Monobenzylethers of (R,R)-1,2-diphenylethane-1,2-diol as a possible alternative to cyclohexyl-based chiral auxiliaries in the stereoselective reduction of α-ketoesters

The monobenzylethers of (R,R)-1,2-diphenylethane-1,2-diol have been used as chiral auxiliaries in the stereoselective reduction of the corresponding phenylglyoxylates. The diastereoselectivity of the reduction with either l-selectride or DIBAL was found to be strictly dependent on the nature of the substitution on the aromatic ring of the auxiliary and a maximum d.r. of 87:13 was obtained with the p-CF3 substituted derivative. This investigation also shows that with open chain chiral auxiliaries diastereoselectivities of preparative interest can be achieved, suggesting that such auxiliaries can constitute a promising alternative to the commonest cyclohexyl-based ones.