Sulfilimines and sulfoximines are found in many biologically active molecules and natural products. Traditional metal-catalyzed syntheses are amination using iminoiodinanes or azides. Disadvantages of these approaches are the use of an excess of these aminating reagents that are either air-sensitive, difficult to handle or potentially explosive. Furthermore, only a few stereoselective reactions have been developed. Recently, our group has reported a straightforward synthesis of sulfilimines and sulfoximines from sulfides or sulfoxides, trichloroethoxysulfonyl azide and iron(III) acetylacetonate in photochemical continuous flow. The reaction proceeds under mild conditions and short residence time. In order to provide a safer and more effective process, we envisioned that known nitrene precursor, N-sulfonyloxycarbamates, could be used for this transformation. N-sulfonyloxycarbamates are safe, bench-stable and readily available in two steps. However, these reagents were never used in continuous flow due to the generation of a sulfonate salt that is insoluble in most common organic solvents. Our initial strategy employs a biphasic mixture of ethyl acetate and water. After careful optimization of the catalyst loading, the solvents ratio and the residence time, the desired sulfilimine derived from thioanisole was obtained in good yield in 150 min. The reaction is applicable to aromatic and aliphatic sulfides but also to the less reactive sulfoxides to provide sulfoximines. Our second strategy uses N-butylimidazole as a base to form in situ a room temperature ionic liquid. Under theses conditions, the reaction proceeds within 30 minutes with excellent yield. Details of both approaches will be disclosed in a poster.

Iron-catalyzed amination of thioethers and sulfoxides in continuous flow

255th National Meeting (2018)

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