N-heterocyclic carbene/Lewis acid strategy for the stereoselective synthesis of spirocyclic oxindole-dihydropyranones.

Under the cooperative catalysis of NHC/Lewis acid, the mild, straightforward [4 + 2] annulation of α-bromo-α,β-unsaturated aldehydes bearing γ-H with isatin derivatives gave spirocyclic oxindole-dihydropyranones stereoselectively. This approach is particularly attractive due to the concise construction, avoidance of external oxidants, and the potential utilization value of final products in molecular biology and pharmacy.