AlCl₃‑Promoted Selective Michael Addition with Allenoate and Methyleneindolinone: Synthesis of Spirocyclic Oxindole by Using Allenoate as a Four-Carbon Component Building Block

The AlCl₃-promoted cyclization of readily available allenoates with methyleneindolinone is disclosed. The present strategy provides a rapid access to spirocyclic oxindole-cyclohexenones in an efficient manner. Remarkably, the allenoate is implemented as a four-carbon (4C) component to form the ring, which shows high synthetic efficiency. Flexibility of this method allows quick synthesis of spirocyclic oxindole-dihydropyrans by varying one of the components. It is also noteworthy that AlCl₃ serves as the chlorine source as well as an effective catalyst to facilitate this interesting transformation.