Improved synthesis of 3-(dialkylaminomethyl)-indole in acetic acid aqueous solution under ultrasound irradiation.

Synthesis of Mannich bases related to gramine via Mannich reaction of secondary amine, formaldehyde and indole or N-methylindole can be carried out in 69-98% yields in acetic acid aqueous solution at 35°C under ultrasound irradiation. Compared with the method using stirring, the present procedure provided several advantages such as milder conditions, shorter reaction time and higher yield.