Stereoselective N‐Heterocyclic‐Carbene‐Catalyzed Spiroannulation as an Access Towards Spirobenzofuranone‐Fused Cyclohexenones

In this work, we present an organocatalytic spiroannulation method that provides access to spirocyclic benzofuran‐2‐ones. The reaction proceeds via the generation of an azolium dienolate from an α‐bromo‐α,β‐unsaturated aldehyde using a chiral N heterocyclic carbene, followed by annulation with benzofuran‐2‐one‐derived alkenes. The resulting chiral spirobenzofuranone‐fused cyclohexenones were obtained with enantioselectivity ranging from 77% to 99% ee and diastereomeric ratios (dr) from 1.2/1 to 20/1. The utility of the protocol was underscored by gram‐scale reaction and follow‐up transformations.