FeCl3-Assisted Niobium-Catalyzed Cycloaddition of Nitriles and Alkynes: Synthesis of Alkyl- and Arylpyrimidines Based on Independent Functions of NbCl5 and FeCl3 Lewis Acids

Article abstract of DOI:10.1021/acs.orglett.7b02708

NbCl₅-catalyzed [2 + 2 + 2] cycloaddition of nitriles with alkynes was used to synthesize pyrimidine derivatives. In this reaction, the use of individual Lewis acids, namely NbCl₅ and FeCl₃, is a key strategy for achieving the reaction using a catalytic amount of NbCl₅. The roles of the two Lewis acids were investigated using FT-IR spectroscopy. The results showed that NbCl₅ served as an efficient Lewis acid catalyst for nitrile activation, whereas FeCl₃ showed stronger Lewis acidity toward pyrimidines, releasing NbCl₅ into the catalytic cycle.