RuO4-Mediated oxidation of N-benzylated tertiary amines. Four- and three-membered azacycloalkanes as substrates

Abstract

Similarly to N-benzylpiperidine and -pyrrolidine, N-benzylazetidine underwent RuO4-catalyzed oxidation by attack at both types of N-methylene C-H bonds: endocyclic and exocyclic (benzylic). If the reaction is performed in the presence of cyanide, α-aminonitriles were obtained instead of amides. The regioselectivity (endocyclic/exocyclic) decreased constantly with the decrease of the azacycle size, from about 2 (for Nbenzylpiperidine) to about 0.6 (for N-benzylazetidine). The highest regioselectivity was found for Nbenzylaziridine, for which only products of benzylic functionalization resulted. Iminium ions, complexed to ruthenium species, were proposed as reactive intermediates during the oxidation of N-benzylated azacycloalkanes.