β-Mercaptoalkanoic carboxylic esters: versatile synthons in heterocyclic chemistry

This review presents approaches to the synthesis of heterocyclic annelated thiophenes of the last 35 years. Annelated thiophenes have been reported by the cyclocondensation reaction of beta-mercaptoalkanoic carboxylic esters with 1,3-bifunctional substrates such as alpha-haloenones, beta-haloenones, alpha-halogenoacrylic acid derivatives. The reaction takes place by nucleophilic addititon, followed by Dieckmann cyclization with the elimination of hydrogen halide. In case of other substrates such as beta-chlorocinnamonitriles, beta-haloacrylonitriles, arylsulfonylacrylonitriles, alpha,beta-unsaturated nitriles, Dieckmann-Thorpe-Ziegler cyclization occurs resulting in aminothiophene derivatives. Functionalized annulated thiophene derivatives have potent industrial applications because of significant biological properties.