Novel chiral dibenzo[ a, c]cycloheptadiene bis(oxazoline) and catalytic enantioselective cyclopropanation of styrene

Abstract

A series of chiral C 2-symmetric bis(oxazoline) ligands containing dibenzo[ a, c]cycloheptadiene units were synthesized. The copper complexes, prepared in situ from copper (I)-triflate and the new enantiopure oxazoline ligands, were assessed as chiral catalysts in the enantioselective cyclopropanation of styrene with diazoacetate. Enantioselectivities up to 82 and 62%, respectively, for trans- and cis-2-phenylcyclopropanecarboxylate were observed.