1262444-47-2Relevant academic research and scientific papers
Control of enantioselectivity with flexible biaryl axes: Terpene-based alkylzinc catalysts in enantioselective dialkylzinc additions
Leven, Matthias,Schloerer, Nils E.,Neudoerfl, Joerg M.,Goldfuss, Bernd
experimental part, p. 13443 - 13449 (2011/03/17)
New enantiopure pyridyl alcohols are efficiently accessible through few synthetic steps from commercially available terpenes, that is, (+)-fenchone, (-)-menthone and (-)-verbenone as well as 2,6-diphenylpyridine. These chelating pyridyl alcohols exhibit flexible pyridyl-phenylene axes, which give rise to P and M conformers. Alkylzincation of the hydroxy groups eliminates equilibria of the conformers and generates alkylzinc complexes with adjusted biaryl axes, as it is demonstrated by NMR studies. These alkylzinc catalysts perform well in the addition of dimethylzinc or diethylzinc to benzaldehyde with yields up to 99% and ee's up to 95%. The adjusted pyridylphenylene conformations in the ligands now control enantioselectivities of the catalysts, which were also analysed by computations at the DFT level. Fixing the biaryl axis: New chiral pyridyl terpenols are derived from 2,6-diphenylpyridine by means of short synthetic routes. The chiral biaryl axes of the metal-free alcohols are conformationally free, almost without any preferences for P or M arrangements. The chiral information of the terpene units is effectively transferred to the pyridylphenylene biaryl axes only if zinc is implemented, giving well-defined conformations in the enantioselective catalyst (see scheme). Copyright
