Abstract
The asymmetric Diels–Alder reaction between N-acryloyloxazolidinone and cyclopentadiene and the Mukaiyama-aldol reaction between methylpyruvate and 1-phenyl-1-trimethylsilyloxyethene have been catalysed by heterogeneous copper(II)-bis(oxazoline)-based polymer immobilised ionic liquid phase (PIILP) systems generated from a range of linear and cross linked ionic polymers. In both reactions selectivity and ee were strongly influenced by the choice of polymer. A comparison of the performance of a range of Cu(II)-bis(oxazoline)-PIILP catalyst systems against analogous supported ionic liquid phase (SILP) heterogeneous catalysts as well as their homogeneous counterparts has been undertaken and their relative merits evaluated.
Highlights
Over the past two decades ionic liquids (ILs) have been shown to be extremely beneficial to a number of transition metal-catalysed reactions including asymmetric catalysis.[1]
A range of chiral metal complexes of Pt, Zn, Cu and Mg have been immobilised in ILs under homogeneous or heterogeneous (Supported Ionic Liquid Phase-supported ionic liquid phase (SILP)) conditions and shown to be excellent catalysts for a host of important asymmetric C–C bond forming reactions such as Diels–Alder and Mukaiyama-aldol reactions, cyclopropanations and oxidations, often with significant and marked enhancements in rate and selectivity compared with the corresponding reaction in conventional solvents.[2]
Having recently developed an efficient and recyclable peroxometalate-based polymer immobilised ionic liquid phase oxidation catalyst using a cation-decorated ring opening metathesis-derived polymer as support,[15] we report that copper(II)-bis(oxazoline)-derived PIILP catalysts A and B either rival or outperform their homogeneous or SILP counterparts for the Diels–Alder (Scheme 1) and the Mukaiyama-aldol reaction (Scheme 2)
Summary
Scheme 1 Asymmetric Diels–Alder reaction between N-acryloyloxazolidinone and cyclopentadiene catalysed by 10 mol% Cu(II)-bis(oxazoline) complexes. Scheme 2 Asymmetric Mukaiyama-aldol reaction between methylpyruvate and 1-phenyl-1-trimethylsilyloxyethene catalysed by 10 mol% Cu(II)-bis(oxazoline) complex A. supported pyrrolidinium tetrafluoroborate has been applied to the asymmetric hydrogenation of methylacetoacetate.[13] Therein, high ee’s were obtained but the activity was lower than in methanol under homogeneous conditions. Having recently developed an efficient and recyclable peroxometalate-based polymer immobilised ionic liquid phase oxidation catalyst using a cation-decorated ring opening metathesis-derived polymer as support,[15] we report that copper(II)-bis(oxazoline)-derived PIILP catalysts A and B either rival or outperform their homogeneous or SILP counterparts for the Diels–Alder (Scheme 1) and the Mukaiyama-aldol reaction (Scheme 2).
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