Advertisement

Chemistry of Heterocyclic Compounds

, Volume 54, Issue 6, pp 650–657 | Cite as

Convenient synthesis of 12-methyl[1]benzoxepino[3,4-b]quinolin-13(6H)-ones

  • Yu Wang
  • Mingqin Chang
  • Hong Zhang
  • Yang LiEmail author
Article
  • 32 Downloads

In this work, a construction of 12-methyl[1]benzoxepino[3,4-b]quinolin-13(6H)-ones, structurally intriguing hybrid molecules consisting of fused 4-methylquinoline and 1-benzoxepin-5-one units, has been successfully achieved via a two-step procedure, involving the onepot synthesis of 2-(aryloxymethyl)-4-methylquinoline-3-carboxylic acids followed by their intramolecular Friedel–Crafts cyclization reaction. Our synthetic protocol described here could be attractive as it is simple, easy to handle and does not involve the use of expensive reagents or catalysts.

Keywords

1-benzoxepin-5-one hybrid molecule 4-methylquinoline Friedel–Crafts cyclization one-pot synthesis 
1-Benzoxepine ring is one of the privileged medicinal scaffolds found in a small number of biologically active natural products, such as pterulone (1),1 ptaeroxylin (2),2 and bauhiniastatins (e.g., bauhiniastatin 1 (3))3 (Fig. 1), and has wide application in the design and discovery of novel bioactive molecules.4,5 Many compounds containing the 1-benzoxepine core are of great pharmaceutical interest due to their potent biological properties, such as antimycobacterial, anticancer,6 and antifungal activities,7 and could be potentially applied as topoisomerase I,8 cyclooxygenase, 9 and PI3-kinase inhibitors.10 As a consequence, considerable synthetic efforts have been devoted surrounding the 1-benzoxepine template for further modification and functionalization by both organic and medicinal chemists with the aim of enhancing the potency of this class of compounds.11, 12, 13
Figure 1.

Structures of 1-benzoxepine-containing natural products 13, bioactive 4-methylquinolines 4, 5, and the target hybrid molecules 6.

On the other hand, the 4-methylquinoline (4-MeQ) scaffold, too, is a pharmacologically significant structural unit, and many 4-methylquinoline-based heterocyclic compounds have been used as drug-like chemical probes in pharmacological studies or for the development of new medicinal products.14,15 For example, 4-methyl-2-phenylquinoline (4) was reported to show potent inhibitory effects against β(1–3) glucan synthase with lower IC50 value (0.23 μg/ml) than the well-known β(1–3) glucan synthase inhibitor aculeacin A (IC50 50.5 μg/ml).16 In this regard, Jain et al.17 have described the synthesis and antituberculosis activity of a series of ring-substituted 4-methylquinolines, such as 2,8-dicyclopentyl-4-methylquinoline (5), and established that these molecules could be regarded as promising lead compounds for antituberculosis drug development. Due to their biological activities, interest in the synthesis of novel and interesting types of 4-methylquinoline-based derivatives continues unabated.18,19

On the basis of the literature data, and considering the fact that combination of different pharmacophores in a molecular framework is an important goal of synthetic organic chemistry and plays a prominent role in modern drug discovery,20 we felt that it would be a worthwhile endeavor to construct 4-methylquinoline–1-benzoxepine fused hybrids as possible drug candidates for current pharmacological studies. Accordingly, with this context and in continuation of our studies concerning the synthesis of novel and potential biologically active quinoline-based heterocycles,21, 22, 23, 24, 25 we herein would like to report the design and synthesis of 4-methylquinoline-based 1-benzoxepine derivatives, wherein the 1-benzoxepine ring is fused at its 3 and 4 positions to the b position of the 4-methylquinoline ring to give a tetracyclic structure exemplified by compounds 6 as shown in Figure 1.

Prior to the current investigation, there have been few reports concerning the synthesis of ethyl 2-chloromethyl-4-methylquinoline-3-carboxylate (9) through the Friedländer annulation reaction.26,27 Although the compound could be considered as a useful building block to participate in a wide array of chemical transformations for the design of new and interesting quinoline derivatives, to our knowledge, the further modification of it has been very limited so far. In this regard, Degtyarenko et al.28 reported its synthetic application with amines or mercaptanes for the synthesis of 4-methylquinoline-based derivatives. Just recently, Xu et al.29 reported the reaction of compound 9 with salicylonitriles or 2-mercaptobenzonitrile for the facile synthesis of benzofuran- or benzothiophene-fused naphthyridines. Due to structural diversity being an essential component of the search for new leads, we became interested in exploring the further synthetic application of compound 9 as an ideal starting material for facile synthesis of the desired 4-methylquinoline-based 1-benzoxepine derivatives. Our synthetic plan, as shown in Scheme 1, was to make use of the active 2-chloromethyl group of compound 9 to generate 2-aryloxymethyl moiety through Williamson ether reaction with substituted phenols 8 followed by a further in situ ethyl ester hydrolysis reaction at position 3 to afford the corresponding 2-aryloxymethylquinoline-3-carboxylic acid intermediates 7. Subsequently, the intramolecular Friedel–Crafts cyclization reaction between 2-aryloxymethyl moiety and 3-carboxylic acid group would construct the desired 1-benzoxepine skeleton through the generation of a new C–C bond.

Scheme 1

Accordingly, with this assumption in mind, starting compound 9 obtained by the described method27 was first subjected to the Williamson reaction with 1.1 equiv of phenols 8al in the presence of K2CO3 as the base and refluxing MeCN as the solvent. The reaction proceeded very smoothly, and the substrates were completely consumed within 3 h as monitored by TLC. It is worthy to mention that the reaction proceeded also in DMF as the solvent. We adopted herein MeCN as the solvent of choice simply because of its low boiling point, thus bringing much convenience to subsequent work-up procedure. Since the resulting aryloxymethyl ethers from the Williamson reaction did not interfere with further ethyl ester hydrolysis reaction, purification at this stage was unnecessary. As such, we simply evaporated MeCN to dryness, added aqueous-ethanolic potassium hydroxide solution directly to the residue, and continued to reflux for additional 2 h. After an acidic work-up followed by purification of the resulting crude products by recrystallization from ethanol, the corresponding 2-aryloxymethylquinoline-3-carboxylic acids 7al were obtained in high yields as listed in Table 1.
Table 1.

Yields and physical properties of compounds 7al and 6al

To the best of our knowledge, these newly synthesized compounds except compound 7a30 have not been reported earlier, and their structures have been confirmed based on their spectroscopic and analytical data which are in good agreement with the proposed structures (see Experimental). As an example, the 1H NMR spectrum of compound 7a did not show signals attributable to chloromethyl and ethoxy protons of its precursor 9, but instead contained a oneproton singlet at 13.61 ppm and a two-proton singlet at 5.36 ppm, readily recognizable as arising from carboxylic and methylene protons, respectively. Moreover, the presence of a total of 9 aromatic protons in the range of 6.95–8.20 ppm exactly matches its structure as well. Further, the structure of compound 7a was confirmed by its 13C NMR spectrum, which revealed the presence of carboxyl carbon at 168.7 ppm and methylene carbon at 70.5 ppm, along with the signals due to the aromatic carbons. The other synthesized compounds exhibited similar spectral characteristics but for the substituents which were recognized by characteristic signals with appropriate chemical shifts.

Having a series of the synthesized precursors 7al in hand, our attention was turned to their intramolecular Friedel–Crafts cyclization reaction for construction of the tetracyclic title compounds. In our first attempts to carry out the transformation of carboxylic acid 7a into benzoxepino-quinolinone 6a using Eaton's reagent as the mild cyclization reagent at 80°C,31 the reaction scarcely proceeded and the desired product 6a was detected only in negligible amount that did not warrant isolation. We also tried the reaction using POCl3 as the cyclization reagent, which has recently been used for this type of transformation.32 However, this purported approach was ineffective in our hands and the reaction did not proceed satisfactorily, giving poor yields of highly impure products. In addition, switching to other cyclization reagents, such as sulfuric acid, hydrogen fluoride, and trifluoroacetic anhydride, was also to no avail.

After these fruitless attempts, we were delight to find that the use of polyphosphoric acid (PPA)21 was suitable to promote the reaction, and the reaction temperature of 145°C was found to be optimal to complete the transformation, giving compound 6a in a good yield of 72%. Upon further increasing the reaction temperature, the crude product was always contaminated with a small amount of impurities, which may be attributed to side reactions, such as polymerization. Due to the simplicity of the procedure requiring no additional solvent, no further optimization in reaction conditions was necessary and the above-mentioned conditions were chosen for the following work. Thereafter, in a similar fashion, we further extended the reaction to other quinoline-3-carboxylic acids 7bl. As expected, these substrates were equally amenable to the reaction process without any experimental difficulties, successfully furnishing the corresponding targeted products 6bl in satisfactory yields. The results of this series of experiments are compiled in Table 1.

The newly synthesized compounds 6al have never been reported, and their structures were all easily established based on their spectral data and elemental analyses, which were in good agreement with the proposed structures (see Experimental). In particular, we would like to comment on the intramolecular cyclization of compounds 7d and 7l (entries 4 and 12, Table 1). In the case of compound 7d, the intramolecular cyclization reaction in principle should give rise to two possible structural isomers 6d and 6d' because of the existence of two vacant ortho sites, C-2' and C-4', in the 3-methoxyphenyl group of compound 6d. But in fact, the 1H NMR spectrum of the product suggested that the cyclization reaction selectively occurred with the C–C bond forming at the C-4' position, thereby affording structure 6d as the sole product as shown in Scheme 2.

Scheme 2

In the 1H NMR spectrum of compound 6d (Fig. 2), particularly characteristic was the signal due to the C-2' hydrogen appeared as a doublet at 6.66 ppm with a small coupling constant J = 2.4, which is a typical value for metaproton coupling with C-6' hydrogen. Correspondingly, the signal due to C-6' hydrogen appears as a doublet of doublets at 6.83 ppm with the J values 8.8 and 2.4 Hz which arose from coupling with both C-5' and C-2' hydrogen atoms. If the cyclization reaction occurred at the C-2' position leading to the corresponding product 6d', the splitting pattern of meta-proton coupling doublet could not appear in its 1H NMR spectrum.
Figure 2.

The 1H NMR spectrum of compound 6d.

Similarly, the cyclization reaction of acid 7l could also occur theoretically at either a- or b-position of the naphthalene ring, resulting in two possible structural isomers. However, the analysis of 1H NMR spectrum revealed that the cyclization reaction selectively took place at the a-position of the naphthalene ring to give product 6l as the sole product as shown in Scheme 3.

Scheme 3

The 1H NMR spectrum of compound 6l (Fig. 3) exhibited two doublet signals that can be assigned to H-b and H-c at 7.22 and 7.95 ppm with a coupling constant J = 8.8, which is a typical value for ortho-protons coupling in naphthalene ring. Especially, the one-proton doublet at markedly high δH value (8.95 ppm) could be easily ascribed to H-d due to the intramolecular interaction between the carbonyl oxygen atom and this proton resulting in the downfield shift. Further, if the cyclization reaction occurred at the C-b position giving compound 6l' as the product, there should have been two one-proton singlet signals due to H-a and H-c in its 1H NMR spectrum.
Figure 3.

The 1H NMR spectrum of compound 6l.

In conclusion, we have provided an easy access to structurally new and biologically promising polycyclic fused 4-methylquinoline-based 1-benzoxepine derivatives through a simple and effective two-step procedure. In view of the synergism of both the 1-benzoxepine ring and 4-methylquinoline unit in a molecular framework, these newly synthesized compounds would likely possess significant biological activities and might be potentially applied for the development of biologically and pharmaceutically important drugs. Currently, the studies concerning their application are underway.

Experimental

Infrared spectra were recorded on a Shimadzu FTIR-8400S spectrophotometer in KBr pellets in the range of 400–4000 cm–1. 1H and 13C NMR spectra were recorded on a Brucker Avance NMR spectrometer (400 and 100 MHz, respectively) in CDCl3 (compounds 6a,b,e,gl) or in DMSO-d6 (compounds 6c,d,f, 7al). The reported chemical shift (δ) values are given in parts per million downfield from TMS as the internal standard. Elemental analyses were performed for C, H, and N using an Elementar vario EL III element analyzer. Melting points were determined using a WRS-1B melting point apparatus. The progress of reactions was monitored by thin-layer chromatography (TLC) on silica gel GF254 using EtOAc – petroleum ether as eluent. The chemicals used in this work were obtained from Fluka and were used without further purification.

Synthesis of 2-(aryloxymethyl)-4-methylquinoline-3-carboxylic acids 7a–l (General method). Phenol or substituted phenol 8al (1.1 mmol) and anhydrous K2CO3 (415 mg, 3 mmol) were added to a stirred solution of ethyl 2-(chloromethyl)-4-methylquinoline-3-carboxylate 9 (264 mg, 1 mmol) in MeCN (15 ml). The resulting mixture was heated at refluxing temperature for 3 h. The conversion was monitored by TLC. After completion, the reaction mixture was evaporated to dryness; a solution of KOH (1.12 g, 20 mmol) in 80% ethanol (25 ml) was added directly to the residue and the reflux was continued for 2 h. After cooling, the reaction mixture was acidified to pH 4–5 with 1 M HCl to induce precipitation. After filtration and washing with water, the crude precipitate was recrystallized from ethanol. The yields and melting points of products 7al are listed in Table 1.

4-Methyl-2-(phenoxymethyl)quinoline-3-carboxylic acid (7a). White solid. IR spectrum, ν, cm–1: 3442 (COOH), 3075, 2961, 1721 (C=O), 1600, 1569, 1490. 1H NMR spectrum, δ, ppm (J, Hz): 2.71 (3H, s, CH3); 5.36 (2H, s, ArCH2O); 6.95 (1H, t, J = 7.2, H Ar); 7.02 (2H, d, J = 8.0, H Ar); 7.29 (2H, t, J = 8.0, H Ar); 7.71 (1H, t, J = 7.6, H Ar); 7.84 (1H, t, J = 7.6, H Ar); 8.05 (1H, d, J = 8.0, H Ar); 8.20 (1H, d, J = 8.4, H Ar); 13.61 (1H, s, COOH). 13C NMR spectrum, δ, ppm: 15.1; 70.5; 114.4; 120.8; 124.5; 126.2; 127.2; 127.5; 129.0; 129.2; 130.1; 141.8; 145.4; 152.6; 157.8; 168.7. Found, %: C 73.92; H 5.00; N 4.62. C18H15NO3. Calculated, %: C 73.71; H 5.15; N 4.78.

4-Methyl-2-[(o-tolyloxy)methyl]quinoline-3-carboxylic acid (7b). White solid. IR spectrum, ν, cm–1: 3447 (COOH), 3059, 2919, 1724 (C=O), 1610, 1572, 1508. 1H NMR spectrum, δ, ppm (J, Hz): 2.16 (3H, s, CH3); 2.72 (3H, s, CH3); 5.38 (2H, s, ArCH2O); 6.83 (1H, t, J = 7.2, H Ar); 7.05 (1H, d, J = 8.0, H Ar); 7.10–7.14 (2H, m, H Ar); 7.73 (1H, t, J = 7.2, H Ar); 7.86 (1H, t, J = 7.2, H Ar); 8.08 (1H, d, J = 8.4, H Ar); 8.22 (1H, d, J = 8.4, H Ar); 13.55 (1H, s, COOH). 13C NMR spectrum, δ, ppm: 15.2; 15.7; 70.3; 110.7; 120.2; 124.6; 125.8; 126.3; 126.5; 127.3; 127.4; 128.8; 130.2; 130.3; 142.3; 145.2; 152.7; 155.9; 168.6. Found, %: C 74.41; H 5.68; N 4.27. C19H17NO3. Calculated, %: C 74.25; H 5.58; N 4.56.

2-[(2-Methoxyphenoxy)methyl]-4-methylquinoline-3-carboxylic acid (7c). White solid. IR spectrum, ν, cm–1: 3430 (COOH), 3077, 2963, 1718 (C=O), 1616, 1569, 1506. 1H NMR spectrum, δ, ppm (J, Hz): 2.76 (3H, s, CH3); 3.77 (3H, s, OCH3); 5.36 (2H, s, ArCH2O); 6.86 (1H, td, J = 7.6, J = 1.2, H Ar); 6.94 (1H, td, J = 7.6, J = 1.2, H Ar); 7.00 (1H, dd, J = 7.6, J = 1.2, H Ar); 7.10 (1H, dd, J = 7.6, J = 1.2, H Ar); 7.74 (1H, t, J = 7.6, H Ar); 7.87 (1H, t, J = 7.6, H Ar); 8.07 (1H, d, J = 8.4, H Ar); 8.24 (1H, d, J = 8.4, H Ar); 13.60 (1H, s, COOH). 13C NMR spectrum, δ, ppm: 15.2; 55.3; 71.3; 112.2; 114.1; 120.3; 121.5; 124.5; 126.2; 127.3; 127.6; 129.0; 130.2; 142.0; 145.4; 147.5; 149.2; 152.5; 168.6. Found, %: C 70.93; H 5.07; N 4.09. C19H17NO4. Calculated, %: C 70.58; H 5.30; N 4.33.

2-[(3-Methoxyphenoxy)methyl]-4-methylquinoline- 3-carboxylic acid (7d). White solid. IR spectrum, ν, cm–1: 3405 (COOH), 3058, 2871, 1716 (C=O), 1614, 1575, 1487. 1H NMR spectrum, δ, ppm (J, Hz): 2.84 (3H, s, CH3); 3.84 (3H, s, OCH3); 5.48 (2H, s, ArCH2O); 6.66 (1H, dd, J = 8.0, J = 1.6, H Ar); 6.71 (1H, d, J = 7.6, H Ar); 6.74 (1H, d, J = 1.6, H Ar); 7.31 (1H, t, J = 8.0, H Ar); 7.84 (1H, t, J = 7.6, H Ar); 7.97 (1H, t, J = 7.6, H Ar); 8.18 (1H, d, J = 8.4, H Ar); 8.33 (1H, d, J = 8.4, H Ar); 13.72 (1H, s, COOH). 13C NMR spectrum, δ, ppm: 15.1; 54.7; 70.6; 100.8; 106.4; 106.7; 124.5; 126.2; 127.2; 127.5; 129.0; 129.6; 130.2; 141.8; 145.4; 152.6; 159.1; 160.1; 168.7. Found, %: C 70.35; H 5.58; N 4.17. C19H17NO4. Calculated, %: C 70.58; H 5.30; N 4.33.

2-[(4-Methoxyphenoxy)methyl]-4-methylquinoline-3-carboxylic acid (7e). White solid. IR spectrum, ν, cm–1: 3441 (COOH), 3058, 2923, 1727 (C=O), 1616, 1558, 1509. 1H NMR spectrum, δ, ppm (J, Hz): 2.70 (3H, s, CH3); 3.67 (3H, s, OCH3); 5.30 (2H, s, ArCH2O); 6.85 (2H, d, J = 8.8, H Ar); 6.95 (2H, d, J = 8.8, H Ar); 7.71 (1H, t, J = 7.6, H Ar); 7.84 (1H, t, J = 7.6, H Ar); 8.04 (1H, d, J = 8.0, H Ar); 8.20 (1H, d, J = 8.4, H Ar); 13.58 (1H, s, COOH). 13C NMR spectrum, δ, ppm: 15.0; 55.0; 71.2; 114.2; 115.5; 124.5; 126.2; 127.2; 127.5; 129.0; 130.1; 141.7; 145.4; 151.8; 152.9; 153.4; 168.7. Found, %: C 70.37; H 5.07; N 4.49. C19H17NO4. Calculated, %: C 70.58; H 5.30; N 4.33.

2-[(2-Fluorophenoxy)methyl]-4-methylquinoline-3-carboxylic acid (7f). White solid. IR spectrum, ν, cm–1: 3384 (COOH), 3066, 2918, 1718 (C=O), 1646, 1592, 1503. 1H NMR spectrum, δ, ppm (J, Hz): 2.72 (3H, s, CH3); 5.43 (2H, s, ArCH2O); 6.92–6.97 (1H, m, H Ar); 7.09 (1H, t, J = 8.0, H Ar); 7.19–7.27 (2H, m, H Ar); 7.72 (1H, t, J = 7.6, H Ar); 7.85 (1H, t, J = 7.6, H Ar); 8.05 (1H, d, J = 8.0, H Ar); 8.21 (1H, d, J = 8.4, H Ar); 13.66 (1H, s, COOH). 13C NMR spectrum, δ, ppm: 15.2; 71.3; 114.8; 115.7; 115.9; 121.2 (2С); 124.4 (2С); 124.5; 124.6; 126.2; 127.4; 129.0; 130.2; 142.1; 145.5; 145.7; 145.8; 150.3; 152.0; 152.7; 168.6. Found, %: C 69.73; H 4.34; N 4.29. C18H14FNO3. Calculated, %: C 69.45; H 4.53; N 4.50.

2-[(2-Chlorophenoxy)methyl]-4-methylquinoline-3-carboxylic acid (7g). White solid. IR spectrum, ν, cm–1: 3431 (COOH), 3019, 2964, 1726 (C=O), 1614, 1578, 1486. 1H NMR spectrum, δ, ppm (J, Hz): 2.69 (3H, s, CH3); 5.41 (2H, s, ArCH2O); 6.84 (1H, t, J = 7.8, H Ar); 7.06 (1H, d, J = 8.4, H Ar); 7.12–7.15 (2H, m, H Ar); 7.72 (1H, t, J = 7.8, H Ar); 7.90 (1H, t, J = 8.4, H Ar); 8.08 (1H, d, J = 8.4, H Ar); 8.16 (1H, d, J = 7.8, H Ar); 13.61 (1H, s, COOH). 13C NMR spectrum, δ, ppm: 15.2; 70.8; 111.6; 120.5; 125.4; 126.0; 126.5; 126.9; 127.8; 128.7; 128.9; 130.4; 131.9; 139.3; 147.2; 155.4; 156.7; 168.6. Found, %: C 65.75; H 4.50; N 4.05. C18H14ClNO3. Calculated, %: C 65.96; H 4.31; N 4.27.

2-[(4-Chlorophenoxy)methyl]-4-methylquinoline-3-carboxylic acid (7h). White solid. IR spectrum, ν, cm–1: 3431 (COOH), 3050, 2964, 1720 (C=O), 1602, 1573, 1486. 1H NMR spectrum, δ, ppm (J, Hz): 2.70 (3H, s, CH3); 5.37 (2H, s, ArCH2O); 7.03 (2H, d, J = 8.8, H Ar); 7.34 (2H, d, J = 8.8, H Ar); 7.71 (1H, t, J = 7.6, H Ar); 7.84 (1H, t, J = 7.6, H Ar); 8.04 (1H, d, J = 8.4, H Ar); 8.20 (1H, d, J = 8.4, H Ar); 13.65 (1H, s, COOH). 13C NMR spectrum, δ, ppm: 15.1; 70.9; 116.2; 124.5 (2C); 126.2; 127.3; 127.4; 128.9; 129.0; 130.2; 141.9; 145.4; 152.2; 156.7; 168.7. Found, %: C 66.32; H 4.52; N 4.05. C18H14ClNO3. Calculated, %: C 65.96; H 4.31; N 4.27.

2-[(2-Bromophenoxy)methyl]-4-methylquinoline-3-carboxylic acid (7i). Pale-yellow solid. IR spectrum, ν, cm–1: 3372 (COOH), 3067, 2855, 1724 (C=O), 1627, 1584, 1508. 1H NMR spectrum, δ, ppm (J, Hz): 2.67 (3H, s, CH3); 5.39 (2H, s, ArCH2O); 6.84 (1H, t, J = 7.2, H Ar); 7.18 (1H, d, J = 7.6, H Ar); 7.26 (1H, t, J = 7.2, H Ar); 7.52 (1H, d, J = 7.6, H Ar); 7.67 (1H, t, J = 7.6, H Ar); 7.79 (1H, t, J = 7.6, H Ar); 8.00 (1H, d, J = 8.0, H Ar); 8.16 (1H, d, J = 7.6, H Ar); 13.57 (1H, s, COOH). 13C NMR spectrum, δ, ppm: 15.2; 71.3; 110.8; 113.6; 122.1; 124.6; 126.3; 127.4; 127.5; 128.6; 129.1; 130.3; 132.8; 142.3; 145.5; 151.8; 154.2; 168.5. Found, %: C 57.95; H 3.54; N 3.94. C18H14BrNO3. Calculated, %: C 58.08; H 3.79; N 3.76.

2-[(4-Bromophenoxy)methyl]-4-methylquinoline-3-carboxylic acid (7j). Pale-yellow solid. IR spectrum, ν, cm–1: 3445 (COOH), 3055, 2974, 1717 (C=O), 1601, 1571, 1488. 1H NMR spectrum, δ, ppm (J, Hz): 2.72 (3H, s, CH3); 5.39 (2H, s, ArCH2O); 6.90 (2H, d, J = 8.4, H Ar); 7.08 (2H, d, J = 8.4, H Ar); 7.71 (1H, t, J = 7.8, H Ar); 7.90 (1H, t, J = 8.4, H Ar); 8.07 (1H, d, J = 8.4, H Ar); 8.17 (1H, d, J = 7.8, H Ar); 13.43 (1H, s, COOH). 13C NMR spectrum, δ, ppm: 15.2; 70.6; 114.7; 125.1; 126.4; 127.7; 128.6; 128.9; 129.5; 129.8; 131.9; 139.5; 147.3; 155.4; 156.6; 168.5. Found, %: C 57.85; H 3.98; N 3.61. C18H14BrNO3. Calculated, %: C 58.08; H 3.79; N 3.76.

4-Methyl-2-[(naphthalen-1-yloxy)methyl]quinoline-3-carboxylic acid (7k). White solid. IR spectrum, ν, cm–1: 3431 (COOH), 3065, 2931, 1718 (C=O), 1611, 1570, 1508. 1H NMR spectrum, δ, ppm (J, Hz): 2.70 (3H, s, CH3); 5.70 (2H, s, ArCH2O); 7.58 (1H, t, J = 7.6, H Ar); 7.62–7.72 (4H, m, H Ar); 7.87 (1H, t, J = 7.2, H Ar); 7.94 (2H, t, J = 8.4, H Ar); 8.11 (1H, d, J = 8.0, H Ar); 8.23 (1H, d, J = 8.4, H Ar); 8.33 (1H, d, J = 8.4, H Ar); 13.64 (1H, s, COOH). 13C NMR spectrum, δ, ppm: 14.8; 76.2; 120.1; 121.2; 122.8; 125.1; 125.2; 125.3; 126.5; 127.1; 127.3; 127.5; 129.1; 129.3; 130.9; 133.0; 136.2; 145.0; 146.6; 151.8; 156.9; 168.6. Found, %: C 77.20; H 4.82; N 3.93. C22H17NO3. Calculated, %: C 76.95; H 4.99; N 4.08.

4-Methyl-2-[(naphthalen-2-yloxy)methyl]quinoline-3-carboxylic acid (7l). White solid. IR spectrum, ν, cm–1: 3438 (COOH), 3035, 2953, 1721 (C=O), 1603, 1569, 1509. 1H NMR spectrum, δ, ppm (J, Hz): 2.70 (3H, s, CH3); 5.48 (2H, s, ArCH2O); 7.20 (1H, d, J = 8.8, H Ar); 7.35 (1H, t, J = 7.6, H Ar); 7.43 (1H, d, J = 7.6, H Ar); 7.47 (1H, s, H Ar); 7.70 (1H, t, J = 7.6, H Ar); 7.77 (1H, d, J = 8.4, H Ar); 7.82–7.85 (3H, m, H Ar); 8.06 (1H, d, J = 8.4, H Ar); 8.19 (1H, d, J = 8.0, H Ar); 13.74 (1H, s, COOH). 13C NMR spectrum, δ, ppm: 15.1; 70.5; 107.1; 118.4; 123.5; 124.5; 126.1; 126.3; 126.4; 127.2; 128.2; 128.4; 129.0 (2С); 130.0; 130.3; 133.8; 141.5; 145.4; 152.3; 155.8; 168.9. Found, %: C 76.82; H 4.68; N 4.29. C22H17NO3. Calculated, %: C 76.95; H 4.99; N 4.08.

Synthesis of 12-methyl[1]benzoxepino[3,4-b]quinolin-13(6H)-one derivatives 6a–j and 8-methylnaphthoxepino-[3,4-b]quinolin-7(14H)-ones 6k,l (General method). The respective carboxylic acid 7al (0.5 mmol) together with PPA (83% P2O5, 7.5 g) was added to a round-bottom flask (25 ml) and stirred at 145 °C for 4–6 h. The conversion was monitored by TLC. After the reaction was complete, the mixture was poured slowly with stirring into cold water followed by neutralization with saturated NaHCO3 solution. The resulting precipitate was purified by flash chromatography (petroleum ether – EtOAc, 1:1). The yields and melting points are listed in Table 1.

12-Methyl[1]benzoxepino[3,4-b]quinolin-13(6H)-one (6a). White needle crystals. IR spectrum, ν, cm–1: 3059, 1706 (C=O), 1562, 1491, 1400, 1259, 1211, 1084, 1022, 871. 1H NMR spectrum, δ, ppm (J, Hz): 2.67 (3H, s, CH3); 5.35 (2H, s, H oxepine); 6.98 (1H, d, J = 8.0, H Ar); 7.04 (1H, t, J = 7.6, H Ar); 7.41 (1H, td, J = 8.4, J = 1.2, H Ar); 7.54 (1H, t, J = 8.0, H Ar); 7.70 (1H, t, J = 7.6, H Ar); 7.94 (1H, dd, J = 8.0, J = 1.2, H Ar); 8.01–8.06 (2H, m, H Ar). 13C NMR spectrum, δ, ppm: 15.2; 75.7; 120.2; 122.0; 125.0; 127.3; 127.7; 130.0; 130.7; 130.8; 131.0; 134.9; 135.4; 145.6; 147.4; 152.2; 160.0; 193.9. Found, %: C 78.82; H 4.56; N 4.98. C18H13NO2. Calculated, %: C 78.53; H 4.76; N 5.09.

4,12-Dimethyl[1]benzoxepino[3,4-b]quinolin-13(6H)-one (6b). White needle crystals. IR spectrum, ν, cm–1: 3065, 2961, 2864, 1710 (C=O), 1592, 1510, 1447, 1395, 1262, 1208, 1176, 1068, 865. 1H NMR spectrum, δ, ppm (J, Hz): 2.19 (3H, s, CH3); 2.66 (3H, s, CH3); 5.38 (2H, s, H oxepine); 6.94 (1H, t, J = 7.6, H Ar); 7.28 (1H, d, J = 7.2, H Ar); 7.54 (1H, t, J = 8.0, H Ar); 7.70 (1H, t, J = 7.6, H Ar); 7.79 (1H, d, J = 8.0, H Ar); 8.02–8.06 (2H, m, H Ar). 13C NMR spectrum, δ, ppm: 15.5; 16.6; 75.6; 121.4; 124.9; 126.4; 127.2; 128.8; 130.0; 130.6; 130.9; 133.7; 135.9; 136.4; 145.4; 147.4; 152.3; 158.2; 194.3. Found, %: C 78.65; H 5.16; N 5.16. C19H15NO2. Calculated, %: C 78.87; H 5.23; N 4.84.

4-Methoxy-12-methyl[1]benzoxepino[3,4-b]quinolin-13(6H)-one (6c). White solid. IR spectrum, ν, cm–1: 3047, 2966, 2818, 1699, 1613, 1592, 1517, 1457, 1410, 1387, 1298, 1235, 1147, 1081, 851. 1H NMR spectrum, δ, ppm (J, Hz): 2.70 (3H, s, CH3); 3.83 (3H, s, OCH3); 5.48 (2H, s, H oxepine); 7.14 (1H, d, J = 8.0, H Ar); 7.30 (1H, d, J = 7.6, H Ar); 7.51 (1H, t, J = 7.6, H Ar); 7.75 (1H, t, J = 7.6, H Ar); 7.90 (1H, t, J = 7.6, H Ar); 8.13 (1H, d, J = 8.4, H Ar); 8.26 (1H, d, J = 8.4, H Ar). 13C NMR spectrum, δ, ppm: 15.4; 56.5; 75.9; 117.2; 121.7; 121.9; 126.0; 127.2; 127.7; 128.2; 129.9; 131.7; 133.5; 145.3; 147.3; 149.9; 150.3; 152.5; 193.2. Found, %: C 74.40; H 5.25; N 4.22. C19H15NO3. Calculated, %: C 74.74; H 4.95; N 4.59.

3-Methoxy-12-methyl[1]benzoxepino[3,4-b]quinolin-13(6H)-one (6d). White needle crystals. IR spectrum, ν, cm–1: 3039, 2972, 2867, 1710, 1608, 1593, 1523, 1474, 1411, 1359, 1226, 1168, 1035, 852. 1H NMR spectrum, δ, ppm (J, Hz): 2.74 (3H, s, CH3); 3.86 (3H, s, OCH3); 5.46 (2H, s, H oxepine); 6.66 (1H, d, J = 2.4, H Ar); 6.83 (1H, dd, J = 8.4, J = 2.4, H Ar); 7.77 (1H, t, J = 8.4, H Ar); 7.92 (1H, t, J = 8.4, H Ar); 7.95 (1H, d, J = 8.4, H Ar); 8.13 (1H, d, J = 8.0, H Ar); 8.30 (1H, d, J = 8.4, H Ar). 13C NMR spectrum, δ, ppm: 15.6; 56.3; 76.1; 103.2; 110.7; 120.3; 126.0; 127.8; 128.2; 129.8; 131.6; 132.9; 133.4; 145.9; 147.1; 152.8; 161.9; 165.4; 191.2. Found, %: C 75.54; H 4.89; N 4.72. C19H15NO3. Calculated, %: C 74.74; H 4.95; N 4.59.

2-Methoxy-12-methyl[1]benzoxepino[3,4-b]quinolin-13(6H)-one (6e). White needle crystals. IR spectrum, ν, cm–1: 3046, 2978, 2890, 1707, 1613, 1588, 1527, 1496, 1406, 1363, 1247, 1190, 1024, 846. 1H NMR spectrum, δ, ppm (J, Hz): 2.82 (3H, s, CH3); 3.92 (3H, s, OCH3); 5.44 (2H, s, H oxepine); 7.05 (1H, d, J = 8.8, H Ar); 7.16 (1H, dd, J = 8.8, J = 3.2, H Ar); 7.54 (1H, t, J = 3.2, H Ar); 7.69 (1H, t, J = 8.0, H Ar); 7.84 (1H, t, J = 8.0, H Ar); 8.17 (1H, d, J = 8.4, H Ar); 8.19 (1H, d, J = 8.4, H Ar). 13C NMR spectrum, δ, ppm: 15.5; 55.9; 76.0; 111.8; 121.4; 123.9; 125.0; 126.2; 127.5; 128.0; 129.9; 130.9; 133.2; 146.0; 147.3; 152.5; 154.3; 154.8; 193.4. Found, %: C 74.96; H 5.07; N 4.51. C19H15NO3. Calculated, %: C 74.74; H 4.95; N 4.59.

4-Fluoro-12-methyl[1]benzoxepino[3,4-b]quinolin-13(6H)-one (6f). White solid. IR spectrum, ν, cm–1: 3059, 2967, 2885, 1707, 1622, 1594, 1534, 1498, 1401, 1378, 1256, 1185, 1036, 872. 1H NMR spectrum, δ, ppm (J, Hz): 2.71 (3H, s, CH3); 5.57 (2H, s, H oxepine); 7.17–7.22 (1H, m, H Ar); 7.60 (1H, t, J = 8.4, H Ar); 7.74–7.78 (2H, m, H Ar); 7.91 (1H, t, J = 7.6, H Ar); 8.12 (1H, d, J = 8.4, H Ar); 8.27 (1H, d, J = 8.4, H Ar). 13C NMR spectrum, δ, ppm: 15.6; 76.3; 121.3; 121.5; 121.9; 122.2; 122.3; 126.1 (2С); 127.6; 127.8; 128.5; 128.7; 129.9; 131.7; 133.2; 133.3; 146.1; 147.3; 151.4; 152.1; 153.8; 192.3. Found, %: C 73.92; H 4.19; N 4.62. C18H12FNO2. Calculated, %: C 73.71; H 4.12; N 4.78.

4-Chloro-12-methyl[1]benzoxepino[3,4-b]quinolin-13(6H)-one (6g). Pale-yellow needle crystals. IR spectrum, ν, cm–1: 3062, 2991, 2875, 1697, 1611, 1588, 1507, 1488, 1414, 1377, 1297, 1164, 1042, 869. 1H NMR spectrum, δ, ppm (J, Hz): 2.74 (3H, s, CH3); 5.47 (2H, s, H oxepine); 6.99 (1H, t, J = 7.6, H Ar); 7.53 (1H, d, J = 7.2, H Ar); 7.58 (1H, t, J = 7.2, H Ar); 7.73 (1H, t, J = 7.2, H Ar); 7.87 (1H, d, J = 7.6, H Ar); 8.04–8.08 (2H, m, H Ar). 13C NMR spectrum, δ, ppm: 14.3; 75.2; 120.8; 123.7; 124.0; 126.7; 126.8; 126.9; 128.6; 129.1; 130.1; 132.2; 134.4; 144.8; 146.5; 150.5; 154.4; 191.9. Found, %: C 69.45; H 4.15; N 4.20. C18H12ClNO2. Calculated, %: C 69.80; H 3.90; N 4.52.

2-Chloro-12-methyl[1]benzoxepino[3,4-b]quinolin-13(6H)-one (6h). Yellow solid. IR spectrum, ν, cm–1: 3050, 2978, 1707, 1617, 1595, 1489, 1402, 1368, 1256, 1126, 1027, 981. 1H NMR spectrum, δ, ppm (J, Hz): 3.32 (3H, s, CH3); 5.93 (2H, s, H oxepine); 7.35 (1H, d, J = 8.0, H Ar); 7.79 (1H, d, J = 7.6, H Ar); 8.27–8.33 (2H, m, H Ar); 8.49–8.53 (2H, m, H Ar); 8.78 (1H, d, J = 8.0, H Ar). 13C NMR spectrum, δ, ppm: 15.6; 75.8; 120.1; 121.9; 127.4; 128.3; 128.4; 128.5; 128.6; 129.2; 132.3; 136.8; 140.0; 148.3; 148.9; 151.6; 157.5; 192.8. Found, %: C 69.52; H 4.01; N 4.23. C18H12ClNO2. Calculated, %: C 69.80; H 3.90; N 4.52.

4-Bromo-12-methyl[1]benzoxepino[3,4-b]quinolin-13(6H)-one (6i). Yellow solid. IR spectrum, ν, cm–1: 3048, 1710, 1613, 1597, 1559, 1478, 1398, 1306, 1279, 1177, 1047, 910. 1H NMR spectrum, δ, ppm (J, Hz): 2.67 (3H, s, CH3); 5.46 (2H, s, H oxepine); 6.93 (1H, t, J = 8.0, H Ar); 7.57 (1H, t, J = 7.6, H Ar); 7.70 (1H, d, J = 8.0, H Ar); 7.74 (1H, d, J = 7.6, H Ar); 7.91 (1H, d, J = 8.4, H Ar); 8.03–8.08 (2H, m, H Ar). 13C NMR spectrum, δ, ppm: 15.6; 76.1; 114.0; 122.3; 122.6; 124.9; 125.0; 127.5; 127.9; 130.0; 130.6; 131.3; 138.6; 145.9; 147.4; 151.5; 156.2; 192.8. Found, %: C 60.75; H 3.19; N 3.74. C18H12BrNO2. Calculated, %: C 61.04; H 3.41; N 3.95.

2-Bromo-12-methyl[1]benzoxepino[3,4-b]quinolin-13(6H)-one (6j). Yellow solid. IR spectrum, ν, cm–1: 3046, 2989, 2876, 1705, 1578, 1519, 1488, 1397, 1310, 1230, 1177, 1047, 939. 1H NMR spectrum, δ, ppm (J, Hz): 2.75 (3H, s, CH3); 5.41 (2H, s, H oxepine); 6.95 (1H, d, J = 8.8, H Ar); 7.55 (1H, dd, J = 8.4, J = 2.4, H Ar); 7.65 (1H, t, J = 7.6, H Ar); 7.80 (1H, t, J = 8.0, H Ar); 8.11–8.14 (3H, m, H Ar). 13C NMR spectrum, δ, ppm: 15.5; 75.8; 110.0; 114.4; 122.1; 125.1; 127.7; 127.8; 128.0; 129.9; 131.2; 133.1; 137.8; 146.4; 147.4; 151.7; 159.0; 192.3. Found, %: C 61.21; H 3.27; N 4.18. C18H12BrNO2. Calculated, %: C 61.04; H 3.41; N 3.95.

8-Methylnaphtho[2',1':6,7]oxepino[3,4-b]quinolin-7(14H)-one (6k). White solid. IR spectrum, ν, cm–1: 3043, 2986, 1691, 1604, 1580, 1527, 1480, 1397, 1308, 1238, 1191, 1051, 906. 1H NMR spectrum, δ, ppm (J, Hz): 2.70 (3H, s, CH3); 5.59 (2H, s, H oxepine); 7.41–7.45 (2H, m, H Ar); 7.51 (1H, d, J = 7.6, H Ar); 7.55 (1H, t, J = 7.6, H Ar); 7.71 (2H, t, J = 8.0, H Ar); 7.97 (1H, d, J = 8.8,

H Ar); 8.04 (1H, d, J = 8.4, H Ar); 8.08 (1H, d, J = 8.4, H Ar); 8.33 (1H, d, J = 8.4, H Ar). 13C NMR spectrum, δ, ppm: 15.9; 76.0; 120.7; 121.0; 122.2; 122.6; 123.7; 124.9; 125.1; 125.8; 126.1; 127.0; 127.8; 128.1; 128.8; 130.0; 130.5; 131.3; 136.9; 152.0; 158.1; 193.6. Found, %: C 80.90; H 4.71; N 4.01. C22H15NO2. Calculated, %: C 81.21; H 4.65; N 4.30.

14-Methylnaphtho[1',2':6,7]oxepino[3,4-b]quinolin-15(8H)-one (6l). White solid. IR spectrum, ν, cm–1: 3056, 1688, 1593, 1507, 1486, 1434, 1397, 1322, 1274, 1218, 1191, 1123, 1051, 906. 1H NMR spectrum, δ, ppm (J, Hz): 2.83 (3H, s, CH3); 5.63 (2H, s, H oxepine); 7.22 (1H, d, J = 8.8, H Ar); 7.53 (1H, t, J = 8.0, H Ar); 7.68 (1H, t, J = 7.6, H Ar); 7.72 (1H, t, J = 8.0, H Ar); 7.83 (1H, t, J = 8.0, H Ar); 7.86 (1H, d, J = 7.6, H Ar); 7.95 (1H, d, J = 8.8, H Ar); 8.13 (1H, d, J = 8.0, H Ar); 8.21 (1H, d, J = 8.4, H Ar); 8.95 (1H, d, J = 8.8, H Ar). 13C NMR spectrum, δ, ppm: 15.0; 74.2; 118.8; 120.7; 124.3; 124.6; 124.8; 127.5; 128.0; 128.6; 128.9; 129.5; 129.8; 130.6; 130.9; 135.4; 136.4; 142.9; 147.0; 150.5; 159.1; 197.6. Found, %: C 81.44; H 4.90; N 4.15. C22H15NO2. Calculated, %: C 81.21; H 4.65; N 4.30.

Notes

The project was financially supported by the National Natural Science Foundation of China (Nos. 21476028 and 21402011) and the Natural Science Foundation of Liaoning Province (No. 201602006).

Supplementary material

10593_2018_2322_MOESM1_ESM.pdf (2.8 mb)
ESM 1 (PDF 2832 kb)

References

  1. 1.
    Huang, S. T.; Kuo, H. S.; Chen, C. T. Tetrahedron Lett. 2001, 42, 7473.CrossRefGoogle Scholar
  2. 2.
    Bruder, M.; Haseler, P. L.; Muscarella, M.; Lewis, W.; Moody, C. J. J. Org. Chem. 2010, 75, 353.CrossRefPubMedGoogle Scholar
  3. 3.
    Pettit, G. R.; Numata, A.; Iwamoto, C.; Usami, Y.; Yamada, T.; Ohishi, H.; Cragg, G. M. J. Nat. Prod. 2006, 69, 323.CrossRefPubMedGoogle Scholar
  4. 4.
    Boonphong, S.; Puangsombat, P.; Baramee, A.; Mahidol, C.; Ruchirawat, S.; Kittakoop, P. J. Nat. Prod. 2007, 70, 795.CrossRefPubMedGoogle Scholar
  5. 5.
    Sarkhel, S.; Sharon, A.; Trivedi, V.; Maulik, P. R.; Singh, M. M.; Venugopalan, P.; Ray, S. Bioorg. Med. Chem. 2003, 11, 5025.CrossRefPubMedGoogle Scholar
  6. 6.
    Saidachary, G.; Prasad, K. V.; Divya, D.; Singh, A.; Ramesh, U.; Sridhar, B.; Raju, B. C. Eur. J. Med. Chem. 2014, 76, 460.CrossRefPubMedGoogle Scholar
  7. 7.
    Kahnberg, P.; Sterner, O. Tetrahedron 2001, 57, 7181.CrossRefGoogle Scholar
  8. 8.
    Lee, S. H.; Van, H. T. M.; Yang, S. H.; Lee, K. T.; Kwon, Y.; Cho, W. J. Bioorg. Med. Chem. Lett. 2009, 19, 2444.CrossRefGoogle Scholar
  9. 9.
    Liu, J. H.; Steigel, A.; Reininger, E.; Bauer, R. J. Nat. Prod. 2000, 63, 403.CrossRefPubMedGoogle Scholar
  10. 10.
    Staben, S. T.; Siu, M.; Goldsmith, R.; Olivero, A. G.; Do, S.; Burdick, D. J.; Heffron, T. P.; Dotson, J.; Sutherlin, D. P.; Zhu, B. Y.; Tsui, V.; Le, H.; Lee, L.; Lesnick, J.; Lewis, C.; Murray, J. M.; Nonomiya, J.; Pang, J.; Prior, W. W.; Salphati, L.; Rouge, L.; Sampath, D.; Sideris, S.; Wiesmann, C.; Wu, P. Bioorg. Med. Chem. Lett. 2011, 21, 4054.CrossRefPubMedGoogle Scholar
  11. 11.
    Kamboj, R. C.; Jindal, P.; Kumar, D.; Khullar, S.; Mandal, S. K. J. Photochem. Photobiol. A: Chem. 2014, 278, 31.CrossRefGoogle Scholar
  12. 12.
    Rao Mangina, N. S. V. M.; Suresh, S.; Sridhar, B.; Karunakar, G. V. Org. Biomol. Chem. 2016, 14, 3526.CrossRefGoogle Scholar
  13. 13.
    Rao Mangina, N. S. V. M.; Kadiyala, V.; Guduru, R.; Goutham, K.; Sridhar, B.; Karunakar, G. V. Org. Lett. 2017, 19, 282.CrossRefGoogle Scholar
  14. 14.
    Johnson, O. H.; Hamilton, C. S. J. Am. Chem. Soc. 1941, 63, 2864.CrossRefGoogle Scholar
  15. 15.
    LaMontagne, M. P.; Dagli, D.; Khan, M. S.; Blumbergs, P. J. Med. Chem. 1980, 23, 981.CrossRefPubMedGoogle Scholar
  16. 16.
    Urbina, J. M.; Cortés, J. C. G.; Palma, A.; López, S. N.; Zacchino, S. A.; Enriz, R. D.; Ribas, J. C.; Kouznetzov, V. V. Bioorg. Med. Chem. 2000, 8, 691.CrossRefPubMedGoogle Scholar
  17. 17.
    Jain, R.; Vaitilingam, B.; Nayyar, A.; Palde, P. B. Bioorg. Med. Chem. Lett. 2003, 13, 1051.CrossRefPubMedGoogle Scholar
  18. 18.
    Ulven, T.; Little, P. B.; Receveur, J. M.; Frimurer, T. M.; Rist, Ø.; Nørregaard, P. K.; Högberg, T. Bioorg. Med. Chem. Lett. 2006, 16, 1070.CrossRefPubMedGoogle Scholar
  19. 19.
    Li, A.; Huang, C.; Luo, C. W.; Li, L. J.; Yi, W. J.; Liu, T. W.; Chao, Z. S. Catal. Commun. 2017, 98, 13.CrossRefGoogle Scholar
  20. 20.
    Dolle, R. E.; Nelson, K. H. J. Comb. Chem. 1999, 1, 235.CrossRefPubMedGoogle Scholar
  21. 21.
    Gao, W. T.; Lin, G. H.; Li, Y.; Tao, X. Y.; Liu, R.; Sun, L. J. Beilstein J. Org. Chem. 2012, 8, 1849.Google Scholar
  22. 22.
    Gao, W. T.; Xing, X. D.; Li, Y.; Lan, S. Tetrahedron 2014, 70, 2180.CrossRefGoogle Scholar
  23. 23.
    Gao, W. T.; Fu, X. B.; Zhang, X. F.; Zhao, Y. N.; Wang, D. F.; Li, Y. Tetrahedron Lett. 2016, 57, 4145.CrossRefGoogle Scholar
  24. 24.
    Li, Y.; Li, K.; Gao, W. T. Chem. Heterocycl. Compd. 2016, 52, 200. [Khim. Geterotsikl. Soedin. 2016, 52, 200.]Google Scholar
  25. 25.
    Li, Y.; Wang, Y.; Zou, H. T. Mol. Diversity 2017, 21, 463.CrossRefGoogle Scholar
  26. 26.
    Jida, M.; Deprez, B. New J. Chem. 2012, 36, 869.Google Scholar
  27. 27.
    Ryabukhin, S. V.; Volochnyuk, D. M.; Plaskon, A. S.; Naumchik, V. S.; Tolmachev, A. A. Synthesis 2007, 1214.Google Scholar
  28. 28.
    Degtyarenko, A. S.; Tolmachev, A. A.; Volovenko, Y. M.; Tverdokhlebov, A. V. Synthesis 2007, 3891.Google Scholar
  29. 29.
    Xu, J.; Wang, D. L.; Liu, Z. P.; Zhang, K. X.; Ma, W.; Liu, B. Heterocycles 2017, 94, 1055.CrossRefGoogle Scholar
  30. 30.
    Nammalwar, B.; Murie, M.; Fortenberry, C.; Bunce, R. A. Tetrahedron Lett. 2014, 55, 3181.CrossRefGoogle Scholar
  31. 31.
    Eaton, P. E.; Carlson, G. R.; Lee, J. T. J. Org. Chem. 1973, 38, 4071.CrossRefGoogle Scholar
  32. 32.
    Meesala, R.; Nagarajan, R. Tetrahedron Lett. 2010, 51, 422.CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Institute of Superfine ChemicalsBohai UniversityJinzhouChina

Personalised recommendations