Arylid-Box: A new family of chiral bis-oxazoline ligands for metal mediated catalytic enantioselective synthesis

A new family of chiral non-racemic bis-oxazolines containing an arylidene bridging unit (and appropriately termed Arylid-Box) have been prepared from malonate esters in satisfactory yields. These ligands have been screened in the Cu(I) catalysed enantioselective cyclopropanation of styrene and α-methylstyrene with ethyl diazoacetate giving enantioselectivities of up to 89% ee. The tBu substituted ligands (2d, 3d and 4d) gave the best ees. Our experiments seemed to indicate that there was no overall dependency of the reaction stereoselectivity or efficiency on reaction conditions, like, solvent, counter ion or temperature.