(PDF) Ullmann-Type Intramolecular C-O Reaction Toward Thieno[3,2

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Cite This: J. Org. Chem. 2017, 82, 10920-10927

Ullmann-Type Intramolecular C−O Reaction Toward Thieno[3,2‑b]furan Derivatives with up to Six Fused Rings Daoliang Chen,†,‡ Dafei Yuan,†,‡ Cheng Zhang,†,‡ Hao Wu,†,‡ Jianyun Zhang,†,‡ Baolin Li,*,† and Xiaozhang Zhu*,†,‡ †

School of Chemistry and Chemical Engineering, University of Chinese Academy of Sciences, Beijing 100049, P. R. China Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China

‡

S Supporting Information *

ABSTRACT: A new strategy for the efficient synthesis of thieno[3,2-b]benzofuran derivatives (15 examples) was achieved on the basis of successive regioselective intermolecular Suzuki and newly developed intramolecular Ullmann C−O reactions in up to a 70% overall yield. The fast intramolecular C−O reaction can be realized by an efficient catalytic combination of CuI/1,10phenanthroline in up to a 97% yield. This method is suitable for the construction of highly fused thieno[3,2-b]furan-containing heterocycles including DTBDF and TTDBF. The π−π and hydrogen-bonding interactions observed for the C8-DTBDF single crystal suggest its great potential for OFET applications in the near future.

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π-electron delocalization,8 and peripheral furan can modify the aromaticity of the pentalene core.9 The introduction of the furan ring into thieno[3,2-b]thiophene can regulate the packing mode from edge-to-face to face-to-face π−π stacking that is more favorable for charge carrier transport attributing to the enhanced π-orbital overlap.10 As BTBT derivatives have achieved a great success in OFETs, we were curious about the packing mode and the charge transport property of benzo[4,5]thieno[3,2-b]benzofuran (BTBF) derivatives with furan rings. One major problem restraining the applications of furancontaining fused-ring systems can be attributed to the difficulty of synthesis. Although oxygen and sulfur in the chalcogen family have many similarities, several valence states of sulfur, −2, 0, +1, and +2, can be used to construct the thiophene ring.11 By contrast, the oxygen atom has an only valence state of −2 to synthesize the furan ring. Over the years, some synthetic methods including transition-metal-catalyzed12 inter13/intramolecular14 heteroannulation reactions have been reported for the synthesis of furan ring. Besides, the construction of fused-ring compounds containing furan rings were reported on the basis of the intramolecular dehydration condensation reaction, which, however, needs harsh reaction

INTRODUCTION Ladder-type thiophene-fused π-conjugated molecules (thienoacenes) such as benzothieno[3,2-b] benzothiophene (BTBT)1 and benzo[1,2-b:4,5-b′]dithiophene (BDT)2 have played a key role in the development of high-performance electronic and optoelectronic devices such as organic field-effect transistors (OFETs) and photovoltaics (OPVs). Compared with thiophene, furan has a similar structure with comparable energy levels according to the density functional theory (DFT) calculations.3 Oxygen and sulfur have the similar valence electron configuration; the difference is that an oxygen atom has a smaller atomic radius, 1.52 vs 1.80 Å, and a larger electronegativity, 3.44 vs 2.58. The short atomic radius of an oxygen atom may increase the intermolecular π-orbital overlap and facilitate the charge transport property in the solid state.4 Thus, ladder-type furan-fused π-conjugated molecules are being viewed as very promising candidates in organic electronics.5 2,7-Bis(4-octylphenyl)naphtho[2,1-b:6,5-b′]difuran showed a high hole mobility of up to 3.6 cm2 V−1 s−1 with an intermolecular short contact of 2.80 Å, which is much smaller than that reported for the thiophene analogue, 2,7diphenylnaphtho[2,1-b:6,5-b′]dithiophene (3.31 Å).6 Furan was also introduced into the n-type furan-thiophene-based quinoidal compound that shows a very high electron mobility of up to 7.7 cm2 V−1 s−1.7 Besides, because of the lower aromaticity of furan, furan-containing compounds have a better © 2017 American Chemical Society

Received: July 12, 2017 Published: September 15, 2017 10920

DOI: 10.1021/acs.joc.7b01745 J. Org. Chem. 2017, 82, 10920−10927

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The Journal of Organic Chemistry conditions.5,15 Thus, developing a new and efficient method is a linchpin for the synthesis of thieno[3,2-b]furan-containing fused heterocycles. As shown in Scheme 1a, thieno[3,2-

Table 1. Optimization of the Reaction Conditions of BTBF (4a)a

Scheme 1. Synthetic Strategies Toward Thieno[3,2b]benzofurans entry

metal

ligand

solvent

base

yield (%)

time (min)

1 2 3 4 5 6 7 8

CuI CuI CuI CuI CuI CuI CuI

phen phen phen phen phen phen phen

PhMe PhMe DMF DMF DMF DMF DMF DMF

Cs2CO3 K2CO3 K2CO3 LiOH tBuOK NaHCO3 CaCO3 K2CO3

17 15 80 42 29 trace trace trace

15 3h 15 15 5 1h 1h 3h

a

b]benzofurans were usually synthesized by palladium-catalyzed double C−H activation from diaryl ethers.16 However, the precursor diaryl ethers need to be synthesized by a multiplestep reaction. As transition-metal-catalyzed intramolecular Cheteroatom bond formations have been developed for the efficient construction of fused heterocycles,17 we assumed that thieno[3,2-b]benzofuran derivatives may alternatively be synthesized by an intramolecular C−O reaction. The Ullmann reaction is well-known to play a critical role in the Cheteroatom bond formation.18 During the last few decades, with the discovery of effective catalytic systems, the substrate scope and yield have been significantly improved.19,22 In fact, some results have been reported regarding copper-catalyzed intramolecular C−O bond formations.20 There are also some successful examples of the copper-catalyzed intramolecular C− O formation for benzofurans from 1-(2-bromophenyl)propan2-one and its derivates,21 but the copper-catalyzed C−O reaction for highly fused furan-containing heterocycles was rare; the only example was reported by Liu et al. for the synthesis of dibenzo[b,d]furan using an equivalent amount of ((thiophene2-carbonyl)oxy)copper (CuTC).22 In this work, we developed a new strategy for the efficient synthesis of thieno[3,2-b]benzofuran derivatives under very mild reaction conditions, i.e., newly developed intramolecular C−O Ullmann reaction with an expedient CuI/phenanthroline (phen) catalytic system (Scheme 1b). We successfully synthesized a series of thieno[3,2-b]benzofuran derivatives with up to a 97% yield. Furthermore, π-extended fused heterocycles including dithieno[2,3-d;2′,3′-d′]benzo[1,2-b;4,5b′]difuran (DTBDF) and thieno[4,5:4′,5′]thieno[3,2-b:3′,2′b′]di(benzofuran) (TTDBF) were synthesized by the double intramolecular C−O reaction. We further investigated the packing mode of these compounds to evaluate the significance of the introduction of furan rings, i.e., endowing BTBF derivatives with an efficient π−π interaction.

All reactions were conducted at 90 °C under a N2 atmosphere.

this reaction. Using the weaker base K2CO3 instead of Cs2CO3 could only achieve a 15% yield in 3 h, with a low conversion of the starting material 3a (entry 2, Table 1). To our delight, when the solvent was changed to N,N-dimethylformamide (DMF) using K2CO3 as the base, the highest yield was up to 80% in just 15 min with 100% conversion (entry 3, Table 1). Besides, when the stronger base tBuOK was used, the reaction finished within 5 min in 29% yield (entry 5). When the weak bases NaHCO3 and CaCO3 were used, only a trace amount of 4a was detected (entries 6 and 7). It appears that stronger bases lead to a lower yield, which can be attributed to the formation of intermolecular coupling byproducts, and weaker bases lead to a lower conversion of the starting material 3a and that K2CO3 is the best reagent with suitable alkalinity. The cyclization reaction can proceed in a good yield even on a gram scale. Using 3.05 g of compound 3a as the starting material, we got 1.75 g of compound 4a in a 78% yield under the optimized condition. X-ray quality crystals of 4a could be grown in ethyl acetate by the solvent evaporation method, which display a slipped π−π stacking with a face-to-face intermolecular distance of 3.42 Å (Figure 1a). Compared with BTBT,23 the introduction of the furan ring successfully regulated the packing structure of BTBF to a more efficient π−π interaction (Figure S8). We performed DFT calculations on BTBF and BTBT, which indicated that the highest occupied molecular orbital (HOMO) (−5.71 eV) and lowest unoccupied molecular orbital (LUMO) energy levels (−1.29 eV) of BTBF are comparable with those of BTBT, −5.72 eV (HOMO) and −1.38 eV (LUMO). As shown in Figure 1b,c, the oxygen atom contributes much less to both the HOMO and LUMO coefficients, which may benefit the π−π interaction, while the sulfur atoms on BTBT show more contribution, which may be favorable to form a strong S−S interaction. All the substrates 3 can be synthesized by the regioselective Suzuki coupling reaction between 2,3-dibromobenzo[b]thiophene 2 and (2-bromophenyl)boronic acid 1 derivatives in good yields of 63−91%. Under optimized conditions, we got compound 4b in a 62% yield (entry 2, Table 2). For compounds 4c, 4d, and 4e with tert-butyl groups, high yields of 81%, 87%, and 97% can be obtained, respectively (entries 3, 4, and 5, Table 2). Then, we chose the electron-deficient functional groups carbonyl and fluorine to examine the utility of this method. Fluorine-substituted 4f was synthesized in a high

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RESULTS AND DISCUSSION As summarized in Table 1, we selected the intramolecular coupling of 2-(3-bromobenzo[b]thiophen-2-yl)phenol (3a) as the model reaction to optimize the reaction conditions. Initially, we got the intramolecular coupling product benzo[4,5]thieno[3,2-b]benzofuran (BTBF, 4a) in a 17% yield within 15 min by a CuI (10 mol %)/phen (20 mol %) precatalyst mixture with Cs2CO3 as the base and toluene as the solvent (entry 1, Table 1), which suggested that CuI and phen can effectively catalyze 10921

DOI: 10.1021/acs.joc.7b01745 J. Org. Chem. 2017, 82, 10920−10927

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Figure 1. (a) Packing structure of BTBF. (b) HOMO (left) and LUMO (right) orbitals of BTBT calculated by the DFT B3LYP/6-31G method. (c) HOMO (left) and LUMO (right) orbitals of BTBF calculated by the DFT B3LYP/6-31G method.

High-quality single crystals of C8-DTBDF were obtained from diethyl ether and analyzed by X-ray diffraction as shown in Figure 3. Similar to the stacking of C6-DTBDT,25 C8DTBDF exhibits a shifted cofacial arrangement with an interplanar distance of 3.52 Å, which is shorter than that of C6-DTBDT (3.63 Å),25a indicating efficient π−π interactions along the stacking axis. The introduction of the furan ring successfully regulated the packing structure, which can be attributed to the higher electronegativity of the oxygen atom. Besides, side-by-side intermolecular interactions of 2.45 Å through the hydrogen bonds were also observed, which is important to form the layer-by-layer packing. The HOMO energy level of C8-DTBDF is determined to be 5.42 eV below the vacuum level by means of cyclic voltammetry (Figure S2), which allows the smooth hole injection and is suitable for OFET applications. Bottom-gate bottom-contact OFETs were fabricated to investigate the semiconducting properties of C8DTBDF. The semiconducting layers were spin-coated onto octadecyltrichlorosilane-modified SiO2 (300 nm)/Si substrates with a prepatterned gold source and drain electrodes. After annealing at 80 °C, the OFETs exhibited typical p-type transistor behavior (Figure S3) with a hole mobility of 6.9 × 10−4 cm2 V−1 s−1 with a high Ion/Ioff value of 106, indicating the potential of the DTBDF framework. In summary, we have shown a highly efficient method, i.e., copper-catalyzed intramolecular C−O Ullmann reaction, for the construction of ladder-type thieno[3,2-b]furan-containing fused heterocycles, which show good functional group tolerance. Although the Ullmann reactions have been widely studied, we achieved an efficient catalytic intramolecular C−O formation for the synthesis of furan-containing fused heterocycles. Compared with thiophene analogues, the introduction of furan changes the packing mode to a more efficient π−π stacking. Thus, we believe that furan-containing fused heterocycles such as the DTBDF framework should be very promising for high-performance organic electronic devices.

yield of 90% (entry 6, Table 2). Compound 4g with a more electron-deficient carbonyl group can also be obtained in a 74% yield (entry 7, Table 2). Typically, Cl and Br are reactive in transition-metal-catalyzed coupling reactions. For 4h and 4i with one bromine attached to the framework, the yields decreased slightly to 72% and 66%, respectively (entries 8 and 9, Table 2). We further found that, with an increasing number of chlorine atoms, the yields of 4j (54%) and 4l (18%) dramatically decreased with K2CO3 as the base (entries 10 and 12, Table 2), which we suppose may be ascribed to the possibility of intermolecular coupling. To improve the yield of the efficient synthesis of 4l, we optimized the reaction conditions. As shown in Table S2 in the Supporting Information, the alkalinity is the key point to influence the efficiency of the reaction. Thus, the yield of 4l can be improved to 63% with the weaker base NaHCO3. Then, for 4k with one chlorine and 4m with one fluorine and one chlorine, the similar yields of 65% were obtained using NaHCO3 as the base (entries 11 and 13, Table 2). Thus, we can synthesize a series of thieno[3,2-b]benzofuran derivatives in good to excellent yields, indicating the good functional group tolerance of our method. The high structural rigidity and extended π-electron delocalization of conjugated molecules can increase the πorbital overlap, efficiently reduce the reorganization energy, and increase the transfer integral, which are very important for charge transport.3b,24 Thus, we further utilized the present method to construct π-extended molecules (Figure 2). Compound 3n was synthesized by the Negishi coupling reaction between (3-bromothiophen-2-yl)zinc(II) chloride and 2,5-diiodo-1,4-phenylene diacetate followed by hydrolysis in a 45% yield. By the double intramolecular C−O Ullmann reaction, π-extended DTBDF was obtained in a 47% yield. Similarly, compound 3o was synthesized by the double Suzuki coupling reaction between 2,3,5,6-tetrabromothieno[3,2-b]thiophene and (2-hydroxyphenyl)boronic acid in a 49% yield. However, we failed to get the compound TTDBF by using the similar condition, which can be attributed to its bad solubility in the highly polar solvent DMF. So, we chose toluene as the solvent, which has a better solubility for the compound. Finally, compound TTDBF was obtained in a 48% yield. To get a πextended compound of good solubility, C8-DTBDF was synthesized from DTBDF through a Friedel−Crafts reaction followed by a reductive reaction with LiAlH4/AlCl3 in a 63% yield.

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EXPERIMENTAL SECTION

General Information. All reagents were purchased from commercial suppliers and used without further purification unless otherwise specified. Proton nuclear magnetic resonance (1H NMR) and carbon nuclear magnetic resonance (13C NMR) spectra were measured on BRUKER AVANCE 300 and BRUKER DMX 400 spectrometers. Chemical shifts (δ) for hydrogens are reported in parts per million (ppm) downfield from tetramethylsilane (CDCl3 δ 7.26). 13 C NMR spectra were recorded at 75 or 100 MHz. High-resolution 10922

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mass spectra (HRMS) were determined on a Bruker Apex IV Fourier transform mass spectrometer (EI), Fourier transform ion cyclotron resonance mass spectrometer (ESI), and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometer. Cyclic voltammetry (CV) was performed on a CHI620D potentiostat. All measurements were carried out in a one-compartment cell under a N2 atmosphere, equipped with a glassy-carbon electrode, a carbon counter electrode, and a Ag/AgCl reference electrode. The supporting electrolyte was a 0.1 mol/L dichloromethane solution of tetrabutylammonium perchlorate (TBAP). All potentials were corrected against Fc/Fc+. CV was measured with a scan rate of 100 mV/s. Single-crystal XRD data were collected on a D8QUEST diffractometer (Bruker, Germany) using Mo Kα radiation (λ = 0.71073 Å) at 100 K. The crystal structures were solved by direct methods (SHELXS97; Sheldrick, 2008) and refined by least-squares on F2 by the full-matrix least-squares method (SHELXS97; Sheldrick, 2008). Anisotropic atomic displacement parameters were applied to all non-hydrogen atoms. The hydrogen atoms were put at calculated positions and refined by applying riding models. General Procedure for Regioselective Suzuki Coupling. (2Bromophenyl)boronic acid 2 (1.5 equiv) and 2,3-dibromobenzo[b]thiophene 1 (1 equiv) derivatives were dissolved in a dioxane/H2O cosolvent (10 mL, v/v = 4:1) in a Schlenk tube, to which K2CO3 (4 equiv) and Pd(PPh3)4 (5 mol %) were added under N2. The reaction was heated to 90 °C overnight under the absence of light. By extraction with CH2Cl2, the organic layer was separated and dried with MgSO4. After evaporation under a vacuum, the residue was purified on silica gel with ethyl acetate and hexane as the eluent to afford the corresponding compounds 3. 2-(3-Bromobenzo[b]thiophene-2yl)phenol) (3a): yield 84% (600 mg), colorless oil (eluent, petroleum ether/EtOAc 4:1); 1H NMR (300 MHz, CDCl3) δ 7.86−7.78 (m, 2H), 7.47−7.32 (m, 4H), 7.04− 6.98 (m, 2H), 5.35 (s, 1H); 13C NMR (75 MHz, CDCl3) δ 153.4, 138.8, 138.4, 133.6, 131.8, 131.3, 126.0, 125.5, 123.7, 122.4, 120.8, 119.1, 116.4, 108.6; HRMS (EI) calcd for C14H9BrOS [M]+ 303.9557, found 303.9560. 2-(3-Bromothiophen-2-yl)phenol (3b): yield 87% (460 mg), colorless oil (eluent, petroleum ether/EtOAc 4:1); 1H NMR (400 MHz, CDCl3) δ 7.43 (d, J = 5.2 Hz, 1H), 7.39−7.32 (m, 1H), 7.28 (dd, J = 8.8, 1.2 Hz, 1H), 7.12 (d, J = 5.6 Hz, 1H), 7.01−6.98 (m, 2H), 5.13 (s, 1H); 13C NMR (101 MHz, CDCl3) δ 153.4, 133.2, 131.9, 131.0, 131.0, 127.4, 120.6, 118.8, 116.2, 111.0; HRMS (EI) calcd for C10H7BrOS [M]+ 253.9401, found 253.9399. 2-(3-Bromo-6-(tert-butyl)benzo[b]thiophen-2-yl)phenol (3c): yield 88% (732 mg), colorless oil (eluent, petroleum ether/EtOAc 4:1); 1H NMR (300 MHz, CDCl3) δ 7.83 (s, 1H), 7.79 (d, J = 7.8 Hz 1H), 7.56 (dd, J = 7.8, 1.5 Hz, 1H), 7.39−7.33 (m, 2H), 7.04−6.98 (m, 2H), 5.31 (s, 1H), 1.40 (s, 9H); 13C NMR (75 MHz, CDCl3) δ 153.4, 149.7, 139.0, 136.2, 132.5, 131.7, 131.2, 123.9, 123.2, 120.7, 119.2, 118.6, 116.4, 108.3, 35.2, 31.6; HRMS (EI) calcd for C18H17BrOS [M]+ 360.0183, found 360.0184. 2-(3-Bromobenzo[b]thiophene-2-yl)-5-(tert-butyl)phenol (3d): yield 76% (275 mg), colorless oil (eluent, petroleum ether/EtOAc 4:1); 1H NMR (400 MHz, CDCl3) δ 7.85 (d, J = 8.0 Hz, 1H), 7.80 (d, J = 8.0 Hz, 1H), 7.50−7.39 (m, 2H), 7.30 (d, J = 8.0 Hz, 1H), 7.08− 7.04 (m, 2H), 5.28 (s, 1H), 1.35 (s, 9H); 13C NMR (101 MHz, CDCl3) δ 155.1, 153.0, 138.8, 138.4, 133.9, 131.2, 125.8, 125.4, 123.6, 122.4, 118.0, 116.0, 113.5, 108.2, 34.9, 31.2; HRMS (EI) calcd for C18H17BrOS [M]+ 360.0183, found 360.0183. 2-(3-Bromo-6-(tert-butyl)benzo[b]thiophen-2-yl)-5-(tert-butyl)phenol (3e): yield 63% (176 mg), colorless oil (eluent, petroleum ether/EtOAc 4:1); 1H NMR (300 MHz, CDCl3) δ 7.82 (d, J = 0.9 Hz, 1H), 7.79 (d, J = 8.4 Hz, 1H), 7.56 (s, J = 8.4, 1.5 Hz, 1H), 7.27 (d, J = 8.4 Hz, 1H), 7.05 (m, 2H), 5.25 (s, 1H), 1.40 (s, 9H), 1.35 (s, 9H); 13 C NMR (75 MHz, CDCl3) δ 155.0, 153.0, 149.6, 138.9, 136.2, 132.8, 131.2, 123.8, 123.1, 118.5, 118.0, 116.1, 113.4, 107.9, 35.1, 34.9, 31.5, 31.2; HRMS (EI) calcd for C22H25BrOS [M]+ 416.0809, found 416.0806. 2-(3-Bromobenzo[b]thiophen-2-yl)-4-fluorophenol (3f): yield 76% (150 mg), colorless oil (eluent, petroleum ether/EtOAc 4:1); 1H

Table 2. Screening the Reaction Substrates

a

Reaction conditions for the general intramolecular C−O Ullmann reaction for the synthesis of 4: CuI (10 mol %), phen (20 mol %), K2CO3 (2 equiv), DMF (10 mL), 15 min. bReaction conditions for the general intramolecular C−O Ullmann reaction for the synthesis of 4: CuI (20 mol %), phen (40 mol %), using NaHCO3 as the base, 1 h. 10923

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Figure 2. Synthesis of π-extended molecules.

Figure 3. Packing structures of C6-DTBDT and C8-DTBDF. NMR (300 MHz, CDCl3) δ 7.88−7.81 (m, 2H), 7.53−7.41 (m, 2H), 7.10−7.03 (m, 2H), 7.00−6.95 (m, 1H), 5.19 (s, 1H); 13C NMR (75 MHz, CDCl3) δ 158.1, 154.9, 149.5 (d, J = 2.2 Hz), 138.7, 138.2, 132.2, 126.2, 125.6, 123.8, 122.5, 119.8 (d, J = 8.5 Hz), 118.1−117.5 (m), 109.0; HRMS (EI) calcd for C14H8BrFOS [M]+ 321.9463, found 321.9462. 1-(3-Bromo-2-(2-hydroxyphenyl)benzo[b]thiophen-6-yl)octan-1one (3g): yield 66% (145 mg), white solid, mp 161.5−162.8 °C (eluent, petroleum ether/EtOAc 4:1); 1H NMR (300 MHz, CDCl3) δ 8.44 (s, 1H), 8.07 (dd, J = 8.4, 1.2 Hz, 1H), 7.92 (d, J = 8.4 Hz, 1H), 7.43−7.37 (m, 2H), 7.08−7.04 (m, 2H), 5.34 (s, 1H), 3.05 (t, J = 7.5 Hz, 2H), 1.77 (m, 2H), 1.31 (m, 8H), 0.89 (t, J = 6.9 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 199.8, 153.3, 141.5, 138.7, 138.1, 134.4, 131.6, 131.6, 124.9, 123.7, 122.9, 120.8, 118.8, 116.6, 108.4, 39.0, 31.7, 29.4, 29.2, 24.5, 22.6, 14.1; HRMS (MALDI-TOF) calcd for C22H23BrO2S [M + H]+ 431.06804, found 431.06763. 4-Bromo-2-(3-bromobenzo[b]thiophen-2-yl)phenol (3h): yield 78% (600 mg), white solid, mp 112.3−113.9 °C (eluent, petroleum ether/EtOAc 4:1); 1H NMR (300 MHz, CDCl3) δ 7.89−7.83 (m, 2H), 7.54−7.43 (m, 4H), 6.94 (dd, J = 8.4, 0.9 Hz, 1H), 5.25 (s, 1H); 13 C NMR (75 MHz, CDCl3) δ 152.6, 138.8, 138.2, 134.0, 133.9, 131.7, 126.3, 125.7, 123.8, 122.5, 121.0, 118.2, 112.5, 109.2; HRMS (EI) calcd for C14H8Br2OS [M]+ 381.8662, found 381.8655. 2-(3,6-Dibromobenzo[b]thiophen-2-yl)phenol (3i): yield 91% (240 mg), white solid, mp 114.6−115.5 °C (eluent, petroleum ether/EtOAc 4:1); 1H NMR (300 MHz, CDCl3) δ 7.98 (d, J = 1.5 Hz, 1H), 7.71 (d, J = 8.4 Hz, 1H), 7.59 (dd, J = 8.7, 1.8 Hz, 1H), 7.40− 7.33 (m, 2H), 7.06−7.01 (m, 2H), 5.19 (s, 1H); 13C NMR (75 MHz, CDCl3) δ 153.3, 140.1, 137.3, 134.2, 131.7, 131.4, 129.0, 124.9, 124.8, 120.8, 112.0, 118.6, 116.5, 108.2; HRMS (EI) calcd for C14H8Br2OS [M]+ 383.8642, found 383.8649. 2-(3-Bromobenzo[b]thiophen-2-yl)-4-chlorophenol (3j): yield 82% (280 mg), colorless oil (eluent, petroleum ether/EtOAc 4:1); 1 H NMR (300 MHz, CDCl3) δ 7.90−7.84 (m, 2H), 7.56−7.41 (m,

2H), 7.35−7.32 (m, 2H), 7.00 (dd, J = 7.5, 1.8 Hz, 1H), 5.21 (s, 1H); C NMR (75 MHz, CDCl3) δ 152.1, 138.8, 138.2, 131.8, 131.1, 131.1, 126.2, 125.7, 125.4, 123.8, 122.5, 120.4, 117.8, 109.2; HRMS (EI) calcd for C14H8BrClOS [M]+ 337.9168, found 337.9170. 2-(3-Bromo-5-chlorobenzo[b]thiophen-2-yl)phenol (3k): yield 70% (325 mg), colorless oil (eluent, petroleum ether/EtOAc 4:1); 1 H NMR (400 MHz, CDCl3) δ 7.84 (d, J = 2.0 Hz, 1H), 7.72 (d, J = 8.8 Hz, 1H), 7.40−7.33 (m, 3H), 7.05−7.01 (m, 2H), 5.19 (s, 1H); 13 C NMR (100 MHz, CDCl3) δ 153.2, 139.6, 136.9, 135.8, 132.0, 131.7, 131.5, 126.4, 123.5, 123.4, 120.9, 118.7, 116.5, 107.6; HRMS (EI) calcd for C14H8BrClOS [M]+ 337.9168, found 337.9172. 2-(3-Bromo-5-chlorobenzo[b]thiophen-2-yl)-4-chlorophenol (3l): yield 64% (330 mg), white solid, mp 134.7−136.9 °C (eluent, petroleum ether/EtOAc 4:1); 1H NMR (300 MHz, CDCl3) δ 7.87 (d, J = 2.1 Hz, 1H), 7.76 (d, J = 8.4 Hz, 1H), 7.42 (dd, J = 8.4 Hz, 2.1 Hz, 1H), 7.36−7.31 (m, 2H), 7.00−6.96 (m, 1H), 5.22 (s, 1H); 13C NMR (75 MHz, CDCl3) δ 152.0, 139.5, 136.9, 134.1, 132.2, 131.3, 131.1, 126.8, 125.6, 123.6, 123.5, 120.1, 117.9, 108.1; HRMS (EI) calcd for C14H7BrCl2OS [M]+ 371.8778, found 371.8772. 2-(3-Bromo-5-chlorobenzo[b]thiophen-2-yl)-4-fluorophenol (3m): yield 81% (144 mg), white solid, mp 124.3−126.7 °C (eluent, petroleum ether/EtOAc 4:1); 1H NMR (300 MHz, CDCl3) δ 7.87 (d, J = 1.5 Hz, 1H), 7.76 (d, J = 8.7 Hz, 1H), 7.42 (dd, J = 8.4, 1.8 Hz, 1H), 7.13−7.07 (m, 2H), 7.01−6.96 (m, 1H), 5.05 (s, 1H); 13C NMR (75 MHz, CDCl3) δ 158.1, 155.0, 149.5 (d, J = 2.2 Hz), 139.5, 136.8, 134.4, 132.2, 126.7, 123.5 (d, J = 3.4 Hz), 119.5 (d, J = 8.4 Hz), 118.3, 118.1−117.4 (m), 108.0; HRMS (EI) calcd for C14H7BrClFOS [M]+ 355.9074, found 355.9076. 2,5-Bis(3-bromothiophen-2-yl)benzene-1,4-diol (3n). 2,3-Dibromothiophene (1.20 g, 5.0 mmol) was dissolved in anhydrous THF (20 mL) under N2, to which iPrMgCl·LiCl (1.3 M in THF, 2 mL, 2.6 mmol) and ZnCl2 (2.6 mL, 1 M in THF) were added at −78 °C successively. The mixture was warmed to room temperature and stirred for 30 min. 2,5-Diiodo-1,4-phenylene diacetate (0.93 g, 2.1 13

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121.0, 120.7, 119.0, 118.7, 117.8, 109.3, 35.2, 31.7, 31.6; HRMS (MALDI-TOF) calcd for C22H24OS [M]+ 336.1548, found 336.1544. 8-Fluorobenzo[4,5]thieno[3,2-b]benzofuran (4f): yield 90% (42 mg), white solid, mp 109.4−111.7 °C (eluent, petroleum ether); 1H NMR (300 MHz, CDCl3) δ 8.00 (d, J = 8.4 Hz, 1H), 7.88 (d, J = 8.1 Hz, 1H), 7.58−7.36 (m, 4H), 7.12−7.05 (m, 1H); 13C NMR (75 MHz, CDCl3) δ 160.9, 157.7, 154.9, 154.6, 142.2, 125.4, 125.1, 124.4, 119.9, 113.2 (d, J = 9.7 Hz), 112.5, 112.2, 105.6 (d, J = 26.2 Hz); HRMS (MALDI-TOF) calcd for C14H7FOS [M]+ 242.0196, found 242.0197. 1-(Benzo[4,5]thieno[3,2-b]benzofuran-2-yl)octan-1-one (4g): yield 74% (20 mg), white solid, mp 104.4−106.2 °C (eluent, petroleum ether/EtOAc 4:1); 1H NMR (300 MHz, CDCl3) δ 8.52 (s, 1H), 8.10−8.03 (m, 2H), 7.78 (dd, J = 7.6, 1.1 Hz, 1H), 7.68 (d, J = 7.8 Hz, 1H), 7.47−7.36 (m, 2H), 3.06 (t, J = 7.5 Hz, 2H), 1.78 (m, 2H), 1.49−1.15 (m, 8H), 0.90 (t, J = 6.7 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 199.6, 159.2, 152.4, 141.9, 133.5, 127.9, 126.0, 125.0, 124.8, 123.7, 123.6, 122.7, 120.1, 119.5, 112.8, 38.8, 31.8, 29.4, 29.2, 24.6, 22.7, 14.1; HRMS (EI) calcd for C22H22O2S [M]+ 350.1341, found 350.1343. 8-Bromobenzo[4,5]thieno[3,2-b]benzofuran (4h): yield 72% (70 mg), white solid, mp 184.5−186.9 °C (eluent, petroleum ether); 1H NMR (300 MHz, CDCl3) δ 8.01 (d, J = 7.5 Hz, 1H), 7.90−7.87 (m, 2H), 7.54−7.39 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 157.5, 154.1, 142.3, 127.7, 125.9, 125.4, 125.1, 124.8, 124.4, 122.3, 119.9, 117.7, 116.4, 113.9; HRMS (MALDI-TOF) calcd for C14H7BrOS [M]+ 301.9401, found 301.9398. 2-Bromobenzo[4,5]thieno[3,2-b]benzofuran (4i): yield 66% (40 mg), white solid, mp 141.6−142.0 °C (eluent, petroleum ether); 1H NMR (400 MHz, CDCl3) δ 8.01 (s, 1H), 7.84 (d, J = 8.4 Hz, 1H), 7.71 (d, J = 7.6 Hz, 1H), 7.63 (d, J = 8.0 Hz, 1H), 7.57 (dd, J = 8.4, 1.2 Hz, 1H), 7.40−7.35 (m, 2H); 13C NMR (75 MHz, CDCl3) δ 158.9, 152.4, 143.3, 128.4, 126.9, 125.3, 123.9, 123.8, 123.5, 120.6, 119.7, 119.1, 118.5, 112.7; HRMS (MALDI-TOF) calcd for C14H7BrOS [M]+ 301.9401, found 301.9397. 8-Chlorobenzo[4,5]thieno[3,2-b]benzofuran (4j): yield 74% (9 mg), white solid (eluent, petroleum ether); 1H NMR (400 MHz, CDCl3) δ 7.99 (d, J = 7.9 Hz, 1H), 7.88 (d, J = 8.1 Hz, 1H), 7.70 (d, J = 2.1 Hz, 1H), 7.56 (d, J = 8.8 Hz, 1H), 7.51−7.43 (m, 2H), 7.34 (dd, J = 8.8, 2.1 Hz, 1H); 13C NMR (75 MHz, CDCl3) δ 157.1, 154.2, 142.3, 129.0, 125.1, 125.0, 124.9, 124.4, 119.9, 119.3, 117.8, 113.5. These data are consistent with those reported in the literature.16 3-Chlorobenzo[4,5]thieno[3,2-b]benzofuran (4k): yield 65% (14 mg), white solid, mp 163.5−166.2 °C (eluent, petroleum ether); 1H NMR (300 MHz, CDCl3) δ 7.96 (d, J = 2.0 Hz, 1H), 7.78−7.70 (m, 2H), 7.63 (d, J = 8.1 Hz, 1H), 7.42−7.31 (m, 3H); 13C NMR (75 MHz, CDCl3) δ 158.9, 151.8, 139.9, 131.4, 126.1, 125,5, 125.3, 125.2, 123.8, 123.5, 120.5, 119.8, 119.5, 112.7; HRMS (EI) calcd for C14H7ClOS [M]+ 257.9906, found 257.9903. 3,8-Dichlorobenzo[4,5]thieno[3,2-b]benzofuran (4l): yield 63% (13 mg), white solid, mp 207.3−210.2 °C (eluent, petroleum ether); 1 H NMR (300 MHz, CDCl3) δ 7.98 (d, J = 1.5 Hz, 1H), 7.79 (d, J = 8.7 Hz, 1H), 7.72 (d, J = 2.1 Hz, 1H), 7.57 (d, J = 9.0 Hz, 1H), 7.39− 7.35 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 157.2, 153.0, 140.2, 131.6, 129.2, 125.8, 125.8, 125.6, 125.4, 125.0, 119.7, 119.5, 113.6; HRMS (EI) calcd for C14H6Cl2OS [M]+ 291.9516, found 291.9518. 3-Chloro-8-fluorobenzo[4,5]thieno[3,2-b]benzofuran (4m): yield 65% (13 mg), white solid, mp 119.8−122.8 °C (eluent, petroleum ether); 1H NMR (300 MHz, CDCl3) δ 7.95 (d, J = 1.8 Hz, 1H), 7.77 (d, J = 8.7 Hz, 1H), 7.56 (dd, J = 9.0, 4.2 Hz, 1H), 7.40−7.34 (m, 2H), 7.15−7.08 (m, 1H); 13C NMR (75 MHz, CDCl3) δ 160.9, 157.7, 155.0, 153.4, 140.1, 131.5, 125.8 (d, J = 18.8 Hz), 125.3, 124.5, 120.1, 119.6, 113.4−113.1 (m), 112.8, 105.8 (d, J = 25.5 Hz); HRMS (EI) calcd for C14H6ClFOS [M]+ 275.9812, found 275.9809. Dithieno[2,3-d;2′,3′-d′]benzo[1,2-b;4,5-b′]difuran (DTBDF). 3n (60 mg, 0.14 mmol) was dissolved into 2 mL of DMF in a screwcap test tube. After the solution was bubbled with N2 for 10 min, the base NaHCO3 (26 mg, 2 mmol) was added to the solution, and then CuI (12 mg, 0.06 mmol) and 4,4′-di-tert-butyl-2,2′-bipyridine (32 mg, 0.12 mmol) were added to the solution. Then the reaction was heated

mmol) and PdCl2(PPh3)2 (74 mg, 0.1 mmol) were added, and the mixture was heated at 60 °C for 10 h. After the removal of the solvent under reduced pressure, the residue was purified by flash chromatography with hexane/ethyl acetate an eluent to afford 2,5bis(3-bromothiophen-2-yl)benzene-1,4-diol diacetate as a white solid (490 mg, 0.95 mmol, 45%): 1H NMR (400 MHz, CDCl3) δ 7.41 (s, 1H), 7.38 (d, J = 5.4 Hz, 1H), 7.07 (d, J = 5.4 Hz, 1H), 2.18 (s, 3H); 13 C NMR (101 MHz, CDCl3) δ 168.5, 145.5, 131.9, 130.9, 127.16, 126.9, 126.4, 110.9, 20.9. 2,5-Bis(3-bromothiophen-2-yl)benzene-1,4diol diacetate was dissolved in THF and MeOH (20 mL, 2:1) and 5 mL of HCl (2 M), which was refluxed for 4 h and cooled to room temperature. After the removal of the solvent under reduced pressure, the residue was purified by flash chromatography to afford compound 3n: yield 93% (380 mg), white solid, mp 196.0−198.3 °C (eluent, petroleum ether/EtOAc 3:1); 1H NMR (400 MHz, DMSO-d6) δ 9.40 (br s, 2H), 7.70 (d, J = 5.4 Hz, 2H), 7.14 (d, J = 5.4 Hz, 2H), 6.94 (s, 2H); 13C NMR (100 MHz, DMSO-d6) δ 147.5, 134.7, 130.6, 127.6, 120.7, 118.7, 109.3; HRMS (EI) calcd for C14H8Br2O2S2 [M]+ 429.8332, found 429.8332. 2,2′-(3,6-Dibromothieno[3,2-b]thiophene-2,5-diyl)diphenol (3o): yield 49% (37 mg), white solid, mp 227.8−229.2 °C (eluent, petroleum ether/EtOAc 4:1); 1H NMR (400 MHz, DMSO-d6) δ 10.08 (s, 2H), 7.41 (dd, J = 7.6, 1.5 Hz, 2H), 7.37−7.26 (m, 2H), 7.00 (d, J = 8.2 Hz, 2H), 6.93 (dd, J = 10.9, 4.1 Hz, 2H); 13C NMR (100 MHz, DMSO-d6) δ 155.8, 138.2, 136.8, 132.2, 131.3, 119.5, 119.2, 116.6, 102.4; HRMS (ESI) calcd for C18H10Br2O2S2 [M]+ 479.8489, found 479.8483. General Procedure for Ullmann-Type Iintramolecular C−O Reaction. Compound 3 (1.0 equiv) was dissolved in DMF (0.1 M) in a Schlenk tube, to which K2CO3 or NaHCO3 (2.0 equiv), CuI (10 mol %), and 1,10-phenanthroline (20 mol %) were added under N2. After heating at 90 °C for 15 min, the reaction solution was evaporated under reduced pressure, and the residue was purified by silica gel chromatography to afford pure compound 4. Benzo[4,5]thieno[3,2-b]benzofuran (4a): yield 80% (520 mg), white solid (eluent, petroleum ether); 1H NMR (300 MHz, CDCl3) δ 8.01 (d, J = 7.8 Hz, 1H), 7.88 (d, J = 8.1 Hz, 1H), 7.73 (d, J = 6.9 Hz, 1H), 7.65 (d, J = 7.8 Hz, 1H), 7.50−7.32 (m, 4H); 13C NMR (75 MHz, CDCl3) δ 158.8, 153.0, 142.0, 125.2, 124.98, 124.95, 124.4, 124.1, 123.3, 119.7, 119.6, 118.6, 112.6. These data are consistent with those reported in the literature.16 Thieno[3,2-b]benzofuran (4b): yield 62% (67 mg), white solid (eluent, petroleum ether); 1H NMR (300 MHz, CDCl3) δ 7.68−7.65 (m, 1H), 7.57−7.54 (m, 1H), 7.36 (d, J = 5.3 Hz, 1H), 7.34−7.28 (m, 2H), 7.15 (d, J = 5.3 Hz, 1H); 13C NMR (75 MHz, CDCl3) δ 159.4, 159.2, 127.6, 124.4, 123.8, 123.0, 119.4, 119.1, 112.5, 111.5. These data are consistent with those reported in the literature.16 2-(tert-Butyl)benzo[4,5]thieno[3,2-b]benzofuran (4c): yield 81% (95 mg), white solid, mp 112.9−115.0 °C (eluent, petroleum ether); 1 H NMR (300 MHz, CDCl3) δ 7.91 (d, J = 8.5 Hz, 1H), 7.86 (d, J = 1.5 Hz, 1H), 7.71−7.65 (m, 1H), 7.65−7.58 (m, 1H), 7.51 (dd, J = 8.4, 1.7 Hz, 1H), 7.38−7.27 (m, 2H), 1.40 (s, 9H); 13C NMR (75 MHz, CDCl3) δ 158.7, 153.0, 148.6, 142.5, 124.6, 124.3, 123.27, 123.23, 122.9, 120.7, 119.5, 119.3, 117.9, 112.5, 35.19, 31.6; HRMS (EI) calcd for C18H16OS [M]+ 280.0922, found 280.0923. 7-(tert-Butyl)benzo[4,5]thieno[3,2-b]benzofuran (4d): yield 87% (56 mg), white solid, mp 80.7−83.4 °C (eluent, petroleum ether); 1H NMR (400 MHz, CDCl3) δ 7.98 (d, J = 8.0 Hz, 1H), 7.87 (d, J = 8.0 Hz, 1H), 7.67 (d, J = 1.2 Hz, 2H), 7.64 (d, J = 8.0 Hz), 7.48−7.43 (m, 3H), 1.42 (s, 9H); 13C NMR (100 MHz, CDCl3) δ 159.3, 152.9, 149.2, 141.8, 125.4, 124.9, 124.6, 124.4, 121.5, 121.1, 119.5, 118.9, 118.6, 109.4, 35.2, 31.7; HRMS (EI) calcd for C18H16OS [M]+ 280.0922, found 280.0922. 2,7-Di-tert-butylbenzo[4,5]thieno[3,2-b]benzofuran (4e): yield 97% (39 mg), white solid, mp 158.8−160.2 °C (eluent, petroleum ether); 1H NMR (300 MHz, CDCl3) δ 7.91 (d, J = 8.4 Hz, 1H), 7.86 (s, 1H), 7.66 (s, 1H), 7.62 (d, J = 8.1 Hz, 1H), 7.51 (dd, J = 8.4, 1.5 Hz, 1H), 7.40 (dd, J = 8.4, 1.5 Hz, 1H), 1.41 (s, 18H); 13C NMR (75 MHz, CDCl3) δ 159.2, 152.9, 148.8, 148.2, 142.2, 123.1, 123.1, 121.7, 10925

DOI: 10.1021/acs.joc.7b01745 J. Org. Chem. 2017, 82, 10920−10927

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The Journal of Organic Chemistry to 90 °C for 24 h. After the reaction cooled to room temperature, the solution was evaporated under a vacuum, and the residue was purified by chromatography (eluting with hexane/CH2Cl2 1:1) to afford the corresponding π-extended fused product DTBDF: yield 47% (18 mg), white solid, mp 234.6−236.3 °C (eluent, petroleum ether/CH2Cl2 1:1); 1H NMR (400 MHz, CDCl2CDCl2) δ 7.80 (s, 2H), 7.41 (d, J = 5.3 Hz, 2H), 7.19 (d, J = 5.3 Hz, 2H); 13C NMR (125 MHz, CDCl2CDCl2, 60 °C) δ 160.2, 156.2, 127.4, 121.2, 119.6, 111.6, 101.9; HRMS (EI) calcd for C14H6O2S2 [M]+ 269.9809, found 269.9807. Thieno[4,5:4′,5′]thieno[3,2-b:3′,2′-b′]di(benzofuran) (TTDBF). 3o (130 mg, 0.27 mmol) was dissolved into 5 mL of toluene in a screwcap test tube, and then the base K2CO3 (130 mg, 1 mmol) was added to the solution. After the solution was bubbled with N2 for 10 min, CuI (21 mg, 0.11 mmol, 41 mol %) and 4,4′-di-tert-butyl-2,2′bipyridine (39 mg, 0.15 mmol, 56 mol %) were added to the solution. Then the reaction was heated to 90 °C for 24 h. After the reaction cooled to room temperature, the solution was evaporated under a vacuum, and the residue was purified by flash chromatography (eluting with hexane/CH2Cl2 1:1) to afford the corresponding π-extended fused product TTDBF: yield 48% (42 mg), white solid, mp 321.3− 324.3 °C (eluent, petroleum ether/CH2Cl2 1:1); 1H NMR (400 MHz, CDCl2CDCl2) δ 7.71 (dd, J = 6.0, 3.0 Hz, 2H), 7.62 (dd, J = 6.2, 3.1 Hz, 2H), 7.41−7.33 (m, 4H); 13C NMR (126 MHz, CDCl2CDCl2, 100 °C) δ 158.4, 150.9, 124.5, 124.2, 124.0, 123.4, 120.8, 118.5, 112.2; HRMS (EI) calcd for C18H8O2S2 [M]+ 319.9966, found 319.9970. 2,7-Dioctyldithieno[2,3-d;2′,3′-d′]benzo[1,2-b;4,5-b′]difuran (C8DTBDF). To compound DTBDF (30 mg, 0.11 mmol) in CH2Cl2 (2 mL) was added AlCl3 (65 mg, 0.5 mmol) at −20 °C, and the mixture was then cooled to −78 °C. Octanoyl chloride (97 mg, 0.6 mmol) was added slowly to this solution, and then the resulting mixture was warmed to room temperature for 24 h. The reaction was quenched slowly with water in an ice bath, extracted with CH2Cl2, and dried over MgSO4. After the removal of the solvent under reduced pressure, the crude product was redissolved in Et2O at −20 °C, to which AlCl3 and LiAlH4 were added successively. The reaction suspension was warmed to room temperature, stirred for 12 h, and then quenched carefully with water in an ice bath. After extraction with hexane, the crude product was purified by silica gel chromatography to give 35 mg of compound C8-DTBDF: yield 63% (35 mg), white solid, mp 159.1− 161.5 °C (eluent, petroleum ether); 1H NMR (400 MHz, CDCl3) δ 7.66 (s, 2H), 6.89 (s, 2H), 2.91 (t, J = 7.6 Hz, 4H), 1.80−1.69 (m, 4H), 1.44−1.22 (m, 10H), 0.88 (t, J = 6.8 Hz, 6H); 13C NMR (100 MHz, CDCl3) δ 159.1, 155.2, 149.0, 120.9, 116.7, 109.0, 101.1, 31.9, 31.7, 31.6, 29.3, 29.2, 29.0, 22.7, 14.1; HRMS (EI) calcd for C30H38O2S2 [M]+ 494.2313, found 494.2308.

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Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the National Basic Research Program of China (973 Program) (no. 2014CB643502) for financial support, the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB12010200), and the National Natural Science Foundation of China (21402194, 91333113, 21572234).

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.7b01745. Synthesis of 3; NMR spectra of all the new compounds; crystallographic information for 4a, 4d, 4j, and C8DTBDF; optimization of reaction conditions of 4l; DFT calculations details and Cartesian coordinates; CV spectra and OFET research of C8-DTBDF; proposed mechanism for intramolecular C−O Ullmann reaction (PDF) Crystal data for 4a (CIF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Baolin Li: 0000-0001-7735-6716 Xiaozhang Zhu: 0000-0002-6812-0856 10926

DOI: 10.1021/acs.joc.7b01745 J. Org. Chem. 2017, 82, 10920−10927

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DOI: 10.1021/acs.joc.7b01745 J. Org. Chem. 2017, 82, 10920−10927