What is "borole"

Borole is a theoretical heterocyclic organic compound, a five-membered ring with the formula C H BH. It is classified as a metallole. It can be viewed as a structural analog of pyrrole, with boron replacing the nitrogen atom of pyrrole. The unsubstituted compound has not been isolated. Substituted derivatives, which have been synthesized, are called boroles. Although the Hückel's rule cannot be strictly applied to borole, it is considered to be anti-aromatic.