Cross-Linked-Polymer-Supported N-{2′-[(Arylsulfonyl)amino][1,1′-binaphthalen]-2-yl}prolinamide as Organocatalyst for the Direct Aldol Intermolecular Reaction under Solvent-Free Conditions

A bottom-up strategy was used for the synthesis of cross-linked copolymers containing the organocatalyst N-{(1R)-2'-{[(4-ethylphenyl)sulfonyl]amino}[1,1'-binaphthalen]-2-yl}-D-prolinamide derived from 2 (Scheme 1). The polymer-bound catalyst 5b containing 1% of divinylbenzene as cross-linker showed higher catalyst activity in the aldol reaction between cyclohexanone and 4-nitrobenzaldehyde than 5a and 5c. Remarkably, the reaction in the presence of 5b was carried out under solvent-free, mild conditions, achieving up to 93% ee (Table 1). The polymer-bound catalyst 5b was recovered by filtration and re-used up to seven times without detrimental effects on the achieved diastereo- and enantioselectivities (Table 2). The catalytic procedure with polymer 5b was extended to the aldol reaction under solvent-free conditions of other ketones, including functionalized ones, and different aromatic aldehydes (Table 3). In some cases, the addition of a small amount of H2O was required to give the best results (up to 95% ee). Under these reaction conditions, the cross-aldol reaction between aldehydes proceeded in moderate yield and diastereo- and enantioselectivity (Scheme 2).