New mesoporous templated silicas of the MCM-41 family covalently linked to chiral ephedrine are used as heterogeneous chiral auxiliaries in the enantioselective alkylation of benzaldehyde by diethylzinc. Promising results are obtained with these inorganic-organic catalysts. Various factors which may affect the activity, selectivity and enantioselectivity are studied. Comparison with homogeneous catalysis is carried out. (C) 1998 Elsevier Science Ltd. All rights reserved.