Tandem 1,4‐Addition/Enantioselective Protonation Catalyzed by Rhodium Complexes: Efficient Access to α‐Amino Acids

Abstract

Conjugate addition of potassium trifluoro(organo)borates 2 (R=aryl, alkenyl) to 2-acetamidoacrylate 1 mediated by a chiral rhodium catalyst and with in situ enantioselective protonation afforded a variety of α-amino acids 3 with high yields and ee values up to 90 % (see scheme, cod=cycloocta-1,5-diene, binap=2,2′-bis(diphenylphosphanyl)-1,1′-binaphthyl). Among the tested chiral ligands and proton sources, binap in combination with 2-methoxyphenol (guaiacol), an inexpensive and nontoxic phenol, afforded the highest asymmetric inductions.