Binaphthyls anion-radicals

The final stage of the reaction in Scheme 3.65 involves protonation, yielding the derivative of 1,4-dihydronaphthalene. The oxidation may produce a 4-substituted binaphthyl, which is not contaminated with the isomeric products. It is worth noting here that the described ion-radical method of introduction of the alkyl group into the aromatic nucleus has an advantage over the radical or heteroly tic alkylation. In these cases, the neutral substrate may produce a composite mixture of isomeric products. The binaphthyl anion-radical reaction proceeds regioselectively and nonstereospecifically. 

It is therefore somewhat surprising that in the biperylenyl anion radical Baumgarten et al. (1993) observed a localization of the unpaired electron in one moiety only, although the steric situation is anticipated to be similar to that in the binaphthyl anion radical. This is explained by the fact that the atomic orbital coefficients of the single-occupied molecular orbital for the bridgehead positions are larger for the binaphthyl anion radical than for the biperynyl anion radical. Therefore, the interaction of the separate entities is more decoupled in the biperynyl case. 

The anion-radical of 1,T-binaphthyl acts as the single 77-system with homogeneous spin distribution. Comparison between 1,1 -binaphthyl and biperylenyl in Scheme 3-9 shows their structural similarity. 

Sometimes transformation of aromatic compounds into ion radicals sets stereochemically unusual forms. For instance, the enantiomeric binaphthyls racemize, being converted into the anion radical state and then being oxidized. Let us examine causes for this racemization. 

The attachment of a R3Si (31) or an biphenylyl (30) group enhances the electron affinity of a benzene ring. Such substitution permits biphenyl rings (33) or the triphenylene system (32) to be generated readily. Collateral evidence in support of radical-anionic intermediates in these reactions has been obtained (5). Another example of the intramolecular cyclization is the formation of perylene from 1,1 -binaphthyl. 

DCA sensitisation of tri-1-naphthyl phosphate or di-l-naphthyl methyl-phosphonate results in formation of l,r-binaphthyl. The reaction occurs only in compounds with at least two naphthyl substituents linked by an 0-P(0)-0 chain. Reaction involves intramolecular face-to-face dimerisation of the two naphthyl units within the radical cation (445), followed by elimination of the 1,1 -binaphthyl radical cation, which is subsequently reduced by the DCA radical anion. In a related reaction DCA-sensitisation of bis(3,4-methylenedioxy-phenyl) methylphosphonate in acetonitrile gives 2-(3,4-methylenedioxyphenyl)-4,5-methylenedioxyphenyl methylphosphonate whereas direct irradiation in methanol gives bis(3,4-methylenedioxy)biphenyl as an additional product. " ... 

A large number of aromatic hydrocarbon radical anions has been reacted with Wurster s Blue-type radical cations, e.g. the radical anions of 1-phenylnaph-thalene, 8,8 -dimethyl-naphthalene, 1,1 -binaphthyl, p-terphenyl, chrysene, 1,2-dimethylchrysene [29]. They all represent energy-deficient systems, so that triplet-triplet annihilation had to be regarded as the mechanism for the production of the emitting singlet state. The quantum yields were in the range 10" to 10" Einstein/mol [29]. 

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