Rationalization of enantioselectivities in dialkylzinc additions to benzaldehyde catalyzed by fenchone derivatives.
Three (-)-fenchyl alcohol derivatives, ¿(1R,2R,4S)-exo-(2-Ar)-1,3, 3-trimethylbicyclo[2.2.1] heptan-2-ol, Ar = o-anisyl (2), 2-N-methylimidazolyl (3), 2-N,N-dimethylbenzylamine (4)¿ were synthesized, characterized by X-ray analyses, and employed as precatalysts in diethyl zinc additions to benzaldehyde. Directions and relative degrees of enantioselectivities are rationalized by QM/MM ONIOM computations of mu-O transition structure models. Enantioselectivities arise from repulsive interactions between "transferring" or "passive" alkyl groups at the zinc centers and the substituents at donor groups or the bicyclo[2.2.1]heptane moieties. These results enable predictions for ligand-tuning to improve catalyst efficiency of fenchone-based ligands in dialkylzinc additions to aldehydes.
Goldfuss
B
B
Organisch-Chemisches Institut der Universität Heidelberg, Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany. Bernd.Goldfuss@urz.uni-heidelberg.de
Steigelmann
M
M
Khan
S I
SI
Houk
K N
KN
D001547:Benzaldehydes / Q000737:chemistry*; D001892:Camphanes; D002384:Catalysis; D008958:Models, Molecular; D015394:Molecular Structure; D009636:Norbornanes / Q000737:chemistry*; D013237:Stereoisomerism; D015032:Zinc / Q000737:chemistry*
D001547:Benzaldehydes; D001892:Camphanes; D009636:Norbornanes; C027327:fenchone; D015032:Zinc; C032175:benzaldehyde