Synthesis of unsymmetrical B2E2 and B2E3 heterocycles by borylene insertion into boradichalcogeniranes.

We report the selective insertion of a range of borylene fragments into the E-E bonds (E = S, Se, Te) of cyclic boron dichalcogenides. This method provides facile synthetic access to a variety of symmetrical and unsymmetrical four- and five-membered rings.