Synthesis of chiral nonracemic c2-symmetric 2,2u27-bipyridines and their evaluation as ligands in copper-catalyzed asymmetric reactions

摘要

This thesis concerns the synthesis and evaluation of a series of new chiral nonracemic C2-symmetric 2,2u27-bipyridines for use as ligands in catalytic asymmetric reactions. The 2,2u27-bipyridines were prepared using a divergent synthetic strategy which employed an asymmetric dihydroxylation reaction of a 2-chloropyrindine as the key step. The resultant chiral diol was condensed with a series of symmetrical ketones to afford chiral acetals which were converted into the requisite ligand series. These ligands were evaluated in the asymmetric copper(I)-catalyzed cyclopropanation reaction of styrene and ethyldiazoacetate. The major trans-cyclopropane products were isolated in good yield and very high enantioselectivities were achieved (up to 94% ee). These are amongst the highest enantioselectivities reported for chiral 2,2u27-bipyridyl ligands. The most effective ligand, an adamantanone derivative, was evaluated in the copper(I)-catalyzed asymmetric allylic oxidation of cyclic alkenes with tert-butyl peroxybenzoate. High enantioselectivities were also obtained in these reactions (up to 91% ee)