Dibenzofurans alkylation

Preformed Carbocationic Intermediates. Propargyl cations stabilized by hexacarbonyl dicobalt have been used to effect Friedel-Crafts alkylation of electron-rich aromatics, such as anisole, /V, /V- dim ethyl a n il in e and 1,2,4,-trimethoxybenzene (24). Intramolecular reactions have been found to be regio and stereo-selective, and have been used ia the preparatioa of derivatives of 9JT- uoreaes and dibenzofurans (25). 

The DszC enzyme was able to convert the following compounds other than DBT thioxanthen-9-one, 2,8-dimethyl DBT, 4,6-dimethyl DBT, and 3,4-benzo DBT. Non-organosulfur compounds such as biphenyl, carbazole, and dibenzofuran did not show any activity. This indicates that dszC specifically recognizes sulfur atom [151]. One study specifically examined the DszC enzyme for oxidation of aryl sulfides [179] and reported oxidation of many sulfides including, naphthyl methyl sulfide, phenyl methyl sulfide, and its alkyl derivatives. 

Ebel s method is an adaptation of the Stoermer synthesis of benzo-[h]furans and involves the 0-alkylation of a phenolate anion (229, Scheme 58) with a 2-halocyclohexanone (230). The resultant 2-phenoxycyclo-hexanone 231 is then cyclized by poly phosphoric acid, usually at 100°C, or sometimes by concentrated sulfuric acid, to afford a 1,2,3,4-tetrahydrodi-benzofuran (232). Dehydrogenation to the dibenzofuran is often effected with palladized charcoal, but 2,3-dichloro-5,6-dicyano-l,4-benzoquinone ... 

Phenol and alkyl-substituted phenols yield dibenzofuran and alkyldiben-zofurans by catalytic dehydration-dehydrogenation over thorium or cerium oxides. This reaction can also be achieved by thermal cracking of... 

Dibenzofuran undergoes Friedel-Crafts alkylation with alkyl ha-lides " " or alkenes in the presence of Lewis acids. The products... 

When an electron-withdrawing group is present in any position of one benzenoid ring of dibenzofuran, then the electrophile usually attacks the other benzenoid ring at the 8-position. Nitration usually occurs, however, at the 7-position. When there is an alkyl group at the 2-position, acylation occurs predominantly at the 8-position, but when there is a methyl group... 

The lithio derivatives of dibenzofuran undergo the expected reactions. Carbonation yields carboxylic acids,reaction with sulfur dioxide yields sulfinic acids, and reaction with methyl sulfate yields methyl compounds. Alkylation can also be achieved by treatment of 4-lithio-dibenzofuran with alkyl halides. Silylation can be achieved with chlorotrimethyl- or chlorotriphenylsilane. " " Reaction of lithiodibenzo-furans with acetaldehyde and with benzonitrile take the expected course. 

The product distribution in the zeolite-catalysed alkylation of polynuclear aromatics depends on the structure of zeolite pores. High regioselectivities were observed in the HM catalysed isopropylation of polynuclear aromatics, such as biphenyl, naphthalene, p-terphenyl, and dibenzofuran, to yield predominantly the least bulky products e.g., 4,4 -DIPB for biphenyl, and 2,6-DIPN for naphthalene. These reactions are controlled by steric restriction at the transition state inside the pores and by the entrance of intermediate products molecules into the pores. On the other hand, the catalysts with large-pore HY and HL zeolite are controlled at low temperature by the electron density of the reactant molecule and at higher temperature by the stability of the product molecules because their pores have enough space for a transition state, which allow the formation of all corresponding isomers. 

Benzofuran derivatives are rare in petroleum, where sulfurated heterocycles predominate among heterocyclic compounds. Benzofurans and 2,3-dihydrobenzofurans are found, however, in the 200°-270° fraction of the distillate of California crude oil, with dibenzofurans and naphthobenzofurans.123 Alkyl-dibenzofurans have been traced in the 275°-305° fraction of petroleum with alkylnaphthalenes, 4-methyl-dibenzofuran among others.124 The distillation of humic acids with zinc powder is said to give benzofuran and hydrobenzofuran derivatives.125... 

Quantitative Property-S T) Relationship Dickhut et al. [67] developed a QP-5VV(7 )R based on experimental mole fraction solubilities for alkylbenzenes, PAHs, PCBs, chlorinated dibenzofuranes and p-dioxins, and alkyl- and halo-substituted naphthalenes and p-terphenyls in the range 4 to 40°C ... 

Another major exposure route for humans is via contaminated food. For example, North America s Great Lakes, which are the largest body of freshwater in the world, are polluted with about 362 contaminants that were found in quantifiable amounts in the water, sediment, and biota (IJC 1983 USEPA 1994). The critical pollutants were identified as PCBs, DDT, dieldrin, toxaphene, mirex, methyl mercury, benzofa) pyrene, hexachlorobenzene, polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and alkylated lead. Some of these pollutants biomagnify in the aquatic food chain and can be detected in increased levels in cooked Great Lakes fish. Consequently, the blood serum levels of these chemicals are significantly increased in consumers of contaminated Great Lakes sport fish compared to people who do not eat such fish (Flumphrey 1983 Fiore et al. 1989 Sonzogni et al. 1991). 

The central ring systems found to yield antiviral compounds have included fluorene (fluorenone), dibenzofuran, dibenzothiophene, fluoranthene, anthraquinone, acenaphthene, xanthene, thioxanthene, phenothiazine, carbazole, phenanthrene and others. The side chains were represented by basic ethers, basic ketones, basic esters plus carboxamides, sulphonamides, alkanols, methylene and others attached to the various ring systems. The amine function was usually substituted to the tertiary amine with various alkyl substituents although a few ring types (e.g., pyrrole or piperidino) were synthesized. 

Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorobiphenyls (PCBs), and polychlorophenols (PCPs) are well-known artifacts ubiquitous in the present environment. Due to their lipophilic-ity and resistance to metabolism or chemical degradation these have the potential to accumulate in the food chain and cause toxic effects [1, 2]. Polycyclic aromatic sulfur heterocycles (PASHs) along with different kinds of polycyclic aromatic compounds (PACs) also occur widely in the environment [3,4]. In particular, alkylated dibenzothiophenes have previously been found to be persistent residues in the marine environment after oil spills. Dibenzothiophene and its alkylated derivatives have been found to accumulate in fish and other marine organisms [5-7]. 

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