Copper-Photocatalyzed Borylation of Organic Halides under Batch and Continuous-Flow Conditions.

The copper-photocatalyzed borylation of aryl, heteroaryl, vinyl and alkyl halides (I and Br) was reported. The reaction proceeded using a new heteroleptic Cu complex under irradiation with blue LEDs, giving the corresponding boronic-acid esters in good to excellent yields. The reaction was extended to continuous-flow conditions to allow an easy scale-up. The mechanism of the reaction was studied and a mechanism based on a reductive quenching (CuI /CuI */Cu0 ) was suggested.

The priming molecule ß-aminobutyric acid is naturally present in plants and is induced by stress.

The defense system of a plant can be primed for increased defense, resulting in an augmented stress resistance and/or tolerance. Priming can be triggered by biotic and abiotic stimuli, as well as by chemicals such as ß-aminobutyric acid (BABA), a nonprotein amino acid considered so far a xenobiotic. Since the perception mechanism of BABA has been recently identified in Arabidopsis thaliana, in the present study we explored the possibility that plants do synthesize BABA. After developing a reliable method to detect and quantify BABA in plant tissues, and unequivocally separate it from its two isomers α- and γ-aminobutyric acid, we measured BABA levels in stressed and nonstressed A. thaliana plants, and in different plant species. We show that BABA is a natural product of plants and that the endogenous levels of BABA increase rapidly after infection with necrotrophic, biotrophic and hemibiotrophic pathogens, as well as after salt stress and submergence. Our results place the rise in endogenous BABA levels to a point of convergence in plant stress response and provide biological significance to the presence of a receptor in plants. These findings can explain the extremely widespread efficacy of BABA and open the way to unravel the early steps of priming.

3-ß-D-Glucopyranosyl-6-methoxy-2-benzoxazolinone (MBOA-N-Glc) is an insect detoxification product of maize 1,4-benzoxazin-3-ones.

In order to defend themselves against arthropod herbivores, maize plants produce 1,4-benzoxazin-3-ones (BXs), which are stored as weakly active glucosides in the vacuole. Upon tissue disruption, BXs come into contact with ß-glucosidases, resulting in the release of active aglycones and their breakdown products. While some aglycones can be reglucosylated by specialist herbivores, little is known about how they detoxify BX breakdown products. Here we report on the structure of an N-glucoside, 3-ß-d-glucopyranosyl-6-methoxy-2-benzoxazolinone (MBOA-N-Glc), purified from Spodoptera frugiperda faeces. In vitro assays showed that MBOA-N-Glc is formed enzymatically in the insect gut using the BX breakdown product 6-methoxy-2-benzoxazolinone (MBOA) as precursor. While Spodoptera littoralis and S. frugiperda caterpillars readily glucosylated MBOA, larvae of the European corn borer Ostrinia nubilalis were hardly able to process the molecule. Accordingly, Spodoptera caterpillar growth was unaffected by the presence of MBOA, while O. nubilalis growth was reduced. We conclude that glucosylation of MBOA is an important detoxification mechanism that helps insects tolerate maize BXs.

Intermolecular Ritter-type C-H amination of unactivated sp3 carbons.

Intermolecular Ritter-type C-H amination of unactivated sp(3) carbons has been developed. This new reaction proceeds under mild conditions using readily available reagents and an inexpensive source of nitrogen (acetonitrile). A broad scope of substrates can be aminated with this method since many functional groups are tolerated. This reaction also allows for the direct, innate C-H amination of a variety of hydrocarbons such as cyclohexane without the need of prefunctionalization or installation of a directing group.

2-(2-Naphth-yl)-1,3-dioxane.

The title compound, C(14)H(14)O(2), crystallizes in the chiral monoclinic space group P2(1). This acetal is composed of a planar naphthalene ring with a 1,3-dioxane ring substituent, which has a chair conformation. In the crystal structure, symmetry-related mol-ecules are connected via a weak C-H⋯O inter-action to form a helical chain propagating in [010]. While there are no π-π stacking inter-actions present, there are weak C-H⋯π inter-actions involving the naphthalene aromatic rings, which link the helical chains to form a two-dimensional network in the (011) plane.

1,4-Bis(hex-yloxy)-2,5-diiodo-benzene.

The centrosymmetric title compound, C(18)H(28)I(2)O(2), crystallized in the monoclinic space group P2(1)/c with the alkyl chains having extended all-trans conformations, similar to those in the centrosymmetric bromo analogue [Li et al. (2008 ▶). Acta Cryst. E64, o1930] that crystallized in the triclinic space group P. The difference between the two structures lies in the orientation of the two alkyl chains with respect to the C(aromatic)-O bond. In the title compound, the O-C(alk-yl)-C(alk-yl)-C(alk-yl) torsion angle is 55.8 (5)°, while in the bromo analogue this angle is -179.1 (2)°. In the title compound, the C-atoms of the alkyl chain are almost coplanar [maximum deviation of 0.052 (5) Å] and this mean plane is inclined to the benzene ring by 50.3 (3)°. In the bromo-analogue, these two mean planes are almost coplanar, making a dihedral angle of 4.1 (2)°. Another difference between the crystal structures of the two compounds is that in the title compound there are no halide⋯halide inter-actions. Instead, symmetry-related mol-ecules are linked via C-H⋯π contacts, forming a two-dimensional network.

1,4-Bis[4-(tert-butyl-diphenyl-silyl)buta-1,3-diyn-yl]benzene.

The title centrosymmetric mol-ecule, C(46)H(42)Si(2), is composed of a central benzene ring with buta-1,3-diynyl chains at positions 1 and 4. These chains are terminated by tert-butyl-diphenyl-silyl groups, hence the molecule is dumbbell in shape. The mol-ecules are connected via C-H⋯π inter-actions in the structure, so forming an undulating two-dimensional network in the bc plane. There is also a weak π-π inter-action involving centrosymmetrically related phenyl rings with a centroid-centroid distance of 3.8359 (11) Å.

Suppressing one-bond correlations in HMBC spectra: improved performance for the BIRD-HMBC pulse sequence.

An improved version of the BIRD-HMBC experiment is proposed. In comparison to the original version, the filtering (suppression of (1) J(CH) signals) is accomplished using a double tuned G-BIRD filter positioned in the middle of the long-range correlations evolution period. Compensation of offset dependence by replacing the rectangular 180 degree pulses with the broadband inversion pulses (BIPs), with superior inversion performance and improved tolerance to B(1) field inhomogeneity, significantly improves the sensitivity of the original BIRD-HMBC experiment. For usual one-bond coupling constants ranges (115-180 Hz), optimal results are easily obtained by adjusting the delays, delta, of the BIRD elements to an average J value. For larger ranges (e.g. 110-260 Hz), the use of a double tuned G-BIRD filter allows excellent suppression degrees for all types of one-bond constants present in a molecule, superior to the original scheme and other purging schemes. These attributes make the improved version of the BIRD-HMBC experiment a valuable and robust tool for rapid spectral analysis and rapid checks of molecular skeletons with a minimum spectrometer time.