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Synthesis 2010(16): 2794-2798  
DOI: 10.1055/s-0030-1258146
PAPER
© Georg Thieme Verlag Stuttgart ˙ New York

Copper-Catalyzed One-Pot Synthesis of Substituted Benzimidazo[1,2-a]quinolines

Bing-Wei Zhou, Jian-Rong Gao, Dong Jiang, Jian-Hong Jia, Zhen-Ping Yang, Hong-Wei Jin*
College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310014, P. R. of China
Fax: +86(571)88320415; e-Mail: jhwei828@zjut.edu.cn;

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Publication History

Received 19 March 2010
Publication Date:
01 July 2010 (online)

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Abstract

A one-pot procedure for the synthesis of substituted benzimidazo[1,2-a]quinolines from the corresponding benzimidazoles and 2-bromobenzaldehydes has been developed. The titled products were prepared through Knoevenagel condensation and copper-catalyzed­ intramolecular Ullmann-type coupling in moderate to good yields.

Key words

Knoevenagel condensation - copper catalyst - Ullmann coupling - quinoline synthesis - cascade process

Substituted benzimidazoles and their azino-fused derivatives show a wide range of biological activity such as antiviral, anticancer, antibacterial, antifungal, DNA intercalator, etc. [¹]

Unsubstituted benzimidazo[1,2-a]quinoline was first prepared in 1938 by Morgan and Stewart via classical condensation from 2-aminoquinoline and picric acid. [²] Substituted benzimidazo[1,2-a]quinolines have been synthesized by photochemical dehydrocyclization and dehydrohalogenation cyclization of acyclic benzimidazolyl-substituted acrylonitriles [³] and by palladium-catalyzed intramolecular Buchwald-Hartwig amination of 2-(2-bromoanilino)quinolines. [4]

Scheme 1 One-pot synthesis of benzimidazo[1,2-a]quinolines

Recently, aza-fused polycyclic quinolines were synthesized by Cai et al. via a copper-catalyzed cascade process. Cai’s method could be applied to a wide range of 2-halogenated arylaldehydes to yield the corresponding products. [5] Herein we wish to report a novel one-pot synthesis of substituted benzimidazo[1,2-a]quinolines that firstly uses the Knoevenagel condensation [6] of the corresponding 2-bromobenzaldehydes and substituted benzimidazoles, followed by copper-catalyzed intramolecular Ullmann-type coupling reaction (Scheme  [¹] ). [7] Reaction conditions such as base, ligand, solvent, and temperature were carefully investigated. The results obtained show different substrate scope and substituent effects compared with those from the group of Cai.

Table 1 Optimization of the Solventa

Entry Solvent Temp (˚C) Time (h) Yieldb (%)
1 THF reflux  8 48
2 MeCN reflux  8 56
3 toluene 90 12 trace
4 dioxane 90  8 84
5 DMSO 90 12 trace
6 DMF 90  8 20
a Reaction conditions: 1. 1a (0.5 mmol), 2a (0.6 mmol), piperidine (0.1 mmol), solvent (2 mL), r.t., 3 h; 2. CuI (0.05 mmol), 1,10-phenanthroline (0.1 mmol), K2CO3 (1 mmol), 90 ˚C, 5-7 h.
b Isolated yield based on 1a.

Initially, benzimidazole-2-acetonitrile (1a) and 2-bromobenzaldehyde (2a) were chosen as model substrates. Since the condensation in the first step proceeded easily in the presence of a catalytic amount of piperidine, we focused our efforts on the coupling reaction (Table  [¹] ). Using copper(I) iodide (0.1 equiv) as the catalyst and 1,10-phenanthroline (0.2 equiv) as the ligand and with potassium carbonate (2 equiv) as the base in refluxing tetrahydrofuran for five hours (entry 1) gave 3a in 48% isolated yield. Varying the solvent (entries 2-6) showed that dioxane was the best and it was used in the next step of the optimization process.

We then evaluated the ligands and bases in the model reaction. The results shown in Table  [²] , entries 1-4, show that 1,10-phenanthroline is the better ligand for this C-N coupling reaction. The yield did not increase when the reaction temperature and time were increased (entry 5). The bases were also investigated and it was found that the yield with cesium carbonate was comparable to that with potassium carbonate, while potassium phosphate was less satisfactory (entries 4, 6, and 7).

Table 2 Optimization of the Ligand and Basea

Entry Ligandb Base Time (h) Yieldc (%)
1 A K2CO3 8 27
2 B K2CO3 8 20
3 C K2CO3 8 trace
4 D K2CO3 8 84
5 D K2CO3 12 84d
6 D K3PO4 8 79
7 D Cs2CO3 8 83
a Reaction conditions: 1. 1a (0.5 mmol), 2a (0.6 mmol), piperidine (0.1 mmol), dioxane (2 mL), r.t., 3 h; 2. CuI (0.05 mmol), ligand (0.1 mmol), base (1 mmol), 90 ˚C, 5-7 h.
b Ligands: A, l-proline; B, N-methylglycine; C, N,N-dimethylglycine; D, 1,10-phenanthroline.
c Isolated yield based on 1a.
d The intramolecular coupling reaction was performed at reflux.

Scheme 2 One-pot synthesis of 3m

Scheme 3 Synthesis of unsubstituted benzimidazo[1,2-a]quinoline (3n)

The optimized reaction conditions for the formation of 3a were applied to a wide range of substrates and the results are summarized in Table  [³] . 2-Bromobenzaldehydes 2a-e reacted well with benzimidazole-2-acetonitriles 1a-c to give the corresponding products 3a-h in moderate to good yields (entries 1-8), however, the reactions of 2-bromobenzaldehydes 2a,b,e,f with ethyl 2-benzimidazolyl­acetate 1d afforded the desired products 3i-l in relatively low yields (entries 9-12). To our delight, 5-methylbenzimidazole-2-acetonitrile (1b) gave 3f in excellent yield, although it was an isomeric mixture as identified by ¹H and ¹³C NMR (entry 6). A similar result was obtained in the reaction of 1b with 2b, which was probably caused by isomerization of the benzimidazole ring in the intermediate (entry 8). Among the benzaldehydes screened, the yields with substrates containing an electron-withdrawing group are generally higher than those with an electron-donating­ group.

The above results promoted us to examine the reaction of imidazo[4,5-b]pyridine-2-acetonitrile (1e) with 2-bromobenzaldehyde (2a) (Scheme  [²] ). As expected, the reaction proceeded smoothly to give 3m in 35% yield.

After carrying out the cascade process for the synthesis of substituted benzimidazo[1,2-a]quinolines 3a-l, we wondered whether this strategy could be extended to the synthesis of unsubstituted benzimidazo[1,2-a]quinoline (3n). However, this one-pot method failed to afford product 3n due to the limitations of the Knoevenagel condensation. To our delight, unsubstituted benzimidazo[1,2-a]quinoline (3n) was obtained from intramolecular coupling of pre-synthesized 2-(2-bromostyryl)benzimidazole (4a) in 60% yield (Scheme  [³] ). [8]

In order to improve the yield of 3n, further optimization was investigated including solvent, ligand, and temperature. The results (Table  [4] ) show that the intramolecular C-N coupling reaction proceeded smoothly at relative low temperatures (76 ˚C) in acetonitrile under CuI/l-proline catalysis to afford the desired product 3n in excellent yield (90%).

Table 3 One-Pot Synthesis of Substituted Benzimidazo[1,2-a]quinolinesa

Entry Substrates
 Product
 Yieldb (%)
1 R¹ R² 2 R³ 3 R³
 1 1a CN H 2a H 3a H 84
 2 1a CN H 2b 5-OMe 3b 3-OMe 75
 3 1a CN H 2c 4-Me 3c 2-Me 68
 4 1a CN H 2d 5-OH 3d 3-OH 43
 5 1a CN H 2e 5-Cl 3e 3-Cl 79
 6 1b CN Me 2a H 3f c H 88
 7 1c CN Cl 2a H 3g H 81
 8 1b CN Me 2b 5-OMe 3h c 3-OMe 72
 9 1d CO2Et H 2a H 3i H 40
10 1d CO2Et H 2f 4-Cl 3j 2-Cl 45
11 1d CO2Et H 2b 5-OMe 3k 3-OMe 20
12 1d CO2Et H 2e 5-Cl 3l 3-Cl 37
a Conditions: 1. 1 (0.5 mmol), 2 (0.6 mmol), piperidine (0.1 mmol), dioxane (2 mL), r.t., 3 h; 2. CuI (0.05 mmol), 1,10-phenanthroline (0.1 mmol), K2CO3 (1 mmol), 90 ˚C, 5-7 h.
b Isolated yield based on benzimidazole.
c The product is a mixture of isomers.

In conclusion, we have developed a one-pot, efficient, general, and practical cascade process for the synthesis of benzimidazo[1,2-a]quinoline derivatives in moderate to good yields. Benzimidazole-2-acetonitriles with electron-withdrawing group or electron-donating group all afforded the corresponding products in good yields. Catalyzed by copper, unsubstituted benzimidazo[1,2-a]quinoline was obtained by intramolecular Ullmann-type coupling in excellent yield. These results are different from those of Cai. Further studies on the practical applications of these compounds is underway in our laboratory.

Table 4 Optimization of the Conditions for the Synthesis of Unsubstituted Benzimidazo[1,2-a]quinolinea

Entry Solvent Ligandb Temp (˚C) Yieldc (%)
1 dioxane D 90 60
2 dioxane E 90 86
3 dioxane A 90 74
4 DMSO A 90 56
5 THF A reflux 45
6 MeCN A 76 90
7 MeCN E 76 73
8 MeCN D 76 59
a Conditions: 4a (0.5 mmol), CuI (0.05 mmol), ligand (0.1 mmol), K2CO3 (1 mmol), solvent (2 mL), 8 h.
b Ligand: A, l-proline; D, 1,10-phenanthroline; E, N,N-dimethylethylenediamine.
c Isolated yield based on 4a.

All reactions were carried out in the Schlenk tubes under N2 atmosphere and solvents were purified and dried by standard procedures. Reactions were followed by TLC using SILG/UV 254 silica gel plates, which were visualized via a UV fluorescent lamp. Melting points were obtained using micro melting point apparatus and are uncorrected. ¹H and ¹³C NMR spectrums were obtained on a Bruker 500 MHz instrument. LR-MS and HRMS were obtained by using EI and ESI ionizations.

Copper-Catalyzed One-Pot Synthesis of Substituted Benzimidazo[1,2- a ]quinolines 3; General Procedure

To a soln of substituted benzimidazole 1 (0.5 mmol) and 2-bromobenzaldehyde 2 (0.6 mmol) in dioxane (2 mL) in a Schlenk tube was added piperidine (0.1 mmol) using a syringe. The mixture was stirred at r.t. for 3 h under N2 and then CuI (0.05 mmol), 1,10-phenanthroline (0.1 mmol), and K2CO3 (1 mmol) were added successively to the soln under N2. The mixture was heated at 90 ˚C for the appropriate time until TLC monitoring indicated no further improvement in the conversion. The mixture was washed with CH2Cl2 (3 × 15 mL) and filtered using a funnel. The filtrate was dried (anhyd Na2SO4) and concentrated in vacuo. The residue was purified by column chromatography (silica gel, CH2Cl2-EtOAc, 30:1).

Benzimidazo[1,2- a ]quinoline-6-carbonitrile (3a)

Yellow solid; mp 254 ˚C.

¹H NMR (500 MHz, CDCl3): δ = 8.64 (d, J = 9.0 Hz, 1 H), 8.41 (d, J = 8.0 Hz, 1 H), 8.21 (s, 1 H), 8.19-8.16 (m, 1 H), 7.96-7.93 (m, 2 H), 7.65-7.57 (m, 3 H).

¹³C NMR (125 MHz, CDCl3): δ = 144.6, 144.5, 138.8, 136.5, 133.0, 130.9, 130.8, 125.4, 125.1, 124.0, 121.5, 121.4, 115.5, 114.9, 114.0, 103.1.

MS (EI): m/z = 243 [M]+.

HRMS (EI): m/z [M]+ calcd for C16H9N3: 243.0796; found: 243.0800.

3-Methoxybenzimidazo[1,2- a ]quinoline-6-carbonitrile (3b)

Yellow solid; mp 250 ˚C.

¹H NMR (500 MHz, DMSO-d 6): δ = 8.64-8.56 (m, 3 H), 7.97 (d, J = 8.0 Hz, 1 H), 7.60-7.50 (m, 3 H), 7.48-7.44 (m, 1 H), 3.89 (s, 3 H).

¹³C NMR (125 MHz, DMSO-d 6): δ = 155.8, 143.9, 143.6, 139.9, 130.3, 130.2, 124.9, 123.4, 122.4, 121.6, 120.2, 117.2, 115.4, 114.5, 112.6, 101.5, 55.7.

MS (EI): m/z = 273 [M]+.

HRMS (EI): m/z [M]+ for C17H11N3O: 273.0902; found: 273.0909.

2-Methylbenzimidazo[1,2- a ]quinoline-6-carbonitrile (3c)

Yellow solid; mp 270 ˚C.

¹H NMR (500 MHz, DMSO-d 6): δ = 8.85 (d, J = 8.0 Hz, 1 H), 8.78 (s, 1 H), 8.64 (s, 1 H), 8.06-8.01 (m, 2 H), 7.65-7.57 (m, 2 H), 7.52 (d, J = 7.5 Hz, 1 H), 2.71 (s, 3 H).

¹³C NMR (125 MHz, DMSO-d 6): δ = 145.1, 144.6, 143.8, 140.4, 136.0, 131.0, 130.5, 126.5, 125.0, 123.4, 120.1, 119.0, 115.5, 115.4, 115.1, 99.9, 21.8.

MS (EI): m/z = 257 [M]+.

HRMS (EI): m/z [M]+ for C17H11N3: 257.0953; found: 257.0961.

3-Hydroxybenzimidazo[1,2- a ]quinoline-6-carbonitrile (3d)

Yellow solid; mp >300 ˚C.

¹H NMR (500 MHz, DMSO-d 6): δ = 10.23 (s, 1 H), 8.72-8.64 (m, 3 H), 7.99 (d, J = 8.0 Hz, 1 H), 7.60-7.54 (m, 2 H), 7.47-7.44 (m, 2 H).

¹³C NMR (125 MHz, DMSO-d 6): δ = 154.4, 144.0, 143.6, 140.3, 130.3, 129.2, 124.8, 123.3, 122.6, 122.2, 120.2, 117.3, 115.6, 114.8, 114.5, 101.3.

MS (EI): m/z = 259 [M]+.

HRMS (EI): m/z [M]+ for C16H9N3O: 259.0746; found: 259.0766.

3-Chlorobenzimidazo[1,2- a ]quinoline-6-carbonitrile (3e)

Yellow solid; mp 263 ˚C.

¹H NMR (500 MHz, DMSO-d 6): δ = 8.76 (d, J = 9.0 Hz, 1 H), 8.67 (s, 1 H), 8.61 (d, J = 8.0 Hz, 1 H), 8.20 (d, J = 2.5 Hz, 1 H), 8.01-7.99 (m, 1 H), 7.92 (q, J = 9.0 Hz, 1 H), 7.63-7.55 (m, 2 H).

¹³C NMR (125 MHz, DMSO-d 6): δ = 144.2, 143.7, 139.4, 134.4, 132.9, 130.4, 129.8, 129.0, 125.3, 124.0, 122.6, 120.4, 117.9, 115.1, 114.7, 102.6.

MS (EI): m/z = 277 [M]+.

HRMS (EI): m/z [M]+ for C16H8ClN3: 277.0407; found: 277.0412.

9/10-Methylbenzimidazo[1,2- a ]quinoline-6-carbonitrile (3f)

Yellow solid; mp 183 ˚C.

¹H NMR (500 MHz, DMSO-d 6): δ = 8.67-8.65 (m, 2 H), 8.45 (d, J = 8.5 Hz, 0.5 H), 8.39 (s, 0.5 H), 8.09-8.05 (m, 1 H), 7.95-7.90 (m, 1 H), 7.81 (d, J = 8.5 Hz, 0.5 H), 7.70 (s, 0.5 H), 7.62-7.58 (m, 1 H), 7.38-7.30 (m, 1 H), 2.52 (s, 3 H).

¹³C NMR (125 MHz, DMSO-d 6): δ = 144.1, 143.9, 143.7, 141.7, 139.9, 139.7, 135.5, 135.4, 134.4, 133.3, 133.3, 133.2, 130.9, 130.8, 130.4, 128.3, 126.4, 124.9, 124.8, 121.0, 120.9, 119.6, 119.5, 115.7, 115.5, 115.4, 114.2, 114.0, 101.1, 101.0, 21.57, 21.14.

MS (EI): m/z = 257 [M]+.

HRMS (EI): m/z [M]+ for C17H11N3: 257.0953; found: 257.0964.

9-Chlorobenzimidazo[1,2- a ]quinoline-6-carbonitrile (3g)

Yellow solid; mp 290 ˚C.

¹H NMR (500 MHz, DMSO-d 6): δ = 8.86-8.83 (m, 3 H), 8.15 (d, J = 7.5 Hz, 1 H), 8.03-7.98 (m, 2 H), 7.69 (t, J = 7.5 Hz, 1 H), 7.66-7.63 (m, 1 H).

¹³C NMR (125 MHz, DMSO-d 6): δ = 145.2, 142.4, 141.1, 135.4, 133.8, 131.2, 130.9, 128.0, 125.5, 125.4, 121.3, 121.2, 116.3, 115.1, 114.5, 101.2.

MS (EI): m/z = 277 [M]+.

HRMS (EI): m/z [M] for C16H8ClN3: 277.0407; found: 277.0414.

3-Methoxy-9/10-methylbenzimidazo[1,2- a ]quinoline-6-carbo­nitrile (3h)

Yellow solid; mp 182 ˚C.

¹H NMR (500 MHz, CDCl3): δ = 8.35-8.30 (m, 1 H), 8.05 (d, J = 8.5 Hz, 0.5 H), 7.97-7.93 (m, 2 H), 7.83 (s, 0.5 H), 7.41-7.36 (m, 1.5 H), 7.31-7.26 (m, 0.5 H), 7.19-7.17 (m, 1 H), 3.95 (s, 3 H), 2.64 (s, 1.5 H), 2.57 (s, 1.5 H).

¹³C NMR (125 MHz, CDCl3): δ = 156.2, 144.7, 144.1, 143.7, 142.4, 137.7, 137.5, 135.2, 133.9, 130.8, 130.8, 130.7, 128.7, 126.9, 125.3, 122.3, 122.2, 121.4, 121.2, 120.8, 120.7, 116.5, 116.5, 115.0, 114.9, 113.4, 113.0, 111.7, 111.6, 103.3, 103.1, 55.8, 22.3, 21.7.

MS (EI): m/z = 287 [M]+.

HRMS (EI): m/z [M]+ for C18H13N3O: 287.1059; found: 287.1074.

Ethyl Benzimidazo[1,2- a ]quinoline-6-carboxylate (3i)

Green solid; mp 119 ˚C.

¹H NMR (500 MHz, CDCl3): δ = 8.61 (d, J = 8.5 Hz, 1 H), 8.43 (s, 1 H), 8.39 (d, J = 8.5 Hz, 1 H), 8.18 (q, J = 8.0 Hz, 1 H), 7.94 (q, J = 8.0 Hz, 1 H), 7.86-7.82 (m, 1 H), 7.58-7.49 (m, 3 H), 4.58 (q, J = 7.0 Hz, 2 H), 1.51 (t, J = 7.0 Hz, 3 H).

¹³C NMR (125 MHz, CDCl3): δ = 163.9, 145.2, 145.0, 136.8, 135.5, 131.9, 131.0, 130.5, 124.7, 124.5, 123.2, 121.8, 121.7, 120.1, 115.2, 113.7, 61.8, 14.4.

MS (EI): m/z = 290 [M]+.

HRMS (EI): m/z [M]+ for C18H14N2O2: 290.1055; found: 290.1068.

Ethyl 2-Chlorobenzimidazo[1,2- a ]quinoline-6-carboxylate (3j)

Yellow solid; mp 129 ˚C.

¹H NMR (500 MHz, CDCl3): δ = 8.60 (d, J = 1.0 Hz, 1 H), 8.40 (s, 1 H), 8.35-8.33 (m, 1 H), 8.20 (d, J = 7.5 Hz, 1 H), 7.88 (d, J = 8.5 Hz, 1 H), 7.61-7.54 (m, 2 H), 7.51 (q, J = 8.5 Hz, 1 H), 4.58 (q, J = 7.0 Hz, 2 H), 1.51 (t, J = 7.0 Hz, 3 H).

¹³C NMR (125 MHz, CDCl3): δ = 163.6, 144.9, 138.2, 137.1, 134.7, 131.9, 130.2, 125.1, 125.1, 123.7, 121.8, 120.2, 115.4, 113.5, 62.0, 14.4.

MS (EI): m/z = 324 [M]+.

HRMS (ESI): m/z [M + H]+ for C18H13ClN2O2: 325.0744 found: 325.0735.

Ethyl 3-Methoxybenzimidazo[1,2- a ]quinoline-6-carboxylate (3k)

Yellow solid; mp 110 ˚C.

¹H NMR (500 MHz, CDCl3): δ = 8.50 (d, J = 9.0 Hz, 1 H), 8.35 (s, 1 H), 8.32 (d, J = 8.5 Hz, 1 H), 8.17 (d, J = 8.0 Hz, 1 H), 7.56-7.52 (m, 1 H), 7.51-7.47 (m, 1 H), 7.40 (q, J = 9.0 Hz, 1 H), 7.31 (d, J = 3 Hz, 1 H), 4.57 (q, J = 7.0 Hz, 2 H), 3.94 (s, 1 H), 1.51 (t, J = 7.0 Hz, 3 H).

¹³C NMR (125 MHz, CDCl3): δ = 163.9, 156.0, 144.7, 135.1, 131.2, 130.3, 124.5, 123.0, 122.8, 121.6, 120.5, 120.4, 116.4, 113.4, 112.1, 61.8, 55.7, 14.4.

MS (EI): m/z = 320 [M]+.

HRMS (EI): m/z [M]+ for C19H16N2O3: 320.1161; found: 320.1177.

Ethyl 3-Chlorobenzimidazo[1,2- a ]quinoline-6-carboxylate (3l)

Yellow solid; mp 130 ˚C.

¹H NMR (500 MHz, CDCl3): δ = 8.48 (d, J = 9.0 Hz, 1 H), 8.29 (s, 1 H), 8.27 (d, J = 8.5 Hz, 1 H), 8.17 (d, J = 8.0 Hz, 1 H), 7.89 (d, J = 2.5 Hz, 1 H), 7.75 (q, J = 9.0 Hz, 1 H), 7.58-7.54 (m, 1 H), 7.52-7.48 (m, 1 H), 4.57 (q, J = 7.0 Hz, 2 H), 1.50 (t, J = 7.0 Hz, 3 H).

¹³C NMR (125 MHz, CDCl3): δ = 163.5, 144.9, 144.7, 135.0, 133.9, 131.7, 130.3, 129.9, 129.9, 124.9, 123.6, 123.0, 121.9, 121.4, 116.4, 113.5, 62.0, 14.3.

MS (EI): m/z = 324 [M]+.

HRMS (EI): m/z [M]+ for C18H13ClN2O2: 324.0666; found: 324.0689.

Pyrido[3′,2′:4,5]imidazo[1,2- a ]quinoline-6-carbonitrile (3m)

Yellow solid; mp 218 ˚C.

¹H NMR (500 MHz, CDCl3): δ = 9.97 (d, J = 8.5 Hz, 1 H), 8.69 (q, J = 4.5 Hz, 1 H), 8.41 (q, J = 8.0 Hz, 1 H), 8.28 (s, 1 H), 7.98-7.90 (m, 2 H), 7.63-7.56 (m, 2 H).

¹³C NMR (125 MHz, CDCl3): δ = 145.6, 144.7, 144.3, 140.4, 136.7, 135.9, 133.7, 129.9, 128.6, 125.8, 121.1, 120.9, 118.1, 114.6, 102.9.

MS (EI): m/z = 244 [M]+.

HRMS (EI): m/z [M]+ for C15H8N4: 244.0749; found: 244.0760.

Benzimidazo[1,2- a ]quinoline-6-carbonitrile (3n)

White solid; mp 160 ˚C.

¹H NMR (500 MHz, CDCl3): δ = 7.94 (d, J = 16.5 Hz, 1 H), 7.68-7.65 (m, 2 H), 7.52 (q, J = 7.5 Hz, 1 H), 7.46 (q, J = 8.0 Hz, 1 H), 7.28-7.25 (m, 2 H), 7.22-7.16 (m, 2 H), 7.09-7.05 (m, 1 H).

¹³C NMR (125 MHz, CDCl3): δ = 150.8, 139.0, 135.5, 133.6, 133.2, 130.0, 127.7, 126.9, 124.5, 123.2, 119.8, 115.2.

MS (EI): m/z = 218 [M]+.

HRMS (EI): m/z [M]+ for C15H10N2: 218.0844; found: 218.0849.

Acknowledgment

We thank the National Natural Science Foundation of China (No. 20876148) as well as the Scientific Research Fund of Educational Bureau of Zhejiang Province (20070304). This work was supported by Chemistry Experiment Demonstration Center of Zhejiang Province.

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Scheme 1 One-pot synthesis of benzimidazo[1,2-a]quinolines

Scheme 2 One-pot synthesis of 3m

Scheme 3 Synthesis of unsubstituted benzimidazo[1,2-a]quinoline (3n)