TY - JOUR T1 - Brønsted acids as additives for the direct asymmetric aldol reaction catalyzed by l-prolinethioamides. direct evidence for enamine-iminium catalysis. AU - Gryko,Dorota, AU - Zimnicka,Magdalena, AU - Lipiński,Radosław, PY - 2007/1/27/pubmed PY - 2007/1/27/medline PY - 2007/1/27/entrez SP - 964 EP - 70 JF - The Journal of organic chemistry JO - J Org Chem VL - 72 IS - 3 N2 - The use of protonated l-prolinethioamide instead of the free base derivative 1 as the organocatalyst for the direct aldol addition has a profound and appreciable effect on both the yield and the stereochemical course of the reaction. 4-Nitrobenzaldehyde (2) reacts with acetone in the presence of the protonated catalyst 1.TFA, affording aldol product 3 with a yield up to 99% and an ee up to 98%. The catalyst loading can be lowered to 2.5 mol %. More than 20 different acids were investigated as an additive, and its role as cocatalyst has been discussed. Furthermore, reactions of l-prolinethioamide salts with acetone have been monitored using ESI-MS and 1H NMR techniques, giving insight into the mechanism of the direct aldol reaction. The presumed formation of the iminium salt 10 has been unambiguously confirmed. SN - 0022-3263 UR - https://www.unboundmedicine.com/medline/citation/17253817/Br��nsted_acids_as_additives_for_the_direct_asymmetric_aldol_reaction_catalyzed_by_l_prolinethioamides__direct_evidence_for_enamine_iminium_catalysis_ L2 - https://doi.org/10.1021/jo062149k DB - PRIME DP - Unbound Medicine ER -