Protonated arginine and lysine as catalysts for the direct asymmetric aldol reaction in ionic liquids

Side chain protonation of basic α-amino acids with Brønsted acids provides new effective catalysts for the direct asymmetric aldol reaction of cyclic ketones with aromatic aldehydes in ionic liquids and DMSO. Increased yields are obtained in N-butyl N-methyl pyrrolidinium triflate ([bmpy][TfO]) with respect to DMSO using argininium tosylate (Arg·PTSA) as a 1.3 M aq solution in 10% molar amount with respect to the limiting aldehyde.