Ultrasound-accelerated Michael addition of indole to α,β-unsaturated ketones catalyzed by ceric ammonium nitrate (CAN)

Ceric ammonium nitrate efficiently catalyzes the Michael addition of indole to alpha,beta-unsaturated carbonyl ketones by means of alkylation of indole under ultrasonic irradiation to afford the corresponding adduct in excellent yields. The substitution on the indole nucleus occurred exclusively at the 3-position, and N-alkylation products have not been observed.