'On Water': Efficient Iron-Catalyzed Cycloaddition of Aziridines with Heterocumulenes

摘要

The use of water as a reaction medium for organic synthesis has attracted much interest in recent years, because water is the most abundant liquid on the planet, cheap, readily available, nontoxic, and nonflammable. The [3+2] cycloaddition reaction of aziridines with heterocumulenes provides a powerful tool to access a wide range of functionalized five-membered heterocycles that exhibit interesting biological and medicinal properties. Thus, the cycloaddition of aziridines with carbodiimides,151 isocyanates, and isothiocya-nates has been studied employing Pd, Ni, HBF4, Mg-MeOH, PBu3, Nal or Ph4SbBr-based systems as either the catalyst or stoichiometric reagent. These reactions are effective in an organic medium and generally involve an inert atmosphere. In continuation of our studies on hetero-cycle synthesis, we wish to herein report the first example of iron(III)-catalyzed cycloaddition of aziridines with heterocumulenes that takes place in aqueous suspension at moderate temperature. The protocol is simple and utilizes environmentally benign nontoxic and cheap iron(III) salt as the catalyst and water as a reaction medium in air.