Regioselective Intramolecular Nucleophilic Addition of Alcohols to C60: One-Step Formation of acis-1 Bicyclic-Fused Fullerene

Abstract

The first example of intramolecular nucleophilic addition of an alcohol to a fullerene double bond is described. In particular, the straightforward one-step reaction of commercially available sarcosine, hydroxyacetaldehyde, and [60]fullerene, in refluxing chlorobenzene, affords a structurally complex novel pyrrolidinofullerene endowed with a furan ring simultaneously fused to both the pyrrolidine and fullerene moieties, which has been spectroscopically and electrochemically characterized. The 2-fold cyclization reaction occurs in a totally regioselective stepwise process leading exclusively to the cis-1 isomer. Theoretical calculations (DFT and ONIOM approach) predict that, in contrast to the previous examples with phenols, which require the existence of an intramolecular H-bond and the presence of a methyl group on C-2 of the pyrrolidine ring to afford the cyclized pyran-fused pyrrolidinofullerenes, the formation of the oxygen pentagonal ring is highly favored and does not present such structural constrains. Actually, the 5-exo-trig cyclization reaction involving the nucleophilic attack of the hydroxyl group to the fullerene surface is moderately exothermic although it has a substantially high energy barrier in accordance with the fact that high temperatures have to be reached to obtain the final product.