Thiophenes reactions

This 1,3-migration of hydrogen was also observed when 40 reacted with Lawesson s reagent to produce the dithiolactone 41. However, when y-hydroxy-a,P-unsaturated aldehyde 42 was reacted under similar conditions, thiophene 43 was prepared efficiently. These results are not surprising considering that the oxidation state of 42 is equivalent to the traditional saturated 1,4-dicarbonyl substrates of the Paal thiophene reaction via tautomerization of the double bond, and aromaticity is reestablished in the fully conjugated 43. 

ETEROAROMATics FURAN AND THIOPHENE. The chemical transformation of thiophene at high pressure has not been studied in detail. However, an infrared [441,445] study has placed the onset of the reaction at 16 GPa when the sample becomes yellow-orange and the C—H stretching modes involving sp carbon atoms are observed. This reaction threshold is lower than in benzene, as expected for the lower stability of thiophene. The infrared spectrum of the recovered sample differs from that of polythiophene, and the spectral characteristics indicate that it is probably amorphous. Also, the thiophene reaction is extremely sensitive to photochemical effects as reported by Shimizu and Matsunami [446]. Thiophene was observed to transform into a dark red material above 8 GPa when irradiated with 50 mW of the 514.5-nm Ar+ laser line. The reaction was not observed without irradiation. This material was hypothesized to be polythiophene because the same coloration is reported for polymeric films prepared by electrochemical methods, but no further characterization was carried out. 

Whereas 2-hydroxymethylthiophene reacts normally with hydrogen halides to give 2-halomethyl-thiophenes, reaction of 2-hydroxymethylfuran (2-furfuryl alcohol) with hydrochloric acid results in formation of laevulinic acid (350) via the intermediate (349). The conversion of 2-furanacrylic acid... 

Cine substitution has also been observed in the reaction of the 3-nitro-4-sulfone (423) with thiophenoxide <76JCS(P1)2264). A mixture of products (424) and (425) is formed, but the major one is (425) where the N02 has been displaced. Preliminary studies have shown that here the mechanism may also be similar to the one described above for the dinitro-thiophene reaction (78JCS(P1)1140). 

The successful application of the Hammett equation to methanolysis of 2-chloro-5-X-methylselenophenes,284 and debromination by sodium thiophenoxide of 2-bromo-5-X-3-nitroselenophenes (EtOH, 20°)275 is also reported. In the latter case p is 3.15 cf. 3.21 for the equivalent thiophene reaction. 

On the other hand, H2S did not prevent cis-trans isomerization and double bond shift reactions from going to completion at 300° or 350°, and the olefin mixtures analyzed were always found to be close to thermodynamic equilibrium, whether they had been formed from thiophene, butadiene, or one of the olefins themselves. Nor did H2S prevent the total conversion of butadiene to butene, even when 10- to 20-cc. samples were used at reaction temperatures down to 200° C. and flow rates up to 10 liters per hour. This may be the explanation of the absence of butadiene from the thiophene reaction products over cobalt molybdate—that if it had been formed as it was over chromia, it would have reacted further too rapidly to survive. 

---