Synthesis of 7‐Allylated Benzofuran Derivatives from o‐Allyloxyethynylbenzene via Claisen Rearrangement and TBAF‐Catalyzed Annulation

Abstract

The 7‐allylated benzofuran derivatives were synthesized via a continuous reaction of Claisen rearrangement and annulation using o‐allyloxyetynylbenzene as starting material. In addition, it was observed that annulation of o‐alkynylphenol proceeded under mild conditions when carried out in the presence of a catalytic amount of TBAF. Furthermore, these continuous reactions could be achieved in a one‐pot reaction and afforded not only 7‐allylbenzofurans but also 7‐alkenylbenzofurans by controlling the reaction temperature and time of the annulation. Finally, we demonstrated that 7‐allylbenzofuran and 7‐alkenylbenzofuran could be converted into 7‐(2‐formylvinyl)benzofuran and 7‐formylbenzofuran derivatives, respectively. Therefore, various 7‐substituted benzofuran derivatives could be synthesized according to this synthetic strategy.

Functionalized Benzofurans via Microwave‐Promoted Tandem Claisen‐Rearrangement/5‐endo‐dig Cyclization

“…During preparation of this manuscript, Mino and coworkers published a closely related two‐step approach to 7‐allylbenzofurans from ortho ‐allyloxyalkinyl benzenes that uses a Lewis acid‐mediated Claisen rearrangement, followed by a TBAF‐catalyzed 5‐ endo ‐dig cyclization. Both steps can be conducted in one pot, but in this case, overstoichiometric amounts of TBAF are required to promote the cyclization .…”