Brønsted base-catalyzed three-component coupling reaction of α-ketoesters, imines, and diethyl phosphite utilizing [1,2]-phospha-Brook rearrangement†
A three-component coupling reaction of α-ketoesters, imines, and diethyl phosphite under Brønsted base catalysis was developed by utilizing the [1,2]-phospha-Brook rearrangement. The reaction involves the generation of ester enolates via the umpolung process, i.e., the chemoselective addition of diethyl phosphite to α-ketoesters followed by the [1,2]-phospha-Brook rearrangement, and the trapping of the resulting enolates by imines preferentially over α-ketoesters and protons. This operationally simple reaction can provide densely functionalized β-amino acid derivatives including an oxygen functionality at the α-position in good yields. The diastereoselectivity is highly dependent on the substrates and reaction temperature, which is attributed to the reversibility of the addition of the ester enolates to the imines. The methodology was further extended to the reaction of α-ketoesters, β-nitrostyrenes, and diethyl phosphite.