4(5)-Monosubstituted imidazoles (9) have been prepared via base-induced cycloaddition of tosylmethyl isocyanide (TosMIC) to N-(dimethylsulfamoyl)aldimines (2) or N-tosylaldimines (3). In the first case, N-(dimethylsulfamoyl)imidazoles 8 are the initial reaction products, from which the dimethylsulfamoyl group is readily removed with aqueous HBr. In the second case, the tosyl group of 1-tosylimidazoles 10 is lost spontaneously to give 4(5)-monosubstituted imidazoles 9 in one operation. (C) 1997 Elsevier Science Ltd.