1. Lewis Acid-Catalyzed 2,3-Dihydrofuran Acetal Ring-Opening Benzannulations toward Functionalized 1-Hydroxycarbazoles
Shaoren Yuan, Gabriel Guerra Faura, Hailey E Areheart, Natalie E Peulen, Stefan France Molecules. 2022 Nov 30;27(23):8344. doi: 10.3390/molecules27238344.
The development of a Lewis acid-catalyzed, intramolecular ring-opening benzannulation of 5-(indolyl)2,3-dihydrofuran acetals is described. The resulting 1-hydroxycarbazole-2-carboxylates are formed in up to 90% yield in 1 h. The dihydrofuran acetals are readily accessed from the reactions of enol ethers and α-diazo-β-indolyl-β-ketoesters. To highlight the method's synthetic utility, a formal total synthesis of murrayafoline A, a bioactive carbazole-containing natural product, was undertaken.
2. Air-stable aryl derivatives of pentafluoroorthotellurate
Daniel Wegener, Kurt F Hoffmann, Alberto Pérez-Bitrián, Ilayda Bayindir, Amiera N Hadi, Anja Wiesner, Sebastian Riedel Chem Commun (Camb). 2022 Aug 25;58(69):9694-9697. doi: 10.1039/d2cc03936b.
We report on two different sets of air-stable derivatives of pentafluoroorthotellurate containing fluorinated and non-fluorinated aryl groups. The acid cis-PhTeF4OH was obtained in gram scale and further transformed to Ag[cis-PhTeF4O], which was used as a cis-PhTeF4O transfer reagent to obtain [PPh4][cis-PhTeF4O]. Furthermore, the synthesis of trans-(C6F5)2TeF3OH was achieved by a selective hydrolysis of trans-(C6F5)2TeF4 in the presence of KF and subsequent protonation by aHF. Quantum-chemical calculations show a higher acidity and robustness against fluoride abstraction for trans-(C6F5)2TeF3OH compared to cis-PhTeF4OH.
3. S-Nitrosation of Aminothiones
Joyeth B Dorado, Bogdan Z Dlugogorski, Eric M Kennedy, John C Mackie, Jeff Gore, Mohammednoor Altarawneh J Org Chem. 2015 Jul 17;80(14):6951-8. doi: 10.1021/acs.joc.5b00313. Epub 2015 Jul 6.
Nitrosation reactions span a diverse range of applications, from biochemistry to industrially important processes. This study examines nitrosation of aminothiones in acidic solutions and re-evaluates currently accepted diffusion limits and the true nature of the nitrosating agent for nitrous acid initiated reactions. Experimental measurements from stopped-flow UV/vis spectrophotometry afforded derivation of equilibrium constants and reaction enthalpies. Apparent Keq corresponds to 559-382 M(-2) for thioacetamide (TA, 15-25 °C) and 12600-5590 M(-2) for thiourea (TU, 15-35 °C), whereas the reaction enthalpies amount to -27.10 ± 0.05 kJ for TA and -29.30 ± 0.05 kJ for TU. Theoretical calculations via a thermochemical cycle agree well with reaction free energies from experiments, with errors of -2-4 kJ using solvation method SMD in conjunction with hybrid meta exchange-correlation functional M05-2X and high-accuracy multistep method CBS-QB3 for gas-phase calculations. The kinetic rates increase with acidity at activation energies of 54.9 (TA) and 66.1 kJ·mol(-1) (TU) for the same temperature range, confirming activation-controlled reactions. At pH 1 and below, the main decomposition pathway for the S-nitroso species leads to formation of nitric oxide.
