Pyridine bis-oxazolines PYBOX

Bis-oxazolines (Box), azabis-oxazolines (azaBox) and pyridine bis-oxazoline (PyBox) with a C2 symmetry form the great majority of various oxazoline-derived ligands which are used in immobilized catalytic cyclopropanation reactions (Scheme 36). For these reactions, immobilized ruthenium and copper complexes which are able to form carbene intermediates have been tested. Most of the time, the reaction involved styrene and ethyl diazoacetate (EDA). However other alkenes (diphenyl ethylene. ..) and other diazo compounds (i.e. tertiobutyl and ethyl 2-phenyl diazoacetate) have also been investigated (Scheme 36). 

Oxazolines are nowadays essential ligands in asymmetric catalysis and also important synthons for stereoselective synthesis [8]. The success of the Cj-symmetric bis(oxazolines) ( BOX ) and pyridine-bis(oxazolines) ( Pybox ) discovered in the early 1990s has established them as a privileged class of ligands [9]. In contrast, the development and application of trisoxazolines lagged behind for a long time. Katsuki and collaborators [10] reported the first example of a chiral trisoxazoline in 1995 and their use in the allylic oxidation of alkenes (Kharasch-Sosnovsky reaction), as well as the enantioselective addition of diethylzinc to aldehydes. 

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