Mesoporous Ionically Tagged Cross-Linked Poly(vinyl imidazole)s as Novel and Reusable Catalysts for the Preparation of N-Heterocycle Spiropyrans.

Herein, two novel mesoporous cross-linked poly(vinyl imidazole)s with sulfonic acid tags, [PVI-SO3H]Cl (1) and [PVI-SO3H]FeCl4 (2), were prepared and characterized by a variety of techniques such as Fourier transform infrared spectroscopy, scanning electron microscopy, elemental mapping, energy dispersive X-ray analysis, transmission electron microscopy, thermal gravimetry, derivative thermal gravimetry, and N2 adsorption-desorption isotherms (Brunauer-Emmett-Teller). In addition, magnetic properties of poly(vinyl imidazole) sulfonic acid iron(IV) chloride [PVI-SO3H]FeCl4 (2) as an ionically tagged magnetic polymer were investigated using a vibrating sample magnetometer. The presented polymers, [PVI-SO3H]Cl (1) and [PVI-SO3H]FeCl4 (2), were successfully applied as reusable and efficient catalysts for the preparation of N-heterocycle spiropyrans. The described catalysts were recycled and reused with a marginal decrease in their catalytic activities. The desired products were prepared under mild and green conditions. The structures of the obtained products were confirmed by various analysis techniques.

Introduction

Polymers and biopolymers represent an attractive research field for academic and industrial processes. Polymers including cations such as imidazolium, pyrrolidonium, and pyridinium and anions such as tetrafluoroborate, hexafluorophosphate, and triflates are called polymeric ionic liquids (PILs).[1−3] In recent years, polymeric ionic liquids (PILs) have become valuable materials because of their applications such as in catalysis, biotechnology, materials science, analytical chemistry, desulfurization of fuels (as extactants), and energy and environmental applications.[4−6] Without any doubt, one of the main applications of polymers and biopolymers as catalysts has advantages due to their nanoporous structures, high surface area, and thermal stability.[7] As a result of the great development made in this field, nanomagnetic properties of polymeric ionic liquids (PILs) can be modified via a task-specific choice of suitable linkers. Recently, an anion-exchange method has been used as a fantastic procedure for the development of ionic liquids (ILs) or molten salts (MSs). Ionic liquids which have the potential for designing and synthesis of various ILs and MSs are those functionalized with N-sulfonic acid(s).[8] To the best of our knowledge, ILs and MSs are designable because by applying the ion-exchange method, we can prepare ILs and MSs with excellent diversity and physical and chemical properties.[9−12] Mesoporous polymer frameworks have been used as catalysts and for gas storage and separation purposes.[13] Hamaguchi and other research groups reported magnetic ionic liquids, which are easily extruded from the reaction mixture using a magnet.[14−16] A variety of materials have been used for the design and synthesis of catalysts, which have revealed various catalytic and chemical properties. These materials as dual-role catalysts with both Brønsted and Lewis acidic properties have high catalytic abilities.[17−21]

Molecules with indole and uracil moieties are of great interest due to their biological and pharmacological activities.[22,23] Spiropyrans have also attracted much attention because of their application within perovskite solar cells[19] and pharmacological properties, e.g., as inhibitors of the human NK-1 receptor and antitumoral, antimicrobial, and antibiotic agents.[20] Moreover, polyhydroquinoline and/or 1,4-dihydropyridine structures are the building blocks of many natural, medicinal, and pharmacological molecular structures.[24−26] For example, antimalarial, spirotryprosatin B aspergillus fumigatus and horsfilline are examples of natural products that have the above-said moieties within their structures (Figure ). Lately, several methods and catalysts such as PEG-OSO3H,[27] SBA-15-PhSO3H,[28] Ag NPs,[29] MSAIL,[30]p-TSA,[31] organometallics (zinc, copper, palladium, scandium, iridium, nickel, gold, silver, and rhodium catalyzed), organocatalysts,[32] Fe2O3@SiO2@vitB1-Np,[33] and rhodium[34] have been reported for the synthesis of spiropyrans. The above-mentioned reported methodologies suffer from some disadvantages such as long reaction time, low yield, nonrecoverable catalysts, etc.

Figure 1

Structure of antimalarial, spirotryprosatin B aspergillus fumigatus and horsfilline in natural products.

Recently, we have reported a wide range of imidazolium- and pyridinium-based ILs and MSs functionalized with N-sulfonic acid tags for preparing heterocyclic compounds, energetic materials, and nitro compounds.[35−40] As a continuation of our previous investigation on the synthesis and applications of organic salts (ILs and MSs), herein, the synthesis of two novel nano-heterogeneous cross-linked and mesoporous ionically tagged polymers [PVI-SO3H]Cl (1) and [PVI-SO3H]FeCl4 (2) are reported (Scheme ). The synthesized polymers were fully characterized by Fourier transform infrared (FT-IR) spectroscopy, thermal gravimetry (TG), derivative thermal gravimetry (DTG), energy dispersive X-ray analysis (EDX), SEM-elemental mapping, scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption–desorption isotherm (Brunauer–Emmett–Teller, BET), and vibrating sample magnetometer (VSM). Both [PVI-SO3H]Cl (1) and [PVI-SO3H]FeCl4 (2) were successfully used as catalysts for producing a range of N-heterocycle spiropyrans via a multicomponent reaction of various carbonyl compounds (A), amino compounds (B), and nucleophilic compounds (C) under refluxing water conditions (Scheme ).

Scheme 1

Structure of [PVI-SO3H]Cl (1) and [PVI-SO3H]FeCl4 (2)

Scheme 2

Preparation of N-Heterocycle Spiropyrans Using Novel Ionically Tagged Polymers [PVI-SO3H]Cl (1) and [PVI-SO3H]FeCl4 (2)

Results and Discussion

Organic and inorganic resins are attractive beds for supporting activators and promoters for preparing heterogeneous catalysts and/or reagents. We have used silica and silica-coated F3O4 for this purpose in the present decade. Among our reported catalysts and/or reagents, silica sulfuric acid as a multipurpose catalyst has been extensively used.[41,42] Herein, we decided to synthesis an organic polymer with sulfonic acid tags. With this aim, initially, we synthesized poly(vinyl imidazole) (PVI) via a reaction of 1-vinyl-1H-imidazole and ethylene glycol dimethacrylate (EDGMA) according to the reported procedure with a slight modification. Then, poly(vinyl imidazole) sulfonic acid chloride [PVI-SO3H]Cl (1) and poly(vinyl imidazole) sulfonic acid iron(IV) chloride [PVI-SO3H]FeCl4 (2) were prepared as ionically tagged polymers in two steps by an anion-exchange method. We designed and synthesized [PVI-SO3H]FeCl4 (2) as a dual-role catalyst due to the presence of Lewis and Brønsted acidic tags within the structure of the polymer. The mentioned polymers, [PVI-SO3H]Cl (1) and [PVI-SO3H]FeCl4 (2), were fully characterized by applying FT-IR spectroscopy, XRD, TG, DTG, EDX analysis, VSM, SEM, and TEM analysis (Scheme ).

Scheme 3

Preparation of Poly(vinyl imidazole) Sulfonic Acid Chloride [PVI-SO3H]Cl (1) and [PVI-SO3H]FeCl4 (2)

The FT-IR spectra of poly(vinyl imidazole) (PVI) and ionically tagged polymers [PVI-SO3H]Cl (1) and [PVI-SO3H]FeCl4 (2) are compared in Figure . The FT-IR spectrum of [PVI-SO3H]Cl (1) and [PVI-SO3H]FeCl4 (2) showed a broad peak of O–H stretching related to the SO3H group at 3000–3500 cm–1, and the peaks observed at 1201–1056 cm–1 were attributed to stretching O–S and N–S, respectively.[43,44] Furthermore, the peak at 1740 cm–1 was related to the stretching C=O bond (Figure ).

Figure 2

FT-IR spectrum of poly(vinyl imidazole) (PVI) and ionically tagged polymers [PVI-SO3H]Cl (1) and [PVI-SO3H]FeCl4 (2).

The elements in the structure of poly(vinyl imidazole) (PVI), [PVI-SO3H]Cl (1), and [PVI-SO3H]FeCl4 (2) were studied by energy dispersive X-ray (EDX) analysis (Figure ). The obtained results were approved due to the presence of expected elements such as carbon, nitrogen, oxygen, sulfur, and chlorine for [PVI-SO3H]Cl (1) and carbon, nitrogen, oxygen, sulfur, chlorine, and iron for [PVI-SO3H]FeCl4 (2) in comparison with carbon, nitrogen, and oxygen in poly(vinyl imidazole) (PVI). Then, SEM-elemental mapping of [PVI-SO3H]Cl (1) (C, N, O, S, and Cl) and [PVI-SO3H]FeCl4 (2) (C, N, O, S, Cl, and Fe) in the desired polymeric catalysts verified well-dispersed elements over the catalyst surface (Figure ).

Figure 3

Energy dispersive X-ray (EDX) analysis of poly(vinyl imidazole) (PVI), [PVI-SO3H]Cl (1), and [PVI-SO3H]FeCl4 (2).

Figure 4

Elemental mapping of C (yellow), O (red), N (blue), Cl (blue), and S (orange) atoms for [PVI-SO3H]Cl (1) and C (red), N (orange), O (yellow), S (violet), Cl (blue), and Fe (green) atoms for [PVI-SO3H]FeCl4 (2).

The scanning electron microscopy (SEM) micrographs of [PVI-SO3H]Cl (1) and [PVI-SO3H]FeCl4 (2) were also studied. As shown in Figures and 6, particles of the catalysts are in the nanoscale which are in a good agreement and are not completely agglomerated.

Figure 5

Scanning electron microscopy (SEM) micrographs of [PVI-SO3H]Cl (1).

Figure 6

Scanning electron microscopy (SEM) micrographs of [PVI-SO3H]FeCl4 (2).

To investigate the structure of poly(vinyl imidazole) sulfonic acid chloride [PVI-SO3H]Cl (1), transmission electron microscopy (TEM) is an efficient technique, which could provide information about the size and morphology of particles. The TEM images of the catalysts were shown to match well with those of the nanostructured cross-linked polymers. Based on these images, the average size of channels is mainly around 50 nm (Figure ).

Figure 7

Transmission electron microscopy (TEM) micrographs of [PVI-SO3H]Cl (1).

In another investigation, magnetic properties of poly(vinyl imidazole) sulfonic acid iron(IV) chloride [PVI-SO3H]FeCl4 (2) were investigated at room temperature using a vibrating sample magnetometer (VSM), as shown in Figure . Based on the magnetization curves, the saturation of the obtained catalyst dropped from 3.2 emu/g. Therefore, it has weak magnetic properties.

Figure 8

Vibrating sample magnetometer (VSM) test results of [PVI-SO3H]FeCl4 (2).

Nitrogen adsorption–desorption isotherms for poly(vinyl imidazole) (PVI) and its sulfonate form [PVI-SO3H]Cl (1) are presented in Figure . Both adsorption isotherms are type III, indicating a weak interaction of N2 with the samples for both systems. Hysteresis loops were observed, which indicate the presence of mesopores. The pore size distribution of both samples is presented in Figure . Pore sizes are mainly between 1 and 50 nm for PVI and 10 and 30 nm for [PVI- SO3H]Cl (1), indicating that most of the pores are mesopores and by sulfonation the pore size range decreased. The mean pore diameter for PVI is 20.6 nm and for [PVI-SO3H]Cl (1) is 11.0 nm. The obtained total pore volumes of PVI and [PVI-SO3H]Cl (1) are 0.2102 and 0.0048 cm3/g, respectively. Calculated BET surface areas for PVI and [PVI-SO3H]Cl (1) are 40.3 and 1.8 m2/g, respectively. All of the structural data obtained based on N2 adsorption–desorption indicate that by sulfonation of PVI most of its pores were blocked, and therefore, the total pore volume and also the surface area decreased.

Figure 9

Nitrogen adsorption–desorption isotherm (BET) (a) and Barrett–Joyner–Halenda (BJH) (b) of poly(vinyl imidazole) (PVI) and [PVI-SO3H]Cl (1).

In another investigation, thermal and behavioral stability of ionically tagged polymers [PVI-SO3H]Cl (1) was studied using thermal gravimetry (TG), derivative thermal gravimetry (DTG), and differential thermal analysis (DTA) (Figure ). The first step is the weight loss, happening between 25 and 100 °C, associated with the removal of possible solvents (organic and water) used in the course of preparation of target catalysts. The main stage of weight loss was related to SO3H release due to the breaking of the N–S bond structure of [PVI-SO3H]Cl (1) and [PVI-SO3H]FeCl4 (2). Therefore, degradation of the structures of [PVI-SO3H]Cl (1) and [PVI-SO3H]FeCl4 (2) happened after 350 °C and gave rise to about 50% weight loss. Thus, these catalysts can be used up to 350 °C.

Figure 10

Thermal gravimetric (TG) and differential thermal gravimetric (DTG) profiles of [PVI-SO3H]Cl (1) and [PVI-SO3H]FeCl4 (2).

After the synthesis and characterization of [PVI-SO3H]FeCl4 (2) and [PVI-SO3H]Cl (1) as catalysts, they were used for the synthesis of N-heterocycle spiropyrans. The mentioned N-heterocycle spiropyran derivatives were synthesized via the one-pot reaction of carbonyl compounds A (isatin derivatives, acenaphthylene-1,2-dione, or 11H-indeno[1,2-b]quinoxalin-11-one) (1 mmol), compounds B (uracil derivatives, 3-methyl-1-phenyl-1H-pyrazol-5-amine, or benzamide) (1 mmol), and compounds C (dimedone, 3-(1H-indol-3-yl)-3-oxopropanenitrile, or phenol) (1 mmol) in the presence of [PVI-SO3H]Cl (1) or [PVI-SO3H]FeCl4 (2) separately. The condensation of 2,6-diaminopyrimidin-4(3H)-one (1 mmol, 0.126 g), isatin (1 mmol, 0.147 g), and dimedone (1 mmol, 0.14 g) was selected as the model reaction to optimize the reaction conditions. As shown in Table , noteworthy results were obtained when the reaction was conducted in the presence of 0.01 g of 1 or 2 (Table , entry 1). No improvement was detected in the yield of reaction using different amounts of the catalyst and temperature (Table entries 2–7). Table clearly shows that in the absence of the catalyst the product was produced in a low yield (entry 8). To investigate the solvent effect on the reaction improvement, several solvents such as dimethylformamide (DMF), EtOH, CH2Cl2, EtOAc, CH3CN, n-hexane, CHCl3, toluene, and MeOH (10 mL) and solvent free conditions were tested and compared with H2O in the presence of 0.01 g of 1 or 2 (Table , entries 9–18). The results are summarized in Table .

Table 1

Effect of Different Amounts of catalysts, Temperature and Solvent (5 mL) in the Synthesis of N-Heterocycle Spiropyrana

	catalyst (g)				time (h)		yield (%)
entry	1	2	temp. (°C)	solvent	A*	B*	A*	B*
1	0.01	0.01	reflux	H2O	4	4	90	90
2	0.01	0.01	70	H2O	4	4	80	80
3	0.01	0.01	50	H2O	6	6	50	50
4	0.01	0.01	rt	H2O	10	10	20	20
5	0.015	0.015	reflux	H2O	4	4	90	90
6	0.02	0.02	reflux	H2O	4	4	90	90
7	0.005	0.005	reflux	H2O	8	8	40	40
8			100	H2O	8	8	20	20
9	0.01	0.01	reflux	DMF	4	4	85	85
10	0.01	0.01	reflux	EtOH	8	8	35	35
11	0.01	0.01	reflux	CH2Cl2	8	8
12	0.01	0.01	reflux	EtOAc	8	8
13	0.01	0.01	reflux	CH3CN	8	8	25	25
14	0.01	0.01	reflux	n-hexane	8	8
15	0.01	0.01	reflux	CHCl3	8	8
16	0.01	0.01	reflux	toluene	8	8	10	10
17	0.01	0.01	reflux	MeOH	8	8	25	25
18	0.01	0.01	100		10	10

Reaction conditions: 2,6-diaminopyrimidin-4(3H)-one (1 mmol, 0.126 g), isatin (1 mmol, 0.147 g) and dimedone (1 mmol, 0.14 g). 1: [PVI-SO3H]Cl; 2: [PVI-SO3H]FeCl4.

As a continuation of our investigations on the use of [PVI-SO3H]FeCl4 (2) and [PVI-SO3H]Cl (1), the efficiency and applicability were studied by the reaction of carbonyl compounds A (isatin derivatives, acenaphthylene-1,2-dione, or 11H-indeno[1,2-b]quinoxalin-11-one) (1 mmol), compounds B (uracil derivatives, 3-methyl-1-phenyl-1H-pyrazol-5-amine, or benzamide) (1 mmol), and compounds C (dimedone, 3-(1H-indol-3-yl)-3-oxopropanenitrile or phenol) (1 mmol). As exposed in Table , the results show that this method is suitable for the synthesis of N-heterocycle spiropyran derivatives such as spiro[indoline-3,5′-pyrimido[4,5-b]quinoline]-triones (1a–17a), 6′-(1H-indol-3-yl)-3′-methyl-2-oxo-1′-phenyl-1′,7′-dihydrospiro[indoline-3,4′-pyrazolo[3,4-b]pyridine]-5′-carbonitrile (1b–2b), and N-(3-(5-chloro-2-hydroxyphenyl)-2-oxoindolin-3-yl)benzamide (1c–2c) in high to excellent yields (40–92%) with in relatively short reaction times (1–5 h).

Table 2

Synthesis of N-Heterocycle Spiropyran Derivatives Using [PVI-SO3H]FeCl4 (2) or [PVI-SO3H]Cl (1) at 90 °C

The efficiency of the described catalysts, [PVI-SO3H]FeCl4 (2) and [PVI-SO3H]Cl (1), was compared for the synthesis of 2′-amino-8′,8′-dimethyl-8′,9′-dihydro-3′H-spiro[indoline-3,5′-pyrimido[4,5-b]quinoline]-2,4′,6′(7′H,10′H)-trione by the reaction of 2,6-diaminopyrimidin-4(3H)-one (1 mmol, 0.126 g), isatin (1 mmol, 0.147 g), and dimedone (1 mmol, 0.14 g) under the above-mentioned optimized reaction conditions. Various organic and inorganic acid catalysts were also tested for the above-said reaction (Table ). The individual role of Brønsted (SO3H) and Lewis (Fe3+) acidic sites was also studied on a model reaction in percent of PVI + FeCl3, PVI, and FeCl3, respectively (entries 18–20, Table ). The applied PVI+FeCl3, PVI, and FeCl3 as catalysts could not be recycled and gave the products with low yield and high reaction times.[45,46] As Table indicates, [PVI-SO3H]FeCl4 (2) and [PVI-SO3H]Cl (1) are the best choice for the synthesis of N-heterocycle spiropyran derivatives due to the shorter reaction times, higher yields, and lowest amounts of the applied catalyst.

Table 3

Synthesis of 1a in the Presence of Various Catalysts under Solvent-Free Conditions at 90 °C

entry	catalyst	(mol %)	time (h)	yield (%)a
1	APVPB[7a]	10 mg	8	58
2	Fe3O4	10 mg	10
3	NH4NO3	10	10
4	CF3SO3H	10	10	trace
5	Al(HSO4)3	10	10
6	NaHSO4	10	10
7	H3[p(W3O10)4]·XH2O	10	10
8	Mg(NO3)2·6H2O	10	10
9	Zn(NO3)2·6H2O	10	10
10	p-TSA	10	10	trace
11	SSA[41,42]	10 mg	10	20
12	SBA-15/(CH2)3N(CH2PO3H2)(CH2)2-N(CH2PO3H2)2[47]	10 mg	5	66
13	trichloroisocyanuric acid	10	10
14	Et3N	20	10
15	[PVI-SO3H]Cl	10 mg	4	90
16	MIL-100(Cr)/NHEtN(CH2PO3H2)2[48]	10 mg	4	80
17	[PVI-SO3H]FeCl4	10 mg	2	92
18	PVI + FeCl3	5 mg + 5 mol %	5	30 and without recycling
19	PVI	10 mg	5	25 and without recycling
20	FeCl3	10	10

Isolated yields.

The proposed mechanism for the synthesis of N-heterocycle spiropyrans is indicated in Scheme . First, the acidic groups (SO3H) of [PVI-SO3H]FeCl4 (2) or [PVI-SO3H]Cl (1) activate the carbonyl group of isatin, and 1,3-dicarbonyl compounds (C) are enolized. Then, the reaction of 1,3-dicarbonyl compounds (C) with isatin leads to a removal of one molecule of H2O to give intermediate I. In the next step, compound B as a nucleophile attacks intermediate (I), which acts as a Michael acceptor, to give II. Finally, the cyclocondensation reaction of II affords III, which is converted into the corresponding N-heterocycle spiropyran derivatives.

Scheme 4

Suggested Mechanism for the Synthesis of N-Heterocycle Spiropyrans Catalyzed by 1 and 2

According to the results in Figure , the recyclability and reuse of the presented catalysts [PVI-SO3H]FeCl4 (2) and [PVI-SO3H]Cl (1) were also studied on a model reaction of 2,6-diaminopyrimidin-4(3H)-one (1 mmol, 0.126 g), isatin (1 mmol, 0.147 g), and dimedone (1 mmol, 0.14 g) under the above-mentioned optimized reaction conditions. The applied [PVI-SO3H]FeCl4 (2) and [PVI-SO3H]Cl (1) could be recycled (see the Experimental Section for details) and efficiently reused up to five and six reaction cycles with a marginal decrease in their catalytic activities. [PVI-SO3H]FeCl4 (2) and [PVI-SO3H]Cl (1) were also characterized by FT-IR spectroscopy (Figure ) and scanning electron microscopy (SEM) (Figures and 14) after their application in the model reaction. The spectra were the same as those of the fresh catalyst.

Figure 11

Recyclability of [PVI-SO3H]FeCl4 (2) and [PVI-SO3H]Cl (1) as catalysts in the synthesis of 1a under refluxing H2O.

Figure 12

FT-IR spectra of reused [PVI-SO3H]FeCl4 and [PVI-SO3H]Cl.

Figure 13

SEM micrographs of reused [PVI-SO3H]Cl.

Figure 14

SEM micrographs of reused [PVI-SO3H]FeCl4.

Conclusions

In conclusion, novel nanostructured and cross-linked poly(vinyl imidazole)s with sulfonic acid tags [PVI-SO3H]Cl (1) and [PVI-SO3H]FeCl4 (2) were synthesized. The synthesized [PVI-SO3H]FeCl4 (2) acts as a dual-role catalyst due to the presence of Lewis and Brønsted acidic tags (SO3H and Fe3+ moieties) within the structure of the polymer. The structures of the mentioned polymers were fully characterized by using various techniques. These catalysts were successfully applied in the multicomponent synthesis of target N-heterocycle spiropyrans by a condensation reaction of their corresponding reactants. Short reaction times, a clean reaction profile, recyclability of catalysts, and mild and green reaction conditions are the major advantages of the described methodology.

Experimental Section

Materials and Apparatus

All of the chemicals were purchased from Merck Chemical Company. The known products were identified by comparison of their melting points and spectral data with those reported in the literature. The progress of the reactions was monitored by TLC using silica gel SIL G/UV 254 plates. Melting points were recorded on a Büchi B-545 apparatus in open capillary tubes. Fourier transform infrared (FT-IR) spectra of the derivatives and catalysts were recorded on an FT-IR spectrometer (PerkinElmer Spectrum 65 or JASCO FT/IR4100LE) using KBr disks. The 1H NMR (400 MHz) and 13C NMR (101 MHz) experiments were run on BRUKER BioSpin GmbH spectrometers (δ in ppm). The scanning electron microscopy (SEM) study was performed using a MIRA3 TESCAN. Thermogravimetric analyses were carried out on a TA (models Q600) under a nitrogen atmosphere at 25 °C and a heating rate of 20 °C/min up to 700 °C. Transmission electron microscopy (TEM) images were obtained using an Agar Scientific. The Brunauer–Emmett–Teller (BET) method was used to calculate the specific surface areas (SBET). By using the BELSORP MINI II (BJH) model, the pore volumes and pore size distributions were derived from the adsorption branches of isotherms.

Preparation of Poly(vinyl imidazole) (PVI)

In a 25 mL round-bottom flask, a mixture of 1-vinyl-1H-imidazole (11 mmol, 1.034 g, 1 mL), ethylene glycol dimethacrylate (EDGMA) (15 mmol, 2.97 g, 3 mL), and azobisisobutyronitrile (0.18 mmol, 30 mg) with H2O (20 mL) as the solvent was stirred for 4 h under reflux conditions.[49,50] Afterward, the residue was washed with H2O (2 × 15 mL) and dried under powerful vacuum at 90 °C to give poly(vinyl imidazole) (PVI) as a white precipitate in 95% (9 g) yield (Scheme ).

Preparation of Poly(vinyl imidazole) Sulfonic Acid Chloride [PVI-SO3H]Cl (1)

In a 25 mL round-bottom flask, a mixture of poly(vinyl imidazole) (PVI) (1 mmol, 0.282 g) and chlorosulfonic acid (1 mmol, 0.067 mL) in dry CH2Cl2 at 0 °C was stirred for 2 h. Afterward, a white precipitate appeared, which was filtered and dried under vacuum to obtain [PVI-SO3H]Cl (2) (Scheme ).

Preparation of Poly(vinyl imidazole) Sulfonic Acid Iron(IV) Chloride [PVI-SO3H]FeCl4 (2)

In an oven, a mixture of poly(vinyl imidazole) sulfonic acid chloride [PVI-SO3H]Cl (1) (1 mmol, 0.398 g) and FeCl3 salt (1 mmol, 0.162 g) was placed at 60 °C for 2 h into a mortar and stirred with a pestle. After completion of the reaction, the reaction mixture was cooled to room temperature. Then, ethanol was used to purify the poly(vinyl imidazole) sulfonic acid iron(IV) chloride [PVI-SO3H]FeCl4 (2). The desired [PVI-SO3H]FeCl4 (2) was obtained with a yield of 94% (0.52 g) (Scheme ).

Preparation of N-Heterocycle Spiropyrans Using [PVI-SO3H]Cl (1) or [PVI-SO3H]FeCl4 (2)

In a 25 mL round-bottom flask, a mixture of carbonyl compounds A (isatin derivatives, acenaphthylene-1,2-dione, or 11H-indeno[1,2-b]quinoxalin-11-one) (1 mmol), compounds B (uracil derivatives, 3-methyl-1-phenyl-1H-pyrazol-5-amine, or benzamide) (1 mmol), compounds C (dimedone, 3-(1H-indol-3-yl)-3-oxopropanenitrile, or phenol) (1 mmol), [PVI-SO3H]Cl (1) or [PVI-SO3H]FeCl4 (2) (0.01 g), and H2O (10 mL) was added and fitted with a reflux condenser. The TLC technique was used for monitoring the progress and completion of the reaction, and the mixture was allowed to cool to room temperature. The solvent of the reaction mixture was removed by simple filtration. Then, the residue was extracted with PEG (10 mL), and the catalyst was recovered by centrifugation (2 × 1000 rpm). The desired products were washed with water/ethanol and collected by simple filtration (Scheme ).

Analysis Data of New Compounds

2′-Amino-8′,8′-dimethyl-8′,9′-dihydro-3′H-spiro[indoline-3,5′-pyrimido[4,5-b]quinoline]-2,4′,6′(7′H,10′H)-trione (1a)

Pale yellow solid; mp: >300 °C; R: (EtOAc/n-hexane 9:1) = 0.2; FT-IR (KBr, cm–1): 3416, 3268, 2926, 2855, 1697, 1646; 1H NMR (400 MHz, DMSO-d6) δppm: 9.97 (s, 1H), 9.48 (s, 1H), 8.57 (s, 1H), 7.03 (td, J = 7.6, 1.2 Hz, 1H), 6.96 (s, 1H), 6.84 (d, J = 6.9 Hz, 1H), 6.76 (t, J = 7.4 Hz, 1H), 6.65 (d, J = 7.6 Hz, 1H), 2.51 (s, 1H), 2.43 (d, J = 16.5 Hz, 1H), 2.15–2.09 (m, 1H), 1.92 (d, J = 15.9 Hz, 1H), 1.06 (s, 3H), 0.98 (s, 3H). 13C NMR (100 MHz, DMSO-d6) δppm: 192.6, 180.3, 166.1, 153.3, 151.8, 143.2, 126.4, 122.3, 120.1, 108.8, 107.5, 50.6, 40.2, 31.8, 28.5, 26.4.

2′-Amino-6-chloro-8′,8′-dimethyl-8′,9′-dihydro-3′H-spiro[indoline-3,5′-pyrimido[4,5-b]quinoline]-2,4′,6′(7′H,10′H)-trione (2a)

White solid; mp: >300 °C; R: (EtOAc/n-hexane 9:1) = 0.1; FT-IR (KBr, cm–1): 3431, 3273, 2963, 1703, 1644; 1H NMR (400 MHz, DMSO-d6) δppm: 10.36 (s, 1H), 10.16 (s, 1H), 9.61 (s, 1H), 7.09 (dd, J = 8.2, 2.2 Hz, 1H), 6.83 (d, J = 2.1 Hz, 1H), 6.67 (d, J = 8.2 Hz, 1H), 6.48 (s, 2H), 2.50 (d, J = 3.5 Hz, 2H), 2.11 (d, J = 16.0 Hz, 1H), 1.99 (d, J = 16.0 Hz, 1H), 1.05 (s, 3H), 1.00 (s, 3H). 13C NMR (100 MHz, DMSO-d6) δppm: 192.8, 180.0, 160.0, 154.2, 153.5, 152.3, 142.3, 138.8, 126.4, 124.0, 122.2, 108.8, 108.3, 91.0, 50.4, 31.8, 28.0, 26.8.

2′-Amino-6-methoxy-8′,8′-dimethyl-8′,9′-dihydro-3′H-spiro[indoline-3,5′-pyrimido[4,5-b]quinoline]-2,4′,6′(7′H,10′H)-trione (5a)

Beige solid; mp: >300 °C; R: (EtOAc/n-hexane 9:1) = 0.4; FT-IR (KBr, cm–1): 3523, 3418, 3140, 2955, 1696; 1H NMR (400 MHz, DMSO-d6) δppm: 10.35 (s, 1H), 9.84 (s, 1H), 9.52 (s, 1H), 6.62 (dd, J = 8.3, 2.5 Hz, 1H), 6.56 (d, J = 8.3 Hz, 1H), 6.43 (d, J = 2.4 Hz, 3H), 3.65 (s, 3H), 2.53 (d, J = 16.9 Hz, 1H), 2.43 (d, J = 16.9 Hz, 1H), 2.12 (d, J = 15.9 Hz, 1H), 1.94 (d, J = 15.9 Hz, 1H), 1.05 (s, 3H), 0.98 (s, 3H). 13C NMR (100 MHz, DMSO-d6) δppm: 192.7, 180.0, 160.0, 154.1, 154.0, 153.4, 151.8, 138.1, 136.9, 110.6, 109.8, 108.8, 107.6, 91.5, 55.1, 50.5, 48.9, 40.1, 31.8, 28.5, 26.3.

2′-Amino-4,6,8′,8′-tetramethyl-8′,9′-dihydro-3′H-spiro[indoline-3,5′-pyrimido[4,5-b]quinoline]-2,4′,6′(7′H,10′H)-trione (6a)

Beige solid; mp: >300 °C; R: (EtOAc/n-hexane 9:1) = 0.6; FT-IR (KBr, cm–1): 3418, 3272, 2957, 2732, 1692; 1H NMR (400 MHz, DMSO-d6) δppm: 10.26 (s, 1H), 9.93 (s, 1H), 9.49 (s, 1H), 6.66 (s, 1H), 6.48 (s, 1H), 6.42 (s, 2H), 2.52 (d, J = 17.0 Hz, 1H), 2.43 (d, J = 16.9 Hz, 1H), 2.18 (s, 3H), 2.15 (s, 3H), 2.10 (s, 1H), 1.93 (d, J = 15.9 Hz, 1H), 1.05 (s, 3H), 0.97 (s, 3H). 13C NMR (100 MHz, DMSO-d6) δppm: 192.7, 180.7, 159.9, 154.0, 153.3, 151.6, 139.3, 136.56, 128.6, 120.6, 116.0, 109.0, 91.8, 50.6, 48.6, 40.1, 31.8, 28.4, 26.4, 20.5, 16.3.

2′-Amino-8′,8′-dimethyl-8′,9′-dihydro-3′H-spiro[indeno[1,2-b]quinoxaline-11,5′-pyrimido[4,5-b]quinoline]-4′,6′(7′H,10′H)-dione (7a)

Gray solid; mp: >300 °C; R: (EtOAc/n-hexane 9:1) = 0.5; FT-IR (KBr, cm–1): 3448, 3285, 2957, 2926, 1645; 1H NMR (400 MHz, DMSO-d6) δppm: 10.57 (s, 1H), 9.77 (s, 1H), 8.12 (d, J = 7.9 Hz, 1H), 8.01 (d, J = 7.3 Hz, 1H), 7.93 (d, J = 7.8 Hz, 1H), 7.75 (t, J = 7.1 Hz, 1H), 7.69 (t, J = 7.1 Hz, 1H), 7.51 (t, J = 7.2 Hz, 1H), 7.42 (dd, J = 15.3, 7.5 Hz, 2H), 6.73 (s, 2H), 2.66 (d, J = 17.0 Hz, 1H), 2.52 (d, J = 17.1 Hz, 1H), 1.98 (d, J = 16.0 Hz, 1H), 1.76 (d, J = 16.0 Hz, 1H), 1.04 (s, 3H), 0.98 (s, 3H). 13C NMR (100 MHz, DMSO-d6) δppm: 192.6, 169.8, 156.6, 154.2, 153.8, 152.9, 140.7, 140.6, 137.0, 131.2, 128.4, 127.9, 127.6, 127.0, 123.9, 120.3, 109.8, 92.5, 79.1, 69.7, 50.3, 49.0, 40.1, 31.9, 28.6, 26.3.

2′-Amino-8′,8′-dimethyl-8′,9′-dihydro-2H,3′H-spiro[acenaphthylene-1,5′-pyrimido[4,5-b]quinoline]-2,4′,6′(7′H,10′H)-trione (8a)

Light brown solid; mp: >300 °C; R: (EtOAc/n-hexane 9:1) = 0.3; FT-IR (KBr, cm–1): 3377, 3135, 2962, 2871, 1662; 1H NMR (400 MHz, DMSO-d6) δppm: 9.88 (s, 1H), 8.86 (s, 1H), 8.18 (d, J = 6.7 Hz, 1H), 7.89 (d, J = 7.4 Hz, 1H), 7.75 (d, J = 8.2 Hz, 1H), 7.72–7.65 (m, 2H), 7.58 (t, J = 7.5 Hz, 1H), 6.51 (s, 2H), 2.47 (d, J = 17.5 Hz, 1H), 2.29 (d, J = 17.6 Hz, 1H), 2.23 (d, J = 15.7 Hz, 1H), 2.05 (d, J = 15.7 Hz, 1H), 1.06 (s, 3H), 0.84 (s, 3H). 13C NMR (100 MHz, DMSO-d6) δppm: 191.4, 174.3, 166.7, 157.5, 157.2, 143.2, 139.2, 135.9, 131.3, 128.5, 127.8, 125.4, 122.7, 122.2, 119.3, 116.2, 115.5, 89.6, 51.1, 37.0, 33.0, 27.8, 27.6.

8′,8′-Dimethyl-8′,9′-dihydro-1′H-spiro[indoline-3,5′-pyrimido[4,5-b]quinoline]-2,2′,4′,6′(3′H,7′H,10′H)-tetraone (9a)

Beige solid; mp: >300 °C; R: (EtOAc/n-hexane 9:1) = 0.4; FT-IR (KBr, cm–1): 3336, 3175, 3030, 2962, 1725; 1H NMR (400 MHz, DMSO-d6) δppm: 10.62 (s, 1H), 10.50 (s, 1H), 10.27 (s, 1H), 10.09 (s, 1H), 7.03 (t, 1H), 6.89 (d, J = 7.1 Hz, 1H), 6.77 (t, J = 7.3 Hz, 1H), 6.65 (d, J = 7.6 Hz, 1H), 2.56 (s, 1H), 2.42 (d, J = 16.8 Hz, 1H), 2.13 (d, J = 15.9 Hz, 1H), 1.94 (d, J = 15.9 Hz, 1H), 1.03 (s, 3H), 0.95 (s, 3H). 13C NMR (100 MHz, DMSO-d6) δppm: 193.2, 179.7, 165.7, 161.3, 153.5, 150.0, 149.8, 143.2, 136.0, 127.0, 122.5, 120.4, 110.1, 107.8, 89.3, 84.8, 50.5, 47.6, 31.9, 28.2, 26.4.

6-Chloro-8′,8′-dimethyl-8′,9′-dihydro-1′H-spiro[indoline-3,5′-pyrimido[4,5-b]quinoline]-2,2′,4′,6′(3′H,7′H,10′H)-tetraone (10a)

Beige solid; mp: >300 °C; R: (acetone/n-hexane 1:1) = 0.1; FT-IR (KBr, cm–1): 3276, 3181, 3078, 1727, 1663; 1H NMR (400 MHz, DMSO-d6) δppm: 10.77 (s, 1H), 10.31 (s, 1H), 9.10 (s, 1H), 7.12 (dd, J = 8.2, 1.9 Hz, 1H), 6.97 (d, J = 1.6 Hz, 1H), 6.70 (d, J = 8.2 Hz, 1H), 2.55–2.46 (m, 2H), 2.15 (d, J = 16.0 Hz, 1H), 2.04 (d, J = 16.0 Hz, 1H), 1.06 (s, 3H), 1.01 (s, 3H). 13C NMR (100 MHz, DMSO-d6) δppm: 193.4, 179.4, 165.7, 161.3, 153.5, 150.4, 149.8, 142.3, 137.8, 126.9, 124.3, 122.6, 109.7, 109.1, 88.8, 84.7, 50.4, 47.9, 40.1, 31.9, 27.8, 26.7.

4,6,8′,8′-Tetramethyl-8′,9′-dihydro-1′H-spiro[indoline-3,5′-pyrimido[4,5-b]quinoline]-2,2′,4′,6′(3′H,7′H,10′H)-tetraone (12a)

Beige solid; mp: >300 °C; R: (acetone/n-hexane 1:1) = 0.5; FT-IR (KBr, cm–1): 3428, 3245, 3177, 3055, 2929, 1717; 1H NMR (400 MHz, DMSO-d6) δppm: 10.55 (s, 1H), 10.02 (s, 1H), 6.69 (s, 1H), 6.56 (s, 1H), 2.61 (s, 1H), 2.55 (s, 1H), 2.44 (d, J = 16.8 Hz, 1H), 2.18 (d, J = 9.7 Hz, 6H), 1.97 (d, J = 15.9 Hz, 1H), 1.06 (s, 3H), 0.98 (s, 3H). 13C NMR (100 MHz, DMSO-d6) δppm: 193.0, 180.3, 161.4, 150.1, 139.3, 136.0, 128.9, 128.8, 120.7, 116.2, 110.0, 89.6, 50.6, 48.0, 40.1, 34.3, 31.9, 28.3, 26.4, 20.5, 16.3.

8′,8′-Dimethyl-8′,9′-dihydro-1′H-spiro[indeno[1,2-b]quinoxaline-11,5′-pyrimido[4,5-b]quinoline]-2′,4′,6′(3′H,7′H,10′H)-trione (13a)

Beige solid; mp: >300 °C; R: (acetone/n-hexane 1:1) = 0.2; FT-IR (KBr, cm–1): 3342, 3189, 2975, 1735; 1H NMR (400 MHz, DMSO-d6) δppm: 10.58 (s, 1H), 9.31 (s, 1H), 8.15 (dd, J = 8.1, 1.5 Hz, 1H), 8.05 (d, J = 7.3 Hz, 1H), 7.97 (dd, J = 8.0, 1.5 Hz, 1H), 7.79 (ddd, J = 8.3, 6.9, 1.6 Hz, 1H), 7.72 (td, J = 7.6, 6.9, 1.6 Hz, 1H), 7.59–7.53 (m, 1H), 7.53–7.46 (m, 2H), 2.73 (d, J = 17.0 Hz, 1H), 2.53 (s, 1H), 2.02 (d, J = 16.1 Hz, 1H), 1.84 (d, J = 16.1 Hz, 1H), 1.06 (s, 3H), 1.00 (s, 3H). 13C NMR (100 MHz, DMSO-d6) δppm: 193.2, 168.8, 165.7, 161.2, 156.4, 153.5, 153.2, 150.9, 149.7, 140.8, 140.5, 137.1, 131.3, 128.5, 128.2, 127.9, 127.5, 124.1, 120.5, 111.2, 90.3, 84.8, 50.3, 48.2, 40.2, 32.0, 28.3, 26.3.

1′,3′,8′,8′-Tetramethyl-8′,9′-dihydro-1′H-spiro[indoline-3,5′-pyrimido[4,5-b]quinoline]-2,2′,4′,6′(3′H,7′H,10′H)-tetraone (14a)

Beige solid; mp: >300 °C; R: (acetone/n-hexane 1:1) = 0.3; FT-IR (KBr, cm–1): 3391, 3187, 2965, 1708, 1667; 1H NMR (400 MHz, DMSO-d6) δppm: 10.07 (s, 1H), 7.59 (s, 1H), 7.06 (td, J = 7.6, 1.1 Hz, 1H), 6.94 (d, J = 7.1 Hz, 1H), 6.79 (t, J = 7.1 Hz, 1H), 6.69 (d, J = 7.6 Hz, 1H), 3.54 (s, 3H), 3.05 (s, 3H), 2.63 (s, 2H), 2.16 (d, J = 6.5 Hz, 1H), 1.98 (d, J = 15.9 Hz, 1H), 1.09 (s, 3H), 1.00 (s, 3H). 13C NMR (100 MHz, DMSO-d6) δppm: 193.1, 163.3, 159.2, 153.6, 150.4, 143.2, 127.0, 122.6, 120.3, 107.7, 84.7, 50.6, 31.7, 30.2, 29.7, 28.4, 27.8, 27.3, 26.4.

1′,3′,4,6,8′,8′-Hexamethyl-8′,9′-dihydro-1′H-spiro[indoline-3,5′-pyrimido[4,5-b]quinoline]-2,2′,4′,6′(3′H,7′H,10′H)-tetraone (16a)

Beige solid; mp: >300 °C; R: (acetone/n-hexane 1:1) = 0.2; FT-IR (KBr, cm–1): 3278, 3081, 2955, 1693, 1655; 1H NMR (400 MHz, DMSO-d6) δppm: 10.04 (s, 1H), 8.78 (s, 1H), 6.68 (s, 1H), 6.56 (s, 1H), 3.55 (s, 3H), 3.04 (s, 3H), 2.67 (s, 2H), 2.19 (s, 3H), 2.14 (s, 3H), 1.98 (d, J = 15.2 Hz, 1H), 1.25 (d, J = 27.8 Hz, 1H), 1.07 (s, 3H), 0.97 (s, 3H). 13C NMR (100 MHz, DMSO-d6) δppm: 193.1, 170.2, 157.1, 155.3, 154.7, 154.3, 153.4, 141.2, 141.1, 137.5, 131.7, 128.9, 128.4, 128.1, 127.5, 124.4, 120.8, 110.3, 93.0, 79.6, 70.2, 50.8, 49.5, 40.6, 32.4, 29.4, 29.0, 26.8.

1′,3′,8′,8′-Tetramethyl-8′,9′-dihydro-1′H,2H-spiro[acenaphthylene-1,5′-pyrimido[4,5-b]quinoline]-2,2′,4′,6′(3′H,7′H,10′H)-tetraone (17a)

White solid; mp: >300 °C; R: (acetone/n-hexane 1:1) = 0.3; FT-IR (KBr, cm–1): 3408, 3167, 3055, 2953, 2868, 1702; 1H NMR (400 MHz, DMSO-d6) δppm: 9.59 (s, 1H), 8.26 (d, 1H), 7.94 (d, J = 6.4 Hz, 1H), 7.85–7.69 (m, 3H), 7.61 (s, 1H), 3.30 (s, 3H), 3.13 (s, 3H), 2.49 (s, 1H), 2.33 (d, J = 17.7 Hz, 1H), 2.25 (d, J = 15.8 Hz, 1H), 2.06 (d, J = 15.4 Hz, 1H), 1.07 (s, 3H), 0.82 (s, 3H). 13C NMR (100 MHz, DMSO-d6) δppm: 191.3, 174.6, 156.9, 154.6, 151.1, 142.1, 138.0, 136.0, 131.3, 128.6, 127.9, 126.0, 123.2, 122.6, 119.9, 115.9, 88.4, 69.6, 51.2, 36.8, 33.1, 30.8, 27.9, 27.4, 27.2.

N-(3-(5-Chloro-2-hydroxyphenyl)-2-oxoindolin-3-yl)benzamide (1c)

White solid; mp: 230–232 °C; R: (EtOAc/n-hexane 2:8) = 0.8; FT-IR (KBr, cm–1): 3448, 3303, 3085, 2925, 2854, 1699; 1H NMR (300 MHz, DMSO-d6) δppm: 10.83 (s, 1H), 7.89–7.82 (m, 2H), 7.56 (t, J = 7.3 Hz, 1H), 7.47 (d, J = 7.5 Hz, 3H), 7.25–7.15 (m, 2H), 6.98–6.87 (m, 3H), 6.83 (d, J = 2.6 Hz, 1H). 13C NMR (75 MHz, DMSO-d6) δppm: 177.7, 165.4, 142.3, 133.8, 132.4, 132.0, 129.4, 129.0, 128.8, 127.8, 127.2, 125.9, 124.0, 122.3, 120.1, 110.2, 66.0.

N-(3-(2-Hydroxy-5-methylphenyl)-2-oxoindolin-3-yl)benzamide (2c)

White solid; mp: 3241–244 °C; R: (EtOAc/n-hexane 2:8) = 0.8; FT-IR (KBr, cm–1): 3138, 3086, 3035, 2846, 1719; 1H NMR (400 MHz, DMSO-d6) δppm: 10.85 (s, 1H), 8.19–8.14 (m, 2H), 7.72 (tt, J = 7.6, 1.2 Hz, 1H), 7.64 (t, J = 7.5 Hz, 2H), 7.46 (td, J = 7.7, 1.4 Hz, 1H), 7.38 (d, J = 8.3 Hz, 1H), 7.33 (dd, J = 8.4, 2.0 Hz, 1H), 7.25–7.22 (m, 1H), 7.14 (t, J = 7.3 Hz, 2H), 6.50 (d, J = 2.0 Hz, 1H), 2.29 (s, 3H). 13C NMR (100 MHz, DMSO-d6) δppm: 176.6, 152.9, 146.1, 141.9, 134.8, 134.4, 131.8, 131.0, 130.2, 129.6, 128.5, 127.2, 125.3, 125.1, 122.7, 119. 115.9, 110.1, 64.5, 20.2.