Acid-promoted Furan Annulation And Aromatization:An Access To Benzo[b]furan Derivatives

Benzofuran is a very important class of oxygen-containing aromatic heterocyclic compounds,which have been found in numerous natural products with potential biological activity and drug molecules,given the good physiological and pharmacological activities,their synthesis has become a stimulating research field in organic synthesis.Due to the low efficiency of extraction and separation of benzofuran derivatives from natural products.Therefore,it is necessary to develop new methods for the construction of benzofuran derivatives.There are two common ways for the construction of benzofuran derivatives.One of the most explored methods for this purpose is the annulation of the furan ring starting from poly-substituted benzene derivatives.Another possible way,for constructing the benzene portion of benzo[b]furan via benzannulation of furan derivatives.These methods including transition metal catalysis,Lewis acid-mediated cyclization,and organocatalytic versions.Despite these achievements,the limitations of the preparation of benzo[b]furan derivatives still exist.Such as,multicomponent catalyst systems,harsh reaction conditions,expensive reagents,and low reaction efficiency.Considering the strategies applicable to our goal as well as atomic economy and operating simplicity,we developed an unprecedented PTSA-promoted furan annulation and aromatization in one pot.This process offers a simple and efficient synthetic route for the construction of various highly substituted benzo[b]furan derivatives,the synthetic process proceeds efficiently at mild conditions without metal catalysts and extra oxygen source,a range of highly substituted benzo[b]furan motifs were synthesized with excellent yields.These motifs are widely used not only in drug active molecules but also in photoelectricity chemistry.The preliminary mechanism study indicated this transformation proceeded sequentially via furan annulation and aromatization in one pot.