Recent Progress in Transition-Metal-Free, Base-Mediated Benzannulation Reactions for the Synthesis of a Diverse Range of Aromatic and Heteroaromatic Compounds

Benzene and its derivatives are the most abundant substructures of several interesting classes of compound, such as bioactive molecules. Owing to their importance, the development of methods for their construction has attracted considerable attention. However, the regioselective synthesis of polysubstituted aromatic and heteroaromatic compounds by using aromatic substitution is challenging, because it provides derivatives with restricted substitution patterns. Therefore, the benzannulation reaction-the assembly of benzene derivatives from acyclic precursors-constitutes a superior and highly versatile approach to polysubstituted aromatic and heteroaromatic compounds, and various efficient benzannulation reactions have been reported. Representative examples include Cs2CO3, t-BuOK, and DBU-catalyzed reactions for the construction of valuable benzene derivatives. The central objective of this Focus Review is to highlight base-mediated benzannulation reactions under transition-metal-free conditions for the construction of aromatic and heteroaromatic compounds.