α‐Funktionalisierung von Ketonen durch metallfreie elektrophile Aktivierung

Recent Applications of Trifluoromethanesulfonic Anhydride in Organic Synthesis

Trifluoromethanesulfonic anhydride has been widely used in synthetic organic chemistry, not only for the conversion of various oxygen-containing compounds to the triflates, but also for the electrophilic activation and further conversion of amides, sulfoxides, and phosphorus oxides. In recent years, the utilization of Tf₂ O as an activator for nitrogen-containing heterocycles, nitriles and nitro groups has become a promising tool for the development of new valuable methods with considerable success. In addition, Tf₂ O has been used as an efficient radical trifluoromethylation and trifluoromethylthiolation reagent due to the contained SO₂ CF₃ fragment, and significant progress has been made in this area. This review summarizes the recent progress in the applications of Tf₂ O in the above two aspects, and aims to illustrate the role and potential application of this reagent in organic synthesis.

Alkyl/Glycosyl Sulfoxides as Radical Precursors and Their Use in the Synthesis of Pyridine Derivatives

We report here the use of simple and readily available alkyl sulfoxides as precursors to radicals and their application in the preparation of pyridine derivatives. We show that alkyl sulfoxides, N-methoxy pyridinium salts and fluoride anions form electron donor-acceptor (EDA) complexes in solution, which, upon visible light irradiation, undergo a radical chain process to afford various pyridine derivatives smoothly. This reaction displays broad scope with respect to both sulfoxides and N-methoxy pyridiniums. The synthetic versatility of sulfoxides as a handle in chemistry adds to their power as radical precursors. Glycosyl sulfoxides are converted to the corresponding pyridyl C-glycosides with high stereoselectivities. Computational and experimental studies provide insights into the reaction mechanism.

Recent Progress in Enolonium Chemistry under Metal-Free Conditions

Umpolung approach through inversion of the polarity of conventional enolates, has opened up an unprecedented opportunity in the cross-coupling via alkylation. The enolonium equivalents can be accessed either by hypervalent iodine reagents, activation/oxidation of amides, or the oxidation of alkynes. Under umpolung conditions, highly basic conditions required for classical enolate chemistry can be avoided, and they can couple with unmodified nucleophiles such as heteroatom donors and electron-rich arenes.