Article pubs.acs.org/joc
Regioselective Synthesis of Methylene-Bridged Naphthalene Oligomers and Their Host−Guest Chemistry San-Jiang Pan,†,‡,⊥ Gang Ye,‡,⊥ Fei Jia,‡ Zhenfeng He,§ Hua Ke,‡ Huan Yao,‡ Zhi Fan,*,† and Wei Jiang*,‡ †
College of Chemical Engineering and Materials Science, Tianjin University of Science & Technology, No. 29, 13th Avenue, TEDA, Tianjin 300457, China ‡ Department of Chemistry, South University of Science and Technology of China, Xueyuan Blvd 1088, Nanshan District, Shenzhen 518055, P. R. China § School of Chemical Engineering and Technology, North University of China, Taiyuan 030051,China S Supporting Information *
ABSTRACT: In this research, we report the regioselective synthesis of methylene-bridged naphthalene oligomers from 2,6dialkoxyl naphthanene and paraformaldehyde by using p-TsOH as the catalyst and CH2Cl2 as the solvent. The structures were characterized by NMR spectroscopy and X-ray crystallography. Their host−guest chemistry with organic cations was studied, and optimal naphthalene numbers in the oligomers were revealed for different guests. In addition, the reason for the unsuccessful synthesis of methylene-bridged naphthalene macrocycles was discussed.
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INTRODUCTION Methylene-bridged aromatic macrocycles (Figure 1a) are versatile supramolecular hosts, and were widely used for host−guest chemistry.1 The classic ones include calix[n]arenes,2 resorcinarenes and pyrogallarenes,3 cyclotriveratrylenes,4 and others.5 Very recent ones are pillar[n]arenes,6 biphen[n]arenes,7 calix[n]imidazoles,8 helic[6]arenes,9 and others.10 These macrocycles are often synthesized through acid/base-catalyzed condensation between paraformaldehyde and aromatics. Phenol, pyrrole, carbazole, imidazole, thiophene, and furan are commonly used as the aromatics. Extension of phenols to naphthols may create a macrocycle with a wider or deeper cavity, promising for rich host−guest chemistry. The research along this direction (Figure 1b) has been extensively explored by Poh,11 Georghiou,12 Böhmer,13 and Glass.14 In analogy to calixarene, this class of macrocycles was termed as calixnaphthalenes by Georghiou.12 Although some host−guest chemistry was demonstrated, calixnaphthalenes generally show poor binding ability when compared to other macrocycles. In addition, multiple isomers were often produced during the synthesis, making it difficult for isolation. Presumably, these problems are due to that the naphthols, used for calixnaphthlanes, often possess a low symmetry, which results in multiple isomers, ill-defined cavity and thus poor host−guest chemistry. In contrast, 2,6-dihydroxylnaphthalenebased molecular receptors, as reported by Glass14 and us,15,16 generally show good host−guest chemistry. Therefore, we wondered whether 2,6-dialkoxyl naphthalene can condense with paraformaldehyde to give a macrocycle (Figure 1c) with a © 2017 American Chemical Society
well-defined cavity for host−guest chemistry. Herein, we report our preliminary results on the synthesis of methylene-bridged naphthalene oligomers and their host−guest chemistry.
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RESULTS AND DISCUSSION Naphthalene possesses a lower symmetry than benzene, and there are eight aromatic protons accessible for electrophilic aromatic substitution. Thus, directing groups, such as alkoxyl group, are needed to control the regioselectivity. Single alkoxyl group on naphthalene will cause even lower symmetry, resulting in multiple isomeric products as observed for calixnaphthalenes. Therefore, we need naphthalenes with symmetrically substituted groups as building blocks for the synthesis of macrocyclic receptors. 2,6-Dialkoxyl naphthalene was chosen. However, the four ortho-positions of the two alkoxyl groups are all reactive (Figure 1c), which may lead to many isomers. A regioselective procedure needs to be developed. In order to simplify the situation, 2-methoxynaphthalene (1, Table 1) and paraformaldehyde were used to find the optimal reaction condition for the macrocyclization between 2,6-dialkoxyl naphthalene and paraformaldehyde. The reaction was performed at room temperature with different catalysts, solvents, and reaction time. The reactions were monitored by thin-layer chromatography (TLC), and the structures of the products were assigned by NMR spectra, mass spectra, and X-ray single-crystal structure. The product yields Received: June 26, 2017 Published: August 24, 2017 9570
DOI: 10.1021/acs.joc.7b01579 J. Org. Chem. 2017, 82, 9570−9575
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The Journal of Organic Chemistry
Figure 1. (a) Well-known aromatic macrocycles with methylenes as bridges; (b) selected calixnaphthalenes; (c) the possible synthesis of a new naphthalene macrocycle from 2,6-dialkoxyl naphthalene and paraformaldehyde; (d) the four possible reactive sites on 2,6-dialkoxyl naphthalene.
With CH2Cl2 as the solvent and 12 h reaction time, five acid catalysts, including CF3SO3H, p-TsOH, FeCl3, CF3CO2H, and BF3·OEt2, were screened. Only with p-TsOH, two products were detected and isolated. Other catalysts either do not catalyze these reactions, or produce nonisolatable products. After careful characterization with NMR spectroscopy and Xray single crystallography (see SI for the crystal structure of 2b), the structures of the two products were assigned (Table 1): the dimeric product 2a consist of two naphthalene which are connected by a methylene group at the 1 position; while in 3a, additional naphthalene is connected to the dimeric naphthalene by methylene at 6 position. No other products were isolated. With p-TsOH as the catalyst, screening reaction times and solvents indicate that entry 2 (Table 1) is still the optimal reaction condition. Although the reaction product of paraformaldehyde at the βposition next to methoxyl group on 1 was not observed, the existence of 2b in the products indicates there are two different reactive sites on 1 which may compete with each other when synthesizing macrocycles. However, when using 2,6-dialkoxyl naphthalene as the reactant, there is no such reactive site anymore. Therefore, the optimal condition for the reaction between 1 and paraformaldehyde is considered to be regioselective and could be applied to the synthesis of macrocycles from 2,6-dialkoxylnaphthalene and paraformaldehyde. 2,6-Dibutoxyl naphthalene 3 was used as the substrate because of good solubility. Using CH2Cl2 as the solvent and p-TsOH as the catalyst, 2,6dibutoxyl naphthalene 3 indeed reacted with paraformaldehyde at room temperature (Figure 2a). After only 1.5 h, 3 already completely disappeared and many products were produced as monitored by TLC. Six major products were then isolated through silica gel column chromatography, and their 1H NMR
Table 1. Reaction Conditions and Product Yields for the Reaction between 1 and Paraformaldehyde at Room Temperature.a
entry
catalyst
solvent
time/h
1 2 3 4 5 6 7 8 9 10 11 12 13 14
CF3SO3H p-TsOH FeCl3 CF3CO2H BF3·OEt2 p-TsOH p-TsOH p-TsOH p-TsOH p-TsOH p-TsOH p-TsOH p-TsOH p-TsOH
CH2Cl2 CH2Cl2 CH2Cl2 CH2Cl2 CH2Cl2 CH2ClCH2Cl THF CH2Cl2 toluene CH2Cl2 CH2Cl2 CH2Cl2 CH2Cl2 CH2Cl2
12 12 12 12 12 12 12 12 12 0.5 1 2 4 8
2a/%b
2b/%b
86
10
46
3.5
4.9 55 11 20 41 52 76
4.9
1.4 2.9 10
a
Reactions were performed at room temperature with 0.2 mmol 2methoxynaphthalene and one equiv of paraformaldehyde in 2.0 mL solvent with 0.02 mmol catalyst. bYields of 2a and 2b were determined using 1H NMR experiments.
were determined by 1H NMR experiments (Figures S1−S3). All the results are listed in Table 1. 9571
DOI: 10.1021/acs.joc.7b01579 J. Org. Chem. 2017, 82, 9570−9575
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Figure 2. (a) Synthetic procedure of methylene-bridged naphthalene oligomers 4a−4f; (b) X-ray single-crystal structures of 4a and 4b; (c) attempted but failed synthesis of methylene-bridged naphthalene macrocycles; (d) chemical structures of the guests involved in this research; (e) energy minimized structures of methylene-bridged naphthalene macrocycles (pentamer, hexamer, and heptamer) at the semiempirical PM6 level of theory. For viewing clarity, alkyl groups were shortened to methyl groups.
spectra are shown in Figure 3. There are rather complex patterns of aromatic peaks, suggesting them to be oligomers instead of the expected macrocycles: the oligomers have a lower symmetry than the macrocycles. All these oligomers should have similar connecting style as in 2a: 2,6-dialkoxyl naphthalenes are connected by methylene at 1,5-positions. Their polarity, mass spectra, and NMR spectra, in particular the splittings of methylene bridges, are indeed consistent with their structures. All the oligomers were assigned, which was further confirmed by X-ray single-crystal structures of 4a and 4b (Figure 2b). The great regioselectivity is rather surprising and may be rationalized by that the α positions of naphthalene are more electron-rich and thus have much higher reactivity than the β position in Friedel−Crafts reaction. Unexpectedly, no macrocycle was isolated or even detected from the product mixture (Figure S4), no matter how we changed the reaction conditions (temperature, reaction time, or the reactant ratio). It is also fruitless by using a stepwise route with 4d and 5 as the reactants (Figure 2c). Instead of the
Figure 3. Partial 1H NMR spectra (400 MHz, CDCl3, 0.5 mM, 25 °C) of the naphthalene oligomers 4a−4f.
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The Journal of Organic Chemistry macrocycles, all these oligomers were again obtained. This suggests that the covalent bonds between methylene and naphthalene in the oligomers are dynamically reversible at the current reaction condition and only thermodynamically stable compounds can be obtained. But addition of organic cations 8D82+ and 8V82+ (Figure 2d) still did not template the macrocyclization products. Energy-minimized structures (Figure 2e) show that the methylene-bridged macrocycles suffer from serious steric hindrance from the neighboring naphthalenes, and thus assume a twisted structure. This may make the macrocycles thermodynamically less stable than the oligomers, and thus cause the failure in the synthesis of macrocycles. The more relaxed conformation of the oligomers, as observed in the crystal structures of 4a and 4b (Figure 2b), is also unfavorable for macrocyclization. With the oligomers in hand, host−guest chemistry was then tested to show the potential of methylene-bridged naphthalene hosts. According to our earlier studies,15,16 viologen and 1,4diazabicyclooctane (DABCO)-based organic cations were selected as the guests (Figure 2d). 1H NMR titrations were performed to determine the association constants (Figure S5− S30). All the data are listed in Table 2. As shown in Figure 4,
Figure 5. Energy-minimized structures of 8D82+@4d, 8D82+@4e, 8V82+@4e, and 8V82+@4f at the semiempirical PM6 level of theory. For viewing clarity, alkyl groups were shortened to methyl groups.
Table 2. Binding Constants (Ka) and Gibbs Free Energies (ΔG°) of Naphthalene Oligomers 4a−4f with 8D82+ or 8V82+ as Determined by 1H NMR Titrations (400 MHz, CD2Cl2, 25 °C) 8D82+ −1
when the optimal number of naphthalenes was reached, the best binding affinity was achieved; additional naphthalene would cause steric hindrance and thus decrease the binding affinities. This observation on binding affinities may further support our explanation on unsuccessful macrocyclization.
8V82+ −1
−1
oligomer
Ka (M )
ΔG° (kJ mol )
Ka (M )
ΔG° (kJ mol−1)
4a 4b 4c 4d 4e 4f
25.4 ± 1.2 1288 ± 65 1685 ± 129 6515 ± 494 1132 ± 77 947 ± 91
−8.0 −17.8 −18.4 −21.8 −17.4 −17.0
39.8 ± 8.2 15.0 ± 2.8 147 ± 16 363 ± 39 1702 ± 94 708 ± 28
−9.1 −6.7 −12.4 −14.6 −18.4 −16.3
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CONCLUSIONS In summary, methylene-bridged naphthalene oligomers were regioselectively synthesized from 2,6-dialkoxyl naphthalene and paraformaldehyde by using p-TsOH as the catalyst and CH2Cl2 as the solvent. Their structures have been characterized by NMR spectroscopy and X-ray single crystallography. These oligomers are able to complex organic cations in nonpolar solvents through wrapping around the guests to maximize the contacts. There is an optimal naphthalene number in the oligomers for each guest to achieve the best binding: oligomers with too less naphthalenes do not have enough contacts with the guest; too many naphthalenes cause steric hindrance between the two ends of the oligomers. Presumably also due to steric hindrance, attempts to obtain methylene-bridged naphthalene macrocycles failed. But the present synthetic method paves the way for further explorations in this direction.
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EXPERIMENTAL SECTION
General Methods. All the reagents involved in this research were commercially available and used without further purification unless otherwise noted. Solvents were either employed as purchased or dried prior to use by standard laboratory procedures. 1H and 13C NMR spectra were recorded on Bruker Avance-400, 500 spectrometers. All chemical shifts are reported in ppm with residual solvents or TMS (tetramethylsilane) as the internal standards. The following abbreviations were used for signal multiplicities: s, singlet; d, doublet; t, triplet; m, multiplet. Electrospray-ionization time-of-flight high-resolution mass spectrometry (ESI-TOF-HRMS) experiments were conducted on an applied biosystems Elite ESI-QqTOF mass spectrometry system. Guests 8D8·2BarF16b and 8 V8·2BarF17 and compound 515 were synthesized by following the literature procedures. All the computations were performed at the semiempirical PM6 level of theory by using Spartan ’14 (Wave Function, Inc.).
Figure 4. Changes of the association Gibbs free energies of 8D82+ and 8V82+ with the naphthalene oligomers 4a−4f.
the Gibbs free energies of the complexes are related to the naphthalene numbers in the oligomers. For guest 8D82+, the pentamer 4d is the strongest binder; while for 8V82+, the hexamer 4e is the best host. This behavior can be rationalized by invoking molecular modeling (Figure 5): the oligomers undergo a conformational change when compared to the crystal structures (Figure 2b), and wrap around the guest to enhance the contacts and thus the cation π interactions; increasing the number of naphthalenes would increase the binding affinities; 9573
DOI: 10.1021/acs.joc.7b01579 J. Org. Chem. 2017, 82, 9570−9575
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The Journal of Organic Chemistry Synthetic Procedures. Compounds 2a and 2b. 1 (316 mg, 2.0 mmol), (HCHO)n (300 mg, 10 mmol), and p-TsOH (34 mg, 0.2 mmol) were dissolved in CH2Cl2 (20 mL) under argon atmosphere. The resulting mixture was stirred at room temperature for 12 h. The solvent was then removed under reduced pressure. The residue was subjected to column chromatography (SiO2, petroleum ether: ethyl acetate = 20:1) to afford 2a (130 mg, yield 48%) and 2b (24 mg, yield 24%) as white solids. 2a: mp = 136 °C - 137 °C 1H NMR (400 MHz, CDCl3, 25 °C): δ [ppm] = 8.21 (d, J = 8.6 Hz, 2H), 7.73 (d, J = 8.7 Hz, 4H), 7.32 (t, J = 9.0 Hz, 4H), 7.25 (t, J = 7.4 Hz, 2H), 4.93 (s, 2H), 3.90 (s, 6H). 13C NMR (101 MHz, CDCl3 25 °C) δ [ppm] = 154.6, 133.8, 129.6, 128.3, 128.0, 125.9, 124.5, 123.9, 123.2, 114.0, 56.8, 21.8. ESI-TOF-HRMS: m/z calcd for [M+Na]+ C23H20O2Na+, 351.1356; found 351.1353 (error = −0.9 ppm). 2b: mp = 186 °C - 187 °C 1H NMR (400 MHz, CDCl3 25 °C) δ [ppm] = 8.15 (dd, J = 8.6, 1.2 Hz, 1H), 8.03 (d, J = 8.9 Hz, 1H), 7.93−7.86 (m, 1H), 7.84−7.76 (m, 2H), 7.73−7.65 (m, 2H), 7.52 (d, J = 9.0 Hz, 1H), 7.40−7.26 (m, 6H), 7.21 (t, J = 9.9 Hz, 3H), 4.86 (s, 2H), 4.53 (s, 2H), 3.91 (s, 3H), 3.87 (s, 3H), 3.85 (s, 3H). 8.17 (d, J = 8.6 Hz, 1H), 8.06 (d, J = 8.9 Hz, 1H), 7.92 (d, J = 8.9 Hz, 1H), 7.87− 7.78 (m, 2H), 7.71 (d, J = 8.8 Hz, 2H), 7.54 (d, J = 9.0 Hz, 1H), 7.40− 7.21 (m, 9H), 4.88 (s, 2H), 4.56 (s, 2H), 3.96−3.85 (t, J = 14.8 Hz, 9H). 13C NMR (101 MHz, CDCl3 25 °C) δ [ppm] = 154.9, 154.5, 154.0, 135.8, 129.7, 129.3, 128.3, 128.3, 128.2, 127.8, 127.5, 127.2, 126.5, 126.4, 125.8, 124.4, 124.4, 124.0, 123.7, 123.3, 123.1, 121.6, 114.0, 114.0, 113.6, 56.9, 56.9, 56.7, 30.5, 21.6. ESI-TOF-HRMS: m/z calcd for [M+NH4]+ C35H34O3N+, 516.2533; found 516.2532 (Error = −0.2 ppm). Oligomers 4a − 4f. 3 (1.4 g, 5.0 mmol), (HCHO)n (165 mg, 5.5 mmol), and p-TsOH (0.17 g, 0.5 mmol) were dissolved in CH2Cl2 (20 mL) under the argon atmosphere. The resulting mixture was stirred at room temperature for 1.5 h. Then, methanol (30 mL) was poured into the mixture. The precipitate was filtered and collected, and was then subjected to column chromatography (SiO2, petroleum ether: CH2Cl2 = 5:1) to afford 4a (40 mg, yield 1.4%), 4b (200 mg, yield 4.9%), 4c (60 mg, yield 1.1%), 4d (160 mg, yield 2.3%), 4e (76 mg, yield 0.9%), and 4f (80 mg, yield 0.8%) as white solids. 4a: mp = 81 °C - 82 °C 1H NMR (400 MHz, CDCl3 25 °C) δ [ppm] = 8.14 (d, J = 9.3 Hz, 2H), 7.59 (d, J = 9.0 Hz, 2H), 7.31 (s, 1H), 7.07−6.89 (m, 4H), 4.95 (s, 2H), 4.18 (t, J = 6.4 Hz, 4H), 4.00 (t, J = 6.5 Hz, 4H), 1.90−1.74 (m, 8H), 1.64−1.44 (m, 9H), 1.06− 0.95 (m, 12H). 8.14 (d, J = 9.3 Hz, 2H), 7.59 (d, J = 9.0 Hz, 2H), 7.30 (d, J = 9.3 Hz, 2H), 7.07−6.89 (m, 4H), 4.95 (s, 2H), 4.18 (t, J = 6.4 Hz, 4H), 4.00 (t, J = 6.5 Hz, 4H), 1.90−1.74 (m, 8H), 1.63−1.46 (m, 8H), 1.00 (q, J = 7.4 Hz, 12H). 13C NMR (101 MHz, CDCl3 25 °C) δ [ppm] = 155.1, 152.1, 130.5, 129.2, 126.4, 126.3, 124.4, 118.6, 115.2, 107.0, 69.5, 67.5, 31.9, 31.3, 21.6, 19.5, 19.3, 14.0, 13.9. ESI-TOFHRMS: m/z calcd for [M+Na]+ C37H48O4Na+, 579.3445; found 579.3439 (Error = −1.1 ppm). 4b: mp = 148 °C - 149 °C 1H NMR (400 MHz, CDCl3 25 °C) δ [ppm] = 8.10 (t, J = 8.8 Hz, 4H), 7.56 (d, J = 8.4 Hz, 2H), 7.27 (d, J = 9.7 Hz, 2H), 7.10 (d, J = 9.4 Hz, 2H), 6.98 (d, J = 2.4 Hz, 2H), 6.91 (dd, J = 9.3, 2.5 Hz, 2H), 4.87 (s, 4H), 4.18−4.04 (m, 8H), 3.98 (t, J = 6.5 Hz, 4H), 1.81−1.72 (m, 12H), 1.57−1.46 (m, 12H), 0.98−0.90 (m, 18H). 13C NMR (126 MHz, CDCl3 25 °C) δ [ppm] = 155.1, 152.0, 151.6, 130.5, 129.9, 129.2, 126.4, 126.2, 125.0, 124.5, 123.7, 118.5, 115.5, 114.6, 106.9, 69.7, 69.1, 67.5, 31.8, 31.8, 31.3, 21.6, 19.5, 19.5, 19.3, 13.9, 13.9, 13.9. ESI-TOF-HRMS: m/z calcd for [M +NH4]+ C56H76O6N+, 858.5667; found 858.5659 (Error = −1.0 ppm). 4c: mp = 160 °C - 161 °C 1H NMR (400 MHz, CDCl3 25 °C) δ [ppm] = 8.14−8.01 (m, 6H), 7.55 (d, J = 8.9 Hz, 2H), 7.25 (d, J = 9.0 Hz, 2H), 7.10−7.02 (m, 4H), 6.98 (d, J = 2.6 Hz, 2H), 6.90 (dd, J = 9.4, 2.6 Hz, 2H), 4.84 (s, 4H), 4.79 (s, 2H), 4.10−3.94 (m, 16H), 1.82−1.64 (m, 16H), 1.54−1.41 (m, 16H), 0.99−0.88 (m, 24H). 13C NMR (101 MHz, CDCl3 25 °C) δ [ppm] = 152.5, 149.6, 149.1, 149.0, 127.9, 127.4, 126.7, 123.8, 123.6, 122.5, 122.1, 121.8, 121.1, 116.0, 113.0, 112.4, 112.0, 104.4, 67.1, 66.8, 66.6, 65.0, 29.3, 29.3, 29.2, 28.8, 19.2, 16.9, 16.9, 16.9, 16.8, 11.4, 11.3, 11.3. ESI-TOF-HRMS: m/z
calcd for [M+NH4]+ C75H100O8N+, 1142.7443; found 1142.7444 (Error = 0.0 ppm). 4d: mp = 209 °C - 210 °C 1H NMR (400 MHz, CDCl3 25 °C) δ [ppm] = 8.15−7.97 (m, 8H), 7.55 (d, J = 9.0 Hz, 2H), 7.26 (d, J = 8.5 Hz, 2H), 7.10−6.96 (m, 8H), 6.90 (dd, J = 9.2, 2.8 Hz, 2H), 4.84 (s, 4H), 4.78 (s, 4H), 4.12−3.94 (m, 20H), 1.78−1.60 (m, 20H), 1.55− 1.36 (m, 20H), 0.99−0.84 (m, 30H). 13C NMR (126 MHz, CDCl3 25 °C) δ [ppm] = 155.1, 152.1, 151.6, 151.6, 151.6, 130.5, 129.9, 129.9, 129.2, 126.4, 126.2, 125.0, 124.6, 124.5, 124.3, 124.3, 124.2, 123.6, 118.6, 115.5, 114.9, 114.9, 114.6, 106.9, 69.7, 69.3, 69.3, 69.1, 67.5, 31.9, 31.8, 31.8, 31.3, 21.7, 21.6, 19.5, 19.5, 19.4, 19.3, 14.0, 13.9, 13.9, 1.1. ESI-TOF-HRMS: m/z calcd for [M+NH4]+ C94H124O10N+, 1426.9220; found 1426.9203 (Error = −1.2 ppm). 4e: mp = 217 °C - 218 °C 1H NMR (400 MHz, CDCl3 25 °C) δ [ppm] = 8.11−8.00 (m, 10H), 7.55 (d, J = 9.0 Hz, 2H), 7.25 (d, J = 9.0 Hz, 2H), 7.08−6.97 (m, 10H), 6.90 (d, J = 9.3 Hz, 2H), 4.84 (s, 4H), 4.77 (s, 4H), 4.76 (s, 2H), 4.09−3.96 (m, 24H), 1.80−1.62 (m, 24H), 1.54−1.38 (m, 24H), 0.94−0.87 (m, 36H). 13C NMR (126 MHz, CDCl3 25 °C) δ [ppm] = 155.1, 152.1, 151.7, 151.7, 151.6, 130.5, 129.9, 126.4, 126.2, 125.1, 124.6, 124.4, 124.3, 123.6, 118.5, 115.6, 115.0, 114.6, 107.0, 69.7, 69.3, 69.1, 67.5, 31.8, 31.8, 31.8, 31.3, 29.7, 19.5, 19.4, 19.3, 13.9, 13.9, 13.8, 1.0. ESI-TOF-HRMS: m/z calcd for [M+NH4]+ C113H148O12N+, 1711.0996; found 1711.1023 (Error = +1.6 ppm). 4f: mp = 233 °C - 234 °C 1H NMR (400 MHz, CDCl3 25 °C) δ [ppm] = 8.13−7.99 (m, 12H), 7.55 (d, J = 9.0 Hz, 2H), 7.26 (d, J = 9.0 Hz, 2H), 7.10−6.95 (m, 12H), 6.90 (dd, J = 9.4, 2.5 Hz, 2H), 4.85 (s, 4H), 4.78 (s, 4H), 4.77 (s, 4H), 4.12−3.95 (m, 28H), 1.79−1.60 (m, 28H), 1.55−1.28 (m, 28H), 0.98−0.85 (m, 42H). 13C NMR (126 MHz, CDCl3 25 °C) δ [ppm] = 155.1, 152.1, 151.6, 130.5, 129.9, 129.2, 126.4, 125.0, 124.5, 127.4, 124.2, 123.6, 118.6, 115.5, 114.9, 114.6, 106.9, 69.7, 69.4, 69.3, 69.1, 67.5, 31.8, 31.8, 31.8, 31.3, 19.5, 19.4, 19.3, 13.9, 13.9, 13.9, 1.0. ESI-TOF-HRMS: m/z calcd for [M +NH4]+ C132H172O14N+, 1995.2772; found 1995.2804 (Error = +1.6 ppm).
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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.7b01579. NMR spectra, mass spectra, Job’s Plots, 1H NMR titration data, X-ray crystallographic data, and computational data (PDF) X-ray crystallographic data of compound 2b (CIF) X-ray crystallographic data of compound 4a (CIF) X-ray crystallographic data of compound 4b (CIF)
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected] *E-mail:
[email protected] ORCID
Wei Jiang: 0000-0001-7683-5811 Author Contributions ⊥
S.-J.P. and G.Y. contributed equally to this work.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This research was financially supported by the National Natural Science Foundation of China (No. 21572097); the Thousand Young Talents Program; and the Shenzhen special funds for the development of biomedicine, Internet, new energy, and new material industries (No. JCYJ20160226192118056, JCYJ20170307105848463). 9574
DOI: 10.1021/acs.joc.7b01579 J. Org. Chem. 2017, 82, 9570−9575
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DOI: 10.1021/acs.joc.7b01579 J. Org. Chem. 2017, 82, 9570−9575