Leonid A. Shundrin

Fused 1,2,3-Dithiazoles: Convenient Synthesis, Structural Characterization, and Electrochemical Properties

A new general protocol for synthesis of fused 1,2,3-dithiazoles by the reaction of cyclic oximes with S2Cl2 and pyridine in acetonitrile has been developed. The target 1,2,3-dithiazoles fused with various carbocycles, such as indene, naphthalenone, cyclohexadienone, cyclopentadiene, and benzoannulene, were selectively obtained in low to high yields. In most cases, the hetero ring-closure was accompanied by chlorination of the carbocyclic moieties. With naphthalenone derivatives, a novel dithiazole rearrangement (15→13) featuring unexpected movement of the dithiazole ring from α- to β-position, with respect to keto group, was discovered. Molecular structure of 4-chloro-5H-naphtho[1,2-d][1,2,3]dithiazol-5-one 13 was confirmed by single-crystal X-ray diffraction. Electrochemical properties of 13 were studied by cyclic voltammetry and a complex behavior was observed, most likely including hydrodechlorination at a low potential.

Radical Anions, Radical-Anion Salts and Anionic Complexes of 2,1,3-Benzochalcogenadiazoles (S, Se, Te)

By means of cyclic voltammetry (CV) and DFT calculations, it was found that the electron-acceptor ability of 2,1,3-benzochalcogenadiazoles 1-3 (chalcogen: S, Se, and Te, respectively) increases with increasing atomic number of the chalcogen. This trend is nontrivial, since it contradicts the electronegativity and atomic electron affinity of the chalcogens. In contrast to radical anions (RAs) [1].- and [2].- , RA [3].- was not detected by EPR spectroscopy under CV conditions. Chemical reduction of 1-3 was performed and new thermally stable RA salts [K(THF)]+ [2].- (8) and [K(18-crown-6)]+ [2].- (9) were isolated in addition to known salt [K(THF)]+ [1].- (7). On contact with air, RAs [1].- and [2].- underwent fast decomposition in solution with the formation of anions [ECN]- , which were isolated in the form of salts [K(18-crown-6)]+ [ECN]- (10, E=S; 11, E=Se). In the case of 3, RA [3].- was detected by EPR spectroscopy as the first representative of tellurium-nitrogen π-heterocyclic RAs but not isolated. Instead, salt [K(18-crown-6)]+ 2 [3-Te2 ]2- (12) featuring a new anionic complex with coordinate Te-Te bond was obtained. On contact with air, salt 12 transformed into salt [K(18-crown-6)]+ 2 [3-Te4 -3]2- (13) containing an anionic complex with two coordinate Te-Te bonds. The structures of 8-13 were confirmed by XRD, and the nature of the Te-Te coordinate bond in [3-Te2 ]2- and [3-Te4 -3]2- was studied by DFT calculations and QTAIM analysis.

Synthesis and electrochemical Reduction of 2,2′-diaryl-5,5,5′,5′-tetramethyl-3,3′-bi(pyrrol-3-ylidene)-4,4′(5H,5′H)-dione 1,1′-dioxides

Abstract2,2′-Diaryl-5,5,5′,5′-tetramethyl-3,3′-bi(pyrrol-3-ylidene)-4,4′(5H,5′H)-dione 1,1′-dioxides containing a carboxy, alkoxycarbonyl, or carbamoyl group in the para position of one or both benzene rings were synthesized. These compounds may be regarded as cyclic dinitrones with conjugated C=C bond. Mild aminolysis of carboxy groups in the title compounds may be used to introduce dinitrone fragments into oligonucleotide or polypeptide structures. Electrochemical reduction of the resulting amides involves reversible oneelectron transfer in the first step at a near-zero potential, which makes it possible to use the title compounds as electrochemically active labels in applied bioorganic electrochemistry.