N-Phosphorylated Imidazolium Salts as Precursors to 2- and 5-Phosphorylated Imidazoles and New Imidazol-2-ylidenes Featuring the PNCN Unit

It has been experimentally proven that the reaction of 1- or 1,2-disubstituted imidazoles with diorganylphosphorus(III) halides proceeds via initial formation of N-phosporylated imidazolium salts. Treatment of these salts with strong bases results in phosphorylation of the parent imidazoles at the 2- or 5-positions, correspondingly. In a previous case, imidazol-2-ylidenes are formed as intermediates. With both N1 and N3 atoms bearing sterically demanding or/and π-donating groups, deprotonation of 1,3-disubstituted imidazolium salts with NaN(SiMe3)2 afforded new stable N-phosphorus-substituted Arduengo-type carbenes.