Preparation of 1,2,5‐Trisubstituted 1 H ‐Imidazoles from Ketenimines and Propargylic Amines by Silver‐Catalyzed or Iodine‐Promoted Electrophilic Cyclization Reaction of Alkynes

From readily available propargylic amines, 1,2,5‐trisubstituted imidazoles are efficiently obtained through a cascade reaction catalyzed by AgOTf or promoted by molecular iodine. The AgOTf‐catalyzed reaction involves nucleophilic addition of propargylic amine to ketenimine, a silver‐catalyzed electrophilic cyclization reaction of alkyne, and a tautomerism/isomerism/metal‐H exchange cascade. The iodine‐mediated counterpart yields 5‐formyl‐1,2‐disubtituted imidazoles, which presumably includes a cascade hydrolysis/oxidation reaction. Furthermore, the presented protocol can be scaled up and the resultant 1,2,5‐trisubstituted imidazole can be converted into fused indeno[1,2‐ d ]imidazole.