Rh(II)-Catalyzed Denitrogenative Transannulation of N-Sulfonyl-1,2,3-triazolyl Cyclohexadienones for the Synthesis of Benzofurans and Cyclopropa[cd]indole-carbaldehydes.

A rhodium-catalyzed intramolecular denitrogenative transannulation of N-sulfonyl-1,2,3-triazole-tethered cyclohexadienones has been achieved for the synthesis of benzofurans and cyclopropa[cd]indole-carbaldehydes in an operationally simple procedure. Remarkably, the reaction pathway is fully dependent on the linker heteroatom (O or N) present between the cyclohexadienone unit and triazole moiety. In the case of O-linked triazoles, a cascade sequence consisting of intramolecular cyclopropanation and rearrangement takes place, leading to the formation of benzofurans, while, in the case of N-linked triazoles, cyclopropa[cd]indole-carbaldehydes were isolated exclusively.