Designed Ligands as Probes for the Catalytic Binding Mode in Mo-Catalyzed Asymmetric Allylic Alkylation We thank the National Science Foundation and the National Institutes of Health for their generous support of the work carried out at Stanford. I.H. thanks the Japan Society for the Promotion of Science for a postdoctoral fellowship. Mass spectra were provided by the Mass Spectrometry Facility at the University of California, San Francisco, which is supported by the NIH Division of Research Resources.
The synthesis of enantiomerically pure C 2-symmetric bis-pyridinium salts was realized through a simple condensation of 2-pyridyl-carboxyaldehydes with a chiral diamine. The catalytic properties of such novel compounds were preliminarily studied and the trifluoracetate salts of chiral bis-imines of 2-picolinaldehydes derivedfrom1,1′-binaphthyl-2,2′-diamine were shown to catalyze the Diels-Alder reaction
The use of (1R,2R)-N,N'-bis(2-pyridinecarboxyamido)-1,2-diphenylethane metal complexes as catalysts for the enantioselective addition of trimethylsilyl cyanide to aldehydes is described. Enantioselectivities up to 70% ee were obtained with a Ti(IV) catalyst. Complexes with Zr(IV), Sc(III), Yb(III) and Cu(II) afforded less selective catalysts. For the Zr(IV) complex, a rate and selectivity enhancement was observed when adding 0.5 equiv. of water with respect to the catalyst. Studies of the metal complexes involved in the reaction were carried out by means of H-1 NMR spectroscopy. A Zr complex was shown by X-ray crystallography to exhibit distorted octahedral coordination, with the four nitrogen atoms of the doubly deprotonated ligand essentially in one plane. (C) 2004 Elsevier B.V. All rights reserved.