This work details the synthesis of 22 new chiral VANOL ligands that differ by the
nature of the substituent in the 3- and 3′-positions of the ligand. These ligands
were incorporated into boroxinate catalysts that were used to screen the catalytic
asymmetric aziridination of benzhydryl imines with ethyl diazoacetate. Each catalyst
was screened in the reaction of imines generated from benzaldehyde and cyclohexanecarboxaldehyde
and some with 4-nitro- and 4-methoxybenzaldehyde. In addition, the first report of
the effect of the ester substituent of the diazoacetate ester on the asymmetric induction
in these aziridination reactions is presented. The first X-ray structure of a boroxinate
catalyst generated from a VANOL-derived ligand is also reported.
Keywords
VANOL - asymmetric catalysis - aziridines - BOROX catalysts - imines
