Stereodivergent construction of [6.5]-spirocycles bearing three contiguous stereogenic centers by Pd-catalyzed [4+2] annulations

Abstract

The stereodivergent synthesis of spirocyclic frameworks with multiple stereogenic centers via a single transformation represents a high-priority challenge in synthetic chemistry. Herein, we report an unprecedented highly efficient stereodivergent [4+2] annulation reaction employing palladium catalysts for the synthesis of spiropyrazolones bearing three contiguous stereogenic centers. Excellent diastereodivergency (up to >20:1) and enantioselectivity (up to >99% ee) have been achieved using different commercially available chiral ligands. This represents the first example of using vinyl benzoxazinanones as the palladium π-allyl precursor to realize stereodivergent reaction. Density functional theory (DFT) calculation profiles have revealed the origin of this stereodivergent annulation process.