Mechanochemical syntheses of sulfinamidines and sulfonimidamides and their derivatizations

Aza-sulfur motifs are gaining increasing attention from chemists due to their potential applications in diverse areas, such as medicines, agrochemicals, chiral auxiliaries, and organic materials. However, unlike the well-developed sulfur components, the synthesis of aza-sulfur compounds remains limited. Mechanochemical reaction is a chemical reaction that is induced by the direct absorption of mechanical energy. The sustainability, greenness, efficiency, and simple operation of mechanochemical reactions have garnered significant interest from chemists, leading to their applications in the synthesis of molecules and materials.This doctoral thesis starts with an overview of aza-sulfur compounds, highlights their importance, traditional synthetic strategies, and applications. Subsequently, the overview of mechanochemistry was given, with the introduction of the history and development, important influencing factors, and the advantages and applications of this green and sustainable synthetic tool. This thesis aims to investigate the mechanochemical syntheses of two classes of aza-sulfur compounds (sulfinamidines and sulfonimidamides) via nitrene transfer, and to explore their further conversions to other high-value sulfur motifs. The specific contents are as follows: 1. A mechanochemical synthesis of N-acyl sulfinamidines starting from either sulfenamides or thiols via iron-nitrenoids is explored. Dioxazolones serve as N-acyl nitrene precursors. The resulting products are formed in good to excellent yields. By subsequent fluorinations, sulfur–fluoride exchange reactions, oxidations, and deprotection procedures, the products can be converted into a range of aza-sulfur(VI) derivatives.2. A mechanochemical nitrene transfer reaction to N-acyl sulfonimidamides from sulfinamides and dioxazolones catalyzed by iron(II) chloride is studied. This one-step solvent-free procedure provides a wide range of N-acyl sulfonimidamides in up to 87% yield under ambient conditions. Compared to its solution-phase counterpart, the developed mechanochemical reaction shows a better conversion rate and chemoselectivity. Mechanistically, crucial nitrene iron complex intermediates are suggested by ESI–MS.3. A metal-catalyzed mechanochemical transformation of sulfiliminium mesitylenesulfonates and dioxazolones is studied. This strategy produces various N-acyl sulfilimines as products rather than the desired sulfondiimines.4. A mechanochemical intramolecular N–O coupling of N-acyl sulfonimidamides under rhodium catalysis is investigated. The solvent-free method proceeds via rhodium-nitrenoids and produces unprecedented 1,3,2,4-oxathiadiazole 3-oxides in a short reaction time with up to 98% yield. This process also enables intramolecular N–S bond coupling. However, the attempts at N–N bond coupling of sulfonimidamides under mechanochemical conditions remain unsuccessful. Potential synthetic applications of the resulting five-membered heterocycles as nitrene precursors were demonstrated by reacting a representative compound with sulfoxide under heat or blue light.