SET-promoted photoaddition reactions of fullerene C-60 with tertiary N-trimethylsilylmethyl substituted alpha-aminonitriles. Approach to the synthesis of fulleropyrrolidine nitriles

Abstract

Photoaddition reactions of C-60 with tertiary N-arylmethyl-N-trimethylsilylmethyl substituted alpha-aminonitriles were explored. The results show that these photoreactions produce both trimethylsilyl- and cyano group containing fulleropyrrolidines as major products through pathways involving 1,3-dipolar cycloaddition of azomethine ylide intermediates. The ylides are formed either by SET from alpha-aminonitriles to the triplet excited state of C-60 (in N-2-purged solutions) followed by desilylation or deprotonation, or by hydrogen atom abstraction by singlet oxygen (in O-2-purged solutions). In contrast, photoreactions of C-60 with analogous amines that do not contain trimethylsilyl group form fulleropyrrolidines that contain aryl- and cyano substitutents on the pyrrolidine ring. The efficiencies of these photoaddition reactions are influenced by several factors including reaction condition (N-2 or O-2-purged), solvent polarity, the electronic and structural nature of alpha-aminonitriles and additive. The presence of trimethylsilyl group in the alpha-aminonitrile substrates plays a crucial role in enhancing the efficiencies of the fulleropyrrolidine forming reactions. (C) 2017 Elsevier Ltd. All rights reserved