Elucidation of architectural requirements from a spacer in supported proline-based catalysts of enantioselective aldol reaction

In order to delineate the properties of the spacer architecture responsible for the strong positive dendritic effect exhibited by polymer-supported proline-based catalysts, we prepared two series of polystyrene-bound model catalysts. The first series was based on a linear and partially dendritic spacers (of reduced branching and valency) imitating the length of the second generation spacer, while the second series was based on the first generation dendron spacer with one functional (proline-terminated) and one non-functional arm. Comparative studies of the model and original (fully dendritic) catalysts in the asymmetric aldol reaction of aromatic aldehydes with acetone disclose the features characteristic to the dendritic architecture, such as proximity between the terminal catalytic units and enhanced branching, as crucial for inducing higher yield and enantioselectivity in catalysis.