Approaches to open fullerenes: Synthesis and kinetic stability of diels-alder adducts of substituted isobenzofurans and C-60

We have examined the reactions of 1,3-disubstituted isobenzofurans with the fullerene C-60 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...

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Published inJournal of organic chemistry Vol. 72; no. 8; pp. 2716 - 2723
Main Authors Chuang, Shih-Ching, Sander, Michael, Jarrosson, Thibaut, James, Scott, Rozumov, Eugene, Khan, Saeed I., Rubin, Yves
Format Journal Article
LanguageEnglish
Published WASHINGTON Amer Chemical Soc 13.04.2007
Subjects
Chemistry
Chemistry, Organic
Physical Sciences
Science & Technology
FUNCTIONALIZATION
ACID DERIVATIVES
MOLECULAR-HYDROGEN
NMR-SPECTROSCOPY
X-RAY-STRUCTURE
OPEN-CAGE FULLERENE
TRIS-SIGMA-HOMOBENZENES
ADDITION PATTERN
CARBON CAGE
ENDOHEDRAL METALLOFULLERENES
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Summary:We have examined the reactions of 1,3-disubstituted isobenzofurans with the fullerene C-60 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 C-60 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 C-60 and the free isobenzofurans 6a and 6c, have rate constants (and activation barriers) of k = 9.29 x 10(-5) s(-1) at 70 degrees C (E-a = 32.6 kcal mol(-1)) and k = 1.36 x 10(-4) s(-1) at 40 degrees C (E-a = 33.7 kcal mol(-1)), respectively, indicating that the addition of isobenzofurans to C-60 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.
ISSN:0022-3263
1520-6904
DOI:10.1021/jo061986j