[2+2] CYCLOADDITIONS OF FULLERENES - SYNTHESIS AND CHARACTERIZATION OF C62O3 AND C72O3, THE FIRST FULLERENE ANHYDRIDES

[2 + 2] Cycloaddition of C-60 With N,N,N',N'-tetraethylethynediamine (1a) and N,N-diethyl-2-ethylthio-ethyneamine (1b) gave the stable, 1,2-dihydrofullerene[60]-1,2-cyclobutenediamine 2a and thioenamine 2b, respec tively, in good yield. Self-sensitized photooxygenation of 2a and 2b produced 1,2-dihydrofullerene[60]-1,2-diamide 3a and thioester amide 3b, from which 1,2-dihydrofullerene[60]-1,2-dicarboxylic acid anhydride (C62O3) was readily prepared. Similarly, C-70 reacted with 1a (regiospecifically at the 1,9-bond) to give 1,9-dihydrofullerene[70]-1,9-cyclobutenediamine 5 or 1,9:61,62-biscyclobutenediamine 6 in good yields. In contrast to 2a, self-sensitized photooxygenation of 5 regenerated C-70 and the oxidized ynamine. 1,9-Dihydrofullerene[70]-1,9-dicarboxylic acid anhydride (C72O3) was prepared from a tert-butylthioester amide 10 in one pot by reaction of N,N-diethyl-2-tert-butylthioethyneamine (1c) with C-70 and photooxygenation of the resultant cycloadduct.