Ruthenium-catalyzed asymmetric epoxidation of olefins using H2O2, part I: synthesis of new chiral N,N,N-tridentate pybox and pyboxazine ligands and their ruthenium complexes.
The synthesis of chiral tridentate N,N,N-pyridine-2,6-bisoxazolines 3 (pybox ligands) and N,N,N-pyridine-2,6-bisoxazines 4 (pyboxazine ligands) is described in detail. These novel ligands constitute a useful toolbox for the application in asymmetric catalysis. Compounds 3 and 4 are conveniently prepared by cyclization of enantiomerically pure alpha- or beta-amino alcohols with dimethyl pyridine-2,6-dicarboximidate. The corresponding ruthenium complexes are efficient asymmetric epoxidation catalysts and have been prepared in good yield and fully characterized by spectroscopic means. Four of these ruthenium complexes have been characterized by X-ray crystallography. For the first time the molecular structure of a pyboxazine complex [2,6-bis-[(4S)-4-phenyl-5,6-dihydro-4H-[1,3]oxazinyl]pyridine](pyridine-2,6-dicarboxylate)ruthenium (S)-2 aa, is presented.
Tse
Man Kin
MK
Leibniz-Institut für Organische Katalyse an der Universität Rostock e.V. Albert-Einstein-Strasse 29a, 18059 Rostock (Germany).
Bhor
Santosh
S
Klawonn
Markus
M
Anilkumar
Gopinathan
G
Jiao
Haijun
H
Döbler
Christian
C
Spannenberg
Anke
A
Mägerlein
Wolfgang
W
Hugl
Herbert
H
Beller
Matthias
M