Fused 1,2,3‐Thiaselenazoles Synthesized from 1,2,3‐Dithiazoles through Selective Chalcogen Exchange

Abstract

A new approach to the synthesis of fused 1,2,3-thiaselenazoles-rare five-membered heterocycles that contain two different chalcogens-from the corresponding 1,2,3-dithiazoles and SeO was accomplished by selective exchange of S and Se atoms. The fused carbo- and heterocyclic units were indene, naphthalenone, cyclohexadienone, cyclopentadiene, benzoannulene, and benzoxazine. The molecular structures of two of the thiaselenadiazole products and one of the dithiazole precursors were confirmed by single-crystal X-ray diffraction. The reaction is highly solvent selective; it only takes place in solvents that contain a C=O group (e.g., DMF or tetramethylurea). According to DFT calculations, the reaction is thermodynamically favorable. Based on the DFT calculations and Se NMR spectroscopy, two tentative mechanisms that feature isomeric transition states and intermediates are suggested for the reaction via ring-opening addition of SeO to the S-X dithiazole bond (X=N or S). The DFT-calculated first adiabatic electron affinities of the compounds were chalcogen independent and positive in all cases, which assumes formation of thermodynamically stable radical anions (RAs). These calculated RAs featured either normal or abnormal elongation of the S1-X2 (X=S or Se) bond relative to their neutral precursors and possessed π* or σ* SOMOs, respectively.

Salts of Sterically Hindered Chalcogen‐Varied Herz Cations Including Those with [Te3Cl14]2– and [Te4Cl18]2– Anions

“…[1b], , Replacement of the S atom by the Se atom at the 2‐position can be achieved by the action of H 2 SeO 3 or SeO 2 . [6d], [10b], [12e] With SeO 2 , the approach also covers neutral 1,2,3‐dithiazoles . Te‐containing cation 18 (Scheme ) was prepared from N , N,S ‐tris(trimethylsilyl)‐2‐aminothiophenole and TeCl 4 .…”

“…Another approach to Te‐containing Herz cations might be the aforementioned chalcogen‐exchange reaction, which is well known for 1,2,3‐dithiazoliums[5k], [5l], [6d], [6e], [6l], [6n], [12e], and 1,2,3,5‐dithiadiazoliums with replacement of the S atom by the Se atom. Recently, mutual exchange of group 16 atoms (O, S, Se, Te) in neutral five‐membered chalcogen–nitrogen heterocycles with three heteroatoms was described,, in particular the selective transformation of 1,2,3‐dithiazoles into 1,2,3‐thiaselenazoles under the action of SeO 2 in DMF . However, on treatment of [ 1 ][Cl] with an excess amount of TeO 2 in hot DMF, the starting salt disappeared, but the desired transformation of 1 into 5 was not detected by solution 1 H NMR spectroscopy, which revealed no signals in the 7.5–10 ppm range characteristic of Herz cations.…”

Antimicrobial and Antifungal Activity of Rare Substituted 1,2,3-Thiaselenazoles and Corresponding Matched Pair 1,2,3-Dithiazoles

“…Despite reaction condition screening varying both temperature and solvent, excess selenium dioxide was always required to compensate for decomposition, which occurred under these relatively harsh conditions of DMF at about 100 • C [47]. FOR PEER REVIEW 3 of 14 was always required to compensate for decomposition, which occurred under these relatively harsh conditions of DMF at about 100 °C [47].…”

Synthesis and Applications of 5‐Membered Chalcogen‐Nitrogen π‐Heterocycles with Three Heteroatoms

“…According to DFT calculations, the reaction is thermodynamically‐attractive. Based on the calculations and 77 Se NMR, two tentative mechanisms, both including three distinct stages, are suggested for the reaction to begin with the ring‐opening addition of SeO 2 to the S−E bond of a dithiazole (E=N or S) …”