engleski

Chiral Macrocyclic Bis(oxazoline) CuI Complexes – Structure/Stereoselectivity Relationships in Catalytic Cyclopropanations

The design and synthesis of 18 chiral macrocycles with built in C-2- symmetric bis(oxazoline) units is described and the catalytic properties of their copper(I) complexes in cyclopropanations of styrene with ethyl diazoacetate are assessed. The bridging of two homochiral centers in the bis(oxazoline) unit gives a macrocyclic ligand, which upon binding of Cu-I is transformed into a macrocyclic catalytic complex containing a chiral cavity. Such a complex represents a conceptually new type of supramolecular organometallic catalyst, possessing a chiral reaction cavity. A clear relationship between catalyst structures and the stereoselectivity outcome in the catalytic cyclopropanations has been established and it is demonstrated that both the enantioselectivity and the diastereoselectivity can be independently modified by variation of the ligand structural parameters. The Cu-I complex of the ligand 3b gave a trans/cis diastereomeric ratio of 94:6 (de = 88%), representing the highest diastereoselectivity obtained to date for cyclopropanations catalyzed by the bis(oxazoline) class of complexes. An explanation of the observed relationship between stereochemical outcome and ligand structure is proposed.

bis(oxazolines) ; catalytic cyclopropanation ; copper(I) complexes ; diastereoselectivity ; macrocyclic ligands

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