Gold-catalyzed cyclization of 1-(indol-3-yl)-3-alkyn-1-ols: facile synthesis of diversified carbazoles

Abstract

Efficient cyclization of 1-(indol-3-yl)-3-alkyn-1-ols in the presence of a cationic gold(I) complex, leading to annulated or specific substituted carbazoles, was observed. Depending on the reaction conditions and substitution pattern, divergent reaction pathways were discovered, furnishing diversified carbazole structures. Cycloalkyl-annulated [b]carbazoles are obtained through 1,2-alkyl migration of the metal-carbene intermediates; cycloalkyl-annulated [a]carbazoles are formed through a Wagner-Meerwein-type 1,2-alkyl shift; carbazole ethers are constructed through ring-opening of the cyclopropyl group by nucleophilic attack of water or an alcohol.

Keywords: carbazoles; catalysis; cyclization; gold; indoles.