Mechanisms of intramolecular transformations of carbanions generated from 2-aza-1,3,5-trienes by the action of potassium tert-butoxide, which could lead to homo-or heteroannular azacycloheptadienes, were studied by quantum-chemical methods in terms of the density functional theory. The corresponding gradient channels were localized for model 1-methylsulfanyl-1-(cyclopentylideneamino)-and 1-methylsulfanyl-1-(cyclohexylideneamino)buta-1,3-dien-2-ols. Analysis of the kinetic and thermodynamic parameters showed that carbanion generated from N-cyclopentylidenebuta-1,3-dien-1-amine undergoes rearrangement mainly into homoannular azacycloheptadiene and that analogous N-cyclohexylidene derivative gives rise to heteroannular isomer. The results of calculations were consistent with the experimental data. * For communication XV, see [1].Seven-membered nitrogen-containing heterocycles constitute structural fragments of many natural and synthetic biologically active compounds which have found wide applications in medicine and pharmacology [2]. Increased interest in these compounds stimulated search for rational ways of their synthesis, including the synthesis of new derivatives. We recently showed that 2-aza-1,3,5-trienes I available in one preparative step from α-lithiated allenes (e.g., methoxyallene or protected allenyl alcohol) and s-alkyl isothiocyanates (e.g., isopropyl isothiocyanate) (Scheme 1) [3] by the action of potassium tert-butoxide in tetrahydrofuran-dimethyl sulfoxide are readily (-30°C, 30 min) transformed into previously unknown 4,5-dihydro-3H-azepines II (Scheme 2); these results were briefly reported in [4,5].

General remarks 1 H, 13 C and 77 Se NMR spectra were measured on a Bruker AV400 (DPX400) spectrometer at 400 MHz, 100.6 MHz and 76.3 MHz, respectively. 1 H NMR chemical shifts were calibrated by residual proton of CDCl 3 (δ 7.27 ppm). 13 C NMR chemical shifts were calibrated by deuterated carbon of CDCl 3 (δ 77.1 ppm). 77 Se NMR spectra were recorded with diphenyl diselenide (δ 463 ppm) as external standards, relative to dimethyl selenide (δ 0.00 ppm). Mass spectra were measured on an Agilent 5975 with electron impact (EI) ionization at 70 eV. X-ray data were collected on a BRUKER D8 VENTURE PHOTON 100 CMOS diffractometer with MoK α radiation (λ = 0.71073 Å) using the φ and ω scans technique. The structures were solved and refined by direct methods using the SHELX [Sheldrick, G. M. Acta Crystallogr. 2008, 64, 112]. Data were corrected for absorption effects using the multi-scan method (SADABS). All non-hydrogen atoms were refined anisotropically using SHELX. The coordinates of the hydrogen atoms were calculated from geometrical positions. Crystal data and experimental details are given in Table S2. А one-pot synthesis of 2-bromomethyl-1,3-thiaselenole (1) Se S Br

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An area of discolored water 50 m wide and 30 m long was found in September 2017 close to the dam of the Irkutsk hydroelectric power station. Water from this spot was sampled for investigation in the present study. Microscopic analysis revealed that the suspended matter in the sample was composed of clumps of filaments, vegetative cells, akinetes and heterocysts that formed short filaments and solitary cells. This matter was found to consist of partially degraded cells of the cyanobacterium Dolichospermum lemmermannii. Nucleotide sequencing of DNA isolated from the biomass revealed the presence of the sxtA gene which is involved in the synthesis of saxitoxin. Water from the polluted area contained 600 ± 100 μg L−1 saxitoxin as measured by HPLC-MS with pre-column modification of the toxin with 2,4-dinitrophenylhydrazine. Immunoassay analysis (ELISA) showed a concentration of saxitoxins in the water of 2900 ± 900 μg L−1. Hydrochemical and microbiological analyses suggested the contaminated area appeared as a result of a D. lemmermannii bloom, followed by its decay and release of saxitoxin and nutrients. The present paper describes the results of a case study. Better understanding of the phenomenon will depend on the possibility to perform implementation of a large-scale monitoring program.

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