Asymmetric aldol reactions between cyclic ketones and benzaldehyde catalyzed by chiral Zn 2+ complexes of aminoacyl 1,4,7,10-tetraazacyclododecane: effects of solvent and additives on the stereoselectivities of the aldol products
Tetrahedron: Asymmetry, ISSN: 0957-4166, Vol: 24, Issue: 24, Page: 1583-1590
2013
- 12Citations
- 14Captures
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Article Description
The direct aldol reaction between cyclic ketones and 4-nitrobenzaldehyde catalyzed by chiral Zn 2+ complexes of aminoacyl 1,4,7,10-tetraazacyclododecane is reported. The anti -aldol products were mainly formed in cyclohexanone/ N -methylpyrrolidone(NMP)/MeOH with good diastereo- and enantioselectivity, while syn -aldol adducts were obtained as major products with good enantioselectivity in cyclohexanone/H 2 O and cyclohexanone/NMP/H 2 O. The fact that the UV/vis spectra of 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)phenolate (Reichardt’s dye) were nearly identical in these solvent systems suggests that the switch in the relative configuration of the aldol products is induced by a large excess of H 2 O rather than the polarity of the solvent system. Furthermore, the addition of a small amount of TFA improved the enantioselectivity of the syn -aldol adducts produced in cyclohexanone/H 2 O with up to 92% ee ( anti / syn ratio = 30:70).
Bibliographic Details
http://www.sciencedirect.com/science/article/pii/S0957416613004849; http://dx.doi.org/10.1016/j.tetasy.2013.10.009; http://www.scopus.com/inward/record.url?partnerID=HzOxMe3b&scp=84890090788&origin=inward; https://linkinghub.elsevier.com/retrieve/pii/S0957416613004849; https://dx.doi.org/10.1016/j.tetasy.2013.10.009
Elsevier BV
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