Construction of heterocycle-fused tetrahydrocarbazoles through a formal [3 + 3]-annulation of 2-indolylmethanols with para -quinone methides.

A metal-free approach for the synthesis of tetrahydroindolo[2,3- b ]carbazoles has been developed through an acid-mediated one-pot [3 + 3]-annulation of 2-indolylmethanols and 3-indolyl-substituted para -quinone methides. This operationally simple protocol allowed us to prepare many unsymmetrical tetrahydroindolo[2,3- b ]carbazoles in good to excellent yields with a broad substrate scope. This concept was also elaborated to the synthesis of tetrahydrothieno[2,3- b ]carbazoles and tetrahydrothieno[3,2- b ]carbazoles.