Synthesis of Prototypical Fullerene Cyclopropanes and Annulenes. Isomer Differentiation via NMR and UV Spectroscopy

Parent cyclopropanes, annulenes, and related derivatives of C{sub 60} and C{sub 70} have been prepared and subjected to extensive spectroscopic scrutiny. Photolysis of the diazomethane adduct of C{sub 60} afforded the C{sub 61}H{sub 2} cyclopropane 2, accompanied by the isomeric annulene 4. Reaction of dimethyldiazomethane with C{sub 60} led to C{sub 63}H{sub 6} annulene 11, which upon heating was smoothly converted to the cyclopropane isomer 10 with an activation energy of 25 {+-} 1 kcal-mol{sup -1}. Addition of diazomethane to a toluene solution of C{sub 70} generated a 12:1:2 mixture of pyrazolines. Photolysis of the mixture gave the C{sub 11}H{sub 2} cyclopropanes 6 and 7, whereas thermolysis furnished the isomeric annulenes 8 and 9. Criteria have been developed for distinguishing fullerene cyclopropane derivatives from the corresponding annulenes via NMR and UV spectroscopy. 57 refs., 12 figs., 1 tab.