CSF-promoted desilylation and ring-contraction reaction of electron-deficient 3-silyl-2ì/-chromenes to 2-benzylbenzofurans

The ring-contraction reaction of electron-deficient 3-silyl-2i7-chromenes to 2-benzylbenzofurans under mild conditions was developed. CsF efficiently promoted the reaction at room temperature or 80 °C to afford a variety of 2-benzylbenzofurans in good yields. 3-Silyl-2i7-chromenes having strong electron-withdrawing groups smoothly afforded the desired products. The reaction is proposed to proceed through an allenyl intermediate or dyotropic rearrangement.