Thiophenes, acetylenic

K. Nakao, M. Nishimura, T. Tamachi, Y. Kuwatani, H. Miyasaka, T. Nishinaga and M. lyoda. Giant macrocycles composed of thiophene, acetylene and ethylene building blocks, J. Am. Chem. Soc., 128, 16740-16747 (2006). 

Butane and higher alkanes, as weU as corresponding alkenes and 1,3-dienes, undergo a cyclodehydrogenation with sulfur in the gas phase, with the formation of thiophenes. Acetylene, as well as 1,3-diynes, also yield thiophenes with H2S under similar conditions ... 

A total of foxuteen new thiophen-acetylenic compounds have been isolated from various species of the S. African tribe Arctotideae of the genus Berkheya, and structures (21)—(24) have been proposed for the compounds. Bohlmann... 

Bohlmann, F., W.R. Abraham, R.M. King, and H. Robinson Polyacetylenic compounds. Part 257. Thiophene Acetylenes and Flavanols from Pterocaulon virgatum. Phytochemistry 20, 825 (1981). 

Benzyne, generated from diphenyliodonium 2-carboxyIate, reacts with various thiophenes by addition to the sulfur and /3-carbon to give, after loss of an acetylene moiety, benzo[Z)]thiophenes in low (<4%) yield (Scheme 52) (81CC124). 

The direct combination of selenium and acetylene provides the most convenient source of selenophene (76JHC1319). Lesser amounts of many other compounds are formed concurrently and include 2- and 3-alkylselenophenes, benzo[6]selenophene and isomeric selenoloselenophenes (76CS(10)159). The commercial availability of thiophene makes comparable reactions of little interest for the obtention of the parent heterocycle in the laboratory. However, the reaction of substituted acetylenes with morpholinyl disulfide is of some synthetic value. The process, which appears to entail the initial formation of thionitroxyl radicals, converts phenylacetylene into a 3 1 mixture of 2,4- and 2,5-diphenylthiophene, methyl propiolate into dimethyl thiophene-2,5-dicarboxylate, and ethyl phenylpropiolate into diethyl 3,4-diphenylthiophene-2,5-dicarboxylate (Scheme 83a) (77TL3413). Dimethyl thiophene-2,4-dicarboxylate is obtained from methyl propiolate by treatment with dimethyl sulfoxide and thionyl chloride (Scheme 83b) (66CB1558). The rhodium carbonyl catalyzed carbonylation of alkynes in alcohols provides 5-alkoxy-2(5//)-furanones (Scheme 83c) (81CL993). The inclusion of ethylene provides 5-ethyl-2(5//)-furanones instead (82NKK242). The nickel acetate catalyzed addition of r-butyl isocyanide to alkynes provides access to 2-aminopyrroles (Scheme 83d) (70S593). 

The polymers which have stimulated the greatest interest are the polymers of acetylene, thiophene, pyrrole and aniline, poly-p-phenylene, polyphenylvinylene and poly-l,6-heptadiyne. Of these materials polypyrrole has been available from BASF under the trade name Lutamer P160 since 1988. 

The Fiesselmann thiophene synthesis involves the condensation reaction of thioglycolic acid derivatives with a,P-acetylenic esters, which upon treatment with base results in the formation of 3-hydroxy-2-thiophenecarboxyIic acid derivatives. 

The mechanism of the Fiesselmann reaction between methylthioglycolate and a,P-acetylenic esters proceeds via consecutive base-catalyzed 1,4-conjugate addition reactions to form thioacetal Enolate formation, as a result of treatment with a stronger base, causes a Dieckmann condensation to occur providing ketone 8. Elimination of methylthioglycolate and tautomerization driven by aromaticity provides the 3-hydroxy thiophene dicarboxylate 9. 

The ease with which thiophenes are formed in the reaction of acetylenic epoxides " and of polyacetylenes with hydrogen sulfide is of great interest in connection with the biosynthesis of the naturally occurring thiophenes (cf. Section VIH,A) and also of preparative importance. 2-Methyl-l,2-oxido-5-hexene-3-yne (56) in water containing barium hydroxide reacts with HzS at 50°C to give 4-... 

The discovery of junipal focused the attention of Sorensen, who had been investigating the occurrence of polyacetylenes in Com-positae, on the possibility that these acetylenes were accompanied by thiophenes. From Coreopsis grandiflora Hogg ex sweet, 2-phenyl 5-(1-propynyl) thiophene (240) was isolated and its structure confirmed by synthesis of the tetrahydro compound, 2-phenyl-5-n-propyl-thiophene. From the root of tansy, the cis and trans isomers of methyl 5-(l-propynyl)-2-thienylacrylate (241) have been isolated. The total synthesis of trans (241) was achieved by reacting junipal with methylcarbethoxy triphenylphosphonium bromide (Wittig reaction) Several monosubstituted thiophenes, (242), (243), and... 

Dithiatopazine 73 serves as a sulfur-transfer reagent under thermal conditions. Tlius, heating 73 and diene 130 in toluene at 100°C formed a cyclic disulfide 131 (25%) and a tetrasulfide 132 (28%) with the formation of the alkene 118 (90%). Under similar conditions, the highly strained acetylene 133 was converted to the 1,2-dithiete 134 (65%) and the congested thiophene 135 (12%) (90JA3029). 

The irradiation of the thiophene in gas phase yields ethylene, allene, methyl-acetylene, carbon disulfide, and vinylacetylene. No Dewar thiophene or cyclo-propene derivatives were isolated (69CJC2965). The irradiation in liquid phase gave the Dewar thiophene which can be trapped as a Diels-Alder adduct with furan (85JA723). The Dewar thiophene and cyclopropene-3-thiocarbaldehyde can be obtained by irradiation in argon matrices at 10 K (86JA1691). 

The versatility of poly(phenylcne) chemistry can also be seen in that it constitutes a platform for the design of other conjugated polymers with aromatic building blocks. Thus, one can proceed from 1,4- to 1,3-, and 1,2-phenylene compounds, and the benzene block can also be replaced by other aromatic cores such as naphthalene or anthracene, helerocyclcs such as thiophene or pyridine as well as by their substituted or bridged derivatives. Conceptually, poly(pheny ene)s can also be regarded as the parent structure of a series of related polymers which arc obtained not by linking the phenylene units directly, but by incorporation of other conjugated, e.g. olefinic or acetylenic, moieties. 

The thiophene analogue (51) of the natural antifeedant product tonghaosu has been prepared <96TL893>. Several acetylenic thiophene derivatives including 52 have been isolated from Blumea obliqua and characterized <96MI733>. 

Fraction 4 (P.E./CHjClj, 1 1) was a bright red solution the T1 NMR spectrum of which indicated a mixture of two acetylenic constituents (A and B) which were separated by preparative TLC on 1 mm silica gel plates. The red band (A), when left in soln for 15 hr at r.t., lost its color. The Tl NMR spectrum of the decolored soln was identical with the spectrum of compound B. Comparison of the physical data (1H NMR and MS) of the two compounds with the spectral data reported for the dithiophene (A) (10) and the thiophene (B)... 

The zinc chloride complex of l-(2-pyridyl)-2-(2-thienyl)ethyne has been structurally characterized by single crystal X-ray diffraction showing the ligand is a monodentate nitrogen donor. The N2Q2 tetrahedral coordination geometry reveals little apparent influence of the acetylene or thiophene groups.110... 

Valence Isomerization of the 2-Thiabicyclo[3.2.0]heptadiene Moiety In principle, a valence isomerization of thiabicyclo[3.2.0]heptadiene skeleton would lead to a thiepin ring system. Wynberg et al. 23) reported that the photochemical adduct (28) from benzo[6]thiophene and dimethyl acetylenedicarboxylate was not thermally stable. When heated in diglyme, it loses sulfur to give dimethyl 1,2-naphthalenedicarboxylate. This reaction presumably proceeds via ring opening of 28 to 2,3-dimethoxycarbonylbenzo[6]thiepin (29) which readily eliminates sulfur. This synthetic route was successfully applied to the reaction of electron-deficient acetylenes with enamines of 2,3-dihydrobenzo[fe]thiophen-3-ones in which the enamine moiety constitutes part of a thiophene system. When 3-pyrrolidin-l-yl-benzo[6]thiophene (30) was allowed to react with dimethyl acetylenedicarboxylate... 

A brown explosive form is produced if excess sodium is used in preparation of thiophene homologues—possibly because of sulfur compounds [1], As normally produced, it is a dry stable solid, but material prepared from acetylene and sodium-oil dispersions ignites in air [2],... 

Goncales CEP, Araldi D, Panatieri R B, Rocha J B T, Zeni G and Nogueira C W (2005), Antinociceptive properties of acetylenic thiophene and furan derivatives Evidence for the mechanism of action , Life Sciences, 76, 2221-2234. 

The 2,5-dihydro-l,3,4-thiadiazole 79 reacts with a range of acetylenic dipolarophiles to afford the 2,5-dihydrothio-phenes 80 in 25-75% yields (Equation 19) <2002HCA451>. The thermal extrusion of dinitrogen from the thiadia-zole affords a thiocarbonyl ylide, which reacts with the dipolarophiles to form the thiophenes. 

Sonogashira reactions of both a-halothiophenes [117] and P-halothiophenes [118] proceed smoothly even for fairly complicated molecules as illustrated by the transformation of brotizolam (134) to alkyne 135 [119]. Interestingly, 3,4-bis(trimethylsilyl)thiophene (137), derived from the intermolecular cyclization of 4-phenylthiazole (136) and bis(trimethylsilyl)acetylene, underwent consecutive iodination and Sonogashira reaction to make 3,4-bisalkynylthiophenes [120], Therefore, a regiospecific mono-i/wo-iodination of 137 gave iodothiophene 138, which was coupled with phenylacetylene to afford alkynylthiophene 139. A second iodination and a Sonogashira reaction then provided the unsymmetrically substituted 3,4-bisalkynylthiophene 140. 

As demonstrated in previous sections, the carbazole unit was introduced as a pendant group or as a chain member in major classes of EL polymers such as PPVs (95-105,141,177, 190) and PFs (62, 63, 242-245). A variety of 2,7-carbazole-derived polymers with different conjugated units, such as 2-alkoxy- and 2,5-dialkoxy-l,4-phenylene (549) and l,l -binaphtha-lene-6,6 -diyl (550 [658]), 2,5-pyridine (551), 2,7-fluorene (245 [345,346]), 2,5 -bithiophene (554 [345]), 5,8-quinoxaline (552), quinquethiophene-SjS -dioxide (450 [550]), 2,5-thiophene (553), 2,5-furan (555), and acetylene (556 [659]) were reported by Leclerc and coworkers... 

Most reactive metabolites produced by CYP metabolic activation are electrophilic in nature, which means that they can react easily with the nucleophiles present in the protein side chains. Several functional groups are recurrent structural features in M Bis. These groups have been reviewed by Fontana et al. [26] and can be summarized as follows terminal (co or co — 1) acetylenes, olefins, furans and thiophenes, epoxides, dichloro- and trichloroethylenes, secondary amines, benzodioxoles (methylenediox-yphenyl, MDP), conjugated structures, hydrazines, isothiocyanates, thioamides, dithiocarbamates and, in general, Michael acceptors (Scheme 11.1). 

Various unsaturated thiophene compounds were investigated viz., polyenes, polyenic acids and aldehydes and various acetylenic derivatives (59), (60), (76-81). 

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