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■ Synthesis of Functionalized Fullerenes by Photoaddition of N-α-Trimethylsilyl-N-carboxymethyl-N-benzylamines to C60

Suk Hyun Lim, Dae Won Cho,* and Patrick S. Mariano*

*Department of Chemistry and Chemical Biology, University of New Mexico, Albuequerque, NM 87131, U.S.A.

Abstract

Photoaddition reactions of fullerene C60 with N-α- trimethylsilyl-N-carboxymethyl-N-benzylamines, which contain various para-substituents, were explored in order to evaluate factors governing efficiencies of this potentially useful method for preparing functionalized fullerene derivatives. Observations made in this study show that two reaction pathways are followed in these photoreactions. The first involves initial formation of α-trimethylsilyl-aminium radicals and the C60 anion radical by SET from the amines to the triplet excited state of C60. This step is followed by desilylation to produce α-amino radicals. Coupling of these radicals with the anion radical of C60 followed by protonation or with the hydrofullerene radical generated by protonation of the anion radical of C60 then produces aminomethyl- 1,2-dihydrofullerenes. When limited amounts of 3O2 are present in the reaction medium, fulleropyrrolidines are generated in low yields by a competitive pathway involving formation of singlet oxygen, which undergoes sequential H-atom abstractions from the N-α-trimethylsilyl-N-carboxymethyl-N-benzylamines to produce azomethine ylide intermediates. Dipolar cyloaddition of the ylides to C60 then produces fulleropyrrolidines. Photoreactions of the C60 and the amines in the presence of high 3O2 concentrations exclusively produce fulleropyrrolidine. In addition, the results show that photoreactions of non-silicon substituted, N-methyl-N-carboxymethyl-N-benzylamines with C60 form fulleropyrrolidines independent of the concentration of 3O2 present in the media.