Chuang Shih-Ching, Sander Michael, Jarrosson Thibaut, James Scott, Rozumov Eugene, Khan Saeed I, Rubin Yves
Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, USA.
J Org Chem. 2007 Apr 13;72(8):2716-23. doi: 10.1021/jo061986j. Epub 2007 Mar 17.
We have examined the reactions of 1,3-disubstituted isobenzofurans with the fullerene C60 in the context of an approach to open a large orifice on the fullerene framework. A variety of substituted isobenzofurans (6a-h), generated from the reaction of 1,4-substituted 1,4-epoxynaphthalenes 3a-h with 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (4a) or 1,2,4,5-tetrazine (4b), were added to C60 to afford the Diels-Alder adducts 7a-h. The thermal stability of these adducts toward retro-Diels-Alder fragmentation differs greatly in solution from that in the solid state. In solution, the relatively facile retro-Diels-Alder fragmentation of monoadducts 7a and 7c, to give C60 and the free isobenzofurans 6a and 6c, have rate constants (and activation barriers) of k=9.29x10(-5) s-1 at 70 degrees C (Ea=32.6 kcal mol-1) and k=1.36x10(-4) s-1 at 40 degrees C (Ea=33.7 kcal mol-1), respectively, indicating that the addition of isobenzofurans to C60 is readily reversible at those temperatures. In the solid state, thermogravimetric analysis of adduct 7a indicates that its decomposition occurs only within the temperature range of 220-300 degrees C. As a result, these compounds can be stored at room temperature in the solid state for several weeks without significant decomposition but have to be handled within several hours in solution.
我们在富勒烯骨架上打开一个大孔口的方法背景下，研究了1,3 - 二取代异苯并呋喃与富勒烯C60的反应。由1,4 - 取代的1,4 - 环氧萘3a - h与3,6 - 双（2 - 吡啶基）-1,2,4,5 - 四嗪（4a）或1,2,4,5 - 四嗪（4b）反应生成的各种取代异苯并呋喃（6a - h），被加入到C60中以得到狄尔斯 - 阿尔德加合物7a - h。这些加合物对逆狄尔斯 - 阿尔德碎片化的热稳定性在溶液中和固态下有很大差异。在溶液中，单加合物7a和7c相对容易发生逆狄尔斯 - 阿尔德碎片化，生成C60和游离异苯并呋喃6a和6c，在70℃时速率常数（和活化能垒）为k = 9.29×10⁻⁵ s⁻¹（Ea = 32.6 kcal mol⁻¹），在4℃时为k = 1.36×10⁻⁴ s⁻¹（Ea = 33.7 kcal mol⁻¹），这表明在这些温度下异苯并呋喃加到C60上的反应很容易可逆。在固态下，加合物7a的热重分析表明其分解仅在220 - 300℃的温度范围内发生。因此，这些化合物在固态下可在室温下储存数周而无明显分解，但在溶液中必须在数小时内处理。
