Structures and Chemistry of Methanofullerenes: A Versatile Route into N‐[(Methanofullerene)carbonyl]‐Substituted Amino Acids

Abstract

AbstractThe reaction of C60 with oxadiazole 13 afforded the dimethoxymethanofullerene 7 in 32% yield as a 6‐6‐ring‐bridged isomer with a closed transannular bond. A literature survey showed that all 6‐6‐ring‐bridged methanofullerenes are σ‐homoaromatic with a closed transannular bond (6‐6‐closed) and all 6‐5‐ring‐bridged are π‐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.