Trans-stilbene derivative

The photochemistry and photophysics of trans-stilbene derivatives (24) have been utilized by Whitten and co-workers to understand the relaxation characteristics of media such as micelles, monolayers, and LB films [144,145]. For example, the d>,rans to Cis for stilbene derivatives show the following trend solvent system methylcyclohexane > SDS micelle multilayer assemblies (with arachidic acid). In fact, no isomerization is observed in multilayer assemblies. This is the trend expected on the basis of how readily the media can respond to stilbene shape changes during isomerization process. 

Stojanovic S, Brede O. (2002) Elementary reactions of the antioxidant action of trans-stilbene derivatives Resveratrol, pinosylvin and 4-hydroxystilbene. Phys Chem Chem Phys A 757-764. 

A series of substituted trans-stilbene derivatives have been prepared and immobilized on a quartz surface [19]. Several immobilization methods have been tried including the silanization technique, cross-linking with cyanuric chloride, surface activation with cyanogen bromide, and surface smoothing with coating proteins. 

Diazonium salts are very useful starting materials for Heck reactions and other cross-coupling reactions (see 4.2.2). The first protocols have been developed by Matsuda and colleagues, and the reaction sometimes is being called Heck-Matsuda reaction. Since the 1970 s, a number of applications have emerged. Moro et al. used an arenediazonium salt in a Heck arylation reaction to obtain the resulting trans-stilbene derivative in excellent yield with complete stereocontrol (Scheme 5-18). ... 

The ultraviolet spectra of these compounds are similar to those of trans stilbene or of 2- and 4-stilbazole. The effect on the ultraviolet spectrum of various substituents have been found to parallel in many respects the efiects produced by the corresponding group in derivatives of aromatic hydrocarbons (142). 

Most of the olefins shown so far, for which reversibility of the bromonium ion formation had been demonstrated, are particular olefins, in which either steric bulk impedes the product forming step, or ring strain in the dibromide product retards this step. In order to check the general occurrence of the reversibility during the bromination reaction, a further approach, based on the cis-trans isomerization of stilbene derivatives during the bromination of the cis isomers, was devised. 

The investigated cw-stilbene derivatives, 4-methoxy, 4,4 -dimethyl, unsubstituted, and 4,4 -bis(trifluoromethyl)stilbenes, had k2 values spanning 6-7 powers of ten both in methanol and in acetic acid. Products 2, 4, 5 and 6 were formed. Table 8 reports the results of the cis-trans isomerization test in acetic acid (ref. 29). No acid catalyzed or free radical process was found to be responsible for these isomerizations. 

Similar results were obtained in methanol (ref. 30), where for the bis-(trifluoromethyl) derivative the ratio between the return of the trans bromonium ion to the trans olefin and its collapse to products 2 and 6 is 4.5 and is again very strongly reduced by the presence of LiC104 (Table 9). In this solvent, however, return was not observed for unsubstituted stilbene, either. It can be observed that both cis - and trans -stilbene gave methoxybromo adducts in an anti stereospecific way, suggesting a nucleophilic assistance by the solvent. 

Compounds containing carboxyl groups on adjacent carbons (succinic acid derivatives) can be bisdecarboxylated with lead tetraacetate in the presence of O2 263 jjjg reaction is of wide scope. The elimination is stereoselective, but not stereospecific (both meso- and dl- 2,3-diphenylsuccinic acid gave trans- stilbene) a concerted mechanism is thus unlikely. The following mechanism is not inconsistent with the data ... 

Steroid and stilbene derivatives e.g. trans-stilbene metabolites [16]... 

The electrophilic bromination of ethylenic compounds, a reaction familiar to all chemists, is part of the basic knowledge of organic chemistry and is therefore included in every chemical textbook. It is still nowadays presented as a simple two-step, trans-addition involving the famous bromonium ion as the key intermediate. T]nis mechanism was postulated as early as the 1930s by Bartlett and Tarbell (1936) from the kinetics of bromination of trans-stilbene in methanol and by Roberts and Kimball (1937) from stereochemical results on cis- and trans-2-butene bromination. According to their scheme (Scheme 1), bromo-derivatives useful as intermediates in organic synthesis... 

Brown s result was supported by later experiments in which bromonium ions were generated by bubbling gaseous hydrobromic acid through a solution of bromohydrins in halogenated solvents. Under these conditions, bromine is eliminated as it is formed, so that the resulting alkene is observed directly (Scheme 15). This method has been applied to the bromohydrins derived from cis- and trans-stilbenes (Scheme 16) and from 5//-dibenzo[a,d]-cycloheptene and -azepine systems ([29a] and [29b] respectively Scheme 17), in which steric constraints should favour elimination (path a) as against substitution (path b). 

Anthronylidene 64 forms no cycloaddition products with cis- or trans-4-methyl-2-pentene, but [1 -f-2]-cycloaddition is observed with stilbene derivatives. This is also attributed to the reacting triplet state I02,i30-i32) ... 

Shing and coworkers reported arabinose-derived uloses (59, 60) as epoxidation catalysts, and phenyl stilbene can be epoxidized by 60 in up to 90% ee (Fig. 20) [113-115]. In 2003, Zhao and coworkers reported aldehyde 61 to epoxidize trans-stilbene in up to 94% ee [116]. 

The bis-barium complex of pure trans-28 (0.10 mM) increases the rate of ethano-lysisof29 (65/35 EtOH/MeCN, 1 mM Me4NOEt, 25 °C) by 230-fold. The corresponding figures for quasi-trans-28-Ba2 and quasi-cis-28-Ba2 are 420- and 1280-fold, respectively. Thus, the behavior of trans and ds isomeric catalysts based on azobenzene closely parallels the behavior of the corresponding stilbene derivatives 26 and 27, in that in both cases the ds form is a superior catalyst in the cleavage of anilide 29. 

Another interesting class of molecules are stilbene derivatives with charge donating groups. These compounds offer the opportunity to explore the role of polar solvation dynamics (dielectric friction) in cis/trans isomerization. Interesting papers on this subject have been published by Waldeck et al. [145] and Rulliere et al. [146]. Other well-studied polar excited state isomerization examples include pinacyanol, l,l -diethyl-4,4 -cyanine, and crystal violet, which have been studied by Sundstrom, Gilbro and their coworkers [148] and Ben-Amotz and Harris [148] and others who are referenced in these papers [148,149],... 

FIGURE 26 Method for calculating the interaction between cellulose tris(phenylcarba-mate) derivatives or cellulose tris(3,5-dimethylphenylcarbamate) derivatives and enantiomers of trans-stilbene or benzoin. (From Ref. 29.)... 

M. Caselli, F. Momicchioli, and G. Ponterini, Chem. Phys. Lett., 216, 41 (1993). Modeling of the cis-trans Partitioning in the Photoisomerizations of Cyanines and Stilbene Derivatives. 

The conclusion that the ac electrolysis of Re rans-SP CCCOjCl proceeds via excited states is also supported by the direction of isomerization. In thermal reactions of stilbene derivatives and radicals cis to trans conversions are generally observed (61). Contrary to this behavior the photolysis and ac electrolysis lead to energetically uphill trans to cis isomerization. 

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