Fluorenes, formation

Photolysis of spiro[fluorene-9,3 -indazole] (384) to the tribenzopentalene (385) has been rationalized in terms of the initial formation of triplet diradical (386) (76JOC2120). The spiroindazole (387) behaves differently and on irradiation in THF is converted into the dimer (388) and the stable iV-ylide (389) (76CB2596). 

Quaternization of harman (235) with ethyl bromoacetate, followed by cyclization of the pyridinium salt 236 with 1,2-cyclohexane-dione in refluxing ethanol yielded an ester which on hydrolysis gave the pseudo-cross-conjugated mesomeric betaine 237. Decarboxylation resulted in the formation of the alkaloid Sempervirine (238). The PCCMB 237 is isoconjugate with the 11/7-benzo[u]fluorene anion—an odd nonalternant hydrocarbon anion—and belongs to class 14 of heterocyclic mesomeric betaines (Scheme 78). 

Non-enolizable imines such as 9-fluorene imines react with alkynylcarbene complexes to afford mixtures of mesoionic pyrrolium carbonyltungstates and dihydropyrrole derivatives [68] (Scheme 23). Although both compounds can be considered as [3C+2S] cycloadducts, formation of each of them follows a very different pathway. However, the first intermediate of the reaction is common for both compounds and supposes the conjugated addition of the imine to the alkynylcarbene complex to form a zwitterionic intermediate. A cyclisation... 

Some diamines carrying very bulky substituents like cardo groups can give colorless polyimides. For example, the bis-9,9-(4-aminophenyl)fluorene (FDA) or brominated and acetylenic FDA derivatives react with 6FDA giving copolymer films62 with low birefringence (low difference between in-plane and out-of-plane refraction index) (Fig. 5.8). A new cardo diamine l,l-bis[4-(4-aminophenoxy)phenyl]cyclododecane (Fig. 5.8) reacts with different aromatic dianhydrides with formation of colorless polyimides.63... 

Monooxygenases. Under nonlignolytic conditions, arene monooxygenase and epoxide hydrolase systems may function to produce trani-dihydrodiols. Hydrogen abstraction mediated by the lipid peroxidase system may operate, for example, in the formation of fluorene-9-one from fluorene by Ph. chrysosporium (Bogan et al. 1996). 

Presumably, 9 is actually formed from carbene 8 in the pyrolysis zone by a P/C phenyl shift, but then apparently succumbs to fast transformation into the thermodynamically stable final products. Formation of the methane derivative 13 should be preceded by a 1,2-phenyl shift to give the shortlived 10, the production of fluorene (14) by the occurrence of diphenylcarbene (II), and the formation of benzophenone (15) by isomerization to the angle-strained three-membered heterocycle 12, which is followed by elimination of phenylphospbinidene. No direct evidence is available for the intermediacy of 10-12. 

Formation of these dinuclear mercury derivatives is accompanied by a red shift of the absorbance of the bis(alk-ynyl) backbone. For example, conversion of 2,7-bis(alkynyl)fluorene into the corresponding bis(methylmercury) derivative 50 leads to a shift of the main absorption band of the bis(alkynyl) backbone from 505 to 567 nm. Similar results have been obtained for 51-56.67 68... 

Intramolecular Friedel-Crafts reactions can sometimes compete with organosil-icon hydride reductions of benzylic-type alcohols to cause formation of undesired products. An example is the attempted reduction of alcohol 26 to the corresponding hydrocarbon. When 26 is treated with triethylsilane in trifluoroacetic acid at room temperature for 15 hours, a mixture of the two fluorene isomers 27 and 28 is obtained in a combined yield of 45%. None of the hydrocarbon structurally related to the substrate alcohol 26 is obtained.171 Whether this problem could be circumvented by running the reduction at a lower temperature or with a different acid remains subject to experimentation. 

Although the exact mechanism of the fluorenone formation is not known, it is believed that the monoalkylated fluorene moieties, present as impurities in poly(dialkylfluorenes), are the sites most sensitive to oxidation. The deprotonation of rather acidic C(9)—H protons by residue on Ni(0) catalyst, routinely used in polymerization or by metal (e.g., calcium) cathode in LED devices form a very reactive anion, which can easily react with oxygen to form peroxides (Scheme 2.26) [293], The latter are unstable species and can decompose to give the fluorenone moiety. It should also be noted that the interaction of low work-function metals with films of conjugated polymers in PLED is a more complex phenomenon and the mechanisms of the quenching of PF luminescence by a calcium cathode was studied by Stoessel et al. [300],... 

Many studies on side-chain modifications in PF were initially based on the idea of excimer formation, resulting in the green emission during LED operation or in solid-state PL on annealing PF films. This resulted in several proposed strategies for the design of fluorene side-chain homopolymers, where bulky substituents at position 9 of the fluorene moiety should sterically prevent (hinder) interchain interaction and thus improve the stability of blue emission. 

Oxidation of p- and m-substituted diphenylmethylidene fluorenes resulted in the formation of a suite of dications, 9 and 10, which were shown to be antiaromatic through magnetic and energetic criteria. ... 

Similar results have been presented by Miller and co-workers, who capped the ends of oligo(dihexylfluorene)s and poly(dihexylfluorene)s with Frechet-type dendrons (Figure 7.17C) [73], Annealing experiments coupled with emission studies revealed that G-3 and G-4 dendrons were effective at preventing excimer formation, even when the poly(fluorene) spacer was 50-80 repeat units long. 

The propargylic alcohol 102, prepared by condensation between 100 and the lithium acetylide 101, was efficiently reduced to the hydrocarbon 103, which on treatment with potassium tert-butoxide was isomerized to the benzannulated enyne-allene 104 (Scheme 20.22) [62], At room temperature, the formation of 104 was detected. In refluxing toluene, the Schmittel cyclization occurs readily to generate the biradical 105, which then undergoes intramolecular radical-radical coupling to give 106 and, after a prototropic rearrangement, the llJ-f-benzo[fo]fluorene 107. Several other HJ-f-benzo[fo]fluorenes were likewise synthesized from cyclic aromatic ketones. 

Treatment of the propargylic alcohol 144, readily prepared from condensation between benzophenone (143) and the lithium acetylide 101, with thionyl chloride promoted a sequence of reactions with an initial formation of the chlorosulfite 145 followed by an SNi reaction to produce in situ the chlorinated and the benzannulated enyne-allene 146 (Scheme 20.30) [62], A spontaneous Schmittel cyclization then generated the biradical 147, which in turn underwent a radical-radical coupling to form the formal [4+ 2]-cycloaddition product 148 and subsequently, after a prototropic rearrangement, 149. The chloride 149 is prone to hydrolysis to give the corresponding 11 H-bcnzo h fluoren-ll-ol 150 in 85% overall yield from 144. Several other llff-benzo[fc]fluoren-ll-ols were likewise synthesized from benzophenone derivatives. 

In mice, also, deacetylation is involved in the hepato-carcinogenesis induced by 2-(acetylamino)fluorene. Indeed, BNPP-inhibited DNA-adduct formation in murine liver microsomes as well as tumor initiation by A-hydroxy-2-(acetylamino)fluorene in infant male B6C3Fj mice [100],... 

Esters of ethenetetracarboxylic acid, (37), and disubstituted (fluoren-9-ylidene)me-thane derivatives, (38), are reduced sequentially to radical anions and dianions [2, 68, 84, 85]. Only the dianions are sufficiently basic to be useful as EGBs [53,86]. For (37), the two reduction potentials are separated by 0.2 V [68], and even with a working potential allowing formation only of the radical anion, the dianion can be formed by disproportionation. The protonated form of the dianionic EGBs, (37H) and (38H) , will normally be stable in solution since the pK values of the dihydro products are expected to be in the range 12 to 16. 

The Ad -E mechanism proposed to account for the kinetics of substitution of 9-(a-bromo-a -arylmethylene)fluorenes by thiolate ions in aqueous acetonitrile also features elimination of the leaving group in a fast step following rate-determining carbanion formation (by nucleophilic addition). ... 

Oxidation of diphenylmethane in basic solutions involves a process where rate is limited by and equal to the rate of ionization of diphenylmethane. The diphenylmethide ion is trapped by oxygen more readily than it is protonated in dimethyl sulfoxide-text-butyl alcohol (4 to 1) solutions. Fluorene oxidizes by a process involving rapid and reversible ionization in text-butyl alcohol solutions. However, in the presence of m-trifluoromethylnitrobenzene, which readily accepts one electron from the carbanion, the rate of oxygen absorption can approach the rate of ionization. 9-Fluorenol oxidizes in basic solution by a process that appears to involve dianion or carbanion formation. Benzhydrol under similar conditions oxidizes to benzophenone by a process not involving carbanion or dianion formation. 

Treatment of fluorene, xanthene, thioxanthene, phenyl-4-pyridyl-methane, phenyl-2-pyridylmethane, 4,5-methylenephenanthrene, tetra-phenylcyclopentadiene, or phenalene with base and a trace of oxygen in DMSO (80% )-tert-buty alcohol (20%) solution gave significant amounts of the ketyls—i.e., Figure 6. These reactions may involve the initial formation of the ketone followed by reduction by the carbanion to yield the ketyl. 

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