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

[IPrAuCl]/AgSbF6-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 angstrom 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 karapinchamineA in 5.2g scale has been realized in 6steps from commercially available chemicals without need for any protection-deprotection.