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.