Halogen-Bonding Interaction between I2 and N-Iodosuccinimide in Lewis Base-Catalyzed Iodolactonization

Catalytic Site-, Diastereo-, and Enantioselective Cascade Iodocyclization of 2-Geranylarenols

A chiral amidophosphate-N-iodosuccinimide cooperative catalysis has been developed for the site-, diastereo-, and enantioselective iodocyclization of 2-geranylarenols with molecular iodine to give the corresponding iodo-containing polycyclic compounds with good levels of selectivity. This is the first example of a catalytic enantioselective iodocarbocyclization. A reactive chiral iodonium species is generated from molecular iodine via the dual halogen-bonding interactions with a chiral Lewis base and Lewis acid. The sterically demanding 3,3'-substituents of the chiral BINOL-derived amidophosphate are critical to induce the site-selective iodination at the less-hindered terminal alkenyl moiety of 2-geranylarenols.

Tetravalent Spiroselenurane Catalysts: Intramolecular Se···N Chalcogen Bond-Driven Catalytic Disproportionation of H2O2 to H2O and O2 and Activation of I2 and NBS

Chalcogen-bonding interactions have recently gained considerable attention in the field of synthetic chemistry, structure, and bonding. Here, three organo-spiroselenuranes, having a Se(IV) center with a strong intramolecular Se···N chalcogen-bonded interaction, have been isolated by the oxidation of the respective bis(2-benzamide) selenides derived from an 8-aminoquinoline ligand. Further, the synthesized spiroselenuranes, when assayed for their antioxidant activity, show disproportionation of hydrogen peroxide into H₂O and O₂ with first-order kinetics with respect to H₂O₂ for the first time by any organoselenium molecules as monitored by ¹H NMR spectroscopy. Electron-donating 5-methylthio-benzamide ring-substituted spiroselenurane disproportionates hydrogen peroxide at a high rate of 15.6 ± 0.4 × 10³ μM min^-1 with a rate constant of 8.57 ± 0.50 × 10^-3 s^-1, whereas 5-methoxy and unsubstituted-benzamide spiroselenuranes catalyzed the disproportionation of H₂O₂ at rates of 7.9 ± 0.3 × 10³ and 2.9 ± 0.3 × 10³ μM min^-1 with rate constants of 1.16 ± 0.02 × 10^-3 and 0.325 ± 0.025 × 10^-3 s^-1, respectively. The evolved oxygen gas from the spiroselenurane-catalyzed disproportion of H₂O₂ has also been confirmed by a gas chromatograph-thermal conductivity detector (GCTCD) and a portable digital polarographic dissolved O₂ probe. Additionally, the synthesized spiroselenuranes exhibit thiol peroxidase antioxidant activities for the reduction of H₂O₂ by a benzenethiol co-reductant monitored by UV-visible spectroscopy. Next, the Se···N bonded spiroselenuranes have been explored as catalysts in synthetic oxidation iodolactonization and bromination of arenes. The synthesized spiroselenurane has activated I₂ toward the iodolactonization of alkenoic acids under base-free conditions. Similarly, efficient chemo- and regioselective monobromination of various arenes with NBS catalyzed by chalcogen-bonded synthesized spiroselenuranes has been achieved. Mechanistic insight into the spiroselenuranes in oxidation reactions has been gained by ⁷⁷Se NMR, mass spectrometry, UV-visible spectroscopy, single-crystal X-ray structure, and theoretical (DFT, NBO, and AIM) studies. It seems that the highly electrophilic nature of the selenium center is attributed to the presence of an intramolecular Se···N interaction and a vacant coordination site in spiroselenuranes is crucial for the activation of H₂O₂, I₂, and NBS. The reaction of H₂O₂, I₂, and NBS with tetravalent spiroselenurane would lead to an octahedral-Se(VI) intermediate, which is reduced back to Se(IV) due to thermodynamic instability of selenium in its highest oxidation state and the presence of a strong intramolecular N-donor atom.

Mechanistic Details of Asymmetric Bromocyclization with BINAP Monoxide: Identification of Chiral Proton-Bridged Bisphosphine Oxide Complex and Its Application to Parallel Kinetic Resolution

The mechanism of our previously reported catalytic asymmetric bromocyclization reactions using 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (BINAP) monoxide was examined in detail by the means of control experiments, NMR studies, X-ray structure analysis, and CryoSpray electrospray ionization mass spectrometry (ESI-MS) analysis. The chiral BINAP monoxide was transformed to a key catalyst precursor, proton-bridged bisphosphine oxide complex (POHOP·Br), in the presence of N-bromosuccinimide (NBS) and contaminating water. The thus-formed POHOP further reacts with NBS to afford BINAP dioxide and molecular bromine (Br₂) simultaneously in equimolar amounts. While the resulting Br₂ is activated by NBS to form a more reactive brominating reagent (Br₂─NBS), BINAP dioxide serves as a bifunctional catalyst, acting as both a Lewis base that reacts with Br₂─NBS to form a chiral brominating agent (P═O⁺─Br) and also as a Brønsted base for the activation of the substrate. By taking advantage of this novel concerted Lewis/Brønsted base catalysis by BINAP dioxide, we achieved the first regio- and chemodivergent parallel kinetic resolutions (PKRs) of racemic unsymmetrical bisallylic amides via bromocyclization.

A new assembly of diiodine molecules at the 1,3-dimethylimidazole-2-thione (Me2ImS) template: crystal structure of (Me2ImS)2·(I2)5

The poly(I2) adduct [(Me2ImS)2·(I2)5] has been synthesised using a two-step process. The FT-Raman spectrum and MEP maps are discussed.

The reaction of thiourea and 1,3-dimethylthiourea towards organoiodines: oxidative bond formation and halogen bonding

By varying the halogen-bond-donor molecule, 11 new halogen-bonding cocrystals involving thiourea or 1,3-dimethylthiourea were obtained, namely, 1,3-dimethylthiourea-1,2-diiodo-3,4,5,6-tetrafluorobenzene (1/1), C₆F₄I₂·C₃H₈N₂S, 1, thiourea-1,3-diiodo-2,4,5,6-tetrafluorobenzene (1/1), C₆F₄I₂·CH₄N₂S, 2, 1,3-dimethylthiourea-1,3-diiodo-2,4,5,6-tetrafluorobenzene (1/1), C₆F₄I₂·C₃H₈N₂S, 3, 1,3-dimethylthiourea-1,3-diiodo-2,4,5,6-tetrafluorobenzene-methanol (1/1/1), C₆F₄I₂·C₃H₈N₂S·CH₄O, 4, 1,3-dimethylthiourea-1,3-diiodo-2,4,5,6-tetrafluorobenzene-ethanol (1/1/1), C₆F₄I₂·C₃H₈N₂S·C₂H₆O, 5, 1,3-dimethylthiourea-1,4-diiodo-2,3,5,6-tetrafluorobenzene (1/1), C₆F₄I₂·C₃H₈N₂S, 6, 1,3-dimethylthiourea-1,3,5-trifluoro-2,4,6-triiodobenzene (1/1), C₆F₃I₃·C₃H₈N₂S, 7, 1,3-dimethylthiourea-1,1,2,2-tetraiodoethene (1/1), C₆H₁₆N₄S₂·C₂I₄, 8, [(dimethylamino)methylidene](1,2,2-triiodoethenyl)sulfonium iodide-1,1,2,2-tetraiodoethene-acetone (1/1/1), C₅H₈I₃N₂S⁺·I^-·C₃H₆O·C₂I₄, 9, 2-amino-4-methyl-1,3-thiazol-3-ium iodide-1,1,2,2-tetraiodoethene (2/3), 2C₄H₇N₂S⁺·2I^-·3C₂I₄, 10, and 4,4-dimethyl-4H-1,3,5-thiadiazine-3,5-diium diiodide-1,1,2,2-tetraiodoethene (2/3), 2C₅H₁₂N₄S²⁺·4I^-·3C₂I₄, 11. When utilizing the common halogen-bond-donor molecules 1,2-, 1,3-, and 1,4-diiodotetrafluorobenzene, as well as 1,3,5-trifluoro-2,4,6-triiodobenzene, bifurcated I...S...I interactions were observed, resulting in the formation of isolated rings, chains, and sheets. Tetraiodoethylene (TIE) provided I...S...I cocrystals as well, but further yielded a sulfonium-containing product through the reaction of the S atom with TIE. This particular sulfonium motif is the first of its kind to be structurally characterized, and is stabilized in the solid state through a three-dimensional I...I halogen-bonding network. Thiourea reacted with acetone in the presence of TIE to provide two novel heterocyclic products, again stabilized in the solid state through I...I halogen bonding.