Heterogeneous Catalytic Asymmetric Direct Aldol Reaction in Water

Significance

Polystyrene resin-supported l-proline 1 was used as a catalyst for the direct aldol reaction of aromatic aldehydes 2 and unmodified ketones 3 in water. Thus, the reaction of 2 with 3 (5 equiv) was carried out with 1 (10 mol%) to give the corresponding aldol products 4 and 5 in 25-97% yield (4/5 = 68:32 to >99:1) with 50-98% ee (4) (21 examples). Catalyst 1 was reused four times without any significant loss of catalytic activity. Screening of solvents showed that the reaction proceeded efficiently only in water.