A General Diversified Synthesis of Carbazoles and the First Synthesis of Karapinchamine A

Abstract [IPrAuCl]/AgSbF 6 ‐catalyzed cyclization of the readily available 4‐benzoxyl‐1‐(indol‐2‐yl)‐2‐alkynols occurred smoothly in 1,2‐dichloroethane (DCE) in the presence of 4 Å MS to form a series of differently polysubstituted 2‐oxygenated carbazole derivatives efficiently. Based on mechanistic study, a possible mechanism involving 1,3‐migration of a benzoate group to form the allene, Au + ‐mediated cyclization–elimination to form a gold–carbene intermediate, and subsequent highly selective 1,2‐migration has been proposed for the formation of carbazoles. Highly selective 1,2‐migration referring to the two substituents R 3 and R 4 (R 4 =H, alkyl, and aryl group) was observed: (1) In the presence of both H and alkyl groups, 1,2‐hydrogen migration is exclusive; (2) in the presence of a methyl group (R 3 ), propyl, isopropyl, 4‐methylphenyl, and 4‐chlorophenyl groups (R 4 ) migrate exclusively. Finally, the first total synthesis of the recently isolated naturally occurring carbazole alkaloid karapinchamine A in 5.2 g scale has been realized in 6 steps from commercially available chemicals without need for any protection–deprotection.