Zinc(II)-Catalyzed [2+2+1] Annulation of Internal Alkenes, Diazooxindoles, and Isocyanates to Access Spirooxindoles

Zinc(II)-catalyzed [2+2+1] annulation of internal alkenes, diazooxindoles, and isocyanates was successfully developed for the construction of multisubstituted spirooxindoles. This multi component transformation involves in situ generation of a sulfur containing spirocyclic intermediate from the [4+1] annulation of diazooxindole to sulfonyl isocyanate, which subsequently reacts as a 1,3-dipole with the internal alkene, that is, alpha-oxo ketene dithioacetal, to furnish a formal [2+2+1] annulation in a one-pot manner. This synthetic protocol features a low-toxicity main group metal catalyst, readily available reagents, and <= 96% yields, offering an efficient route to multisubstituted spirooxindole derivatives.

Automated summary

A zinc(II)-catalyzed [2+2+1] annulation reaction of internal alkenes, diazooxindoles, and isocyanates was developed for the efficient synthesis of multisubstituted spirooxindoles. This multi-component transformation involves the in situ formation of a sulfur-containing spirocyclic intermediate, followed by a 1,3-dipolar addition reaction of the intermediate with the internal alkene, resulting in a formal [2+2+1] annulation in a one-pot manner. The synthetic protocol utilizes a low-toxicity main group metal catalyst, readily available reagents, and provides high yields of up to 96% for the synthesis of multisubstituted spirooxindole derivatives.