Scope and limitations of chiral bis(oxazoline) ligands in the copper-catalysed asymmetric cyclopropanation of trisubstituted alkenes

A series of derivatives of 3-methyl-2-buten-1-ol has been used to test the scope and limitations of the copper-catalysed asymmetric cyclopropanation of trisubstituted alkenes by ethyl diazoacetate in the presence of C-2-symmetric bis(oxazoline) ligands. In the best case, a trans/cis ratio of 91:9, with 92% ee for the major isomer, was obtained from the reaction of the p-methoxybenzoate derivative. The highest ee was 95%, for the trans isomer of a 80:20 diastereomer mixture (acetate derivative).