Hydrotelluration of acetylenic esters: structural characterization of stereoisomers of methyl/ethyl β-(aryltelluro)acrylates

Abstract

Synthesis and complete characterization of some ester functionalized vinylic tellurides bearing an aryl ligand with varying steric and electronic effects bound to tellurium is described. Hydrotelluration of methyl propiolate using Ar₂Te₂/NaBH₄ in methanol results in a mixture of stereoisomers of methyl β-(aryltelluro)acrylates, ArTeCH=CHCOOMe (Ar = 4-MeOC₆H₄, 1A; 1-C₁₀H₇, 2A; 2,4,6-Me₃C₆H₂, 3A; C₅H₅FeC₅H₄, 4A; 4-Me₂NC₆H₄, 5A; and 2-C₄H₃S, 6A). The same reaction in ethanol provides isomeric mixtures of the ethyl esters ArTeCH=CHCOOEt (1B–6B). However, in the reactions between methyl propiolate and Ar₂Te₂ (Ar = 2,4,6-Me₃C₆H₂, 4-Me₂NC₆H₄) in isopropanol or t-butanol, no exchange of alkyl groups between the parent ester and the solvent is observed, instead detelluration of the Ar₂Te₂ to Ar₂Te is a competing reaction along with almost exclusive formation of the (Z)-isomers (3Aa, 5Aa). The geometry of the separated stereoisomers is established in solution, with the help of ¹H, ¹³C and ¹²⁵Te NMR spectrometry. Of particular interest is the observation that ¹²⁵Te chemical shifts {deshielded in (Z) compared to (E); Δδ = 106–136 ppm} and the geminal heteronuclear coupling constants {²J(¹H–¹²⁵Te) values for (E) are more than seven times that of the corresponding (Z) isomer} can be used to distinguish between liquid isomers. Structural characterization in the solid state by single-crystal X-ray diffraction for the 2Ba, 3Aa, 3Ba, 5Aa, 8 (Z)-isomers as well as for both stereoisomers of 4-Me₂NC₆H₄TeCH=CHCOOEt (5Ba and 5Bb) is also presented. The carbonyl O atom of the ester group is invariably involved, at least in the solid state, in a secondary bonding interaction with the Te(II) atom. While an intermolecular Te⋯O interaction gives rise to one-dimensional supramolecular arrays in the crystal lattice of 5Bb with (E) configuration, it is realized intramolecularly in the case of the (Z)-isomers due to the cis position of the chalcogen atoms.

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Introduction

The hydrotelluration of alkynes under reducing (Bu₂Te₂/NaBH₄/EtOH) or non reducing (Te⁰/BuLi/THF) conditions is highly regio- and stereoselective and is a commonly practiced method of preparing (Z)-vinylic tellurides. Compounds of this class have proved to be useful synthetic intermediates in transition metal catalyzed cross-coupling reactions and as precursors in the preparation of highly reactive vinyllithiums, vinylcuprates or vinylzinc chlorides with retention of double bond geometry via transmetallation.^1,2 In the hydrotelluration process, the aryl/alkyltellurium radical, RTe˙ and the hydrogen (from the alcohol used as reaction solvent) add to the alkynes and depending upon the nature of the substituent on the acetylene or the hydrotelluration reagent, the products often consist of mixtures of regio/stereoisomers. Thus, among terminal alkynes, while the aryl acetylenes are suitable substrates for the preparation of (Z)-vinylic tellurides, alkyl-substituted alkynes suffer from poor regioselectivity and give rise to a mixture of regioisomers, though the 1,2-addition product predominates.³ Hydrotelluration of propargylic alcohols and amines affords synthetically important allylic derivatives. In the case of the former, though the regioselectivity of the reaction is reported to favour the 1,2-addition, both the regioisomers have been characterized recently by NMR spectroscopy.⁴ On the other hand, hydrotelluration of tertiary propargyl amines was found to be highly regio- and stereospecific to afford (Z)-β-(organotelluro)allylic amines, but that of primary and secondary propargyl amines suffers from considerable loss of regiochemical control.⁵ While carbonyl functionalized alkynes were among the first to be studied under hydrotelluration reactions,⁶ there are only a few reports on the hydrotelluration of propargyl aldehydes⁷ and esters of propiolic acid^8–11 as a synthetic route to obtain β-tellurovinylcarbonyl compounds with well defined geometry. Instead, β-organyltellurovinyl aldehydes and ketones have been prepared by employing β-chlorovinylaldehydes/ketones or β-acylvinyltriethylammonium chlorides as precursors.^{12 125}Te chemical shifts (unlike δ ¹H values) and ¹H–¹²⁵Te coupling constants have scarcely been used to characterize the stereoisomers in the product of a hydrotelluration reaction of an alkyne. Also, among the known β-substituted vinylorganyltellurides which are mostly liquids or low-melting solids, structural characterization of only a few of these in solid state is limited to either the (Z)^12–15 or (E)^16–19 isomers and to the best of our knowledge is not reported for both the stereoisomers of a given vinylorganyltelluride.

Keeping with our interest in the synthesis of functionalized organotelluriums and in continuation to our studies on chlorotelluration of 1-alkynes using bulky substituents on Te and the terminal acetylenes,¹⁵ we report herein hydrotelluration of methyl propiolate under reducing conditions (Ar₂Te₂/NaBH₄/ROH; Ar = 4-MeOC₆H₄, 1-C₁₀H₇, 2,4,6-Me₃C₆H₂, (C₅H₅)FeC₅H₄, 4-Me₂NC₆H₄ and 2-C₄H₃S). Our aim was twofold, (i) to examine how the reaction solvent and the nature of the aryl ligand bound to tellurium affect the stereospecificity of acetylenic ester hydrotelluration and (ii) study the stereochemistry of the products in the solid state. Reactions of phenylacetylene are also included for comparison.

Results and discussion

Methyl propiolate, when subjected to hydrotelluration under reducing conditions in methanol afforded methyl β-(aryltelluro)acrylates, ArTeCH=CHCOOMe (Ar = 4-MeOC₆H₄, 1A; 1-C₁₀H₇, 2A; 2,4,6-Me₃C₆H₂, 3A; (C₅H₅)FeC₅H₄, 4A; 4-Me₂NC₆H₄, 5A; 2-C₄H₃S, 6A) (Scheme 1).

Scheme 1 Hydrotelluration of methyl propiolate and Z : E ratio in the products.

The ¹H NMR spectra recorded for the crude products showed the formation of both the (Z) and (E) stereoisomers in each case, but signals owing to the corresponding regioisomers were absent. The Z : E isomeric ratio (determined from the intensity of the ¹H NMR doublet due to the proton attached to the β-carbon) varied between 89 : 11 (1Aa : 1Ab) and 72 : 28 (5Aa : 5Ab). The same reaction was repeated in ethanol, iso-propanol and tertiary butanol in place of methanol. Interestingly, the reaction in ethanol provided the aryltellurated ethyl ester analogues, 1Ba–6Ba and 1Bb–6Bb in comparable yields. In the hydrotelluration reaction of methyl propiolate using dimesitylditelluride, or bis(4-(N,N-dimethylamino)phenyl)ditelluride in iso-propanol or tertiary butanol, detelluration of the ditelluride to the corresponding telluride, Ar₂Te (Ar = 3, 5) was a competing reaction along with the dominant formation of the (Z) isomers, 3Aa or 5Aa. The role of a Te moiety in the Me/Et exchange of the ester functionality appears to be little as the signal due to the methoxy protons of methyl propiolate (δ 3.80 ppm) was absent in the ¹H NMR spectrum of the isolated crude product of heating methyl propiolate with NaBH₄/EtOH in absence of a diarylditelluride. Hydrotelluration of phenylacetylene under the similar conditions, using the ditellurides with sterically demanding aryl ligands (2 and 3) gave exclusively the (Z)-isomers of ArTeCH=CHPh (Ar = 1-naphthyl, 7; mesityl, 8) in excellent yield. Compound 8 has been reported earlier²⁰ but lacks complete characterization, while the (E) isomer of 7 has been isolated as an oil in the reaction between (E)-β-(phenylvinyl)phenyliodonium tetrafluoroborate and (1-C₁₀H₇)₂Te₂/NaBH₄ in ethanol.²¹ Chromatographic separation of the stereoiosomers has been carried out on a silica column and complete structural characterization of each isomer was made by IR and NMR (¹H, ¹³C and ¹²⁵Te) spectroscopy and in the case of 2Ba, 3Aa, 3Ba, 5Aa, 5Ba, 5Bb and 8 by single-crystal X-ray diffraction techniques.

¹H NMR chemical shifts of the signals due to vinylic protons and their ³J(¹H–¹H) coupling constant are diagnostic of the regio- and stereochemistry of the isolated new β-(aryltelluro)acrylates. The vinylic proton attached to the tellurated β-carbon is appreciably deshielded {δ ranges between 8.59 (5Ab) and 8.18 (3Ba)} compared to the other attached to the ester functionalized vinylic carbon {δ ranges between 7.02 (3Aa) and 5.75 (3Ab)}. The magnitude of ³J(¹H–¹H) parameter for (E) isomers (lying in the range 12.0–16.5 Hz) is significantly higher compared to that of the corresponding (Z) isomers (lying in the range 8.0–9.6 Hz). The ¹H–¹²⁵Te magnetic couplings in the cases where measured, reveal an interesting trend. While the vicinal coupling constants are independent of the stereochemistry and have usual values {³J(¹H–¹²⁵Te) ≈ 12 Hz}, the geminal coupling constants are unusual and differ markedly in a pair of stereoisomers. A strong two-bond heteronuclear magnetic interaction may be inferred among the aryltellurated acrylates with E-geometry {²J(¹H–¹²⁵Te) = 74–91 Hz}, while it is very weak for their (Z) counterparts {²J(¹H–¹²⁵Te) ≤ 11 Hz}, even weaker than the three-bond heteronuclear coupling. This indicates significant intramolecular C=O⋯Te interaction for the Z-isomer in solution, effectively holding the C–Te–C=C fragment in the s-trans configuration, orientating the tellurium lone pair away from the geminal proton and resulting in a very low ²J(¹H–¹²⁵Te) coupling constant compared to the E-isomer.²² Considerable difference in the δ(¹²⁵Te) values in an isomeric pair is also observed, with significant deshielding of Te(II) nucleus in the (Z) isomer compared to that of (E) isomer (E/Z Δδ = 106–136 ppm), suggesting the carbonyl effects can be effectively transmitted in conjugative sense in the Z-geometry via an intramolecular ring possible due to a Te⋯O secondary bonding interaction. The ¹²⁵Te chemical shifts for 7 and 8 are comparable with other (Z) isomers reported herein suggesting similar influence, of the phenyl and alkoxycarbonyl β-substituents if any, on the shielding of the tellurium nucleus.

The CO stretching frequency of methyl acrylate (1732 cm⁻¹) is significantly lowered upon telluration, probably owing to the mass effect as well as due to Te←O=C coordinative interaction. This absorption appearing in the region 1718–1687 cm⁻¹ in the infrared spectrum of (E)-isomers is further shifted to a lower frequency in the corresponding (Z)-isomers (1680–1672 cm⁻¹). A comparison with the solution spectra, recorded for both the stereo isomers of methyl/ethyl β-(4-N,N-dimethylaminophenyltelluro)acrylates (5Aa and 5Ab/5Ba and 5Bb) reveals appreciable shifting of ν(CO) absorption to higher frequency in solution among the (E)-isomers [ν(CO), solution(solid): 5Ab, 1703(1687); 5Bb, 1713(1688) cm⁻¹], but little change in it in case of the (Z)-isomers [ν(CO), solution(solid): 5Aa, 1678(1680); 5Ba, 1674(1670) cm⁻¹]. Thus, while intramolecular coordinative interaction present in the solid state of the (Z)-isomers due to the cis position of the two chalcogen atoms is retained in solution as well, the weaker intermolecular Te←O interaction in the solid state among (E)-isomers appears to vanish in solution resulting in the observed enhancement in ν(CO). These conclusions are further substantiated from interatomic distances obtained from the single-crystal diffraction data presented herein.

Crystal structures

Single crystals of compounds, 2Ba, 3Aa, 3Ba, 5Aa, 5Ba, 5Bb and 8, were obtained by slow evaporation of a hexane or hexane/ethyl acetate solvent mixture at ambient temperature. The asymmetric unit in the crystal lattice of each of these compounds consists of a single molecule, other than 3Ba where there are two independent molecules in it. The relevant bond parameters are listed in Table 1 and the crystal data are given in Table 2. ORTEP diagrams of both stereo isomers of ethyl β-(4-N,N-dimethylaminophenyltelluro)acrylate (5Ba and 5Bb) are shown in Fig. 1 while those of 2Ba, 3Aa, 3Ba, 5Aa and 8 presented as Fig. S1–S5 are part of the ESI.†

Table 1 Relevant bond parameters (Å, °) in aryl(β-substituted vinyl)tellurides

Parameter	2Ba	3Aa	3Ba	5Aa	5Ba	5Bb	8
Te–C1	2.075(3)	2.075(2)	2.085(4), 2.076(4)	2.081(4)	2.073(2)	2.078(3)	2.094(3)
Te–Cx, x = 5, 6 or 9	2.140(3)	2.135(2)	2.141(4), 2.138(4)	2.114(4)	2.114(2)	2.108(3)	2.135(4)
C1–C2	1.337(5)	1.331(2)	1.334(6), 1.341(6)	1.335(5)	1.338(3)	1.324(3)	1.340(5)
Te⋯O1	2.849(3)	2.883(1)	2.842(3), 2.842(3)	2.970(2)	2.848(2)	—	—
C1–Te–Cx, x = 5, 6 or 9	90.9(1)	91.4(2)	92.0(2), 92.5(1)	90.6(1)	95.6(1)	93.3(1)	93.9(1)
Cx–Te⋯O1, x = 5 or 6	158.6(1)	158.8(1)	159.8(1), 159.2(1)	156.6(1)	163.6(2)	—	—

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Table 2 Crystallographic data and structure refinement parameters of aryl(β-substituted vinyl)tellurides

	2Ba	3Aa	3Ba	5Aa	5Ba	5Bb	8
Chemical formula	C15H14O2Te	C13H16O2Te	C14H18O2Te	C12H15NO2Te	C13H17NO2Te	C13H17NO2Te	C17H18Te
Formula weight	353.86	331.86	345.88	332.85	346.87	346.88	349.91
Crystal system	Orthorhombic	Monoclinic	Triclinic	Monoclinic	Monoclinic	Monoclinic	Monoclinic
Space group	Pbca	P21/n	P1̄	Pn	P21/n	P21/n	C2/c
a (Å)	16.6948(7)	5.63177(9)	7.4608(2)	7.969(5)	8.6633(3)	6.2387(2)	17.9956(6)
b (Å)	7.1386(4)	15.3211(3)	10.2199(3)	5.535(5)	11.3506(3)	12.7873(5)	10.9480(3)
c (Å)	23.0042(12)	15.0625(3)	18.9450(7)	14.965(5)	14.3428(5)	18.0003(8)	15.7185(5)
α (°)	90	90	88.279(3)	90	90	90	90
β (°)	90	98.566(2)	86.598(3)	103.239(5)	103.460(3)	93.021(4)	109.940(3)
γ (°)	90	90	79.657(2)	90	90	90	90
V (Å^3)	2741.6(2)	1285.16(4)	1418.28(8)	642.5(7)	1371.66(8)	1434.00(10)	2911.14(16)
Z	8	4	4	2	4	4	8
ρcalcd (Mg m^−3)	1.715	1.715	1.620	1.720	1.680	1.607	1.597
T (K)	100(2)	100(2)	120(2)	100(2)	173(2)	173(2)	120(2)
λ (Å)	0.71073	0.71073	0.71073	0.71073	0.71073	0.71073	1.54184
μ (MoKα, mm^−1)	2.161	2.298	2.086	2.301	2.159	2.065	15.950
F(000)	1376	648	680	324	680	680	1376
θ Range (°)	3.228–32.840	2.735–41.176	2.925–29.844	2.797–41.189	3.011–32.825	3.382–32.867	4.811–74.214
Index (hkl) ranges	−24 ≤ h ≤ 25, −10 ≤ k ≤ 10, −34 ≤ l ≤ 33	−5 ≤ h ≤ 10, −28 ≤ k ≤ 27, −27 ≤ l ≤ 27	−9 ≤ h ≤ 9, −13 ≤ k ≤ 13, −26 ≤ l ≤ 25	−13 ≤ h ≤ 14, −10 ≤ k ≤ 6, −27 ≤ l ≤ 27	−13 ≤ h ≤ 12, −17 ≤ k ≤ 17, −13 ≤ l ≤ 21	−8 ≤ h ≤ 9, −19 ≤ k ≤ 18, −24 ≤ l ≤ 27	−22 ≤ h ≤ 17, −13 ≤ k ≤ 12, −18 ≤ l ≤ 19
Reflection collected	34 454	19 013	22 076	8095	17 901	16 574	5951
Independent reflections	4822 (R(int) = 0.0852)	8312 (R(int) = 0.0315)	7036 (R(int) = 0.0430)	5439 (R(int) = 0.0297)	4708(R(int) = 0.0438)	4854 (R(int) = 0.0444)	2885 (R(int) = 0.0339)
Completeness to θmax (%)	94.4	97.0	86.1	97.4	92.4	90.4	97.2
Absorption correction	Multi-scan	Analytical	Analytical	Analytical	Multi-scan	Multi-scan	Analytical
Refinement method	Full-matrix least squares on F^2
Data/restraints/parameters	4822/0/164	8312/0/149	7036/0/315	5439/2/148	4708/0/158	4854/0/158	2885/0/166
GOF on F^2	1.068	1.082	1.035	0.992	1.071	1.128	1.077
Final R indices (I > 2 σ(I))	R1 = 0.0524, wR2 = 0.0942	R1 = 0.0334 wR2 = 0.0716	R1 = 0.0405, wR2 = 0.0846	R1 = 0.0317 wR2 = 0.0557	R1 = 0.0310 wR2 = 0.0643	R1 = 0.0310 wR2 = 0.0796	R1 = 0.0329 wR2 = 0.0844
R indices (all data)	R1 = 0.0736 wR2 = 0.1047	R1 = 0.0481 wR2 = 0.0799	R1 = 0.0584 wR2 = 0.0970	R1 = 0.0397 wR2 = 0.0607	R1 = 0.0451 wR2 = 0.0718	R1 = 0.0533 wR2 = 0.0865	R1 = 0.0356 wR2 = 0.0866
Max., min. residual electron density (e Å^−3)	1.763, −1.061	2.978, −1.190	3.011, −1.053	0.901, −0.930	0.707, −0.666	0.671, −0.796	2.669, −0.878

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Fig. 1 ORTEP diagrams for the isomeric pair of ethyl β-(4-N,N-dimethylaminophenyltelluro)acrylate. Hydrogen atoms other than the vinylic are omitted for clarity.

The observed molecular structures of the (β-aryltelluro)acrylates, ArTeCH=CHCOOR (Ar = 2, 3, 5; R = Me, Et) structurally characterized in the solid state in the present study, bearing a methyl/ethyl ester-functionalized vinyl ligand, are quite similar in the sense that Te(II) adopts a putative angular geometry with the Te–C_sp2 bonds subtending an angle slightly greater than 90° at the Te atom (∠C–Te–C ranges between 90.89(12)° in 2Ba and 95.63(8)° in 5Ba). In each case, all the skeletal atoms of the methyl/ethyl ester-functionalized vinyl ligand are nearly coplanar and the mean planes of the two organic ligands are almost orthogonal. Compound 8 also possesses Z-configuration at the carbon–carbon double bond and the ring plane of the phenyl substituent is inclined at 29.67° with the mean plane of the disubstituted alkene. The bond parameters of the organic ligands are influenced little by the steric and electronic effects of the aryl and alkoxy groups and the Te–C_vinyl bond is always the shorter of the two Te–C_sp2 bonds.

The C=C–C=O fragment of the trans disubstituted vinyl ligand, in case of the (E)-isomer of ethyl β-(4-N,N-dimethylaminophenyltelluro)acrylate (5Bb) has s-trans configuration but remarkably it adopts s-cis configuration in the cis disubstituted vinyl ligand present in the molecular structure of each of the (Z)-isomers structurally characterized in the solid state in the present study. Such a change in the orientation of the ester group may be attributed to the propensity of chalcogen atoms in these compounds with Z-geometry to be involved in an intramolecular Te⋯O(=C) secondary bonding interaction. The observed appreciably shorter interatomic distance between Te and carbonyl O atoms [d(Te, O) lies in the range 2.842(1) Å (3Ba)–2.969(2) Å (5Aa)] compared to the sum of van der Waals radii for Te and O [Σr_vdr(Te, O) = 3.60 Å] is in agreement to the conclusion based on the lower ν(CO) values for the (Z) isomers compared to that observed for the corresponding (E) isomer or their parent ester (vide supra). Furthermore, the measure of the angle at the ester-functionalized C_sp2 atom among the (Z)-isomers (∠C–C=C = 119.8(4)° in 3Ba–121.8(2)° in 5Aa) is close to the ideal value of 120°, compared with the larger values observed in case of 5Bb {125.1(3)°}, an (E)-isomer or 8 {127.8(3)°}, a (Z)-isomer lacking a carbonyl O atom. The latter compounds are devoid of such an intramolecular secondary bonding interaction. However, an appreciable closure approach observed between Te and carbonyl O atoms drawn from two different but adjacent molecules in the crystal lattice of 5Bb [d{Te, O1(1 + x, y, z)} = 3.278(1) Å < Σr_vdr(Te, O) = 3.60 Å] appears to qualify an attractive interaction between them. Such an intermolecular Te⋯O(=C) secondary bonding interaction cooperated with the C9–H9A⋯O1 hydrogen bonding interaction (H-bond parameters: D–H, H⋯A, D–A and ∠D–H⋯A are 0.950, 2.470(1), 3.101(1) Å and 123.8(1)° respectively) gives rise to a one-dimensional supramolecular self-assembly extended along a-axis (Fig. S6†). The observed linearity of the intra- as well as intermolecular C_aryl–Te⋯O_carbonyl triads (∠C–Te⋯O ranges between 156.6(1)° in 5Aa and 163.6(1)° in 5Ba) that makes an n(O)→σ*(Te–C) overlap feasible is indicative of the significant covalent contribution to the Te⋯O bonding interaction. The chelate effect owing to the formation of a five-membered ring as a consequence of the intramolecular Te⋯O bonding among the tellurated acrylates with Z-geometry may be attributed to the predominance of this isomeric form in their formation.

Experimental

Preparative work was performed under dry nitrogen. The solvents were purified by standard procedures prior to their use. Phenyl acetylene, methyl propiolate and tellurium powder were procured from Aldrich, while ferrocene, 1-bromonaphthalene, 2-bromomesitylene, 2-bromothiophene and N,N-dimethyl aniline were obtained from Merck. All were used as received. Diaryl ditellurides were prepared by the reported method.^8,23–26 Melting points were recorded in capillary tubes and are uncorrected. ¹H NMR spectra (300.13 MHz and 400.16 MHz) in CDCl₃ were recorded on Bruker DRX300 and Bruker Advance 400 Spectrometers using Me₄Si as the internal standard. Solution ¹³C{¹H} (100.54 MHz) and ¹²⁵Te{¹H} (126.19 MHz) NMR spectra were recorded in CDCl₃ on a JEOL Eclipse Plus 400 NMR spectrometer and are referenced to Me₄Si and Me₂Te. Microanalyses were carried out using a Carlo Erba 1108 analyser. IR spectra were recorded as KBr pellets for all the tellurides reported herein as well as that of the (Z)- and (E)-isomers of methyl/ethyl β-(4-N,N-dimethylaminophenyltelluro)acrylates (5Aa and 5Ab/5Ba and 5Bb) in CHCl₃ using a Perkin Elmer 577 spectrometer. The electrospray ionization-mass spectra (ESI-MS) of some representative compounds in acetonitrile solution were recorded on a Micromass Quattro II triple quadrupole mass spectrometer.

General procedure

Synthesis of methyl β-(aryltelluro)acrylates (ArTeCH=CHCOOMe, 1A–6A). The hydrotelluration of methyl propiolate with Ar₂Te₂/NaBH₄ was achieved in methanol under dry nitrogen. In a representative experiment, sodium borohydride powder (0.113 g, 3.0 mmol) was added in small portions to a stirred solution of the dianisylditelluride (0.469 g, 1.0 mmol) and the methyl propiolate (0.18 mL, 2 mmol) in dry deoxygenated methanol (25 mL) under nitrogen at room temperature until the red colored solution turned pale yellow. The reaction mixture was further refluxed for 3 h. The resulting solution was concentrated under reduced pressure and 60 mL of brine added. The organic material was extracted with ethyl acetate (4 × 15 mL) and the combined organic phase dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The residue was screened by ¹H NMR without purification to determine the isomeric ratio in the product. It was subjected to chromatographic separation of the (Z) and (E) isomers from the unreacted ditelluride on a silica column using hexane : ethyl acetate (100 : 0 to 80 : 20) mixtures as eluent. The usual work up of the fractions from column yielded isomerically pure methyl β-(anisyltelluro)acrylates 1Aa and 1Ab. The reactions using other ditellurides were carried out similarly.
1Aa. Pale yellow crystalline solid, yield: 0.351 g, 55%. M.p. 46–47 °C. Elemental analysis calcd (%) for C₁₁H₁₂O₃Te: C 41.31, H 3.78; found: C 41.56, H 3.74. ¹H NMR (300.13 MHz, CDCl₃, Me₄Si): δ 8.44 (d, ³J(¹H–¹H) = 9.3 Hz, 1H, vinyl, ²J(¹H–¹²⁵Te) = 10.0 Hz), 7.73 (d, ³J(¹H–¹H) = 8.7 Hz, 2H, anisyl o-H), 6.93 (d, ³J(¹H–¹H) = 9.3 Hz, 1H, vinyl, ³J(¹H–¹²⁵Te) = 14.0 Hz), 6.82 (d, ³J(¹H–¹H) = 8.7 Hz, 2H, anisyl m-H), 3.82 (s, 3H, anisyl OMe), 3.81 (s, 3H, ester OMe) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 169.3 (CO), 160.0, 142.0, 140.2, 121.7, 115.2, 109.0 (anisyl and vinyl), 55.1 (anisyl OMe), 52.0 (ester OMe) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 728 ppm. IR (KBr, cm⁻¹): 1680 ν(C=O). ESI-MS: m/z calcd for C₁₁H₁₃O₄Te: 338.9 [M + OH]⁺; found: 339.0.
1Ab. Pale yellow crystalline solid, yield: 0.014 g, 2%. M.p. 51–52 °C. ¹H NMR (300.13 MHz, CDCl₃, Me₄Si): δ 8.56 (d, ³J(¹H–¹H) = 16.2 Hz, 1H, vinyl, ²J(¹H–¹²⁵Te) = 74.0 Hz), 7.72 (d, ³J(¹H–¹H) = 9.0 Hz, 2H, anisyl o-H), 6.85 (d, ³J(¹H–¹H) = 9.0 Hz, 2H, anisyl m-H), 6.04 (d, ³J(¹H–¹H) = 16.2 Hz, 1H, vinyl, ³J(¹H–¹²⁵Te) = 13.0 Hz), 3.83 (s, 3H, anisyl OMe), 3.68 (s, 3H, ester OMe) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 164.9 (CO), 160.7, 142.0, 130.8, 127.2, 116.0, 100.1 (anisyl and vinyl), 55.2 (anisyl OMe), 51.5 (OMe) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 613 ppm. IR (KBr, cm⁻¹): 1701 ν(C=O). ESI-MS: m/z calcd for C₁₁H₁₃O₄Te: 338.9 [M + OH]⁺; found: 339.0.
2Aa. Pale yellow powder, yield: 0.385 g, 57%. M.p. 55–56 °C. Elemental analysis calcd (%) for C₁₄H₁₂O₂Te: C 49.48, H 3.56; found: C 49.67, H 3.52. ¹H NMR (300.13 MHz, CDCl₃, Me₄Si): δ 8.41 (d, ³J = 9.3 Hz, 1H, vinyl), 8.27–8.30 (m, 1H, naphthyl), 8.18 (dd, ³J = 1.2 Hz, ³J = 1.2 Hz, 1H, naphthyl), 7.89 (d, ³J = 8.1 Hz 1H, naphthyl), 7.48–7.84 (m, 3H, naphthyl), 7.36 (t, 1H, naphthyl), 6.98 (d, ³J = 9.3 Hz, 1H, vinyl), 3.85 (s, 3H, OMe) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 169.5 (CO), 141.0, 139.7, 136.2, 133.6, 132.3, 130.0, 128.9, 126.9, 126.2, 122.2, 122.0 (naphthyl and vinyl), 52.0 (OMe) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 636 ppm. IR (KBr, cm⁻¹): 1673 ν(C=O).
2Ab. Yellow oil, yield: 0.019 g, 3%. ¹H NMR (300.13 MHz, CDCl₃, Me₄Si): δ 8.56 (d, ³J = 16.5 Hz, 1H, vinyl), 8.18 (t, 2H, naphthyl), 7.95 (d, ³J = 8.1 Hz, 1H, naphthyl), 7.51–7.85 (m, 3H, naphthyl), 7.38 (t, 1H, naphthyl), 5.96 (d, ³J = 16.5 Hz, 1H, vinyl), 3.63 (s, 3H, OMe) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 164.8 (CO), 141.3, 136.0, 133.7, 132.1, 131.1, 129.2, 128.1, 128.0, 127.6, 126.7, 126.6, 114.4 (naphthyl and vinyl), 51.5 (OMe) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 516 ppm. IR (KBr, cm⁻¹): 1707 ν(C=O).
3Aa. Pale yellow crystalline solid, yield: 0.394 g, 59%. M.p. 85–87 °C. Elemental analysis calcd (%) for C₁₃H₁₆O₂Te: C 47.05, H 4.86; found: C 47.32, H 4.80. ¹H NMR (400.16 MHz, CDCl₃, Me₄Si): δ 8.21 (d, ³J(¹H–¹H) = 8.0 Hz, 1H, vinyl, ²J(¹H–¹²⁵Te) = 10.0 Hz), 7.01 (s, 2H, mesityl m-H), 6.99 (d, ³J(¹H–¹H) = 8.0 Hz, 1H, vinyl, ³J(¹H–¹²⁵Te) = 13.0 Hz), 3.85 (s, 3H, OMe), 2.56 (s, 6H, o-Me), 2.32 (s, 3H, p-Me) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 169.5 (CO), 144.7, 140.9, 139.2, 127.6, 122.3, 122.0 (mesityl and vinyl), 51.9 (OMe), 29.3 (o-Me), 20.9 (p-Me) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 516 ppm. IR (KBr, cm⁻¹): 1675 ν(C=O).
3Ab. Yellow powder, yield: 0.019 g, 3%. M.p. 44–46 °C. ¹H NMR (400.16 MHz, CDCl₃, Me₄Si): δ 8.51 (d, ³J(¹H–¹H) = 16.0 Hz, 1H, vinyl, ²J(¹H–¹²⁵Te) = 90.0 Hz), 6.91 (s, 2H, mesityl m-H), 5.80 (d, ³J(¹H–¹H) = 16.0 Hz, 1H, vinyl, ³J(¹H–¹²⁵Te) = 12.0 Hz), 3.60 (s, 3H, OMe), 2.47 (s, 6H, o-Me), 2.23 (s, 3H, p-Me) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 165.0 (CO), 145.4, 140.3, 129.8, 127.9, 126.2, 115.6 (mesityl and vinyl), 51.4 (OMe), 29.0 (o-Me), 21.0 (p-Me) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 387 ppm. IR (KBr, cm⁻¹): 1709 ν(C=O).
4Aa. Orange crystalline solid, yield: 0.486 g, 61%. M.p. 98–99 °C. Elemental analysis calcd (%) for C₁₄H₁₄FeO₂Te: C 42.28, H 3.55; found: C 42.53, H 3.53. ¹H NMR (300.13 MHz, CDCl₃, Me₄Si): δ 8.40 (d, ³J(¹H–¹H) = 9.6 Hz, 1H, vinyl, ²J(¹H–¹²⁵Te) = 8.0 Hz), 6.85 (d, ³J(¹H–¹H) = 9.6 Hz, 1H, vinyl, ³J(¹H–¹²⁵Te) = 12.0 Hz), 4.38 (t, 2H, ferrocenyl), 4.27 (t, 2H, ferrocenyl), 4.18 (s, 5H, ferrocenyl), 3.81 (s, 3H, OMe) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 169.5 (CO), 143.2, 121.1 (vinyl), 78.3, 71.3, 69.0, 51.9 (ferrocenyl), 50.2 (OMe) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 585 ppm. IR (KBr, cm⁻¹): 1677 ν(C=O). ESI-MS: m/z calcd for C₁₄H₁₅FeO₂Te: 398.9 [M + H]⁺, found: 398.4; m/z calcd for C₁₄H₁₇FeO₃Te: 416.9 [M + H₂O + H]⁺, found: 417.2.
4Ab. Yellow powder, yield: 0.032 g, 4%. M.p. 124–126 °C. ¹H NMR (400.16 MHz, CDCl₃, Me₄Si): δ 8.46 (d, ³J(¹H–¹H) = 16.5 Hz, 1H, vinyl, ²J(¹H–¹²⁵Te) = 77.0 Hz), 6.05 (d, ³J(¹H–¹H) = 16.5 Hz, 1H, vinyl, ³J(¹H–¹²⁵Te) = 11.0 Hz), 4.39 (t, 2H, ferrocenyl), 4.34 (t, 2H, ferrocenyl), 4.19 (s, 5H, ferrocenyl), 3.67 (s, 3H, OMe) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 164.9 (CO), 131.7, 127.0 (vinyl), 79.1, 72.2, 69.3, 51.4 (ferrocenyl), 43.3 (OMe) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 464 ppm. IR (KBr, cm⁻¹): 1718 ν(C=O).
5Aa. Pale yellow crystalline solid, yield: 0.395 g, 59%. M.p. 99–100 °C. Elemental analysis calcd (%) for C₁₂H₁₅NO₂Te: C 43.30, H 4.54, N 4.21; found: C 43.53, H 4.52, N 4.10. ¹H NMR (400.16 MHz, CDCl₃, Me₄Si): δ 8.50 (d, ³J = 8.0 Hz, 1H, vinyl), 7.70 (d, ³J = 12.0 Hz, 2H, N,N-dimethylaniline o-H), 6.93 (d, ³J = 8.0 Hz, 1H, vinyl), 6.65 (d, ³J = 12.0 Hz, 2H, N,N-dimethylaniline m-H), 3.83 (s, 3H, OMe), 2.99 (s, 6H, NMe₂) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 169.2 (CO), 150.5, 143.0, 140.1, 121.4, 113.3, 103.0 (N,N-dimethylaniline and vinyl), 51.8 (OMe), 40.2 (NMe₂) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 715 ppm. IR (KBr, cm⁻¹): 1680 ν(C=O). ESI-MS: m/z calcd for C₁₂H₁₆NO₂Te: 336.0 [M + H]⁺; found: 336.0.
5Ab. Pale yellow crystalline solid, yield: 0.035 g, 5%. M.p. 119–120 °C. ¹H NMR (400.16 MHz, CDCl₃, Me₄Si): δ 8.59 (d, ³J = 16.0 Hz, 1H, vinyl), 7.64 (d, ³J = 12.0 Hz, 2H, N,N-dimethylaniline o-H), 6.64 (d, ³J = 12.0 Hz, 2H, N,N-dimethylaniline m-H), 6.04 (d, ³J = 16.0 Hz, 1H, vinyl), 3.70 (s, 3H, OMe), 3.03 (s, 6H, NMe₂) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 165.0 (CO), 151.0, 141.8, 132.0, 126.7, 113.7, 94.0 (N,N-dimethylaniline and vinyl), 51.4 (OMe), 40.1 (NMe₂) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 594 ppm. IR (KBr, cm⁻¹): 1687 ν(C=O). ESI-MS: m/z calcd for C₁₂H₁₆NO₂Te: 336.0 [M + H]⁺; found: 336.0.
6Aa. Pale yellow crystalline solid, yield: 0.338 g, 57%. M.p. 43–45 °C. Elemental analysis calcd (%) for C₈H₈SO₂Te: C 32.48, H 2.73; found: C 32.72, H 2.70. ¹H NMR (400.16 MHz, CDCl₃, Me₄Si): δ 8.43 (d, ³J(¹H–¹H) = 8.0 Hz, 1H, vinyl, ²J(¹H–¹²⁵Te) = 8.0 Hz), 7.43 (d, ³J(¹H–¹H) = 4.0 Hz, 1H, thiophene), 7.37 (d, ³J(¹H–¹H) = 4.0 Hz, 1H, thiophene), 6.93 (dd, 1H, thiophene), 6.95 (d, ³J(¹H–¹H) = 8.0 Hz, 1H, vinyl, ³J(¹H–¹²⁵Te) = 14.0 Hz), 3.76 (s, 3H, OMe) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 170.0 (CO), 143.2, 140.4, 133.8, 128.9, 121.5, 108.0 (thiophene and vinyl), 52.2 (OMe) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 610 ppm. IR (KBr, cm⁻¹): 1672 ν(C=O). ESI-MS: m/z calcd for C₈H₉O₃STe: 314.9 [M + OH]⁺, found: 315.4; m/z calcd for C₄H₅O₂Te: 215.0 [MeOOCCH=CHTe]⁺, found: 215.4.
6Ab. Yellow oil, yield: 0.018 g, 3%. ¹H NMR (400.16 MHz, CDCl₃, Me₄Si): δ 8.57 (d, ³J = 16.0 Hz, 1H, vinyl), 7.58 (d, ³J = 4.0 Hz, 1H, thiophene), 7.50 (d, ³J = 4.0 Hz, 1H, thiophene), 7.06 (dd, 1H, thiophene), 6.05 (d, ³J = 16.0 Hz, 1H, vinyl), 3.69 (s, 3H, OMe) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 164.8 (CO), 142.9, 136.0, 130.5, 129.5, 127.7, 123.8 (thiophene and vinyl), 51.6 (OMe) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 475 ppm. IR (KBr, cm⁻¹): 1717 ν(C=O).

Synthesis of ethyl β-(aryltelluro)acrylates (ArTeCH=CHCOOEt) 1B–6B. Compounds 1B–6B were prepared following the similar procedure mentioned above, except ethanol was used in the place of methanol as the solvent. The isolated crude products were almost all solids except 1B, 2B and 6B.
1Ba. Pale yellow crystalline solid, yield: 0.335 g, 50%. M.p. 30–31 °C. Elemental analysis calcd (%) for C₁₂H₁₄O₃Te: C 43.17, H 4.23; found: C 43.53, H 4.20. ¹H NMR (300.13 MHz, CDCl₃, Me₄Si): δ 8.42 (d, ³J(¹H–¹H) = 9.3 Hz, 1H, vinyl, ²J(¹H–¹²⁵Te) = 9.0 Hz), 7.73 (d, ³J(¹H–¹H) = 8.7 Hz, 2H, anisyl o-H), 6.92 (d, ³J(¹H–¹H) = 9.3 Hz, 1H, vinyl, ³J(¹H–¹²⁵Te) = 14.0 Hz), 6.82 (d, ³J(¹H–¹H) = 8.7 Hz, 2H, anisyl m-H), 4.27 (q, ³J = 7.2 Hz, 2H, OCH₂), 3.81 (s, 3H, OMe), 1.32 (t, ³J = 7.2 Hz, 3H, Me) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 169.0 (CO), 160.0, 141.5, 140.2, 122.1, 115.2, 109.1 (anisyl and vinyl), 61.0 (OCH₂), 55.1 (OMe), 14.3 (Me) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 726 ppm. IR (KBr, cm⁻¹): 1674 ν(C=O).
1Bb. Yellow oil, yield: 0.013 g, 2%. ¹H NMR (300.13 MHz, CDCl₃, Me₄Si): δ 8.54 (d, ³J(¹H–¹H) = 16.2 Hz, 1H, vinyl), 7.65 (d, ³J(¹H–¹H) = 8.7 Hz, 2H, anisyl o-H), 6.73 (d, ³J(¹H–¹H) = 8.7 Hz, 2H, anisyl m-H), 6.05 (d, ³J(¹H–¹H) = 16.2 Hz, 1H, vinyl), 4.15 (q, ³J = 7.2 Hz, 2H, OCH₂), 3.82 (s, 3H, OMe), 1.27 (t, ³J = 7.2 Hz, 3H, Me) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 164.7 (CO), 160.6, 145.4, 144.8, 127.5, 115.9, 102.0 (anisyl and vinyl), 60.4 (OCH₂), 55.2 (OMe), 14.2 (Me) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 611 ppm. IR (KBr, cm⁻¹): 1710 ν(C=O).
2Ba. Pale yellow crystalline solid, yield: 0.349 g, 49%. M.p. 48–50 °C. Elemental analysis calcd (%) for C₁₅H₁₄O₂Te: C 50.91, H 3.99; found: C 50.74, H 3.96. ¹H NMR (300.13 MHz, CDCl₃, Me₄Si): δ 8.40 (d, ³J = 9.6 Hz, 1H, vinyl), 8.29–7.36 (m, 7H, naphthyl), 6.98 (d, ³J = 9.6 Hz, 1H, vinyl), 4.31 (q, ³J = 7.2 Hz, 2H, OCH₂), 1.35 (t, ³J = 7.2 Hz, 3H, Me) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 169.0 (CO), 140.3, 139.6, 136.2, 133.5, 132.2, 129.9, 128.8, 126.8, 126.2, 122.6, 122.2 (naphthyl and vinyl), 61.0 (OCH₂), 14.3 (Me) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 634 ppm. IR (KBr, cm⁻¹): 1672 ν(C=O). ESI-MS: m/z calcd for C₁₅H₁₅O₃Te: 373.0 [M + OH]⁺; found: 373.3, m/z calcd for C₅H₇O₂Te: 229.0 [EtOOCCH=CHTe]⁺; found: 229.2.
2Bb. Yellow oil, yield: 0.015 g, 2%. ¹H NMR (300.13 MHz, CDCl₃, Me₄Si): δ 8.55 (d, ³J = 16.5 Hz, 1H, vinyl), 7.38–8.27 (m, 7H, naphthyl), 5.96 (d, ³J = 16.5 Hz, 1H, vinyl), 4.09 (q, ³J = 7.2 Hz, 2H, OCH₂), 1.20 (t, ³J = 7.2 Hz, 3H, Me) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 169.1 (CO), 140.4, 139.7, 136.3, 133.6, 132.3, 130.0, 128.9, 126.9, 126.3, 122.7, 122.2 (naphthyl and vinyl), 61.0 (OCH₂), 14.4 (Me) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 512 ppm. IR (KBr, cm⁻¹): 1708 ν(C=O).
3Ba. Pale yellow crystalline solid, yield: 0.352 g, 51%. M.p. 66–68 °C. Elemental analysis calcd (%) for C₁₄H₁₈O₂Te: C 48.61, H 5.25; found: C 48.94, H 5.20. ¹H NMR (300.13 MHz, CDCl₃, Me₄Si): δ 8.18 (d, ³J = 9.3 Hz, 1H, vinyl), 6.98 (s, 2H, mesityl m-H), 6.98 (d, ³J = 9.3 Hz, 1H, vinyl), 4.28 (q, ³J = 7.2 Hz, 2H, OCH₂), 2.55 (s, 6H, o-Me), 2.29 (s, 3H, p-Me), 1.33 (t, ³J = 7.2 Hz, 3H, Me) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 169.0 (CO), 144.7, 140.4, 139.1, 127.5, 122.6, 122.2, (mesityl and vinyl), 60.7 (OCH₂), 29.3 (o-Me), 20.9 (p-Me), 14.3 (Me) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 514 ppm. IR (KBr, cm⁻¹): 1676 ν(C=O). ESI-MS: m/z calcd for C₁₄H₁₉O₃Te: 365.0 [M + OH]⁺; found: 365.3, m/z calcd for C₅H₇O₂Te: 228.9 [EtOOCCH=CHTe]⁺; found: 229.3.
3Bb. Yellow oil, 0.016 g, 2%. ¹H NMR (300.13 MHz, CDCl₃, Me₄Si): δ 8.47 (d, ³J(¹H–¹H) = 16.0 Hz, 1H, vinyl, ²J(¹H–¹²⁵Te) = 91.0 Hz), 6.88 (s, 2H, mesityl m-H), 5.78 (d, ³J(¹H–¹H) = 16.0 Hz, 1H, vinyl, ³J(¹H–¹²⁵Te) = 12.0 Hz), 4.04 (q, ³J = 7.2 Hz, 2H, OCH₂), 2.28 (s, 6H, o-Me), 2.19 (s, 3H, p-Me), 1.19 (t, ³J = 7.2 Hz, 3H, Me) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 164.5 (CO), 145.3, 140.1, 129.1, 127.8, 126.6, 115.5 (mesityl and vinyl), 60.1 (OCH₂), 29.0 (o-Me), 21.0 (p-Me), 14.1 (Me) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 384 ppm. IR (KBr, cm⁻¹): 1717 ν(C=O).
4Ba. Orange crystalline solid, yield: 0.448 g, 54%. M.p. 79–80 °C. Elemental analysis calcd (%) for C₁₅H₁₆FeO₂Te: C 43.76, H 3.92; found: C 43.98, H 3.89. ¹H NMR (300.13 MHz, CDCl₃, Me₄Si): δ 8.39 (d, ³J = 9.6 Hz, 1H, vinyl), 6.85 (d, ³J = 9.6 Hz, 1H, vinyl), 4.23–4.31 (m, 6H (2H for OCH₂ and 4H for ferrocenyl)), 4.17 (s, 5H, ferrocenyl), 1.32 (t, ³J = 7.2 Hz, 3H, Me) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 169.2 (CO), 142.7, 121.6 (vinyl), 78.3, 71.3, 69.0, 60.9 (ferrocenyl), 50.3 (OCH₂), 14.3 (Me) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 582 ppm. IR (KBr, cm⁻¹): 1673 ν(C=O).
4Bb. Yellow solid, yield: 0.026 g, 3%. M.p. 61–62 °C. ¹H NMR (300.13 MHz, CDCl₃, Me₄Si): δ 8.45 (d, ³J = 16.5 Hz, 1H, vinyl), 6.10 (d, ³J = 16.5 Hz, 1H, vinyl), 4.33–4.40 (m, 6H, (2H for OCH₂ and 4H for ferrocenyl)), 4.19 (s, 5H, ferrocenyl), 1.23 (t, ³J = 7.2 Hz, 3H, Me) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 166.2 (CO), 146.8, 121.0 (vinyl), 79.0, 71.4, 69.3, 69.1 (ferrocenyl), 50.20 (OCH₂), 14.31 (Me) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 475 ppm. IR (KBr, cm⁻¹): 1713 ν(C=O).
5Ba. Pale yellow crystalline solid, yield: 0.368 g, 53%. M.p. 93–94 °C. Elemental analysis calcd (%) for C₁₃H₁₇NO₂Te: C 45.01, H 4.94, N 4.04; found: C 45.23, H 4.92, N 4.01. ¹H NMR (300.13 MHz, CDCl₃, Me₄Si): δ 8.45 (d, ³J(¹H–¹H) = 9.6 Hz, 1H, vinyl, ²J(¹H–¹²⁵Te) = 9.0 Hz), 7.66 (d, ³J(¹H–¹H) = 9.0 Hz, 2H, N,N-dimethylaniline o-H), 6.90 (d, ³J(¹H–¹H) = 9.6 Hz, 1H, vinyl, ³J(¹H–¹²⁵Te) = 13.0 Hz), 6.61 (d, ³J(¹H–¹H) = 9.0 Hz, 2H, N,N-dimethylaniline m-H), 4.26 (q, ³J = 7.2 Hz, 2H, OCH₂), 2.96 (s, 6H, NMe₂), 1.32 (t, ³J = 7.2 Hz, 3H, Me) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 168.8 (CO), 150.4, 142.4, 140.0, 121.8, 113.3, 103.2 (N,N-dimethylaniline and vinyl), 60.7 (OCH₂), 40.2 (N–Me), 14.3 (Me) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 712 ppm. IR (KBr, cm⁻¹): 1670 ν(C=O). ESI-MS: m/z calcd for C₁₃H₁₈NO₂Te: 350.0 [M + H]⁺, found: 350.1; m/z calcd for C₁₃H₁₈NO₃Te: 366.0 [M + OH]⁺, found: 366.0.
5Bb. Pale yellow crystalline solid, yield: 0.030 g, 4%. M.p. 74–76 °C. ¹H NMR (300.13 MHz, CDCl₃, Me₄Si): δ 8.56 (d, ³J(¹H–¹H) = 16.5 Hz, 1H, vinyl, ²J(¹H–¹²⁵Te) = 78.0 Hz), 7.63 (d, ³J(¹H–¹H) = 9.0 Hz, 2H, N,N-dimethylaniline o-H), 6.63 (d, ³J(¹H–¹H) = 9.0 Hz, 2H, N,N-dimethylaniline m-H), 6.02 (d, ³J(¹H–¹H) = 16.5 Hz, 1H, vinyl, ³J(¹H–¹²⁵Te) = 13.0 Hz), 4.13 (q, ³J = 7.2 Hz, 2H, OCH₂), 2.99 (s, 6H, NMe), 1.24 (t, ³J = 7.2 Hz, 3H, Me) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 164.6 (CO), 150.9, 141.8, 131.4, 127.2, 113.7, 94.0 (N,N-dimethylaniline and vinyl), 60.2 (OCH₂), 40.1 (NMe₂), 14.2 (Me) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 591 ppm. IR (KBr, cm⁻¹): 1688 ν(C=O). ESI-MS: m/z calcd for C₁₃H₁₈NO₂Te: 350.0 [M + H]⁺, found: 350.0.
6Ba. Yellow oil, yield: 0.299 g, 49%. Elemental analysis calcd (%) for C₉H₁₀O₂STe: C 34.89, H 3.25; found: C 34.98, H 3.22. ¹H NMR (400.16 MHz, CDCl₃, Me₄Si): δ 8.40 (d, ³J(¹H–¹H) = 8.0 Hz, 1H, vinyl, ²J(¹H–¹²⁵Te) = 8.0 Hz), 7.43 (d, ³J(¹H–¹H) = 4.0 Hz, 1H, thiophene), 7.36 (d, ³J(¹H–¹H) = 4.0 Hz, 1H, thiophene), 6.93 (dd, 1H, thiophene), 6.94 (d, ³J(¹H–¹H) = 8.0 Hz, 1H, vinyl, ³J(¹H–¹²⁵Te) = 14.0 Hz), 4.23 (q, ³J = 7.2 Hz, 2H, OCH₂), 1.26 (t, ³J = 7.2 Hz, 3H, Me) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 169.5 (CO), 142.7, 140.3, 133.8, 128.8, 121.9, 108.2 (thiophene and vinyl), 61.2 (OCH₂), 14.3 (Me) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 608 ppm. IR (KBr, cm⁻¹): 1667 ν(C=O).
6Bb. Yellow oil, yield: 0.014 g, 2%. ¹H NMR (400.16 MHz, CDCl₃, Me₄Si): δ 8.44 (d, ³J = 12.0 Hz, 1H, vinyl), 7.52 (d, ³J = 4.0 Hz, 1H, thiophene), 7.45 (d, ³J = 4.0 Hz, 1H, thiophene), 7.03 (dd, 1H, thiophene), 6.97 (d, ³J = 12.0 Hz, 1H, vinyl), 4.32 (q, ³J = 7.2 Hz, 2H, OCH₂), 1.36 (t, ³J = 7.2 Hz, 3H, Me) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 164.3 (CO), 142.8, 136.0, 130.1, 129.5, 128.2, 121.9 (thiophene and vinyl), 60.9 (OCH₂), 14.2 (Me) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 472 ppm. IR (KBr, cm⁻¹): 1713 ν(C=O).

Synthesis of arylvinyltellurides (ArTeCH=CHPh). Hydrotelluration of phenyl acetylene (0.21 mL, 2 mmol) in ethanol using dinaphthyl- or dimesitylditelluride (1 mmol) following the general procedure gave 7 or 8 as yellow solid.
7. (Ar = 1-C₁₀H₇). Yield: 0.467 g, 65%. M.p. 38–40 °C. Elemental analysis calcd (%) for C₁₈H₁₄Te: C 60.41, H 3.94; found: C 60.64, H 3.88. ¹H NMR (400.16 MHz, CDCl₃, Me₄Si): δ 8.23 (d, ³J = 8.0 Hz, 1H, naphthyl), 8.14 (d, ³J = 8.0 Hz, 1H, naphthyl), 7.79–7.86 (dd, ³J = 8.0 Hz, ³J = 8.0 Hz, 2H, naphthyl), 7.21–7.55 (m, 8H, aryl), 7.48 (d, ³J = 8.0 Hz, 1H, vinyl), 7.03 (d, ³J = 8.0 Hz, 1H, vinyl) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 139.1, 138.9, 136.9, 135.9, 133.6, 132.1, 129.8, 128.8, 128.5, 127.5, 127.5, 127.0, 126.3, 126.3, 118.3, 108.9 (aryl and vinyl) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 451 ppm. ESI-MS: m/z calcd for C₁₈H₁₅OTe: 377.0 [M + OH]⁺, found: 377.3.
8. (2,4,6-Me₃C₆H₂). Yield: 0.463 g, 66%. M.p. 88–89 °C. Elemental analysis calcd (%) for C₁₇H₁₈Te: C 58.35, H 5.18; found: C 58.43, H 5.16. ¹H NMR (400.16 MHz, CDCl₃, Me₄Si): δ 7.31 (d, ³J = 8.0 Hz, 1H, vinyl), 7.22–7.43 (m, 5H, Ph), 6.98 (s, 2H, mesityl, m-H), 6.77 (d, ³J = 8.0 Hz, 1H, vinyl), 2.57 (s, 6H, o-Me), 2.29 (s, 3H, p-Me) ppm. ¹³C{¹H} NMR (100.54 MHz, CDCl₃, Me₄Si): δ 144.8, 139.2, 139.0, 136.0, 128.4, 127.5, 127.2, 119.3, 109.1 (aryl and vinyl), 29.5 (o-Me), 20.9 (p-Me) ppm. ¹²⁵Te{¹H} NMR (126.19 MHz, CDCl₃, Me₂Te): δ 337 ppm. ESI-MS: m/z calcd for C₁₇H₁₉OTe: 369.0 [M + OH]⁺, found: 369.1.

Crystallography

Single crystals of compounds 2Ba, 3Aa, 3Ba, 5Aa, 5Ba, 5Bb and 8 were obtained by slow evaporation of hexane and hexane : ethyl acetate solvent mixture at ambient temperature. Intensity data for the crystals of 2Ba, 5Ba and 5Bb were collected on a Xcalibur, EOS, Gemini diffractometer equipped with a graphite monochromated Mo-Kα radiation (λ = 0.71073 Å), while data for crystal of other compounds was collected on a Supernova dual Atlas diffractometer system using Mo-Kα radiation (λ = 0.71073 Å for 3Aa, 3Ba and 5Aa and Cu-Kα radiation (λ = 1.54184 Å for 8)). CrysAlisPro²⁷ was used for data collection, cell refinement and data reduction with either empirical or analytical absorption corrections applied. The structures were solved by direct methods and difference Fourier synthesis using Sir92 (ref. 28) or Superflip.²⁹ SHELXL³⁰ was used to perform full-matrix least-squares refinements on F², using all data, with anisotropic displacement parameters applied to non-hydrogen atoms. Hydrogen atoms attached to carbon were included in geometrically calculated positions using a riding model and were refined isotropically. Figures of molecular structures showing 50% probability displacement ellipsoids were generated using ORTEP-3 version 2.02.†³¹

Conclusions

Hydrotelluration of methyl propiolate using Ar₂Te₂/NaBH₄ in methanol provides stereoisomers of arylvinyltellurides, ArTeCH=CHCOOMe. In ethanol, however the corresponding ethyl esters ArTeCH=CHCOOEt are formed while in higher alcohols detelluration to result in the diaryltellurides, Ar₂Te, is a strongly competing reaction and the alkyl group of the ester functionality remains unaltered. The presence of sterically demanding aryl ligands at Te, while not affecting the mode of hydrotelluration, tends to provide crystalline products suitable for X-ray analysis. The present study signifies the usefulness of δ(¹²⁵Te) and ²J(¹H–¹²⁵Te) NMR parameters in distinguishing the stereoisomers, especially when the products are oils or in absence of suitable crystals for X-ray diffraction. The secondary bonding Te⋯O(C) interaction observed, at least in the solid state, among the (Z)-vinylic tellurides appears to improve the stereospecificity of the hydrotelluration reaction of carbonyl functionalized alkynes towards Z-geometry.

Acknowledgements

B. S. thanks University Grant Commission, New Delhi, India, for the award of ‘Dr D. S. Kothari post-doctoral fellowship’. The structure solutions provided by Dr Jerry Jasinski for compounds 2Ba, 5Ba and 5Bb and Dr Jan Wikaira for 8 is gratefully acknowledged.

Notes and references

1. G. Zeni, D. S. Lüdtke, R. B. Panatieri and A. L. Braga, Chem. Rev., 2006, 106, 1032.
2. J. L. Princival, A. A. D. Santos and J. V. Comasseto, J. Braz. Chem. Soc., 2010, 21, 2042.
3. S. M. Barros, M. J. Dabdoub, V. M. B. Dabdoub and J. V. Comasseto, Organometallics, 1989, 8, 1661.
4. J. C. R. Freitas, D. J. Palmeira, R. A. Oliveira, P. H. Menezes and R. O. Silva, Magn. Reson. Chem., 2012, 50, 481.
5. G. Zeni, O. S. do R. Barros, A. V. Moro, A. L. Braga and C. Peppe, Chem. Commun., 2003, 1258.
6. (a) S. R. Buzilova, L. I. Vereshchagin, I. D. Sadekov and V. I. Minkin, Zh. Obshch. Khim., 1976, 46, 932 (Chem. Abstr., 1976, 85, 20761g); (b) S. R. Buzilova, I. D. Sadekov, T. V. Lipovich, T. M. Filippova and L. I. Vereshchagin, Zh. Obshch. Khim., 1977, 47, 1999 (Chem. Abstr., 1978, 88, 22289v).
7. X.-S. Mo and Y.-Z. Huang, Tetrahedron Lett., 1995, 36, 3539.
8. M. R. Detty, B. J. Murray, D. L. Smith and N. Zumbulyadis, J. Am. Chem. Soc., 1983, 105, 875.
9. M. R. Detty and B. J. Murray, J. Am. Chem. Soc., 1983, 105, 883.
10. S. Uemura, S.-I. Fukuzawa and S. R. Patil, J. Organomet. Chem., 1983, 243, 9.
11. H. Takashashi, K. Ohe, S. Uemura and N. Sugita, Nippon Kagaku Kaishi, 1987, 7, 1508.
12. V. I. Minkin, I. D. Sadekov, B. B. Rivkin, A. V. Zakharov, V. L. Nivorozhkin, O. E. Kompan and Y. T. Struchkov, J. Organomet. Chem., 1997, 536–537, 233.
13. S. Fujiwara, Y. Shimizu, T. Shin-ike and N. Kambe, Org. Lett., 2001, 3, 2085.
14. X. Huang, C.-G. Liang, Q. Xu and Q.-W. He, J. Org. Chem., 2001, 66, 74.
15. A. K. S. Chauhan, S. N. Bharti, R. C. Srivastava, R. J. Butcher and A. Duthie, J. Organomet. Chem., 2012, 708–709, 75.
16. G. Le Guillanton, A. V. Martynov, J. Delaunay, N. Mercier and A. Riou, J. Chem. Res., 1998, 681, 3001.
17. S. Yamago, M. Miyoshi, H. Miyazoe and J. Yoshida, Angew. Chem., Int. Ed., 2002, 41, 1407.
18. S. Kawaguchi, T. Ohe, T. Shirai, A. Nomoto, M. Sonoda and A. Ogawa, Organometallics, 2010, 29, 312.
19. A. Nomoto, S. Hayashi, T. Fujiyama, T. Ikeda, K. Hirata, J. Tohoma, K. Kakiuchi, W. Nakanishi and A. Ogawa, Bull. Chem. Soc. Jpn., 2014, 87, 550.
20. J. Terao, N. Kambe and N. Sonoda, Tetrahedron Lett., 1998, 39, 5511.
21. J. Yan and Z.-C. Chen, Synth. Commun., 2000, 30, 2359.
22. Y. Yu. Rusakov, L. B. Krivdin, F. F. Østerstrøm, S. P. A. Sauer, V. A. Potapov and S. V. Amosova, Phys. Chem. Chem. Phys., 2013, 15, 13101.
23. M. Akiba, M. V. Lakshmikantham, K.-Y. Jen and M. P. Cava, J. Org. Chem., 1984, 49, 4819.
24. G. Mugesh, A. Panda, S. Kumar, S. D. Apte, H. B. Singh and R. J. Butcher, Organometallics, 2002, 21, 884.
25. L. Engman and J. Persson, J. Organomet. Chem., 1990, 388, 71.
26. L. Engman and M. P. Cava, Organometallics, 1982, 1, 470.
27. CrysAlis PRO, Agilent Technologies, Yarnton, England, 2014.
28. A. Altomare, G. Cascarano, C. Giacovazzo and A. Guagliardi, J. Appl. Crystallogr., 1993, 26, 343–350.
29. L. Palatinus and G. Chapuis, J. Appl. Crystallogr., 2007, 40, 786–790.
30. G. M. Sheldrick, Acta Crystallogr., Sect. C: Struct. Chem., 2015, 71, 3–8.
31. L. J. Farrugia, J. Appl. Crystallogr., 1997, 30, 565.

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Footnote

† Electronic supplementary information (ESI) available: ORTEP diagram for compounds 2Ba, 3Aa, 3Ba, 5Aa and 8 are given in Fig. S1–S5. One-dimensional supramolecular architecture in 5Bb are given in Fig. S6. Bond parameters for C–H⋯O interaction in 5Bb are given in Table S1. CCDC 1061067–1061073. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5ra07854g

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