9-Fluorenone synthesis

Other reactions such as alkane dehydrogenation [159, 160], decarbonylation reactions [161], cyclization of alkynoic acids [162,163], three-component coupling reactions of boronic acids, allenes and imines [164], fluorenone synthesis by sequential reactions of 2-bromobenzaldehydes with arylboronic acids [165], and hydrosilylation reactions [166, 167] using cyclometalation compounds as their catalysts have also been reported. 

Recently, Hoye and coworkers [257, 258] reported a new fluorenone synthesis by a novel hexadehydro-Diels-Alder (HDA) reaction (Scheme 6.109). In the HDA reaction, a 1,3-diyne 418 is engaged in a [4+2] cycloisomerization with a diynophile to produce the highly reactive benzyne intermediate 419. When trapping reagents are absent, the generated benzyne 419 undergoes a cycloaddition reaction with benzene as the solvent to form adduct 420. 

The authors used a synthesis of 9,9-spirobitluorenes 32 which was developed by Clarksen and Gomberg [60] and which includes the addition of biphenyl-2-yl-magnesium iodide to fluorenone and subsequent cyclization with protic acids. To obtain 2,2,, 7,7 -arylated 9,9-spirobifluorenes 33, 9,9-spirobifluorene (32) was tetrabrominated [58] to yield 34 followed by a Suzuki-type aryl-aryl cross-coupling with various oligoaryl and oligoheteroaryl boronic acids to obtain the 2,2, 7,7 -tetraarylated derivatives 33. 

The synthesis principle we are using is based on the fact that molecules can diffuse into individual channels [3,4,31]. This means that, under appropriate conditions, they can also leave the zeolite by the same manner. In some cases, however, it is desirable to block their way out, so as to stabilize the structure. This can be done by adding a closure molecule after the synthesis has been completed. A variety of closure molecules which seal the channels completely or only partially can be used, depending on the requirement. An example already used is the addition of fluorenone which enters readily but leaves the structure reluctantly. If more complete sealing is needed, molecules bearing appropriate reactive groups can be used. Functionalization of the closure molecules is an option for tuning wettability, refractive index, chemical reactivity, and other properties. 

The Balz-Schiemann synthesis can be applied not only to substituted anilines but also to aminobiphcnyls1,131 or amino-substituted fused polyaromatic compounds, such as naphthalene,1114,119,129 anthracene,136 phenanthrene,1135 acenaphthene,133 fluorene,1,131,134 benzanthracene,130 136 pyrene,136 chrysene,136 fluoranthene,131 fluorenone,1,131 anthra-quinone,1,137,139,140 benzanthrone,1,117,118 phenanthraquinone,138 or xanthone.132 Fluorinated pyridines,1,141"146 methylpyridincs,126,147 149 pyridinecarboxylic acids,150 quinolines,1,151 isoquinolines,152 quinazolone,1 thiazoles,153,154 isothiazoles,156 benzothiazoles,157 thiadiazoles,155 and thiophenes154 can also be obtained from the corresponding aminated heterocycles. Modified Balz-Schiemann methods are recommended for amino nitrogen-containing heterocycles, the diazonium salts of which are rather water-soluble and unstable (a violent explosion was reported for pyridine-3-diazonium tetrafluoroborate).159 These new techniques have also been specially adapted for pyrazol-, imidazol-, or triazolamines which fail to react under classical conditions.158... 

Interesting possibilities of synthesis arise when elimination leads to cyclic products. Such cyclization is fairly common with aromatic compounds. The mixture of products obtained from diphenylmethane contains about 25 per cent fluorene 2S> (Table 3). Similarly, benzophenone yields about 30 per cent fluorenone 20). The same method can be applied to the synthesis of heterocyclic compounds. Diphenylamine yields up to 30 per cent carbazol 26 di-phenylether about 10 per cent dibenzofurane 16). 

V. Remote aromatic metalation. An anionic Friedel-Crafts equivalent for the regioselective synthesis of condensed fluorenones from biaryl and m-teraryl 2-amides. /. Org. Chem. 1991, 56,1683-1685. 

Table 2. Synthesis of fluorenones via 1,4-palladium migration and subsequent arylation of imines.

Ipaktschi and Sharifl reported the palladium-catalyzed synthesis of 2,7-diamino fluorenones by two indirect routes due to the base sensitivity of fluorenones [182]. First, 2,7-dibromofluorene was reacted with secondary amines, and subsequent oxidation of the product formed the diaminofluorenone. Alternatively, reaction of ami-nostannanes derived from secondary amines with 2,7-dibromofluorenone gave yields of the fluorenone ranging from 42 to 58%. Beletskaya has used the DPPF-ligated palladium system to conduct selective monoarylation of ethylene diamine, diethylene triamine, triethylene tetra-amines, and 2,2-dimethyl butane-1,3-diamine [183]. 

Scheme 43. Synthesis of fluorenones by tandem remote metalation-amide DMG translocation.

Traditionally cyanohydrins have been prepared by processes that require the establishment of an equilibrium between a ketone and its corresponding cyanohydrin. For many ketones, especially those that are sterically hindered, the position of the equilibrium is unsatisfactory for the effective synthesis of the cyanohydrin. We describe herein a general method for the synthesis of cyanohydrins which does not depend on an equilibrium process. As a result this synthetic procedure can be used to convert a wide variety of dialkyl, diaryl, and arylalkyl ketones into their corresponding cyanohydrins. In addition to the described conversion of benzophenone into its cyanohydrin, acetophenone, fluorenone, tert-butyl phenyl ketone, and a wide variety of aliphatic ketones have been converted into cyanohydrins by this general procedure (Table... 

BPF Polycarbonate. The synthesis of bisphenol fluorenone polycarbonate was first reported by Morgan (2). As in that study, the BPF carbonate family reported here was made by an aqueous caustic/organic liquid interfacial polymerization. In our case the monosodium salt of... 

Our work on fluorenones and alkaloids was extended to design convenient, expeditious and stereocontrolled total synthesis of several naturally occuring diterpenoids [55] namely ( )-ferruginol (5), ( )-nimbidiol (6), ( )-nimbiol (7), ( )-totarol (8) and abietatriene (9) (Schemes 4-8) via a concerted mechanism of domino acylation-cycloalkylation/ alkylation-cycloacylation as the principal step to construct the basic carbocyclic framework required for the trans-fused... 

Favorski-type rearrangement, 228-229 Ferric chloride, 185 Fetizon s reagent, 366 Fisher indole synthesis, 318, 322 Fluorenone, 431 Fluorodimethoxyborane, 186... 

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