Formation of zwitterionic salts via three-component reaction of benzimidazolium bromides, aromatic aldehydes and 1,3-indanedione

Abstract

The three-component reaction of N-butyl-N′-phenacylbenzimidazolium bromide, aromatic aldehydes and 1,3-indanedione in ethanol in the presence of triethylamine as base catalyst resulted in the unusual charge-separated zwitterionic salts in good yields. Similar reactions with N-butyl-N′-(4-nitrobenzyl)- and N-butyl-N′-ethoxycarbonylmethylbenzimidazolium bromide also afforded the corresponding zwitterionic salts. Furthermore, ¹H NMR spectra and single crystal structures indicated that the zwitterionic salts usually exist as two kinds of conformational isomers due to hindered interconversion of the different conformations.

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Introduction

1,3-Indanedione is one of the most important cyclic 1,3-dicarbonyl compounds that has drawn great attention in various organic reactions because it is not only a readily available starting material, but also has versatile reaction patterns in various organic reactions.^1–3 More importantly, many indenone-fused and spiro compounds are important components of many naturally occurring biologically active substances with a wide range of pharmacological reactivities.^4,5 In recent years, various domino and multicomponent reactions containing 1,3-indanedione and its readily accessible 2-arylidene-1,3-indanediones as key components have been successfully developed to give diverse indenone-fused heterocycles.^6–8 The 2-arylidene-1,3-indane-diones are highly reactive α,β-unsaturated carbonyl compounds and have been extensively used as 1,3-dipolarophiles, dienophiles and active alkenes in many cycloaddition, Michael addition and condensation reactions.^9–11 However, there are very few reports about the cycloaddition reaction of heterocyclic nitrogen ylides with 2-arylidene-1,3-indanediones.¹² It has been reported that the reaction of base promoted reaction of N-phenacylpyridium salts with in situ generated 2-arylidene-1,3-indandione to give spiro[cyclopropane-1,2′-inden]-1′,3′-diones.¹³ However, the similar three-component reaction under microwave-irradiation in solvent-free conditions afforded dihydroindeno[1,2-b]furans, in which the pyridyl moiety was eliminated off from the reaction.¹⁴ The base mediated reaction N-phenacylbenzothiazolium bromides, aromatic aldehydes and 1,3-indanedione afforded functionalized spiro[benzo[d]pyrrolo[2,1-b]thiazole-3,2′-indenes] in good yields and with high diastereoselectivity.¹⁵ On the other hand, the three-component reaction of N-phenacylisoquinolinium salts with isatins and 1,3-indanedione resulted in special 2′-isatylidene spiro[indan-2,1′-pyrrolo[2,1-a]isoquinolines] via a unusual [4 + 1] cycloaddition reaction.¹⁶ Notably, the three-component reaction N-phenacylpyridium salts with isatins and 1,3-indanedione produced the functionalized dibenzo[b,d]azepin-6-one with unique two-carbon ring expansion of isatin.¹⁷ The above mentioned results displayed that it has rich contents in the cycloaddition reaction of heterocyclic nitrogen ylides with 2-arylidene-1,3-indane-diones. In order to further explore versatile reactivity of heterocyclic nitrogen N-ylides in the 1,3-dipolar cycloadditions and provided more efficient synthetic methodology for spirocyclic compounds,^18,19 herein we wish to report the three-component reaction of N-butylbenzimidazolium bromide, aromatic aldehydes and 1,3-indanedione for the convenient synthesis of the unusual charge-separated zwitterionic salts.

Results and discussion

According to our previously established reaction conditions for the preparing functionalized spiro[benzo[d]pyrrolo[2,1-b]thiazole-3,2′-indenes],¹⁵ a mixture of N-butyl-N′-(p-chlorophenacyl)benzimidazolium bromide, benzaldehyde and 1,3-indanedione was stirred in ethanol in the presence of triethylamine at room temperature. TLC monitor indicated that the reaction was finished in several hours. After workup, we are surprised to find that the expected spiro compound was not formed, while a zwitterionic salt 1a was obtained in 88% yield. The formation of the zwitterion salt 1a clearly indicated that the expected 1,3-dipolar cycloaddition just stopped at first addition step and the further cyclization did not occur. Although the reaction of N-butyl-N′-(p-chlorophenacyl)benzimidazolium bromide did not give the expected cyclized product as the that of the similar reaction of N-phenacylbenzothiazolium bromides,¹⁵ the formation of the zwitterionic salts have been found in the 1,3-dipolar cycloaddition reactions of pyridinium and isoquinolinium salts with some α,β-unsaturated carbonyl compounds.¹⁹ Under similar conditions, various aromatic aldehydes were employed in the three-component reaction. All reactions proceeded smoothly to give the corresponding zwitterionic salts 1b–1i in high yields (Table 1). Additionally, other substituted N-butyl-N′-phenacylbenzimidazolium bromides were also employed in the three-component reaction, more zwitterionic salts 1j–1m were produced in satisfactory yields. It should be pointed out that N-benzyl-N′-phenacylbenzimidazolium bromides can be used in this three-component reaction to give the expected zwitterionic salts in very high yields. However, the solubility of the obtained zwitterionic salts in common organic solvents such as chloroform, ethanol and N,N-dimethylforamide is too bad. It is difficult for us to give the satisfactory characterization data for these products. Thus, these results were not listed in the Table 1.

Table 1 Three-component reaction for synthesis of zwitterionic salts 1a–1m^a

Entry	Compd	Ar	Ar′	Yield^b (%, A/B conformation)
a Reaction conditions: benzimidazolium bromide (0.5 mmol), aromatic aldehyde (0.5 mmol), indan-1,3-dione (0.6 mmol), Et3N (0.5 mmol) in EtOH (10.0 mL), r.t., 6 h.b Isolated yield.
1	1a	p-ClC6H4	C6H5	88 (50 : 50)
2	1b	p-ClC6H4	p-CH3C6H4	82 (50 : 50)
3	1c	p-ClC6H4	m-CH3C6H4	65 (50 : 50)
4	1d	p-ClC6H4	m-CH3OC6H4	90 (54 : 46)
5	1e	p-ClC6H4	p-(CH3)3CC6H4	80 (60 : 40)
6	1f	p-ClC6H4	p-ClC6H4	80 (50 : 50)
7	1g	p-ClC6H4	p-BrC6H4	90 (53 : 47)
8	1h	p-ClC6H4	m-NO2C6H4	84 (54 : 46)
9	1i	p-ClC6H4	p-NO2C6H4	90 (57 : 43)
10	1j	C6H5	p-CH3C6H4	80 (52 : 48)
11	1k	C6H5	p-OCH3C6H4	80 (55 : 44)
12	1l	p-CH3OC6H4	p-CH3C6H4	80 (52 : 48)
13	1m	p-FC6H4	p-CH3C6H4	85 (50 : 50)

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The above prepared zwitterionic salts were fully characterized by IR, HRMS, ¹H and ¹³C NMR spectra. The ¹H NMR spectra usually displayed that the zwitterionic salts 1a–1m contain two isomers with nearly equal molecular ratio. As for an example, the ¹H NMR spectra of compound 1g displayed two singlet at 10.36, 10.43 ppm for the one proton at 2-position of imidazole ring, two doublets at 4.83, 4.88 ppm for the one CH unit and two triplets at 0.67, 0.80 ppm for the one methyl group. In order to elucidate the isomerism, the single crystal structures of the three compounds 1a, 1c and 1j (Fig. 1–3) were determined by X-ray diffraction method. From Fig. 1 and 2, it can be seen that the imidazole ring and moiety of indanedione exist in cis-position around the C–C single bond, while the phenyl group and p-chlorobenzoyl group stand to other direction around the C–C single bond. This structure was assigned as A-conformation isomer. In the Fig. 3, the imidazole ring and moiety of indanedione exist in trans-position around the C–C single bond, which was assigned as B-conformation isomer. It might be the rotation around the middle C–C single bond is hindered by the steric effect of the connecting four groups, both A-conformation isomer and B-conformation isomer existed in the obtained products and the two conformation isomers are in equilibrium (Scheme 1), which in turn caused the ¹H NMR spectra displaying two sets of characteristic absorptions for the two conformation isomers. However, the ¹H NMR spectra at the elevated temperature did not show any changes for the relative intensity of the characteristic absorptions, which reflected the two conformation isomers cannot easily change between themselves.

Fig. 1 Single crystal structure of zwitterionic salt 1a (A-conformation).

Fig. 2 Single crystal structure of zwitterionic salt 1c (A-conformation).

Fig. 3 Single crystal structure of zwitterionic salt 1j (B-conformation).

Scheme 1 Illustrated hindered interconvert of two conformations.

In order to develop the generality of this three-component reaction, other substrates were also examined in the reactions. At first, N-butyl-N′-(4-nitrobenzyl)benzimidazolium bromide and N-butyl-N′-ethoxycarbonylmethylbenzimidazolium bromide were employed to react with aromatic aldehydes and 1,3-indanedione under same reaction conditions. The corresponding zwitterionic salts 2a–2e were successfully obtained in good yields (Table 2). Secondly, other cyclic 1,3-dicarbonyl compounds such as Meldrum acid, barbituric acid and N,N-dimethylbarbituric acid were used to replace 1,3-indanedione in the reaction. The expected zwitterionic salts 2f–2h were also produced in satisfactory yields. These experiments indicated that this three-component reaction has a widely variety of substrates. The ¹H NMR spectra also displayed that the obtained products have two kinds of conformations with nearly same proportion. The single crystal structure of compound 2e indicated that the molecule has the B-conformation, in which the moiety of benzimidazole and the unit of 1,3-indanedione exist at trans-position (Fig. 4).

Table 2 Three-component reaction for synthesis of zwitterionic salts 2a–2h^a

Entry	Compd	R	Ar	E	Yield^b (%)
a Reaction conditions: benzimidazolium bromide (0.5 mmol), aromatic aldehyde (0.5 mmol), 1,3-diketone (0.5 mmol), Et3N (0.6 mmol) in EtOH (10.0 mL), r.t., 6 h.b Isolated yield.c 1,3-indanedione.d Meldrum acid.e Barbituric acid.f N,N-Dimethylbarbituric acid.
1	2a	p-NO2C6H5	p-CH3C6H4	C6H4^c	65
2	2b	p-NO2C6H5	p-ClC6H4	C6H4^c	70
3	2c	CO2Et	p-CH3C6H4	C6H4^c	65
4	2d	CO2Et	p-CH3OC6H4	C6H4^c	68
5	2e	CO2Et	p-ClC6H4	C6H4^c	65
6	2f	p-CH3OC6H4	p-CH3C6H4	OC(CH3)2O^d	80
7	2g	p-CH3OC6H4	p-CH3C6H4	NHCONH^e	91
8	2h	p-CH3OC6H4	p-CH3C6H4	CH3NCONCH3^f	95

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Fig. 4 Single crystal structure of zwitterionic salt 2e (B-conformation).

For explaining the formation mechanism of the zwitterionic compounds, a brief reaction mechanism is proposed based on the previously reported 1,3-dipolar cycloaddition reactions^18,19 (Scheme 2). In the basic medium, the condensation of aromatic aldehyde with 1,3-indanedione afforded 2-arylidene-1,3-indanedione (A). In the meantime, the base promoted deuteration of benzimidazolium bromide resulted in a cyclic nitrogen ylide (B). Then, the addition of nitrogen ylide (B) to 2-arylidene-1,3-indanedione (A) afforded the zwitterionic salt 1. The further intramolecular cyclization process for the zwittionic salt 1 to give the spiro compound (C) did not occur as that of the most common 1,3-dipolar cycloaddition reactions of the cyclic nitrogen ylides with the activated alkenes.^18,19 Thus, the zwitterionic salt 1 was separated as final product. At present the reason for this result is not very clear. It has recently reported that the similar reaction of N-phenacylbenzothiazolium bromides, aromatic aldehydes and 1,3-indanedione in ethanol at room temperature in the presence of triethylamine as base afforded functionalized spiro[benzo[d]pyrrolo[2,1-b]thiazole-3,2′-indenes] in good yields and with high diastereoselectivity. This result provided an excellent example for us to observe the diverse reaction patterns of N-phenacylbenzimidazolium salts to N-phenacylbenzothiazolium salts in cycloaddition reaction.

Scheme 2 The proposed reaction mechanism for three-component reaction.

Conclusion

In summary, we have investigated the base mediated three-component reaction of various benzimidazolium bromide, aromatic aldehydes and 1,3-indanedione as well as other cyclic 1,3-dicarbonyl compounds. The reaction afforded the unusual charge-separated zwitterionic salts in good yields. Furthermore, ¹H NMR spectra and single crystal structures revealed that the zwitterionic salts usually exist in two kinds of conformation isomers due to hindered rotation around the C–C single bond because of the steric effect of the substituents. This reaction not only provided new efficient synthetic protocol for the zwitterionic salts, but also further exploited the potential reactivity of the heterocyclic nitrogen ylides. The further study of the synthetic applications of various cyclic nitrogen ylides was on the way from our laboratory.

Experimental section

General procedure of three-component reaction for the preparation of zwitterionic salts 1a–1m and 2a–2h

A mixture of N-butyl-N′-phenacylbenzimidazolium bromide (0.5 mmol), aromatic aldehyde (0.5 mmol), indan-1,3-dione (0.5 mmol), and triethylamine (0.6 mmol) in ethanol (10.0 mL) was stirred at room temperature for four hours. The solvent was removed by evaporation at the reduced pressure and the residue was subjected to column chromatography with a mixture of light petroleum and ethyl acetate (V/V = 1 : 2) to give the pure product for analysis.

2-(2-(1-Butyl-1H-benzo[d]imidazol-3-ium-3-yl)-3-(4-chlorophenyl)-3-oxo-1-phenylpropyl)-1,3-dioxo-2,3-dihydro-1H-inden-2-ide (1a). Yellow solid, 88%, mp 168–170 °C; ¹H NMR (600 MHz, DMSO-d₆) δ: A-conformation: 10.30 (s, 1H, CH), 8.17–8.14 (m, 2H, ArH), 7.96–7.89 (m, 2H, ArH), 7.86–7.84 (m, 1H, ArH), 7.69–7.66 (m, 1H, ArH), 7.63–7.56 (m, 2H, ArH), 7.52 (d, J = 7.2 Hz, 1H, ArH), 7.47–7.45 (m, 2H, ArH), 7.10–7.08 (m, 2H, ArH), 7.05–7.03 (m, 1H, ArH), 6.98–6.94 (m, 1H, ArH), 6.92–6.88 (m, 3H, ArH, CH), 4.88–4.83 (m, 1H, CH), 4.58–4.42 (m, 2H, CH), 1.74–1.69 (m, 2H, CH), 0.99–0.88 (m, 2H, CH), 0.83–0.81 (m, 3H, CH₃); B-conformation: 10.38 (s, 1H, CH), 8.25–8.22 (m, 1H, ArH), 0.67 (t, J = 7.2 Hz, 3H, CH₃). ¹³C NMR (150 MHz, DMSO-d₆) δ: 194.8, 188.6, 188.2, 142.0, 140.0, 139.8, 138.9, 133.6, 130.5, 130.2, 129.1, 128.9, 128.8, 128.7, 128.5, 128.2, 128.0, 127.7, 127.0, 126.6, 126.5, 126.4, 125.9, 116.6, 116.5, 113.7, 113.5, 46.5, 30.4, 30.3, 18.6, 18.5, 13.2; IR (KBr) ν: 3051, 2959, 1691, 1598, 1533, 1427, 1317, 1206, 1088, 1004, 961, 859, 810, 729 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₅H₃₀ClN₂O₃ ([M + H]⁺): 561.1939. Found: 561.1933.

2-(2-(1-Butyl-1H-benzo[d]imidazol-3-ium-3-yl)-3-(4-chlorophenyl)-3-oxo-1-(p-tolyl)propyl)-1,3-dioxo-2,3-dihydro-1H-inden-2-ide (1b). Yellow solid, 82%, mp 179–181 °C; ¹H NMR (600 MHz, DMSO-d₆) δ: A-conformation: 10.34 (s, 1H, CH), 8.25 (d, J = 8.0 Hz, 1H, ArH), 8.18–8.13 (m, 1H, ArH), 7.97–7.81 (m, 3H, ArH), 7.70–7.57 (m, 2H, ArH), 7.49–7.45 (m, 3H, ArH), 7.38 (d, J = 7.6 Hz, 1H, ArH), 7.09 (brs, 2H, ArH), 6.90–6.89 (m, 2H, ArH, CH), 6.84 (d, J = 7.6 Hz, 1H, ArH), 6.79 (d, J = 8.0 Hz, 1H, ArH), 4.85–4.80 (m, 1H, CH), 4.58–4.52 (m, 1H, CH), 4.46–4.40 (m, 1H, CH), 2.07 (s, 3H, CH₃), 1.74–1.66 (m, 2H, CH), 0.96–0.87 (m, 3H, CH₃), 0.81 (brs, 2H, CH); B-conformation: 10.39 (s, 1H, CH), 2.03 (s, 3H, CH₃), 0.66 (t, J = 7.2 Hz, 3H, CH₃). ¹³C NMR (150 MHz, DMSO-d₆) δ: 194.8, 188.5, 188.1, 143.0, 140.0, 139.8, 138.9, 138.8, 133.7, 133.6, 130.6, 130.4, 129.4, 129.1, 129.0, 128.9, 128.8, 128.6, 128.5, 128.4, 128.2, 128.1, 127.0, 126.6, 116.5, 116.4, 113.5, 46.5, 30.4, 30.3, 20.4, 19.3, 18.6, 18.5, 13.4, 13.2; IR (KBr) ν: 3036, 2957, 1690, 1601, 1535, 1426, 1208, 1091, 1004, 963, 860, 822, 731 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₆H₃₂ClN₂O₃ ([M + H]⁺): 575.2096. Found: 575.2105.

2-(2-(1-Butyl-1H-benzo[d]imidazol-3-ium-3-yl)-3-(4-chlorophenyl)-3-oxo-1-(m-tolyl)propyl)-1,3-dioxo-2,3-dihydro-1H-inden-2-ide (1c). Yellow solid, 65%, mp 174–176 °C; ¹H NMR (600 MHz, DMSO-d₆) δ: A-conformation: 10.27 (s, 1H, CH), 8.26 (d, J = 8.4 Hz, 1H, ArH), 8.18–8.15 (m, 1H, ArH), 7.97–7.92 (m, 1H, ArH), 7.91–7.90 (m, 1H, ArH), 7.86–7.84 (m, 1H, ArH), 7.70–7.67 (m, 1H, ArH), 7.64–7.56 (m, 1H, ArH), 7.48–7.46 (m, 2H, ArH), 7.32 (s, 1H, ArH), 7.27 (d, J = 7.8 Hz, 1H, ArH), 7.10–7.08 (m, 2H, ArH), 6.92–6.89 (m, 2H, ArH, CH), 6.74 (d, J = 7.5 Hz, 1H, ArH), 6.70 (d, J = 7.4 Hz, 1H, ArH), 4.82–4.76 (m, 1H, CH), 4.58–4.50 (m, 1H, CH), 4.47–4.42 (m, 1H, CH), 2.09 (s, 3H, CH₃), 1.73–1.66 (m, 2H, CH), 0.99–0.91 (m, 3H, CH₃), 0.88–0.81 (m, 2H, CH); B-conformation: 10.34 (s, 1H, CH), 7.39 (brs, 1H, ArH), 6.84–6.82 (m, 1H, ArH), 2.04 (s, 3H, CH₃), 0.66 (t, J = 7.2 Hz, 3H, CH₃). ¹³C NMR (150 MHz, DMSO-d₆) δ: 195.0, 188.5, 188.1, 140.0, 139.8, 138.9, 138.8, 136.9, 136.6, 130.5, 129.9, 129.1, 128.9, 128.8, 128.5, 127.9, 127.5, 126.9, 126.6, 126.5, 126.4, 126.1, 116.5, 116.4, 113.6, 113.5, 110.3, 46.5, 30.4, 20.9, 19.3, 18.6, 18.5, 13.2; IR (KBr) ν: 3032, 2962, 1688, 1607, 1538, 1486, 1425, 1209, 1089, 1007, 967, 850, 730 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₆H₃₂ClN₂O₃ ([M + H]⁺): 575.2096. Found: 575.2098.

2-(2-(1-Butyl-1H-benzo[d]imidazol-3-ium-3-yl)-3-(4-chlorophenyl)-1-(3-methoxyphenyl)-3-oxopropyl)-1,3-dioxo-2,3-dihydro-1H-inden-2-ide (1d). Yellow solid, 90%, mp 156–158 °C; ¹H NMR (600 MHz, DMSO-d₆) δ: A-conformation: 10.40–10.37 (m, 1H, CH), 8.16 (d, J = 8.5 Hz, 2H, ArH), 7.96–7.93 (m, 2H, ArH), 7.84–7.82 (m, 1H, ArH), 7.70–7.68 (m, 1H, ArH), 7.62–7.56 (m, 1H, ArH), 7.49–7.45 (m, 2H, ArH), 7.28–7.25 (m, 1H, ArH), 7.14–7.09 (m, 3H, ArH), 6.96–6.90 (m, 2H, ArH), 6.89–6.86 (m, 1H, ArH), 6.46–6.45 (m, 1H, CH), 4.84–4.80 (m, 1H, CH), 4.58–4.50 (m, 1H, CH), 4.46–4.43 (m, 1H, CH), 3.55 (s, 3H, OCH₃), 1.74–1.67 (m, 2H, CH), 0.99–0.91 (m, 1H, CH), 0.88–0.80 (m, 4H, CH); B-conformation: δ: 8.26 (d, J = 8.4 Hz, 1H, ArH), 7.89–7.87 (m, 1H, ArH), 7.18 (brs, 1H, ArH), 7.04–7.03 (m, 1H, ArH), 6.52–6.50 (m, 1H, CH), 3.60 (s, 3H, OCH₃), 0.68 (t, J = 7.2 Hz, 3H, CH₃). ¹³C NMR (150 MHz, DMSO-d₆) δ: 194.7, 188.6, 188.3, 159.0, 158.7, 140.0, 139.8, 139.0, 133.6, 130.5, 129.0, 128.9, 128.8, 128.7, 128.6, 128.5, 127.0, 126.6, 121.4, 120.5, 116.6, 116.5, 115.0, 113.7, 113.5, 111.6, 54.8, 54.7, 46.5, 30.4, 30.3, 18.7, 18.5, 13.2; IR (KBr) ν: 2967, 2873, 1691, 1643, 1601, 1528, 1425, 1349, 1222, 1165, 1087, 983, 837, 733 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₆H₃₂ClN₂O₄ ([M + H]⁺): 591.2045. Found: 591.2043.

2-(1-(4-(tert-Butyl)phenyl)-2-(1-butyl-1H-benzo[d]imidazol-3-ium-3-yl)-3-(4-chlorophenyl)-3-oxopropyl)-1,3-dioxo-2,3-dihydro-1H-inden-2-ide (1e). Yellow solid, 80%, mp 183–185 °C; ¹H NMR (600 MHz, DMSO-d₆) δ: A-conformation: 10.18 (s, 1H, CH), 8.17–8.13 (m, 2H, ArH), 7.97–7.95 (m, 1H, ArH), 7.82–7.80 (m, 1H, ArH), 7.62–7.58 (m, 2H, ArH), 7.46–7.45 (m, 2H, ArH), 7.39–7.36 (m, 3H, ArH), 7.09–7.08 (m, 2H, ArH), 6.99–6.96 (m, 2H, ArH), 6.90 (brs, 2H, ArH, CH), 4.71 (d, J = 10.6 Hz, 1H, CH), 4.58–4.53 (m, 2H, CH), 1.72–1.68 (m, 2H, CH), 1.09 (s, 9H, 3CH₃), 0.98–0.93 (m, 2H, CH), 0.66 (t, J = 7.2 Hz, 3H, CH₃); B-conformation: 10.35 (s, 1H, CH), 8.22–8.21 (m, 1H, ArH), 7.92–7.90 (m, 2H, ArH), 7.68–7.65 (m, 1H, ArH), 4.83 (d, J = 11.4 Hz, 1H, CH), 4.43 (brs, 2H, CH), 1.05 (s, 9H, 3CH₃), 0.82 (t, J = 7.2 Hz, 3H, CH₃). ¹³C NMR (150 MHz, DMSO-d₆) δ: 193.2, 190.4, 150.2, 143.9, 143.4, 141.4, 138.6, 135.8, 134.6, 133.8, 130.5, 129.8, 129.4, 129.2, 129.1, 128.9, 128.8, 128.3, 124.8, 124.5, 122.6, 122.1, 121.3, 119.4, 116.5, 110.3, 47.0, 43.8, 41.5, 34.2, 33.8, 31.4, 31.0, 30.4, 19.3, 18.6, 13.4, 13.2, 13.2; IR (KBr) ν: 3054, 2962, 2872, 1688, 1599, 1533, 1425, 1317, 1271, 1210, 1093, 1004, 963, 842, 726 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₉H₃₈ClN₂O₃ ([M + H]⁺): 617.2565. Found: 617.2567.

2-(2-(1-Butyl-1H-benzo[d]imidazol-3-ium-3-yl)-1,3-bis(4-chlorophenyl)-3-oxopropyl)-1,3-dioxo-2,3-dihydro-1H-inden-2-ide (1f). Yellow solid, 80%, mp 174–176 °C; ¹H NMR (600 MHz, DMSO-d₆) δ: A-conformation: 10.40–10.35 (m, 1H, CH), 8.26 (d, J = 8.4 Hz, 1H, ArH), 8.17–8.14 (m, 1H, ArH), 7.98–7.93 (m, 2H, ArH), 7.82–7.80 (m, 1H, ArH), 7.64–7.56 (m, 3H, ArH), 7.54–7.50 (m, 2H, ArH), 7.46 (d, J = 7.8 Hz, 1H, ArH), 7.11–7.09 (m, 3H, ArH), 7.05 (d, J = 9.0 Hz, 1H, ArH), 6.92–6.90 (m, 2H, ArH, CH), 4.90–4.84 (m, 1H, CH), 4.57–4.45 (m, 2H, CH), 1.71 (brs, 2H, CH), 0.97–0.82 (m, 5H, CH); B-conformation: 7.88–7.86 (m, 1H, ArH), 7.71–7.69 (m, 1H, ArH), 0.68 (t, J = 7.2 Hz, 3H, CH₃). ¹³C NMR (150 MHz, DMSO-d₆) δ: 188.5, 188.1, 139.9, 139.7, 139.0, 138.9, 133.9, 131.1, 130.9, 130.6, 130.4, 130.0, 129.1, 129.0, 128.9, 128.7, 128.5, 127.9, 127.7, 127.1, 126.7, 126.6, 126.4, 116.6, 116.5, 113.8, 113.5, 46.6, 30.4, 30.3, 18.6, 13.2, 13.1; IR (KBr) ν: 3039, 2957, 1690, 1599, 1536, 1485, 1426, 1208, 1087, 1006, 963, 825, 732 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₅H₂₉Cl₂N₂O₃ ([M + H]⁺): 595.1550. Found: 595.1550.

2-(1-(4-Bromophenyl)-2-(1-butyl-1H-benzo[d]imidazol-3-ium-3-yl)-3-(4-chlorophenyl)-3-oxopropyl)-1,3-dioxo-2,3-dihydro-1H-inden-2-ide (1g). Yellow solid, 90%, mp 194–196 °C; ¹H NMR (600 MHz, DMSO-d₆) δ: A-conformation: 10.40–10.36 (m, 1H, CH), 8.17–8.14 (m, 2H, ArH), 7.98–7.96 (m, 2H, ArH), 7.82–7.80 (m, 1H, ArH), 7.71–7.69 (m, 1H, ArH), 7.64–7.61 (m, 1H, ArH), 7.59–7.50 (m, 2H, ArH), 7.47–7.45 (m, 2H, ArH), 7.19 (d, J = 8.3 Hz, 2H, ArH), 7.10–7.09 (m, 2H, ArH), 6.91–6.90 (m, 2H, ArH, CH), 4.88 (d, J = 11.4 Hz, 1H, CH), 4.57–4.50 (m, 1H, CH), 4.45 (brs, 1H, CH), 1.72 (brs, 2H, CH), 0.99–0.88 (m, 2H, CH), 0.80 (t, J = 7.2 Hz, 3H, CH₃); B-conformation: δ: 8.26 (d, J = 8.4 Hz, 1H, ArH), 7.94–7.92 (m, 2H, ArH), 7.87–7.85 (m, 1H, ArH), 7.24 (d, J = 8.3 Hz, 2H, ArH), 4.83 (d, J = 10.8 Hz, 1H, CH), 0.68 (t, J = 7.2 Hz, 3H, CH₃). ¹³C NMR (150 MHz, DMSO-d₆) δ: 188.5, 188.1, 139.9, 139.7, 133.6, 131.3, 130.8, 130.6, 130.4, 130.3, 129.0, 128.9, 128.7, 128.5, 127.2, 126.7, 122.1, 119.4, 119.1, 116.6, 116.5, 113.8, 113.6, 110.3, 46.6, 46.5, 43.7, 31.4, 30.4, 19.3, 18.6, 13.4, 13.2; IR (KBr) ν: 3049, 2965, 1690, 1601, 1533, 1426, 1276, 1206, 1083, 1004, 962, 857, 813, 729 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₅H₂₉BrClN₂O₃ ([M + H]⁺): 639.1045. Found: 639.1033.

2-(2-(1-Butyl-1H-benzo[d]imidazol-3-ium-3-yl)-3-(4-chlorophenyl)-1-(4-nitrophenyl)-3-oxopropyl)-1,3-dioxo-2,3-dihydro-1H-inden-2-ide (1h). Yellow solid, 90%, mp 153–155 °C; ¹H NMR (600 MHz, DMSO-d₆) δ: A-conformation: 10.36 (s, 1H, CH), 8.32 (d, J = 8.4 Hz, 1H, ArH), 8.18 (d, J = 8.4 Hz, 2H, ArH), 7.97–7.90 (m, 4H, ArH), 7.88–7.80 (m, 2H, ArH), 7.72–7.70 (m, 1H, ArH), 7.64–7.57 (m, 1H, ArH), 7.49–7.46 (m, 2H, ArH), 7.12–7.11 (m, 2H, ArH), 6.94–6.92 (m, 2H, ArH, CH), 5.10 (d, J = 11.4 Hz, 1H, CH), 4.58–4.43 (m, 2H, CH), 1.74–1.69 (m, 2H, CH), 0.82–0.80 (m, 1H, CH), 0.74–0.72 (m, 4H, CH); B-conformation: δ: 10.43 (s, 1H, CH), 8.20 (d, J = 8.4 Hz, 1H, ArH), 4.99 (d, J = 10.2 Hz, 1H, CH), 0.98–0.92 (m, 2H, CH), 0.69–0.66 (m, 3H, CH₃). ¹³C NMR (150 MHz, DMSO-d₆) δ: 194.1, 188.5, 188.1, 145.9, 145.6, 139.7, 139.5, 139.1, 133.6, 133.5, 130.7, 130.5, 130.2, 129.1, 128.8, 128.5, 127.3, 126.9, 126.7, 126.5, 123.2, 123.1, 116.8, 116.7, 113.8, 113.6, 46.7, 46.6, 30.4, 30.1, 18.6, 18.5, 13.2, 12.9; IR (KBr) ν: 3039, 2957, 1690, 1599, 1537, 1487, 1425, 1275, 1207, 1092, 1007, 964, 828, 731 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₅H₂₉ClN₃O₅ ([M + H]⁺): 606.1790. Found: 606.1778.

2-(2-(1-Butyl-1H-benzo[d]imidazol-3-ium-3-yl)-3-(4-chlorophenyl)-1-(3-nitrophenyl)-3-oxopropyl)-1,3-dioxo-2,3-dihydro-1H-inden-2-ide (1i). Yellow solid, 84%, mp 143–145 °C; ¹H NMR (600 MHz, DMSO-d₆) δ: A-conformation: 10.47–10.42 (m, 1H, CH), 8.54 (brs, 1H, ArH), 8.32 (d, J = 8.4 Hz, 1H, ArH), 8.17 (d, J = 8.4 Hz, 2H, ArH), 7.97–7.90 (m, 2H, ArH), 7.87–7.82 (m, 1H, ArH), 7.80–7.79 (m, 1H, ArH), 7.70–7.68 (m, 1H, ArH), 7.63–7.57 (m, 1H, ArH), 7.46 (d, J = 8.4 Hz, 2H, ArH), 7.31–7.28 (m, 1H, ArH), 7.12–7.10 (m, 2H, ArH), 6.94–6.93 (m, 2H, ArH, CH), 5.06 (d, J = 10.8 Hz, 1H, CH), 4.60–4.49 (m, 1H, CH), 4.43 (brs, 1H, CH), 1.75–1.69 (m, 2H, CH), 0.92–0.85 (m, 1H, CH), 0.77–0.71 (m, 4H, CH); B-conformation: δ: 8.47 (s, 1H, ArH), 8.22 (d, J = 8.4 Hz, 1H, ArH), 8.09–7.99 (m, 1H, ArH), 7.37–7.34 (m, 1H, ArH), 4.99 (d, J = 10.8 Hz, 1H, CH), 1.03–0.97 (m, 2H, CH). ¹³C NMR (150 MHz, DMSO-d₆) δ: 188.6, 188.2, 147.4, 147.3, 139.7, 139.5, 139.1, 139.0, 134.7, 133.5, 130.5, 129.6, 129.3, 129.2, 129.1, 128.7, 128.5, 127.2, 126.8, 126.6, 121.4, 121.1, 116.8, 116.7, 113.7, 113.5, 56.0, 46.7, 46.6, 30.4, 30.2, 18.7, 18.5, 13.2, 13.1; IR (KBr) ν: 2991, 1691, 1599, 1535, 1418, 1280, 1210, 1062, 1008, 959, 891, 853, 725 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₅H₂₉ClN₃O₅ ([M + H]⁺): 606.1790. Found: 606.1779.

2-(2-(1-Butyl-1H-benzo[d]imidazol-3-ium-3-yl)-3-oxo-3-phenyl-1-(p-tolyl)propyl)-1,3-dioxo-2,3-dihydro-1H-inden-2-ide (1j). Yellow solid, 80%, mp 171–173 °C; ¹H NMR (600 MHz, DMSO-d₆) δ: A-conformation: 10.24 (s, 1H, CH), 8.21–8.18 (m, 1H, ArH), 8.11 (d, J = 8.6 Hz, 1H, ArH), 7.96–7.90 (m, 3H, ArH), 7.64–7.61 (m, 1H, ArH), 7.59–7.53 (m, 2H, ArH), 7.45–7.40 (m, 4H, ArH), 7.08–7.07 (m, 2H, ArH), 6.89–6.88 (m, 2H, ArH, CH), 6.84 (d, J = 7.2 Hz, 1H, ArH), 6.78 (d, J = 7.8 Hz, 1H, ArH), 4.88–4.81 (m, 1H, CH), 4.58–4.48 (m, 1H, CH), 4.43–4.42 (m, 1H, CH), 2.06 (s, 3H, CH₃), 1.68 (brs, 2H, CH), 0.95–0.80 (m, 5H, CH); B-conformation: δ: 10.36 (s, 1H, CH), 7.00–7.68 (m, 1H, ArH), 2.03 (s, 3H, CH₃), 0.64 (t, J = 7.2 Hz, 3H, CH₃). ¹³C NMR (150 MHz, DMSO-d₆) δ: 188.5, 188.1, 142.9, 140.1, 139.9, 135.3, 134.9, 134.8, 134.1, 134.0, 129.4, 129.0, 128.9, 128.8, 128.7, 128.6, 128.4, 128.2, 128.0, 127.1, 126.7, 126.6, 126.4, 116.5, 116.4, 113.8, 113.6, 46.5, 30.4, 30.3, 20.4, 18.6, 18.5, 13.2; IR (KBr) ν: 3032, 2959, 1686, 1608, 1535, 1429, 1209, 1005, 962, 827, 733 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₆H₃₃N₂O₃ ([M + H]⁺): 541.2486. Found: 541.2504.

2-(2-(1-Butyl-1H-benzo[d]imidazol-3-ium-3-yl)-1-(4-methoxyphenyl)-3-oxo-3-phenylpropyl)-1,3-dioxo-2,3-dihydro-1H-inden-2-ide (1k). Yellow solid, 80%, mp 174–176 °C; ¹H NMR (600 MHz, DMSO-d₆) δ: A-conformation: 10.17 (s, 1H, CH), 8.19–8.16 (m, 1H, ArH), 8.09 (d, J = 8.4 Hz, 1H, ArH), 7.94–7.87 (m, 3H, ArH), 7.61–7.56 (m, 2H, ArH), 7.45–7.41 (m, 5H, ArH), 7.07 (brs, 2H, ArH), 6.90 (brs, 2H, ArH, CH), 6.58 (d, J = 7.2 Hz, 2H, ArH), 4.80 (d, J = 10.8 Hz, 1H, CH), 4.56–4.42 (m, 2H, CH), 3.55 (s, 3H, OCH₃), 1.71–1.70 (m, 2H, CH), 0.99–0.90 (m, 2H, CH), 0.67 (t, J = 7.2 Hz, 3H, CH₃); A-conformation: 10.32 (s, 1H, CH), 7.70–7.67 (m, 1H, ArH), 7.53–7.52 (m, 1H, ArH), 7.48–7.47 (m, 2H, ArH), 6.53 (d, J = 7.2 Hz, 2H, ArH), 4.85 (d, J = 11.4 Hz, 1H, CH), 3.52 (s, 3H, OCH₃), 0.82 (t, J = 7.2 Hz, 3H, CH₃). ¹³C NMR (150 MHz, DMSO-d₆) δ: 188.6, 188.2, 157.8, 157.4, 140.1, 139.9, 135.0, 134.8, 134.3, 134.0, 130.2, 129.3, 128.9, 128.7, 128.6, 127.1, 126.7, 126.4, 116.5, 116.4, 113.7, 113.6, 113.3, 113.0, 54.9, 54.7, 46.5, 30.4, 30.3, 18.6, 13.2, 13.1; IR (KBr) ν: 3032, 2958, 1684, 1607, 1535, 1426, 1249, 1209, 1177, 1037, 964, 840, 729 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₆H₃₃N₂O₄ ([M + H]⁺): 557.2435. Found: 557.2442.

2-(2-(1-Butyl-1H-benzo[d]imidazol-3-ium-3-yl)-3-(4-methoxyphenyl)-3-oxo-1-(p-tolyl)propyl)-1,3-dioxo-2,3-dihydro-1H-inden-2-ide (1l). Yellow solid, 80%, mp 177–179 °C; ¹H NMR (600 MHz, DMSO-d₆) δ: A-conformation: 10.10 (s, 1H, CH), 8.21–8.16 (m, 1H, ArH), 8.06 (d, J = 7.8 Hz, 1H, ArH), 7.92–7.89 (m, 2H, ArH), 7.82–7.80 (m, 1H, ArH), 7.62–7.54 (m, 2H, ArH), 7.43–7.42 (m, 2H, ArH), 7.08–7.07 (m, 2H, ArH), 6.96–6.92 (m, 3H, ArH), 6.88–6.86 (m, 3H, ArH, CH), 4.81 (d, J = 10.8 Hz, 1H, CH), 4.54–4.41 (m, 2H, CH), 3.81 (s, 3H, OCH₃), 2.08 (s, 3H, CH₃), 1.69–1.67 (m, 2H, CH), 0.96–0.80 (m, 2H, CH), 0.64 (t, J = 7.2 Hz, 3H, CH₃); B-conformation: 10.29 (s, 1H, CH), 7.69–7.67 (m, 1H, ArH), 6.77 (d, J = 7.2 Hz, 2H, CH), 4.87 (d, J = 11.4 Hz, 1H, CH), 3.78 (s, 3H, OCH₃), 2.03 (s, 3H, CH₃). ¹³C NMR (150 MHz, DMSO-d₆) δ: 188.5, 188.1, 164.0, 163.9, 140.2, 139.9, 135.2, 134.7, 131.5, 131.3, 128.9, 128.8, 128.7, 128.4, 128.2, 128.0, 127.8, 127.1, 126.7, 126.6, 126.3, 116.4, 114.0, 113.8, 113.6, 55.7, 55.6, 46.5, 30.4, 30.3, 20.5, 20.4, 18.6, 18.5, 13.2; IR (KBr) ν: 3026, 2958, 1674, 1601, 1534, 1424, 1317, 1270, 1208, 1171, 1021, 962, 828, 732 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₇H₃₅N₂O₄ ([M + H]⁺): 571.2591. Found: 571.2604.

2-(2-(1-Butyl-1H-benzo[d]imidazol-3-ium-3-yl)-3-(4-fluorophenyl)-3-oxo-1-(p-tolyl)propyl)-1,3-dioxo-2,3-dihydro-1H-inden-2-ide (1m). Yellow solid, 85%, mp 183–185 °C; ¹H NMR (600 MHz, DMSO-d₆) δ: A-conformation: 10.26 (s, 1H, CH), 8.24–8.23 (m, 2H, ArH), 8.00–7.98 (m, 1H, ArH), 7.94–7.92 (m, 1H, ArH), 7.87–7.84 (m, 1H, ArH), 7.62–7.55 (m, 2H, ArH), 7.44 (d, J = 6.0 Hz, 1H, ArH), 7.39 (d, J = 7.2 Hz, 1H, ArH), 7.24–7.20 (m, 2H, ArH), 7.08 (brs, 2H, ArH), 6.90 (brs, 2H, ArH, CH), 6.84 (d, J = 7.8 Hz, 1H, ArH), 6.77 (d, J = 7.2 Hz, 1H, ArH), 4.85–4.80 (m, 1H, CH), 4.57–4.39 (m, 2H, CH), 2.07 (s, 3H, CH₃), 1.74–1.66 (m, 2H, CH), 1.00–0.80 (m, 5H, CH); B-conformation: δ: 10.32 (s, 1H, CH), 8.12 (d, J = 8.4 Hz, 1H, ArH), 7.70–7.67 (m, 1H, ArH), 2.03 (s, 3H, CH₃), 0.68 (t, J = 7.2 Hz, 3H, CH₃). ¹³C NMR (150 MHz, DMSO-d₆) δ: 194.3, 188.5, 188.2, 140.0, 139.8, 131.9, 131.8, 129.4, 129.0, 128.9, 128.8, 128.6, 128.4, 128.2, 128.0, 127.0, 126.6, 121.3, 116.5, 116.4, 115.7, 115.6, 115.4, 113.7, 113.6, 46.5, 43.7, 31.4, 30.4, 30.3, 20.4, 18.6, 18.5, 13.4, 13.2; IR (KBr) ν: 3036, 2959, 1689, 1603, 1536, 1425, 1276, 1237, 1210, 1161, 964, 828, 731 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₆H₃₂FN₂O₃ ([M + H]⁺): 559.2391. Found: 559.2395.

2-(2-(1-Butyl-1H-benzo[d]imidazol-3-ium-3-yl)-2-(4-nitrophenyl)-1-(p-tolyl)ethyl)-1,3-dioxo-2,3-dihydro-1H-inden-2-ide (2a). Yellow solid, 65%, mp 210–212 °C; ¹H NMR (600 MHz, DMSO-d₆) δ: 9.86 (s, 1H, CH), 8.15–8.13 (m, 1H, ArH), 8.05–8.03 (m, 2H, ArH), 7.96–7.94 (m, 1H, ArH), 7.90 (brs, 2H, ArH), 7.60–7.56 (m, 2H, ArH), 7.36 (brs, 2H, ArH), 7.29–7.26 (m, 1H, CH), 7.08 (s, 2H, ArH), 6.92–6.90 (m, 4H, ArH, CH), 4.85–4.82 (m, 1H, CH), 4.56–4.51 (m, 1H, CH), 4.38–4.33 (m, 1H, CH), 2.15 (brs, 3H, CH₃), 1.68–1.57 (m, 2H, CH), 0.84–0.69 (m, 2H, CH), 0.48–0.47 (m, 3H, CH₃). ¹³C NMR (150 MHz, DMSO-d₆) δ: 188.4, 162.3, 147.1, 145.3, 141.9, 139.9, 138.9, 134.8, 130.8, 130.4, 129.4, 129.3, 128.8, 128.6, 128.5, 126.8, 126.5, 123.4, 121.3, 116.5, 113.9, 113.6, 102.5, 62.0, 46.7, 45.0, 42.6, 35.7, 30.7, 30.2, 20.5, 18.6, 13.0; IR (KBr) ν: 2960, 2780, 1607, 1527, 1431, 1345, 1255, 1182, 1118, 1010, 964, 886, 821, 725 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₅H₃₂N₃O₄ ([M + H]⁺): 558.2387. Found: 558.2393.

2-(2-(1-Butyl-1H-benzo[d]imidazol-3-ium-3-yl)-1-(4-chlorophenyl)-2-(4-nitrophenyl)ethyl)-1,3-dioxo-2,3-dihydro-1H-inden-2-ide (2b). Yellow solid, 70%, mp 225–227 °C; ¹H NMR (600 MHz, DMSO-d₆) δ: 9.88 (s, 1H, CH), 8.15 (d, J = 7.8 Hz, 1H, ArH), 8.07–8.06 (m, 2H, ArH), 7.96–7.92 (m, 3H, ArH), 7.62–7.56 (m, 2H, ArH), 7.50 (d, J = 7.8 Hz, 2H, ArH), 7.30–7.29 (m, 1H, ArH), 7.19 (d, J = 8.4 Hz, 2H, ArH), 7.11–7.10 (m, 2H, ArH), 6.92–6.91 (m, 2H, ArH, CH), 4.88 (d, J = 11.9 Hz, 1H, CH), 4.56–4.52 (m, 1H, CH), 4.38–4.33 (m, 1H, CH), 1.69–1.58 (m, 2H, CH), 0.85–0.72 (m, 2H, CH), 0.49 (t, J = 7.2 Hz, 3H, CH₃). ¹³C NMR (100 MHz, DMSO-d₆) δ: 188.9, 188.8, 181.2, 147.7, 145.3, 142.2, 141.5, 140.2, 131.3, 131.1, 131.0, 130.9, 129.9, 129.5, 129.4, 128.4, 128.4, 127.3, 127.0, 124.0, 117.0, 114.3, 114.1, 105.5, 102.1, 96.2, 62.2, 47.2, 45.3, 30.7, 19.1, 13.5; IR (KBr) ν: 3055, 2958, 2870, 1608, 1531, 1427, 1345, 1258, 1189, 1099, 1015, 963, 862, 817, 733 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₄H₂₉ClN₃O₄ ([M + H]⁺): 578.1841. Found: 578.1849.

2-(2-(1-Butyl-1H-benzo[d]imidazol-3-ium-3-yl)-3-ethoxy-3-oxo-1-(p-tolyl)propyl)-1,3-dioxo-2,3-dihydro-1H-inden-2-ide (2c). Yellow solid, 65%, mp 175–177 °C; ¹H NMR (600 MHz, DMSO-d₆) δ: 10.30 (s, 1H, CH), 7.99–7.98 (m, 2H, ArH), 7.72–7.63 (m, 2H, ArH), 7.38 (s, 2H, ArH), 7.18 (s, 2H, ArH), 7.04 (s, 2H, ArH), 6.84–6.82 (m, 1H, CH), 6.76 (s, 2H, ArH), 4.78–4.76 (m, 1H, CH), 4.45–4.44 (m, 2H, CH), 4.08–3.93 (m, 2H, CH), 2.02 (s, 3H, CH₃), 1.70–1.69 (m, 2H, CH), 0.89–0.82 (m, 8H, CH). ¹³C NMR (150 MHz, DMSO-d₆) δ: 188.3, 188.0, 168.4, 142.9, 140.5, 138.8, 135.5, 130.9, 130.3, 129.2, 128.8, 128.6, 128.0, 126.8, 126.7, 126.5, 116.4, 113.7, 101.1, 61.7, 61.6, 61.5, 46.6, 46.5, 42.9, 30.4, 20.6, 18.6, 13.3, 13.1; IR (KBr) ν: 3027, 2960, 1734, 1609, 1535, 1426, 1318, 1199, 1030, 826, 733 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₂H₃₃N₂O₄ ([M + H]⁺): 509.2435. Found: 509.2452.

2-(2-(1-Butyl-1H-benzo[d]imidazol-3-ium-3-yl)-3-ethoxy-1-(4-methoxyphenyl)-3-oxopropyl)-1,3-dioxo-2,3-dihydro-1H-inden-2-ide (2d). Yellow solid, 70%, mp 170–172 °C; ¹H NMR (600 MHz, DMSO-d₆) δ: 10.30 (s, 1H, CH), 7.99–7.96 (m, 2H, ArH), 7.73–7.70 (m, 1H, ArH), 7.65–7.62 (m, 1H, ArH), 7.43 (d, J = 7.8 Hz, 2H, ArH), 7.18–7.17 (m, 2H, ArH), 7.04–7.03 (m, 2H, ArH), 6.78 (d, J = 11.4 Hz, 1H, CH), 6.51 (d, J = 8.4 Hz, 2H, ArH), 4.74 (d, J = 11.4 Hz, 1H, CH), 4.46–4.44 (m, 2H, CH), 4.10–4.05 (m, 1H, CH), 3.95–3.90 (m, 1H, CH), 3.51 (s, 3H, OCH₃), 1.74–1.70 (m, 2H, CH), 0.96–0.87 (m, 5H, CH), 0.82 (t, J = 7.2 Hz, 3H, CH₃). ¹³C NMR (150 MHz, DMSO-d₆) δ: 188.2, 188.0, 168.4, 158.0, 157.3, 140.4, 139.8, 133.8, 129.7, 129.2, 128.7, 127.0, 126.7, 116.4, 113.8, 113.4, 113.0, 101.3, 61.5, 61.4, 55.0, 54.7, 46.5, 42.5, 30.3, 18.5, 13.4, 13.3, 13.1; IR (KBr) ν: 3020, 2962, 1737, 1610, 1538, 1429, 1250, 1191, 1031, 842, 736 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₂H₃₃N₂O₅ ([M + H]⁺): 525.2384. Found: 525.2391.

2-(2-(1-Butyl-1H-benzo[d]imidazol-3-ium-3-yl)-1-(4-chlorophenyl)-3-ethoxy-3-oxopropyl)-1,3-dioxo-2,3-dihydro-1H-inden-2-ide (2e). Yellow solid, 68%, mp 176–178 °C; ¹H NMR (600 MHz, DMSO-d₆) δ: 10.32 (s, 1H, CH), 8.00 (d, J = 8.4 Hz, 2H, ArH), 7.74–7.72 (m, 1H, ArH), 7.66–7.64 (m, 1H, ArH), 7.54 (d, J = 7.2 Hz, 2H, ArH), 7.20–7.19 (m, 2H, ArH), 7.06–7.02 (m, 4H, ArH), 6.82 (d, J = 11.4 Hz, 1H, CH), 4.83 (d, J = 11.4 Hz, 1H, CH), 4.46–4.44 (m, 2H, CH), 4.12–4.06 (m, 1H, CH), 3.96–3.91 (m, 1H, CH), 1.73–1.70 (m, 2H, CH), 0.90–0.88 (m, 4H, CH), 0.86–0.81 (m, 4H, CH). ¹³C NMR (150 MHz, DMSO-d₆) δ: 188.2, 188.0, 167.8, 142.6, 140.7, 140.3, 139.6, 130.5, 130.4, 129.9, 128.9, 128.0, 127.6, 127.1, 126.8, 116.6, 116.5, 113.8, 100.4, 61.6, 46.6, 42.6, 30.3, 18.6, 13.4, 13.3, 13.1; IR (KBr) ν: 3050, 2964, 2924, 1732, 1624, 1532, 1485, 1425, 1318, 1199, 1100, 867, 733 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₁H₃₀ClN₂O₄ ([M + H]⁺): 529.1889. Found: 529.1898.

5-(2-(1-Butyl-1H-benzo[d]imidazol-3-ium-3-yl)-3-(4-methoxyphenyl)-3-oxo-1-(p-tolyl)propyl)-2,2-dimethyl-4,6-dioxo-1,3-dioxan-5-ide (2f). White solid, 80%, mp 196–198 °C; ¹H NMR (400 MHz, DMSO-d₆) δ: A-conformation: 10.02 (s, 1H, CH), 8.08–8.04 (m, 1H, ArH), 7.94–7.89 (m, 2H, ArH), 7.82–7.80 (m, 1H, ArH), 7.68–7.62 (m, 2H, ArH), 7.60–7.56 (m, 1H, ArH), 7.38–7.36 (m, 2H, ArH, CH), 6.92 (d, J = 8.4 Hz, 2H, ArH), 6.87 (d, J = 7.7 Hz, 2H, ArH), 4.89–4.84 (m, 1H, CH), 4.65–4.54 (m, 1H, CH), 4.42 (brs, 1H, CH), 3.79 (s, 3H, OCH₃), 2.10 (s, 3H, CH₃), 1.86–1.78 (m, 1H, CH), 1.66–1.60 (m, 1H, CH), 1.28–1.22 (m, 1H, CH), 1.04 (brs, 4H, CH), 0.92–0.88 (m, 3H, CH₃), 0.75–0.72 (m, 1H, CH), 0.67–0.62 (m, 1H, CH); B-conformation: 10.28 (s, 1H, CH), 8.31 (d, J = 8.6 Hz, 2H, ArH), 8.20–8.18 (m, 1H, ArH), 7.08 (d, J = 8.4 Hz, 2H, ArH), 6.77 (d, J = 7.7 Hz, 2H, ArH), 5.01 (d, J = 11.8 Hz, 1H, CH), 3.87 (s, 3H, OCH₃), 2.05 (s, 3H, CH₃), 1.18–1.17 (m, 2H, CH). ¹³C NMR (100 MHz, DMSO-d₆) δ: 193.7, 165.0, 164.4, 164.1, 163.7, 142.7, 139.1, 134.9, 134.2, 131.4, 131.1, 131.0, 130.7, 130.2, 128.5, 128.1, 127.7, 126.9, 126.5, 126.4, 126.3, 113.9, 113.6, 113.4, 99.0, 72.5, 72.0, 55.5, 55.5, 46.4, 46.2, 45.6, 30.6, 30.1, 25.3, 25.1, 20.3, 18.7, 18.2, 13.2, 13.0; IR (KBr) ν: 2957, 1673, 1599, 1511, 1434, 1382, 1319, 1260, 1170, 1104, 1030, 920, 757 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₄H₃₇N₂O₆ ([M + H]⁺): 569.2646. Found: 569.2644.

5-(2-(1-Butyl-1H-benzo[d]imidazol-3-ium-3-yl)-3-(4-methoxyphenyl)-3-oxo-1-(p-tolyl)propyl)-2,4,6-trioxohexahydropyrimidin-5-ide (2g). White solid, 91%, mp 205–207 °C; ¹H NMR (400 MHz, DMSO-d₆) δ: A-conformation: 9.86 (s, 1H, CH), 9.00 (s, 2H, NH), 8.11–8.08 (m, 1H, ArH), 8.05–8.01 (m, 2H, ArH), 7.94–7.90 (m, 2H, ArH), 7.69–7.65 (m, 1H, ArH), 7.61–7.58 (m, 1H, ArH), 7.45–7.43 (m, 2H, ArH, CH), 6.93 (d, J = 8.6 Hz, 2H, ArH), 6.86 (d, J = 7.9 Hz, 2H, ArH), 5.02 (d, J = 11.3 Hz, 1H, CH), 4.62–4.55 (m, 1H, CH), 4.45–4.40 (m, 1H, CH), 3.80 (s, 3H, OCH₃), 2.10 (s, 3H, CH₃), 1.82–1.78 (m, 2H, CH), 1.18–1.04 (m, 2H, CH), 0.88–0.84 (m, 3H, CH₃); B-conformation: 10.28 (s, 1H, CH), 8.27 (d, J = 8.8 Hz, 2H, ArH), 8.16–8.13 (m, 1H, ArH), 7.00 (d, J = 8.6 Hz, 2H, ArH), 5.17 (d, J = 11.6 Hz, 1H, CH), 3.82 (s, 3H, OCH₃), 2.05 (s, 3H, CH₃), 1.65–1.61 (m, 2H, CH), 0.76–0.73 (m, 3H, CH₃). ¹³C NMR (100 MHz, DMSO-d₆) δ: 164.5, 163.8, 151.7, 151.5, 135.0, 134.4, 131.2, 131.0, 130.1, 128.9, 128.1, 128.0, 127.9, 127.9, 127.8, 126.6, 126.3, 122.1, 121.2, 119.3, 114.0, 113.8, 113.6, 110.3, 83.1, 55.6, 55.5, 30.4, 20.5, 20.4, 19.3, 18.6, 18.3, 13.2, 13.1; IR (KBr) ν: 2958, 1685, 1574, 1455, 1389, 1244, 1174, 973, 847 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₂H₃₃N₄O₅ ([M + H]⁺): 553.2445. Found: 553.2454.

5-(2-(1-Butyl-1H-benzo[d]imidazol-3-ium-3-yl)-3-(4-methoxyphenyl)-3-oxo-1-(p-tolyl)propyl)-1,3-dimethyl-2,4,6-trioxohexahydropyrimidin-5-ide (2h). Yellow solid, 95%, mp 178–180 °C; ¹H NMR (400 MHz, DMSO-d₆) δ: A-conformation: 9.86 (s, 1H, CH), 8.18–8.16 (m, 1H, ArH), 8.07–8.04 (m, 2H, ArH), 8.00–7.94 (m, 2H, ArH), 7.71–7.66 (m, 1H, ArH), 7.62–7.59 (m, 1H, ArH), 7.44–7.39 (m, 2H, ArH, CH), 6.95 (d, J = 8.6 Hz, 2H, ArH), 6.86 (d, J = 7.6 Hz, 2H, ArH), 5.16 (d, J = 11.4 Hz, 1H, CH), 4.62–4.52 (m, 1H, CH), 4.47–4.42 (m, 1H, CH), 3.80 (s, 3H, OCH₃), 3.13–3.06 (m, 6H, 2CH₃), 2.09 (s, 3H, CH₃), 1.80–1.71 (m, 2H, CH), 1.06–0.93 (m, 2H, CH), 0.82–0.79 (m, 3H, CH₃); A-conformation: δ: 10.26 (s, 1H, CH), 8.23–8.21 (m, 1H, ArH), 8.11–8.09 (m, 1H, ArH), 7.82–7.80 (m, 1H, ArH), 7.00 (d, J = 8.6 Hz, 2H, ArH), 6.75 (d, J = 7.6 Hz, 2H, ArH), 5.25 (d, J = 11.4 Hz, 1H, CH), 3.83 (s, 3H, OCH₃), 2.04 (s, 3H, CH₃), 1.64–1.60 (m, 2H, CH), 0.74–0.71 (m, 3H, CH₃). ¹³C NMR (100 MHz, DMSO-d₆) δ: 193.7, 163.9, 162.1, 161.6, 152.3, 152.2, 142.9, 142.5, 138.4, 135.0, 134.4, 131.3, 130.9, 130.8, 130.0, 128.7, 128.1, 128.0, 127.8, 126.4, 126.3, 114.0, 113.5, 83.5, 55.6, 46.3, 45.5, 30.3, 30.2, 26.7, 20.4, 18.4, 18.2, 13.2, 13.1; IR (KBr) ν: 2938, 2744, 2676, 1668, 1581, 1435, 1383, 1315, 1268, 1163, 1031, 915, 845, 752 cm⁻¹; MS (m/z): HRMS (ESI) calcd for C₃₄H₃₇N₄O₅ ([M + H]⁺): 581.2758. Found: 581.2765.

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (Grant No. 21272200) and the Priority Academic Program Development of Jiangsu Higher Education Institutions. We also thank the Analysis and Test Center of Yangzhou University providing instruments for analysis.

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Footnote

† Electronic supplementary information (ESI) available: ¹H and ¹³C NMR spectra for all new compounds are available. CCDC 1a (1488215), 1c (1488216), 1j (1488217) and 2e (1488218). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6ra16838h

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