Synthesis of 1,3-diynes via detelluration of bis(ethynyl)tellurides

ARTICLE

Synthesis of 1,3-diynes via detelluration of bis(ethynyl)tellurides

Hélio A. Stefani^I,*; Jesus M. Pena^I; Julio Zukerman-Schpector^II; Edward R. T. Tiekink^III

^IFaculdade de Ciências Farmacêuticas, Universidade de São Paulo, São Paulo-SP, Brazil

^IIDepartamento de Química, Universidade Federal de São Carlos, 13565-905 São Carlos-SP, Brazil

^IIIDepartment of Chemistry, University of Malaya, Kuala Lumpur 50603, Malaysia

ABSTRACT

The synthesis of symmetric conjugated diyne systems with electron-withdrawing or electron-donating substituents via a palladium-catalyzed detelluration of bis(arylethynyl)tellurides and bis(alkylethynyl)tellurides is described. This procedure is effected under atmospheric conditions in DMF using Pd(OAc)₂ as a catalyst and AgOAc as an additive in the presence of triethylamine. This route offers efficient access to conjugated diyne systems in short reaction time. X-ray crystallographic structure and solid-state conformation of bis(p-tolylethynyl)telluride show a supramolecular chain aligned along the b axis, sustained by C-H...π interactions.

Keywords: tellurium, bis(phenylethynyl)tellurides, bis(alkynylethynyl)tellurides, detelluration, diynes, palladium

RESUMO

Neste artigo é descrita a síntese de sistemas diínicos conjugados contendo substituintes elétronatratores e elétron-doadores via a deteluração catalizada por paládio de bis-(ariletinil)teluretos e bis-(alquiletinil)teluretos. Este procedimento foi realizado sob condições atmosféricas em DMF usando Pd(Oac)₂ como catalisador e AgOAc como um aditivo na presença de trietilamina. Esta rota oferece acesso eficiente a sistemas diínicos conjugados em um curto período de tempo. A estrutura cristalográfica por difração de raios X do telureto de bis(p-toluiletinila) e a conformação no estado sólido mostram uma cadeia supramolecular alinhada ao longo do eixo b, sustentada por interações CH...π.

Introduction

Organotellurium compounds play an important role in organic synthesis, and they have received considerable attention because of their potential availability and useful biological activity.¹ As reported by Bergman and co-workers² more than three decades ago, aryltelluriums undergo detelluration upon treatment with degassed Raney nickel to afford biaryl compounds. Although the reaction is interesting and synthetically useful, the necessity of more than a stoichiometric amount of the required metal is still a serious drawback. However, attempted transition metal-catalyzed detellurations have been unsuccessful to date.^2,3

Compounds containing chains of conjugated triple bonds^4,5 are of paramount importance as versatile and useful building blocks in organic synthesis. Among these compounds, 1,3-butadiynes⁶ have been prominently utilized as substructures in the formation of valuable intermediates for natural products⁷ and pharmaceuticals such as antitumor,⁸ antibacterial,⁹ anti-inflammatory,¹⁰ and antifungal agents.¹¹

These conjugated diynes also serve as the core functional group in organic molecular materials such as linearly σ-conjugated acetylenic oligomers and polymers,¹² macrocycles¹³ (Figure 1), and supramolecular scaffolds.¹⁴ Oxidative dimerization of sp-hybridized terminal alkynes mediated by Cu(I) or Cu(II) salts under either catalytic or stoichiometric conditions is the most commonly used synthetic methodology for obtaining symmetrically substituted 1,3-butadiyne.

These approaches include Glaser's coupling,¹⁵ Eglinton's coupling,¹⁶ and Hay's coupling.¹⁷ In these reactions, the transmetalation of an alkynyl group to copper is proposed to generate an alkynylcopper species that undergoes subsequent oxidative dimerization to give the corresponding 1,3-butadiynes.¹⁸

Results and Discussion

Herein, we describe a convenient protocol for the synthesis of symmetrical conjugated diynes through the palladium-catalyzed detelluration of functionalized bis(arylethynyl)tellurides and bis(alkylethynyl) tellurides at room temperature in presence of air (Scheme 1).

The approach to preparing symmetrical conjugated diynes 2a-j was based on a palladium-catalyzed detelluration reaction of functionalized bis(phenylethynyl)tellurides and bis(alkylethynyl) tellurides 1a-j. The parent precursors bis(arylethynyl)telluride 1a-j were conveniently prepared in good to moderate yields according to the procedure described by Engman and Stern .¹⁹

We initially optimized the conditions for the detelluration of functionalized bis(phenylethynyl)telluride 1. To find optimal conditions for the detelluration reaction, bis(phenylethynyl) telluride 1a was selected as a model substrate, and a variety of catalysts were screened as described in Table 1. All reactions were monitored by TLC and GC/MS.

We initially surveyed palladium catalysts for use in this detelluration reaction. A comparison of different palladium catalysts such as PdCl₂(dppf)·CH₂Cl_2, Pd(OAc)₂, PdCl₂PEPPSI-ⁱPr, PdCl₂, and PdCl₂(PhCN)₂ (72%, 52%, 50%, 31% and 46% yields, respectively). Although the best yield (72% yield) was obtained using PdCl₂(dppf)·CH₂Cl₂, we choose Pd(OAc)₂ as catalyst due its availability in our laboratory. No product formation was observed using catalysts such as Fe(acac)₂, CuCl and NiCl₂(dppe) (entries 8-10). The reaction also did not proceed in the absence of a Pd catalyst (Table 1, entry 1).

One equiv. of AgOAc was used as an additive, along with 4 equiv. of triethylamine, and MeOH as solvent.

After the determination of the optimal catalyst for this transformation, we then studied the influence of the base. In our initial attempts, we used triethylamine, and the desired compound was obtained in 72% yield. We also attempted the same reaction with some other organic and inorganic bases such as NaOAc, Cs₂CO₃, K₂CO₃, DIPEA, pyridine and cyclohexylamine, obtaining the detelluration product in yields ranging from 27% to 67%.

To further determine the optimal conditions for the detelluration reaction, we performed the model reaction in various solvents. When MeOH, 1,4-dioxane, toluene and CH₃CN were employed, the reaction yields were poor or moderate (52%, 44%, 38% and 58%, respectively). While using DMSO as solvent provided a good yield (72%), DMF provided the best yield of the desired product (86%).

From these studies, it was determined that a reaction mixture containing 1.0 equiv. of bis(phenylethynyl)telluride 1a, 4 equiv. of Et₃N, 1 equiv. of AgOAc, and 10 mol % of Pd(OAc)₂ in 5 mL of DMF at room temperature stirred under atmospheric conditions for 60 min provided the best conditions for the synthesis of conjugated diyne 2a. To demonstrate the efficiency of this detelluration reaction, we then explored its generality with a variety of bis(arylethynyl)tellurides and bis(alkylethynyl)tellurides. The results are summarized in Table 2.

After optimizing the conditions for the synthesis of symmetrical conjugated diyne 2a, it was synthesized a series of conjugated diynes (2a-j) in 21-86% yields (see Table 2 and Experimental). The reaction was carried out at room temperature. The reaction proceeded with electron-withdrawing substituents attached to the alkynyltelluride and with electron-donation substituents. All of the obtained products provided ¹H and ¹³C NMR spectra that were in full agreement with their assigned structures.

On the basis of available literature²⁰ we propose a possible catalytic cycle for the detelluration reaction of bis(arylethynyl)tellurides and bis(alkylethynyl)tellurides as described in Figure 2.

According to this cycle the reaction proceeds by the formation of Pd(II) complex with acetylene followed by the conversion of this intermediate into another palladium species B, which leads the formation of conjugated diyne C along the reduction of the Pd(II) complex to Pd(0). The palladium species is later oxidized in the presence of O₂ to give the initial Pd(II) species completing the cycle.

Due to our ongoing interest in tellurium structures, especially those involving π-interactions, the crystal and molecular structure of the bis-(p-tolylethynyl)telluride starting material was determined.²¹ The tellurium atom is located on a crystallographic twofold axis with the C-Te-C angle being 92.23 (15)º. The dihedral angle formed between the phenyl rings is 87.27 (7)º (Figure 3).

In the crystal structure, the telluride molecules are connected into supramolecular chains along the b axis via C-H...π interactions, as shown in Figure 4.

Conclusions

In summary, we demonstrated the synthesis of functionalized symmetrical 1,3-diyne systems through the palladium-catalyzed detelluration reaction of bis(arylethynyl) tellurides and bis(alkylethynyl)tellurides. The use of this methodology for the synthesis of more complex polyacetylenic compounds is currently under study in our laboratory.

Experimental

Proton nuclear magnetic resonance spectra (¹H NMR) were obtained at 300 MHz. Spectra were recorded in CDCl₃ solutions. Chemical shifts are reported in ppm, referenced to the solvent peak of CDCl₃ or tetramethylsilane (TMS) as the external reference. Data are reported as follows: chemical shift (δ), multiplicity, coupling constant (J) in Hertz and integrated intensity. Carbon-13 nuclear magnetic resonance spectra (¹³C NMR) were obtained at 75 MHz. Spectra were recorded in CDCl₃ solutions. Chemical shifts are reported in ppm, referenced to the solvent peak of CDCl₃. Abbreviations to denote the multiplicity of a particular signal are s (singlet), d (doublet), t (triplet), q (quartet), quint (quintet), sex (sextet) and m (multiplet). Column chromatography was performed using silica gel (230-400 mesh) following the methods described by Still et al.²² Thin layer chromatography (TLC) was performed using silica gel F₂₅₄, 0.25 mm thickness from Merck. For visualization, TLC plates were either placed under ultraviolet light, or stained with iodine vapor, or acidic vanillin. The following solvents were dried and purified by distillation from the reagents indicated: tetrahydrofuran from sodium with a benzophenone ketyl indicator. All other solvents were ACS or HPLC grade unless otherwise noted. Air and moisture-sensitive reactions were conducted in flame-dried or oven dried glassware equipped with tightly fitted rubber septa and under a positive atmosphere of dry nitrogen or argon. Reagents and solvents were handled using standard syringe techniques. Temperatures above room temperature were maintained by use of a mineral oil bath with an electrically heated coil connected to a controller.

General experimental procedure for preparing conjugated diyne compounds 2a-j

A suspension of bis(phenylethynyl)telluride (1a) (0.0824 g, 0.25 mmol), PdOAc₂ (5.6 mg, 10% mol), triethylamine (0.101 g, 1 mmol) and silver(I) acetate (0.041 g, 0.25 mmol) in 5 mL of DMF was stirred at room temperature under air for 60 min. The reaction mixture was then diluted with ethyl acetate (25 mL), and the organic layer was washed with a saturated solution of NH₄Cl (2 × 10 mL) and water (2 × 10 mL), dried over MgSO₄ and concentrated under vacuum. The crude product was purified by flash silica column chromatography using hexane as the eluent and subsequently characterized.

Bis(phenylethynyl)telluride (1a)¹⁹

Yield 86%; ¹H NMR (300 MHz, CDCl₃) δ (ppm) 7.30-7.38 (m, 6H), 7.47-7.56 (m, 4H). ¹³C NMR (CDCl₃, 75.5 MHz,) δ (ppm) 73.7; 81.3; 121.6; 128.4; 129.5; 132.3; EM m/z (%) 202 (100), 200 (24), 150 (8), 101 (13), 88 (10).

1,4-Bis(2,5-fluorophenylethynyl)telluride (1b)

Red solid; mp 187-188 ºC. Yield 60%; ¹H NMR(CDCl₃, 300 MHz) δ (ppm) 6.84 (dd, 1H, J 5.2 Hz, J 13.0 Hz) 7.45 (dd, 1H, J 8.0 Hz, J 15.3 Hz). ¹³C NMR (CDCl₃, 75.5 MHz) δ (ppm) 165.4 (d, J 11.9 Hz, C-F), 161.8 (d, J 46.4 Hz, C-F), 135.1 (d, J 2.3 Hz, C-F), 1 1.76 (d, J 3.7 Hz, C-F), 108.0 (d, J 4.2 Hz, C-F),104.8 (d, J 19 Hz, C-F), 48.6 (2C), 29.4 (2C). ¹²⁵Te NMR (CDCl₃, 95 MHz) δ (ppm) 374.1. EM m/z (%) 274.2 (100), 275.2 (16), 138.2 (15), 223.2 (6). IR (KBr) ν_max/cm^-1: 3440, 3099, 2139, 1613, 1586, 1142, 1096, 967, 855, 779, 729, 512, 498, 485. HRMS (ESI) calc. for C₁₆H₆F₄TeNa⁺ 426.9365; found 426.9368.

1,3-Bis(m-fluorophenylethynyl)telluride (1c)

White solid; mp 129-130 ºC. Yield 58%; ¹H NMR(CDCl₃, 300 MHz) δ (ppm) 6.96-7.14 (m, 8H). ¹³C NMR (CDCl₃, 75.5 MHz ) δ (ppm) 44.5 (2C); 111.5 (2C); 116.4 (d, J¹21.1 Hz, C-F); 118.8 (d, J² 22.8 Hz, C-F); 124.4 (d, J³ 9.36 Hz, C-F); 129.9 (d, J⁴ 3.03 Hz, C-F); 129.8 (d, J⁵ 8.64 Hz, C-F); 162.2 (d, J ⁶ 245.5 Hz, C-F). ¹²⁵Te NMR(CDCl₃, 95 MHz) δ (ppm) 374.1. EM m/z (%) 238.1 (100), 236.1 (13), 218.1 (6), 217.2 (5), 168.2 (4), 119.2 (16). IR (KBr) ν_max/cm^-1: 3440, 3067, 2143, 1604, 1581, 1484, 1423, 1266, 1136, 941, 872, 784, 678, 571, 517, 457. HRMS (ESI) calc. for C₁₆H₈F₂TeNa⁺ 390.9553; found 390.9538.

1,4-Bis(p-tolylphenylethynyl)telluride (1d)²³

Yield 52%; ¹H NMR (CDCl3, 300 MHz) δ (ppm) 2.35 (s, 6H); 7.40 (d, J 7.8 Hz, 4H); 7.12 (d, J 7.8 Hz, 4H); ¹³C NMR (CDCl₃, 75.5 MHz,) δ (ppm) 21.6 (2C); 73.5 (2C); 81.6 (2C); 118.8 (2C); 129.2 (4C); 132.4 (4C); 139.5 (2C); EM m/z (%) 230 (100); 215 (17); 115 (17); 101 (15).

1,4-Bis(p-fluorophenylethynyl)telluride (1e)

White solid, mp 129-130 ºC. Yield 51%; ¹H NMR (CDCl₃, 300 MHz) δ (ppm) 6.91 (t, J¹ and J² 8.52 Hz, 4H); 7.45 (dd, J¹ and J² 5.37 Hz, 4H). ¹³C NMR (CDCl₃, 75.5 MHz) δ (ppm) 42.7 (2C); 111.6 (2C); 115.6 (d, J¹ 22.0 Hz, C-F); 118.9 (d, J² 3.5 Hz, C-F); 134.2 (d, J³ 8.5 Hz, C-F); 162.9 (d, J⁴ 249.3 Hz, C-F). ¹²⁵Te NMR(CDCl₃, 95 MHz) δ (ppm) 364.5. EM m/z (%) 264.2 (100), 265.1 (33), 249.2 (32), 233.6 (6), 231.4 (6), 221.1 (41), 220,2 (95), 201.5 (5.75), 200,4 (6) 132.3 (13), 117.1(5), 116.1 (8). IR (KBr) ν_max/cm^-1: 3443, 3099, 3080, 2143, 1595, 1503, 1480, 1224, 1209, 1150, 1096, 838, 749, 533. HRMS (ESI) calc. for C₁₆H₈F₂TeNa⁺ 390.9553, found 390.9538.

1,4-Bis(3-thyenyletynyl)telluride (1f)

White solid, mp 100-101ºC. Yield 67%, ¹H NMR (CDCl₃, 300 MHz) δ (ppm) 7.14 (dd, J¹ and J² 1.14 Hz, 2H); 7.25 (t, J 3.0 Hz, 2H); 7.57 (dd, J¹ 1.2 Hz and J² 1.14 Hz, 2H). ¹³C NMR (CDCl₃, 75.5 MHz) δ (ppm) 42.7 (2C); 107.6 (2C); 122.1 (2C); 125.2 (2C); 130.1 (2C); 130.8 (2C). ¹²⁵Te NMR (CDCl₃, 95 MHz) δ (ppm) 364.4. EM m/z (%) 214.1 (100), 169,2 (19), 156.2 (4), 144.2 (6), 126.2 (4), 107.2 (11), 69.1 (6), 45.0. IR (KBr) ν_max/cm^-1: 3431, 3099, 2129, 1352, 1075, 940, 933, 865, 825, 783, 692, 670, 621, 582. HRMS (ESI) calc. for C₁₂H₆S₂TeNa⁺ 366.887; found 366.8855.

1,4-Bis(4-methoxyphenylethynyl)telluride (1g)²³

Yield: 58% ¹H NMR (CDCl₃, 300 MHz) δ (ppm) 7.37 (d, J 8.5 Hz, 4H); 6.67 (dd, J¹ 2.6 Hz and J² 8.5 Hz, 4H); 3.79 (s, 6H). ¹³C NMR (CDCl₃, 75.5 MHz,) δ (ppm) 20.9 (2C), 55.2 (2C), 111.2 (2C), 115.0 (4C), 129,8 (2C), 134.0 (4C), 143.1 (2C), 160.1 (2C), EM m/z (%) 264.2 (100), 220.2 (95), 221.1 (41), 249.2 (32), 110.2 (21), 218.2 (10). IR (KBr) ν_max/cm^-1: 3437, 3005, 2984, 2958, 2936, 2903, 2891, 2838, 2824, 2154, 1463, 1440, 1432, 1427, 1348, 1273, 1187, 1082, 1069, 995, 976, 899, 880, 606, 590. HRMS (ESI) calc. for C₁₈H₁₄O₂TeNa⁺, found 414.9851.

1,4-Bis(p-pentylphenylethynyl)telluride (1h)

Yellow solid; mp 57-58 ºC. Yield: 50%. ¹H NMR (CDCl₃, 300 MHz) δ (ppm) 0.89 (t, J 6.6 Hz, 6H); 1.33 (m, 8H); 1.60 (m, 4H); 2.61 (m, 4H); 7.14 (d, J 8.0 Hz, 4H), 7.39 (d, J 7.8 Hz, 4H). ¹³C NMR (CDCl₃, 75.5 MHz) δ (ppm) 14.0 (2C); 22.5 (2C); 30.96 (2C); 35.9 (2C); 42.1(2C); 112.8 (2C); 120.1 (2C); 128.4 (2C); 132.1 (2C); 144.3 (2C). ¹²⁵Te NMR(CDCl₃, 95 MHz) δ (ppm) 357.6. EM m/z (%) 285.3 (100), 342.3 (92), 228.1 (61), 343.3 (25), 226.1 (12), 41.1 (9). IR (KBr) ν_max/cm^-1: 3435, 3024, 2955, 2929, 2855, 2141, 1503, 1466, 842, 825, 815, 723, 572, 530. HRMS (ESI) calc. for C₂₆H₃₀TeNa⁺ 495.1307; found 495.1286.

1,4-Bis(methoxyethynyl)telluride (1i)

Yellow solid, mp 44-45 ºC. Yield 78%. ¹H NMR (CDCl₃, 300 MHz) d (ppm) 4.32 (s, 4H); 3.39 (s, 6H). ¹³C NMR (CDCl₃, 75.5 MHz,) d (ppm) 40.2 (2C); 57.4 (2C); 60.6 (2C); 109.9 (2C). EM m/z (%) 69.0 (100), 77.1 (14), 78.1(14), 63.1 (13), 51.1 (11), 53.0 (8).

1,4-Bis(butylethynyl)telluride (1j)²⁴

Yellow oil; ¹H NMR (CDCl₃,300 MHz) δ (ppm) 0.90 (t, J 7.2 Hz, 6H); 1.36-1.57 (m, 8H); 2.50 (t, J 6.9 Hz, 4H). ¹³C NMR (CDCl₃, 75.5 MHz) δ (ppm) 13.6 (2C); 20.7 (2C); 21.9 (2C); 30.8 (4C); 114.3 (2C).

General procedure to homocoupling reaction

A suspension of bis(phenylethynyl)telluride (1a) (0.0824 g; 0.25 mmol), Pd(OAc)₂ (0.0056 g, 10% mol), triethylamine (0.101 g; 1 mmol) and silver acetate (0.041 g, 0.5 mmol) in 5 mL of DMF was stirred at room temperature, under air atmospheric by 60 min. The reaction mixture was diluted with ethyl acetate (25 mL), and the organic layer washed with NH₄Cl (2 × 10 mL), dried over MgSO₄ and concentrated under reduced pressure. The crude product was purified by flash silica column chromatography using hexane as eluent and subsequently characterized.

1,4-Bis(phenylbuta-1,3-diyne (2a)²⁵

Yield 86%. ¹H NMR (CDCl₃, 300 MHz) δ (ppm) 7.30-7.38 (m, 6H), 7.47-7.56 (m, 4H). ¹³C NMR (CDCl₃, 75.5 MHz,) δ (ppm) 73.7; 81.3; 121.6; 128.4; 129.5; 132.3.

1,4-Bis(2,4-difluorophenyl)buta-1,3-diyne (2b)

White solid; mp 187-188 ºC. Yield 60%. ¹H NMR (CDCl₃, 300 MHz) δ (ppm) 6.83-6.90 (m, 4H); 7.54-7.46 (m, 2H). ¹³C NMR (CDCl₃, 75.5 MHz) δ (ppm) 29.7 (2C); 74.8 (2C); 104.6 (d, J 1.3 Hz, C-F); 111.9 (d, J 25.7, C-F); 135.3 (d, J 9.9 Hz, C-F); 160.1 (d, J 196.0 Hz, C-F); 165.6 (d, J 53.8 Hz, C-F). IR (KBr) ν_max/cm^-1: 3439, 3101, 2955, 2924, 2854, 1730, 1609, 1582, 1496, 1468, 1435, 1299, 1268, 1143, 1098, 965, 857, 852, 812, 741, 710, 612, 601, 508, 475, 429. Microanalysis Calc. 70.25% C, 2.46% H; found 70.44% C; 2.54% H.

1,3-Bis(m-fluorophenyl)buta-1,3-diyne (2c)²⁶

Yield 65%; ¹H NMR (CDCl₃, 300 MHz) δ (ppm) 7.22 7.29 (m, 8H). ¹³C NMR (CDCl₃, 75.5 MHz,) δ (ppm) 74.4 (2C); 80.6 (2C); 116.9 (d, J¹ 21.0 Hz, C-F); 119.2 (d, J² 22.9 Hz, C-F); 123.4 (d, J³ 9.5 Hz, C-F); 128.4 (d, J ⁴ 3.1 Hz, C-F); 130.1 (d, J ⁵ 8.6 Hz, C-F); 162.2 (d, J ⁶ 245.8 Hz, C-F).

1,4-Bis(p-tolyl)buta-1,3-diyne (2d)²⁷

Yield 52%. ¹H NMR (CDCl₃, 300 MHz,) δ (ppm) 2.35 (s, 6H); 7.40 (d, J 7.8 Hz, 4H); 7.12 (d, J 7.8 Hz, 4H); ¹³C NMR (CDCl₃, 75.5 MHz,) δ (ppm) 21.6 (2C); 73.5 (2C); 81.6 (2C); 118.8 (2C); 129.2 (4C); 132.4 (4C); 139.5 (2C).

1,4-Bis(p-fluorophenyl)buta-1,3-diyne (2e)²⁸

Yield 47%. ¹H NMR (CDCl₃, 300 MHz) δ(ppm) 7.03 (dd, 1H, J 7.8 Hz, J 9.7 Hz); 7.51 (ddd, J 2.2 Hz, J 5.3 Hz, J 6.9 Hz). ¹³C NMR (CDCl₃,75.5 MHz) δ (ppm) 73.5 (2C); 80.4 (2C); 115.9 (d, J¹ 22.1 Hz, C-F); 117.8 (d, J² 3.56 Hz, C-F); 134.5 (d, J³ 8.50 Hz, C-F); 163.0 (d, J⁴ 250.1 Hz, C-F).

1,3-Bis(3-thyenyl)buta-1,3-diyne (2f)²⁸

Yield 44%; ¹H NMR (CDCl₃, 300 MHz,) δ (ppm) 7.12 (d, J 5.0 Hz, 2H); 7.25-7.28 (m, 2H); 7.58 (d, J 2.9 Hz, 2H). ¹³C NMR (CDCl₃, 75.5 MHz) δ (ppm) 73.6 (2C); 121.0 (2C); 125.6 (4C); 131.2 (4C).

1,4-Bis(p-methoxyphenyl)buta-1,3-diyne (2g)²⁸

Yield 39%; ¹H NMR (CDCl₃, 300 MHz) δ (ppm) 7.42 (d, J 8.5 Hz, 4H); 6.69 (dd, J¹ 2.5 Hz and J² 8.5 Hz, 4H); 3.80 (s, 6H). ¹³C NMR (CDCl₃, 75.5 MHz) δ (ppm) 55.2 (2C); 55.2 (2C); 67.9 (2C); 80.8 (2C); 111.4 (2C); 115.2 (4C); 134.3 (4C); 160,0 (2C).

1,4-Bis(p-penthylphenyl)buta-1,3-diyne (2h)²⁹

Yield 38%; ¹H NMR (CDCl₃, 300 MHz) δ (ppm) 0.87 (m, 6H); 1.30 (m, 8H); 1.59 (t, J 7.0 Hz, 4H); 2.59 (m, 4H); 7.12 (dd, J¹ 3.8 Hz and J² 7.9 Hz, 4H); 7.40 (t, J 8.6 Hz, 4H). ¹³C NMR (CDCl₃, 75.5 MHz) δ (ppm) 13.9 (2C); 22.5 (2C); 31.4 (4C); 35.9 (2C); 73.5 (2C); 83.9 (2C); 119.0 (2C); 128.5 (4C); 132.4 (4C); 144.4 (2C).

1,6-Dimethoxy-2,4-hexadiyne (2i)²⁹

Yield 21%; ¹H NMR (CDCl₃, 300 MHz) δ (ppm) 3.39 (s, 6H); 4.18 (s, 4H). ¹³C NMR (CDCl₃, 75.5 MHz) δ (ppm) 57.4 (2C); 59.8 (2C); 70.1 (2C); 75.1 (2C).

Supplementary Information

Supplementary data are available free of charge at http://jbcs.sbq.org.br as PDF file.

Acknowledgments

The authors thank FAPESP (2007/59404-2) and CNPq for fellowships to H. A. S. and J. M. P. (300.613/2007-5 and 142.741/2008, respectively) for financial support.

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Submitted: November 11, 2010

Published online: April 5, 2011

FAPESP has sponsored the publication of this article.

Supplementary Information

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Publication Dates

• Publication in this collection
  04 Aug 2011
• Date of issue
  Aug 2011

History

• Received
  11 Nov 2010
• Accepted
  05 Apr 2011