M. V. Penzik

Conformational analysis and diastereotopic assignments in the series of selenium-containing heterocycles by means of 77Se-1H spin-spin coupling constants: a combined theoretical and experimental study.

A combined theoretical and experimental study on the stereochemical behavior of 77Se‐1H spin‐spin coupling constants has been performed at the second‐order polarization propagator approach level together with heteronuclear multiple‐bond correlation technique in the series of selenium‐containing four‐, five‐ and six‐membered heterocycles including the derivatives of thiaselenetane, selenasilole, thiaselenole, thiaselenolane and dihydrothiaselenine. Geminal and vicinal 77Se‐1H spin‐spin couplings were shown to have the pronounced stereochemical dependences in respect with the topology of the coupling pathway, internal rotation of the side‐chain substituents and ring inversion providing a straightforward tool for the conformational analysis and diastereotopic assignments in the chiral organoselenium compounds. Copyright

Reaction of selenium dibromide with divinyl sulfide

We found that the reaction of selenium dibromide with divinyl sulfide leads to an earlier unknown heterocyclic compound 5-bromo-2-bromomethyl-1,3thiaselenolane (I) in 80% yield. Selenium dibromide was prepared in situ by the reaction of selenium with bromine in chloroform. 5-Bromo-2-bromomethyl-1,3-thiaselenolane (I). Major diastereomer. Н NMR spectrum, δ, ppm: 3.79– 3.84 m (2Н, СН2Se), 3.86 m (1Н, СН2Br), 3.99 d. d (1Н, СН2Br, J 9.4, J 8.0 Hz), 5.03 t (1H, SСНSe, J 8.0 Hz), 6.10 d.d (1Н, SСНBr, J 3.3, J 3.4 Hz). С NMR spectrum, δ, ppm: 38.47 (CH2Br), 45.97 (CH2Se), 48.18 (SCHSe), 59.69 (SCHBr). Se NMR spectrum, δ, ppm: 410. Minor diastereomer. Н NMR spectrum, δ, ppm: 3.69–3.73 m (2Н, СН2Br), 3.70 m, 3.89 m (2Н, СН2Se), 5.05 t (1H, SСНSe, J 7.9 Hz), 5.91 d. d (1Н, SeСНBr, J 4.1, J 4.3 Hz). С NMR spectrum, δ, ppm: 37.50 (CH2Br), 44.39 (CH2Se), 47.27 (SCHSe), 58.36 (SCHBr). Se NMR, δ, ppm: 415. Found, %: С 15.00; Н 1.69; Br 49.38. C4H6Br2SSe. Calculated, %: С 14.79; Н 1.86; Br 49.18. The NMR spectra were taken on a Bruker DPX-400 instrument in CCl4 at working frequencies of 400.13 (Н, HMDS), 100.61 (С, HMDS), and 76.30 MHz (Se, Me2Se). ACKNOWLEDGMENTS

Synthesis of 2,6-dichloro-1,4-thiaselenane from divinyl sulfide and selenium dichloride

Se SO2Cl2 SeCl2 CHCl3 I Selenium dichloride in a solution exists in an equilibrium with SeCl4 and Se2Cl2 [1]. Prior to our research [2, 3] no data were published on the possibility of the synthesis of organoselenium compounds from the selenium dichloride. We performed the reactions of SeCl2 and SeBr2 with dimethyldiethynylsilane which led to the formation of 3,6-dihalo-4,4-dimethyl-1,4-selenasilafulvenes [2, 3]. This reaction extended further to dialkyldiethynylsilanes and –germanes showed the way to new classes of heterocycles containing in the ring atoms of selenium and the elements of 16 group [4–8]. We previously reported that on adding divinyl sulfide to a solution of SeCl2 in chloroform at room temperature a five-membered heterocycle was formed, 2-chloromethyl-1,3-thiaselenol [9]. At –50°C the simultaneous uniform addition into a reactor of the solutions of the mentioned reagents in chloroform (at equimolar ratio of selenium dichloride and divinyl sulfide) resulted in the formation in 90% yield of the previously unknown six-membered heterocycle, 2,6-dichloro-1,4-thiaselenane (I).

New reaction accompanied with rearrangement of 2-(bromomethyl)-1,3-thiaselenol with furan-2- and thiophene-2-carboxylic acids

Substituted 2-aryl-5-phenyl-1,4-oxaselenines exhibited characteristics of potential antitumor agents [1]. A method was developed of the fusion of a benzene ring to 2,3-dihydro-1,4-thiaselenine based on a regionand stereoselective reaction of selenium dichloride with allyl or propargyl phenyl ether resulting in the formation of 3-chloromethyland E-3-chloromethylene-2,3-dihydrobenzo[b][1,4]oxaselenines [2-4]. A procedure is described of the preparation of 1,4-thiaselenine and its 3,5-dialkyl-substituted derivatives from di(1-alkynyl) and its oxygen analog are not known. Only some syntheses are described of 5-alkyl-substituted 2,3-dihydro-1,4-thiaselenines obtained by reaction of 1-(2-chloroethylsulfanyl)-1-alkyne with lithium selenide [6] and of 5-substituted 2,3-dihydro-1-oxoand 1,1-dioxo-1,4-thiaselenines obtained by adding sodium selenide to 1-alkynyl vinyl sulfoxide and –sulfone [7].

Open-chain unsaturated selanyl sulfides: stereochemical structure and stereochemical behavior of their 77Se–1H spin–spin coupling constants

Stereochemical structure of nine Z‐2‐(vinylsulfanyl)ethenylselanyl organyl sulfides has been investigated by means of experimental measurements and second‐order polarization propagator approach calculations of their 1H–1H, 13C–1H, and 77Se–1H spin–spin coupling constants together with a theoretical conformational analysis performed at the MP2/6‐311G** level. All nine compounds were shown to adopt the preferable skewed s‐cis conformation of their terminal vinylsulfanyl group, whereas the favorable rotational conformations with respect to the internal rotations around the C–S and C–Se bonds of the internal ethenyl group are both skewed s‐trans. Stereochemical trends of 77Se–1H spin–spin coupling constants originating in the geometry of their coupling pathways and the selenium lone pair effect were rationalized in terms of the natural J‐coupling analysis within the framework of the natural bond orbital approach. Copyright

Unexpected reaction of 2-(bromomethyl)-1,3-thiaselenole with ammonium thiocyanate

An efficient procedure of 2-(bromomethyl)-1,3thiaselenole 1 preparation by a new reaction of selenium dibromide with divinyl sulfide was developed [1]. The reaction was extended to selenium dichloride [2, 3]. The reactions proceed via the formation of six-membered rings, 2,6-dihalo-1,4thiaselenanes that underwent a rearrangement into five-membered rings, 5-halo-2-(halomethyl)-1,3thiaselenoles, with the subsequent dehydrochlorination and the formation of an endocyclic double bond resulting in 2-(halomethyl)-1,3-thiaselenoles. The driving force of the rearrangement is the anchimeric assistance of the selenium atom that essentially exceeds the sulfur atom effect [4].

Unexpected reaction of 2-bromomethyl-1,3-thiaselenole with salts of carboxylic acids

Previously we have reported that 2-bromomethyl1,3-thiaselenole, when reacted with ethanol in the presence of KOH, undergoes an unusual rearrangement to afford six-membered heterocycle, 2-ethoxy-2,3-dihydro-1,4-thiaselenine [1]. Before our investigations, the synthesis of 2,3-dihydro-1,4-thiaselenines was disclosed in work [2], where it was showed that the reaction of 1-(2-chloroethylsulfanyl)-1-alkynes with lithium selenide delivered 2,3-dihydro-1,4-thiaselenines (in low yields) bearing methyl or ethyl substituents in the position 5 at the endocyclic double bond. 2-Bromomethyl-1,3-thiaselenole became available due to a one-pot synthetic procedure [3, 4] involving the reaction of divinyl sulfide [5, 6] with selenium dibromide generated in situ from element selenium and bromine followed by dehydrobromination of the fivemembered heterocycle. A chlorine analog, 2-chloromethyl-1,3-thiaselenole, was obtained from the reaction of divinyl sulfide with selenium dichloride [7, 8]. Carboxylic acid salts are known to be among the weakest nucleophiles. Therefore, their alkyl derivatives (esters) are synthesized, as a rule, not via alkylation of carboxylic acid salts, but by the reaction of acids with alcohols. However, these esters can be prepared in moderate to good yields via the alkylation of carboxylic acid salts only when special approaches, for example, phase-transfer catalysis, are employed. Another route to these esters is the application of highly reactive electrophilic alkylating reagents. Among the latter are the compounds where a halogen atom is activated by a chalcogen atom through the effect of anchimeric assistance. Recent kinetic studies have shown that the effect of anchimeric assistance of selenium atom is by the order higher than that of sulfur atom [9].

Unexpected regio- and stereoselective reaction of 2-bromomethyl-1,3-thiaselenole with ketones. Formation of 1-[(Z)-2-(vinylsulfanyl)ethenyl]selanylalkan-2-ones

α-Selanyl ketones constitute an important class of organic compounds which exhibit antioxidant [1–3] and antimicrobial properties [4] and are used in organic synthesis for the preparation of various heterocycles [5–8]. The simplest representative of α-selanyl ketones is 1-(methylselanyl)propan-2-one [9]. α-Selanyl ketones of the general formula RSeCH2C(O)R′ (R = Bu, R′ = Ph [10, 11]; R = All, R′ = Ph, Ar [12, 13]; R = CN, R′ = Ph [6–8, 14, 15]; R = R′ = Ph [1, 4, 5, 16]) have been reported. There are no published data on α-selanyl ketones in which the selenium atom is directly linked to a double-bonded carbon atom.

Synthesis of 2,6-dichloro-1,4-dithiane. The effect of the chalcogen nature on the stability of 2,6-dichloro-1,4-thiachalcogenanes

Two of the three possible structural isomers of dichloro-substituted 1,4-dithiane have been reported, viz. the 2,3-dichloro-1,4-dithiane [1] and the 2,5-dichloro-1,4-dithiane [1, 2]. Evidence for 2,6-dichloro-1,4-dithiane and other 2,6-disubstituted 1,4-dithianes is absent. Only 3,5-dichloro-2,2,6,6-tetramethyl-1,4-dithiane is known amongst substituted analogs [3]. We have previously studied the electrophilic addition reaction of selenium dichloride to divinyl sulfide (DVS) at -50°C in chloroform [4, 5] or at room temperature in carbon tetrachloride [5, 6], which gives a nearly quantitative yield of the selenium analog 2,6-dichloro-1,4-thiaselenane (as two diastereomers). In chloroform solution at room temperature, the latter undergoes a spontaneous rearrangement to the five-membered 5-chloro2-chloromethyl-1,3-thiaselenolane (as two diastereomers) with a subsequent spontaneous dehydrochlorination to give an endocyclic double bond. The ease of rearrangement of the 2,6-dichloro-1,4-thiaselenane to the 5-chloro-2-chloromethyl-1,3-thiaselenolane is mainly due to the anchimeric effect of the selenium atom [5, 6].

Electrophilic addition of selenium and telluriom halides to methyldiethynylsilane

Regio- and stereoselective electrophilic addition reactions of SeCl2, SeBr2, SeCl4, SeBr4 to methyldiethynylsilane lead to predominant formation of the Z-isomers of 3,6-dihalo-4-methyl-1,4-selenasilafulvenes, disiloxanes on their bases, as well as disiloxanes formed upon the reaction with methyldiethynylsilane. TeCl4 reacts with methyldiethynylsilane with predominant formation of the E-isomer of 1,1,3,6-tetrachloro-1-methyl-1-(methyldiethynylsiloxy)-1,4-tellura(IV)silafulvene as a result of the reaction of the intermediate E-isomer of 4-methyl-1,1,3,6-tetrachloro-1,4-tellura(IV)silafulvene with methyldiethynylsilane. The structure of the products was proved by the methods of 1H, 77Se NMR, IR spectroscopy and chromatomass spectrometry.