Organocatalytic Asymmetric Formal ‐Cycloaddition to Access 2,3‐Diazaspirodeca‐3,6‐dien‐1‐ones

Medicinally important 2,3‐diazaspiro[4.5]deca‐3,6‐dien‐1‐ones having vicinal quaternary centers were constructed in very good yields with high enantio‐ and diastereoselectivities through an organocatalytic formal [3+3]‐cycloaddition or domino Michael/aldol reactions, which is driven by the double sequence of in situ isoaromatization and dearomatization steps from the α‐arylidene pyrazolinones and (E)‐alkyl 2‐oxo‐4‐arylbut‐3‐enoates.