Thiophenes ring synthesis

Gold catalyzed reactions are currently enjoying considerable interest, and have also found applications in thiophene ring synthesis. A series of (a-alkoxyalkyl)(o-alkynylphenyl) sulfides 14 was subjected to treatment with catalytic amounts of AuCl, giving the benzo[fe]thiophenes 15 in excellent yields. Some additional, more complex examples were also provided <06AG(E)4473>. 

A thiophene ring synthesis has been achieved by reactions of 1,3-dicarbonyl compounds with carbon disulfide, followed by annulation with ethyl bromoacetate, giving for instance the system 13 <07T2724>. 

According to the classification mentioned above, the thiophene ring synthesis by forming one carbon-sulfur bond adjacent to sulfur is described first (Equation 1). 

The thiophene ring synthesis by forming a carbon-carbon bond 7 to sulfur atom is described (Equation 10). Several new syntheses that belong to this category have been developed. 

Condensed systems including thiophene ring, synthesis of 84PHA4 ... 

Several routes involving thiophene ring synthesis towards more complex heterocycle fused thiophene systems should also be mentioned. Thus for example, the alkaloid thienodolin 56 has been prepared by reaction of l-(/ert-butoxycarbonyl)-2,6-dichloroindole-3-carboxaldehyde with 2-mercaptoacetamide <04EJO2589>, while a double cyclization of 2,6-dichloropyridine-3,5-dicarbonitrile or the corresponding pyrazine derivative with ethyl 2-... 

Thiophene ring synthesis from active methylene groups... 

Hinsberg thiophene ring synthesis 7, 773 Hofmann degradation... 

Scheme 1 General sequence for thiophene ring synthesis from a 1,4-dicarbonyl compound...

Scheme 10 Alkylation of a 1,3-keto-ester with a 2-haloketone then hydrolysis and decarboxylation to form a 1,4-diketone for thiophene ring synthesis [20]. N.B. The original method for enolate formation is shown - an alternative method would be used nowadays...

The methods for de novo thiophene ring synthesis described in this chapter, many of which have been known for some time, continue to dominate the field. No doubt there will be future innovations, but the range of substituted thiophenes which can already be readily produced by these known methods, taken with the well-developed substitution chemistry of thiophenes (Chapter 3, Thiophene Substitution Chemistry), makes accessing any desired thiophene-containing compound a relatively well-developed art. 

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