Facile syntheses of N-heterocyclic carbene precursors through Cu(ii)- or Ag(i)-catalyzed amination of N-alkynyl formamidines

Abstract

We have developed a facile method for the synthesis of novel five- and six-membered cyclic formamidinium salts bearing an unsaturated backbone through Cu(II)- or Ag(I)-catalyzed amination of N-alkynyl formamidines. Cu(II)- or Ag(I)-promoted cyclization in a stoichiometric mode was also investigated, and it could offer some desirable cyclic formamidinium salts, which cannot be prepared through a catalytic reaction mode. Two rhodium(I) complexes were prepared through the treatment of [Rh(cod)Cl]₂ with the free carbenes obtained in situ by the deprotonation of the corresponding resulting formamidinium salts.