713508-60-2Relevant articles and documents
The stability of imidazolidinones is the primary influence on the catalytic activity of proline amides and proline sulfonamides in enamine catalysis using alkyl aldehyde substrates
Tin, Sergey,Fuentes, Jose A.,Lebl, Tomas,Clarke, Matthew L.
, p. 141 - 147 (2013/02/22)
Some N-substituted proline derivatives catalyse the reactions of alkyl aldehydes with electrophilic partners, and others give negligible amounts of product. The key reaction between the aldehyde and the proline derivative has been studied, and a rationale for the reactivity observed is presented. Simple proline amides derived from aromatic amines (poor catalysts) form stable imidazolidinones quite rapidly at the expense of enamines, the latter being detected, if at all, for less than an hour. Less basic proline amides form a kinetic diastereomer of an imidazolidinone that very slowly inverts its stereochemistry to give a final thermodynamic product. The stereochemistry of these diastereomers was fully assigned by 1H NMR, NOE, and TOCSY experiments. A proline amide derived from an alkylamine (good catalyst) forms high concentrations of enamine that is only slowly (days) converted into a single diastereomer of an inert imidazolidinone. In contrast, another good catalyst, a proline sulfonamide, immediately forms a reactive imidazolidinone, that rapidly ring-opens and exchanges with other aldehydes. This presumably drip-feeds iminium ions and enamines into the catalytic cycle. Thus, there are two quite different mechanistic regimes that lead to efficient catalysis. These mechanistic insights should now allow some element of rational design of prolinamides for enamine reactions using aldehydes. Some proline amides are poor catalysts when aldehydes are used as substrates since the catalysts irreversibly form imidazolidinones. Proline amides with more basic amide groups form long-lived enamines, which allows catalysis to proceed. Proline sulfonamides only form imidazolidones, but these are unstable. Copyright
Evaluation of ligands for ketone reduction by asymmetric hydride transfer in water by multi-substrate screening
Zeror, Saoussen,Collin, Jacqueline,Fiaud, Jean-Claude,Zouioueche, Louisa Aribi
experimental part, p. 197 - 204 (2009/04/08)
Various ligands for the ruthenium-catalyzed enantioselective reduction of ketones in water have been investigated. Multi-substrate reactions have been carried out for the comparison of various proline amides and aminoalcohol ligands. Two sets of six aromatic ketones have been selected in order to evaluate the enantiomeric excesses of all the resulting alcohols by a single chromatographic analysis. The proline amide derivative prepared from (1R,2S)-cis-aminoindanol revealed as the best ligand for most of the ketones used in the multi-substrate reductions. This ligand has been employed for the enantioselective reduction of a variety of other aromatic ketones and in all cases the enantiomeric excesses were improved compared to those obtained with phenylprolineamide used in our previous work.
