Fluorenyl anion

That is, just as oxidation of tetrabenzo[5.5]fulvalene resulted in formation of two antiaromatic fluorenyl cations linked by a single bond, reduction should give two aromatic fluorenyl anions, linked by a single bond, 20. We call this relationship the aromaticity/antiaromaticity continuum and can apply the same measures of aromaticity to 20 as were applied to 3, to evaluate relative aroma-... 

The rates of oxidation of fluorenyl and diphenylmethyl anions are correlated by simple Hiickel MO calculations. Loss of an electron from fluorene anion involves electron transfer from a bonding orbital (0.18 / ). On the other hand, the electron lost from the diphenylmethide ion will come from a nonbonding orbital. Thus, the transfer of an electron to oxygen will occur more readily from the diphenylmethide ion than from the fluorenyl anion. 

By aromatization of the five-membered ring with Li the helicene 62 is obtained. In this compound the ring current in ring B is restored, but the distance between the terminal rings is enlarged compared to hexahelicene. By an accurate analysis of the shifts and comparison with the 8-values of the fluorenyl-anion the shifts of all protons except that of H(16) could be ascribed to the effects of i, ii and iii. The large downfield value of H(16) must be ascribed to the neighbourhood of the Li+-ion in the contact ionpair. 

A typical cyclic voltammetric trace for the anodic oxidation of the fluorenyl anion 2 at platinum is shown in Figure 1. The oxidation potential for this and several other resonance stabilized carbanions lies conveniently within the band gap of n-type Ti02 in the non-aqueous solvents, and hence in a range susceptible to photoinduced charge transfer. Furthermore, dimeric products (e. g., bifluorenyl) can be isolated in good yield (55-80%) after a one Faraday/mole controlled potential (+1.0 eV vs Ag quasireference) oxidation at platinum. 

Activated nitro and halo substituents have been efficiently replaced by a variety of alkyl groups via SsAx reaction with carbanions. Examples include the displacement of the nitro group in compounds (10 X = 4-PhCO, 4-MeOCO, 4-CN, 4-N02, 4-PhS02, 3,5-(CF3>2) by the anion of 2-nitropropane in HMPA at room temperature (equation 2),83 and the reaction of p-dinitrobenzene with several ketones, esters and nitriles (RH equation 3) in Bu OK/liquid NH3 at -70 C.84 Interestingly, under the latter reaction conditions, p-chloronitrobenzene gave the product of alkylation rather than of SNAr displacement of chloride, as in equation (4).85 Further examples include the dehalogenation of p-halonitrobenzenes by 9-fluorenyl anions in DMSO at room temperature,34 and dehalogenation and denitration reactions by the carbanions of phenyl- and diphenyl-acetonitrile in DMSO or under PTC conditions.86... 

Electron photodetachment spectra for indenyl and fluorenyl anions have been measured and the electron affinities of the corresponding radical and bond dissociation energies of the corresponding neutrals determined. Comparison has been made with solution-phase data in an attempt to determine the dependence of gas and solution properties on ionic size and extent of charge distribution.3 Benzocyclopropenyl anion... 

The unique feature of the alkyllithium compounds that makes them useful as diene initiators is their character as exceedingly powerful bases yet they are soluble in organic solvents and quite thermally stable. Alkyllithium compounds are sufficiently basic to add to hydrocarbon monomers. However, lithium salts of stabilized anions, such as acetylide and fluorenyl anions, are too weakly basic to add to such double bonds. Similarly, alkoxides and mercaptides fail to react with hydrocarbon monomers, but lithium alkyl amides react analogously to alkyllithium compounds. 

Contrary to the resonance stabilized triphenylmethyl-4), benzyl-5) and fluorenyl-anions 8, phenyllithium did not leave the tetramethylammonium ion unaffected. Instead, it removed a proton to form trimethylammonium-methylide (<5) 19), the prototype of that interesting class of zwitter-ionic compounds for which Wittig coined the name ylides 20). 

Further sulfone pyrolyses of both-sided benzylic disulfones by Haenel et al. led to the [2.2]phanes 150 and 151 possessing the fluorene skeleton [58]. By reduction to the 9-fluorenyl anion an aromatic unit can be incorporated into these phanes. Even fluorene units tolerate the conditions for the pyrolysis giving an example for carbonyl-containing phanes that can be synthesized by sulfone pyrolysis. 

A route has been developed by Shu, Jen, and co-workers for the synthesis of a fluorene monomer 63 bearing two aryloxadiazole groups at the bridgehead by nucleophilic substitution of 4-fluorobenzonitrile with the fluorenyl anion, followed by conversion of the nitriles to oxadiazoles via tetrazole intermediates (Scheme 29) [98]. The EL efficiency of the alternating copolymer 64 in a single-layer device is considerably higher than for the PDAF homopolymer... 

Hydride abstraction of 1-(cycloprop-2-enyl)indenes and 9-(cycloprop-2-enyl)fluorenes 15 (obtainable by the reactions of 1,2-disubstituted cyciopropenylium ions and the indenyl or fluorenyl anion) with the tritylium cation, followed by treatment with tertiary amines, is one of the earliest calicene syntheses affording 1,2-benzocalicenes and 1,2 3,4-dibenzocalicenes 16. ... 

Hie cleavage of ethylene oxide by alkali salts of 9-methyl-fluorenyl anion was investigated in several ethereal solvents by Sigwalt and Boileau112. At a salt concentration lower than 1(T4 M, the reaction is first order in the oxide and in the salt. However, at... 

The fluorenyl moiety on the end of a polymer may act as a chain transfer agent. Its acidic 9-proton may terminate a growing polymer yielding a fluorenyl anion substituted in 9 position by a polymer chain... 

By reaction with n-butyllithium, 17 and 18 can be converted into the red syn- and anti-[2.2] (2,7)fluorenophane dianions in which the electron-rich 9-fluorenyl anions are the interacting arenes (27). A second example of such double-layered dianions, the [2.2](4,7)indenophane dianion, has been described recently (47). 

The 9-fluorenylmethyl group, in the guise of the 9-fluorenylmethoxycarbonyl or Fmoc group, is the keystone in modern solid-phase peptide synthesis and we will examine its enormous influence in section 8.3.5. The great virtues of the 9-fluorenylmethyl group have also been adapted to the protection of carboxylic acids as 9-fluorenylmethyl esters (see section 6.5.3). Bodanszky and Bednarek realised the opportunity for extending the principle of 9-fluorenylmethyl activation, the aromaticity of the fluorenyl anion, to the protection of cysteine in peptide synthesis. 9-Fluorenylmethyl thioethers are stable towards iodine and acidic conditions, including HF, but they easily eliminate on treatment with piperidine or DBU. 

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