9-Fluorenone, reactions

The rho values (2.78 overall, 3.78 for reduction to the cis product and 1.96 for reduction to the trans), determined from a study of the rates of reduction with NaBH4 of a series of 4-substituted cyclohexanones, have been interpreted as supporting a transition state late in the reaction.Other groups have observed positive rho values (2.5 to 3.1) for the reduction with NaBH4 of fluorenones and acetophenones. These results show clearly... 

By analogy, thermal cyclization was described also for 6-nitro-2 -hydroxy-biphenyl-2-carboxylic acids, e.g. 14, obtained by other methods. The same product 15 was also formed from lactone 17, prepared by oxidation of fluorenone 16 (Scheme 2). If the reaction was performed in DMF, the corresponding dimethylamide was isolated (82KGS703, 86KGS852, 87KGS314, 89MI1). 

Lewin and Cohen (1967) determined the products of dediazoniation of ben-zophenone-2-diazonium salt (10.42, Scheme 10-77) in five different aqueous systems (Table 10-7). About one-third of the yield is 2-hydroxybenzophenone (10.46) and two-thirds is fluorenone (10.45, run 1) copper has no effect (run 2). On the other hand, addition of cuprous oxide (run 3) has a striking effect on product ratio and rate. The reaction occurs practically instantaneously and yields predominantly fluorenone. As shown in Scheme 10-77, the authors propose that, after primary dediazoniation and electron transfer from Cu1 to 10.43 the sigma-complex radical 10.44 yields fluorenone by retro-electron-transfer to Cu11 and deprotonation. In the presence of the external hydrogen atom source dioxane (run 12) the reaction yields benzophenone cleanly (10.47) after hydrogen atom abstraction from dioxane by the radical 10.43. 

The electron transfer reaction from fluorenyl carbanions adjacent to sulfoxide or sulfone (9) to fluorenone (FIO) has been studied by means of flash photolysis37. For n — 1 as well as n — 2 the transient F10T, M + (contact ion pair) appeared in THF and F10T(free ion)... 

Thus for the photoreduction of benzophenone in the presence of benzhydrol (RH = < 2CHOH, C—H x 78 kcal/mole) the overall reaction is exothermic by 26 kcal/mole. For the photoreduction of acetophenone the value calculated in this way is —31 kcal/mole, while for fluorenone the abstraction is still exothermic by 10 kcal/mole. Clearly, the energetics of the abstraction reaction is not the reason why benzophenone and acetophenone photoreduce but fluorenone does not, since the values for the overall reaction would indicate that all three compounds should react. However, this conclusion is not necessarily valid if large activation energies are involved. ... 

Fluorenone and sodium sorbate served to quench the unsensitized reaction, indicating a triplet excited state. Similarly, recent investigations of the photosubstitution of 3,5-dinitroanisole indicate a reactive triplet species(143) ... 

We have also been able to generate carbocycles by annulation processes. For example, the reaction of halobiaryls and 1 atm of CO in the presence of a Pd catalyst affords excellent yields of fluorenones (Scheme 15).16... 

The stereoselective 1,4-addition of lithium diorganocuprates (R2CuLi) to unsaturated carbonyl acceptors is a valuable synthetic tool for creating a new C—C bond.181 As early as in 1972, House and Umen noted that the reactivity of diorganocuprates directly correlates with the reduction potentials of a series of a,/ -unsaturated carbonyl compounds.182 Moreover, the ESR detection of 9-fluorenone anion radical in the reaction with Me2CuLi, coupled with the observation of pinacols as byproducts in equation (40) provides the experimental evidence for an electron-transfer mechanism of the reaction between carbonyl acceptors and organocuprates.183... 

On the contrary, the oxidation of fluorene in a basic solution is not limited by the deprotonation of hydrocarbon [284]. This is in agreement with the oxidation of fluorene and 9,9-dideuterofluorene at the same rate in DMSO and 1,1-dimethylethanol solution. The stoichiometry of fluorene oxidation is close to unity (except oxidation in HMPA) and the main product of the reaction is fluorenone. The stoichiometry and the initial rate of the reaction depends on the solvent (conditions 300 K, [fluorene] = 0.1 mol L 1, [Me3COK] = 0.2mol L 1,p02 = 97kPa). 

The use of l-iodo-9-fluorenone (59) for cross-coupling with phenylacetylene produced 60, which on treatment with 51 gave the benzannulated enyne-allenes 61 (Scheme 20.14) [43], Thermolysis of 61 in 1,4-CHD at 75 °C promoted the Myers-Saito cyclization reaction, leading to 63 in excellent yields. Again, the benzylic radical center in 62 is a stabilized triarylmethyl radical. 

Quinones [124] and aromatic ketones such as flavones, [116] fluorenone, anthra-quinone, and similar compounds [121] dissociate by competing and consecutive losses of CO and C2H2. Multiple CO losses may also occur subsequent to the RDA reaction of flavones. [116,125] As these molecules all have large 71-electron... 

SET processes do not occur among moderately electrophilic olefinic acceptors, but are likely to be involved in highly electrophilic substrates. Some recent examples are the polyadditions of cuprate to fullerenes (Sect. 10.1.1). Fluorenone ketyl radical has been detected in a cuprate reaction of fluorenone [20]. Doubly activated olefins [67-69] and bromonaphthoquinone [70] also probably react through SET. 

Oxidation of fluorene (C13H10) with chromic acid gives fluorenone (CnHgO). If the reaction does not go to completion, then a mixture of the starting material and the product is usually obtained. The H NMR spectrum below is from a partially oxidized sample of fluorene so it contains a mixture of fluorene and fluorenone. Determine the relative amounts (mole %) of fluorene and fluorenone in the mixture. 

Table III summarizes some information on the initial rates of oxidation of fluorene in several solvents. In the alcohol-containing solvents the stoichiometry was nearly one molecule of oxygen per mole of fluorene, an observation that excludes 9-fluorenol as an intermediate. In all solvents, including HMPA, interrupted oxidations yielded only fluorenone (or the DMSO-fluorenone adduct) and fluorene. Apparently Reaction 6 or 7 occurs readily in the presence of hydroxylic solvents. In HMPA the high...

This process has been demonstrated to occur in the reaction between fluorenone and the fluorene anion in the absence of oxygen in tert-butyl... 

Oxidation of xanthenol or fluorenol with deficient quantities of oxygen in tert-butyl alcohol produced large quantities of the ketyl, as did reaction of equal molar amounts of the ketone and alcohol in basic solution. In fact, the reaction of the pinacol of fluorenone with excess base in tert-butyl alcohol produced an essentially quantitative yield of the ketyl (19). 

Background and Possible Intermediates. Accepting the premise of carbanion formation in the basic media, the mode of reaction with molecular oxygen can now be considered. Sprinzak (8) reported that the autoxidation of fluorene in basic media proceeds by direct reaction of the fluorenyl carbanion with oxygen to form initially the hydroperoxide, which decomposes to yield 9-fluorenone, as depicted below. 

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