Proline-beta(3)-amino-ester dipeptides as efficient catalysts for enantioselective direct aldol reaction in aqueous medium.

Dipeptides obtained from l-proline and beta(3)-l-amino acids are reported to catalyze enantioselective direct aldol reaction in aqueous medium, leading to significant anti:syn diastereomeric ratios and enantiomeric excesses. The simple introduction of a polar substituent at the C-2 position of the beta(3)-l-amino acid was also found to enhance appreciably both diastereo- and enantioselectivity of the catalyst.

(Z)-Ethyl 4-chloro-2-[(4-chloro-phen-yl)hydrazono]-3-oxobutanoate.

The title compound, C(12)H(12)Cl(2)N(2)O(3), crystallizes as a non-merohedral twin with a twinning ratio of 0.51:0.49. The mol-ecule adopts a keto-hydrazo tautomeric form stabilized by an intra-molecular N-H⋯O hydrogen bond. The configuration around the N-N bond is trans.