Abstract
Abstract: An expeditious method for the synthesis of chiral boxand pybox ligands is reported. The approach is based on a one-potcondensation reaction of chiral b-amino alcohols with a dinitrileusing stoichiometric or catalytic amounts of zinc triflate. Yieldsgreater than 90% are obtained in many cases without the need forfurther purification of the product. Key words: bis(oxazolines), pybox, synthesis, zinc triflate, tolu-ene, chiral ligands Chiral bis(oxazolines) (box) are widely used in the asym-metric catalysis of an increasing variety of organic reac-tions including cyclopropanations, Diels–Alder, ene,aziridination, allylic substitutions, Mukaiyama–Michael,Mukaiyama aldol reactions, 1,2 to mention just a few. Boxsystems bearing a one-carbon spacer between the twooxazoline rings are the most frequently used.Since 1997 many attempts have also been made to supportbox ligands in heterogeneous systems. 3 The introduction of a third coordinating atom into the linkbetween the two oxazoline rings has led to the develop-ment of tridentate bis(oxazoline) ligands, among whichpyridine bis(oxazoline) (pybox) derivatives represent thebest known examples. These ligands have been success-fully used in the same types of reactions as bis(oxazol-ines),
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