4,5,6,7-Tetrahydroindoles, due to their easy aromatization, are good intermediates to synthesize indoles. 4,5,6,7-Tetrahydroindole on condensation with cyanoacetate leads to 1-ethylthio-2-cyano-4,5,6,7-tetrahydrocyclohexa-[c]-3H-pyrrolizin-3-one.