Additive-controlled divergent annulation of ynamide-ynes: Selective synthesis of benzo[b]carbazoles and furo[3,4-b]indoles

An additive-controlled divergent annulation strategy enables the selective synthesis of benzo[ b ]carbazoles and furo[3,4- b ]indoles from ynamide-ynes. The reaction pathway is modulated by additive selection such that Zn(OTf) 2 alone catalyzes benzo[ b ]carbazole formation, while the addition of TMSOTf to the Zn(OTf) 2 system redirects the transformation toward furo[3,4- b ]indoles. This method demonstrates excellent additive control, broad functional group tolerance, and operational simplicity under moderate conditions, providing an efficient approach to these privileged N -heterocyclic scaffolds.