M. V. Musalova

Synthesis of Novel E-2-Chlorovinyltellurium Compounds Based on the Stereospecific Anti-addition of Tellurium Tetrachloride to Acetylene

The reaction of tellurium tetrachloride with acetylene proceeds in a stereospecific anti-addition manner to afford the novel products E-2-chlorovinyltellurium trichloride and E,E-bis(2-chlorovinyl)tellurium dichloride. Reaction conditions for the selective preparation of each of these products were found. The latter was obtained in 90% yield in CHCl3 under a pressure of acetylene of 10–15 atm, whereas the former product was formed in up to 72% yield in CCl4 under a pressure of acetylene of 1–3 atm. Synthesis of the previously unknown E,E-bis(2-chlorovinyl) telluride, E,E-bis(2-chlorovinyl) ditelluride, E-2-chlorovinyl 1,2,2-trichloroethyl telluride and E,E-bis(2-chlorovinyl)-tellurium dibromide is described.

A regio- and stereospecific reaction of tellurium tetrachloride with (trimethyl)(propargyl)silane

 Halovinyl tellurides are used in cross coupling reac tions for the synthesis of functionalized alkenes.1 A com mon route to these compounds involves addition of tellu rium tetrahalides to alkynes followed by reduction to tellurium(II) products.1 Our systematic investigations2—5 of the addition of se lenium and tellurium halides to alkynes have yielded un expected results in the case of trimethylsilyl containing alkynes. For instance, a reaction of SeCl2 with (tri methyl)(propargyl)silane (1) proceeds regio and ste reospecifically to form Z,E bis[2 chloro 3 (trimethyl silyl)prop 1 enyl] selenide in quantitative yield.3 We have assumed3 that the reaction begins with anti addition of SeCl2 to one molecule of silane 1 followed by syn addition of the resulting monoadduct to a second molecule of si lane 1. No reaction of TeCl4 with compound 1 has been documented; however, it is known4 that TeCl4 reacts with (ethynyl)(trimethyl)silane to give Z 2 chloro 1 (trimeth ylsilyl)vinyltellurium trichloride, an anti Markownikoff adduct. It turned out that the bulky trimethylsilyl group substantially influences the regio and stereochemical out comes of the reaction.4 We were the first to study a reaction of TeCl4 with propargylsilane 1. We found that the reaction proceeds regio and stereospecifically to give a Markownikoff ad duct, namely, Z 2 chloro 3 (trimethylsilyl)prop 1 enyl tellurium trichloride (2), in 96% yield (Scheme 1). The reaction is performed by adding a solution of an equimolar amount of propargylsilane 1 in benzene to a cooled (5 C) solution of TeCl4 in benzene; the reaction mixture is stirred at 5 C for 3 h and then at room temper ature for 12 h. If no cooling is used, the room temperature reaction yields compound 2 contaminated with small amounts of by products. We failed to obtain the bisadduct Z,Z bis[2 chloro 3 (trimethylsilyl)prop 1 enyl]tellurium dichloride by a re action of TeCl4 with an excess of reactant 1 in benzene or chloroform at room temperature or at 60 C. This may probably be due to the poor stability of monoadduct 2, which decomposes partially when heated in solution or in the solid state to 45—48 C. At room temperature, mono adduct 2 does not react with a second molecule of com pound 1, while heating results in the decomposition of both monoadduct 2 and, probably, the bisadduct formed. Reduction of compound 2 with the system Na2S2O5— H2O—C6H6 at room temperature gave the novel com pound Z,Z bis[2 chloro 3 (trimethylsilyl)prop 1 enyl] ditelluride (3) in 94% yield. Despite the presence of water, no desilylation occurs. So the silyl group, as well as the Z configuration, is retained in the final product 3. The structures of products 2 and 3 were proved by 1H and 13C NMR spectroscopy (with a NOESY experiment used to determine the stereoconfiguration) and confirmed by elemental analysis. The spin spin coupling between the Te atom and the carbon atom of =CH is characterized by coup ling constants of 260 and 328 Hz (for 2 and 3, respectively), which correspond to direct constants JTe,C. 5 This sug gests the attachment of the Te atom to the terminal C atom of silane 1 and the formation of a Markownikoff adduct. To sum up, in contrast to the reaction of TeCl4 with (ethynyl)(trimethyl)silane, the addition of TeCl4 to prop argylsilane 1 gives a Markownikoff adduct. The resulting organotellurium compounds 2 and 3 are of interest as semi finished products for fine organic synthesis.

Synthesis of ( E )-2-chlorovinyltellurium trichloride and ( E,E )-bis(2-chlorovinyl) ditelluride

The reaction of tellurium tetrachloride with acetylene in CCl4 at atmospheric pressure and ambient temperature affords earlier unknown (E)-2-chlorovinyltellurium trichloride in 30% yield, whose reduction with sodium bisulfite gives (E,E)-bis(2-chlorovinyl) ditelluride in 64% yield.

Regioselective synthesis of bis[(2,3-dihydro-1-benzofuran-2-yl)methyl]selenide

Electrophilic selenium-containing reagents play an important role in the modern organic synthesis. They are used in cyclization reactions for the preparation of heterocyclic compounds with the formation of new selenium-carbon bonds [1]. Lately the chemistry of selenium dihalides is intensively developed. These compounds turned out to be efficient reagents in the synthesis of heterocyclic compounds [2–14]. Effective methods of preparation of new 4-, 5-, and 6-membered heterocycles are underlain by the addition of selenium dichloride and dibromide to divinyl chalcogenides [4–6], diallyl chalcogenides [7–9], and divinyl sulfone [10–12]. The fusion of 2,3-dihydro-1,4-oxaselenine to a benzene ring occurs in the reaction of selenium dichloride with allyl and propargyl phenyl ethers [13]. In this case the addition of selenium dichloride to the unsaturated moiety is accompanied with electrophilic aromatic substitution and the formation of a selenium-carbon bond. From selenium dichloride and cyclooctadiene 2,6-dichloro-9-selenabicyclo-[3.3.1]nonane was synthesized [14]. The cyclization reactions involving selenium dihalides and resulting in carbon–oxygen bonds formation have not been described.

Stereospecific synthesis of E,E-bis(2-bromovinyl)tellurium dibromide

Reactions of TeCl4 and RTeCl3 with alkynes mostly follow the syn addition pattern and yield Z adducts1 ac cording to the mechanism involving a four membered transition state.2 The literature data on reactions of tellu rium tetrabromide with alkynes are very scarce.3 For in stance, TeBr4 reacts with phenylacetylene and hept 1 yne to form Z,E isomeric mixtures of the Markownikoff ad ducts, the Z isomers being dominant. Data on a reaction of TeBr4 with acetylene are lacking in the literature. Earli er, we have studied reactions of selenium halides4 and tellurium tetrachloride5 with acetylene. The reaction of TeCl4 with acetylene produces E,E bis(2 chlorovinyl) tellurium dichloride and E (2 chlorovinyl)tellurium tri chloride and is a first example of stereospecific anti addi tion of TeCl4 to alkynes. 5 In the present work, we carried out addition of TeBr4 onto acetylene. The reaction proceeds stereospecifically as anti addition leading to earlier unknown E,E bis (2 bromovinyl)tellurium dibromide (1). The formation of possible Z isomers was not detected. Under optimized conditions (autoclave, acetylene pressure 12—14 atm, CHCl3 as a solvent, 40—70 C), the yield of compound 1 was 96%. The structure of compound 1 was proved by 1H and 13C NMR spectroscopy and elemental analysis. The cou pling constant of the vinylic protons that are trans to each other (J = 14.0 Hz) in product 1 is typical of E 2 halo vinyl tellurides.5 Vinyltellurium containing compounds are widely used in modern organic synthesis.6,7 They are substrates for the Heck, Suzuki, Sonogashira, Stille, Negishi, and other cross coupling reactions.6 Compounds containing the 2 bromovinyltellurium fragment are employed for the stereoselective synthesis of alkenes via cross coupling re actions during which the Br and Te atoms are sequentially replaced by organic substituents.7 To sum up, unlike reported1—3 reactions of tellurium tetrahalides, the reaction of TeBr4 with acetylene pro ceeds stereospecifically as anti addition. Compound 1 ob tained in high yield is a promising intermediate for organic synthesis. This reaction is a first example of stereospecific anti addition of TeBr4 to the triple bond.

Regioselective reaction of tellurium tetrabromide with 1-hexene and methanol

Published information on the reactions of tellurium tetrabromide with alkenes [1] and alkynes [2] is scanty. The known feature of tellurium tetrabromide is its low solubility in most organic solvents resulting often in incomplete conversion of this reagent. The purifi cation of reaction products from tellurium tetrabromide is a complicated problem. Tellurium tetrabromide is well soluble in methanol but this solvent has not been virtually used in the reactions of tellurium tetrabromide apparently because of the apprehension of the alcoholysis of the Te–Br bond. No published information exists on the reactions of tellurium tetrabromide with 1-hexene. In continuation of research on the reactions of tellurium [3] and selenium [4] halides with unsaturated compounds we performed the reaction between tellurium tetrabromide with 1-hexene in methanol. The reaction proceeds chemoand regioselectively with the selective formation in a quantitative yield of the product of TeBr4 addition to the hexane molecule in keeping with Markovnikoff rule, 2-methoxyhexyltellurium tribromide (I). The quantitative yield of compound I was obtained by heating the reagents at 40–60°С during 8 h. We did not observe bisadduct formation and the possible alcoholysis of the Te–Br bond.

Reaction of tellurium tetrachloride with hex-3-yne

Reactions of tellurium tetrachloride and its derivatives with alkynes are used for the preparation of compounds useful in the stereoselective synthesis of alkenes.1,2 The reaction of tellurium tetrachloride with both the terminal (phenylacetylene,2,3 tert butylacetylene4) and disubstitut ed arylacetylenes (diphenylacetylene,2,3 arylalkynes2) pro ceeds as a syn addition with the formation of Z products. It is believed that the mechanism of syn addition of tellu rium tetrachloride includes the formation of a four mem bered cyclic transition state.4 For a long time, the syn addition of tellurium tetra chloride was considered to operate for all the acetylene hydrocarbons.2—4 However, recently it was found that the reaction of tellurium tetrachloride with unsubstituted acetylene proceeded as an anti addition and led to the products with E configuration.5—7 There is no other liter ature examples of the anti addition of tellurium tetra chloride to acetylene hydrocarbons. In the present work, we describe an example of the anti addition of tellurium tetrachloride to the internal hex 3 yne with highly stereoselective formation of the product with E configuration (Scheme 1). The product is the ear lier unknown E (4 chlorohex 3 en 3 yl)tellurium trichlo ride (1), its yield was 95%. The process was carried out upon heating of the equimolar amounts of reagents in tetrachloromethane. Apparently, in this case the anti addition proceeds through the formation of the intermediate three mem bered tellurirenium intermediate. The formation of such three membered intermediates was suggested in the reac tions of sulfenyl and selenenyl chlorides with alkynes, pro ceeding as electrophilic anti addition.8 The reduction of compound 1 with sodium meta bisulfite in a two phase system CCl4—H2O led to earlier unknown bis(E 4 chlorohex 3 en 3 yl) ditelluride (2) in 82% yield (see Scheme 1).

Allylation of acetylene under atmospheric pressure

We previously found that the reaction of acetylene with allyl bromide in aprotic solvents (DMSO, DMF, HMPA) in the presence of a base (K2CO3, alkali metal hydroxide) and a catalytic amount of CuI yields 60% of pent-1-en-4-yne (I) [2]. The reaction was carried out under an acetylene pressure of 10–14 atm. In continuation of these studies we have developed procedures for the synthesis of enyne I in up to 80% yield and of octa1,7-dien-4-yne (II) in up to 72% yield by cross-coupling of acetylene with allyl halides under atmospheric pressure in the presence of copper(I) iodide, base, and reducing agent.

Stereoselective synthesis of (E)-(2-bromovinyl)tellurium tribromide

There are a few published data on reactions of tellurium tetrabromide with acetylenes [1, 2]. The addition of TeBr4 to phenylacetylene and hept-1-yne was reported to give bis(2-bromo-2-phenylvinyl)tellurium dibromide and bis(2-bromohept-1-en-1-yl)tellurium dibromide in 89 and 70% yield, respectively, as mixtures of Z and E isomers, the former prevailing [1]. We have developed an efficient procedure for the synthesis of E,E-bis(2-bromovinyl)tellurium dibromide in 96% yield by reaction of tellurium tetrabromide with acetylene [2]. The reaction was carried out in chlorooform under an acetylene pressure of 12–14 atm at 40–70°C. The addition of tellurium tetrachloride to acetylene, depending on the conditions, led to the formation of both bisand monoadducts, E,E-bis(2-chlorovinyl) tellurium dichloride and E-(2-chlorovinyl)tellurium trichloride [3]. Unlike vinyltellurium trichlorides, vinyltellurium tribromides have not been reported previously. Z isomers [1, 4, 5]. We detected no possible Z-configured product in the reaction of tellurium tetrabromide with acetylene. The process was stereoselective anti-addition. Presumably, the reaction involves formation of three-membered cyclic tellurirenium intermediate, as in electrophilic anti-addition of sulfenyl and selenenyl halides to triple C≡C bond through thiirenium and selenirenium cations [6]. It is known that compounds containing a 2-bromovinyltellanyl group are used in stereoselective syntheses of alkenes via consecutive replacement of bromine and tellurium atoms by organic groups in cross-coupling reactions [4]. To conclude, we have developed an efficient procedure for the stereoselective synthesis of (E)-2-bromovinyltellurium tribromide (I) which is promising as intermediate product and building block for organic synthesis and is the first representative of previously unknown vinyltellurium tribromides. (E)-2-Bromovinyltellurium tribromide (I). Light grey powder which darkens on heating to 60–64°C and begins to decompose. H NMR spectrum, δ, ppm: 7.56 d and 7.92 d (1H each, J = 13.5 Hz). C NMR spectrum, δC, ppm: 120.04 (CHBr), 137.72 (TeCH). Found, %: C 4.88; H 0.38; Br 68.02; Te 27.45. C2H2Br4Te. Calculated, %: C 5.08; H 0.43; Br 67.54; Te 26.96. The H and C NMR spectra were recorded on a Bruker DPX-400 spectrometer at 400.13 and 100.61 MHz, respectively, using DMSO-d6 as solvent and hexamethyldisiloxane as internal reference. This study was performed in the framework of the Basic Research Program of the Russian Academy of ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 9, pp. 1397–1398.

Stereoselective addition of tellurium tetrachloride to 4-octyne

Reaction of tellurium tetrachloride with 4-octyne occurs as an anti-addition and leads to the formation of trichloro[(Е)-1-propyl-2-chloropent-1-enyl]tellane which was reduced sodium metabisulfite in a two-phase system C6Н6–H2O affording bis[(Е)-1-propyl-2-chloropent-1-enyl]ditellane.