Benzannulation of Indoles to Carbazoles and Its Applications for Syntheses of Carbazole Alkaloids
摘要:
A novel and efficient method for the benzannulation of indoles to carbzaoles is reported gamma-Carbonyl tert butylperoxide is applied as a new diene building block for the pi-extension of simple indoles. The synthetic utility of this method is demonstrated by concise and selective total syntheses of naturally occurring carbazole alkaloids, olivacine, and asteropusazole A.
2‐Alkoxy‐2,3‐dihydrofurans were found to be versatile benzannulation reagents. Indoles can be synthesized in good to excellent yields via the [4+2] annulation of 2‐butoxy‐2,3‐dihydrofuran with pyrroles catalyzed by copper bromide. With the same protocol, carbazoles can also be obtained when indoles are used as starting material with the aid of p‐toluenesulfonic acid. This type of benzannulation reagent