One-Pot Synthesis of 2-Arylquinolines via in situ Acid Catalysis

Abstract

A simple, efficient, and practical protocol is reported, allowing quick access to diverse 2-arylquinolines from 2-vinylanilines and benzyl halides. This reaction is additive and metal catalyst-free with only solvent needed. A preliminary mechanistic investigation discloses the driving force comes from the in situ released HBr, which catalyzes the subsequent cyclization. The present synthetic route featured high functional group tolerance and simple post-processing. A variety of 2-arylquinolines were obtained up to 96% yield.

Nitrogen-containing heteroaromatics are the prevalent framework in various pharmaceutical molecules. Among them, quinoline is one of the most privileged heteroaromatics, in view of its excellent biological and pharmacological activities. For instance, it possesses antibacterial,[1] antifungal,[2] [3] antimalarial,[4] antipsychotic,[5] anticancer,[6] [7] anthelmintic,[8] antiglaucoma,[9] and cardiotonic[9] activities. Besides, quinoline skeletons are utilized in ligands,[10] [11] [12] [13] agrochemicals,[14] functional materials,[15] [16] [17] and so on. Several typical applications of 2-arylquinolines are shown in Figure [1].

Given the various properties of quinoline, many synthetic strategies have been developed, such as Skraup reaction,[18] Doebner–von Miller synthesis,[19] Pfitzinger synthesis,[20] Doebner synthesis,[19] Friedländer synthesis,[21] and Combes synthesis.[22] In addition to these traditional methods, it has sprung up that 2-vinylanilines serve as a potential synthon for the construction of quinoline in recent years. Generally, this transformation has been demonstrated by employing various transition metal catalysts, such as palladium,[23] [24] [25] copper,[26] iron,[27] along with suitable acids or bases (Scheme [1, a–e]). Likewise, acids[28] [29] or bases[30] can also catalyze the same processes individually for some substrates (Scheme [1, e, f]). We envisioned using 2-vinylanilines to synthesize 2-arylquinolines. The current 2-position aryl groups have several sources, like arylhydrazines, arylboronic acids, α-diazocarbonyl compounds, N-tosylhydrazones, benzaldehydes and β-keto esters (Scheme [1, a–f]). Besides, when benzyl bromide was used, to our delight, the 2-arylquinolines were successfully obtained. Due to the better-leaving property of bromine, benzyl bromide is widely known as a reagent for establishing C–N bonds,[31] [32] [33] but the by-product HBr is also produced. Considering acids could play a role as catalysts in the previous reaction, we audaciously designed a synthetic strategy of 2-arylquinolines from 2-vinylanilines and benzyl bromide by employing in situ released HBr catalytic cyclization. This strategy avoids acid additives, further reducing environmental pollution with high atom economy.

Initially, we tested the reaction of 2-(1-phenylvinyl)aniline (1a; 0.3 mmol) and benzyl bromide (2a; 0.3 mmol) in the presence of KI (0.3 mmol) in DMSO (2.0 mL) at 120 °C. To our delight, the target compound 2,4-diphenylquinoline (3a) was obtained in 66% yield (Table [1], entry 1). Then TBAI, CuI, ZnI₂, NaI, NH₄I, NIS, and I₂ were investigated as additives and the product was obtained in 44%, 48%, 64%, 43%, 52%, 7%, and 8% yield, respectively. However, KI showed the best reactivity among these iodides (entries 1–8). To improve the yield of 2,4-diphenylquinoline (3a), the temperature was raised to 130 °C and 140 °C to form 3a in 68% and 72% yield, respectively (entries 9, 10). Moreover, when the amount of 1a was increased to 1.5 equivalents and 2.0 equivalents under the same conditions as those of entry 10, the yield of 3a was increased (entries 11, 12). When the polar solvent NMP was used instead of DMSO, the yield of 3a was increased slightly (entry 13). Subsequently, we tried to reduce the amount of KI, and were surprised that the yield of 3a did not drop significantly without KI (entries 14, 15). Finally, DMF was used and proved not to be a good solvent for this reaction (entry 16). The optimized reaction conditions were 1a (0.6 mmol) with 2a (0.3 mmol) in NMP (2 mL) at 140 °C under air atmosphere for 12 hours (entry 15).

Table 1 Optimization of the Reaction Conditions^a

Entry	Additive	Temp (°C)	Solvent	Yield (%)b
1	KI	120	DMSO	66
2	TBAI	120	DMSO	44
3	CuI	120	DMSO	48
4	ZnI2	120	DMSO	64
5	NaI	120	DMSO	43
6	NH4I	120	DMSO	52
7	NIS	120	DMSO	7
8	I2	120	DMSO	8
9	KI	130	DMSO	68
10	KI	140	DMSO	72
11c	KI	140	DMSO	76
12d	KI	140	DMSO	82
13d	KI	140	NMP	85
14d,e	KI	140	NMP	82
15d	–	140	NMP	81
16d	–	140	DMF	30

^a Reaction conditions: 2-(1-phenylvinyl)aniline (1a; 0.3 mmol), benzyl bromide (2a: 0.3 mmol), additive (0.3 mmol), solvent (2 mL), 12 h in air.

^b Isolated yields.

^c 1a: 45 mmol.

^d 1a: 0.6 mmol.

^e KI: 0.15 mmol.

Having established the optimized conditions, we explored the scope and limitations of 2-vinylanilines, and the results are shown in Scheme [2]. First, the effect of various substituents on the aryl moiety of aniline was studied. The yield of 2-arylquinolines was not sensitive to the electronic property of the groups. Both electron-donating groups (3b–f) and electron-withdrawing groups (3g, 3h) all worked well, affording the desired products in good to excellent yields. Furthermore, substituents of aniline at ortho-, meta- and para-positions also worked well (3b, 3c, 3d, 3e). Sterically challenging 3,5-dimethyl-2-vinylaniline afforded the corresponding 2-arylquinolines 3j in 76% yield. Formation of 2-arylquinolines 3i and 3k, containing phenyl and isopropyl, were obtained in 63% and 71% yield, respectively. Then, the substituents on the benzene ring of the styryl moiety were tested. Electron-donating groups are slightly more favorable than electron-withdrawing groups (3l, 3m, 3n vs. 3p). For the position of substituents, ortho-, meta-, and para-positions had little difference (3l, 3m, 3n). The tert-butyl group also was successfully introduced in moderate yield (3o). Pleasantly, 4-methylquinoline 3q could be obtained from 2-(1-methylvinyl)aniline under the standard conditions in 55% yield. Moreover, this protocol was not limited to the aniline, the naphthalene ring with the amino group also provided the desired products 3r and 3s.

Next, the effect of various substituents on the benzyl bromide also was investigated. As shown in Scheme [3], methyl substituent at meta-position gave a lower yield than ortho- and para-positions (4b vs 4a, 4c). The electron-donating or -withdrawing properties of substituted groups produced slight effect on their yields (4d, 4e, 4f, 4g vs 4h, 4i, 4j, 4k). The yield of 4d was lower than we expected, probably due to the low boiling point of p-methoxybenzyl bromide, which vaporized and was not fully involved in the reaction. Importantly, cyano, trifluoromethyl and ester substituents were well tolerated under the present conditions to afford the corresponding 2-arylquinolines 4h, 4i, 4k in moderate yields. The presence of double fluorine substituents appeared to be detrimental for the yield of 2-arylquinoline 4l. Other halogenated hydrocarbons were also tried, such as 2-bromoacetophenone, cinnamyl bromide, and allyl bromide. The results indicated that the role of the phenyl is crucial. It is disadvantageous that the phenyl group was far from the bromine or was absent. Finally, to our delight, 2,4-diphenylquinoline (3a) could be obtained from benzyl chloride in a slightly lower yield of 71% (Scheme [2]).

Subsequently, the synthetic utility of our method was demonstrated. Gram scale reaction of 1b with 2a under standard conditions afforded the product 3b in 85% yield, which makes large-scale synthesis possible (Scheme [4, a]). The functionalization of 2-arylquinolines could be achieved by employing corresponding strategies. For instance, 2,4-diphenylquinoline (3a) was reacted with an oxirane catalyzed by Pd(OAc)₂ to afford functionalized quinoline 5a with a secondary alcohol moiety in 76% yield (Scheme [4, b]). Moreover, the heterocyclic ring of 3a could be stereoselectively reduced to afford tetrahydroquinoline[34] (Scheme [4, b]).

We started to get insight into the reaction mechanism by performing various control experiments. According to previous literature, NMP could be decomposed to form 4-(methylamino)butanoic acid[35] at very high temperatures, but the corresponding acid was not detected at 140 °C, which suggests that NMP may not be the potential catalyst (Scheme [5, a]). Next, to identify the generation of potential intermediate, the reaction of 1a and 2a was quenched with H₂O after 0.5 hours. Nucleophilic substitution product A was obtained in 70% yield (Scheme [5, b]). Treatment of the obtained intermediate A under HBr-catalyzed conditions for 12 hours gave the 2,4-diphenylquinoline (3a) in 52% yield and recycled 2-(1-phenylvinyl)aniline (1a) in 17% yield at the same time (Scheme [5, c]). Compared to the reaction under standard conditions, the lower yield of 3a may be due to the decomposition of intermediate A. Considering the amount of 1a under optimized conditions, intermediate A was treated with HBr and 2 equivalents 1a in NMP at 140 °C for 12 hours. As expected, higher yield (77%) of 3a was observed, indicating that 1a surely inhibited the decomposition of A and made the overall transformation better (Scheme [5, d]). To demonstrate the catalytic effect of HBr, reaction was performed with 1a and A without HBr, leading to the formation of 3a in only 32% yield (Scheme [5, e]). Finally, the reaction was performed under N₂ atmosphere and a lower yield of 3a was obtained, indicating oxygen from the air was confirmed to be an essential condition (Scheme [5, f]).

Based on the above investigation and previous literature, we propose a plausible reaction mechanism as shown in Scheme [6]. Initially, the reaction of 2-(1-phenylvinyl)aniline 1a with benzyl bromide 2a would generate intermediate A, followed by oxidization with oxygen from the air to form imine species B. And by-product HBr is generated simultaneously to catalyze the following cyclization.[28] Then, imine species B is protonated to active imine C and intramolecular nucleophilic addition occurred, producing carbocation D, which undergoes deprotonation toward alkenyl compound E. At last, aromatization takes place to deliver product 3a.

In summary, we have successfully developed a simple, efficient, and practical protocol for the synthesis of 2-arylquinolines from 2-vinylanilines and benzyl halide under additive and metal catalyst-free conditions. A total of 31 different quinolines were synthesized in good to excellent yields. The catalyst HBr comes from by-product instead of external addition, achieving less environmental pollution. Moreover, the reaction is solvent-only, and the optimized reaction conditions allow the presence of a wide range of typical organic functional groups. The related studies are now in progress.

Substituted substrates 1 was obtained according to the literature reports. Other reagents and solvents were commercially available and were used directly without further purification. The characterization data for the product 6a were obtained from the literature.[34] All the reactions were monitored by TLC. ¹H NMR and ¹³C NMR spectra were recorded on a Bruker A Avance 400 (400 MHz) spectrometer using CDCl₃ or DMSO-d ₆ as the solvents and TMS as internal standard. HRMS spectra (ESI) were confirmed on a Bruker impact II spectrograph in positive-ion mode with an ESI ion source.

2,4-Diphenylquinoline (3a); Typical Procedure

Under air, a 25 mL open flask equipped with a stir bar was charged with 2-(1-phenylvinyl)aniline (1a; 117.1 mg, 0.6 mmol), benzyl bromide (2a; 51.3 mg 0.3 mmol), and solvent NMP (2 mL). The reaction mixture was stirred at 140 °C for about 12 h and was monitored by TLC. Once the reaction was complete, the mixture was extracted with EtOAc (4 × 25 mL). The organic layers were combined and dried (anhyd Na₂SO₄), filtered, and concentrated in vacuo. The residue was purified by column chromatography (PE/EtOAc 25:1 and PE/CH₂Cl₂ 3:2) on silica gel to afford 2,4-diphenylquinoline (3a) as a yellowish oil; yield: 0.068 g (81%).

¹H NMR (400 MHz, CDCl₃): δ = 8.24 (d, J = 8.8 Hz, 1 H), 8.18–8.15 (m, 2 H), 7.86 (d, J = 8.4 Hz, 1 H), 7.77 (s, 1 H), 7.69–7.65 (m, 1 H), 7.69–7.65 (m, 9 H).

¹³C NMR (100 MHz, CDCl₃): δ = 156.9, 149.2, 148.9, 139.7, 138.5, 130.2, 139.7, 129.6, 129.5, 128.9, 128.7, 128.5, 127.7, 126.4, 125.9, 125.7, 119.4.

HRMS (ESI): m/z calcd for C₂₁H₁₅N for [M + H]⁺: 282.1276; found: 282.1271.

6-Methyl-2,4-diphenylquinoline (3b)

Yellowish oil; yield: 0.085 g (96%).

¹H NMR (400 MHz, CDCl₃): δ = 8.17–8.13 (m, 3 H), 7.76 (s, 1 H), 7.64 (s, 1 H), 7.55–7.50 (m, 8 H), 7.44–7.41 (m, 1 H), 2.45 (s, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 156.0, 148.5, 147.4, 139.8, 138.7, 136.3, 131.8, 129.9, 129.6, 129.2, 128.9, 128.6, 128.4, 127.6, 125.8, 124.5, 119.5, 21.9.

HRMS (ESI): m/z calcd for C₂₁H₁₇N [M + H]⁺: 296.1433; found: 296.1430.

5-Methyl-2,4-diphenylquinoline (3c)

Yellowish oil; yield: 0.062 g (70%).

¹H NMR (400 MHz, CDCl₃): δ = 8.19–8.13 (m, 3 H), 7.68 (s, 1 H), 7.61–7.57 (m, 1 H), 7.51–7.36 (m, 8 H), 7.24 (d, J = 8.0 Hz, 1 H), 2.02 (s, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 155.4, 149.9, 149.7, 142.8, 139.2, 135.5, 129.7, 129.4, 129.2, 129.0, 128.9, 128.8, 128.0, 127.8, 127.5, 125.3, 121.4, 24.5.

HRMS (ESI): m/z calcd for C₂₁H₁₇N [M + H]⁺: 296.1433; found: 296.1429.

7-Methyl-2,4-diphenylquinoline (3d)

Yellowish oil; yield: 0.081 g (91%).

¹H NMR (400 MHz, CDCl₃): δ = 8.19–8.17 (m, 2 H) 8.04 (s, 1 H), 7.78 (d, J = 8.4 Hz, 1 H), 7.74 (s, 1 H), 7.54–7.42 (m, 8 H), 7.29 (dd, J = 8.8, 2.0 Hz, 1 H), 2.56 (s, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 156.9, 149.0, 139.9, 139.8 138.6, 129.6, 129.3, 129.1, 128.8, 128.7, 128.6, 128.4, 127.6, 125.4, 123.2, 118.7, 21.3.

HRMS (ESI): m/z calcd for C₂₁H₁₇N [M + H]⁺: 296.1433; found: 296.1428.

6-Methyl-2,4-diphenylquinoline (3e)

Colorless oil; yield: 0.074 g (83%).

¹H NMR (400 MHz, CDCl₃): δ = 8.28–8.25 (m, 2 H) 7.82 (s, 1 H), 7.70 (d, J = 8.4 Hz, 1 H), 7.56–7.41 (m, 9 H), 7.34–7.30 (m, 1 H), 2.95 (s, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 155.0, 149.4, 147.7, 139.9, 138.0, 129.7, 129.6, 129.3, 128.8, 128.6, 128.3, 127.6, 126.0, 125.8, 123.7, 118.7, 17.7

HRMS (ESI): m/z calcd for C₂₁H₁₇N [M + H]⁺: 296.1433; found: 296.1438.

6-Methoxy-2,4-diphenylquinoline (3f)

Yellowish oil; yield: 0.072 g (77%).

¹H NMR (400 MHz, CDCl₃): δ = 8.16–8.14 (m, 3 H), 7.76 (s, 1 H), 7.57–7.37 (m, 9 H), 7.18 (d, J = 2.8 Hz, 1 H), 3.77 (s, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 157.9, 154.6, 147.9, 144.9, 139.7, 138.8, 131.6, 129.4, 129.1, 128.8, 128.7, 128.4, 127.4, 126.7, 121.9, 119.7, 103.7, 55.5.

HRMS (ESI): m/z calcd for C₂₁H₁₇NO [M + H]⁺: 312.1382; found: 312.1386.

6-Fluoro-2,4-diphenylquinoline (3g)

Yellowish oil; yield: 0.078 g (87%).

¹H NMR (400 MHz, CDCl₃): δ = 8.22 (dd, J = 8.8, 5.6 Hz, 1 H), 8.17–8.14 (m, 2 H), 7.82 (s, 1 H), 7.56–7.43 (m, 10 H).

¹³C NMR (100 MHz, CDCl₃): δ = 160.6 (d, J _C,F = 247.5 Hz), 156.3 (d, J _C,F = 2.0 Hz), 148.7 (d, J _C,F = 5.1 Hz), 146.0, 139.4, 138.0, 132.6 (d, J _C,F = 9.1 Hz), 129.5, 129.4, 128.9, 128.8, 128.7, 127.5, 126.5 (d, J _C,F = 9.1 Hz), 119.9, 119.8, 119.5, 109.1 (d, J _C,F = 23.2 Hz).

¹⁹F NMR (376 MHz, CDCl₃): δ = –112.86.

HRMS (ESI): m/z calcd for C₂₁H₁₄FN [M + H]⁺: 300.1182; found: 300.1186.

6-Chloro-2,4-diphenylquinoline (3h)

Yellowish oil; yield: 0.085 g (90%).

¹H NMR (400 MHz, CDCl₃): δ = 8.18–8.15 (m, 3 H), 7.82 (d, J = 2.4 Hz, 1 H), 7.81 (s, 1 H), 7.64 (dd, J = 8.8, 2.4 Hz, 1 H), 7.58–7.43 (m, 8 H).

¹³C NMR (100 MHz, CDCl₃): δ = 157.1, 148.5, 147.2, 139.2, 137.8, 132.3, 131.7, 130.5, 129.7, 129.5, 128.9, 128.9, 128.8, 127.6, 126.5, 124.5, 120.1.

HRMS (ESI): m/z calcd for C₂₁H₁₄ClN [M + H]⁺: 316.0887, 318.0857; found: 316.0886, 318.0860.

For 4-chloro-2-(1-phenylvinyl)aniline (1h): m/z calcd for C₁₄H₁₂ClN (M + H)⁺: 230.0730, 232.0701; found: 230.0733, 232.0704.

2,4,6-Triphenylquinoline (3i)

Yellowish oil; yield: 0.068 g (63%).

¹H NMR (400 MHz, CDCl₃): δ = 8.31 (d, J = 8.8 Hz, 1 H), 8.22–8.19 (m, 2 H), 8.09 (d, J = 2.0 Hz, 1 H), 7.98 (dd, J = 8.8, 2.0 Hz, 1 H), 7.83 (s, 1 H), 7.62–7.42 (m, 12 H), 7.33–7.32 (m, 1 H).

¹³C NMR (100 MHz, CDCl₃): δ = 156.3, 149.4, 148.3, 140.71, 139.6, 139.1, 138.4, 130.6, 129.6, 129.5, 129.3, 128.9, 128.9, 128.8, 128.5, 127.6, 127.5, 126.0, 123.4, 119.8.

HRMS (ESI): m/z calcd for C₂₇H₁₉N [M + H]⁺: 358.1589; found: 358.1585.

5,7-Dimethyl-2.4-diphenylquinoline (3j)

Yellowish oil; yield: 0.071 g (76%).

¹H NMR (400 MHz, CDCl₃): δ = 8.17–8.15 (m, 2 H), 7.92 (s, 1 H), 7.60 (s, 1 H), 7.49–7.34 (m, 8 H), 7.08 (s, 1 H), 2.50 (s, 3 H), 1.98 (s, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 155.3, 150.3, 149.5, 142.9, 139.4, 139.2, 135.0, 132.0, 129.3, 128.9, 128.8, 128.1, 128.0, 127.7, 127.5, 123.4, 120.6, 24.4, 21.5.

HRMS (ESI): m/z calcd for C₂₃H₁₉N [M + H]⁺: 310.1589; found: 310.1592.

6-Isopropyl-2,4-diphenylquinoline (3k)

Colorless oil; yield: 0.069 g (71%).

¹H NMR (400 MHz, CDCl₃): δ = 8.21–8.16 (m, 3 H), 7.77 (s, 1 H), 7.70 (d, J = 2.0 Hz, 1 H), 7.65 (dd, J = 8.4, 2.0 Hz, 1 H), 7.59–7.42 (m, 8 H), 3.02 (m, J = 6.8 Hz, 1 H), 1.28 (d, J = 6.8 Hz, 6 H).

¹³C NMR (100 MHz, CDCl₃): δ = 156.19, 148.80, 147.8, 147.1, 139.8, 138.7, 130.1, 129.6, 129.2, 129.2, 128.9, 128.6, 128.4, 127.6, 125.7, 121.9, 119.5, 34.4, 23.9.

HRMS (ESI): m/z calcd for C₂₄H₂₁N [M + H]⁺: 324.1746; found: 324.1751.

2-Phenyl-4-(o-tolyl)quinoline (3l)

Yellowish oil; yield: 0.062 g (70%).

¹H NMR (400 MHz, CDCl₃): δ = 8.25 (d, J = 8.4 Hz, 1 H), 8.21–8.19 (m, 2 H), 7.76 (s, 1 H), 7.73–7.69 (m, 1 H), 7.53–7.26 (m, 9 H), 2.08 (s, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 156.9, 149.3, 148.5, 139.6, 137.9, 136.2, 130.3, 130.1, 129.7, 129.7, 129.4, 128.9, 128.5, 127.7, 126.4, 126.3, 125.9, 125.8, 119.4, 20.1.

HRMS (ESI): m/z calcd for C₂₂H₁₇N [M + H]⁺: 296.1433; found: 296.1437.

2-Phenyl-4-(p-tolyl)quinoline (3m)

Yellowish oil; yield: 0.067 g (76%).

¹H NMR (400 MHz, CDCl₃): δ = 8.24 (d, J = 8.4 Hz, 1 H), 8.19–8.16 (m, 2 H), 7.92 (dd, J = 8.4, 1.6 Hz, 1 H), 7.79 (s, 1 H), 7.72–7.68 (m, 1 H), 7.53–7.42 (m, 6 H), 7.33 (d, J = 8.0 Hz, 2 H), 2.45 (s, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 156.9, 149.3, 148.9, 139.8, 138.4, 135.5, 130.1, 129.5, 129.4, 128.9, 127.7, 126.3, 125.9, 125.8, 119.4, 21.4.

HRMS (ESI): m/z calcd for C₂₁H₁₇N [M + H]⁺: 296.1433; found: 296.1431.

2-Phenyl-4-(p-tolyl)quinoline (3n)

Yellowish oil; yield: 0.062 g (70%).

¹H NMR (400 MHz, CDCl₃): δ = 8.24 (d, J = 8.8 Hz, 1 H), 8.20–8.18 (m, 2 H), 7.91 (dd, J = 8.4, 1.2 Hz, 1 H), 7.80 (s, 1 H) 7.73–7.69 (m, 1 H), 7.53–7.29 (m, 8 H), 2.45 (s, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 156.9, 149.4, 148.8, 139.7, 138.4, 130.3, 130.1, 129.6, 129.4, 129.2, 128.9, 128.5, 127.7, 126.7, 126.3, 125.9, 125.8, 119.4, 21.6.

HRMS (ESI): m/z calcd for C₂₁H₁₇N [M + H]⁺: 296.1433; found: 296.1436.

4-(4-(tert-Butyl)phenyl)-2-phenylquinoline (3o)

Yellowish oil; yield: 0.054 g (53%).

¹H NMR (400 MHz, CDCl₃): δ = 8.27 (d, J = 8., 1.0 Hz, 1 H), 8.20–8.18 (m, 2 H), 7.97 (dd, J = 8.4, 1.6 Hz, 1 H), 7.82 (s, 1 H), 7.75–7.71 (m, 1 H), 7.58–7.47 (m, 8 H), 1.42 (s, 9 H).

¹³C NMR (100 MHz, CDCl₃): δ = 156.9, 151.6, 149.4, 148.7, 139.6, 135.4, 130.0, 129.6, 129.4, 129.4, 128.9, 127.7, 126.3, 125.9, 125.9, 125.6, 119.5, 34.8, 31.4.

HRMS (ESI): m/z calcd for C₂₅H₂₃N [M + H]⁺: 338.1452; found: 338.1455.

4-(4-Chlorophenyl)-2-quinoline (3p)

Yellowish oil; yield: 0.062 g (65%).

¹H NMR (400 MHz, CDCl₃): δ = 8.25 (d, J = 8.8 Hz, 1 H), 8.19–8.16 (m, 2 H), 7.83 (dd, J = 8.4, 1.6 Hz, 1 H), 7.77 (s, 1 H), 7.75–7.71 (m, 1 H), 7.54–7.44 (m, 8 H).

¹³C NMR (100 MHz, CDCl₃): δ = 156.9, 148.8, 148.0, 139.4, 136.8, 134.7, 130.9, 130.2, 129.8, 129.5, 128.9, 127.6, 126.6, 125.5, 125.3, 119.3.

HRMS (ESI): m/z calcd for C₂₁H₁₄ClN [M + H]⁺: 316.0887, 318.0857; found: 316.0888, 318.0862.

For 2-(1-(4-chlorophenyl)vinyl)aniline (1p): m/z calcd for C₁₄H₁₂ClN (M + H)⁺: 230.0730, 232.0701; found: 230.0730, 232.0702.

4-Methyl-2-phenylquinoline (3q)

Yellowish oil; yield: 0.036 g (55%).

¹H NMR (400 MHz, CDCl₃): δ = 8.18 (d, J = 8.4 Hz, 1 H), 8.16–8.13 (m, 2 H), 7.98 (dd, J = 8.8, 2.0 Hz, 1 H), 7.73–7.69 (m, 2 H), 7.55–7.43 (m, 4 H), 2.75 (d, J = 0.8 Hz, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 157.1, 148.1, 144.9, 139.8, 130.3, 129.4, 129.2, 128.8, 127.6, 127.3, 126.1, 123.6, 119.8, 19.0.

HRMS (ESI): m/z calcd for C₁₆H₁₃N [M + H]⁺: 220.1120; found: 220.1125.

1,3-Diphenylbenzo[f]quinoline (3r)

Brown oil; yield: 0.075 g (75%).

¹H NMR (400 MHz, CDCl₃): δ = 8.23–8.21 (m, 2 H), 8.13 (d, J = 9.2 Hz, 1 H), 7.96 (d, J = 8.8, 1.2 Hz, 1 H), 7.84 (dd, J = 7.6, 1.6 Hz, 1 H), 7.79 (s, 1 H), 7.65 (d, J = 8.4 Hz, 1 H), 7.52–7.42 (m, 9 H), 7.15–7.11 (m, 1 H).

¹³C NMR (100 MHz, CDCl₃): δ = 155.5, 149.8, 149.3, 143.1, 139.1, 133.0, 131.6, 129.8, 129.4, 129.3, 129.2, 128.9, 128.7, 128.5, 128.2, 128.1, 127.5, 126.5, 125.6, 122.8, 121.9.

HRMS (ESI): m/z calcd for C₂₅H₁₇N [M + H]⁺: 332.1433; found: 332.1430.

2,4-Diphenylbenzo[h]quinoline (3s)

Yellowish oil; yield: 0.062 g (62%).

¹H NMR (400 MHz, CDCl₃): δ = 9.481 (d, J = 8.4 Hz, 1 H), 8.27–8.25 (m, 2 H), 7.83 (s, 1 H), 7.76 (d, J = 8.0 Hz, 1 H), 7.68–7.56 (m, 4 H), 7.47–7.34 (m, 8 H).

¹³C NMR (100 MHz, CDCl₃): δ = 154.9, 149.1, 146.8, 139.8, 138.9, 133.7, 132.1, 129.8, 129.3, 128.9, 128.7, 128.4, 128.3, 127.7, 127.5, 127.4, 127.0, 125.3, 123.4, 122.9, 119.5.

HRMS (ESI): m/z calcd for C₂₅H₁₇N [M + H]⁺: 332.1433; found: 332.1436.

4-Phenyl-2-(p-tolyl)quinoline (4a)

Yellowish oil; yield: 0.065 g (74%).

¹H NMR (400 MHz, CDCl₃): δ = 8.23 (d, J = 8.4 Hz, 1 H), 8.09 (d, J = 8.4 Hz, 2 H), 7.88 (d, J = 8.4 Hz, 1 H), 7.79 (s, 1 H), 7.72–7.68 (m, 1 H), 7.55–7.42 (m, 6 H), 7.31 (d, J = 8.0 Hz, 2 H), 2.41 (s, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 156.9, 149.1, 148.8, 139.5, 138.5, 136.8, 130.1, 129.6, 129.5, 128.6, 128.4, 127.5, 126.2, 125.7, 125.7, 119.3, 21.4.

HRMS (ESI): m/z calcd for C₂₂H₁₇N [M + H]⁺: 296.1433; found: 296.1431.

4-Phenyl-2-(m-tolyl)quinoline (4b)

Yellowish oil; yield: 0.055 g (62%).

¹H NMR (400 MHz, CDCl₃): δ = 8.25 (d, J = 8.8 Hz, 1 H), 8.03 (s, 1 H), 7.95 (d, J = 8.0 Hz, 1 H), 7.89 (d, J = 8.4 Hz, 1 H), 7.80 (s, 1 H), 7.74–7.70 (m, 1 H), 7.56–7.38 (m, 7 H), 7.27 (d, J = 7.6 Hz, 1 H), 2.47 (s, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 157.1, 149.2, 148.8, 139.6, 138.6, 138.5, 130.2, 130.1, 129.6, 129.6, 128.8, 128.6, 128.4, 128.3, 126.3, 125.8, 125.7, 124.8, 119.6, 21.6.

HRMS (ESI): m/z calcd for C₂₂H₁₇N [M + H]⁺: 296.1433; found: 296.1429.

4-Phenyl-2-(o-tolyl)quinoline (4c)

Yellowish oil; yield: 0.065 g (73%).

¹H NMR (400 MHz, CDCl₃): δ = 8.25 (d, J = 8.4 Hz, 1 H), 7.96 (d, J = 8.4 Hz, 1 H), 7.75–7.71 (m, 1 H), 7.57–7.48 (m, 8 H), 7.33–7.28 (m, 3 H), 2.47 (s, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 159.9, 148.6, 148.4, 140.6, 138.2, 136.1, 131.0, 130.0, 129.8, 129.7, 129.6, 128.7, 128.6, 128.5, 126.5, 126.1, 125.7, 125.3, 122.7, 20.5.

HRMS (ESI): m/z calcd for C₂₂H₁₇N [M + H]⁺: 296.1433; found: 296.1428.

2-(4-Methoxyphenyl)-4-phenylquinoline (4d)

Yellowish oil; yield: 0.050 g (53%).

¹H NMR (400 MHz, CDCl₃): δ = 8.21 (d, J = 8.8 Hz, 1 H), 8.18–8.15 (m, 2 H), 7.87 (d, J = 8.4 Hz, 1 H), 7.77 (s, 1 H), 7.73–7.68 (m, 1 H), 7.56–7.41 (m, 6 H), 7.06–7.02 (m, 2 H), 3.87 (s, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 160.9, 156.4, 149.1, 148.8, 138.5, 132.2, 129.9, 129.6, 129.5, 129.0, 128.6, 128.4, 126.0, 125.7, 125.5, 119.0, 114.3, 55.4.

HRMS (ESI): m/z calcd for C₂₂H₁₇NO [M + H]⁺: 312.1382; found: 312.1387.

2-(4-(tert-Butyl)phenyl-4-phenylquinoline (4e)

Yellowish oil; yield: 0.074 g (73%).

¹H NMR (400 MHz, CDCl₃): δ = 8.24 (d, J = 8.4 Hz, 1 H), 8.13–8.09 (m, 2 H), 7.88 (d, J = 8.4 Hz, 1 H), 7.79 (s, 1 H), 7.72–7.67 (m, 1 H), 7.55–7.41 (m, 8 H), 1.37 (s, 9 H).

¹³C NMR (100 MHz, CDCl₃): δ = 157.0, 152.6, 149.1, 148.9, 138.5, 137.0, 130.1, 129.6, 129.5, 128.6, 128.4, 127.4, 126.2, 125.9, 125.7, 125.7, 119.4, 34.8, 31.4.

HRMS (ESI): m/z calcd for C₂₅H₂₃N [M + H]⁺: 338.1902; found: 338.1900.

2-([1,1′-Biphenyl]-4-yl)-4-phenylquinoline (4f)

White solid; yield: 0.088 g (82%).

¹H NMR (400 MHz, CDCl₃): δ = 8.26 (d, J = 8.4 Hz, 3 H), 7.89 (d, J = 8.4 Hz, 1 H), 7.83 (s, 1 H), 7.74–7.64 (m, 5 H), 7.53–7.32 (m, 9 H).

¹³C NMR (100 MHz, CDCl₃): δ = 156.4, 149.3, 148.9, 142.2, 140.6, 138.5, 138.5, 130.2, 129.7, 128.9, 128.7, 128.5, 128.1, 127.7, 127.6, 127.2, 126.4, 125.9, 125.7, 119.3.

HRMS (ESI): m/z calcd for C₂₇H₁₉N [M + H]⁺: 358.1589; found: 358.1584.

2-(Naphthalen-2-yl)-4-phenylquinoline (4g)

Yellowish oil; yield: 0.071 g (71%).

¹H NMR (400 MHz, CDCl₃): δ = 8.63 (s, 1 H), 8.40 (dd, J = 8.8, 2.0 Hz, 1 H), 8.29 (d, J = 8.4 Hz, 1H), 7.98–7.85 (m, 5 H), 7.75–7.71 (m, 1 H), 7.59–7.44 (m, 8 H).

¹³C NMR (100 MHz, CDCl₃): δ = 156.7, 149.3, 148.9, 138.5, 136.9, 133.9, 133.6, 130.2, 129.7, 129.7, 128.9, 128.7, 128.7, 128.5, 127.8, 127.2, 126.8, 126.5, 126.4, 125.9, 125.8, 125.1, 119.5.

HRMS (ESI): m/z calcd for C₂₅H₁₇N [M + H]⁺: 332.1433; found: 332.1429.

4-(4-Phenylquinolin-2-yl)benzonitrile (4h)

White solid; yield: 0.065 g (71%).

¹H NMR (400 MHz, CDCl₃): δ = 8.33–8.30 (m, 2 H), 8.24 (d, J = 8.0 Hz, 1 H), 7.93 (d, J = 8.4 Hz, 1 H), 7.81–7.75 (m, 4 H), 7.59–7.50 (m, 6 H).

¹³C NMR (100 MHz, CDCl₃): δ = 154.5, 149.9, 148.8, 143.7, 138.0, 132.6, 130.3, 130.1, 129.5, 128.8, 128.7, 128.1, 127.2, 126.2, 125.8, 119.0, 118.9, 112.8.

HRMS (ESI): m/z calcd for C₂₂H₁₄N₂ [M + H]⁺: 307.1229; found: 307.1234.

4-Phenyl-2-(4-(trifluoromethyl)phenyl)quinoline (4i)

Yellowish oil; yield: 0.066 g (63%).

¹H NMR (400 MHz, CDCl₃): δ = 8.30 (d, J = 8.0 Hz, 2 H), 8.25 (d, J = 8.8 Hz, 1 H), 7.92 (d, J = 8.4 Hz, 1 H), 7.81 (s, 1 H), 7.77–7.72 (m, 3 H), 7.54–7.47 (m, 6 H).

¹³C NMR (100 MHz, CDCl₃): δ = 155.2, 149.7, 148.8, 142.9, 138.1, 131.1 (q, J _C,F = 32.3 Hz), 130.3, 130.0, 129.6, 128.7, 128.6, 127.9, 126.9, 126.1, 125.8 (q, J _C,F = 3.0 Hz), 124.3 (q, J _C,F = 272.7 Hz), 119.15.

¹⁹F NMR (376 MHz, CDCl₃): δ = –62.50.

HRMS (ESI): m/z calcd for C₂₂H₁₄F₃N [M + H]⁺: 350.1150; found: 350.1147.

2-(3-Fluorophenyl)-4-phenylquinoline (4j)

Yellowish oil; yield: 0.055 g (61%).

¹H NMR (400 MHz, CDCl₃): δ = 8.25 (d, J = 8.4 Hz, 1 H), 8.12 (td, J = 7.6, 2.0 Hz, 1 H), 7.94 (d, J = 8.4 Hz, 1 H), 7.83 (d, J = 2.4 Hz, 1 H), 7.75–7.71 (m, 1 H), 7.57–7.46 (m, 6 H), 7.44–7.39 (m, 1 H), 7.32 (td, J = 7.6, 1.6 Hz, 1 H), 7.21–7.16 (m, 1 H).

¹³C NMR (100 MHz, CDCl₃): δ = 160.08 (d, J _C,F = 251.5 Hz), 153.7 (d, J _C,F = 2.0 Hz), 148.8, 148.7, 138.2, 131.6 (d, J _C,F = 3.0 Hz), 130.9 (d, J _C,F = 9.1 Hz), 130.1, 129.7, 129.6, 128.6, 128.5, 128.0 (d, J _C,F = 12.1 Hz), 126.7, 125.8, 125.7, 124.7, 124.7, 122.8 (d, J _C,F = 8.1 Hz), 116.3 (d, J _C,F = 23.2 Hz).

¹⁹F NMR (376 MHz, CDCl₃): δ = –116.82.

HRMS (ESI): m/z calcd for C₂₁H₁₄FN [M + H]⁺: 300.1182; found: 300.1178.

Ethyl 4-(4-Phenylquinolin-2-yl)benzoate (4k)

Yellowish oil; yield: 0.074 g (70%).

¹H NMR (400 MHz, CDCl₃): δ = 8.28–8.25 (m, 3 H), 8.19 (d, J = 8.4 Hz, 2 H), 7.91 (d, J = 8.4 Hz, 1 H), 7.83 (s, 1 H), 7.76–7.72 (m, 1 H), 7.56–7.47 (m, 6 H), 4.41 (q, J = 7.2 Hz, 2 H), 1.43 (t, J = 6.8 Hz, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 166.5, 155.6, 149.6, 148.8, 143.6, 138.2, 131.1, 130.2, 130.1, 129.8, 129.6, 128.7, 128.6, 127.5, 126.9, 126.0, 125.7, 119.4, 61.2, 14.4.

HRMS (ESI): m/z calcd for C₂₄H₁₉NO₂ [M + H]⁺: 354.1488; found: 354.1493.

2-(2,6-Difluorophenyl)-4-phenylquinoline (4l)

Yellowish oil; yield: 0.048 g (50%).

¹H NMR (400 MHz, CDCl₃): δ = 8.26 (d, J = 8.8 Hz, 1 H), 7.97 (d, J = 8.4 Hz, 1 H), 7.78–7.74 (m, 1 H), 7.57–7.46 (m, 7 H), 7.42–7.34 (m, 1 H), 7.08–7.01 (m, 2 H).

¹³C NMR (100 MHz, CDCl₃): δ = 160.7 (dd, J _C,F = 251.5, 7.1 Hz), 149.5, 148.9, 148.6, 137.8, 130.4 (t, J _C,F = 10.1 Hz), 130.1, 129.7, 129.7, 128.6, 128.6, 127.2, 125.9, 125.8, 123.5, 118.45 (t, J _C,F = 18.2 Hz), 112.0 (dd, J _C,F = 19.2, 7.1 Hz).

¹⁹F NMR (376 MHz, CDCl₃): δ = –114.01.

HRMS (ESI): m/z calcd for C₂₁H₁₃F₂N [M + H]⁺: 318.1088; found: 318.1092.

Phenyl(4-phenylquinolin-2-yl)methanone (4m)

Yellowish oil; yield: 0.034 g (37%).

¹H NMR (400 MHz, CDCl₃): δ = 8.28–8.25 (m, 3 H), 8.05 (s, 1 H), 8.01 (d, J = 8.0 Hz, 1 H), 7.80–7.76 (m, 1 H), 7.65–7.48 (m, 9 H).

¹³C NMR (100 MHz, CDCl₃): δ = 193.9, 154.3, 149.8, 147.3, 137.7, 136.2, 133.2, 131.5, 130.9, 130.0, 129.6, 128.8, 128.7, 128.5, 128.2, 127.5, 125.9, 121.0.

HRMS (ESI): m/z calcd for C₂₂H₁₅NO [M + H]⁺: 310.1226; found: 310.1222

N-Benzyl-2-(1-phenylvinyl)aniline (A)

Yellowish oil; yield: 0.060 g (70%).

¹H NMR (400 MHz, DMSO-d ₆): δ = 7.40–7.31 (m, 5 H), 7.26–7.08 (m, 6 H), 7.00 (dd, J = 7.2, 1.6 Hz, 1 H), 6.65 (t, J = 7.2 Hz, 1 H), 6.56 (d, J = 8.0 Hz, 1 H), 5.92 (d, J = 1.6 Hz, 1 H), 5.35 (d, J = 1.6 Hz, 1 H), 4.88 (t, J = 6.0 Hz, 1 H), 4.25 (d, J = 5.2 Hz, 2 H).

¹³C NMR (100 MHz, CDCl₃): δ = 146.8, 145.5, 140.4, 139.8, 130.4, 129.1, 128.9, 128.7, 128.5, 127.3, 127.2, 127.0, 126.9, 116.9, 116.5, 111.0, 46.9.

HRMS (ESI): m/z calcd for C₂₁H₁₉N [M + H]⁺: 286.1589; found: 286.1589.

1-Phenoxy-3-(2-(4-phenylquinolin-2-yl)phenyl)propan-2-ol (5a)

Yellowish oil; yield: 0.098 g (76%).

¹H NMR (400 MHz, CDCl₃): δ = 8.32 (d, J = 8.4 Hz, 1 H), 7.98 (d, J = 8.4 Hz, 1 H), 7.79–7.75 (m, 1 H), 7.66 (s, 1 H), 7.62–7.43 (m, 10 H), 7.37 (td, J = 7.6, 1.6 Hz, 1 H), 7.29–7.24 (m, 2 H), 6.95–6.91 (m, 3 H), 4.45–4.39 (m, 1 H), 4.22 (dd, J = 9.2, 4.4 Hz, 1 H), 4.04 (dd, J = 9.2, 6.8 Hz, 1 H), 3.24 (dd, J = 13.2, 9.2 Hz, 1 H), 3.13 (dd, J = 13.6, 3.6 Hz, 1 H).

¹³C NMR (100 MHz, CDCl₃): δ = 159.1, 157.8, 150.5, 146.5, 139.7, 137.9, 137.8, 131.6, 130.5, 130.4, 129.6, 129.4, 128.8, 128.8, 128.7, 127.1, 126.7, 125.8, 125.3, 122.9, 120.7, 114.6, 72.0, 71.6, 36.8, 29.8.

HRMS (ESI): m/z calcd for C₂₁H₁₃F₂N [M + H]⁺: 432.1957; found: 432.1956.

Conflict of Interest

The authors declare no conflict of interest.

Acknowledgment

We are grateful to the Analytical Center for Structural Constituent and Physical Property of Core Facilities Sharing Platform, Shandong University for their technology and services support.

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Corresponding Authors

Publication History

Received: 24 May 2022

Accepted after revision: 01 July 2022

Accepted Manuscript online:
01 July 2022

Article published online:
08 August 2022

© 2022. Thieme. All rights reserved

Georg Thieme Verlag KG
Rüdigerstraße 14, 70469 Stuttgart, Germany

• References

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• Supplementary Material