Copper-catalyzed enantioselective propargylic amination of propargylic esters with amines: copper-allenylidene complexes as key intermediates.
The scope and limitations of the copper-catalyzed propargylic amination of various propargylic esters with amines are presented, where optically active diphosphines such as Cl-MeO-BIPHEP and BINAP work as good chiral ligands. A variety of secondary amines are available as nucleophiles for this catalytic reaction to give the corresponding propargylic amines with a high enantioselectivity. The results of some stoichiometric and catalytic reactions indicate that the catalytic amination proceeds via copper-allenylidene complexes formed in situ, where the attack of amines to the electrophilic gamma-carbon atom in the allenylidene complex is an important step for the stereoselection. Investigation of the relative rate constants for the reaction of several para-substituted propargylic acetates with N-methylanilines reveals that the formation of the copper-allenylidene complexes is involved in the rate-determining step. The result of the density functional theory calculation on a model reaction also supports the proposed reaction pathway involving copper-allenylidene complexes as key intermediates. The catalytic procedure presented here provides a versatile and direct method for the preparation of a variety of chiral propargylic amines.
Hattori
Gaku
G
Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113-8656, Japan.
Sakata
Ken
K
Matsuzawa
Hiroshi
H
Tanabe
Yoshiaki
Y
Miyake
Yoshihiro
Y
Nishibayashi
Yoshiaki
Y
D000480:Alkynes / Q000737:chemistry*; D000586:Amination; D000588:Amines / Q000737:chemistry*; D002384:Catalysis; D003300:Copper / Q000737:chemistry*; D004952:Esters / Q000737:chemistry; D013237:Stereoisomerism
D000480:Alkynes; D000588:Amines; D004952:Esters; D003300:Copper