A Mild Benzannulation through Directed Cycloaddition Reactions

摘要

The synthesis and study of aromatic compounds is a fundamental endeavor in organic chemistry. With regard to benzene, classical synthesis methods have been dominated by electrophilic and nucleophilic aromatic substitution processes, whereas ring synthesis has largely been the domain of heteroaromatic chemistry. However, ring synthesis has the advantage that it is not limited to specific substitution patterns dictated by pre-existing directing groups. For this reason, the use of cycloaddition strategies for the assembly of aromatic rings is of significance. Studies conducted in our group in this area have placed a particular emphasis on incorporating boronic ester functionality.Whilst some catalytic variants have emerged recently, a significant drawback of this chemistry to date has been the requirement of high temperatures and long reaction times. For example, as outlined in Scheme 1, the cycloaddition of 2-pyrones and alkynylboronates requires harsh reaction conditions, is restricted to electron-deficient substrates, and provides products with variable levels of regiocontrol.