radical anion (DCA ) and H abstraction.61... 

A number of electrocyclic reactions under PET conditions have been reported. In this way, A-benzyl-2.3-diphcnylaziridinc (40) underwent a 3 + 2-cycloaddition with alkene and alkyne dipolarophiles to afford substituted pyrrole cycloadducts (41) via the radical cation intermediate (42) see Scheme 7.80 Elsewhere, novel arylallenes have been used as dienophiles in a radical cation-catalysed Diels-Alder cycloaddition reaction with 1,2,3,4,5-pentafluromethylcyclopentadiene, which often occurred with peri-, chemo-, facial- and stereo-selectivity.81... 

The novel arenium ion 95 was synthesized266 by one-electron oxidation of the triphenylene-based starting compound to form a radical cation which abstracted a chlorine atom with a concomitant rearrangement to yield the hexachloroantimonate salt. The arenium ion character is apparent from the 13C spectrum (three signals at 813C 212.9, 187.6, and 173.6) and from the bond distances, which are very close to those shown for ion 91. Cation 95 can be stored at room temperature for months. This exceptional stability was attributed to the annelation to the two bicyclo[2.2.2]octane units and the spiroconjugation effect of the fluorenyl moiety.267... 

TTF (tetrathiafulvalene) and related compounds have been the subject of intense interest in the materials chemistry community because of their semi-conduction and superconduction properties. Recently, TTF has emerged as a unique radical initiator because its radical cation can be easily formed. The ease of formation is presumably derived from the favorable structure of the radical cation that incorporates an aromatic disulfonium salt and a very delocalized radical [49a]. Murphy et al. demonstrated a novel one-pot reaction cascade... 

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