Aromatic compounds from stilbenes

Miscellaneous Dyes. Other classes of dyes that stiU have some importance are the stilbene dyes and the forma2an dyes. Stilbene ( es are in most cases mixtures of dyes of indeterminate constitution that are formed from the condensation of sulfonated nitroaromatic compounds ia aqueous caustic alkah either alone or with other aromatic compounds, typically arylarnines (5). The sulfonated nitrostilbene [128-42-7] (79) is the most important nitroaromatic, and the aminoa2oben2enes are the most important arylarnines. Cl Direct Orange 34 [2222-37-6] (Cl 40215-40220), the condensation product(s) of (79) and the aminoa2oben2ene [104-23-4] (80), is a typical stilbene dye. 

Intermediates generated at an electrode surface may react while still near the electrode. If so, one side of the intermediate may be wholly or partly shielded from attack by other reactants by the electrode itself. Such behavior is particularly common in the electrochemical oxidation of aromatic compounds since, as we have already seen with coumarin, aromatic compounds are generally tightly adsorbed parallel to the electrode surface at potentials positive of the p.z.c. For example, electrochemical oxidation of the stilbenes in alkaline methanol affords a mixture of dl and meso-1,2 dimethoxy-1,2-diphenylethane (1) 10>. It is found that c/s-stilbene affords a mixture of isomers of 1 in which the... 

A very large number of substituted phenanthrenes have been made from stilbenes by this photocydization method, as have more complex polycyclic aromatic compounds by related reactions involving a single cydizatlon (e.g. 3.64 for chrysenes) or two, or more, successive cydizations le.g. 3.65). The reaction can be nicely adapted to provide a route from 1-benzylidenetetra-hydroisoquinolines to alkaloids of the aporphine family (e.g. 3.66). 

The reaction is considered to arise from the stilbene singlet 7t,7t excited state and is useful for the synthesis of a great variety of polynuclear aromatic compounds, such as helicenes and large [n]phenacenes (n = 3 up to n = 7) [25], The arene positions involved in photocyclization are predictable the preferred route corresponds to the dihydro intermediate with the higher degree of aromaticity (Scheme 9.18). 

By contrast to the thermal process, the photochemistry of 2-vinylbiphenyl (249) and 4-vinylphenan-threne (250) has been widely used in connection with syntheses of polycyclic aromatic compounds, complementing the most commonly used stilbene to phenanthrene transformation/ For example, the product obtained from the ctnirotatory photocyclization of 2-(a-styryl)biphenyl (252) can be trapped by an oxidant to give the phenanthrene (254) or suffers a 1,5-H shift to give the dihydro d)enandiieiie... 

Photoamination of a variety of aromatic compounds with ammonia and alkyl-amines under photosensitized electron transfer mediated reaction conditions has been extensively investigated by Yasuda and coworkers (Scheme 70) [320-324]. The photoamination reactions of stilbene derivatives with ammonia have been utilized for the synthesis of a variety of isoquinoline derivatives [324]. The photoamination is initiated by photochemical electron transfer from the arenes to the electron acceptor followed by nucleophilic attack of ammonia or primary amines on the aromatic radical cations (Scheme 70). 

Phenolics and their functional derivatives are widely found throughout the plant kingdom. One defining characteristic of these compounds is that their aromatic ring usually contains at least one hydroxyl substituent. In a broad sense, phenolics, which are classified according to their structural skeleton, are basically derivatives from simple phenols and phenolic acids, phenylpropanoids including coumarins and lignans, flavonoids and related compounds, and stilbenes. Some of these compounds which show anti-inflammatory activity are reviewed in this section. 

The selective nucleophilic displacement of one ortho nitro group from 2,4,6-trinitrotoluene by esters of mercap-toacetic acid followed by oxidation leads to 2-(alkoxycarbonyl)methylsulfonyl compounds. These sulfones react with aromatic aldehydes under Knoevenagel conditions to produce thiochroman 1,1-dioxides 477, probably via a stilbene and a subsequent intramolecular Michael addition. Activating groups other than nitro are compatible with the route (Scheme 167) <2003RJ0397>. 

For lignin substructures containing a carbon substituent in the aromatic C-5 position, or for stilbenes originating from phenylcoumaran structures, the oxidative degradation leads to the formation of isohemipinic acid methyl ester (4) (Fig. 6.3.2, R=CH3). However, Gellerstedt and co-workers have shown that model compounds of the biphenyl type also give rise to isohemipinic acid in addition to the expected bis-vanillic acid structure (7). The reason seems to be incomplete alkylation (pH 11, 24 h) with the result that the substrate is alkylated at only one of the available positions. To achieve a more complete alkylation, it is necessary to increase the pH to 13 or alternatively, to extend the alkylation time to 84 h. In both cases, the yield of the bis-vanillic acid structure is substantially increased as shown in Table 6.3.1 nevertheless, the concomitant formation of isohemipinic acid cannot be completely avoided. 

Discussion Point DP2 Devise a palladium-catalyzed C-C bond-forming process for the synthesis of an industrially significant compound, for example a stilbene (1,2-diphenylethylene) derivative starting from an aromatic bromo-derivative. 

The compounds of organic chemistry, and especially the substances in the aromatic series, are, in a great number of cases, capable of forming mixed crystals two by two. This property is often correlative of a true crystallographic isomorphism this is what takes place, for example, with azobenzol and stilbene, studied from this point of view by G. Bruni. Furthermore, the s3anbols of these two substances... 

The shock against benzene produced H2, light alkanes from Ci to C3, light alkenes from C2 to C3, C2H2, and aromatic hydrocarbons witli molecular weights ranging from 102 (phenylacetylene) to 306 (quaterphenyl). Tliis reaction produced H2, CH4, polyphenyl compounds such as biphenyl, terphenyl, and quaterphenyl. Otlier major products were naphthalene, fluorene, trans-stilbene, phe-nanthrene, isomers of phenylnaphthalene and chrysene. The shock produced ethenyl in greater abundance than etliyl derivatives. 

---