Zeolites significantly enhance the influence of chiral auxiliaries during photochemical reactions. The generality of this phenomenon has been tested with three independent examples. Chiral auxiliaries that lead to 1:1 mixtures of diastereomers in solution give products in up to 80% diastereomeric excess in the presence of faujasite type zeolites. (C) 2000 Elsevier Science Ltd. All rights reserved.