Study of ligand and base effects on enantioselective allylation catalyzed by Pd(0) phosphine complexes in [bmim][PF6] ionic liquid

Abstract

Enantioselective Pd-catalyzed allylic substitution of (rac)-(E)-1,3-diphenyl-3-acetoxyprop-1-ene with dimethyl malonate was studied in 3-butyl-1-methylimidazolium hexafluorophosphate ([bmim][PF 6 ]) as an ionic liquid. The reactions were catalyzed by Pd(0) complexes of three homochiral ferrocenylphosphine ligands, (S,S)-iPr-Phosferrox, (S,R)-iPr-Phosferrox, (R,S)-BCyPFA and (R)-BINAP. Potassium carbonate and bis(trimethylsilyl)acetamide (BSA)/AcOK were tested as the bases and simple optimization of the reaction procedure was performed. Experiments with other soft nucleophiles also were carried out under optimized conditions.

Assessment of the suitability of imidazolium ionic liquids as reaction medium for base-catalysed reactions Case of Knoevenagel and Claisen–Schmidt reactions

“…Ethyl benzoate should be formed by the same mechanism depicted in Scheme 3. However, for the reaction between 1 and 7, the amount of ethyl benzoate (6) formed was very minor. Again the mass balances in the first run were very low and increased significantly in the second run, although the conversion decreased remarkably (Table 3).…”

“…Addition of the base to the [(bmim)PF 6 ] was accomplished by adding alkali metal hydroxide dissolved in the minimum amount of alcohol. The alcohol was used to facilitate the addition and solubilisation of the hydroxide and it was subsequently removed by heating at 50 • C under vacuum.…”

“…The alcohol was used to facilitate the addition and solubilisation of the hydroxide and it was subsequently removed by heating at 50 • C under vacuum. For the amount of base and the volume of [(bmim)PF 6 ] used a clear ionic liquid was obtained after incorporation of the hydroxide.…”

“…A solution of 7.2 mg KOH (0.2 mmol) in ethanol (0.2 ml) was added to 0.5 g [(bmim)PF 6 ]. The clear solution was outgassed at 50 • C under vacuum for 12 h. To this basic solution, 10.6 mg benzaldehyde (0.1 mmol) and 6.6 mg malononitrile (0.1 mmol) were added.…”

“…Most of the reports in this area have focused on Lewis acid or noble metal-catalysed reactions. In comparison, reports dealing with basic catalysis in ionic liquids are considerably more scarce although it is attracting growing interest [3][4][5][6][7]. At the present they are limited to O-alkylation of phenols, benzoin condensation and more recently to the Robinson annulation and Knoevenagel condensation.…”