Organocatalytic asymmetric [4 + 2]‐annulation of 2‐nitroallylic alcohols with isatin‐derived ketimines: Diastereo‐ and enantioselective synthesis of spirooxindole‐1,3‐oxazinanes

A novel strategy for the diastereo‐ and enantioselective synthesis of spiro N,O ‐heterocyclic oxindoles has been developed via asymmetric [4 + 2]‐annulation between 2‐nitroallylic alcohols and isatin‐derived ketimines. This organocatalytic protocol employs a bifunctional squaramide‐based catalyst capable of multiple hydrogen‐bonding interactions, enabling precise stereocontrol. The method provides efficient access to structurally complex chiral spirooxindole‐1,3‐oxazinane frameworks bearing quaternary stereogenic centers, delivering high yields and excellent stereoselectivities (up to 86% yield, 99% ee, and >20:1 dr).