Thienothiophens

In some sulfur extrusions from 2,7-di-/ Tt-butylthiepins a byproduct containing two sulfur atoms is obtained, along with the aromatic compound. The byproduct has been characterized as a thienothiophene by single crystal X-ray analysis.92... 

The bromination behavior of isomeric thienothiophenes (53-55) has been studied in detail. Both the [2,3-b] (53) and the [3,2-h](54) isomers reacted with one equivalent of NBS in acetic acid to give an a-monobrominated product, with some evidence of 2,5-dibromo species also being formed. With 2 mol of NBS these latter products were formed in good yield three molar equivalents led to 2,3,5-tribromothieno-[2,3-h]-and -[3,2-6]-thiophenes (Scheme 28). The monobromo compounds can also be prepared from lithium derivatives quenched with bromine [76AHC( 19) 123]. Apparently the [2,3-c]isomer (55) also reacted initially in the 2-position. 

Anmerkung bei der Korrektur In einer neueren Mitteilung [L. Brandsma u. D. Schuijl-Laros Recueil 89, 110 (1970)] wird jedoch fiber die Bildung der entsprechenden Thienothiophene bei der Behandlung mit Diisopropylamin in Dimethylsulfoxid berichtet. 

An alternative approach to thienothienopyridines involves intramolecular electrophilic attack at C-3 of the thiophene ring. In this way, the thienothiophene 82 can be cyclized to the benzothieno[2,3-/]thieno[2,3-c]pyridine 83 upon treatment with polyphosphoric acid (PPA) at 150°C (Equation 3). Similarly, treatment of the amide 84 with POCI3 gives the corresponding 1-alkyl-3,4-dihydro-benzothieno[3,2-g]thieno[3,2-f]pyridine 85 <1999PS(153)401> (Equation 4). 

Several useful specialized reviews have appeared during the reporting period of this chapter. The chemistry of thienothiophenes <06AHC(90)125> and thienopyrimidines <06AHC(92)83> has been discussed in detail, whereas accounts of related interest highlight the field of thiaheterohelicenes <06OBC2518> as well as similar fused thiophene systems <06AG(E)8092>. 

Thiophene and thienothiophene units have been frequently used in thienoquinoid or condensed forms in the design of new molecular architecture (16). Incorporation of the thiophene or thienothiophene unit as a rc-bridge linker could stabilize the quinoidal structure in the reduced forms (Figures 13 and 14). These two-types of new dications (222+ and 232+) stabilize the presumed two-electron reduction state by contribution of the thienoquinoid substructures (22 and 23) instead of the quinoidal form in the dication 212+ (77). 

Fig. 1 Building units of conducting polymers, (1) polyacetylene (PA) (2) polypyrrole (PPy), polythiophene (PTh), polyfurane (PFu) (3) polyphenylene (PP) (4) polyaniline (PANI) 5 polyindole (PIND) (6) polycarbazole (PCaz) (7) polyazulene (Paz) (8) polynaphthalene (PNa) (9) polyanthracene (PAnth) (10) polypyrene (PPyr) (11) polyfluorene (PFiu) (12) poly(isothionaphthalene) (PITN) (13) poly(dithienothiophene) (14) poly(thienopyrrole) (15) poly(dithienylbenzene) (1G) poly(3-alkylthiophene) (17) poly(phenylene vinylene) (18) poly(bipyrrole) (PBPy), poly(bithiophene) (PBT) (19) poly(phenylenesulfide) (20) 4-poly(thienothiophene) (21) poly(thienyl vinylene), poly(furane vinylene) (22) poly(ethylenedioxythiophene) (PEDOT).

A tandem ring-opening of 3,4- and 3,6-dilithiated thienothiophenes has been used to synthesize polyfunctionalized enediynes (e.g. Scheme 9). ... 

A. Isotope Exchange of Deuterated Thienothiophenes Quantum-Chemical... 

Further Chemical Reactions and Possible Applications of the Isomeric Thienothiophenes... 

The present review deals with condensed systems of heteroaromatic five-membered rings—thienothiophenes, di enothiophenes, seleno-phenoselenophenes, and selenophenothiophenes. The number of publications devoted to such compounds has grown rapidly in recent years. This is indicative of the mounting interest in various aspects of this field of heterocyclic chemistry, which, however, has not been reviewed since the 1954 monograph of Hartough and Meisel. ... 

All isomeric thienothiophenes are now known thieno[2,3-b]thiophene (1), thieno[3,2-b]thiophene (2), thieno[3,4-b]thiophene (3), and thieno-[3,4-clthiophene (4) (the last as a tetraphenyl-substituted derivative... 

According to the available literature, two main routes to the synthesis of isomeric thienothiophenes have been studied cyclization of various aliphatic substances, and cyclization of derivatives of the thiophene series. 

A synthetic route developed by Capelle and deConinck in 1908 produced thienothiophene 1 in somewhat better yields. By passing acetylene through the vapors of boiling sulfur and then trapi g the reaction products by carbon disulfide, they isolated, together with benzo[bl-thiophene, a compound, b.p. 225°, which formed a picrate similar to that obtained by Biedermann and Jacobson. ... 

Meyer et a/. obtained in low yields thiophene, 2-methylthiophene, benzo[6]thiophene, traces of thienothiophene 1, and some other products on passing a mixture of acetylene, hydrogen (or methane), and hydrogen sulfide at 640°-670° through a tube filled wth FeSj. 

Later authors established the approximate composition of products formed in the reaction of acetylene with sulfur at different temperatures. At 325° the composition was found to be CSj 77%, thiophene 9%, thienothiophene 1 6% at 500°, CSj 77%, thiophene 12%, and thienothiophene 1 6% at 650° CS2 83%, thiophene 5%, and thienothiophene 1 3%, with sulfur conversion being 38%, 74%, and 77%, respectively. When studying this reaction at 290°-390°, Bhatt et isolated thiophenol in addition to the above compounds but failed to increase the yield of thienothiophene 1. 

Compound 19 (R = Me, R = H) produced in the above reaction differs slightly in melting point (122° and 116°-117°, respectively) from the dimethylthienothiophene (17) obtained by Friedmann. This supports Horton s assumption that the action of sulfur on the linear Cg hydrocarbons is more likely to lead to thienothiophene 19 (R = Me, R = H) than to its isomer (17), the formation of the latter requiring a deep-seated rearrangement of the skeleton. 

None of the above authors ever considered the presence of a mixture of isomeric thienothiophenes in their reaction products, though some obtained different tetrabromo derivatives of 1 (m.p. 172° and 229°-230°) this was explained by isomorphism. 

Challenger also assumed that both thienothiophenes 1 and 3 could be formed in the reaction of citric acid with P2S3. This may be supported by the representations of the citric acid skeleton of Eqs. (7) and (8). 

Challenger and Harrison found both thienothiophene 1 and its isomer 2 in the products of the reaction between acetylene and sulfur. To identify these compounds, Challenger et developed syntheses of unsubstituted and 2-alkyl-substituted thieno[3,2-f>]thiophene (2) from thiophene derivatives. Cyclization of (3-thienylthio)acetic acid in the presence of sulfuric acid gave 2,3-dihydrothieno[3,2-6]thiophen-3-one (22) (R = H) in 14% yield reducing the latter with lithium aluminum hydride resulted in thienothiophene (2) formation in 80% yield [Eq. (9)]. Similarly 2-methyl- and 2-ethyl-2,3-dihydrothieno[3,2-/>]thiophen-3-one were obtained from a-(3-thienylthio)propionic and a-(3-tWenylthio)-butyric acids in 30% and 27% yields, respectively their reduction yielded 2-methyl (32%) and 2-ethylthieno[3,2-6]thiophenes (52%). The parent acids were prepared from 3-mercaptothiophene. ... 

When studying the carcinogenic activity of polycyclic hydrocarbons and their antdogs containing thiophene rings (cf. Tilak "), Tilak et al synthesized both thienothiophene 1 and its isomer 2 in low yield from 2-thienyl dimethoxyethyl sulfide (23) and 3-thienyl diethoxyethyl sulfide (24), respectively, by the method developed for synthesis of thiophenes and thiopyrans - [Eqs. (10) and (11)]. The compounds 23 and 24 were prepared from 2- and 3-mercaptothiophenes. ... 

Another method for e preparation of aryl w-dimethoxyethyl sulfides was described by Pandya and Tilak. The procedure consists in allowing aryl lithium derivatives to react with 2,2,2, 2 -tetramethoxy-diethyl disulfide. Subsequent cyclization of the sulfides by polyphos-phoric acid yields 2-35% of condensed thiophenes and thiopyrans. By this method, thienothiophene 1 was prepared from 2-thienyllithium [Eq. (12)] and the previously unknown dithieno[2,3-6 3, 2 -i/]thiophene (5) was obtained from thienyl-2,5-dilithium. The possibility of synthesizing a heterocyclic analog (25) of pentacene from dithieno[2,3-6 3 2 -[Pg.130]

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