Diels–Alder reaction in protic ionic liquids

Applications of Chiral Ionic Liquids

“…Even higher splitting up to 63 Hz in 19 F and 60 Hz in 1 H NMR spectroscopy was reported by Clavier et al using the (S)-valine-derived CILs 46 (entry 3). [56] Once again, the presence of a phenyl group, in this case with an additional bulky tert-butyl substituent in ortho position was crucial for strong interactions.…”

“…Protic imidazolium ILs have been tested as solvent and reaction media in the Diels-Alder reaction of dimethylmaleate and methyl acrylate (Scheme 3). [19] High conversion of 95 % and endo/exo selectivities of 3.7:1 with protic 1-alkylimidazolium and 1-alkoxyimidazolium lactates 6 were obtained. However, the differences in yield and diastereoselectivity between the racemic (rac)-lactates and the enantiopure (S)-lactates were negligible.…”

“…[54] In order to investigate interionic diastereomeric interactions between the enantiopure CIL and a racemic substrate, the authors performed 19 F NMR spectroscopy of a mixture of racemic Mosher's acid sodium salt and the ephedrinebased CIL 40 in a common NMR solvent ( Table 2, entry 1). Depending on the ratio of CIL applied in the experiment, a splitting of the 19 F signal of the CF 3 group was observed, thus giving evidence for the presence of chiral environment. The chemical shift difference made it possible to determine the amount of CIL indicating a minimum concentration of 0.3 mmol/mL in order to achieve sufficient resolution.…”

Chiral ionic liquids: A compendium of syntheses and applications (2005–2012)

“…35 Since then ionic liquids have been In 2006, Pernak and coworkers used protic imidazolium ionic liquids as the reaction media for cyclopentadiene and two dienophiles (dimethyl maleate and methyl acrylate) that resulted in good endo/exo selectivities (up to 3.9:1; Table 4, entry 1). 99 The chiral L-lactate ionic liquid 227 and racemic DL-lactate ionic liquid 226 both performed almost identically. Vo-Thanh and coworkers designed different CILs to be used as the reaction media in an aza-Diels-Alder reaction between Danishefsky's diene and a chiral imine (see Table 4, entry 2).The reactions involved only the diene, chiral imines, and the CIL, whereas no other acid catalyst or organic solvent was used.…”

Ionic liquid promoted Diels-Alder Reaction between anthrone and maleimides

“…Some researchers have postulated that due to their characteristic hydrogen bonding ability, ionic liquids can act as a catalyst [3] or as an organocatalyst [4]. Semiempirical computational analysis of the Diels-Alder reactions in protic imidazolium ionic liquids supported this view and concluded that hydrogen bonding of the protic ionic liquids to the dienophile could provide a rationale for the observed Brønsted acid catalysis [5].…”