Synthesis of substituted carbazoles and β-carbolines by cyclization of diketoindole derivatives

A new route to substituted β-carbolines and carbazoles is described. Diketoindole intermediates, prepared by Friedel–Crafts acylations of 3-substituted indoles, have been converted to 3-hydroxycarbazoles and β-carbolines in good yields, 51–96% and 82–97%, respectively. This method also allows for the formation of 4-substituted β-carbolines. The application of this methodology to the synthesis of the natural products hyellazole and 6-chlorohyellazole is also described.