Synthesis of 9-biarylfluorenes by one-pot,three-step reactions of N -tosylhydrazones,p -bromobenzeneboronic acid,and arylboronic acids

Abstract

A one-pot, three-step reaction of N-tosylhydrazones, p-bromobenzeneboronic acid, and arylboronic acids is established for the synthesis of 9-biarylfluorenes. Sequential formation of Csp³–Csp² bond and Csp²–Csp² bonds using readily available starting materials leads to the 9-biarylfluorene products in good yields. The present transformation features a broad substrate scope and good functional group tolerance.

Keywords

9-biarylfluorenes boronic acids one-pot

Introduction

Biaryl units are important building blocks that have been found in natural products, pharmaceutical intermediates, conducting polymers, pesticides, and liquid crystals.¹ The palladium-catalyzed Suzuki–Miyaura reaction has become one of the most powerful methods for the formation of C_aryl–C_aryl bonds because organoboranes are air- and moisture-stable and show relatively low toxicity.^2,3 In addition, 9-arylfluorenes have attracted considerable attention due to their important physical properties, which can be utilized in organic light-emitting materials, thin-film transistors, photovoltaic cells, and so on.^4–10 Recently, 9-biarylfluorenes have been employed in organic chemical reactions and in fluorescent materials applications.^11–14 However, the preparation of such compounds typically requires complex catalytic systems, non-readily available substrates, and harsh reaction conditions. Thus, it is highly desirable to develop efficient synthetic routes to 9-biarylfluorenes.

Structural analysis of the 9-biarylfluorene skeleton (Scheme 1) reveals that both the Csp²–Csp² and Csp²–Csp³ bonds are constructed separately. As is known, the Csp²–Csp² bond can be formed by a palladium-catalyzed Suzuki reaction of an aryl halide with an arylboronic acid (Scheme 1(a)), and the Csp²–Csp³ bond can be easily achieved via our previously reported metal-free coupling reaction of an N-tosylhydrazone with an aryl boronic acid (Scheme 1(b)).¹⁵ Hence, if we use p-bromobenzeneboronic acid as a bifunctional substrate, it is possible to easily achieve access to 9-biarylfluorenes via a one-pot, multi-step reaction. Based on the above analysis and other research,^16–21 we herein report an efficient approach for the synthesis of 9-biarylfluorenes via the sequential formation of one Csp²–Csp³ bond and one Csp²–Csp² bond by one-pot, three-step reactions of N-tosylhydrazones, p-bromobenzeneboronic acid, and arylboronic acids (Scheme 1(c)).

Scheme 1.

Construction of Csp²–Csp² and Csp²–Csp³ bonds. (a) Classical coupling reaction, (b) our previous work, and (c) this work: one-pot, multi-step reaction.

Results and discussion

First, N-tosylhydrazone was prepared by treating 9-fluorenone (1a) (0.5 mmol) with tosylhydrazide (0.75 mmol) in toluene (5 mL) at 80 °C for 2 h. Addition of an arylboronic acid (0.55 mmol) and K₂CO₃ (1.5 equiv.) to the above solution and stirring at 110 °C for 5 h provided 9-(4-bromophenyl)-9H-fluorene as the product. Sub-sequently, the palladium-catalyzed coupling reaction of phenylboronic acid (2a) (0.75 mmol) with the intermediate 9-(4-bromophenyl)-9H-fluorene was carried out by using K₂CO₃ as the base at 110 °C for 12 h, affording the desired product 3a in 64% yield (Table 1, entry 1). On this basis, a series of bases were screened for applicability in the Suzuki reaction. The use of a strong base, such as NaOH, gave a good yield (entry 5 vs entries 2–4). With the amount of Pd(PPh₃)₄ increased to 5 mol%, the yield was not improved (entry 6). The effect of temperature on the reaction was also examined, which led to a further improvement of the yield at 80 °C (76%, entry 9 vs entries 7 and 8). When the second-step reductive coupling reaction was conducted in the presence of 2.0 equiv. of K₂CO₃, an 86% yield of 3a was obtained (entry 10 vs entry 11). Finally, the optimized reaction conditions were identified as follows: (i) 9-fluorenone (0.5 mmol), tosylhydrazide (0.75 mmol), toluene (5 mL), 80 °C, 2 h, argon atmosphere; (ii) 4-bromophenylboronic acid (0.55 mmol), K₂CO₃ (1.0 mmol), 110 °C, 5 h, argon atmosphere; and (iii) Pd(PPh₃)₄ (2 mol%), NaOH (0.75 mmol), 80 °C, 12 h, argon atmosphere.

Table 1.

Optimization of the reaction conditions.^a

Entry	(ii) K₂CO₃	(iii) Base	T (°C)	Yield (%)^b
1	1.5 equiv.	K₂CO₃	110	64
2	1.5 equiv.	Na₂CO₃	110	66
3	1.5 equiv.	Cs₂CO₃	110	30
4	1.5 equiv.	K₃PO₄	110	67
5	1.5 equiv.	NaOH	110	70
6^c	1.5 equiv.	NaOH	110	70
7	1.5 equiv.	NaOH	100	64
8	1.5 equiv.	NaOH	90	63
9	1.5 equiv.	NaOH	80	76
10	2.0 equiv.	NaOH	80	86
11	3.0 equiv.	NaOH	80	86

Reaction conditions: (i) 9-fluorenone (1a) (0.5 mmol), tosylhydrazide (0.75 mmol), toluene (5 mL), 80 °C, 2 h; (ii) 4-bromophenylboronic acid (0.55 mmol), K₂CO₃ (1.5–3.0 equiv.), 110 °C, 5 h, Ar; (iii) 2a (0.75 mmol), Pd(PPh₃)₄ (2 mol%), 12 h, Ar.

Isolated yields.

Pd(PPh₃)₄ (5 mol%).

Using the optimized conditions, we further investigated the scope of arylboronic acids in this one-pot, three-step reaction. As shown in Scheme 2, 4-substituted phenylboronic acids bearing electron-donating groups afforded the desired products 3b–e in 70%–85% yields. Moreover, 3- and 2-substituted phenylboronic acids were also suitable reactants, giving the desired products 3f–i in 75%–85% yields. Naphthalene-2-ylboronic acid, as a coupling partner, reacted to provide the corresponding product 3j in 69% yield. In addition, 3-F-, 4-F-, and 2,4-difluoro-substituted phenylboronic acids were found to produce the desired products 3k–m in 72%–78% yields. However, the use of 3,4,5-trifluorophenylboronic acid as the substrate only afforded product 3n in a low yield under the present current reaction conditions. Fortunately, when lithium t-butoxide (LiO^tBu) was used instead of NaOH as the base, a yield of 78% of 3n was obtained. Under these conditions, 2,3-difluoro- and 4-trifluoromethyl-substituted phenylboronic acids were used in the coupling reaction to afford yields of 55% (3o) and 53% (3p), respectively. In addition, 4-vinylbenzeneboronic acid and 3-thiopheneboronic acid were also suitable substrates, giving yields of 48% (3q) and 46% (3r), respectively. Finally, to broaden the substrate scope of this transformation, we tested other substituted 9-fluorenones under the modified reaction conditions. For example, 2-bromo- and 2-amino-substituted 9-fluorenones were used as starting materials to give the desired products in 46% (3s) and 40% (3t) yields via the one-pot, three-step reaction.

Scheme 2.

One-pot reductive coupling of substituted 9-fluorenones with boronic acids.^a

Conclusion

In summary, we have developed an efficient procedure for synthesizing 9-biarylfluorenes in moderate to good yields, via one-pot, three-step reactions of N-tosylhydrazones of 9-fluorenone, p-bromobenzeneboronic acid, and arylboronic acids. The process involves sequential formation of Csp³–Csp² and Csp²–Csp² bonds. Importantly, the system is capable of using readily available starting materials and the intermediates do not need to be separated, and it has a wide substrate scope and good functional group tolerance.

Experimental

General materials and instruments

Unless otherwise noted, all reactions were performed under an argon atmosphere in Schlenk tubes. Melting points were determined with a fusiometer and are not corrected. Materials obtained from commercial suppliers were used without further purification. For chromatography, Qingdao Ocean Chemical 200–300 mesh silica gel was employed. ¹H NMR and ¹³C NMR spectra were recorded on Bruker Avance III HD 400 MHz spectrometer in CDCl₃ or dimethyl sulfoxide (DMSO)-d₆ solution and the chemical shifts are reported in ppm (δ) relative to the internal standard tetramethylsilane (TMS) (0 ppm). High-resolution mass spectrometry (HRMS) was performed on a Thermo Scientific LTQ or bitrap XL mass spectrometer. Please see the supplemental material for the NMR spectra of all compounds.

General procedure for the one-pot, three-step reaction of N-tosylhydrazones, p-bromobenzeneboronic acid, and arylboronic acids

(i) To a Schlenk tube (25 mL) was added 9-fluorenone (1) (0.5 mmol), and tosylhydrazide (0.75 mmol). The tube was degassed for 30 s and then charged with Ar. This operation was repeated three times. After adding toluene (5 mL) under an Ar atmosphere, the tube was sealed and heated at 80 °C for 2 h. The N-tosylhydrazone intermediate was not isolated. (ii) Under an Ar atmosphere, p-bromobenzeneboronic acid (0.55 mmol) and K₂CO₃ (1.0 mmol) were added to the mixture, which was heated at 110 °C for 5 h. (iii) The arylboronic acid (2) (0.75 mmol), Pd(PPh₃)₄ (2 mol%), and NaOH or LiO^tBu (0.75 mmol) were added to the above solution under Ar. The tube was sealed and heated at 80 °C or 110 °C for 12 h. The mixture was allowed to reach room temperature. EtOAc (5 mL) and saturated NaCl solution (5 mL) were added and the layers were separated. The aqueous phase was extracted with EtOAc (5 mL × 3). The organic layer was then dried over anhydrous Na₂SO₄. The solvent was removed under reduced pressure and the residue was purified by silica gel column chromatography to afford the product 3.

9-([1,1′-biphenyl)-4-yl)-9H-fluorene (3a).¹³ Yield: 86%; white solid; m.p. = 139.8–139.5 °C; ¹H NMR (400 MHz, CDCl₃): δ 7.81 (d, J = 7.6 Hz, 2H), 7.55 (d, J = 7.1 Hz, 2H), 7.49 (d, J = 8.3 Hz, 2H), 7.41 (q, J = 6.7 Hz, 4H), 7.35 (t, J = 8.2 Hz, 2H), 7.28 (q, J = 7.9, 7.4 Hz, 3H), 7.16 (d, J = 8.2 Hz, 2H), 5.09 (s, 1H); ¹³C NMR (101 MHz, CDCl₃): δ 147.83, 141.05, 140.90, 140.71, 139.77, 128.73, 127.45, 127.39, 127.37, 127.16, 127.02, 125.38, 119.94, 119.94, 54.11.

9-(4′-methyl-[1,1′-biphenyl)-4-yl)-9H-fluorene (3b). Yield: 85%; white solid; m.p. = 140.3–140.4 °C; ¹H NMR (400 MHz, CDCl₃): δ 7.81 (d, J = 7.5 Hz, 2H), 7.45 (t, J = 8.2 Hz, 4H), 7.37 (dd, J = 15.8, 7.9 Hz, 4H), 7.27 (d, J = 7.4 Hz, 2H), 7.21 (d, J = 8.2 Hz, 2H), 7.13 (d, J = 8.1 Hz, 2H), 5.08 (s, 1H), 2.37 (s, 3H); ¹³C NMR (101 MHz, CDCl₃): δ 147.88, 141.06, 140.38, 139.70, 138.02, 136.92, 129.47, 128.70, 127.37, 127.26, 126.86, 125.39, 119.93, 54.12, 21.13. HRMS (ESI): m/z [M+Na]⁺ calcd for C₂₆H₂₀Na: 355.1457; found: 355.1461.

9-(4′-methoxy-[1,1′-biphenyl)-4-yl)-9H-fluorene (3c). Yield: 78%; white solid; m.p. = 205.3–207.1 °C; ¹H NMR (400 MHz, CDCl₃): δ 7.73 (d, J = 7.6 Hz, 2H), 7.38 (dd, J = 16.3, 7.0 Hz, 4H), 7.29 (dd, J = 16.2, 7.6 Hz, 4H), 7.18 (t, J = 7.4 Hz, 2H), 7.04 (d, J = 7.0 Hz, 2H), 6.86 (d, J = 8.6 Hz, 2H), 4.99 (s, 1H), 3.74 (s, 3H); ¹³C NMR (101 MHz, CDCl₃): δ 159.08, 147.91, 141.06, 140.04, 139.38, 133.46, 128.72, 128.03, 127.38, 127.02, 125.39, 119.94, 114.20, 55.35, 54.11. HRMS (ESI): m/z [M+Na]⁺ calcd for C₂₆H₂₀ONa: 371.1406; found: 371.1412.

9-(4′-propyl-[1,1′-biphenyl)-4-yl)-9H-fluorene (3d). Yield: 76%; white solid; m.p. = 170.9–171.2 °C; ¹H NMR (400 MHz, CDCl₃): δ 7.81 (d, J = 7.6 Hz, 2H), 7.47 (dd, J = 8.2, 3.4 Hz, 4H), 7.37 (dd, J = 15.2, 7.5 Hz, 4H), 7.31–7.18 (m, 4H), 7.14 (d, J = 8.2 Hz, 2H), 5.08 (s, 1H), 2.64–2.58 (t, J =6.0 Hz, 2H), 1.74–1.60 (m, 2H), 0.96 (t, J = 7.3 Hz, 3H); ¹³C NMR (101 MHz, CDCl₃): δ 147.88, 141.74, 141.05, 140.34, 139.74, 138.26, 128.86, 128.68, 127.36, 127.28, 126.83, 125.39, 119.92, 54.12, 37.71, 24.56, 13.92. HRMS (ESI): m/z [M+H]⁺ calcd for C₂₈H₂₅: 361.1951; found: 361.1953.

9-(4′-pentyl-[1,1′-biphenyl)-4-yl)-9H-fluorene (3e). Yield: 70%; white solid; m.p. = 143.2–143.5 °C; ¹H NMR (400 MHz, CDCl₃): δ 7.81 (d, J = 7.6 Hz, 2H), 7.47 (dd, J = 7.8, 3.8 Hz, 4H), 7.37 (dd, J = 15.4, 7.5 Hz, 4H), 7.27 (t, J = 7.4 Hz,2H), 7.22 (d, J = 7.9 Hz, 2H), 7.14 (d, J = 8.0 Hz, 2H), 5.08 (s, 1H), 2.66–2.58 (t, J = 7.8 Hz, 2H), 1.64 (p, J = 7.1 Hz, 2H), 1.41–1.28 (m, 4H), 0.90 (t, J = 6.5 Hz, 3H); ¹³C NMR (101 MHz, CDCl₃): δ 147.89, 142.01, 141.05, 140.33, 139.74, 138.22, 128.80, 128.68, 127.36, 127.28, 126.85, 125.40, 119.92, 54.12, 35.61, 31.60, 31.19, 22.60, 14.09. HRMS (ESI): m/z [M+Na]⁺ calcd for C₃₀H₂₈Na: 411.2083; found: 411.2089.

9-(3′-methyl-[1,1′-biphenyl)-4-yl)-9H-fluorene (3f). Yield: 85%; white solid; m.p. = 141.7–141.8 °C; ¹H NMR (400 MHz, CDCl₃): δ 7.81 (d, J = 7.6 Hz, 2H), 7.47 (d, J = 8.3 Hz, 2H), 7.37 (dd, J = 17.9, 7.4 Hz, 6H), 7.32–7.24 (m, 3H), 7.18–7.10 (m, 3H), 5.09 (s, 1H), 2.39 (s, 3H); ¹³C NMR (101 MHz, CDCl₃): δ 147.86, 141.05, 140.91, 140.58, 139.91, 138.28, 128.68, 128.64, 127.91, 127.86, 127.47, 127.37, 125.38, 124.14, 119.92, 54.12, 21.57. HRMS (ESI): m/z [M+Na]⁺ calcd for C₂₆H₂₀Na: 355.1457; found: 355.1455.

9-(3′-methoxy-[1,1′-biphenyl)-4-yl)-9H-fluorene (3g). Yield: 80%; white solid; m.p. = 187.1–188.2 °C; ¹H NMR (400 MHz, CDCl₃): δ 7.81 (d, J = 7.6 Hz, 2H), 7.48 (d, J = 8.3 Hz, 2H), 7.39 (t, J = 7.5 Hz, 2H), 7.37–7.30 (m, 3H), 7.28 (t, J = 6.4 Hz, 2H), 7.14 (dd, J = 7.4, 5.3 Hz, 3H), 7.09 (s, 1H), 6.87 (d, J = 8.2 Hz, 2H), 5.09 (s, 1H), 3.84 (s, 3H); ¹³C NMR (101 MHz, CDCl₃): δ 159.90, 147.80, 142.44, 141.04, 140.89, 139.64, 129.72, 128.70, 127.49, 127.39, 127.37, 125.37, 119.93, 119.56, 112.75, 112.58, 55.29, 54.10. HRMS (ESI): m/z [M+H]⁺ calcd for C₂₆H₂₁O: 349.1593; found: 349.1587.

9-(3′-chloro-[1,1′-biphenyl)-4-yl)-9H-fluorene (3h). Yield: 75%; white solid; m.p. = 156.1–158.7 °C; ¹H NMR (400 MHz, CDCl₃): δ 7.82 (d, J = 7.6 Hz, 2H), 7.53 (s, 1H), 7.45 (d, J = 8.3 Hz, 2H), 7.43–7.37 (m, 3H), 7.33 (t, J = 7.9 Hz, 3H), 7.27 (q, J = 7.0 Hz, 3H), 7.16 (d, J = 8.3 Hz, 2H), 5.09 (s, 1H); ¹³C NMR (101 MHz, CDCl₃): δ 147.69, 142.74, 141.48, 141.05, 138.36, 134.62, 129.96, 128.87, 127.45, 127.42, 127.40, 127.17, 127.15, 125.33, 125.15, 119.97, 54.07. HRMS (ESI): m/z [M+Na]⁺ calcd for C₂₅H₁₇ClNa: 375.0911; found: 375.0916.

9-(2′-methyl-[1,1′-biphenyl)-4-yl)-9H-fluorene (3i). Yield: 82%; white solid; m.p. = 138.8–139.0 °C; ¹H NMR (400 MHz, CDCl₃): δ 7.83 (d, J = 8.0 Hz, 2H), 7.45–7.37 (m, 4H), 7.30 (d, J = 14.8 Hz, 2H), 7.26–7.21 (m, 6H), 7.14 (d, J = 8.1 Hz, 2H), 5.12 (s, 1H), 2.27 (s, 3H); ¹³C NMR (101 MHz, CDCl₃): δ 147.83, 141.65, 141.05, 140.41, 140.00, 135.39, 130.30, 129.82, 129.50, 127.96, 127.35, 127.31, 127.15, 125.72, 125.42, 119.91, 54.16, 20.54. HRMS (ESI): m/z [M+Na]⁺ calcd for C₂₆H₂₀Na: 355.1457; found: 355.1459.

9-(4-(naphthalen-2-yl)phenyl)-9H-fluorene (3j). Yield: 69%; white solid; m.p. = 216.1–218.7 °C; ¹H NMR (400 MHz, CDCl₃): δ 7.99 (s, 1H), 7.90–7.84 (t, J = 8.0 Hz, 3H), 7.82 (d, J = 7.4 Hz, 2H), 7.70 (d, J = 8.6 Hz, 1H), 7.61 (d, J = 8.3 Hz, 2H), 7.46 (ddd, J = 6.8, 4.4, 1.7 Hz, 2H), 7.38 (dd, J = 13.3, 7.0 Hz, 4H), 7.27 (t, J = 8.0 Hz, 2H), 7.19 (d, J = 8.2 Hz, 2H), 5.11 (s, 1H); ¹³C NMR (101 MHz, CDCl₃): δ 147.85, 141.09, 140.87, 139.67, 138.24, 133.70, 132.60, 128.87, 128.42, 128.20, 127.74, 127.66, 127.43, 127.41, 126.29, 125.90, 125.63, 125.51, 125.41, 119.98, 54.15. HRMS (ESI): m/z [M+Na]⁺ calcd for C₂₉H₂₀Na: 391.1457; found: 391.1458.

9-(4′-fluoro-[1,1′-biphenyl)-4-yl)-9H-fluorene (3k). Yield: 78%; white solid; m.p. = 187.1–188.2 °C; ¹H NMR (400 MHz, CDCl₃): δ 7.82 (d, J = 7.6 Hz, 2H), 7.50 (dd, J = 8.8, 5.3 Hz, 2H), 7.43 (d, J = 8.2 Hz, 2H), 7.39 (t, J = 7.5 Hz, 2H), 7.35 (d, J = 7.2 Hz, 2H), 7.28 (d, J = 7.5 Hz, 2H), 7.15 (d, J = 8.2 Hz, 2H), 7.09 (t, J = 8.7 Hz, 2H), 5.09 (s, 1H); ¹³C NMR (101 MHz, CDCl₃): δ 163.61, 161.17, 147.77, 141.04, 140.76, 138.79, 137.01, 128.79, 128.57, 128.49, 127.41, 127.37, 127.30, 125.33, 119.95, 115.69, 115.48, 54.05. HRMS (ESI): m/z [M+H]⁺ calcd for C₂₅H₁₈F: 337.1387; found: 337.1389

9-(3′-fluoro-[1,1′-biphenyl)-4-yl)-9H-fluorene (3l). Yield: 73%; white solid; m.p. = 189.7–190.2 °C; ¹H NMR (400 MHz, CDCl₃): δ 7.81 (d, J = 7.6 Hz, 2H), 7.46 (d, J = 8.3 Hz, 2H), 7.39 (t, J = 7.4 Hz, 2H), 7.38–7.30 (m, 4H), 7.27 (d, J = 7.4 Hz, 2H), 7.24 (d, J =12 Hz, 1H), 7.15 (d, J = 8.2 Hz, 2H), 7.00 (td, J = 8.4, 2.6 Hz, 1H), 5.08 (s, 1H); ¹³C NMR (101 MHz, CDCl₃): δ 147.71, 143.21, 141.46, 141.07, 138.50, 138.47, 130.24, 130.15, 128.87, 127.46, 127.41, 125.35, 122.63, 122.60, 119.98, 114.06, 113.96, 113.85, 113.75, 54.08. HRMS (ESI): m/z [M+Na]⁺ calcd for C₂₅H₁₇F Na: 359.1206; found: 359.1209.

9-(2′,4′-difluoro-(1,1′-biphenyl) (3m). Yield: 72%; white solid; m.p. = 138.4–139.1 °C; ¹H NMR (400 MHz, CDCl₃): δ 7.81 (d, J = 7.6 Hz, 2H), 7.43–7.35 (m, 4H), 7.35 (d, J = 6.6 Hz, 3H), 7.27 (t, J = 7.4 Hz, 2H), 7.15 (d, J = 8.2 Hz, 2H), 6.94–6.85 (m, 2H), 5.09 (s, 1H); ¹³C NMR (101 MHz, CDCl₃): δ 163.43 (d, J = 11.8 Hz), 160.97 (dd, J = 11.8, 2.8 Hz), 158.49 (d, J = 11.8 Hz), 147.68, 141.27, 141.07, 133.50, 131.34 (dd, J = 9.4, 5.0 Hz), 129.22 (d, J = 2.9 Hz), 128.51, 127.42 (d, J = 5.9 Hz), 125.39, 119.97, 111.65 (d, J = 3.8 Hz), 111.44 (d, J = 3.8 Hz), 104.37 (dd, J = 26.9, 25.1 Hz), 54.12. HRMS (ESI): m/z [M+Na]⁺ calcd for C₂₅H₁₆F₂Na: 377.1112; found: 377.1119.

9-(3′,4,′5′-trifluoro-(1,1′-biphenyl) (3n). Yield: 78%; white solid; m.p. = 132.8–132.9 °C; ¹H NMR (400 MHz, CDCl₃): δ 7.81 (d, J = 7.6 Hz, 2H), 7.44–7.34 (m, 4H), 7.32 (d, J = 6.5 Hz, 2H), 7.28 (q, J = 8.3 Hz, 2H), 7.14 (dd, J = 14.5, 7.4 Hz, 4H), 5.08 (s, 1H); ¹³C NMR (101 MHz, CDCl₃): δ 152.65 (dd, J = 10.0, 4.2 Hz), 150.15 (d, J = 10.0 Hz), 147.52, 142.19, 141.07, 140.42, 137.92, 137.03 (d, J = 4.6 Hz), 136.76, 129.05, 127.49 (d, J = 10.0 Hz), 127.18, 125.28, 120.03, 110.87 (d, J = 21.8 Hz), 54.00. HRMS (ESI): m/z [M+Na]⁺ calcd for C₂₅H₁₅F₃Na: 395.1018; found: 395.1014.

9-(2′,3′-difluoro-(1,1′-biphenyl) (3o). Yield: 55%; white solid; m.p. = 188.5–191.5 °C; ¹H NMR (400 MHz, CDCl₃): δ 7.82 (d, J = 7.6 Hz, 2H), 7.44 (dd, J = 8.3, 1.7 Hz, 2H), 7.40 (t, J = 7.5 Hz, 2H), 7.36 (d, J = 6.7 Hz, 2H), 7.28 (t, J = 7.5 Hz, 2H), 7.18 (d, J = 8.2 Hz, 2H), 7.15–7.08 (m, 3H), 5.11 (s, 1H); ¹³C NMR (101 MHz, CDCl₃): δ 147.60, 141.77, 141.06, 133.25, 131.00 (d, J = 10.3 Hz), 129.27 (d, J = 3.0 Hz), 128.55, 127.43 (d, J = 6.8 Hz), 125.38, 125.21 (d, J = 2.4 Hz), 124.02 (dd, J = 7.2, 4.9 Hz), 119.96, 115.93 (d, J = 17.5 Hz), 54.12; HRMS (ESI): m/z [M+Na]⁺ calcd for C₂₅H₁₆F₂Na: 377.1112; found: 377.1109.

9-(4′-(trifluoromethyl)-[1,1′-biphenyl]-4-yl)-9H-fluorene (3p). Yield: 53%; white solid; m.p. = 238.7–239.2 °C; ¹H NMR (400 MHz, CDCl₃): δ 7.82 (d, J = 7.6 Hz, 2H), 7.64 (d, J = 2.5 Hz, 4H), 7.48 (d, J = 8.3 Hz, 2H), 7.39 (t, J = 7.1 Hz, 2H), 7.34 (d, J = 7.2 Hz, 2H), 7.27 (t, J = 7.4 Hz, 2H), 7.18 (d, J = 8.2 Hz, 2H), 5.10 (s, 1H); ¹³C NMR (101 MHz, CDCl₃): δ 147.63, 144.39, 141.90, 141.08, 138.29, 128.96, 127.60, 127.50, 127.43, 127.25, 125.76, 125.72, 125.68, 125.64, 125.33, 120.01, 54.07; HRMS (ESI): m/z [M+Na]⁺ calcd for C₂₆H₁₇F₃Na: 409.1175; found: 409.1177.

9-(4′-vinyl-[1,1′-biphenyl)-4-yl)-9H-fluorene (3q). Yield: 48%; white solid; m.p. = 221.9–222.3 °C; ¹H NMR (400 MHz, CDCl₃): δ 7.82 (d, J = 7.6 Hz, 2H), 7.56–7.50 (m, 3H), 7.48 (d, J = 8.2 Hz, 3H), 7.39 (t, J = 7.5 Hz, 2H), 7.36 (d, J = 6.7 Hz, 2H), 7.28 (d, J = 7.4 Hz, 2H), 7.16 (d, J = 8.2 Hz, 2H), 6.74 (dd, J = 17.6, 10.9 Hz, 1H), 5.77 (d, J = 18.4 Hz, 1H), 5.26 (d, J = 11.7 Hz, 1H), 5.10 (s, 1H); ¹³C NMR (101 MHz, CDCl₃): δ 147.79, 141.04, 140.80, 140.24, 139.25, 136.48, 136.41, 128.75, 127.38, 127.36, 127.24, 127.06, 126.62, 125.35, 119.93, 113.81, 54.09; HRMS (ESI): m/z [M+H]⁺ calcd for C₂₇H₂₁: 345.1638; found: 345.1641.

3-(4-(9H-fluoren-9-yl)phenyl)thiophene (3r). Yield: 46%; white solid; m.p. = 247.3–248.7 °C; ¹H NMR (400 MHz, CDCl₃): δ 7.81 (d, J = 7.6 Hz, 2H), 7.49 (d, J = 8.3 Hz, 2H), 7.42–7.31 (m, 7H), 7.28 (t, J = 7.4 Hz, 2H), 7.12 (d, J = 8.2 Hz, 2H), 5.07 (s, 1H); ¹³C NMR (101 MHz, CDCl₃): δ 147.79, 142.07, 141.03, 140.54, 134.51, 128.76, 127.37, 127.35, 126.77, 126.28, 126.13, 125.32, 120.04, 119.91, 54.11. HRMS (ESI): m/z [M+Na]⁺ calcd for C₂₃H₁₆SNa: 347.0865; found: 347.0867.

9-([1,1′-biphenyl)-4-yl)-2-bromo-9H-fluorene (3s). Yield: 46%; white solid; m.p. = 201.6–203.2 °C; ¹H NMR (400 MHz, CDCl₃): δ 7.85 (d, J = 7.9 Hz, 1H), 7.81 (d, J = 7.6 Hz, 1H), 7.63 (d, J = 8.4 Hz, 1H), 7.57 (d, J = 7.1 Hz, 2H), 7.49 (s, 1H), 7.39 (dd, J = 8.2, 1.8 Hz, 5H), 7.32 (d, J = 7.3 Hz, 1H), 7.29 (t, J = 5.3 Hz, 2H), 7.00 (d, J = 8.4 Hz, 1H), 5.05 (s, 1H); ¹³C NMR (101 MHz, CDCl₃): δ 148.04, 147.62, 141.11, 140.67, 140.61, 140.20, 131.87, 130.13, 128.76, 127.64, 127.45, 127.27, 127.13, 126.73, 125.25, 123.97, 120.76, 120.26, 120.07, 53.87. HRMS (ESI): m/z [M+Na]⁺ calcd for C₂₅H₁₇BrNa: 419.0406; found: 419.0411.

9-([1,1′-biphenyl)-4-yl)-9H-fluoren-2-amine (3t). Yield: 40%; yellow solid; m.p. = 224.8–226.3 °C; ¹H NMR (400 MHz, DMSO-d₆): δ 7.66 (d, J = 7.5 Hz, 1H), 7.62 (d, J = 7.1 Hz, 2H), 7.56 (dd, J = 8.3, 2.0 Hz, 3H), 7.44 (t, J = 7.6 Hz, 2H), 7.34 (t, J = 7.3 Hz, 1H), 7.28 (t, J = 7.4 Hz, 1H), 7.18 (d, J = 7.0 Hz, 1H), 7.14 (d, J = 8.2 Hz, 2H), 7.08 (t, J = 6.9 Hz, 1H), 6.60 (d, J = 8.1 Hz, 1H), 6.52 (s, 1H), 5.23 (s, 2H), 5.06 (s, 1H); ¹³C NMR (101 MHz, DMSO-d₆): δ 154.55, 154.11, 151.55, 146.96, 145.23, 143.73, 134.11, 133.85, 133.82, 132.48, 132.36, 132.18, 131.78, 130.02, 125.94, 123.31, 118.43, 115.56, 58.09. HRMS (ESI): m/z [M+H]⁺ calcd for C₂₅H₂₀N: 334.1590; found: 334.1588.

Supplemental Material

HJ-20190220-SI – Supplemental material for Synthesis of 9-biarylfluorenes by one-pot, three-step reactions of N-tosylhydrazones, p-bromobenzeneboronic acid, and arylboronic acids

Supplemental material, HJ-20190220-SI for Synthesis of 9-biarylfluorenes by one-pot, three-step reactions of N-tosylhydrazones, p-bromobenzeneboronic acid, and arylboronic acids by Jing He, Jie Zhang, Bin Dai and Ping Liu in Journal of Chemical Research

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship and/or publication of this article: This work was supported by the National Natural Science Foundation of China (No. 21563025), the Program for Changjiang Scholars and Innovative Research Team in University (No. IRT_15R46), and Yangtze River Scholar Research Project of Shihezi University (No. CJXZ201601).

ORCID iD

Ping Liu

Supplemental material

Supplemental material for this article is available online.

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