A Simple Synthesis of Alkyl 2-Aminobenzo[b]thiophene-3-carboxylates via an Unexpected Dehydrogenation of Alkyl 2-Amino-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylates

A simple method for the preparation of alkyl 2-aminobenzo[b]thiophene-3-carboxylates is described. Alkyl 2-amino-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylates, generated from the Gewald three-component reaction between cyclohexanones, alkyl cyanoacetates and sulfur, undergo dehydrogenation in benzonitrile under an air atmosphere to afford alkyl 2-aminobenzo[b]thiophene-3-carboxylates in good to excellent yields.