TY - JOUR
T1 - Recyclable copper catalysts based on imidazolium-tagged bis(oxazolines)
T2 - A marked enhancement in rate and enantioselectivity for Diels-Alder reactions in ionic liquid
AU - Doherty, Simon
AU - Goodrich, Peter
AU - Hardacre, Christopher
AU - Knight, Julian G.
AU - Nguyen, Mimi T.
AU - Pârvulescu, Vasile I.
AU - Paun, Cristina
PY - 2007/4
Y1 - 2007/4
N2 - Imidazolium-tagged bis(oxazolines) have been prepared and used as chiral ligands in the copper(II)-catalysed Diels-Alder reaction of N-acryloyland N-crotonoyloxazolidinones with cyclopentadiene and 1,3-cyclohexadiene in the ionic liquid 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, [emim] [NTf2]. A significant and substantial enhancement in the rate and enantioselectivity was achieved in [emim] [NTf2] compared with dichloromethane. For example, complete conversion and enantioselectivities up to 95 % were obtained for the reaction between N-acryloyloxazolidinone and cyclopentadiene within 2 min in [emim] [NTf2] whereas the corresponding reaction in dichloromethane required 60 min to reach completion and gave an ee of only 16%. The enhanced rates obtained in the ionic liquid enabled a catalyst loading as low as 0.5 mol % to give complete conversion within 2 min while retaining the same level of enantioselectivity. The imidazolium-tagged catalysts can be recycled ten times without any loss in activity or enantioselectivity and showed much higher affinity for the ionic liquid phase during the recycle procedure than the analogous uncharged ligand.
AB - Imidazolium-tagged bis(oxazolines) have been prepared and used as chiral ligands in the copper(II)-catalysed Diels-Alder reaction of N-acryloyland N-crotonoyloxazolidinones with cyclopentadiene and 1,3-cyclohexadiene in the ionic liquid 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, [emim] [NTf2]. A significant and substantial enhancement in the rate and enantioselectivity was achieved in [emim] [NTf2] compared with dichloromethane. For example, complete conversion and enantioselectivities up to 95 % were obtained for the reaction between N-acryloyloxazolidinone and cyclopentadiene within 2 min in [emim] [NTf2] whereas the corresponding reaction in dichloromethane required 60 min to reach completion and gave an ee of only 16%. The enhanced rates obtained in the ionic liquid enabled a catalyst loading as low as 0.5 mol % to give complete conversion within 2 min while retaining the same level of enantioselectivity. The imidazolium-tagged catalysts can be recycled ten times without any loss in activity or enantioselectivity and showed much higher affinity for the ionic liquid phase during the recycle procedure than the analogous uncharged ligand.
KW - Asymmetric Diels-Alder reaction
KW - Ionic liquids
KW - Rate and enantioselectivity enhancements
KW - Recyclability
KW - Task-specific ionic liquids
UR - http://www.scopus.com/inward/record.url?scp=34547221117&partnerID=8YFLogxK
U2 - 10.1002/adsc.200600531
DO - 10.1002/adsc.200600531
M3 - Article
AN - SCOPUS:34547221117
SN - 1615-4150
VL - 349
SP - 951
EP - 963
JO - Advanced synthesis & catalysis
JF - Advanced synthesis & catalysis
IS - 6
ER -