Thiophenes, fused

Armulated thiophenes of types 195 and 197 (A benzo, naphtho) were studied concerning keto-enol tautomerism. The ring fusion has a remarkable influence upon these equilibria. Whereas for the c-fused thiophenes 197 only keto tautomers were present, for h-fused derivatives 195 also the enol forms 196 were found (the equilibria are solvent dependent) (82JOC705). 

Synthetic principles for bandgap control in tt-conjugated systems of poly-(thiophene) and related systems with fused thiophene rings 97CRV173. 

The key intermediate 21 is in principle accessible in any of several ways. Thus reaction of thiophenecarbox-aldehyde with amninoacetal would lead to the Schiff base 20 treatment with acid would result in formation of the fused thiophene-pyridine ring (21). Alkylation of that intermediate with benzyl chloride gives the corresponding ternary imini urn salt 23. Treatment with sodium borohydride leads to reduction of the quinolinium ring and thus formation of ticlopidine (24). ... 

Electrocyclization reactions are often used to synthesize fused thiophenes. Diazotization of an aminoisoquinoline gave a mixture of products including a 6-thiaellipticine and a pyrazolo[3,4-A]isoquinoline in 34% and 41% yields, respectively (Eq. 30) <96CC2711>. A diazotization... 

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>. 

Generation and trapping of tropothione 29 with dienophiles has been utilized in an approach to partially saturated fused thiophene molecules. For example, treatment of tropone with Lawesson s reagent in benzene, followed by introduction of jV-phenylmaleimide gave the adduct 30 in excellent yield <06TL9329>. 

The condensation of activated thiols onto adjacent nitriles is a common method for the preparation of amine-substituted thiophenes. A three component condensation was utilized to prepare a-aminothiophene 11 <00TL1597>. An alternate method for preparing amino-substituted thiophenes involved the treatment of ketene S,JV-acetal 12 with an activated carbonyl compound 13 which gave thiophene 14 <00JOC3690>. This type of reaction has also been utilized to prepare building blocks for the synthesis of fused thiophenes <00JHC363>. 

The electron-rich thiophene ring system can be elaborated into complex, fused thiophenes by acid-mediated intramolecular annelation reactions. For example, treatment of alcohol 96 with trimethylsilyl triflate promoted a Friedel-Crafts acylation and subsequent dehydration giving benzo[b]thiophene 97, a potential analgesic <00JMC765>. Treatment of ketone 98 with p-toluenesulfonic acid resulted in the formation of fused benzo[b]thiophene 99 <00T8153>. Another variant involved the cyclization of epoxide 100 to fused benzo[f>]thiophene 101 mediated by boron trifluoride-etherate . 

Membered Aromatic Rings a) Non-Fused Thiophene Compounds... 

Polymeric materials invented by CDT are conjugated homo- or copolymers. Examples are poly(arylenevinylene)s, [ArCRy CR2L] , polymers with triarylamine and triazine groups (Figure 11.17), and fused thiophenes as structural repeating units (Figure 11.18). 

FIGURE 11.18 Polymers derived from fused thiophenes. 

Dithioacetals derived from heteropine 177 smoothly react with methylene iodide in the presence of a zinc-copper couple in refluxing ether to give the corresponding fused thiophenes 178. The suggested mechanism involves formation of an ylide which undergoes intramolecular aldol-type condensation assisted by coordination of zinc with a carbonyl followed by demethylation of the S-methylthiophenium species (Scheme 35 (1989TL3093)). 

As for benzo[f7]pyrrolo[3,4-e][l,4]diazepin-3(4H)-ones 241, a fused thiophene (X = S) can be synthesized using a two-step reaction sequence (Scheme 51, Section 3.1.1.3 (1991CE495)). 

DHEs based on fused thiophenes and other heterocycles... 

The thermal decomposition of l,3-oxathiolane-5-one (112) produces the fused thiophene 113 via a transient thiocarbonyl ylide followed by intramolecular [3 - - 2]... 

The preparation of norbomadiene-fused thiophene (17) involved a double-Wittig reaction of 1,2-dione 15 with the bis-ylide derived from phosphonium salt 16 <99BCSJ1597>. The effect of the fused heteroaromatic ring of 17 (neighboring group participation) on electrophilic substitution of the norbomadiene ring was examined. 

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