Proline derivatives as organocatalysts for the aldol reaction in conventional and non-conventional reaction media

Abstract

Different l -proline derivatives were investigated as organocatalysts for the aldol condensation reaction between acetone and 4-nitrobenzaldehyde, in a conventional organic solvent (DMSO), in supercritical carbon dioxide, and in mixtures of this solvent and 1-allyl-3-alkyllimidazolium chlorides ionic liquids. The catalysts evaluated were:and (2S,3R,4R,5S,6R)-6-(acetoxymethyl)-3-[(S)-pyrrolidine-2-carboxamido]-tetrahydro-2H-pyran-2,4,5-triyl triacetate (peracetylated glucosamine-l -proline). One of the catalysts tested, the tert-butyldimethylsilyloxy-l -proline, was very effective, allowing lower reaction times, resulting in better yields and enantiomeric excesses than l -proline itself, both in organic solvent (DMSO) and in sc-CO 2 or a mixture of sc-CO 2 and ionic liquids. The use of the ionic liquid resulted in better yields and enantiomeric excesses in sc-CO 2 . The other catalysts tested were not as effective, resulting in yields and enantiomeric excesses similar or inferior to the ones obtained with l -proline.

Phase Behavior for the System Carbon Dioxide + p-Nitrobenzaldehyde: Experimental and Modeling

“…For the CO 2 (1) + p-nitrobenzaldehyde(2) system, the set molar fractions of the solute in CO 2 (2.638 × 10 −3 , 3.525 × 10 −3 , 4.415 × 10 −3 , and 5.903 × 10 −3 ) have values that were selected based on the previously considered concentrations of this compound in the model aldol reaction of p-nitrobenzaldehyde + acetone. 18 Experiments at higher molar fraction of p-nitrobenzaldehyde were not carried out in this work due to the maximum operating pressure limit of the 2) System. In this work, we modeled the phase behavior of the system carbon dioxide(1) + pnitrobenzaldehyde(2).…”

“…Within the range of compounds that are employed as solvents in reactions at high pressure, the use of supercritical carbon dioxide is of great interest. ,,,,− This is due to some characteristics of CO 2 as its low cost and easy separation after a reaction, and to the possibility of controlling several physicochemical properties of this solvent by adjusting the solvent temperature and pressure…”

Organocatalysts Derived from Unnatural α‐Amino Acids: Scope and Applications

“…Organocatalyst 40 and other congeners have also been studied in aldol reactions under nonstandard conditions. For example, Cassaro et al . described the use of a set of 4‐silyloxyproline derivatives as organocatalysts for the aldol reaction between acetone and p ‐nitrobenzaldehyde in supercritical CO 2 and in biphasic systems that contain supercritical CO 2 and imidazole‐derived ionic liquids.…”

Investigation of proline derivatives for the efficient organocatalysis of an Aldol type reaction in supercritical CO2

“…Our group has recently studied a series of proline derivatives for the organocatalysis of Aldol type reactions in sc-CO 2 . 5 In this work, we continue this investigation using proline, a proline based helical polymer and a silane proline derivative to study the behavior of a model Aldol reaction using a cyclic ketone in sc-CO 2 (Scheme 1).…”