A chiral solvent effect in asymmetric organocatalysis.

Proline-catalyzed aldol reactions between enolizable ketones and aromatic aldehydes can be carried out in propylene carbonate. When enantiomerically pure propylene carbonate is used, the combination of (R)-proline and (R)-propylene carbonate constitutes a matched pair, while (S)-proline and (R)-propylene carbonate constitutes a mismatched pair.