β-Mercaptoalkanoic carboxylic esters: versatile synthons in heterocyclic chemistry

Dedicated to Dr. C. Someswara Rao on the occasion of his 72^nd birthday

Abstract

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 β -mercaptoalkanoic carboxylic esters with 1,3-bifunctional substrates such as α -haloenones, β -haloenones, α -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 β -chlorocinnamonitriles, β -haloacrylonitriles, arylsulfonylacrylonitriles, α,β -unsaturated nitriles, Dieckmann–Thorpe–Ziegler cyclization occurs resulting in aminothiophene derivatives. Functionalized annulated thiophene derivatives have potent industrial applications because of significant biological properties.

Dedicated to Dr. C. Someswara Rao on the occasion of his 72^nd birthday

Keywords:

• β-mercaptoalkanoic carboxylic esters
• cyclocondensation
• Thorpe–Ziegler cyclization
• Dieckmann cyclization
• Michael addition
• Knoevenagel-type condensation

Acknowledgements

The author thanks Dr S.R. Ramadas, Professor of Chemistry (Retd), IIT-Chennai and Dr S.P. Hiremath, President Indian Council of Chemists for their technical help and constant encouragement.

Notes

Dedicated to Dr. C. Someswara Rao on the occasion of his 72^nd birthday