| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 1347495 | Tetrahedron: Asymmetry | 2013 | 8 Pages |
The direct aldol reaction between cyclic ketones and 4-nitrobenzaldehyde catalyzed by chiral Zn2+ 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/H2O and cyclohexanone/NMP/H2O. 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 H2O 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/H2O with up to 92% ee (anti/syn ratio = 30:70).
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1-(S)-Decanylglycyl-1,4,7,10-tetraazacyclododecane 3TFA saltC26H48F9N5O8[α]D26=+10.8 (c 1.00, H2O)Source of chirality: N-tert-butoxycarbony-l-2-amino-dodecanoic acidAbsolute configuration: (S)
1-(S)-Ethylglycyl-1,4,7,10-tetraazacyclododecane 3TFA saltC18H30F9N5O7[α]D26=+18.0 (c 1.00, H2O)Source of chirality: N-tert-butoxycarbonyl-l-2-amino-butanoic acidAbsolute configuration: (S)
1-(S)-Valyl-1,4,7,10-tetraazacyclododecane 3TFA saltC21H36F9N5O8[α]D26=+31.3 (c 1.00, H2O)Source of chirality: N-tert-butoxycarbony-l-valineAbsolute configuration: (S)
1-(S)-Phenylethylglycyl-1,4,7,10-tetraazacyclododecane 3TFA saltC24H34F9N5O7[α]D26=+11.6 (c 1.00, H2O)Source of chirality: N-tert-butoxycarbonyl-l-homophenylalanineAbsolute configuration: (S)
