Thiophenes activations

A modular and flexible approach to polythiophene sensors based on the polymerization of a thiophene-activated ester has been reported (Bernier et al. 2002). Subsequent reaction of the pol5mierized NHS ester with a variety of diamines permits the synthesis of sensors for different analytes from a common platform. For example, reaction of the NHS polymer with an aminomethyl-modified 15-crown-5 derivative yielded a polymer that underwent color changes in the presence of alkah cations (Fig. 12.14). 

Effect of Variables on Thiophene Activity over CoMo/Al Catalyst... 

The pentaammineosmium(II) metal center also binds in a dihapto fashion to several other classes of aromatic molecules, including benzenes, naphthalenes, phenols, anisoles, anilines, furans, and thiophenes, activating them toward further functionalization. The reactivity and synthetic utility of these complexes are the subject of a recent review Harman, W. D. Chem. Rev. 1997, 97,1953. 

P-22 - A DFT study of the cracking reaction of thiophene activated by zeotype catalysts role of the basic Lewis site... 

When the thiophene activations were performed with 234, a transient intermediate of type F (Chart 7) was observed,presumed to arise through interaction of the thiophene donor with 234. This was confirmed by the synthesis and isolation of a range of such materials (302-316, Chart 7), generated thermally... 

Sivaraman, P, A. Thakur, R. K. Kushwaha, D. Ratna, and A. B. Samui. 2006. Poly(3-methyl thiophene)-activated carbon hybrid supercapacitor based on gel polymer electrolyte. Electrochemical and Solid-State Letters 9 A435-A438. 

X. Rozanska, R. A. van Santen and F. Hutschka. A DFT study of the cracking reaction of thiophene activated on zeolite catalysts The role of the basic Lewis site. Stud. Surf. Sci. Catal. 135, 2001, 2611-2617. 

Organosulfur Adsorbates on Metal and Semiconductor Surfaces. Sulfur compounds (qv) and selenium compounds (qv) have a strong affinity for transition metal surfaces (206—211). The number of reported surface-active organosulfur compounds that form monolayers on gold includes di- -alkyl sulfide (212,213), di- -alkyl disulfides (108), thiophenols (214,215), mercaptopyridines (216), mercaptoanilines (217), thiophenes (217), cysteines (218,219), xanthates (220), thiocarbaminates (220), thiocarbamates (221), thioureas (222), mercaptoimidazoles (223—225), and alkaneselenoles (226) (Fig. 11). However, the most studied, and probably most understood, SAM is that of alkanethiolates on Au(lll) surfaces. 

Pharmaceuticals and Agrochemicals. Thioglycohc acid and its esters are useful as a raw material to obtain biologically active molecules. In cephalosporine syntheses, (4-pyridyl)thioacetic acid [10351 -19-8] (65) and trifluoromethane (ethyl) thioglycolate [75-92-9] (66) are used as intermediates. Methyl-3-ainino-2-thiophene carboxylate can be used as intermediate for herbicidal sulfonylureas (67) and various thiophenic stmctures (68). 

Agrochemical Products. The principal thiophene derivative in herbicidal protection, one of a range of sulfonylurea herbicides, is Harmony [79277-27-3] (Du Pont) (60), based on the intermediate methyl 3-aminothiophene-2-carboxylate (9). The product is characterized by a rapid biodegradabHity in the soil. Many other thiophene derivatives have been shown to have agrochemical activity, but few of these have been developed to the commercial level. 

The catalyst commonly used in this method is 5 wt % palladium supported on barium sulfate inhibited with quinoline—sulfur, thiourea, or thiophene to prevent reduction of the product aldehyde. A procedure is found in the Hterature (57). Suitable solvents are toluene, benzene, and xylene used under reflux conditions. Interestingly, it is now thought that Rosenmund s method (59) originally was successful because of the presence of sulfur compounds in the xylene used, since the need for an inhibitor to reduce catalyst activity was not described until three years later (60). 

The effect of substituents on the reactivity of heterocyclic nuclei is broadly similar to that on benzene. Thus mem-directing groups such as methoxycarbonyl and nitro are deactivating. The effects of strongly activating groups such as amino and hydroxy are difficult to assess since simple amino compounds are unstable and hydroxy compounds exist in an alternative tautomeric form. Comparison of the rates of formylation and trifiuoroacetylation of the parent heterocycle and its 2-methyl derivative indicate the following order of sensitivity to substituent effects furan > tellurophene > selenophene = thiophene... 

Aminothiophenes and 3-aminobenzo[Z)]thiophene undergo thermal [2 + 2] cycloaddi-tion reactions with activated alkynes. The reactions are solvent dependent thus in non-polar solvents at -30 °C, 3-pyrrolidinothiophene adds to DMAD to give a [2 + 2] cycloadduct which is ultimately converted into a phthalic ester. In methanol, however, a tricyclic product is formed (Scheme 54) (81JOC424. ... 

In many cases, substituents linked to a pyrrole, furan or thiophene ring show similar reactivity to those linked to a benzenoid nucleus. This generalization is not true for amino or hydroxyl groups. Hydroxy compounds exist largely, or entirely, in an alternative nonaromatic tautomeric form. Derivatives of this type show little resemblance in their reactions to anilines or phenols. Thienyl- and especially pyrryl- and furyl-methyl halides show enhanced reactivity compared with benzyl halides because the halogen is made more labile by electron release of the type shown below. Hydroxymethyl and aminomethyl groups on heteroaromatic nuclei are activated to nucleophilic attack by a similar effect. 

A quantitative study has been made on the effect of a methyl group in the 2-position of five-membered heteroaromatic compounds on the reactivity of position 5 in the formylation and trifluoroacetylation reaction. The order of sensitivity to the activating effect of the substituent is furan > tellurophene >selenophene = thiophene (77AHC(2l)ll9). 

Rates of debromination of bromonitro-thiophenes and -selenophenes with sodium thio-phenoxide and sodium selenophenoxide have been studied. Selenophene compounds were about four times more reactive than the corresponding thiophene derivatives. The rate ratio was not significantly different whether attack was occurring at the a- or /3-position. As in benzenoid chemistry, numerous nucleophilic displacement reactions are found to be copper catalyzed. Illustrative of these reactions is the displacement of bromide from 3-bromothiophene-2-carboxylic acid and 3-bromothiophene-4-carboxylic acid by active methylene compounds (e.g. AcCH2C02Et) in the presence of copper and sodium ethoxide (Scheme 77) (75JCS(P1)1390). 

The reactivities of the isoxazoles are compared with those of benzene and some five-membered ring heterocycles in Table 7. Isoxazole is more reactive than benzene (by 4.3 log units) and isothiazole (0.8) and is less reactive than 1-methylpyrazole, furan, thiophene and 1-methylpyrrole. A 5-methyl substituent activates the nucleus more than does a... 

Benzo[6]thiophene, 4-N-methylcarbamoyl-biological activity, 4, 913 Benzo[6]thiophene, 2-methyl-3-vinyl-cycloaddition reactions, 4, 795 Benzo[fc]thiophene, 2-( 1 -naphthyl)-synthesis, 4, 915 Benzo[6]thiophene, 2-nitro-reduction, 4, 815 synthesis, 4, 923 Benzo[6]thiophene, 3-nitro-cycloaddition reactions, 4, 789 Benzo[6]thiophene, 4-nitro-synthesis, 4, 923 Benzo[6]thiophene, 5-nitro-synthesis, 4, 923... 

Benzo[b]thiophene-2,3-quinone, 5-chloro-oxidation, 4, 824 Benzothiophenes, 4, 863-934 biological activity, 4, 911-913 intramolecular acylation, 4, 761 mass spectrometry, 4, 739 metabolism, 1, 242 phosphorescence, 4, 16 reactivity, 4, 741-861 spectroscopy, 4, 713-740 structure, 4, 713-740 substituents reactivity, 4, 796-839... 

At low temperatures unstable adsorption products or reaction intermediates could be trapped. Thus, carbonite CO, ions arise on CO interaction with basic oxygen ions which account for catalytic reaction of isotopic scrambling of CO or thiophene on activated CaO. 

In this fashion, an a-ketoester was utilized as a means of studying the antiviral and antitumor activity of thiophene derivatives of pyrazofurin 14." Reactions between dimethylthiodiglycolate and 15 provided intermediate 16, which was elaborated to 17 and 18 for comparisons with the antitumor activity of the C-nucleoside pyrazofurin 14. 

Finally, the Hinsberg synthesis has been extended to the use of a-aryl-a-carboethoxydimethyl sulfide in conjunction with a series of 1,2-dicarbonyl compounds. Specifically, the 4-nitroaryl substituent provides for sufficient activation of the a-proton to allow condensation and ring closure. These examples appear general and suggest future opportunities for the Hinsberg thiophene protocol. 

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