Thiophenes multi-ring

Zhou, A.N., Ma, X.L., and Song, C.S. Liquid-phase adsorption of multi-ring thiophenic sulfur compounds on carbon materials with different surface properties. The Journal of Physical Chemistry. B, 2006, 110, 4699. 

Multi-ring heteroaromatic compounds containing furan and thiophene rings have been prepared by pressured cycloaddition of 2-vinylbenzo[ ]furan (40a) and 2-vinylbenzo[Z)]thiophene (40b) with 3-nitro-2-cyclohexen-l-one (41) and 2-inden-l-one (42), respectively, generated in situ. ... 

Replacement of a benzene ring by its isostere, thiophene, is one of the more venerable practices in medicinal chemistry. Application of this stratagem to the NSAID piroxicam, gives tenoxicam, 136, a drug with substantially the same activity, nie synthesis of this compound starts by a multi-step conversion of hydroxy thiophene carboxylic ester 130, to the sulfonyl chloride 133. Reaction of that with N-methylglycinc ethyl ester, gives the sulfonamide 134. Base-catalyzed Claisen type condensation serves to cyclize that intermediate to the p-keto ester 135 (shown as the enol tautomer). The final product tenoxicam (136) is obtained by heating the ester with 2-aminopyridine [22]. 

Benzoheteropines with fused pyrrole, furan, and thiophene rings, of great interest because of their biological activity, are surveyed by Dr. D.O. Tymoshenko of the Albany Molecular Research Institute, New York. These compound classes were considered in both the first and second editions of Comprehensive Heterocyclic Chemistry as part of a host of related multi-atom heterocyclic systems. Other specialized reviews have appeared. However, the present survey is the first comprehensive treatment. 

There has probably been more work carried out on the synthesis of indoles than on any other single heterocyclic system and consequently many routes are available ring syntheses of benzo[Z ]furans and benzo[fc]thiophenes have been much less studied. The Fischer indole synthesis, now more than 100 years old, is still widely used - an arylhydrazone is heated with an acid, a multi-step sequence ensues, ammonia is lost and an indole is formed. 

---