Highly enantioselective ring opening of cyclic meso-anhydrides to isopropyl hemiesters with Ti-TADDOLates:: An alternative to hydrolytic enzymes?

The Lewis acid mediated transfer of an alkoxide ligand from the chiral ligand sphere of Ti-TADDOLate (1) to cyclic meso anhydrides to afford the corresponding hemiesters is described. By using this method a variety of structurally different anhydrides can be converted to isopropyl hemiesters with high enantioselectivities (enantiomer ratios up to 99:1). We have also investigated Lewis acidic titanium complexes, which differ from 1 in the chiral ligand or the alkoxide ligand that is transferred. Finally, a catalytic version, which allows the substoichiometric use of Ti-TADDOLate in the presence of stoichiometric amounts of Al(Oi-Pr)(3), is presented.