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Brønsted acids as additives for the direct asymmetric aldol reaction catalyzed by l-prolinethioamides. direct evidence for enamine-iminium catalysis.
J Org Chem. 2007 Feb 02; 72(3):964-70.JO

Abstract

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.

Authors+Show Affiliations

Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, Warsaw, Poland. dgryko@icho.edu.plNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article

Language

eng

PubMed ID

17253817

Citation

Gryko, Dorota, et al. "Brønsted Acids as Additives for the Direct Asymmetric Aldol Reaction Catalyzed By L-prolinethioamides. Direct Evidence for Enamine-iminium Catalysis." The Journal of Organic Chemistry, vol. 72, no. 3, 2007, pp. 964-70.
Gryko D, Zimnicka M, Lipiński R. Brønsted acids as additives for the direct asymmetric aldol reaction catalyzed by l-prolinethioamides. direct evidence for enamine-iminium catalysis. J Org Chem. 2007;72(3):964-70.
Gryko, D., Zimnicka, M., & Lipiński, R. (2007). Brønsted acids as additives for the direct asymmetric aldol reaction catalyzed by l-prolinethioamides. direct evidence for enamine-iminium catalysis. The Journal of Organic Chemistry, 72(3), 964-70.
Gryko D, Zimnicka M, Lipiński R. Brønsted Acids as Additives for the Direct Asymmetric Aldol Reaction Catalyzed By L-prolinethioamides. Direct Evidence for Enamine-iminium Catalysis. J Org Chem. 2007 Feb 2;72(3):964-70. PubMed PMID: 17253817.
* Article titles in AMA citation format should be in sentence-case
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/Brønsted_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 -
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