Journal of the American Chemical Society, Vol.136, No.2, 705-712, 2014
Stereodivergent Synthesis of Chiral Fullerenes by [3+2] Cycloadditions to C-60
A wide range of new dipoles and catalysts have been used in 1,3-dipolar cycloadditions of N-metalated azomethine ylides onto C-60 yielding a full stereodivergent synthesis of pyrrolidino[60]fullerenes with complete diastereoselectivities and very high enantioselectivities. The use of less-explored chiral alpha-iminoamides as starting 1,3-dipoles leads to an interesting double asymmetric induction resulting in a matching/mismatching effect depending upon the absolute configuration of the stereocenter in the starting alpha-iminoamide. An enantioselective process was also found in the retrocycloaddition reaction as revealed by mass spectrometry analysis on quasi-enantiomeric pyrrolidino[60]fullerenes. Theoretical DFT calculations are in very good agreement with the experimental data. On the basis of this agreement, a plausible reaction mechanism is proposed.