Gold-catalyzed annulations of N-aryl ynamides with benzisoxazoles to construct 6H-indolo[2,3-b]quinoline cores

This work reports new annulations of N-aryl ynamides with benzisoxazoles to form 6H-indolo[2,3-b]quinoline derivatives. The synthetic utility of this new method is manifested by its applicability to access naturally occurring alkaloids including norcryptotackeine, neocryptolepine and 11-methylneocryptol-epine. Our experimental data indicate that high-temperature conditions allow N-aryl nucleophiles to become conformationally flexible, rendering the attack at gold carbenes effective to generate reactive indoles that attack again the benzaldehyde to furnish the observed products.