319489-97-9Relevant academic research and scientific papers
Bis(oxazoline)copper complexes covalently bonded to insoluble support as catalysts in cyclopropanation reactions
Burguete,Fraile,Garcia,Garcia-Verdugo,Herrerias,Luis,Mayoral
, p. 8893 - 8901 (2001)
Chiral bis(oxazolines) are readily dialkylated in the methylene bridge, opening the way to immobilization at that position, keeping the C2 symmetry of the chiral ligand. Bis(oxazolines) functionalized with two allyl or vinylbenzyl groups are easily grafted onto mercaptopropylsilica. Another approach to immobilization is the polymerization of the ligands bearing vinylbenzyl groups to yield insoluble polymers. The Cu(OTf)2 complexes of the immobilized ligands promote the enantioselective cyclopropanation reaction between styrene and ethyl diazoacetate. The results depend on the nature of the support and the method of immobilization. With regard to the type of solid, the best results, which are similar to or even better than those obtained with the corresponding dibenzylated homogeneous catalysts, are obtained with homopolymers. With regard to the bis(oxazoline), that bearing indan groups leads to good results both onto silica and polymers, whereas with the ligand bearing tert-butyl groups good enantioselectivities are only obtained with homopolymeric catalysts. Some of the heterogeneous catalysts can be easily recovered and reused, as much as five times, with the same yield and stereoselectivities.
Polymer-supported Bis(oxazoline)-copper Complexes as Catalysts in Cyclopropanation Reactions
Burguete, M. Isabel,Fraile, Jose M.,Garcia, Jose I.,Garcia-Verdugo, Eduardo,Luis, Santiago V.,Mayoral, Jose A.
, p. 3905 - 3908 (2007/10/03)
equation presented Bis(oxazolines) are easily immobilized by functionalization of the central methylene bridge with polymerizable groups and subsequent polymerization. Polymers are transformed into copper catalysts active in the cyclopropanation of styrene with ethyl diazoacetate. The results are similar or even better than those obtained with the similar homogeneous systems, and the catalysts can be easily recovered and reused. The substitution in the methylene bridge leads to a slight reduction in the enantioselectivity and an unexpected cis-preference.
