Synthesis and Study of 1-Aryl-1H-4,5-dihydroimidazoles

An easy synthesis of 1-aryl-1H-4,5-dihydroimidazoles 1 by cyclocondensation of N-aryl-N'-formylethylenediamines 2 is described. Such precursors were synthesized by selective formylation of N-arylethylenediamines 3 with p-nitrophenyl formate. Cyclizations were performed using trimethylsilyl polyphosphate. Chemical properties of compounds 1, typical of amidine system, were studied. Reaction of 1 with methyl iodide leads to the corresponding 1-aryl-3-methyl-1H-4,5-dihydroimidazolium salts 5. Reduction of dihydroimidazoles 1 with sodium cyanoborohydride provides a convenient access to N-aryl-N'-methylethylenediamines 4.