Thiophene chemistry

Nuclear Magnetic Resonance Spectroscopy. Nmr is a most valuable technique for stmeture determination in thiophene chemistry, especially because spectral interpretation is much easier in the thiophene series compared to benzene derivatives. Chemical shifts in proton nmr are well documented for thiophene (CDCl ), 6 = 7.12, 7.34, 7.34, and 7.12 ppm. Coupling constants occur in well-defined ranges J2-3 = 4.9-5.8 ... 

An important extension of these reactions is the Mannich reaction, in which aminomethyl-ation is achieved by the combination of formaldehyde, a secondary amine and acetic acid (Scheme 24). The intermediate immonium ion generated from formaldehyde, dimethyl-amine and acetic acid is not sufficiently reactive to aminomethylate furan, but it will form substitution products with alkylfurans. The Mannich reaction appears to be still more limited in its application to thiophene chemistry, although 2-aminomethylthiophene has been prepared by reaction of thiophene with formaldehyde and ammonium chloride. The use of A,iV-dimethyf (methylene) ammonium chloride (Me2N=CH2 CF) has been recommended for the iV,iV-dimethylaminomethylation of thiophenes (83S73). 

In the development of thiophene chemistry three periods can be clearly distinguished the Victor Meyer era, the Steinkopf period, and the modem development starting with the discovery of the synthesis of thiophene from butane and sulfur, making thiophene potentially available in unlimited amounts. Hartough in his well-known monograph, has reviewed the intense and hectic thiophene research toward the end of the 1940 s carried out mainly at the Socony-Vacuum laboratories, but also at many academic institutions. An article by Nord et al. appeared in 1955 in which the research work in thiophene chemistry at Fordham University, as well as progress in general up to 1954, was reviewed. 

Although the present rapid development of thiophene chemistry is owang to the commercial availability of thiophene, many thiophene derivatives can still advantageously be prepared by means of ring-closure reactions instead of by a complex series of substitution reactions starting with thiophene. 

One of the most striking differences between benzene and thiophene chemistry is the instability and difficult accessibility of the thiophene analogs of such important, well-known, and easily available compounds as phenol, aniline, and thiophenol. 

The literature search for this chapter has uncovered a typically large number of references for papers published in 1996. These references were culled to remove repetition and to provide the most interesting examples of thiophene chemistry and its applications. As in the past, the authors apologize for omissions and oversights. 

Nord, F. F., A. Vaitiekunas and L. J. Owen, Some Recent Developments in Thiophene Chemistry. . 309... 

Thiophene chemistry has recently been the subject of extensive investigations in various academic institutions as well as in numerous industrial research laboratories. Although these studies led to few practical applications for thiophene and its derivatives, our fundamental knowledge in this field was appreciably advanced. Since Hartoughs critical review (35) several hundred articles and patents were published dealing with various phases of thiophene chemistry. It is not the purpose of this review to consider all the reports which have been published since October 1949, but rather to discuss the more basic advances which have contributed towards explaining all phases of the progress of the chemistry of this series. 

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