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151.
Cardona CM Kitaygorodskiy A Echegoyen L 《Journal of the American Chemical Society》2005,127(29):10448-10453
The first derivatives of Y(3)N@C(80) have been synthesized and fully characterized. 1,3-Dipolar cycloaddition of N-ethylazomethine ylide yielded mainly the pyrrolidine monoadduct of the icosahedral (I(h)()) symmetry cage exclusively at a [6,6] double bond. The same regioselectivity on a [6,6] double bond was observed when the endohedral compound was cyclopropanated with diethyl bromomalonate. These results are in pronounced contrast to those observed for icosahedral symmetry Sc(3)N@C(80), for which all reported derivatives add completely regioselectively to [5,6] double bonds. (1)H NMR, (13)C NMR, and HMQC spectroscopy revealed that the addition pattern on Y(3)N@C(80) resulted in a pyrrolidinofullerene derivative with unsymmetric pyrrolidine carbons and symmetric geminal protons. The cyclopropanated monoadduct exhibited symmetric ethyl groups on the malonate, consistent with regioselective addition at a [6,6] double bond. Attempts to perform the same cyclopropanation reaction on (I(h)()) Sc(3)N@C(80) failed to yield any identifiable products. These observations clearly indicate that the reactivity of trimetallic nitride endohedral metallofullerenes toward exohedral chemical functionalization is profoundly affected and effectively controlled by the nature of the endohedral metal cluster. 相似文献
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Cycloadditions of chiral pyrroline N-oxides to levoglucosenone (1) and isolevoglucosenone (2) proceed with a high level of double asymmetric induction. Partial kinetic resolutions (KR) of both enantiomers of a racemic nitrone 3 were achieved, and a parallel kinetic resolution (PKR) experiment allowed the stereoselective divergent synthesis of two quasienantiomeric imino-C-disaccharide precursors. 相似文献
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Several distinct features have been observed in the photoluminescence spectrum of heavily Zn-doped GaAs, in the range between 1.65eV to 2.25eV. They are attributed to direct recombination across the Eo+?o gap and to indirect processes related to Xc1 and Xc3. The Xc1 minima are thus located to be 1.935±0.01eV above the top of the valence band at 100K. Their shear deformation potential X2 is found to be . 相似文献
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