Improving the Catalytic Performance of (S)-Proline as Organocatalyst in Asymmetric Aldol Reactions in the Presence of Solvate Ionic Liquids: Involvement of a Supramolecular Aggregate

Abstract

For the first time, a highly efficient and stereoselective asymmetric aldol reaction employing (S)-proline in the presence of solvate ionic liquids is reported. The reaction seems to proceed via a supramolecular aggregate of (S)-proline, the solvate ionic liquid, and water, affording high yields and excellent stereoselectivities with low catalyst loadings.

Green Asymmetric Organocatalysis

“…A molecule of water operates as a bridge to the aldehyde. Various aldehydes and ketones were tested, and the aldol products were obtained in excellent yields and high enantioselectivities …”

A Review of some catalysts and promoters used in organic transformations

“…[7] Asymmetric aldol reaction employing (S)proline as catalyst in the presence of ionic liquids was reported by Juaristi and co-workers (scheme 15). [116] Amino acid-derived bifunctional phosphines are found to be effective catalyst for organic transformations such as enantioselective annulations of allenes, enantio selective [4+2] annulations, enantio selective [4+1] annulation, enantio selective Michael addition, asymmetric γ-umpolung addition, enantio selective allylic substitutions etc. [117] L-glutamine derived γamino acids were effieient catalyst for nitroaldol condensation between aromatic aldehydes and nitromethane.…”

Ionic Liquids in Asymmetric Synthesis: An Overall View from Reaction Media to Supported Ionic Liquid Catalysis

“…In 2017, for the first time Juaristia nd co-workersr eported the asymmetric aldol reaction of variousa ldehydes andk etones by using l-proline as an organocatalyst in the presence of solvate ionic liquids( SILs) and water as an additive. [23] They outline the preparationo ff our lithium-containing SILs by mixing equimolar amounts of lithium perchlorate (LiClO 4 )o r lithium bis(trifluoromethanesulfonyl)imide (LiNTf 2 )a nd triglyme (G3) or tetraglyme (G4) (Scheme4). Initial experimentss how that G3NTf 2 is the best solvate ionic liquid.…”