Accessing unnatural α-amino acids with tetrasubstituted stereogenic centers via catalytic enantioselective reactions of ketimine-type α-iminoesters/α-iminoamides

Abstract

Catalytic enantioselective synthesis methodologies have been actively explored and developed owing to the significance of chiral molecules and their utilities. In particular, unnatural α-amino acids with tetrasubstituted stereogenic carbon centers (α-tertiary amino acids; ATAAs) are undoubtedly among the most valuable compounds. Asymmetric addition to an α-iminoester or α-iminoamide is widely recognized as a straightforward, powerful, and atom-economical strategy for accessing optically active α-amino acids and their derivatives. However, this type of chemistry, which relies on ketimine-type electrophiles, was quite limited only a few decades ago owing to low reactivities and difficulties associated with enantiofacial control. This feature article comprehensively overviews this research field and highlights the significant progress that has been made. In particular, it focuses on the chiral catalyst system and the transition state as the key parameters for such reactions.