Oxidant promoted 1,3-dipolar cycloaddition of benzimidazolium ylides to alkenes for preparation of 4H-pyrrolo[1,2-a]benzimidazole

An oxidant promoted 1,3-dipolar cycloaddition of benzimidazolium ylides to alkenes was developed for the preparation of 4H-pyrrolo[1,2-a]benzimidazole derivatives in moderate yields under mild conditions. In the presence of a suitable oxidant, the most commercially available "normal" alkenes, instea d of alkynes or "abnormal" alkenes, could be used as dipolarophiles success fully. Moreover, CrO3/Et3N has been proved to be a more effective dehydroge nating reagent than MnO2 or tetrakispyridine cobalt (II) dichromate (TPCD) in this procedure.