Chiral Phosphoric Acid Catalyzed (4+1) Annulation of 3‐Diazooxindoles/4‐Diazooxisoquinolines with para‐Quinone Methides to Access Chiral Spiro[dihydrobenzofuran‐2,3′‐oxindoles/2,4′‐oxisoquinolines]

An asymmetric (4+1) annulation of 3‐diazooxindoles/4‐diazooxisoquinolines with para‐quinone methides, catalyzed by a chiral phosphoric acid, has been described. A wide range of spiro[dihydrobenzofuran‐2,3′‐oxindoles/2,4′‐oxisoquinoline] derivatives were afforded with excellent diastereo‐ and enantioselectivities. In this study, the possible reaction pathway was proposed and the synthetic applications were shown by a tenfold scale‐up conversion as well as the further transformations into other structurally more complex spirocyclic compounds. The significance of this protocol is highlighted by its metal‐free participation with heterocyclic diazo compounds as the direct nucleophile and extremely high efficiency in a straightforward and mild reaction process to access the structurally‐diverse spiro‐heterocyclic 2,3‐dihydrobenzofuran derivatives with good to excellent stereocontrol.