Construction of Isoxazolidin-5-ones with a Tetrasubstituted Carbon Center: Enantioselective Conjugate Addition Mediated by Phase-Transfer Catalysis

An efficient enantioselective Michael reaction of readily available -substituted N-Boc isoxazolidin-5-ones is described under phase transfer conditions with up to 95:5 er. The organocatalytic process is promoted by a low catalytic loading of a commercially available N-spiro quaternary ammonium salt. This sequence opens an entry to chiral heterocyclic platforms displaying a -amino carbonyl motif with an -all-carbon quaternary stereogenic center. The methodology was also successfully extended to the asymmetric amination reaction using an azodicarboxylate electrophile.