Enantioselective trapping of oxonium ylide intermediates by N-benzhydryl-α-imino ester: Synthesis of β-tetrasubstituted α-amino acids

A synergistic rhodium(II)/phosphoric acid catalyzed three component reaction of 3-diazooxindoles, alcohols and N-benzhydryl-α-imino ester is developed for the efficient construction of chiral β-alkoxy C^β-tetrasubstituted α-amino acid derivatives in good yields and with excellent diastereoselectivities and high enantioselectivities. The synthetic application of the resulting products was illustrated by reducing with Pd/C under H₂ atmosphere followed reacting with CSCl₂ at room temperature to rapid afford 3-spirocyclic oxindole in a good yield with a chirality retainment. The three-component reaction is proposed to proceed through an electrophilic trapping of the oxonium ylides by N-benzhydryl-α-imino ester.