Photochemical Approach for the Preparation of N-Alkyl/Aryl Substituted Fulleropyrrolidines: Photoaddition Reactions of Silyl Group Containing α-Aminonitriles with Fullerene C₆₀

The photochemical reactions of C-60 with N-(trimethylsilyl)methyl substituted and N-alkyl/aryl substituted alpha-aminonitriles were explored to evaluate the scope and reaction efficiency depending on the structural nature of amine substrates. The results showed that photoreactions of C-60 with trimethylsilyl group containing N-alkyl amines produced predominantly both trimethylsilyl and cyano group containing trans-pyrrolidine ring fused fulleropyrrolidines in a chemo- and stereo-selective manner. Interestingly, photoreactions of C-60 with N-branched alkyl substituted amines led to exclusive formation of non-silyl containing cycloadducts. In contrast to those of N-alkyl substituted alpha-aminonitriles, photoreactions of N-(trimethylsilyl)methyl and N-aryl substituted alpha-aminonitriles gave rise to the formation of both trans- and cis-isomeric fulleropyrrolidines with an inefficient and non-stereoselective manner. The feasible mechanistic pathways leading to generation of fulleropyrrolidines are 1,3-dipolar cycloaddition of the azomethine ylides, generated by either a single electron transfer (SET) (under N-2-purged conditions) or H atom abstraction (under O-2-purged conditions) process, to fullerene C-60. The stereoselectivities of photoproducts depending on the nature of amines are likely to be associated with conformational stabilities of in situ generated azoemthine ylides.