Polycyclic aromatic compounds synthesis

Polycyclic aromatic compounds, synthesis by photocyclization of stilbenes, 30, 1... 

Weyand EH, Amin S, Sodhi R, et al. 1991c. Effects of methyl substitution on the metabolism and binding of benz[e]acephenanthrylene. In Garriques P, Lamotte M, eds. Polycyclic aromatic compounds. Synthesis, properties, analytical measurements, occurence, and biological effects. Proceedings of the thirteenth international symposium on polynuclear aromatic hydrocarbons. Philadelphia, PA Gordon and Breach. 

Dihydro-1-vinylnaphthalene (67) as well as 3,4-dihydro-2-vinylnaphtha-lene (68) are more reactive than the corresponding aromatic dienes. Therefore they may also undergo cycloaddition reactions with low reactive dienophiles, thus showing a wider range of applications in organic synthesis. The cycloadditions of dienes 67 and 68 and of the 6-methoxy-2,4-dihydro-1-vinylnaphthalene 69 have been used extensively in the synthesis of steroids, heterocyclic compounds and polycyclic aromatic compounds. Some of the reactions of dienes 67-69 are summarized in Schemes 2.24, 2.25 and 2.26. In order to synthesize indeno[c]phenanthrenones, the cycloaddition of diene 67 with 3-bromoindan-l-one, which is a precursor of inden-l-one, was studied. Bromoindanone was prepared by treating commercially available indanone with NBS [64]. 

Dihydrovinylphenanthrenes are more reactive than the corresponding vinyl phenanthrenes and undergo Diels-Alder reactions easily. They have been used in the synthesis of polycyclic aromatic compounds and helicenes. Examples of cycloaddition reactions of the 3,4-dihydro-1-vinylphenanthrene (70), [61] 3,4-dihydro-2-vinylphenanthrene (71) [68] and l,2-dihydro-4-vinylphenanthrene (72) [69] are reported in Equation 2.22 and Schemes 2.27 and 2.28. 

When 2D or 3D PAHs are considered then the choice becomes much larger. An exhaustive review on the advances in the synthesis of polycyclic aromatic compounds can be found in Harvey, 2004. The most used strategies are flash vacuum pyrolysis, cross-coupling, oxidative photocyclization, Diels-Adler cycloaddition, etc. 

Effect of Heteroelements in Modifying Some Cyclizations — Polycyclic Aromatic Compounds from the Diene Synthesis , W. Davies and O. N. Porter, in Proceedings of a Symposium on Current Trends in Heterocyclic Chemistry , ed. A. Albert, G. M. Badger and C. W. Shoppee, Academic Press, New York, 1958, pp. 56-58. 

Superacid-promoted dicationic species containing heteroaromatic rings, where positive charge centres migrate through consecutive deprotonation-reprotonation steps, undergo cyclization reactions followed by aromatization and superacid-promoted elimination of benzene (Scheme 10).31 The process leads to the synthesis of aza-polycyclic aromatic compounds in moderate to good yields. Seven examples include pirazole, oxazole, and thiazole heterocycles. 

Luijk R, Dorland K, Smit P, Govers HAJ (1993), in Polycyclic aromatic compounds", prediction of the gas chromatographic retention behaviour of polybrominated dibenzo-p-dioxins , p. 565-572, Garrigues Ph, Lamotte M (Eds.), Gordon and Breach, Yverdon Weber R, Hagenmaier H (1994), Organohalogen Compounds 19 7-11. Polyfluorinated diben-zodioxins/furans - Synthesis, analysis and formation", Eds. University of Kyoto, Japan... 

This method has been applied to the synthesis of various polycyclic aromatic compounds [91]. Among the interesting applications are lactone formation in the preparation of natural products having biaryl skeletons (Eq. 42) [87] and double cyclization leading to spirocyclic compounds (Eq. 43) [92] and a fullerene fragment (Eq.44) [93]. 

Bifunctional Initiation. The bifunctional initiators like alkali metal complexes of polycyclic aromatic compounds can be used to produce ABA triblock copolymers even when the A anion is not sufficiently basic to initiate polymerization of B monomers. In these cases polymerization would be started with monomer B to produce a polymeric dianion which could initiate polymerization of the A monomer which is added later. These initiators can be prepared only in aliphatic ethers, however. This precludes their use for the synthesis of useful styrene-diene ABA copolymers because polydienes made anionically in such solvents have low 1,4 contents and are not good rubbers. 

In tMs approach, conjugate addition of the anion from an isocyano-acetate to an a,p-unsaturated nitrocompound with evenmal loss of nitrous acid, produces 5-unsubstituted pyrrole-2-esters. The example below shows a mechanistic sequence that can be seen to parallel that in the van Leusen synthesis. The most useful route to the a,P-unsaturated nitro-compound involves the base-catalysed condensation of an aldehyde with a nitroalkane giving an a-hydroxy-nitroalkane it can alternatively be generated in situ, in the presence of the isonitrile, using diazabicycloundecane (DBU) as base on the 0-acetate of the a-hydroxy-nitroalkane (for an example see 16.16.2.1). The process works even when the unsaturated nitro unit is a component of a polycyclic aromatic compound. ... 

The topic Polycyclic Aromatic Hydrocarbons has been reviewed by different authors in the last decades [26]. The most complete summary of classical synthetic routes to PAHs may still be found in Eric Clar s Polycyclic Hydrocarbons [26a]. Most recently, Ronald G. Harvey reviewed the syntheses and characteristics of PAHs up to seven rings in a very comprehensive fashion [26 f] in his book Polycyclic Aromatic Compounds . Recent advances in the synthesis of PAHs are published in all major journals of organic chemistry, in Polycyclic Aromatic Hydrocarbons [27], and presented during the regular ISNA [28] and ISPAC [29] conferences. 

Many of the organic contaminants which were found in Lippe river water were also present in the source samples (see Table 3). The sewage effluent sample and the Seseke river showed the best accordance with the compound spectrum of the Lippe river. However, also in the two tributaries from the rural upper reaches of the river, numerous specific contaminants like 9-methylacridine (No. 8), alkyl phosphates (Nos. 31, 32) and chlorinated alkyl phosphates (Nos. 34, 36) appeared. In the effluent of a pharmaceutical plant, only a few Lippe river contaminants like n-alkanes (No. 1), naphthalene (No. 3), TXIB (No. 21) and caffeine (No. 67) were detected (see Table 3). Therein, mainly structural relatives of androstanone like 3p-hydroxy-5p-androstan-17-one, 3a-hydroxy-5p-androstan-17-one and androstan-50-3,17-dione were present. These compounds are probably by-products of the synthesis of hormone preparations. Some polycyclic aromatic compounds, halogenated compounds and terpenoids were not detected in the source samples (see the underlined compounds in Table 3) and probably have another origin. Representative sampling of various input sources have to be carried out to prove the origin of these compounds. Hexachlorobutadiene (No. 38) and bis(chloropropyl)ethers (No. 44) appear exclusively at the lower reaches of the Lippe river (see Table 1), downstream the chemical plants in Marl. They are attributed to inputs of the chlorochemical industry (see section 3.1). Hence, this suggests their input by an industrial point source. 

Methodology used for the synthesis of polycyclic aromatic compounds can be applied to the annelation of benzene rings on to (benzo)pyridazines. For example 6,9-difluorobenzo[ ]phthalazine-... 

An alkene unit can also be used to generate a cation and cyclize to form a polycyclic aromatic compound. When 229 reacted with acetaldehyde, 230 was produced and this was cyclized by treatment with sulfuric acid to give hydronapthalene (231). This modification does not incorporate the additional ring of the cyclic ketones used in the Bogert-Cook reaction it is sometimes called the Bogert synthesis. 

Several reviews have been published within the year which are of general relevance to the photoreactions of aromatic compounds. The subjects of these reviews include photochemistry in ionic liquids and in isotropic and anisotropic media, organic synthesis utilizing photoinduced electron-transfer reactions," heteroatom-directed photoarylation processes, photochromism, and photochemical molecular devices. Reviews more directly pertinent to the sections in the present chapter include those of the photoisomerization of five-membered heteroaromatic azoles, the photocycloaddition of benzene derivatives to alkenes, Diels-Alder additions of anthracenes, advances in the synthesis of polycyclic aromatic compounds, diarylethene-based photochromic switches, the photo-Fries rearrangement, and the application of Diels-Alder trapping of photogenerated o-xylenols to the synthesis of novel compounds. " A number of chapters in the two recently published handbooks of photochemistry and photobiology and in the revised edition of the text on photochromism are also pertinent to the current subject matter. 

The use of ort/ c>-quinodimethanes in the Diels-Alder reaction provides an efficient approach to polycyclic aromatic compounds. A recent example is the cycloaddition of the benzocyclobutene 56 with the quinone 57, which occurs on heating in toluene (3.49). The adduct 58 was used in a synthesis of rishirilide B. 

There are many examples of this type of reaction with both aromatic and heteroaromatic substrates. For successful electrocyclization, the central alkene must have Z geometry, however, as the action of light on stilbenes promotes E-Z isomerization, it is possible to start with either geometrical isomer of the substrate, or indeed a mixture of isomers. In a synthesis of cervinomycin A, photochemical electrocyclization of the mixture of E- and Z-diaryl alkenes 347 gave the polycyclic aromatic compound 348 after oxidation with iodine (3.219). ... 

A third compound, cervinomycin closely related in structural complexity and biological activity with the other molecules described above, is relatively new. Much of the synthetic efforts have already started appearing while only one total synthesis has been reported. We have taken a decision to involve ourselves, primarily due to our belief that much is to be done, in polycyclic aromatic compounds by way of designing new strategies and discovering new reactions and would wish to see resurgence of interest among synthetic chemists in this area. 

Many polycyclic aromatic compounds have been synthesized by a cyclization reaction known as the Bradsher reaction or aromatic cyclodehydration. This method can be illustrated by the following synthesis of 9-methylphenanthrene ... 

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