Design of redox-mediatory systems for electro-organic synthesis

Halide ion-promoted desulfo-halogenation was applied successfully to synthesis of 4-chloro-2-azetidinone 1, a potent intermediate for carbapenem synthesis and stereoselective N-glycosylation of 2,3-deoxyglycosides. Bromide ion/N-oxyl compounds (TEMPO) double mediatory systems enabled us to develop several aqueous electrolysis media free from organic solvents, e.g., silica gel or polymer particles/water disperse systems and water-soluble TEMP-Omediated oil-in-water emulsion systems, in which electrooxidation of alcohols was carried out successfully in a simple beaker-type undivided cell under a constant current condition. Notably, the work-up process was very simple and the solid particles (disperse phase) and the aqueous solutions (disperse media) were easily recovered and reused, offering a totally closed system. In Pd(OAc) ₂/TEMPO double mediatory systems, electrogeneration of active cationic palladium catalysts was integrated into electrooxidative Wacker-type reaction. In a similar manner, Wacker-type cyclization and homo-coupling of arylboronic acids were successfully achieved.