Centrally chiral bisoxazolines connected directly to a planar chiral [2.2]paracyclophane backbone were synthesized and evaluated as asymmetric ligands in Cu-catalyzed intermolecular ethanolic O-H insertion reactions of α-diazo esters. The reactivities and enantioselectivities of Cu complexes of the synthesized bisoxazoline ligands were lower than those of ligands without central chirality. However, planar chiral [2.2]paracyclophane-based bisoxazoline ligands with an inserted benzene spacer that had a sterically demanding isopropyl substituent showed good enantioselectivities in inter- and intramolecular aromatic O-H insertion reactions, without the aid of central chirality.

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http://dx.doi.org/10.1248/cpb.c18-00519DOI Listing

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