Proline dipeptides containing fluorine moieties as oganocatalysts for the asymmetric aldol reaction

A series of dipeptide analogues consisting of proline, phenylalanine and aniline- or phenol-fluorine derivatives were synthesized. Their catalytic ability was evaluated in the intermolecular asymmetric aldol reaction, both in organic and aqueous media. Aniline-fluorine derivatives proved to be superior and the best results were obtained, when 2-CF₃ aniline was employed. A diverse substrate scope consisting of both aromatic and aliphatic aldehydes, as well as different ketones was demonstrated, where aromatic aldehydes afforded products in high yields (up to 100%) with excellent diastereo- (up to 95:5) and enantioselectivities (up to 97%), whereas the aliphatic aldehydes afforded also excellent selectivities, but relatively low yield. A simple addition of fluorine to a dipeptide analogue affords organocatalysts with new interesting properties that can catalyze the aldol reaction more efficiently.