Synthesis of C2-symmetrical bis(1,2-hydroxy sulfonamide) ligands and application in the enantioselective addition of dialkylzinc to aldehydes

The preparation of several C-2-symmetric disulfonamides derived from 1,2-amino alcohols and disulfonyl derivatives, as well as their use in the titanium tetraisopropoxide-promoted enantioselective additions of dialkylzinc to aldehydes are described. The enantiomeric ratio is up to 96:4, the best results being obtained for aromatic aldehydes with electron-donating groups in the para-position. There are some differences in the enantioselectivity depending on the relative positioning of the amino alcohol moieties in the chiral ligand, the 1,3-disulfonyl derivative being the best system. In the case of para-substituted benzaldehyde derivatives, a negative relationship between the electron-withdrawing character of the para-substituted group and the enantioselectivity of the addition was seen, whereas the more electronic-donating character the substituent has, the higher the observed enantioselectivity. (C) 2002 Elsevier Science Ltd. All rights reserved.