Oxidation of allylic and benzylic alcohols to aldehydes and carboxylic acids

An oxidation of allylic and benzylic alcohols to the corresponding carboxylic acids is effected by merging a Cu-catalyzed oxidation using O2 as a terminal oxidant with a subsequent chlorite oxidation (Lindgren oxidation). The protocol was optimized to obtain pure products without chromatography or crystallization. Interception at the aldehyde stage allowed for Z/E-isomerization, thus rendering the oxidation stereoconvergent with respect to the configuration of the starting material

Conversion of Pyridine <i>N</i>‑Oxides to Tetrazolopyridines

An efficient and convenient procedure for the conversion of pyridine <i>N</i>-oxides to tetrazolopyridines by treatment with 4-toluene sulfonyl chloride and sodium azide in toluene at elevated temperature is described

Nitrene–nitrene rearrangement under thermal, photochemical, and electron-impact conditions: the 2-azidopyridines/tetrazolo[1,5-a]pyridines

N-15-Labeling demonstrates that the two nitrogen atoms in the 2-pyridylnitrene radical cation 2(+) become equivalent prior to fragmentation in the mass spectrometer. Furthermore, the mass spectra of 6- and 7-tetrazolo[1,4-a]pyridine are identical, as are those of 5- and 8-tetrazolo[1,5-a]pyridine, thereby again demonstrating interconversion of the nitrogen atoms in 2-pyridylnitrenes. These rearrangements parallel the reactions established under thermal (flash vacuum pyrolysis) and photochemical condition. Calculations of the energies of ground and transition states at the CASPT2(7,8) level support the notion that 2-pyridylnitrenes undergo very easy and exothermic ring expansion to 1,3-diazacycloheptatetraene 3, both in the neutrals and the radical cations. In addition, the ring opening to 4-cyanobutadienylnitrene 4 can take place in both the neutrals and the radical cations with modest activation barriers

Monitoring the Transmembrane Proton Gradient Generated by Cytochrome <i>bo</i>₃ in Tethered Bilayer Lipid Membranes Using SEIRA Spectroscopy

Membrane proteins act as biocatalysts or ion/proton pumps to convert and store energy from ubiquitous environmental sources. Interfacing these proteins to electrodes allows utilizing the energy for enzymatic biofuel cells or other auspicious biotechnological applications. To optimize the efficiency of these devices, appropriate membrane models are required that ensure structural and functional integrity of the embedded enzymes and provide structural insight. We present a spectroelectrochemical surface-enhanced infrared absorption (SEIRA) and electrical impedance spectroscopy (EIS) study of the bacterial respiratory ubiquinol/cytochrome <i>bo</i>₃ (cyt <i>bo</i>₃) couple incorporated into a tethered bilayer lipid membrane (tBLM). Here, we employed a new lipid tether (WK3SH, dihydrocholesteryl (2-(2-(2-ethoxy)­ethoxy)­ethanethiol), which was synthesized using a three-step procedure with very good yield and allowed measuring IR spectra without significant spectral interference of the tBLM. The functional integrity of the incorporated cyt <i>bo</i>₃ was demonstrated by monitoring the enzymatic O₂ reduction current and the formation of the transmembrane proton gradient. Based on a SEIRA-spectroscopic redox titration, a shift of the pH-dependent redox potential of the ubiquinones under turnover conditions was correlated with an alkalinization of the submembrane reservoir by +0.8 pH units. This study demonstrates the high potential of tBLMs and the SEIRA spectroscopic approach to study bioenergetic processes

Palladium-Catalyzed Directed Halogenation of Bipyridine <i>N</i>‑Oxides

The palladium-catalyzed directed C–H halogenation of bipyridine <i>N</i>-oxides was investigated. Using NCS or NBS (<i>N</i>-chloro- or <i>N</i>-bromosuccinimide) and 5 mol % Pd­(OAc)₂ in chlorobenzene (0.10 molar) at 110 °C, pyridine-directed functionalization took place and 3-chloro- or 3-bromobipyridine <i>N</i>-oxides were obtained in high yields. The reaction is sensitive to steric hindrance by 4- and 6′-substituents. Only in the latter case, where coordination of palladium by the pyridine is hindered, 3′-halogenation directed by the <i>N</i>-oxide function was observed. The halogenated products were deoxygenated by PCl₃ or PBr₃

Palladium-Catalyzed Directed Halogenation of Bipyridine <i>N</i>‑Oxides

The palladium-catalyzed directed C–H halogenation of bipyridine <i>N</i>-oxides was investigated. Using NCS or NBS (<i>N</i>-chloro- or <i>N</i>-bromosuccinimide) and 5 mol % Pd­(OAc)₂ in chlorobenzene (0.10 molar) at 110 °C, pyridine-directed functionalization took place and 3-chloro- or 3-bromobipyridine <i>N</i>-oxides were obtained in high yields. The reaction is sensitive to steric hindrance by 4- and 6′-substituents. Only in the latter case, where coordination of palladium by the pyridine is hindered, 3′-halogenation directed by the <i>N</i>-oxide function was observed. The halogenated products were deoxygenated by PCl₃ or PBr₃