期刊
ADVANCED SYNTHESIS & CATALYSIS
卷 350, 期 2, 页码 295-302出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adsc.200700425
关键词
asymmetric synthesis; heterogeneous catalysis; ionic liquids; Mukaiyama aldol; recyclable catalyst
资金
- Engineering and Physical Sciences Research Council [EP/D029538/1] Funding Source: researchfish
Lewis acid complexes based on copper(II) and an imidazolium-tagged bis(oxazoline) have been used to catalyse the asymmetric Mukaiyama aldol reaction between methyl pyruvate and 1-methoxy-1-tri-methylsilyloxypropene under homogeneous and heterogeneous conditions. Although the ees obtained in ionic liquid were similar to those found in dichloromethane, there was a significant rate enhancement in the ionic liquid with reactions typically reaching completion within 2 min compared with only 55% conversion after 60 min in dichloromethane. However, this rate enhancement was offset by lower chemoselectivity in ionic liquids due to the formation of 3-hydroxy-1,3-diphenylbutan-1-one as a by-product. Supporting the catalyst on silica or an imidazolium-modified silica using the ionic liquid or in an ionic liquid-diethyl ether system completely suppressed the formation of this by-product without reducing the enantioselectivity. Although the heterogeneous systems were characterised by a drop in catalytic activity the system could be recycled up to five times without any loss in conversion or ee.
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