A New Preparative Route to Substituted Carbazoles by Benzannulation

A new regioselective pathway to substituted carbazole derivatives is described here. According to this procedure substituted 2-alkoxycarbonyl4-acetoxy-9-(p-toluenesulfonyl) carbazoles are obtained by treatment of substituted 6-[2-(p-toluenesulfonylamino)-aryl]-3-alkoxycarbonylhex-3-en5-ynoic acids with acetic anhydride in the presence of sodium acetate. The latter acids are prepared from the easily available substituted o-iodo-anilines by Sonogashira coupling with propargylic alcohol and Wittig reaction as the key steps. The described benzannulation reaction proceeds in regiospecific fashion and a range of substituents are tolerated.