SYNTHESIS OF PROTOTYPICAL FULLERENE CYCLOPROPANES AND ANNULENES - ISOMER DIFFERENTIATION VIA NMR AND UV SPECTROSCOPY

Parent cyclopropanes, annulenes, and related derivatives of C-60 and C -70 have been prepared and subjected to extensive spectroscopic scruti ny. Photolysis of the diazomethane adduct of C-60 afforded the C61H2 c yclopropane 2, accompanied by the isomeric annulene 4. Reaction of dim ethyldiazomethane with C-60 led to C63H6 annulene 11, which upon heati ng was smoothly converted to the cyclopropane isomer 10 with an activa tion energy of 25 +/- 1 kcal . mol(-1). Addition of diazomethane to a toluene solution of C-70 generated a 12:1:2 mixture of pyrazolines. Ph otolysis of the mixture gave the C71H2 cyclopropanes 6 and 7, whereas thermolysis furnished the isomeric annulenes 8 and 9. Criteria have be en developed for distinguishing fullerene cyclopropane derivatives fro m the corresponding annulenes via NMR and UV spectroscopy.