176. Structures and Chemistry of Methanofullerenes: A Versatile Route into N--Substituted Amino Acids

Article abstract of DOI:10.1002/hlca.19930760705

The reaction of C60 with oxadiazole 13 afforded the dimethoxymethanofullerene 7 in 32 percent yields as a 6-6-ring-bridged isomer with a closed transannular bond.A literature survey showed that all 6-6-ring-bridged methanofullerenes are ?-homoaromatic with a closed transannular bond (6-6-closed) and all 6-5-ring-bridged are ?-homoaromatic with an open transannular bond (6-5-open).The preference for 6-6-closed and 6-5-open structures is not due to substituent effects but is best explained with the conservation in these isomers of the favorable bonding seen in C60 with higher double- bond character at 6-6-bonds and higher single-bond character at 6-5-bonds.Reaction of C60 with diazo diester 15 gave the fullerene diester 14 which was hydrolyzed with BBr3 in benzene to the methanofullerenecarboxylic acid 10, a versatile synthon for the preparation of amphiphilic fullerene derivatives.Treatment of 10 with alcohols and amino acid esters under DCC coupling conditions afforded the esters 5 and 17 and the amino-acid derivatives 11 and 12, respectively.