Simple, one-step syntheses of tri- and tetracyclic B,N,S-heterocycles from reactions of a diboracumulene with thiols.

Boron-containing fused heterocycles have received considerable attention due to their unique structures, bonding, and intriguing properties. However, progress in this area has been hampered by a lack of efficient synthetic methodologies. In this study, we demonstrate the reactivity of a diboracumulene, LBBL (L = cyclic (alkyl)(amino)carbene, CAAC), with various nitrogen-containing heterocyclic thiols. These straightforward reactions result in the partial or complete cleavage of the B-B multiple bonds in the diboracumulene, along with S-H bond activation in the thiol units, leading to the formation of a range of tricyclic and tetracyclic B,N,S-heterocycles. Notably, the tricyclic B,N,S-heterocycle exhibits π aromaticity in all three of its rings.