Conformational study of five derivatives of 2‐(pyrazol‐4‐yl)‐1,3‐diselenane together with related 1,2‐diselenolane in respect to the stereochemical trends of geminal and vicinal 77Se‐1H spin‐spin coupling constants has been carried out by means of high‐level theoretical calculations in combination with experiment. The marked dihedral angle dependences for both types of couplings accounted for the lone pair effect in the case of geminal coupling constants and the Karplus‐type relationship for vicinal couplings have been established, which is of major importance for the stereochemical analysis of saturated selenium containing heterocycles. Copyright © 2012 John Wiley & Sons, Ltd.

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The reaction of 3,5‐dimethyl‐4‐formylpyrazoles, bearing various substituents at N‐1 atom, with propane‐1,3‐diselenol and 2‐hydroxypropane‐1,3‐diselenol in the presence of ТМSCl proceeds without heating to chemoselectively give hitherto unknown 2‐(pyrazol‐4‐yl)‐1,3‐diselenane hydrochlorides in high yields. The latter are easily transformed to the corresponding free bases—2‐(pyrazol‐4‐yl)‐1,3‐diselenanes. The 15N chemical shifts of the pyrazole ring in 2‐(pyrazol‐4‐yl)‐1,3‐diselenanes obtained by 2D HMBC‐gp (15N‐1H) technique are indicative of the N‐2 atom protonation in hydrochlorides.

SHORT COMMUNICATIONSPyrazoles are important building blocks in the synthesis of novel pharmaceutical agents possessing analgesic, antiphlogistic, antibacterial, antidepressant, and other kinds of biological activity [1], as well as of insectoacaricides [2], dyes, luminophores, and ligands [3]. Water-soluble pyrazole derivatives are of particular significance. The ability of pyrazoles to form hydrohalides is determined by the presence of a pyridinetype nitrogen atom in their molecules, which possesses enhanced nucleophilicity [4]. It is known that pyrazole hydrochlorides are unstable. If pyrazole molecule contains another nucleophilic center, e.g., double C=C bond, their reactions with hydrohalic acids could follow two pathways. Hydrochlorination of 1-alkenylpyrazoles occurs at the N 2 atom only on cooling (-70°C), whereas at room temperature the process involves the alkenyl substituent [5,6].We were the first to reveal that acetalization of pyrazole-4-carbaldehydes Ia-Ic with 2-sulfanylethanol in the presence of 5-6 equiv of chlorotrimethylsilane at room temperature leads to the formation of the corresponding dithioacetal hydrochlorides IIa-IIc in good yield. Protonation of the N 2 atom in the heteroring of compounds IIa-IIc is indicated by the presence in their IR spectra of a broadened NH + absorption bands at 2500-2800 cm -1 . Hydrochlorides IIa-IIc are colorless water-soluble oily substances that are stable under usual conditions. 4-Bis(2-hydroxyethylsulfanyl)methyl-3,5-dimethyl-1H-pyrazole hydrochlorides IIa-IIc (general procedure). 2-Sulfanylethanol, 0.156 g (2 mmol), was added dropwise under stirring to a mixture of 1 mmol of pyrazolecarbaldehyde Ia-Ic and 0.77 ml (6 mmol) of chlorotrimethylsilane. The reaction was accompanied by heat evolution, and the mixture divided into two layers. The mixture was stirred for 15-20 min at room temperature, the upper layer was separated, and the viscous residue was washed with hot hexane and with diethyl ether and dried under reduced pressure. S,S′-[(1-Isopropyl-3,5-dimethyl-1H-pyrazol-4-yl)-methanediyl]bis(2-sulfanylethanol) hydrochloride (IIa). Yield 0.315 g (93%). IR spectrum (film), ν, cm -1 : 3339 br (OH), 2713-2540 br (NH + ). 1 H NMR spectrum, δ, ppm: 1.57 d [6H, CH(CH 3 ) 2 , 3 J = 6.7 Hz], 2.55 s and 2.56 s (3H each, CH 3 ), 2.69 d.t and 2.82 d.t (2H each, CH 2 S, 2 J = 14.1, 3 J = 6.3 Hz), 3.70 d.t and 3.76 d.t (2H each, CH 2 O, 2 J = 11.3, 3 J = 6.3 Hz), 4.91 m (1H, NCH), 5.44 s (1H, SCHS). 13 C NMR spectrum, δ C , ppm: 10.43 and 10.63 (CH 3 ), 21.47 [CH (CH 3 ) 2 ], 36.20 (CH 2 S), 43.54 (SCHS), 53.67 (NCH), 62.79 (OCH 2 ), 119.96 (C 4 ), 144.70 and 145.56 (C 3 , C 5 ). Found, %: C 45.76; H 7.38; Cl 10.38; N 8.21; R = i-Pr (a), CH 2 =CHCH 2 (b), PhCH 2 (c).

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