Formal Umpolung Research Articles

Iminosemiquinone radical ligands enable access to a well-defined redox-active Cu(II)-CF₃ complex.

The reaction of a copper complex bearing iminosemiquinone ligands with a CF3(+) source provides an unprecedented Cu(II)-CF3 complex through ligand-based oxidation. Reactivity of this complex leads to nucleophilic trifluoromethylation of the ligand, suggesting an electronic interplay that results in a formal umpolung of the initial CF3(+).

Enantioselective Synthesis of α-Stereogenic γ-Keto Esters via Formal Umpolung

A feasible method has been developed for the enantioselective synthesis of α-stereogenic γ-keto esters. By employing nitro(phenylsulfonyl)methane as an acyl anion equivalent, the integrated Michael addition reaction-oxidative methanolysis protocol allows the preparation of various γ-keto esters with high optical purities.

Click-alkynylation of N- and P-nucleophiles by oxidative cross-coupling with alkynylcopper reagents: a general synthesis of ynamides and alkynylphosphonates

Nitrogen- and phosphorus-based nucleophiles can be smoothly transformed to the corresponding heteroatom-substituted alkynes by simple reaction at room temperature and under an oxygen atmosphere with copper acetylides. These stable, readily available, polymers act as especially efficient reagents for the introduction of an alkyne group under remarkably mild oxidative conditions which allow for their formal umpolung. Chelating ligands such as TMEDA and N-methylimidazole are efficient organic promoters, allowing for clean and fast oxidative cross-couplings, even with complex substrates.

Novel 10‐I‐3 Hypervalent Iodine‐Based Compounds for Electrophilic Trifluoromethylation

The synthesis of a new family of 10-I-3 hypervalent iodine compounds is described in which the CF3 functionality participates directly in the hypervalent bond. These materials are accessible by nucleophilic ligand substitution at iodine using Me3SiCF3 in the presence of a substoichiometric amount of fluoride. The expected T-shaped geometry at iodine was verified by X-ray crystallographic analyses of three of the products (1-trifluoromethyl-1,2-benziodoxol-3-(1 H)-one and two substituted 1-trifluoromethyl-1,3-dihydro-1,2-benziodoxoles). Preliminary results for the direct electrophilic transfer of the trifluoromethyl moiety onto organic nucleophiles show modest reactivity in polar aprotic solvents under relatively mild conditions. The overall process can be understood as a formal umpolung of the CF3 group.