Skeletal rearrangement of a boron-containing annulenic molecule into a macrocycle bridged by an electronically stabilized boron cation.

An annulenic molecule containing a three-coordinate chloroborane moiety, which exhibits a borane-olefin proximity effect, undergoes a skeletal rearrangement upon chloride abstraction, to generate a three-dimensional macrocyclic molecule featuring a borocenium (η5-cyclopentadienyl-B+-R) structure.

Antibiotic Practice in Patients With Acute Abdomen Admitted to a Danish Regional Hospital: A Clinical Qualitative Assurance Study.

Background Acute abdomen is often complicated by intra-abdominal infection requiring antibiotic therapy. Danish regional antibiotic guidelines emphasize the restricted use of broad-spectrum antibiotics such as cephalosporins. In this study, we aimed to evaluate antibiotic practices in relation to hospitalized patients with acute abdomen. Methodology This retrospective quality assurance study was conducted among patients admitted to the surgical emergency department at the North Denmark Regional Hospital during a four-month observation period. Data were extracted from electronic patient journals and entered in the Research Electronic Data Capture data management system for further analytical work. Results Of 331 patients, 174 (53%) were treated with antibiotics, of whom 98 (56%) had been treated with cephalosporin, 47 (27%) with benzylpenicillin and gentamicin, 22 (13%) with piperacillin/tazobactam, and seven (4%) with ciprofloxacin. Use of a cephalosporin-based antibiotic regimen was significantly more common in patients with acute appendicitis (75%) compared to other diagnostic groups, such as acute cholecystitis (57%), incarcerated hernia with strangulation (56%), acute pancreatitis (50%), and acute diverticulitis (30%). However, patients with uncomplicated diverticulitis (53%) were significantly more often treated with benzylpenicillin and gentamicin, whereas patients with complicated diverticulitis Hinchey stage 3-4 were significantly more often treated with piperacillin/tazobactam. In addition, as the severity of acute cholecystitis increased, it was more frequently treated with piperacillin/tazobactam. Conclusions The study revealed that cephalosporins are frequently used in patients hospitalized with acute abdomen. This finding conflicts with current regional antibiotic guidelines. Reinforcement of the guidelines is required as an essential measure against the development of antibiotic resistance associated with the use of cephalosporins.

Observation of Borane-Olefin Proximity Interaction Governing the Structure and Reactivity of Boron-Containing Macrocycles.

While attractive interactions between borane and olefin have been postulated to trigger various boron-mediated organic transformations, proximity structures of these functional groups, other than the formation of weak van der Waals complexes, have never been directly observed. Here we show that a close intramolecular borane-olefin interaction operates in macrocyclic systems containing borane and olefinic groups obtained by multi-step 1,2-carboboration between a strained alkyne and 9-borafluorene derivatives. Depending on Lewis acidity of the borane moiety and the size of the macrocycles, the magnitude of interaction changes, resulting in different reaction modes. The whole picture of the multi-step reactions has been revealed experimentally with theoretical supports. The present finding may not only provide a deeper understanding of the fundamental boron-mediated interaction but also lead to the development of new organic transformations involving molecular activation by boranes.

A Theoretical Study on the Mechanism of the Oxidative Deborylation/C-C Coupling Reaction of Borepin Derivatives.

One-electron oxidation of borepin derivatives that consists of a boron-containing seven-membered ring has been reported to cause deborylation/C-C coupling, yielding aromatic compounds. The reaction can be achieved not only by transition metal compounds but also by oxidants without transition metal such as O2 and other organic compounds. Despite numerous experimental attempts, the mechanism of this peculiar reaction as well as the fate of the BCl part eliminated from borepin remain unclear to date. Based on theoretical approaches using the artificial force induced reaction method, here we address the mechanism of the unusual boron-mediated C-C coupling. For this purpose, two borepin derivatives (1 and 35), bearing ethyl and phenyl groups, respectively, were used as reactants, and FeCl3/MeNO2 and O2 were chosen as oxidants. The calculations revealed reaction pathways that provided an overall picture of the mechanism of the target reaction, which features four key steps, namely, (i) quaternization of the boron atom by the coordination of oxidant, (ii) intersystem crossing, (iii) skeletal rearrangement to form a six-membered ring, and (iv) elimination of a boron moiety. The intrinsic nature of boron, i.e., a strong tendency to accept a coordination ligand even under oxidative conditions, is responsible for the oxidative deborylation/C-C coupling of borepin.

The mechanism of copper-catalyzed azide-alkyne cycloaddition reaction: a quantum mechanical investigation.

In this study, the mechanism of CuAAC reaction and the structure of copper acetylides have been investigated with quantum mechanical methods, namely B3LYP/6-311+G(d,p). A series of possible copper-acetylide species which contain up to four copper atoms and solvent molecules as ligand has been evaluated and a four-copper containing copper-acetylide, M1A, was proposed more likely to form based on its thermodynamic stability. The reaction has been modeled with a representative simple alkyne and a simple azide to concentrate solely on the electronic effects of the mechanism. Later, the devised mechanism has been applied to a real system, namely to the reaction of 2-azido-1,1,1-trifluoroethane and ethynylbenzene in the presence of copper. The copper catalyst transforms the concerted uncatalyzed reaction to a stepwise process and lowers the activation barrier. The pre-reactive complexation of the negatively charged secondary nitrogen of azide and the positively charged copper of copper-acetylide brings the azide and the alkyne to a suitable geometry for cycloaddition to take place. The calculated activation barrier difference between the catalyzed and the uncatalyzed reactions is consistent with faster and the regioselective synthesis of triazole product.