Copper-catalyzed multi-component synthesis of acrylamidines and benzoimidazoles

Abstract

Acrylamidines were synthesized via the copper-catalyzed three-component reaction of propargyl acetates, sulfonyl azides and amines, which are readily accessible materials. The synthesized N,N′-bis(aryl)amidines could be converted into 2-styrylbenzoimidazoles by iodobenzene-catalyzed oxidative C–H amination using m-CPBA as a terminal oxidant.

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Introduction

Since the breakthrough in the generation of ketenimines via the copper-catalyzed azide–alkyne cycloaddition (CuAAC),¹ the chemistry of ketenimines has emerged as a powerful tool in the synthesis of diverse nitrogen containing cyclic and acyclic motifs of biological and pharmaceutical interest.² Chang,³ our group,⁴ and others⁵ have reported a number of elegant studies that involve the transformation of ketenimines generated in situ by the CuAAC route. Most recently, Reddy and coworkers developed a Cu-catalyzed conversion of propargyl acetates to α,β-unsaturated amides via the CuAAC process and 1,3-migration of the acetyl group ([3,3]-sigmatropic rearrangement) (Scheme 1a).⁶ Similarly, Talukdar's group⁷ converted propargyl amines to α,β-unsaturated amidines through 1,3-amino group migration of the in situ generated ketenimine intermediate (Scheme 1b). Encouraged by these results and in continuation of our interest in ketenimine chemistry, we herein report a three-component synthesis of acrylamidines via the Cu(I)-catalyzed reaction of readily accessible propargyl acetates, sulfonyl azides and amines, involving the formation of ketenimine and a nucleophilic addition–elimination process (Scheme 1c). The synthesized acrylamidines, i.e. α,β-unsaturated amidines, are an important class of nitrogen-containing compounds due to their synthetic applications.⁸

Scheme 1 Previous work and our design.

Results and discussion

Initially, we selected tosyl azide (1a), 1-phenylprop-2-ynyl acetate (2a) and aniline (1c) as the model substrates to test the feasibility of this transformation. When the reaction was performed in the presence of 10 mol% copper(I) bromide using K₂CO₃ as the base in acetonitrile at room temperature for 1 hour, α,β-unsaturated amidine 4a was isolated in 60% yield (Table 1, entry 1). The addition of 4 Å MS in the reaction system improved the yield to 76% (Table 1, entry 2). Shortening the reaction time led to a decrease in the yield of 4a (Table 1, entry 3), while the formation of 4a was not favoured when the reaction was performed for an additional reaction time (Table 1, entry 4). Increasing the amount of aniline improved the yield to 85% (Table 1, entry 5). Changing the catalyst (Table 1, entries 6–8), base (Table 1, entries 9–11) or solvent (Table 1, entries 12–15) led to decreases in the yield of 4a. The reaction proceeded at 0 °C for 3 hours and furnished 4a with only 45% yield (Table 1, entry 16). Increasing the reaction temperature to 50 °C also led to a decrease in the yield (Table 1, entry 17).

Table 1 Screening of the reaction conditions^a

Entry	Catalyst	Base	3a (equiv.)	Solvent	Time (h)^c	Yield^d (%)
a Reaction conditions: 1a (0.5 mmol), 2a (0.5 mmol), Cu salt (0.05 mmol), 4 Å MS (100 mg), base (1.0 mmol), solvent (2 mL), room temperature. b Without 4 Å MS, base (2.0 mmol). c The reaction time was determined by TLC. d Isolated yield. e The reaction was carried out at 0 °C. f The reaction was carried out at 50 °C.
1	CuBr	K2CO3	1	MeCN	1	60^b
2	CuBr	K2CO3	1	MeCN	1	76
3	CuBr	K2CO3	1	MeCN	0.5	57
4	CuBr	K2CO3	1	MeCN	1.5	75
5	CuBr	K2CO3	2	MeCN	1	85
6	CuI	K2CO3	2	MeCN	1	71
7	CuCl	K2CO3	2	MeCN	1	38
8	CuOTf	K2CO3	2	MeCN	1	56
9	CuBr	Cs2CO3	2	MeCN	1	40
10	CuBr	Pyridine	2	MeCN	1	46
11	CuBr	NEt3	2	MeCN	1	42
12	CuBr	K2CO3	2	THF	1	42
13	CuBr	K2CO3	2	DMF	1	47
14	CuBr	K2CO3	2	PhMe	1	23
15	CuBr	K2CO3	2	DCE	1	46
16	CuBr	K2CO3	2	MeCN	3	45^e
17	CuBr	K2CO3	2	MeCN	1	49^f

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To establish the scope of the methodology, the optimized conditions were applied to a wide range of substrates. As shown in Table 2, p-methylbenzenesulfonyl, phenylsulfonyl and p-methoxybenzenesulfonyl azides (1a–1c) gave the desired products 4a–4c with satisfactory yields (Table 2, entries 1–3), whereas naphthalen-2-ylsulfonyl, 4-(acetylamino)-benzenesulfonyl, 4-nitrobenzenesulfonyl, 4-fluorobenzene-sulfonyl and methylsulfonyl azides (1d–1h) yielded the corresponding products 4d–4h in much lower yields (Table 2, entries 4–8). When the R² group on propargyl acetates 2 was 4-methoxyphenyl (2b), 4-methylphenyl (2c), styryl (2d), and 2-furanyl (2e), the corresponding products 4i–4l were isolated in 54%–67% yields (Table 2, entries 9–12). In the case where R² was 4-nitrophenyl (2f), a lower yield (43%) of 4m was obtained (Table 2, entry 13). The substituted anilines were also examined for their reaction with 1a and 2a under the standard conditions. 4-Methylaniline (3b), 4-methoxyaniline (3c), and 2-methylaniline (3d) gave the corresponding products 4n–4p in good to excellent yields (Table 2, entries 14–16), whereas 4-chloroaniline (3e) furnished the desired product 4q in poor yield due to the electron-withdrawing properties of the chlorine atom (Table 2, entry 17).

Table 2 Substrate scope of azides^a

Entry	1 (R^1)	2 (R^2)	3 (R^3)	4/yield^b (%)
a Reaction conditions: 1 (0.5 mmol), 2a (0.5 mmol), 3a (1 mmol), CuBr (0.05 mmol), 4 Å MS (100 mg), acetonitrile (2 mL), Ar, room temperature, 1 h. b Product yields are given for compounds isolated after purification from a silica gel column.
1	1a (4-MeC6H4)	2a	3a (H)	4a/88
2	1b (Ph)	2a	3a	4b/67
3	1c (4-MeOC6H4)	2a	3a	4c/97
4	1d (2-naphthalenyl)	2a	3a	4d/34
5	1e (4-AcNHC6H4)	2a	3a	4e/43
6	1f (4-NO2C6H4)	2a	3a	4f/26
7	1g (4-FC6H4)	2a	3a	4g/39
8	1h (Me)	2a	3a	4h/39
9	1a	2b (4-MeOC6H4)	3a	4i/60
10	1a	2c (4-MeC6H4)	3a	4j/67
11	1a	2d (PhCH=CH)	3a	4k/63
12	1a	2e (2-furanyl)	3a	4l/54
13	1a	2f (4-NO2C6H4)	3a	4m/43
14	1a	2a	3b (4-Me)	4n/95
15	1a	2a	3c (4-MeO)	4o/88
16	1a	2a	3d (2-Me)	4p/84
17	1a	2a	3e (4-Cl)	4q/20

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As a synthetic application of our methodology, we converted the synthesized N,N′-bis(aryl)amidines 4a–4h (Table 3, entries 1–8) and 4n–4p (Table 3, entries 9–11) into 2-styrylbenzoimidazoles 5a–5k by iodobenzene-catalyzed oxidative C–H amination in the presence of m-CPBA as a terminal oxidant at room temperature (Table 3).⁹ The reaction is general although the target products were obtained in lower yields in most cases. Taking into consideration the great importance of benzoimidazoles in medicinal chemistry¹⁰ and organic materials,¹¹ our two-step approach provided a new strategy to construct 2-styrylbenzoimidazoles.

Table 3 Preparation of benzoimidazoles^a

Entry	4 (R^1/R^2/R^3)	5/yield^b (%)
a Reaction conditions: 4 (0.2 mmol), PhI (5 μL), m-CPBA (0.3 mmol), HFIP (0.4 mL), room temperature, 8 h. b Product yields are given for compounds isolated after purification from a silica gel column.
1	4a (4-MeC6H4/Ph/H)	5a/64
2	4b (Ph/Ph/H)	5b/44
3	4c (4-MeOC6H4/Ph/H)	5c/45
4	4d (2-naphthalenyl/Ph/H)	5d/44
5	4h (Me/Ph/H)	5e/25
6	4f (4-NO2C6H4/Ph/H)	5f/22
7	4g (4-FC6H4/Ph/H)	5g/41
8	4e (4-AcNHC6H4/Ph/H)	5h/29
9	4o (4-MeC6H4/Ph/4-MeO)	5i/30
10	4n (4-MeC6H4/Ph/4-Me)	5j/36
11	4p (4-MeC6H4/Ph/2-Me)	5k/30

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Conclusions

We developed a copper-catalyzed three-component synthesis of α,β-unsaturated amidines from propargyl acetates, sulfonyl azides and amines, which are readily accessible materials. The reaction proceeded through a cascade process involving ketenimine formation via copper-catalyzed alkyne–azide cycloaddition, nucleophilic addition of amine to ketenimine, and elimination of acetate. Furthermore, the synthesized N,N′-bis(aryl)amidines could be converted into 2-styrylbenzoimidazoles by iodobenzene-catalyzed oxidative C–H amination using m-CPBA as a terminal oxidant.

Experimental section

General methods

Infrared spectra were obtained on a FTIR spectrometer. ¹H NMR spectra were recorded on a 400 MHz spectrometer, referred to the internal solvent signals (0 for TMS in CDCl₃ or 2.5 for the residue of DMSO). The following abbreviations were used to describe peak patterns where appropriate: b = broad, s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet. Coupling constants were reported in Hertz (Hz). ¹³C NMR spectra were recorded on a 100 MHz spectrometer, referred to the internal solvent signals (77.27 for CDCl₃ or 40.0 for DMSO-d₆). High resolution mass spectra (HRMS) were recorded on an electron ionization time-of-flight (EI-TOF) mass spectrometer. Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDITOF-MS) was performed with a Bruker's ultrafleXtreme. Melting points were uncorrected and measured with a micro melting point apparatus.

General procedure for the synthesis of (E)-acrylimidamide 4

To a solution of K₂CO₃ (1.0 mmol), 4 Å MS (100 mg) and CuBr (0.05 mmol) in MeCN (0.5 mL) protected by argon was added sulfonyl azide 1 (0.5 mmol) in MeCN (0.5 mL), 2-yn-1-yl acetate 2 (0.5 mmol) in MeCN (0.5 mL) and aniline 3 (0.5 mmol) in MeCN (0.5 mL) in turns via a syringe, and the mixture was reacted at room temperature for 1 h. After filtration, the reaction mixture was diluted with CH₂Cl₂ (10 mL), washed with water and brine, dried over anhydrous Na₂SO₄, and evaporated in a vacuum. The residue was subjected to silica gel column chromatography with EA/Pet (1 : 3, v/v) as the eluent to give pure product 4.

(E)-N-Phenyl-N′-tosylcinnamimidamide (4a). A yellow powder (166 mg, 88%); m.p. 170.0–171.6 °C; ¹H NMR (400 MHz, CDCl₃) δ 10.14 (b, 1H), 7.93 (d, J = 8.4 Hz, 2H), 7.85 (d, J = 15.6 Hz, 1H), 7.42 (dd, J₁ = 7.6 Hz, J₂ = 7.2 Hz, 2H), 7.37–7.27 (m, 8H), 7.19 (d, J = 7.6, 2H), 6.51 (d, J = 11.2 Hz, 1H), 2.43 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 160.2, 144.7, 143.1, 140.0, 136.6, 134.7, 130.7, 129.8, 129.7, 129.1, 128.5, 127.8, 126.7, 117.8, 21.8; IR (neat) ν 3298, 3060, 3021, 1635, 1561, 1519, 1445, 1389, 1350, 1276, 1142, 1089, 758, 691 cm⁻¹; HRMS (EI) calcd for chemical formula: C₂₂H₂₀N₂O₂S, 376.1245; found, 376.1241.

(E)-N-Phenyl-N′-(phenylsulfonyl)cinnamimidamide (4b). A yellow powder (121 mg, 67%); m.p. 164.1–165.3 °C; ¹H NMR (400 MHz, CDCl₃) δ 10.16 (b, 1H), 8.05 (d, J = 8.4 Hz, 2H), 7.87 (d, J = 15.2 Hz, 1H), 7.59–7.50 (m, 3H), 7.43 (dd, J₁ = 8.0 Hz, J₂ = 7.2 Hz, 2H), 7.37–7.29 (m, 6H), 7.19 (d, J = 7.2 Hz, 2H), 6.51 (b, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 160.4, 142.8, 136.5, 134.6, 132.5, 130.8, 129.9, 129.1, 129.1, 128.6, 127.9, 126.6, 126.1, 117.7; IR (neat) ν 3299, 33048, 3026, 1635, 1561, 1518, 1445, 1397, 1346, 1277, 1143, 1089, 754, 689 cm⁻¹; HRMS (EI) calcd for C₂₁H₁₈N₂O₂S, 362.1089; found, 362.1084.

(E)-N′-((4-Methoxyphenyl)sulfonyl)-N-phenyl cinnamimidamide (4c). A yellow powder (191 mg, 97%); m.p. 146.2–47.5 °C; ¹H NMR (400 MHz, CDCl₃) δ 10.11 (b, 1H), 7.98 (d, J = 8.8 Hz, 2H), 7.83 (d, J = 15.2 Hz, 1H), 7.42 (dd, J₁ = 7.6 Hz, J₂ = 7.2 Hz, 2H), 7.36–7.28 (m, 6H), 7.19 (d, J = 6.8 Hz, 2H), 6.98 (d, J = 9.2 Hz, 2H), 6.52 (b, 1H), 3.86 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 162.8, 160.0, 144.5, 136.7, 134.8, 134.7, 130.7, 129.8, 129.1, 128.7, 128.5, 127.8, 126.0, 117.8, 114.2, 55.8; IR (neat) ν 3293, 3060, 2944, 2837, 1650, 1596, 1562, 1519, 1497, 1444, 1257, 1141, 1090, 1026, 805, 759, 692 cm⁻¹; HRMS (EI) calcd for C₂₂H₂₀N₂O3S, 392.1195; found, 392.1190.

(E)-N′-(Naphthalen-2-ylsulfonyl)-N-phenylcinnamimidamide (4d). A light yellow powder (71 mg, 34%); m.p. 167.0–168.2 °C; ¹H NMR (400 MHz, CDCl₃) δ 10.23 (b, 1H), 8.59 (s, 1H), 8.05 (dd, J₁ = 8.4 Hz, J₂ = 1.6 Hz, 1H), 7.98 (d, J = 8.4 Hz, 2H), 7.92–7.85 (m, 2H), 7.64–7.57 (m, 2H), 7.43 (dd, J₁ = J₂ = 7.6 Hz, 2H), 7.36–7.28 (m, 6H), 7.21 (d, J = 7.2 Hz, 2H), 6.53 (b, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 160.4, 139.7, 136.5, 135.0, 134.6, 132.4, 130.8, 129.9, 129.6, 129.4, 129.1, 128.7, 128.6, 128.1, 127.9, 127.5, 127.3, 126.1, 122.7, 117.7; IR (neat) ν 3289, 3054, 1635, 1563, 1520, 1445, 1382, 1348, 1278, 1143, 1124, 1073, 756, 690 cm⁻¹; HRMS (EI) calcd for C₂₅H₂₀N₂O₂S, 412.1245; found, 412.1252.

N-(4-((E)-N-((E)-3-Phenyl-1-(phenylamino)allylidene)sulfamoyl)phenyl)acetamide (4e). A yellow powder (90 mg, 43%); m.p. 172.2–173.5 °C; ¹H NMR (400 MHz, CDCl₃) δ 10.10 (b, 1H), 8.01 (s, 1H), 7.93 (d, J = 8.8 Hz, 2H), 7.82 (d, J = 14.8 Hz, 1H), 7.67 (d, J = 7.6 Hz, 2H), 7.42 (dd, J₁ = 7.2 Hz, J₂ = 8.0 Hz, 2H), 7.36–7.28 (m, 6H), 7. 17 (d, J = 5.2 Hz, 2H), 6.50 (b, 1H), 2.20 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 169.2, 160.4, 145.0, 142.0, 137.4, 136.4, 134.5, 130.8, 129.9, 129.1, 128.6, 128.0, 127.7, 126.1, 119.6, 117.6, 24.9; IR (neat) ν 3315, 3048, 2920, 1676, 1635, 1593, 1519, 1446, 1400, 1315, 1262, 1141, 1091, 754 cm⁻¹; HRMS (EI) calcd for C₂₃H₂₁N3O₃S, 419.1304; found, 419.1305.

(E)-N′-((4-Nitrophenyl)sulfonyl)-N-phenylcinnamimidamide (4f). A white powder (53 mg, 26%); m.p. 148.8–149.6 °C; ¹H NMR (400 MHz, CDCl₃) δ 10.15 (b, 1H), 8.37 (d, J = 8.8 Hz, 2H), 8.23 (d, J = 8.8 Hz, 2H), 7.87 (d, J = 13.6 Hz, 1H), 7.47 (dd, J₁ = J₂ = 7.6 Hz, 2H), 7.42–7.32 (m, 6H), 7.22 (d, J = 7.2 Hz, 2H), 6.52 (b, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 161.1, 150.0, 148.5, 146.1, 136.1, 134.3, 131.2, 130.0, 129.2, 128.7, 128.4, 127.9, 126.2, 124.4, 117.0; IR (neat) ν 3319, 3024, 1635, 1521, 1447, 1348, 1262, 1145, 1092, 745, 680 cm⁻¹; MALDITOF-MS (DHB) calcd for C₂₁H₁₈N₃O₄S [M + H]⁺, 408.102; found, 408.101.

(E)-N′-((4-Fluorophenyl)sulfonyl)-N-phenylcinnamimidamide (4g). A yellow powder (74 mg, 39%); m.p. 162.6–163.5 °C; ¹H NMR (400 MHz, CDCl₃) δ 10.12 (b, 1H), 8.07–8.04 (m, 2H), 7.85 (d, J = 14.4 Hz, 1H), 7.44 (dd, J₁ = 7.2 Hz, J₂ = 8.0 Hz, 2H), 7.36–7.30 (m, 6H), 7.21–7.17 (m, 4H), 6.53 (b, 1H); ¹³C NMR (100 MHz, CDCl₃) δ 165.1 (d, J_C–F = 252 Hz), 160.4, 145.1, 139.0 (d, J_C–F = 3.1 Hz), 136.4, 134.6, 130.9, 129.9, 129.3 (d, J_C–F = 9.2 Hz), 129.2, 128.6, 128.0, 126.1, 117.6, 116.2 (d, J_C–F = 22.4 Hz); IR (neat) ν 3424, 2997, 2911, 1636, 1518, 1494, 1445, 1281, 1146, 1092, 1028, 953, 762, 696 cm⁻¹; HRMS (EI) calcd for C₂₁H₁₇FN₂O₂S, 380.0995; found, 380.0994.

(E)-N′-(Methylsulfonyl)-N-phenylcinnamimidamide (4h). A yellow oil (59 mg, 39%); ¹H NMR (400 MHz, CDCl₃) δ 9.86 (b, 1H), 7.85 (d, J = 11.2 Hz, 1H), 7.45–7.39 (m, 4H), 7.38–7.31 (m, 4H), 7.22 (d, J = 5.2 Hz, 2H), 6.55 (b, 1H), 3.16 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 160.2, 144.3, 136.5, 134.6, 130.7, 129.8, 129.2, 128.5, 127.8, 125.9, 117.8, 42.9; IR (neat) ν 3290, 3057, 3024, 2929, 1637, 1577, 1525, 1445, 1275, 1124, 1028, 969, 791, 758, 692 cm⁻¹; HRMS (EI) calcd for C₁₆H₁₆N₂O₂S, 300.0932; found, 300.0933

(1E,2E)-3-(4-Methoxyphenyl)-N-phenyl-N′-tosylacrylimidamide (4i). A yellow powder (123 mg, 60%); m.p. 174.8–176.2 °C; ¹H NMR (400 MHz, CDCl₃) δ 10.08 (b, 1H), 7.92 (d, J = 8.4 Hz, 2H), 7.82 (d, J = 15.2 Hz, 1H), 7.42 (dd, J₁ = J₂ = 7.6 Hz, 2H), 7.36–7.30 (m, 5H), 7.18 (d, J = 7.6 Hz, 2H), 6.83 (d, J = 8.8 Hz, 2H), 6.38 (d, J = 14.0 Hz, 1H), 3.80 (s, 3H), 2.42 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 161.8, 160.6, 143.0, 140.1, 136.8, 130.4, 129.8, 129.6, 127.7, 127.5, 126.6, 126.1, 115.1, 114.6, 55.6, 21.8; IR (neat) ν 3304, 3060, 2965, 2929, 2834, 1633, 1601, 1558, 1510, 1444, 1254, 1174, 1141, 1090, 1029, 825, 757, 691 cm⁻¹; HRMS (EI) calcd for C₂₃H₂₂N₂O₃S, 406.1351; found, 406.1350.

(1E,2E)-N-Phenyl-3-(p-tolyl)-N′-tosylacrylimidamide (4j). A yellow powder (131 mg, 67%); m.p. 166.7–168.0 °C; ¹H NMR (400 MHz, CDCl₃) δ 10.11 (b, 1H), 7.92 (d, J = 8.4 Hz, 2H), 7.83 (d, J = 15.2 Hz, 1H), 7.42 (dd, J₁ = J₂ = 7.6 Hz, 2H), 7.35 (d, J = 7.2 Hz, 1H), 7.31 (d, J = 8.0 Hz, 2H), 7.25 (d, J = 6.4 Hz, 2H), 7.18 (d, J = 7.6 Hz, 2H), 7.12 (d, J = 6.4 Hz, 2H), 6.47 (b, 1H), 2.42 (s, 3H), 2.33 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 160.5, 144.9, 143.1, 141.3, 140.0, 136.7, 132.0, 129.9, 129.8, 129.7, 128.6, 127.8, 126.7, 126.1, 116.6, 21.8, 21.7; IR (neat) ν 3300 3054, 2920, 1634, 1599, 1561, 1520, 1444, 1275, 1142, 1089, 810, 757 cm⁻¹; HRMS (EI) calcd for C₂₃H₂₂N₂O₂S, 390.1402; found, 390.1402.

(1E,2E,4E)-N,5-Diphenyl-N′-tosylpenta-2,4-dienimidamide (4k). A yellow powder (127 mg, 63%); m.p. 170.6–172.2 °C; ¹H NMR (400 MHz, CDCl₃) δ 10.03 (b, 1H), 7.91 (d, J = 8.0 Hz, 2H), 7.63 (dd, J₁ = 12.4 Hz, J₂ = 13.2 Hz, 1H), 7.43–7.38 (m, 4H), 7.35–7.28 (m, 6H), 7.16 (d, J = 7.6, 2H), 6.89 (d, J = 15.6 Hz, 1H), 6.73 (dd, J₁ = 15.6 Hz, J₂ = 11.2 Hz, 1H), 6.07 (b, 1H), 2.42 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 160.3, 145.1, 143.0, 141.6, 140.1, 136.7, 136.1, 130.0, 129.6, 129.5, 129.0, 127.8, 127.5, 126.6, 126.2, 120.8, 21.8; IR (neat) ν 3297, 3059, 3021, 1622, 1557, 1444, 1386, 1352, 1276, 1142, 1090, 996, 748, 691 cm⁻¹; HRMS (EI) calcd for C₂₄H₂₂N₂O₂S, 402.1402; found, 402.1406.

(1E,2E)-3-(Furan-2-yl)-N-phenyl-N′-tosylacrylimidamide (4l). A yellow powder (98 mg, 54%); m.p. 120.5–121.4 °C; ¹H NMR (400 MHz, CDCl₃) δ 10.09 (b, 1H), 7.91 (d, J = 8.0 Hz, 2H), 7.64 (d, J = 16.8 Hz, 1H), 7.45–7.29 (m, 6H), 7.17 (d, J = 7.6 Hz, 2H), 6.58 (d, J = 3.6 Hz, 1H), 6.43–6.37 (m, 2H), 2.42 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 160.2, 151.3, 145.4, 143.1, 140.1, 136.6, 131.1, 129.8, 129.6, 127.9, 126.6, 126.2, 116.3, 115.1, 112.8, 21.8; IR (neat) ν 3286, 2956, 2923, 2851, 1733, 1635, 1571, 1515, 1444, 1378, 1276, 1142, 1090, 1017, 744 cm⁻¹; HRMS (EI) calcd for C₂₀H₁₈N₂O₃S, 366.1038; found, 366.1039.

(1E,2E)-3-(4-Nitrophenyl)-N-phenyl-N′-tosylacrylimidamide (4m). A yellow powder (91 mg, 43%); m.p. 222.4–223.2 °C; ¹H NMR (400 MHz, CDCl₃) δ 10.22 (b, 1H), 8.17 (d, J = 8.8 Hz, 2H), 7.93 (d, J = 8.4 Hz, 2H), 7.84 (d, J = 14.4 Hz, 1H), 7.50–7.44 (m, 4H), 7.39 (dd, J₁ = 7.6 Hz, J₂ = 6.8 Hz, 1H), 7.33 (d, J = 8.4 Hz, 2H), 7.19 (d, J = 6.8, 2H), 6.61 (d, J = 14.4 Hz, 1H), 2.44 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 159.0, 148.6, 143.5, 141.4, 140.7, 139.5, 136.3, 130.0, 129.8, 129.0, 128.3, 126.7, 126.1, 124.4, 122.1, 21.8; IR (neat) ν 3289, 1599, 1560, 1519, 1445, 1343, 1276, 1143, 1089, 758, 692 cm⁻¹; HRMS (EI) calcd for C₂₂H₁₉N₃O₄S, 421.1096; found, 421.1088.

(E)-N-(p-Tolyl)-N′-tosylcinnamimidamide (4n). A yellow powder (185 mg, 95%); m.p. 169.4–170.7 °C; ¹H NMR (400 MHz, CDCl₃) δ 10.08 (b, 1H), 7.92 (d, J = 8.4 Hz, 2H), 7.85 (d, J = 15.2 Hz, 1H), 7.37–7.30 (m, 7H), 7.21 (d, J = 8.4 Hz, 2H), 7.05 (d, J = 8.4 Hz, 2H), 6.49 (d, J = 14.0 Hz, 1H), 2.42 (s, 3H), 2.39 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 160.3, 144.7, 143.1, 140.0, 134.7, 133.9, 130.6, 130.4, 129.6, 129.1, 128.5, 127.3, 126.6, 126.0, 117.8, 21.8, 21.3; IR (neat) ν 3298, 3021, 2920, 2858, 1745, 1640, 1557, 1510, 1449, 1407, 1275, 1139, 1088, 815, 760, 694 cm⁻¹; HRMS (EI) calcd for C₂₃H₂₂N₂O₂S, 390.1402; found, 390.1405.

(E)-N-(4-Methoxyphenyl)-N′-tosylcinnamimidamide (4o). A light yellow powder (178 mg, 88%); m.p. 150.3–151.5 °C; ¹H NMR (400 MHz, CDCl₃) δ 10.01 (b, 1H), 7.93 (d, J = 8.0 Hz, 2H), 7.85 (d, J = 15.2 Hz, 1H), 7.36–7.30 (m, 7H), 7.09 (d, J = 8.0 Hz, 2H), 6.93 (d, J = 8.8 Hz, 2H), 6.43 (d, J = 15.2 Hz, 1H), 3.85 (s, 3H), 2.43 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 160.6, 159.3, 144.7, 143.1, 140.1, 134.7, 130.6, 129.6, 129.2, 129.1, 128.5, 127.9, 126.6, 117.6, 115.0, 55.8, 21.8; IR (neat) ν 3298, 3021, 2926, 2828, 1636, 1557, 1509, 1449, 1250, 1138, 1088, 1031, 808, 760, 694 cm⁻¹; HRMS (EI) calcd for C₂₃H₂₂N₂O₃S, 406.1351; found, 406.1353.

(E)-N-(o-Tolyl)-N′-tosylcinnamimidamide (4p). A light yellow powder (163 mg, 84%); m.p. 113.6–114.8 °C; ¹H NMR (400 MHz, CDCl₃) δ 9.96 (b, 1H), 7.94 (d, J = 8.0 Hz, 2H), 7.90 (d, J = 15.2 Hz, 1H), 7.35–7.29 (m, 9H), 7.27–7.23 (m, 1H), 7.12 (d, J = 7.2 Hz, 1H), 6.33 (d, J = 15.2 Hz, 1H), 2.43 (s, 3H), 2.24 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 160.6, 145.0, 143.1, 140.0, 135.2, 134.8, 134.7, 131.6, 130.8, 129.7, 129.1, 128.6, 128.6, 127.6, 127.3, 126.7, 117.3, 21.8, 18.2; IR (neat) ν 3271, 3060, 3021, 1637, 1557, 1449, 1386, 1275, 1138, 1084, 758, 694 cm⁻¹; HRMS (EI) calcd for C₂₃H₂₂N₂O₂S, 390.1402; found, 390.1408.

(E)-N-(m-Tolyl)-N′-tosylcinnamimidamide (4q). A light yellow powder (98 mg, 84%); m.p. 186.7–187.7 °C; ¹H NMR (400 MHz, CDCl₃) δ 10.11 (b, 1H), 7.92 (d, J = 8.4 Hz, 2H), 7.85 (d, J = 14.8 Hz, 1H), 7.37–7.28 (m, 8H), 7.16 (d, J = 7.6 Hz, 1H), 7.00–6.96 (m, 2H), 6.52 (d, J = 13.6 Hz, 1H), 2.43 (s, 3H), 2.38 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 160.2, 144.6, 143.1, 140.1, 140.0, 136.5, 134.7, 130.7, 129.7, 129.6, 129.1, 128.7, 128.6, 126.7, 123.2, 117.9, 21.8, 21.6; IR (neat) ν 3291, 2920, 1637, 1563, 1525, 1486, 1447, 1276, 1143, 1087, 811, 781, 760 cm⁻¹; HRMS (EI) calcd for C₂₃H₂₂N₂O₂S, 390.1402; found, 390.1399.

(E)-N-(4-Chlorophenyl)-N′-tosylcinnamimidamide (4r). A white powder (42 mg, 20%); m.p. 193.1–193.8 °C; ¹H NMR (400 MHz, CDCl₃) δ 10.06 (b, 1H), 7.91 (d, J = 8.0 Hz, 2H), 7.83 (d, J = 14.4 Hz, 1H), 7.40–7.30 (m, 9H), 7.14 (d, J = 7.6, 2H), 6.48 (b, 1H), 2.43 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 160.0, 143.3, 139.8, 135.2, 134.5, 130.9, 130.0, 129.7, 129.2, 128.6, 127.2, 126.7, 117.4, 100.2, 21.8; IR (neat) ν 3295, 2975, 1635, 1513, 1491, 1401, 1273, 1143, 1088, 688 cm⁻¹; HRMS (EI) calcd for C₂₂H₁₉ClN₂O₂S, 410.0856; found, 410.0851.

General procedure for the synthesis of (E)-2-vinyl-1-sulfonyl-1H-benzo[d]imidazole (5)

A mixture of (E)-acrylimidamide 4 (0.2 mmol), PhI (5.0 μL) and m-CPBA (0.3 mmol) in HFIP (0.4 mL) was stirred at room temperature for 8 h, and then subjected to silica gel column chromatography with EA/Pet (1 : 4, v/v) as the eluent to give pure product 5.

(E)-2-Styryl-1-tosyl-1H-benzo[d]imidazole (5a). A fresh solid (48 mg, 64%); m.p. 152.1–153.5 °C; ¹H NMR (400 MHz, CDCl₃) δ 8.11–8.06 (m, 1H), 7.92 (s, 2H), 7.78 (d, J = 8.4 Hz, 2H), 7.70–7.66 (m, 3H), 7.46–7.33 (m, 5H), 7.22 (d, J = 8.4 Hz, 2H), 2.34 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 151.4, 146.2, 142.9, 140.1, 136.0, 135.5, 133.4, 130.4, 129.9, 129.2, 128.0, 127.1, 125.5, 125.3, 120.1, 114.6, 114.2, 21.9; IR (neat) ν 3099, 3050, 3018, 2923, 2852, 1625, 1396, 1512, 1448, 1378, 1344, 1200, 1167, 1121, 1089, 1050, 811, 764, 670 cm⁻¹; HRMS (EI) calcd for C₂₂H₁₈N₂O₂S, 374.1089; found, 374.1086.

(E)-1-(Phenylsulfonyl)-2-styryl-1H-benzo[d]imidazole (5b). A yellow oil (32 mg, 44%); ¹H NMR (400 MHz, CDCl₃) δ 8.11–8.07 (m, 1H), 7.93–7.89 (m, 4H), 7.72–7.66 (m, 3H), 7.57 (dd, J₁ = J₂ = 7.6 Hz, 1H), 7.47–7.43 (m, 4H), 7.41–7.34 (m, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 151.4, 142.9, 140.2, 138.5, 136.0, 134.8, 133.4, 129.9, 129.8, 129.2, 128.0, 127.0, 125.6, 125.4, 120.2, 114.5, 114.2; IR (neat) ν 3057, 3021, 1625, 1513, 1379, 1344, 1201, 1167, 1088, 1049, 749, 723, 684, 649 cm⁻¹; HRMS (EI) calcd for C₂₁H₁₆N₂O₂S, 360.0932; found, 360.0931.

(E)-1-((4-Methoxyphenyl)sulfonyl)-2-styryl-1H-benzo[d]imidazole (5c). A pink oil (36 mg, 45%); ¹H NMR (400 MHz, CDCl₃) δ 8.09–8.07 (m, 1H), 7.93 (d, J = 2.4 Hz, 2H), 7.84 (d, J = 9.2 Hz, 2H), 7.70–7.66 (m, 3H), 7.46–7.33 (m, 5H), 6.87 (d, J = 8.8 Hz, 2H), 3.78 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 164.6, 151.4, 142.9, 140.0, 136.0, 133.4, 129.9, 129.8, 129.4, 129.2, 128.0, 125.5, 125.3, 120.1, 115.0, 114.7, 114.2, 56.0; IR (neat) ν 3060, 3025, 1593, 1497, 1448, 1377, 1343, 1266, 1201, 1164, 1090, 1050, 745, 674 cm⁻¹; HRMS (EI) calcd for C₂₂H₁₈N₂O₃S, 390.1038; found, 390.1035.

(E)-1-(Naphthalen-2-ylsulfonyl)-2-styryl-1H-benzo[d]imidazole (5d). A yellow oil (36 mg, 44%); ¹H NMR (400 MHz, CDCl₃) δ 8.55 (d, J = 1.6 Hz, 1H), 8.16–8.13 (m, 1H), 8.04–7.89 (m, 3H), 7.84 (dd, J₁ = 7.2, J₂ = 10.4 Hz, 2H), 7.46 (dd, J₁ = 8.8, J₂ = 2.0 Hz, 1H), 7.69–7.56 (m, 5H), 7.48–7.34 (m, 5H); ¹³C NMR (100 MHz, CDCl₃) δ 151.4, 142.9, 140.3, 136.0, 135.7, 135.2, 133.4, 132.0, 130.4, 130.1, 129.9, 129.8, 129.2, 129.1, 128.3, 128.2, 128.0, 125.6, 125.4, 121.3, 120.2, 114.7, 114.2; IR (neat) ν 3057, 3027, 2920, 2852, 1625, 1512, 1448, 1380, 1345, 1231, 1199, 1167, 1072, 1050, 857, 811, 746, 662 cm⁻¹; HRMS (EI) calcd for C₂₅H₁₈N₂O₂S, 410.1089; found, 410.1086.

(E)-1-(Methylsulfonyl)-2-styryl-1H-benzo[d]imidazole (5e). A yellow solid (15 mg, 25%); m.p. 192.4–193.4 °C; ¹H NMR (400 MHz, CDCl₃) δ 8.03 (d, J = 16.0 Hz, 1H), 7.95–7.93 (m, 1H), 7.80–7.74 (m, 2H), 7.66–7.64 (m, 2H), 7.45–7.36 (m, 5H), 3.24 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 151.2, 142.9, 140.8, 135.8, 133.3, 130.0, 129.2, 128.1, 125.8, 125.5, 120.4, 113.9, 113.7, 42.6; IR (neat) ν 2923, 2846, 1626, 1513, 1172, 1233, 1200, 1163, 1144, 1054, 964, 764, 739, 696 cm⁻¹; HRMS (EI) calcd for C₁₆H₁₄N₂O₂S, 298.0776; found, 298.0780.

(E)-1-((4-Nitrophenyl)sulfonyl)-2-styryl-1H-benzo[d]imidazole (5f). A yellow oil (18 mg, 22%); ¹H NMR (400 MHz, CDCl₃) δ 8.27 (d, J = 9.2 Hz, 2H), 8.16–8.03 (m, 3H), 7.97–7.85 (m, 2H), 7.72–7.66 (m, 3H), 7.49–7.37 (m, 5H); ¹³C NMR (100 MHz, CDCl₃) δ 151.3, 151.3, 143.5, 143.1, 141.2, 135.6, 132.9, 130.3, 129.3, 128.4, 128.1, 126.3, 125.9, 125.1, 120.6, 114.0, 113.8; IR (neat) ν 3099, 2923, 2846, 1730, 1625, 1533, 1387, 1346, 1231, 1200, 1167, 1087, 1048, 854, 759, 680 cm⁻¹; HRMS (EI) calcd for C₂₁H₁₅N₃O₄S, 405.0783; found, 405.0780.

(E)-1-((4-Fluorophenyl)sulfonyl)-2-styryl-1H-benzo[d]imidazole (5g). A yellow oil (31 mg, 41%); ¹H NMR (400 MHz, CDCl₃) δ 8.09–8.04 (m, 1H), 7.96–7.88 (m, 4H), 7.71–7.66 (m, 3H), 7.47–7.35 (m, 5H), 7.14–7.08 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ 166.3 (d, J_C–F = 257.2 Hz), 151.3, 143.0, 140.5, 135.9, 134.4 (d, J_C–F = 3.4 Hz), 133.2, 130.0, 129.9, 129.3, 128.0, 125.8, 125.5, 120.3, 117.4, 117.2, 114.2 (d, J_C–F = 21.6 Hz); IR (neat) ν 3102, 3066, 3027, 2923, 2855, 1626, 1590, 1514, 1493, 1449, 1382, 1344, 1242, 1200, 1087, 1049, 836, 750, 675 cm⁻¹; HRMS (EI) calcd for C₂₁H₁₅FN₂O₂S, 378.0838; found, 378.0836.

(E)-N-(4-((2-Styryl-1H-benzo[d]imidazol-1-yl)sulfonyl)phenyl)acetamide (5h). A yellow solid (24 mg, 29%); m.p. 106.1–107.2 °C; ¹H NMR (400 MHz, CDCl₃) δ 8.08–8.06 (m, 1H), 7.91 (s, 2H), 7.84 (d, J = 8.8 Hz, 2H), 7.70–7.63 (m, 3H), 7.59 (d, J = 8.8 Hz, 2H), 7.46–7.34 (m, 6H), 2.15 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 168.7, 151.4, 143.7, 142.9, 140.2, 136.0, 133.3, 132.8, 129.9, 129.2, 128.6, 128.0, 125.6, 125.4, 120.2, 119.6, 114.6, 114.2, 25.0; IR (neat) ν 3316, 3101, 2293, 1697, 1589, 1531, 1376, 1313, 1263, 1230, 1166, 1084, 1046 cm⁻¹; HRMS (EI) calcd for C₂₃H₁₉N₃O₃S, 417.1147; found, 417.1142.

(E)-6-Methoxy-2-styryl-1-tosyl-1H-benzo[d]imidazole (5i). A yellow solid (24 mg, 30%); m.p. 132.6–133.6 °C; ¹H NMR (400 MHz, CDCl₃) δ 7.90–7.80 (m, 2H), 7.77 (d, J = 8.4 Hz, 2H), 7.65–7.61 (m, 3H), 7.56 (d, J = 8.8 Hz, 1H), 7.45–7.36 (m, 3H), 7.23 (d, J = 8.0 Hz, 2H), 7.97 (dd, J₁ = 2.4, J₂ = 8.8 Hz, 1H), 3.92 (s, 3H), 2.35 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 158.3, 150.4, 146.2, 138.8, 137.2, 136.2, 135.6, 134.3, 130.4, 129.6, 129.2, 127.9, 127.0, 120.5, 114.8, 114.2, 98.5, 56.3, 21.9; IR (neat) ν 3024, 2917, 2846, 1736, 1625, 1596, 1510, 1447, 1378, 1021, 1170, 1089, 1045, 812, 753, 668 cm⁻¹; HRMS (EI) calcd for C₂₃H₂₀N₂O₃S, 404.1195; found, 404.1198.

(E)-6-Methyl-2-styryl-1-tosyl-1H-benzo[d]imidazole (5j). A yellow solid (28 mg, 36%); m.p. 183.2–184.7 °C; ¹H NMR (400 MHz, CDCl₃) δ 7.88 (d, J = 3.0 Hz, 3H), 7.77 (d, J = 8.4 Hz, 2H), 7.66–7.64 (m, 2H), 7.56 (d, J = 8.4 Hz, 1H), 7.46–7.42 (m, 2H), 7.40–7.38 (m, 1H), 7.23 (d, J = 8.0 Hz, 2H), 7.57 (dd, J₁ = 1.2, J₂ = 8.4 Hz, 1H), 2.52 (s, 3H), 2.34 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 150.8, 146.1, 141.0, 139.5, 136.1, 135.7, 133.6, 130.4, 129.7, 129.2, 128.4, 127.9, 127.0, 127.0, 119.6, 114.8, 114.2, 22.4, 21.9; IR (neat) ν 3390, 3063, 2920, 2846, 1739, 1623, 1593, 1447, 1378, 1200, 1170, 1147, 1089, 1043, 812, 748 cm⁻¹; HRMS (EI) calcd for C₂₃H₂₀N₂O₂S, 388.1245; found, 388.1245.

(E)-4-Methyl-2-styryl-1-tosyl-1H-benzo[d]imidazole (5k). A fresh solid (23 mg, 30%); m.p. 165.3–166.3 °C; ¹H NMR (400 MHz, CDCl₃) δ 7.93 (s, 2H), 7.90 (d, J = 8.0 Hz, 1H), 7.77 (d, J = 8.4 Hz, 2H), 7.69–7.66 (m, 2H), 7.46–7.37 (m, 3H), 7.24–7.20 (m, 3H), 7.15 (d, J = 7.6 Hz, 1H), 2.63 (s, 3H), 2.33 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ 150.6, 146.0, 142.2, 139.7, 136.2, 135.6, 133.1, 130.4, 129.7, 129.2, 128.4, 128.0, 127.1, 126.0, 125.2, 115.0, 111.6, 21.9, 16.8; IR (neat) ν 3060, 3027, 2923, 2852, 1636, 1597, 1512, 1447, 1376, 1344, 1200, 1176, 1101, 1016, 972, 814, 759 cm⁻¹; HRMS (EI) calcd for C₂₃H₂₀N₂O₂S, 388.1245; found, 388.1249.

Acknowledgements

The authors thank the National Natural Science Foundation of China (nos. 21272204) for financial support.

Notes and references

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c5qo00196j

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