Electron deficient borane-mediated hydride abstraction in amines: stoichiometric and catalytic processes

The manipulation of amino C–H bonds has garnered significant interest from the synthetic community due to its inherently high atom, step and redox economy. This Tutorial Review summarises the ability of boranes to mediate hydride abstraction from α-amino and γ-amino conjugated C–H bonds. Borane-mediated hydride abstraction results in the generation of reactive iminium hydridoborate salts that participate in a variety of stoichiometric and catalytic processes. The reactions that have utilised this unusual reactivity include those that manipulate amino scaffolds (including dehydrogenation, racemisation, isomerisation, α- and β-functionalisation, and C–N bond cleavage) and those that use amine-based reagents (transfer hydrogenation, and alkylation)

Photoproduction of mesons off nuclei

Recent results for the photoproduction of mesons off nuclei are reviewed. These experiments have been performed for two major lines of research related to the properties of the strong interaction. The investigation of nucleon resonances requires light nuclei as targets for the extraction of the isospin composition of the electromagnetic excitations. This is done with quasi-free meson photoproduction off the bound neutron and supplemented with the measurement of coherent photoproduction reactions, serving as spin and/or isospin filters. Furthermore, photoproduction from light and heavy nuclei is a very efficient tool for the study of the interactions of mesons with nuclear matter and the in-medium properties of hadrons. Experiments are currently rapidly developing due to the combination of high quality tagged (and polarized) photon beams with state-of-the-art 4pi detectors and polarized targets

Effect of Village-wide Use of Long-Lasting Insecticidal Nets on Visceral Leishmaniasis Vectors in India and Nepal: A Cluster Randomized Trial

Visceral leishmaniasis (VL) is a vector-borne disease causing at least 60,000 deaths each year amongst an estimated half million cases, and until recently there have been no significant initiatives to reduce this burden. However, in 2005, the governments of India, Bangladesh and Nepal signed a memorandum of understanding at the World Health Assembly in Geneva for the elimination of the disease by 2015. In the absence of an effective vaccine, the program will rely on the active detection and prompt treatment of cases throughout the endemic region, combined with a recurrent indoor residual spraying (IRS) of all villages at risk. Vector control programs based on IRS are notorious for failing to maintain comprehensive spray coverage over time owing to logistical problems and lack of compliance by householders. Long-lasting insecticidal nets (LNs) have been postulated as an alternative or complement to IRS. Here we describe how comprehensive coverage of LN in trial communities reduced the indoor density of sand flies by 25% compared to communities without LNs. This provides an indication that LNs could be usefully deployed as a component of the VL control program in the Indian subcontinent

Quasi-free photoproduction of eta-mesons off the deuteron

Precise data for quasi-free photoproduction of $\eta$ mesons off the deuteron have been measured at the Bonn ELSA accelerator with the combined Crystal Barrel/TAPS detector for incident photon energies up to 2.5 GeV. The $\eta$-mesons have been detected in coincidence with recoil protons and neutrons. Possible nuclear effects like Fermi motion and re-scattering can be studied via a comparison of the quasi-free reaction off the bound proton to $\eta$-production off the free proton. No significant effects beyond the folding of the free cross section with the momentum distribution of the bound protons have been found. These Fermi motion effects can be removed by an analysis using the invariant mass of the $\eta$-nucleon pairs reconstructed from the final state four-momenta of the particles. The total cross section for quasi-free $\eta$-photoproduction off the neutron reveals even without correction for Fermi motion a pronounced bump-like structure around 1 GeV of incident photon energy, which is not observed for the proton. This structure is even narrower in the invariant mass spectrum of the $\eta$-neutron pairs. Position and width of the peak in the invariant mass spectrum are $W\approx 1665$ MeV and FWHM $\Gamma\approx 25$ MeV. The data are compared to the results of different models.Comment: accepted for publication in Eur. Phys. J.

Applications of [4+2] Anionic Annulation and Carbonyl-Ene Reaction in the Synthesis of Anthraquinones, Tetrahydroanthraquinones, and Pyranonaphthoquinones

Hexa-2,5-dienoates, susceptible to isomerization by acids and bases, are suitable for the [4+2] anionic annulation to give 3-(2-alkenyl)­naphthoates in regiospecific manner. When combined with intramolecular carbonyl-ene reaction (ICE), the accessibility of the naphthoates culminates in a new synthesis of anthraquinones and diastereoselective synthesis of tetrahydroanthraquinones. This strategy has also resulted in a 3-step synthesis of dehydroherbarin from a 3-methallylnaphthoate

Experiment and Computational Study on the Regioselectivity of Nucleophilic Addition to Unsymmetrical <i>p</i>‑Benzynes Derived from Bergman Cyclization of Enediynes

The regioselectivity in addition of nucleophiles to the <i>p</i>-benzyne intermediates derived from unsymmetrical aza-substituted enediynes via Bergman cyclization was studied. Computational studies [using UB3LYP/6-31G­(d,p) level of theory] suggest that the <i>p</i>-benzyne intermediate retains its similar electrophilic character at the two radical centers even under unsymmetrical electronic perturbation, thus supporting the predicted model of nucleophilic addition to <i>p</i>-benzyne proposed by Perrin and co-workers (Perrin et al. <i>J. Am. Chem. Soc.</i> <b>2007</b>, <i>129</i>, 4795–4799) and later by Alabugin and co-workers (Peterson et al. <i>Eur. J. Org. Chem.</i> <b>2013</b>, <i>2013</i>, 2505–2527). However, observed experimental results suggest that there was small but definite regioselectivity (∼5–25%), the extent varying with the electronic nature of the substituents. Differential solvated halide ion concentrations around the vicinity of two radical centers arising due to surrounding surface electrostatic potential (computationally calculated) may be one of the possible factors for such selectivity in some of the examined <i>p-</i>benzynes. However, other complicated dynamical issues like the trajectory of the attacking nucleophile to the radical center which can be influenced by electronic and/or steric perturbation of starting enediyne conformation cannot be ruled out. The overall yield of the anionic addition was in the range of 80–99%

Experiment and Computational Study on the Regioselectivity of Nucleophilic Addition to Unsymmetrical <i>p</i>‑Benzynes Derived from Bergman Cyclization of Enediynes

The regioselectivity in addition of nucleophiles to the <i>p</i>-benzyne intermediates derived from unsymmetrical aza-substituted enediynes via Bergman cyclization was studied. Computational studies [using UB3LYP/6-31G­(d,p) level of theory] suggest that the <i>p</i>-benzyne intermediate retains its similar electrophilic character at the two radical centers even under unsymmetrical electronic perturbation, thus supporting the predicted model of nucleophilic addition to <i>p</i>-benzyne proposed by Perrin and co-workers (Perrin et al. <i>J. Am. Chem. Soc.</i> <b>2007</b>, <i>129</i>, 4795–4799) and later by Alabugin and co-workers (Peterson et al. <i>Eur. J. Org. Chem.</i> <b>2013</b>, <i>2013</i>, 2505–2527). However, observed experimental results suggest that there was small but definite regioselectivity (∼5–25%), the extent varying with the electronic nature of the substituents. Differential solvated halide ion concentrations around the vicinity of two radical centers arising due to surrounding surface electrostatic potential (computationally calculated) may be one of the possible factors for such selectivity in some of the examined <i>p-</i>benzynes. However, other complicated dynamical issues like the trajectory of the attacking nucleophile to the radical center which can be influenced by electronic and/or steric perturbation of starting enediyne conformation cannot be ruled out. The overall yield of the anionic addition was in the range of 80–99%

Experiment and Computational Study on the Regioselectivity of Nucleophilic Addition to Unsymmetrical <i>p</i>‑Benzynes Derived from Bergman Cyclization of Enediynes

The regioselectivity in addition of nucleophiles to the <i>p</i>-benzyne intermediates derived from unsymmetrical aza-substituted enediynes via Bergman cyclization was studied. Computational studies [using UB3LYP/6-31G­(d,p) level of theory] suggest that the <i>p</i>-benzyne intermediate retains its similar electrophilic character at the two radical centers even under unsymmetrical electronic perturbation, thus supporting the predicted model of nucleophilic addition to <i>p</i>-benzyne proposed by Perrin and co-workers (Perrin et al. <i>J. Am. Chem. Soc.</i> <b>2007</b>, <i>129</i>, 4795–4799) and later by Alabugin and co-workers (Peterson et al. <i>Eur. J. Org. Chem.</i> <b>2013</b>, <i>2013</i>, 2505–2527). However, observed experimental results suggest that there was small but definite regioselectivity (∼5–25%), the extent varying with the electronic nature of the substituents. Differential solvated halide ion concentrations around the vicinity of two radical centers arising due to surrounding surface electrostatic potential (computationally calculated) may be one of the possible factors for such selectivity in some of the examined <i>p-</i>benzynes. However, other complicated dynamical issues like the trajectory of the attacking nucleophile to the radical center which can be influenced by electronic and/or steric perturbation of starting enediyne conformation cannot be ruled out. The overall yield of the anionic addition was in the range of 80–99%

Experiment and Computational Study on the Regioselectivity of Nucleophilic Addition to Unsymmetrical <i>p</i>‑Benzynes Derived from Bergman Cyclization of Enediynes

The regioselectivity in addition of nucleophiles to the <i>p</i>-benzyne intermediates derived from unsymmetrical aza-substituted enediynes via Bergman cyclization was studied. Computational studies [using UB3LYP/6-31G­(d,p) level of theory] suggest that the <i>p</i>-benzyne intermediate retains its similar electrophilic character at the two radical centers even under unsymmetrical electronic perturbation, thus supporting the predicted model of nucleophilic addition to <i>p</i>-benzyne proposed by Perrin and co-workers (Perrin et al. <i>J. Am. Chem. Soc.</i> <b>2007</b>, <i>129</i>, 4795–4799) and later by Alabugin and co-workers (Peterson et al. <i>Eur. J. Org. Chem.</i> <b>2013</b>, <i>2013</i>, 2505–2527). However, observed experimental results suggest that there was small but definite regioselectivity (∼5–25%), the extent varying with the electronic nature of the substituents. Differential solvated halide ion concentrations around the vicinity of two radical centers arising due to surrounding surface electrostatic potential (computationally calculated) may be one of the possible factors for such selectivity in some of the examined <i>p-</i>benzynes. However, other complicated dynamical issues like the trajectory of the attacking nucleophile to the radical center which can be influenced by electronic and/or steric perturbation of starting enediyne conformation cannot be ruled out. The overall yield of the anionic addition was in the range of 80–99%

Experiment and Computational Study on the Regioselectivity of Nucleophilic Addition to Unsymmetrical <i>p</i>‑Benzynes Derived from Bergman Cyclization of Enediynes

The regioselectivity in addition of nucleophiles to the <i>p</i>-benzyne intermediates derived from unsymmetrical aza-substituted enediynes via Bergman cyclization was studied. Computational studies [using UB3LYP/6-31G­(d,p) level of theory] suggest that the <i>p</i>-benzyne intermediate retains its similar electrophilic character at the two radical centers even under unsymmetrical electronic perturbation, thus supporting the predicted model of nucleophilic addition to <i>p</i>-benzyne proposed by Perrin and co-workers (Perrin et al. <i>J. Am. Chem. Soc.</i> <b>2007</b>, <i>129</i>, 4795–4799) and later by Alabugin and co-workers (Peterson et al. <i>Eur. J. Org. Chem.</i> <b>2013</b>, <i>2013</i>, 2505–2527). However, observed experimental results suggest that there was small but definite regioselectivity (∼5–25%), the extent varying with the electronic nature of the substituents. Differential solvated halide ion concentrations around the vicinity of two radical centers arising due to surrounding surface electrostatic potential (computationally calculated) may be one of the possible factors for such selectivity in some of the examined <i>p-</i>benzynes. However, other complicated dynamical issues like the trajectory of the attacking nucleophile to the radical center which can be influenced by electronic and/or steric perturbation of starting enediyne conformation cannot be ruled out. The overall yield of the anionic addition was in the range of 80–99%