[4 + 3] Cycloadditions with Bromo-Substituted Morita–Baylis–Hillman Adducts of Isatins and N‑(ortho-Chloromethyl)aryl Amides

Efficient construction of a challenging aza-spirocycloheptane oxindole scaffold is reported through an unprecedented [4 + 3] cycloaddition reaction with bromo-substituted Morita–Baylis–Hillman adducts of isatins and N-(ortho-chloromethyl)­aryl amides. Both reactive intermediates, the allylic phosphonium ylides and aza-o-quinone methides, were in situ generated, chemoselectively facilitated by a Lewis base and Brønsted base, respectively.