Takamasa Tanabe

Palladium-Catalyzed Aromatic C−H Halogenation with Hydrogen Halides by Means of Electrochemical Oxidation

A new strategy for catalytic functionalization of C-H bonds by means of electrochemical oxidation is described. Combination of palladium-catalyzed aromatic C-H bond cleavage and halogenation with electrochemically generated halonium ions enables highly efficient, selective halogenations of aromatic compounds in a green-sustainable manner. The required reagents for this reaction are an arene and an aqueous hydrogen halide as substrates, a palladium salt as a catalyst, and an organic solvent. No further additives such as electrolytes, oxidants, or ligands are necessary to achieve effective catalytic activity. Several remarkable advantages of the use of the electrochemical method are also described.

Catalytic Electrochemical C–H Iodination and One-Pot Arylation by ON/OFF Switching of Electric Current

Palladium-catalyzed electrochemical iodination and one-pot arylation of arylpyridines are described. Ortho-selective C-H iodination proceeded via dual activation of each substrate by a palladium catalyst and an electrode. Various aryl groups were introduced at the ortho positions of arylpyridines by ON/OFF switching of two different catalytic cycles using the same palladium catalyst in a one-pot fashion.

Synthesis and antitumor activity of combretastatin D-4

Combretastatin D-4 1 was synthesized using electrochemical dimerization of phenols as the key step. Anodic oxidation of bromochloro-phenol 7 provided the corresponding diaryl ether 8. Manipulation of the two hydroxyl groups differenciated, provided the seco-acid, which on Mitsunobu reaction gave the target molecule. Its biological assay showed new potent inhibitory activity against cellular proliferation of human HT-29 colon carcinoma cells.

Oxidative cyclization of isodityrosine tripeptides : Optimized condition and application of electrochemically generated thallium(III) ion

Thallium(III) trinitrate oxidation of the tripeptide, which was a synthetic precursor of the 17-membered isodityrosine natural product, eurypamide, was investigated to give the desired cyclized compound in 96% yield at best. In addition, the thallium(III) species generated by electrochemical oxidation of thallium(I) successfully produced the target compounds.

Electrochemical Behavior of Thallium Ion in Organic Solvents and its Application to Organic Synthesis

Anodic oxidation of thallium (I) salts using an anion exchange membrane with organic solvent, produced thallium (III) oxidant with high current efficiency. Evaluation of electro-generated thallium (III) was performed by oxidation of some cyclic olefins carrying aromatic moieties.