Hydride Transfer-EnabledDearomative Spirocyclizationof Isoxazoles with <i>O</i>‑Alkyl <i>ortho</i>-Oxybenzaldehydes

The TfOH-catalyzed dearomative [5 + 1] annulations were developed for the construction of chromane-fused spiroisoxazolines from readily available 5-amino-isoxazoles and <i>O</i>-alkyl <i>ortho</i>-oxybenzaldehydes. The “two-birds-with-one-stone” strategy featuring dearomatization of 5-amino-isoxazoles and α-C(sp³)–H bond functionalization of oxygen was disclosed via a cascade condensation/[1,5]-hydride transfer/dearomative spirocyclization process. In addition, the unprecedented direct dearomative spirocyclization of isoxazoles was achieved, which introduced a new family member of dearomative spirocyclization for dearomatization chemistry.