ENANTIOSELECTIVE MUKAIYAMA-ALDOL REACTION BETWEEN ENOL SILANES AND KETOMALONATE CATALYZED BY THE COPPER(II) COMPLEX OF TIPS-SUBSTITUTED BIS-OXAZOLINE

The stable complex [(4'S,5'S)-4b/Cu(Tf)(2)/H2O] (5), obtained from TIPS-Box and Copper triflate, catalyzes enantioselectively the Mukaiyama-aldol reactions between two silyl enol ethers (1a,b) and diethyl ketomalonate (2). Yields are very good and the ee of (R)-3b is up to 94%. When the reaction was catalyzed by 4-Ph-Box complex [(4'R)-4a/Cu(Tf)(2)], in which the configuration at the C-4 centre is opposite to that of 5, the same enantiomer was obtained. The undistorted square pyramidal structure of complex 5, determined by crystallographic structure, and the effect of water and molecular sieves on efficiency and selectivity of the catalyst, suggest some proposals to rationalize the resulting stereoselectivity