Monosubstituted thiophene derivatives

Carbon-13 resonances for twelve monosubstituted thiophen derivatives have been observed at 15.085 MHz. In 2-substituted thiophens the C-4 shifts fall into a narrow range of 5.2 p.p.m. (as do the C-5 shifts of 3-sub-stituted compounds), whereas the C-5 shifts are spread over a range of 21.1 p.p.m., indicating the sensitivity of the chemical shifts to resonance effects. There has been active interest in the n.m.r. spectra of thienyl-substituted phosphorus and silicon derivatives. The H n.m.r. spectra of... 

Thiophenes and their Benzo Derivatives (i) Structure Table 3 UV Spectra of Monosubstituted Thiophenes... 

Mono- and disubstituted-3,4-dihydroxythiophenes can potentially exist in four tautomeric forms (116)-(119), For unsubstituted and for most disubstituted derivatives, the hydroxyketo form (117) or (118) is observed. In monosubstituted products (R H, R = H), (117) is the only one observed <71T3839>. These compounds also follow a trend similar to that found in the furan series with the exception of the parent compound 3,4-dihydroxyfuran which exists in the dioxo form <60JA3219>. The only thiophene derivative not to follow the trend is the 2,5-diethoxycarbonyl substituted compound which exists in the dihydroxy form (116 R, R = C02Et). 

Ag2C03 in the arylation of thiophenes with iodoarenes. This is a remarkably general phenomenon, applicable to unsubstituted, monosubstituted, and disubstituted thiophene derivatives, as well as thiophene-containing fused aromatic compounds (eq 3). ... 

The conformational preferences of 2- and 3-monosubstituted derivatives of furans, thiophenes and pyrroles have been the subject of ab initio MO studies (77JCS(P2)160l, 78JA3981,79JA311). Of the systems considered, experimental information from microwave spectroscopy is available for 2- and 3-methyl... 

Prominent bands in the vapor phase UV spectra of 3-chloro-,179 5-chloro-,180,181 and 7-bromobenzo[6]thiophene181 have been tentatively assigned. Spectra of substituted benzo [6]thiophenes in various solvents have been recorded but not examined in detail data for a number of monosubstituted derivatives have been collected in Table I. 

Attempts to correlate the position of the substituent with the UV spectrum have been largely unsuccessful, but some general comments may be made. The spectra of most monosubstituted derivatives resemble that of benzo [6]thiophene and the three distinct zones usually remain. Methyl or halo substituents cause an overall bathochromic shift relative to benzo [6]thiophene—zone B is most affected by 3-, 5-, or 6-substituents zone C by 5-substituents.134,159,162 3-Alkyl-benzo[6]thiophenes are characterized by zone-B bands of lower intensity than those of benzo [6]thiophene and its other alkyl derivatives.134 The UV spectra of 2-methylbenzo[6]thiophene and its selenium analog have been compared.182... 

In this chapter, selenienyl is used (analogously to thienyl in thiophene chemistry) to denote derivatives of the monosubstituted ring Chemical Abstracts uses selenophene-yl. ... 

Unsubstituted pyrrole, thiophene and furan are typical 7r-excessive heteroaromatics and readily react with electrophiles under mild conditions. The products of monosubstitution are mainly or solely 2-substituted derivatives. 

The Grignard reagent of 2-chloro thiophene underwent the Kumada reaction with 2,6-dichloropyridine 84 to produce the monosubstituted pyridine 85. Mixed heteroarene 86 was afforded when 85 was allowed to react with the Grignard derived from, V-methyl-2-bromoindole [29]. 

Friedel-Crafts acylation, nitration, sulfonation, and bromination of benzo[ )naphtho[l,2-d]thio-phene take place at the position shown in (369) <84PJCI243>. Nitration as well as Friedel-Crafts acetylation of phenanthro[4,5-Z>c. 

Many substituted thiophenes are commercially available. Thus, the study of the effects of substituents on polythiophene is relatively straightforward in comparison with pyrrole, whose 3-monosubstituted and 3,4-substituted derivatives are not easily synthesized. Table 3 gives many substituted thiophenes that can be electrochemi-cally oxidized to produce conducting polymers. Some derivatives, such as 3-thiophene acetic acid, 3-thiophene malonic acid, 3-thiophene carboxylic acid, and 3-thiophene carboxaldehyde do not polymerize at all [205). 

Other monosubstituted polyisothianaphthenes have been reported. In 1989 a report appeared stating that poly(5-benzoyIbenzo[c]thiophene) (80) had been prepared by electrochemical polymerization of the monomer, 5-benzoylbenzo[c]thiophene, which had been prepared by the sulfoxide route similar to that shown in Scheme 1 for the parent polymer 1 and in Scheme 2 [28]. Unfortunately, no other data were given. A variety of other substituted derivatives were prepared by the sulfoxide route (Schemes 1 and 2) as described in a Japanese patent, and four-point probe conductivities (electrochemical doping/Bu4N Cl /CHaCN) of 10 S/cm were reported for poly(5-octyloxybenzo[c]thiophene) (81) and poIy(5-octyIaminobenzo[f]thiophene) (82)... 

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