An efficient [2+3] cycloaddition approach to the synthesis of pyridyl- appended fullerene ligands

We have used 2-, 3-, and 4-picolylamines and their various N-substituted derivatives as substrates to generate azomethine ylides for [2+3] cycloaddition to [60]fullerene. A considerable difference in the reactivity of isomeric picolylamines was observed; however, even less reactive 3-picolylamines afford high yields of products under acid or base catalysis. This method provides easy access to a large family of valuable ligands (pyridyl-substituted pyrrolidinofullerenes) that can be used in the design of transition-metal complexes and non-covalently bonded dyads with metalloporphyrins. Unusually high yields of products and convenience of synthetic procedures (2–10 min heating the reagents at reflux in 1,2-dichlorobenzene in air in most cases) as well as a wide synthetic potential make this reaction a good alternative to the commonly used Prato method. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)