Synthesis of N-Fused Benzimidazole-4,7-diones via Sequential Copper-Catalyzed C-N Coupling/Cyclization and Oxidation.

2-(2-Bromovinyl)- and 2-(2-bromoaryl)-benzimidazoles, including their 4,7-dimethoxy analogs, react with primary amides by microwave irradiation (or usual heating) in dimethylformamide in the presence of a catalytic amount of CuI along with a base to give the corresponding benzo[4,5]imidazo[1,2-c]-pyrimidines and -quinazolines in good yields. Treatment of benzo[4,5]imidazo[1,2-c]-pyrimidines and -quinazolines having methoxy group on benzimidazole moiety with aqueous ceric ammonium nitrate affords unprecedented N-fused hybrid scaffolds, benzo[4,5]imidazo[1,2-c]-pyrimidin-6,9-diones and -quinazoline-8,11-diones, respectively, in high yields.

Introduction

It is known that N-fused hybrid structures exhibit characteristic biological activities that are not shown in each homonuclear scaffolds. Pyrimidine- and n class="Chemical">quinazoline-fused benzimidazole hybrid scaffolds, benzo[4,5]imidazo[1,2-c]-pyrimidines (Scheme , A) and -quinazolines (Scheme , B), have been synthesized due to their intrinsic biological activities.[1−3] We have also recently reported that 2-(2-bromovinyl)- and 2-(2-bromophenyl)-benzimidazoles are coupled and cyclized with cyanamide in the presence of a copper catalyst to give such N-fused hybrid scaffolds.[4] In connection with this report, it is known that primary amides can serve as building blocks for the construction of N-heterocycles by a copper-catalyzed coupling and cyclization reaction.[5,6] Ma and co-workers reported that N-substituted o-bromobenzamides react with primary amides in the presence of CuI to give quinazolinones.[7] While the present work was being performed, such a similar coupling and cyclization reaction leading to imidazo[1,2-c]quinazolines was also exemplified by the reaction of 2-(2-bromoaryl)-1H-imidazoles and formamide under CuI catalysis.[8] As part of our continuing studies directed toward transition-metal-catalyzed synthesis of N-fused hybrid scaffolds,[4,9] we provide here a new synthetic method for benzo[4,5]imidazo[1,2-c]-pyrimidines and -quinazolines by copper-catalyzed coupling and cyclization of 2-(2-bromovinyl)- and 2-(2-bromoaryl)-benzimidazoles with primary amides as building blocks. In addition, this report also shows the synthesis of unprecedented N-fused hybrid scaffolds, benzo[4,5]imidazo[1,2-c]pyrimidin-6,9-diones (Scheme , C) and benzo[4,5]imidazo[1,2-c]quinazoline-8,11-diones (Scheme , D), from methoxy-substituted A and B derivatives on benzimidzole moiety. To the best of our knowledge, no reports are found for the synthesis of C and D scaffolds. Only one example for the synthesis of N-fused hybrid analogue of C, benzo[4,5]imidazo[1,2-a]pyrimidin-6,9-dione, is known.[10] However, several [1,2-a]alicyclic ring-fused benzimidazolequinones have been synthesized and tested for biological activity.[11] Benzimidazole-based 1,4-quinone (1H-benzo[d]imidazole-4,7-dione)-containing compounds has received pivotal attention in the development of bioreductive quinone-based drugs due to a wide spectrum of biological activities, such as anticancer, cytotoxic, antitumor, and antiproliferative activities.[11,12]

Scheme 1

N-Fused Hybrid Scaffolds

Results and Discussion

Treatment of 2-(2-bromovinyl)benzimidazole 1a with equimolar amount of n class="Chemical">formamide (2a) in dimethylformamide (DMF) at 110 °C for 24 h in the presence of CuI along with Cs2CO3 afforded 1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline (3a) in 31% isolated yield (Table , entry 1). It is known that N-substituted o-bromobenzamides are effectively coupled and cyclized with primary amides in the presence of CuI along with additional amino acid to give quinazolinones.[7] Higher yield of 3a was observed with further addition of l-proline (L1) as ligand (Table , entry 2). The yield of 3a gradually increased with an increase of the molar ratio of 2a to 1a up to 2 (Table , entries 2–4). Other ligands, such as glycine (L2), 2-picolinic acid (L3), and 1,10-phenanthroline (L4), combined with CuI were not effective for the formation of 3a like l-proline (Table , entries 4–7). The reaction proceeded with other bases, such as K2CO3, K3PO4, NaOBu, and Bu3N, using CuI and l-proline, but the yield of 3a was generally lower than that by the use of Cs2CO3 (Table , entries 8–11). Among solvents examined under the employed conditions, DMF was shown to be the solvent of choice (Table , entries 4, 12, and 13). Other copper catalysts, such as CuBr, CuCl, or Cu powder, combined with l-proline showed lower catalytic activity than CuI (Table , entries 14–16). However, the reaction did not proceed at all toward 3a in the absence of copper catalyst (Table , entry 17). We have recently reported the synthesis of heterocycles by copper-catalyzed coupling and cyclization under microwave irradiation to increase the reaction rate and to obtain an acceptable yield of product.[4,9a,13] When 1a was treated with 2a in DMF at 110 °C for 1 h in the presence of CuI/l-proline and Cs2CO3 under microwave irradiation (initial power, 100 W), 3a was obtained in 71% yield (Table , entry 18). Higher reaction temperature up to 130 °C resulted in a slightly increased yield of 3a (Table , entry 19). As is the case for the usual heating conditions, lower yield of 3a was observed in the absence of l-proline (Table , entry 20).

Table 1

Optimization of Conditions for the Reaction of 1a and 2aa

entry	[2a]/[1a]	Cu catalyst	ligand	base	solvent	yieldb (%)
1	1	CuI		Cs2CO3	DMF	31
2	1	CuI	L1	Cs2CO3	DMF	51
3	1.5	CuI	L1	Cs2CO3	DMF	59
4	2	CuI	L1	Cs2CO3	DMF	70
5	2	CuI	L2	Cs2CO3	DMF	64
6	2	CuI	L3	Cs2CO3	DMF	49
7	2	CuI	L4	Cs2CO3	DMF	32
8	2	CuI	L1	K2CO3	DMF	41
9	2	CuI	L1	K3PO4	DMF	37
10	2	CuI	L1	NaOtBu	DMF	51
11	2	CuI	L1	Bu3N	DMF	28
12	2	CuI	L1	Cs2CO3	DMSO	42
13	2	CuI	L1	Cs2CO3	1,4-dioxane	11
14	2	CuBr	L1	Cs2CO3	DMF	51
15	2	CuCl	L1	Cs2CO3	DMF	41
16	2	Cu powder	L1	Cs2CO3	DMF	43
17	2		L1	Cs2CO3	DMF	0
18c	2	CuI	L1	Cs2CO3	DMF	71
19c,d	2	CuI	L1	Cs2CO3	DMF	78
20c,d	2	CuI		Cs2CO3	DMF	64

Reaction conditions: 1a (0.3 mmol), 2a (0.6 mmol), Cu catalyst (0.03 mmol), ligand (0.09 mmol), base (0.9 mmol), solvent (3 mL), 110 °C, 24 h, unless otherwise stated.

Isolated yield.

Under microwave irradiation (100 W of initial power), 110 °C, 1 h, unless otherwise stated.

At 130 °C.

Having optimized the reaction conditions (condition A: entry 4 of Table ; condition B: entry 19 of Table ), various 2-(2-bromovinyl)- and 2-(2-bromoaryl)-benzimidazoles 1 were subjected to the reaction with primary n class="Chemical">amides 2 to investigate the reaction scope, and several representative results are summarized in Table . The coupling and cyclization of 1a with primary amides 2b–d also proceeded to give the corresponding benzo[4,5]imidazo[1,2-c]pyrimidines 3b–d in good yields. Benzo[4,5]imidazo[1,2-c]pyrimidine 3e was also formed from 1b and 2a in similar yields irrespective of methyl substituent on 1b. The six-membered 2-(2-bromovinyl)benzimidazoles (1c and 1d) also reacted with 2a to give the corresponding benzo[4,5]imidazo[1,2-c]pyrimidines (3f and 3g), irrespective of the presence of the methyl and phenyl substituents on 1c and 1d. With cyclic 2-(2-bromovinyl)benzimidazoles 1e–g having various ring sizes, the corresponding benzo[4,5]imidazo[1,2-c]pyrimidines 3h–j were also produced in 54–80% yields and the yield decreased with the increase in ring size. The coupling and cyclization of benzo-fused 2-(2-bromovinyl)benzimidazole 1h took place with 1a to give 5,6-dihydrobenzo[f]benzo[4,5]imidazo[1,2-c]quinazoline (3k) in 57% yield. The reaction of acyclic 2-(2-bromovinyl)benzimidazoles (1i and 1j) with 2a also afforded the coupled and cyclized products 3l and 3m in 53 and 51% yields, respectively. Similar treatment of 2-(2-bromoaryl)benzimidazoles 1k–m with primary amides 2a–c under the employed conditions also afforded the corresponding quinazoline-fused benzimidazoles 3n–r in 53–71% yields. As shown in Table , higher product yields were observed under condition B compared to condition A.

Table 2

Cu-Catalyzed Coupling and Cyclization of 1 with 2 Leading to 3a

Reaction conditions: 1 (0.3 mmol), 2 (0.6 mmol) CuI (0.03 mmol), l-proline (0.09 mmol), Cs2CO3 (0.9 mmol), and DMF (3 mL). Condition A: 110 °C, 24 h. Condition B: 130 °C, 1 h, under microwave irradiation (100 W of initial power).

Reaction conditions: 1 (0.3 mmol), 2 (0.6 mmol) CuI (0.03 mmol), n class="Chemical">l-proline (0.09 mmol), Cs2CO3 (0.9 mmol), and DMF (3 mL). Condition A: 110 °C, 24 h. Condition B: 130 °C, 1 h, under microwave irradiation (100 W of initial power).

On the basis of the reaction of 2-(2-bromovinyl)- and 2-(2-bromoaryl)-benzimidazoles with primary n class="Chemical">amides, the present protocol can be extended to the reaction with 4,7-dimethoxy-substituted benzimidazole analogues. Table shows several results for further optimization with 2-(2-bromophenyl)-4,7-dimethoxy-1H-benzo[d]imidazole (4a) and 2a to realize the effective formation of quinazoline-fused dimethoxybenzimidazole 5. Similar treatment of 4a with 2a under condition B (Table , entry 19) afforded 5a in only 43% yield along with concomitant formation of 4,7-dimethoxy-2-phenyl-1H-benzo[d]imidazole (6, 46% yield) by debromination of 4a (Table , entry 1). When 4a was treated in the absence of 2a under the employed conditions, 4a was recovered almost completely (99%). This result indicates that formamide (2a) plays a significant role in debromination. In contrast to the results from the reaction of 1a with 2a (Table , entries 1 and 2, 19 and 20), performing the reaction in the absence of l-proline resulted in similar yield of 5a without the formation of debromination byproduct (Table , entry 2). Higher loading of CuI was needed for an allowable yield of 5a (Table , entry 3). After further tuning reaction variants, such as Cu catalyst, base, and solvent (Table , entries 4–11), the best result in terms of the yield of product 5a and complete conversion of 4a was obtained with the standard set of reaction conditions shown in entry 7 of Table .

Table 3

Optimization of Conditions for the Reaction of 4a and 2aa

entry	Cu catalyst	base	solvent	yieldb (%)
1c,d	CuI	Cs2CO3	DMF	43
2d	CuI	Cs2CO3	DMF	47
3	CuI	Cs2CO3	DMF	63
4	CuBr	Cs2CO3	DMF	59
5	CuCl	Cs2CO3	DMF	51
6	Cu powder	Cs2CO3	DMF	28
7	CuI	K2CO3	DMF	81
8	CuI	K3PO4	DMF	77
9	CuI	NaOtBu	DMF	69
10	CuI	K2CO3	DMSO	51
11	CuI	K2CO3	1,4-dioxane	42

Reaction conditions: 4a (0.3 mmol), 2a (0.6 mmol), Cu catalyst (0.06 mmol), base (0.9 mmol), solvent (3 mL), microwave irradiation (initial power, 100 W), 130 °C, 1 h, unless otherwise stated.

Isolated yield.

In the presence of l-proline (0.09 mmol).

CuI (0.03 mmol).

The coupling and cyclization could be applied to many 4,7-dimethoxybenzimidazoles 4 with primary n class="Chemical">amides under the conditions shown in entry 7 of Table (condition C), and several representative results are summarized in Table . From the reaction of 4a with an array of primary amides 2b–g, the corresponding quinazoline-fused 4,7-dimethoxybenzimidazoles 5b–g also invariably formed irrespective of the identity of primary amides. 2-(2-Bromovinyl)-4,7-dimethoxybenzimidazole 4b was also readily coupled and cyclized with primary amides 2a–e to give the corresponding pyrimidine-fused 4,7-dimethoxybenzimidazoles 5h–l in the range of 71–81% yields. As is the case for the reaction of 1 with 2, cyclic 2-(2-bromovinyl)-4,7-dimethoxybenzimidazoles 4c–f having various ring sizes also reacted with 2a to afford pyrimidine-fused 4,7-dimethoxybenzimidazoles 5m–p in similar yields. Acyclic 2-(2-bromovinyl)-4,7-dimethoxybenzimidazoles (4g and 4h) were also reacted with 2a to give pyrimidine-fused 4,7-dimethoxybenzimidazoles (5q and 5r).

Table 4

Cu-Catalyzed Coupling and Cyclization of 4 with 2 Leading to 5a

Reaction conditions: 4 (0.3 mmol), 6 (0.6 mmol) CuI (0.06 mmol), K2CO3 (0.9 mmol), DMF (3 mL), 130 °C, 1 h, under microwave irradiation (100 W of initial power).

Reaction conditions: 4 (0.3 mmol), 6 (0.6 mmol) CuI (0.06 mmol), n class="Chemical">K2CO3 (0.9 mmol), DMF (3 mL), 130 °C, 1 h, under microwave irradiation (100 W of initial power).

As shown in Table , all quinazoline- and n class="Chemical">pyrimidine-fused dimethoxybenzimidazoles 5a–r could be converted into unprecedented quinazoline- and pyrimidine-fused benzimidazolequinones 7a–r with 70–89% yields by treatment of ceric ammonium nitrate (CAN) in aqueous acetonitrile.[12a,12f,14−16]

Table 5

CAN-Mediated Oxidation of 5–7a

Reaction conditions: 5 (0.1 mmol), CAN (0.4 mmol), acetonitrile/H2O (4 mL), rt, 20 min.

Reaction conditions: 5 (0.1 mmol), CAN (0.4 mmol), acetonitrile/n class="Chemical">H2O (4 mL), rt, 20 min.

The reaction pathway seems to proceed via an initial formation of C–N-coupled intermediate by copper-catalyzed Ullmann-type coupling between 1 (or 4) and 2, followed by cyclization and n class="Disease">dehydration.[8,17] We confirmed that a similar treatment of N-methyl-2-(2-bromophenyl)benzimidazole 8 with benzamide (2c) under the employed conditions afforded C–N-coupled intermediate 9 in 70% yield (Scheme ).

Scheme 2

Conclusions

In summary, we have developed a new synthetic method for benzo[4,5]imidazo[1,2-c]-pyrimidines and n class="Chemical">-quinazolines by copper-catalyzed coupling and cyclization of 2-(2-bromovinyl)- and 2-(2-bromoaryl)-benzimidazoles with primary amides. Such scaffolds having methoxy group on benzimidzole moiety could be transformed into unprecedented N-fused hybrid scaffolds, benzo[4,5]imidazo[1,2-c]pyrimidin-6,9-diones and benzo[4,5]imidazo[1,2-c]quinazoline-8,11-diones, by treatment with aqueous ceric ammonium nitrate. Further challenges on the synthesis of novel benzimidazole-based 1,4-quinone-containing N-fused hybrid heterocyclic compounds using the present protocol are expected.

Experimental Section

General Information

1H (400 and 500 MHz) and n class="Chemical">13C NMR (100 and 125 MHz) spectra were recorded in CDCl3 or DMSO-d6. Melting points were determined on a microscopic melting point apparatus. High-resolution mass data were recorded by electronic ionization (HRMS-EI, magnetic sector–electric sector double-focusing mass analyzer) at Korea Basic Science Center, Daegu, Korea. All microwave reactions (CEM, Discover LabMate) were carried out in sealed tube (5 mL), and maintenance of the reaction temperature was monitored by an external infrared sensor. Isolation of pure products was carried out by thin-layer (a glass plate coated with Kieselgel 60 GF254, Merck) chromatography. 2-(2-Bromovinyl)benzimidazoles and 2-(2-bromoaryl)benzimidazoles were prepared from the corresponding carboxylic acids (or aldehydes) and 1,2-phenylenediamines by literature procedures.[3g,11a,18] Commercially available organic and inorganic compounds were used without further purification.

General Procedure for the Synthesis of 3 (Condition A)

To a 5 mL screw-capped vial was added 1 (0.3 mmol) and 2 (0.6 mmol), together with CuI (0.006 g, 0.03 mmol), n class="Chemical">l-proline (0.010 g, 0.09 mmol), Cs2CO3 (0.293 g, 0.9 mmol), and DMF (3 mL). The reaction mixture was stirred at 110 °C for 24 h. The mixture was then cooled to room temperature and filtered through a short silica gel column (ethyl acetate) to remove inorganic components. Removal of the solvent left a crude mixture, which was separated by thin-layer chromatography (TLC) (dichloromethane/MeOH = 99:1) to give 3.

General Procedure for the Synthesis of 3 (Condition B)

A 5 mL microwave reaction tube was charged with 1 (0.3 mmol) and 2 (0.6 mmol), together with CuI (0.006 g, 0.03 mmol), n class="Chemical">l-proline (0.010 g, 0.09 mmol), Cs2CO3 (0.293 g, 0.9 mmol), and DMF (3 mL). The reaction mixture was heated to 130 °C for 1 h by microwave irradiation at 100 W initial power. The mixture was then cooled to room temperature and filtered through a short silica gel column (ethyl acetate) to remove inorganic components. Removal of the solvent left a crude mixture, which was separated by TLC (dichloromethane/MeOH = 99:1) to give 3. Except for known 3n,[19]3o,[19] and 3p,[3g] all new products were characterized spectroscopically.

1,2,3,4-Tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline (3a)

Pale yellow solid (52 mg, 78%). Mp 204–206 °C. 1H NMR (400 MHz, n class="Chemical">CDCl3): δ 1.89–1.99 (m, 4H), 2.88–2.91 (m, 2H), 3.06–3.09 (m, 2H), 7.36–7.40 (m, 1H), 7.52–7.56 (m, 1H), 7.91–7.94 (m, 2H), 9.10 (s, 1H). 13C NMR (100 MHz, CDCl3): δ 21.7, 22.7, 23.5, 31.5, 110.6, 119.8, 120.2, 122.2, 126.8, 127.2, 135.9, 144.8, 148.4, 150.7. HRMS (EI) anal. calcd for C14H13N3 (M+): 223.1109. Found: 223.1108.

6-Methyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline (3b)

Pale yellow solid (47 mg, 66%). Mp 174–176 °C. 1H NMR (400 MHz, n class="Chemical">CDCl3): δ 1.84–1.87 (m, 4H), 2.76–2.77 (m, 2H), 2.98–2.99 (m, 2H), 3.02 (s, 3H), 7.26–7.30 (m, 1H), 7.44–7.48 (m, 1H), 7.86–7.92 (m, 2H). 13C NMR (100 MHz, CDCl3): δ 21.9, 22.8, 23.3, 23.7, 31.3, 114.5, 117.2, 120.0, 121. 9, 126.2, 128.7, 145.3, 147.6, 149.8, 150.1. HRMS (EI) anal. calcd for C15H15N3 (M+): 237.1266. Found: 237.1265.

6-Phenyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline (3c)

Pale yellow solid (64 mg, 71%). Mp 186–188 °C. 1H NMR (400 MHz, n class="Chemical">CDCl3): δ 1.94–2.02 (m, 4H), 2.92–2.95 (m, 2H), 3.13–3.16 (m, 2H), 6.67 (d, J = 8.3 Hz, 1H), 7.01–7.04 (m, 1H), 7.41–7.45 (m, 1H), 7.59–7.68 (m, 5H), 7.90 (d, J = 8.4 Hz, 1H). 13C NMR (100 MHz, CDCl3): δ 21.9, 22.8, 23.5, 31.5, 114.7, 118.2, 119.8, 121.5, 126.2, 128.3, 128. 5, 129.4, 131.0, 134.3, 145.1, 148.8, 150.0, 150.4. HRMS (EI) anal. calcd for C20H17N3 (M+): 299.1422. Found: 299.1420.

6-Benzyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline (3d)

Pale yellow solid (55 mg, 59%). Mp 190–192 °C. 1H NMR (400 MHz, n class="Chemical">CDCl3): δ 1.86–1.94 (m, 4H), 2.81–2.84 (m, 2H), 3.02–3.05 (m, 2H), 4.71 (s, 2H), 7.10–7.16 (m, 6H), 7.38–7.42 (m, 1H), 7.72 (d, J = 8.6 Hz, 1H), 7.84 (d, J = 8.4 Hz, 1H). 13C NMR (100 MHz, CDCl3): δ 22.0, 22.8, 23.5, 31.4, 41.8, 115.0, 117.8, 119.9, 122.0, 126.2, 127.4, 127.9, 128.3, 129.9, 134.7, 145.3, 148.5, 150.1, 150.2. HRMS (EI) anal. calcd for C21H19N3 (M+): 313.1579. Found: 313.1579.

9,10-Dimethyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline (3e)

Pale yellow solid (57 mg, 76%). Mp 203–204 °C. 1H NMR (400 MHz, CDCl3): δ 1.93–1.94 (m, 4H), 2.43 (s, 3H), 2.44 (s, 3H), 2.86–2.88 (m, 2H) 3.06 (s, 2H), 7.66 (d, J = 8.6 Hz, 2H), 9.01 (s, 1H). 13C NMR (100 MHz, CDCl3): δ 20.7, 20.9, 21.8, 22.7, 23.4, 31.4, 110.6, 119.6, 120.0, 125.5, 131.7, 135.8, 136.1, 143.4, 147.9, 149.9. HRMS (EI) anal. calcd for C16H17N3 (M+): 251.1422. Found: 251.1421.

2-Methyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline (3f)

Pale yellow solid (43 mg, 61%). Mp 223–226 °C. 1H NMR (400 MHz, n class="Chemical">CDCl3): δ 1.11 (d, J = 6.6 Hz, 3H), 1.49–1.57 (m, 1H), 1.89–1.9 (m, 2H), 2.49–2.56 (m, 1H), 2.85–2.89 (m, 2H) 3.20–3.25 (m, 1H), 7.31–7.35 (m, 1H), 7.46–7.50 (m, 2H), 9.05 (s, 1H). 13C NMR (100 MHz, CDCl3): δ 21.6, 28.1, 30.9, 31.4, 31.7, 110.7, 119.4, 120.3, 122.3, 126.8, 127.3, 136.0, 144.9, 148.4, 150.5. HRMS (EI) anal. calcd for C15H15N3 (M+): 237.1266. Found: 237.1265.

2-Phenyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline (3g)

Pale yellow solid (63 mg, 70%). Mp 201–203 °C. 1H NMR (400 MHz, n class="Chemical">CDCl3): δ 2.09–2.19 (m, 1H), 2.33–2.36 (m, 1H), 3.05–3.21 (m, 4H), 3.51–3.61 (m, 1H), 7.25–7.2 (m, 1H), 7.35–7.37 (m, 4H), 7.42–7.46 (m, 1H), 7.56–7.60 (m, 1H), 7.94–7.99 (m, 1H), 9.18 (s, 1H). 13C NMR (100 MHz, CDCl3): δ 29.9, 30.9, 31.8, 39.1, 110.8, 119.4, 120.3, 122.4, 126.7, 126.9, 127.0, 127.3, 128.7, 136.3, 144.9, 145.1, 148.2, 150.2. HRMS (EI) anal. calcd for C20H17N3 (M+): 299.1422. Found: 299.1422.

2,3,4,5-Tetrahydro-1H-benzo[4,5]imidazo[1,2-c]cyclohepta[e]pyrimidine (3h)

Pale yellow solid (57 mg, 80%). Mp 212–214 °C. 1H NMR (400 MHz, n class="Chemical">CDCl3): δ 1.72–1.83 (m, 4H), 1.93–1.98 (m, 2H), 3.08–3.10 (m, 2H), 3.27–3.30 (m, 2H), 7.36–7.40 (m, 1H), 7.53–7.57 (m, 1H), 7.92–7.95 (m, 2H), 9.10 (s, 1H). 13C NMR (100 MHz, CDCl3): δ 26.1, 26.6, 26.7, 32.6, 38.1, 110.9, 120.1, 122.0, 125.2, 127.0, 127.5, 135.6, 145.1, 149.2, 156.4. HRMS (EI) anal. calcd for C15H15N3 (M+): 237.1266. Found: 237.1264.

1,2,3,4,5,6-Hexahydrobenzo[4,5]imidazo[1,2-c]cycloocta[e]pyrimidine (3i)

Pale yellow solid (52 mg, 69%). Mp 205–208 °C. 1H NMR (400 MHz, CDCl3): δ 1.33–1.44 (m, 4H), 1.76–1.85 (m, 4H), 2.91–2.94 (m, 2H), 3.13–3.16 (m, 2H), 7.30–7.34 (m, 1H), 7.46–7.50 (m, 1H), 7.87 (d, J = 9.08 Hz, 2H), 9.08 (s, 1H). 13C NMR (100 MHz, CDCl3): δ 25.8, 26.2, 26.6, 29.9, 30.2, 33.5, 110.8, 120.1, 122.1, 122.9, 126.9, 127.4, 136.5, 145.1, 148.51, 153.7. HRMS (EI) anal. calcd for C16H17N3 (M+): 251.1422. Found: 251.1422.

1,2,3,4,5,6,7,8,9,10-Decahydrobenzo[4,5]imidazo[1,2-c]cyclododeca[e]pyrimidine (3j)

Pale yellow solid (50 mg, 54%). Mp 202–204 °C. 1H NMR (400 MHz, n class="Chemical">CDCl3): δ 1.29–1.42 (m, 8H), 1.47–1.53 (m, 2H), 1.83–1.90 (m, 2H), 1.92–1.99 (m, 2H), 2.76–2.80 (m, 2H), 3.01–3.05 (m, 2H), 7.30–7.34 (m, 1H), 7.46–7.50 (m, 1H), 7.85–7.90 (m, 2H), 9.08 (s, 1H). 13C NMR (100 MHz, CDCl3): δ 22.6, 23.1, 24.5, 25.5, 25.8, 26.0, 26.8, 27.0, 30.8, 110.7, 120.2, 122.1, 122.9, 126.7, 127.1, 136.2, 145.0, 149.1, 153.4. HRMS (EI) anal. calcd for C20H25N3 (M+): 307.2048. Found: 307.2051.

5,6-Dihydrobenzo[f]benzo[4,5]imidazo[1,2-c]quinazoline (3k)

Pale yellow solid (46 mg, 57%). Mp 191–193 °C. 1H NMR (400 MHz, n class="Chemical">CDCl3): δ 3.07–3.11 (m, 2H), 3.15–3.20 (m, 2H), 7.28–7.44 (m, 2H), 7.45–7.49 (m, 2H), 7.60–7.64 (m, 2H), 9.22 (s, 1H), 9.29 (d, J = 7.6 Hz, 1H). 13C NMR (100 MHz, CDCl3): δ 28.3, 30.8, 110.7, 117.6, 120.6, 122.5, 126.7, 127.1, 127.3, 127.8, 128.7, 128.8, 130.3, 136.5, 136.9, 145.3, 146.0, 151.8. HRMS (EI) anal. calcd for C18H18N3 (M+): 271.1109. Found: 271.1111.

4-Methyl-3-phenylbenzo[4,5]imidazo[1,2-c]pyrimidine (3l)

Pale yellow solid (41 mg, 53%). Mp 234–236 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 2.18 (s, 3H), 6.52 (d, J = 8.5 Hz, 1H), 7.24–7.27 (m, 1H), 7.70–7.73 (m, 1H), 7.74–7.76 (m, 2H), 7.98–8.03 (m, 3H), 8.25 (d, J = 8.3 Hz, 1H), 9.03 (s, 1H). 13C NMR (125 MHz, CDCl3): δ 14.5, 110.5, 110.8, 119.4, 120.3, 124.7, 126.6, 127.5, 129.2, 129.9, 130.6, 140.9, 142.2, 147.2, 154.2. HRMS (EI) anal. calcd for C17H13N3 (M+): 259.1109. Found: 259.1111.

3,4-Diphenylbenzo[4,5]imidazo[1,2-c]pyrimidine (3m)

Pale yellow solid (49 mg, 51%). Mp 262–264 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 7.12–7.14 (m, 4H), 7.17–7.19 (m, 3H), 7.20–7.24 (m, 2H), 7.30–7.32 (m, 3H), 7.52–7.55 (m, 1H), 8.30–8.32 (m, 1H), 9.33 (s, 1H). 13C NMR (125 MHz, CDCl3): δ 110.6, 120.7, 121.4, 122.0, 126.4, 126.9, 127.9, 128.1, 128.8, 129.7, 130.2, 132.7, 136.1, 137.8, 145.3, 150.2, 163.4. HRMS (EI) anal. calcd for C22H15N3 (M+): 321.1266. Found: 321.1267.

Benzo[4,5]imidazo[1,2-c]quinazoline (3n)[19]

Pale yellow solid (47 mg, 71%). Mp 245–247 °C (lit.[2] 247–249 °C). 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 7.40–7.43 (m, 1H), 7.47–7.51 (m, 1H), 7.56–7.60 (m, 2H), 7.68–7.72 (m, 1H), 7.96 (d, J = 8.0 Hz, 1H), 8.75 (dd, J = 7.8 and 0.8 Hz, 1H), 8.78 (d, J = 8.3 Hz, 1H), 9.17 (s, 1H). 13C NMR (125 MHz, CDCl3): δ 110.2, 114.4, 119.1, 122.4, 123.2, 123.8, 124.4, 125.1, 128.2, 131.8, 143.9, 144.7, 146.5, 148.5.

6-Methylbenzo[4,5]imidazo[1,2-c]quinazoline (3o)[19]

Pale yellow solid (43 mg, 61%). Mp 176–177 °C (lit.[2] 177–179 °C). 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 3.13 (s, 3H), 7.36–7.39 (m, 1H), 7.52–7.57 (m, 1H), 7.61–7.65 (m, 1H), 7.73–7.77 (m, 1H), 7.83 (d, J = 8.0 Hz, 1H), 7.93–7.97 (m, 2H), 8.64–8.65 (m, 1H). 13C NMR (125 MHz, CDCl3): δ 24.2, 114.4, 118.1, 120.2, 123.8, 124.4, 125.1, 127.3, 127.6, 129.2, 131.8, 142.2, 144.7, 147.5, 148.5.

6-Phenylbenzo[4,5]imidazo[1,2-c]quinazoline (3p)[3g]

Pale yellow solid (61 mg, 69%). Mp 227–228 °C (lit.[3] 230–231). 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 6.60 (d, J = 8.3 Hz, 1H), 7.17–7.20 (m, 2H), 7.45–7.48 (m, 1H), 7.59–7.63 (m, 2H), 7.68–7.71 (m, 3H), 7.77–7.81 (m, 2H), 7.95–8.00 (m, 2H), 8.73 (dd, J = 7.8 and 0.8 Hz, 1H). 13C NMR (125 MHz, CDCl3): δ 114.5, 118.2, 120.2, 122.5, 123.3, 124.5, 125.2, 128.2, 128.4, 128.6, 129.3, 131.1, 132.0, 134.2, 142.1, 144.0, 148.1, 148.6.

2-Fluorobenzo[4,5]imidazo[1,2-c]quinazoline (3q)

Pale yellow solid (38 mg, 53%). Mp 268–271 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 7.51–7.54 (m, 2H), 7.59–7.63 (m, 1H), 7.99–8.04 (m, 3H), 8.32 (dd, J = 8.4 and 2.9 Hz, 1H), 9.13 (s, 1H). 13C NMR (125 MHz, CDCl3): δ 109.6 (d, J = 24.4 Hz), 110.2, 113.7 (d, J = 23.6 Hz), 120.3, 120.5, 123.4, 123.7, 126.4, 130.8 (d, J = 8.1 Hz), 131.0 (d, J = 9.1 Hz), 135.5 (d, J = 2.6 Hz), 139.2, 144.0, 161.9 (d, J =247.7 Hz). HRMS (EI) anal. calcd for C14H8FN3 (M+): 237.0702. Found: 237.0704.

2,3-Dimethoxybenzo[4,5]imidazo[1,2-c]quinazoline (3r)

White solid (54 mg, 64%). Mp 227–229 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 3.92 (s, 3H), 3.94 (s, 3H), 7.13 (s, 1H), 7.32–7.35 (m, 1H), 7.59 (s, 1H), 7.66–7.70 (m, 1H), 7.75 (dd, J = 7.8 and 1.5 Hz, 1H), 9.18 (d, J = 8.7 Hz, 1H), 9.35 (s, 1H). 13C NMR (125 MHz, CDCl3): δ 56.5, 57.1, 107.5, 107.8, 121.3, 122.5, 123.3, 127.0, 131.4, 136.1, 138.8, 140.3, 143.3, 149.1, 152.3, 160.6. HRMS (EI) anal. calcd for C16H13N3O2 (M+): 279.1008. Found: 279.1009.

General Procedure for the Synthesis of 5 (Condition C)

A 5 mL microwave reaction tube was charged with 4 (0.3 mmol) and 2 (0.6 mmol), together with CuI (0.011 g, 0.06 mmol), n class="Chemical">K2CO3 (0.124 g, 0.9 mmol), and DMF (3 mL). The reaction mixture was heated to 130 °C for 1 h by microwave irradiation at 100 W initial power. The mixture was then cooled to room temperature and filtered through a short silica gel column (ethyl acetate) to remove inorganic components. Removal of the solvent left a crude mixture, which was separated by TLC (hexane/EA = 2:1) to give 5.

8,11-Dimethoxybenzo[4,5]imidazo[1,2-c]quinazoline (5a)

Pale yellow solid (23 mg, 81%). Mp 190–193 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 4.02 (s, 6H), 7.00 (s, 2H), 7.36–7.40 (m, 1H), 7.52–7.56 (m, 1H), 7.91–7.94 (m, 2H), 9.10 (s, 1H). 13C NMR (125 MHz, CDCl3): δ 55.2, 110.2, 119.5, 120.2, 124.1, 126.6, 128.4, 128.5, 131.4, 132.9, 135.5, 135.2, 142.4, 145.7. HRMS (EI) anal. calcd for C16H13N3O2 (M+): 279.1008. Found: 279.1009.

8,11-Dimethoxy-6-methylbenzo[4,5]imidazo[1,2-c]quinazoline (5b)

Pale yellow solid (63 mg, 72%). Mp 188–190 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 1.25 (s, 3H), 4.00 (s, 6H), 6.64 (s, 2H), 6.93–6.96 (m, 1H), 7.13 (dd, J = 8.3 Hz, 1H), 7.33–7.37 (m, 1H), 7.60 (dd, J = 7.8 and 1.5 Hz, 1H). 13C NMR (125 MHz, CDCl3): δ 29.7, 56.5, 104.1, 112.0, 116.0, 118.1, 119.0, 124.5, 129.0, 131.8, 137.1, 138.7, 139.4, 150.1, 158.7. HRMS (EI) anal. calcd for C17H15N3O2 (M+): 293.1164. Found: 293.1166.

8,11-Dimethoxy-6-phenylbenzo[4,5]imidazo[1,2-c]quinazoline (5c)

Pale yellow solid (88 mg, 83%). Mp 214–217 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 3.97 (s, 3H), 4.09 (s, 3H), 6.64–6.68 (m, 2H), 7.18–7.21 (m, 1H), 7.48–7.52 (m, 1H), 7.54–7.58 (m, 3H), 7.74 (dd, J = 7.9 and 1.4 Hz, 1H), 8.49–8.51 (m, 2H), 9.10 (dd, J = 8.5 and 1.0 Hz, 1H). 13C NMR (125 MHz, DMSO-d6): δ 55.8, 56.1, 102.6, 104.2, 115.6, 119.8, 123.0, 124.9, 127.7, 127.8, 128.8, 130.6, 132.1, 133.3, 134.3, 138.3, 140.4, 145.0, 149.7, 164.7. HRMS (EI) anal. calcd for C22H17N3O2 (M+): 355.1321. Found: 355.1318.

6-Benzyl-8,11-dimethoxybenzo[4,5]imidazo[1,2-c]quinazoline (5d)

Pale yellow solid (95 mg, 86%). Mp 210–212 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 3.86 (s, 2H), 3.95 (s, 3H), 4.08 (s, 3H), 6.66 (s, 2H), 7.04–7.07 (m, 1H), 7.18–7.21 (m, 1H), 7.25–7.28 (m, 2H), 7.34–7.37 (m, 1H), 7.60–7.63 (m, 3H), 8.73 (dd, J = 8.4 and 0.9 Hz, 1H). 13C NMR (125 MHz, CDCl3): δ 46.4, 55.8, 56.1, 102.6, 104.2, 115.5, 116.8, 121.2, 122.8, 125.8, 126.9, 128.6, 129.4, 129.5, 130.9, 135.4, 136.9, 138.6, 149.0, 164.4, 170.4. HRMS (EI) anal. calcd for C23H19N3O2 (M+): 369.1477. Found: 369.1474.

8,11-Dimethoxy-6-propylbenzo[4,5]imidazo[1,2-c]quinazoline (5e)

Pale yellow solid (76 mg, 79%). Mp 206–209 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 0.97 (t, J = 7.4 Hz, 3H), 1.83–1.90 (m, 2H), 2.46–2.49 (m, 2H), 3.88 (s, 6H), 6.53 (s, 2H), 6.94–6.97 (m, 1H), 7.20–7.23 (m, 1H), 7.71 (dd, J = 7.9, 1.4 Hz, 1H), 8.65 (dd, J = 8.4, 0.7 Hz, 1H). 13C NMR (125 MHz, CDCl3): δ 14.0, 19.1, 40.9, 55.9, 56.2, 103.2, 103.6, 115.7, 121.4, 122.8, 126.2, 127.1, 128.9, 130.4, 130.7, 138.5, 149.2, 149.9, 173.0. HRMS (EI) anal. calcd for C19H19N3O2 (M+): 321.1477. Found: 321.1476.

8,11-Dimethoxy-6-(pyridin-3-yl)benzo[4,5]imidazo[1,2-c]quinazoline (5f)

Pale yellow solid (79 mg, 74%). Mp 251–254 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 3.68 (s, 3H), 4.00 (s, 3H), 6.42–6.44 (m, 1H), 6.60 (s, 2H), 7.00–7.07 (m, 2H), 7.24–7.28 (m, 2H), 7.29–7.32 (m, 1H), 7.44–7.47 (m, 1H), 7.64–7.66 (m, 1H). 13C NMR (125 MHz, CDCl3): δ 55.9, 56.0, 102.2, 104.3, 121.4, 124.1, 125.7, 126.6, 127.0, 127.2, 127.5, 125.5, 131.3, 131.6, 132.4, 132.5, 132.7, 137.4, 141.6, 146.2, 151.8. HRMS (EI) anal. calcd for C21H16N4O2 (M+): 356.1273. Found: 356.1275.

8,11-Dimethoxy-6-(thiophen-2-yl)benzo[4,5]imidazo[1,2-c]quinazoline (5g)

Pale yellow solid (78 mg, 72%). Mp 233–236 °C. 1H NMR (500 MHz, n class="Chemical">DMSO-d6): δ 3.64 (s, 3H), 3.90 (s, 3H), 6.39 (dd, J = 7.7 and 1.6 Hz, 1H) 6.67 (d, J = 8.7 Hz, 1H), 6.72 (d, J = 8.7 Hz, 1H), 7.11–7.14 (m, 1H), 7.16–7.20 (m, 1H), 7.42–7.45 (m, 1H), 7.53 (dd, J = 7.9 and 1.3 Hz, 1H), 7.77–7.79 (m, 1H). 13C NMR (125 MHz, DMSO-d6): δ 55.8, 56.2, 103.2, 104.9, 120.7, 123.3, 126.8, 127.8, 128.0, 129.1, 131.1, 132.0, 132.4, 132.8, 134.3, 136.5, 141.0, 145.7, 150.9, 162.3. HRMS (EI) anal. calcd for C20H15N3O2S (M+): 361.0885. Found: 361.0887

8,11-Dimethoxy-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline (5h)

Pale yellow solid (65 mg, 76%). Mp 191–193 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 1.88–1.98 (m, 4H), 2.88–2.91 (m, 2H), 3.12–3.14 (m, 2H), 4.03 (s, 3H), 4.05 (s, 3H), 6.70 (d, J = 8.6 Hz, 1H), 6.81 (d, J = 8.6 Hz, 1H), 9.55 (s, 1H). 13C NMR (125 MHz, CDCl3): δ 21.6, 22.6, 23.3, 31.3, 56.0, 102.1, 105.2, 118.0, 119.6, 136.6, 138.5, 143.0, 145.4, 147.5, 149.6. HRMS (EI) anal. calcd for C16H17N3O2 (M+): 283.1321. Found: 283.1318.

8,11-Dimethoxy-6-methyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline (5i)

Pale yellow solid (63 mg, 71%). Mp 179–181 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 1.14 (s, 3H), 1.89–1.98 (m, 4H), 2.88–2.91 (m, 2H), 3.12–3.14 (m, 2H), 4.03 (s. 3H), 4.05 (s, 3H), 6.70 (d, J = 8.6 Hz, 1H), 6.81 (d, J = 8.6 Hz, 1H). 13C NMR (125 MHz, CDCl3): δ 18.8, 21.6, 22.6, 23.3, 31.3, 56.0, 56.2, 102.1, 105.2, 118.0, 119.6, 136.6, 138.5, 143.0, 145.4, 147.4, 149.6. HRMS (EI) anal. calcd for C17H19N3O2 (M+): 297.1477. Found: 297.1475.

8,11-Dimethoxy-6-phenyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline (5j)

Pale yellow solid (82 mg, 76%). Mp 186–188 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 1.97–2.07 (m, 4H), 2.97–2.99 (m, 2H), 3.20–3.23 (m, 2H), 3.96 (s, 3H), 4.00 (s, 3H), 6.61 (d, J = 8.6 Hz, 1H), 6.79 (d, J = 8.6 Hz, 1H), 7.00–7.07 (m, 2H), 7.24–7.28 (m, 2H), 7.29–7.32 (m, 1H). 13C NMR (125 MHz, CDCl3): δ 21.6, 22.6, 23.3, 31.3, 55.8, 56.1, 102.6, 104.2, 119.9, 127.7, 127.9, 128.8, 130.6, 132.2, 133.3, 134.3, 138.4, 140.4, 145.1, 149.7. HRMS (EI) anal. calcd for C22H21N3O2 (M+): 359.1634. Found: 359.1633.

6-Benzyl-8,11-dimethoxy-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline (5k)

Pale yellow solid (91 mg, 81%). Mp 193–196 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 1.95–2.05 (m, 4H), 2.95–2.97 (m, 2H), 3.18–3.21 (m, 2H), 3.92 (s, 2H), 4.10 (s, 3H), 4.11 (s, 3H), 6.76 (d, J = 8.6 Hz, 1H), 6.88 (d, J = 8.6 Hz, 1H), 7.24–7.27 (m, 1H), 7.31–7.34 (m, 2H), 7.66–7.69 (m, 2H). 13C NMR (125 MHz, CDCl3): δ 22.6, 23.6, 24.3, 32.3, 45.9, 55.6, 56.2, 103.1, 106.2, 115.0, 120.7, 122.3, 125.3, 126.4, 128.1, 129.0, 130.4, 135.0, 138.1. 148.5, 169.9. HRMS (EI) anal. calcd for C22H21N3O2 (M+): 373.1790. Found: 373.1792.

8,11-Dimethoxy-6-propyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline (5l)

Pale yellow solid (76 mg, 78%). Mp 197–199 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 0.91 (t, J = 7.4, 3H), 1.62–1.70 (m, 2H), 1.81–1.89 (m, 4H), 2.41–2.44 (m, 2H), 2.79–2.82 (m, 2H), 3.03–3.05 (m, 2H), 3.94 (s, 3H), 3.95 (s, 3H), 6.61 (d, J = 8.6 Hz, 1H), 6.72 (d, J = 8.6 Hz, 1H). 13C NMR (125 MHz, CDCl3): δ 14.0, 19.1, 21.6, 22.6, 23.3, 31.3, 40.9, 55.9, 56.2, 103.2, 103.6, 121.4, 122.8, 126.2, 127.1, 128.9, 130.7, 138.5, 149.2. HRMS (EI) anal. calcd for C19H23N3O2 (M+): 325.1790. Found: 325.1791.

8,11-Dimethoxy-2-methyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline (5m)

Pale yellow solid (62 mg, 70%). Mp 173–176 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 1.10 (d, J = 5.9 Hz, 3H), 1.45–1.52 (m, 1H), 1.88–1.96 (m, 2H), 2.41–2.45 (m, 1H), 2.80–2.85 (m, 2H), 3.15–3.22 (m, 1H), 3.92 (s, 3H), 4.00 (s, 3H), 6.84 (d, J = 8.5 Hz, 1H), 6.93 (d, J = 8.5 Hz, 1H), 9.48 (s, 1H). 13C NMR (125 MHz, CDCl3): δ 21.1, 27.0, 29.9, 30.4, 30.8, 55.8, 56.0, 102.7, 106.6, 117.8, 120.0, 135.5, 138.2, 142.5, 144.5, 145.7, 148.9. HRMS (EI) anal. calcd for C17H19N3O2 (M+): 297.1477. Found: 297.1474.

9,12-Dimethoxy-2,3,4,5-tetrahydro-1H-benzo[4,5]imidazo[1,2-c]cyclohepta[e]pyrimidine (5n)

Pale yellow solid (73 mg, 82%). Mp 194–196 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 1.74–1.78 (m, 2H), 1.90–1.99 (m, 4H), 2.87–2.89 (m, 2H), 3.57–3.59 (m, 2H), 3.96 (s, 3H), 4.05 (s, 3H), 6.65 (d, J = 8.6 Hz, 1H), 6.85 (d, J = 8.6 Hz, 1H), 9.17 (s, 1H). 13C NMR (125 MHz, CDCl3): δ 25.1, 27.4, 30.7, 32.0, 34.0, 56.3, 56.5, 102.0, 105.8, 118.8, 122.7, 132.5, 136.3, 139.8, 145.5, 148.1, 150.2. HRMS (EI) anal. calcd for C17H19N3O2 (M+): 297.1477. Found: 297.1479.

10,13-Dimethoxy-1,2,3,4,5,6-hexahydrobenzo[4,5]imidazo[1,2-c]cycloocta[e]pyrimidine (5o)

Pale yellow solid (74 mg, 79%). Mp 210–212 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 1.33–1.37 (m, 2H), 1.44–1.48 (m, 2H), 1.72–1.77 (m, 2H), 1.88–1.92 (m, 2H), 2.79–2.82 (m, 2H), 3.65–3.67 (m, 2H), 3.93 (s, 3H), 4.03 (s, 3H), 6.66 (d, J = 8.7 Hz, 1H), 6.82 (d, J = 8.7 Hz, 1H), 9.14 (s, 1H). 13C NMR (125 MHz, CDCl3): δ 25.8, 26.1, 29.1, 29.5, 29.7, 31.8, 56.0, 56.3, 102.2, 105.4, 118.8, 119.8, 132.0, 135.5, 139.8, 144.8, 145.4, 150.5. HRMS (EI) anal. calcd for C18H21N3O2 (M+): 311.1634. Found: 311.1631.

14,17-Dimethoxy-1,2,3,4,5,6,7,8,9,10-decahydrobenzo[4,5]imidazo[1,2-c]cyclododeca[e]pyrimidine (5p)

Pale yellow solid (72 mg, 65%). Mp 199–202 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 1.35–1.47 (m, 8H), 1.51–1.59 (m, 4H), 1.61–1.69 (m, 2H), 1.78–1.83 (m, 2H), 2.79–2.82 (m, 2H), 3.65–3.68 (m, 2H), 3.98 (s, 3H), 4.06 (s, 3H), 6.72 (d, J = 8.7 Hz, 1H), 6.87 (d, J = 8.7 Hz, 1H), 9.27 (s, 1H). 13C NMR (125 MHz, CDCl3): δ 21.9, 22.8, 24.6, 24.7, 25.5, 25.9, 26.5, 27.0, 28.2, 29.7, 56.0, 56.4, 102.3, 105.4, 119.3, 119.5, 130.1, 134.0, 138.0, 143.1, 143.3, 149.6. HRMS (EI) anal. calcd for C22H29N3O2 (M+): 367.2260. Found: 367.2261.

6,9-Dimethoxy-4-methyl-3-phenylbenzo[4,5]imidazo[1,2-c]pyrimidine (5q)

Pale yellow solid (65 mg, 68%). Mp 219–221 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 2.14 (s, 3H), 3.94 (s, 3H), 4.05 (s, 3H), 6.37 (d, J = 8.6 Hz, 1H), 6.78 (d, J = 8.6 Hz, 1H), 7.31–7.34 (m, 2H), 7.51–7.53 (m, 3H), 9.37 (s, 1H). 13C NMR (125 MHz, CDCl3): δ 15.9, 55.7, 56.4, 101.7, 105.7, 115.5, 118.6, 128.2, 128.3, 129.2, 130.6, 132.8, 137.1, 140.4, 142.2, 146.0, 152.4. HRMS (EI) anal. calcd for C19H17N3O2 (M+): 319.1321. Found: 319.1319.

6,9-Dimethoxy-3,4-diphenylbenzo[4,5]imidazo[1,2-c]pyrimidine (5r)

Pale yellow solid (80 mg, 70%). Mp 211–212 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 4.02 (s, 3H), 4.09 (s, 3H), 6.68 (d, J = 8.6 Hz, 1H), 6.85 (d, J = 8.6 Hz, 1H), 7.25–7.28 (m, 4H), 7.31–7.37 (m, 4H), 7.51–7.53 (m, 2H), 9.79 (s, 1H). 13C NMR (125 MHz, CDCl3): δ 56.3, 57.4, 102.0, 107.2, 118.1, 121.7, 128.2. 129.1, 129.9, 130.3, 130.6, 136.4, 136.9, 137.8, 138.4, 143.9, 146.1, 149.6, 162.7. HRMS (EI) anal. calcd for C24H19N3O2 (M+): 381.1477. Found: 381.1474.

4,7-Dimethoxy-2-phenyl-1H-benzo[d]imidazole (6)

White solid (37 mg, 48%). Mp 223–225 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 3.88 (s, 6H), 6.63 (s, 2H), 7.72–7.76 (m, 3H), 8.07–8.11 (m, 2H). 13C NMR (125 MHz, DMSO): δ 55.9, 103.0, 125.4, 129.1, 130.1, 130.4, 131.0, 147.1. HRMS (EI) anal. calcd for C15H14N2O2 (M+): 254.1055. Found: 254.1056.

General Procedure for the Oxidation of 5–7[10,12]

To a stirred solution of 5 (0.1 mmol) in acetonitrile/n class="Chemical">H2O (7:3, 2 mL) in ice bath was added dropwise a solution of ceric ammonium nitrate (0.4 mmol) in acetonitrile/H2O (9:1, 2 mL). The reaction mixture was stirred for 20 min at room temperature, during which time the color turned brown. The reaction mixture was poured into cold water and then extracted with ethyl acetate (40 mL). Removal of the solvent and recrystallization from dichloromethane and hexane mixture gave 7.

Benzo[4,5]imidazo[1,2-c]quinazoline-8,11-dione (7a)

Brown solid (21 mg, 84%). Mp 216–219 °C. 1H NMR (500 MHz, n class="Chemical">DMSO-d6): δ 7.11 (s, 2H), 7.34–7.38 (m, 1H), 7.50–7.54 (m, 1H), 7.89–7.92 (m, 2H), 9.08 (s, 1H). 13C NMR (125 MHz, DMSO-d6): δ 119.5, 120.2, 124.1, 126.6, 128.4, 128.5, 131.4, 132.8, 135.6, 136.4, 142.2, 179.7, 182.8. HRMS (EI) anal. calcd for C14H7N3O2 (M+): 249.0538. Found: 249.0540.

6-Methylbenzo[4,5]imidazo[1,2-c]quinazoline-8,11-dione (7b)

Brown solid (23 mg, 86%). Mp 202–205 °C. 1H NMR (500 MHz, n class="Chemical">DMSO-d6): δ 2.00 (s, 3H), 6.52 (d, J = 8.8 Hz, 1H), 6.57 (d, J = 8.8 Hz, 1H), 6.79–6.82 (m, 1H), 6.93 (d, J = 7.8 Hz, 1H), 7.09–7.12 (m, 1H), 7.86 (dd, J = 7.9 Hz and 1.1 Hz, 1H). 13C NMR (125 MHz, DMSO-d6): δ 10.9, 113.4, 118.9, 122.4, 123.1, 123.7, 123.8, 124.2, 128.4, 130.6, 131.8, 140.9, 146.9, 178.9, 179.9. HRMS (EI) anal. calcd for C15H9N3O2 (M+): 263.0695. Found: 263.0693.

6-Phenylbenzo[4,5]imidazo[1,2-c]quinazoline-8,11-dione (7c)

Brown solid (26 mg, 81%). Mp 239–241 °C. 1H NMR (500 MHz, n class="Chemical">DMSO-d6): δ 6.91 (d, J = 10.3 Hz, 1H), 7.00 (d, J = 10.3 Hz, 1H), 7.23–7.26 (m, 1H). 7.54–757 (m, 1H), 7.59–7.64 (m, 3H), 7.80 (dd, J = 7.9, 1.4 Hz, 1H), 8.54–8.56 (m, 2H), 9.16 (dd, J = 8.5, 1.0 Hz, 1H). 13C NMR (125 MHz, DMSO-d6): δ 119.9, 122.2, 123.0, 124.9, 127.7, 127.9, 128.8, 130.6, 132.2, 133.3, 134.3, 138.4, 140.4, 145.1, 149.7, 164.7, 178.8, 180.9. HRMS (EI) anal. calcd for C20H11N3O2 (M+): 325.0851. Found: 325.0852.

6-Benzylbenzo[4,5]imidazo[1,2-c]quinazoline-8,11-dione (7d)

Brown solid (27 mg, 79%). Mp 250–253 °C. 1H NMR (500 MHz, n class="Chemical">DMSO-d6): δ 3.87 (s, 2H), 6.68 (d, J = 10.3 Hz, 1H), 6.73 (d, J = 10.3 Hz, 1H), 7.05–7.09 (m, 1H). 7.19–7.22 (m, 1H), 7.26–7.29 (m, 2H), 7.35–7.38 (m, 1H), 7.61–7.64 (m, 3H), 8.73–8.75 (m, 1H). 13C NMR (125 MHz, DMSO-d6): δ 45.7, 114.8, 116.2, 120.5, 122.2, 125.1, 126.2, 127.9, 128.7, 128.8, 130.2, 134.8, 136.3, 137.9, 148.3, 163.8, 169.7, 178.1, 182.8. HRMS (EI) anal. calcd for C21H13N3O2 (M+): 339.1008. Found: 339.1009.

6-Propylbenzo[4,5]imidazo[1,2-c]quinazoline-8,11-dione (7e)

Brown solid (26 mg, 88%). Mp 232–235 °C. 1H NMR (500 MHz, n class="Chemical">DMSO-d6): δ 0.96 (t, J = 7.4 Hz, 3H), 1.82–1.89 (m, 2H), 2.35–2.39 (2, 2H), 6.53 (d, J = 10.4 Hz, 1H), 6.71 (d, J = 10.4 Hz, 1H), 6.93–6.96 (m, 1H), 7.19–7.22 (m, 1H), 7.70 (dd, J = 7.9, 1.4 Hz, 1H), 8.64 (dd, J = 8.4, 0.7 Hz, 1H). 13C NMR (125 MHz, DMSO-d6): δ 12.2, 17.3, 34.8, 119.6, 121.0, 124.4, 125.3, 126.7, 127.1, 128.6, 128.9, 136.7, 147.4, 148.1, 171.2, 179.6, 181.1. HRMS (EI) anal. calcd for C17H13N3O2 (M+): 291.1008. Found: 291.1006.

6-(Pyridin-3-yl)benzo[4,5]imidazo[1,2-c]quinazoline-8,11-dione (7f)

Brown solid (26 mg, 80%). Mp 278–280 °C. 1H NMR (500 MHz, n class="Chemical">DMSO-d6): δ 6.42–6.44 (m, 1H), 6.65 (d, J = 10.3 Hz, 1H), 6.83 (d, J = 10.3 Hz, 1H), 7.00–7.07 (m, 2H), 7.24–7.28 (m, 2H), 7.29–7.32 (m, 1H), 7.44–7.47 (m, 1H), 7.64–7.66 (m, 1H). 13C NMR (125 MHz, DMSO-d6): δ 122.1, 124.8, 126.4, 127.3, 127.7, 127.9, 128.2, 129.2, 132.0, 133.1, 133.2, 133.4, 138.1, 142.3, 146.9, 152.5, 178.3, 180.3. HRMS (EI) anal. calcd for C19H10N4O2 (M+): 326.0804. Found: 326.0802.

6-(Thiophen-2-yl)benzo[4,5]imidazo[1,2-c]quinazoline-8,11-dione (7g)

Brown solid (26 mg, 77%). Mp 268–269 °C. 1H NMR (500 MHz, n class="Chemical">DMSO-d6): δ 6.42 (dd, J = 7.7, 1.6 Hz, 1H), 6.69 (d, J = 10.3 Hz, 1H), 6.78 (d, J = 10.3 Hz, 1H), 7.13–7.16 (m, 1H), 7.18–7.22 (m, 1H), 7.44–7.49 (m, 2H), 7.55 (dd, J = 7.9, 1.3 Hz, 1H), 7.79–7.81 (m, 1H). 13C NMR (125 MHz, DMSO-d6): δ 124.3, 126.2, 127.8, 128.8, 129.0, 130.1, 132.1, 133.0, 133.4, 133.8, 135.3, 137.5, 142.0, 146.7, 151.9, 163.3, 177.5, 180.6. HRMS (EI) anal. calcd for C18H9N3O2S (M+): 331.0415. Found: 331.0416.

1,2,3,4-Tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline-8,11-dione (7h)

Brown solid (21 mg, 81%). Mp 215–217 °C. 1H NMR (500 MHz, n class="Chemical">DMSO-d6): δ 1.90–2.00 (m, 4H), 2.90–2.93 (m, 2H), 3.14–3.16 (m, 2H), 6.72 (d, J = 10.3 Hz, 1H), 6.83 (d, J = 10.3 Hz, 1H), 9.58 (s, 1H). 13C NMR (125 MHz, DMSO-d6): δ 22.6, 23.6, 24.3, 32.3, 119.0, 120.6, 137.6, 139.5, 144.0, 146.4, 148.5, 150.6, 180.8, 181.3. HRMS (EI) anal. calcd for C14H11N3O2 (M+): 253.0851. Found: 253.0854.

6-Methyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline-8,11-dione (7i)

Brown solid (23 mg, 87%). Mp 197–200 °C. 1H NMR (500 MHz, n class="Chemical">DMSO-d6): δ 1.55 (s, 3H), 1.77–1.92 (m, 4H), 2.90–2.94 (m, 2H), 2.98–3.00 (m, 2H), 6.95 (d, J = 10.4 Hz, 1H), 7.01 (d, J = 10.4 Hz, 1H). 13C NMR (125 MHz, DMSO-d6): δ 21.0, 21.2, 21.5, 25.0, 32.7, 123.4, 129.6, 132.5, 136.0, 137.0, 143.6, 148.9, 166.5, 176.0, 181.8. HRMS (EI) anal. calcd for C15H13N3O2 (M+): 267.1008. Found: 267.1007.

6-Phenyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline-8,11-dione (7j)

Brown solid (27 mg, 83%). Mp 233–235 °C. 1H NMR (500 MHz, n class="Chemical">DMSO-d6): δ 1.77–1.82 (m, 2H), 1.87–1.92 (m, 2H), 2.90–2.94 (m, 2H), 2.98–3.00 (m, 2H), 6.84 (d, J = 10.4 Hz, 1H), 6.90 (d, J = 10.4 Hz, 1H), 7.31–7.32 (m, 2H), 7.51–7.53 (m, 3H). 13C NMR (125 MHz, DMSO-d6): δ 20.7, 20.9, 24.7, 32.4, 123.1. 126.3, 128.2, 128.4, 129.8, 132.2, 135.7, 136.7, 139.2, 143.3, 148.6, 166.2, 175.7, 181.5. HRMS (EI) anal. calcd for C20H15N3O2 (M+): 329.1164. Found: 329.1162.

6-Benzyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline-8,11-dione (7k)

Brown solid (27 mg, 80%). Mp 219–222 °C. 1H NMR (500 MHz, n class="Chemical">DMSO-d6): δ 1.90–1.98 (m, 4H), 2.88–2.91 (m, 2H), 3.12–3.14 (m, 2H), 3.92 (s, 2H), 6.81 (d, J = 10.4 Hz, 1H), 6.87 (d, J = 10.4 Hz, 1H), 7.24–7.27 (m, 1H), 7.31–7.34 (m, 2H), 7.66–7.69 (m, 2H). 13C NMR (125 MHz, DMSO-d6): δ 22.2, 23.0, 23.7, 31.6, 42.0, 115.2, 118.0, 126.4, 127.6, 128.0, 128.5, 129.4, 134.9, 145.5, 148.6, 150.3, 150.4, 176.9, 179.5. HRMS (EI) anal. calcd for C21H17N3O2 (M+): 343.1321. Found: 343.1322.

6-Propyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline-8,11-dione (7l)

Brown solid (24 mg, 80%). Mp 208–210 °C. 1H NMR (500 MHz, n class="Chemical">DMSO-d6): δ 0.83–0.86 (m, 3H), 1.77–1.82 (m, 2H), 1.87–1.92 (m, 2H), 1.98–2.06 (m, 2H), 2.35–2.38 (m, 2H), 2.90–2.92 (m, 2H), 2.98–3.00 (m, 2H), 6.81 (d, J = 10.4 Hz, 1H), 6.87 (d, J = 10.4 Hz, 1H). 13C NMR (125 MHz, DMSO-d6): δ 14.0, 19.1, 21.8, 22.0, 25.7, 33.4, 40.9, 124.2, 125.7, 133.3, 136.8, 137.8, 144.4, 149.7, 167.3, 176.8, 182.6. HRMS (EI) anal. calcd for C17H17N3O2 (M+): 295.1321. Found: 295.1322.

2-Methyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]quinazoline-8,11-dione (7m)

Brown solid (20 mg, 76%). Mp 207–209 °C. 1H NMR (500 MHz, n class="Chemical">DMSO-d6): δ 1.12 (d, J = 6.6 Hz, 3H), 1.53–161 (m, 1H), 1.92–2.06 (m, 2H), 2.43–2.49 (m, 1H), 2.90–2.95 (m, 1H), 2.98–3.05 (m, 1H), 3.15–3.19 (m, 1H), 6.71 (d, J = 10.4 Hz, 1H), 6.77 (d, J = 10.4 Hz, 1H), 9.03 (s, 1H). 13C NMR (125 MHz, DMSO-d6): δ 21.1, 28.6, 30.3, 32.9, 34.3, 116.1, 117.1, 133.2, 136.5, 143.1, 145.3, 149.2, 165.3, 177.2, 180.7. HRMS (EI) anal. calcd for C15H13N3O2 (M+): 267.1008. Found: 267.1009.

2,3,4,5-Tetrahydro-1H-benzo[4,5]imidazo[1,2-c]cyclohepta[e]pyrimidine-9,12-dione (7n)

Brown solid (24 mg, 89%). Mp 216–218 °C. 1H NMR (500 MHz, n class="Chemical">DMSO-d6): δ 1.80–1.84 (m, 2H), 1.97–2.02 (m, 4H), 2.92–2.95 (m, 2H), 3.62–3.64 (m, 2H), 6.88 (d, J = 10.4 Hz, 1H), 6.94 (d, J = 10.4 Hz, 1H), 9.06 (s, 1H). 13C NMR (125 MHz, DMSO-d6): δ 24.1, 26.4, 29.7, 31.0, 33.0, 120.2, 123.2, 132.3, 135.8, 143.4, 148.7, 166.3, 175.8, 181.6. HRMS (EI) anal. calcd for C15H13N3O2 (M+): 267.1008. Found: 267.1009.

1,2,3,4,5,6-Hexahydrobenzo[4,5]imidazo[1,2-c]cycloocta[e]pyrimidine-10,13-dione (7o)

Brown solid (21 mg, 73%). Mp 229–231 °C. 1H NMR (500 MHz, n class="Chemical">DMSO-d6): δ 1.27–1.32 (m, 2H), 1.38–1.42 (m, 2H), 1.66–1.71 (m, 2H), 1.82–1.87 (m, 2H), 2.73–2.76 (m, 2H), 3.59–3.61 (m, 2H), 6.85 (d, J = 10.3 Hz, 1H), 6.89 (d, J = 10.3 Hz, 1H), 9.10 (s, 1H). 13C NMR (125 MHz, DMSO-d6): δ 24.7, 25.3, 27.7, 28.3, 28.9, 31.1, 122.9, 125.8, 133.6, 140.1, 146.3, 151.0, 151.6, 157.1, 174.0, 181.9. HRMS (EI) anal. calcd for C16H15N3O2 (M+): 281.1164. Found: 281.1162.

1,2,3,4,5,6,7,8,9,10-Decahydrobenzo[4,5]imidazo[1,2-c]cyclododeca[e]pyrimidine-14,17-dione (7p)

Brown solid (24 mg, 70%). Mp 245–247 °C. 1H NMR (500 MHz, n class="Chemical">DMSO-d6): δ 1.29–1.39 (m, 8H), 1.43–1.53 (m, 4H), 1.56–1.61 (m, 2H), 1.70–1.76 (m, 2H), 2.82–2.85 (m, 2H), 3.57–3.60 (m, 2H), 6.85 (d, J = 10.3 Hz, 1H), 6.91 (d, J = 10.3 Hz, 1H), 9.30 (s, 1H). 13C NMR (125 MHz, DMSO-d6): δ 20.9, 21.2, 24.1, 24.4, 24.7, 25.0, 25.1, 25.3, 26.5, 28.1, 123.0, 124.9, 133.3, 139.7, 146.0, 150.4, 151.0, 157.8, 173.9, 181.5. HRMS (EI) anal. calcd for C20H23N3O2 (M+): 337.1790. Found: 337.1792.

4-Methyl-3-phenylbenzo[4,5]imidazo[1,2-c]pyrimidine-6,9-dione (7q)

Brown solid (21 mg, 73%). Mp 228–230 °C. 1H NMR (500 MHz, n class="Chemical">DMSO-d6): δ 2.17 (s, 3H), 6.56 (d, J = 10.4 Hz, 1H), 6.75 (d, J = 10.4 Hz, 1H), 7.47–7.50 (m, 3H), 7.51–7.54 (m, 2H), 9.42 (s, 1H). 13C NMR (125 MHz, DMSO-d6): δ 14.6, 120.6, 122.1, 127.4, 127.5, 129.0, 131.9, 133.4, 138.3, 144.8, 145.9, 150.4, 157.5, 172.4, 181,4. HRMS (EI) anal. calcd for C17H11N3O2 (M+): 289.0851. Found: 289.0849.

3,4-Diphenylbenzo[4,5]imidazo[1,2-c]pyrimidine-6,9-dione (7r)

Brown solid (25 mg, 71%). Mp 249–252 °C. 1H NMR (500 MHz, n class="Chemical">DMSO-d6): δ 6.74 (d, J = 10.2 Hz, 1H), 6.89 (d, J = 10.2 Hz, 1H), 7.24–7.27 (m, 2H), 7.29–7.31 (m, 2H), 7.33–7.36 (m, 6H), 9.11 (s, 1H). 13C NMR (125 MHz, DMSO-d6): δ 120.7, 125.8, 127.5, 127.8, 128.1, 128.9, 129.0, 129.3, 134.2, 134.3, 136.1, 136.5, 136.7, 144.1, 148.5, 162.2, 176.0, 181.3. HRMS (EI) anal. calcd for C22H13N3O2 (M+): 351.1008. Found: 351.1005.

Experimental Procedure for Mechanism Study

A 5 mL microwave reaction tube was charged with 8 (0.086 g, 0.3 mmol) and 2 (0.073 g, 0.6 mmol), together with CuI (0.006 g, 0.03 mmol), n class="Chemical">l-proline (0.010 g, 0.09 mmol), Cs2CO3 (0.293 g, 0.9 mmol), and DMF (3 mL). The reaction mixture was heated to 130 °C for 1 h by microwave irradiation at 100 W initial power. The mixture was then cooled to room temperature and filtered through a short silica gel column (ethyl acetate) to remove inorganic components. Removal of the solvent left a crude mixture, which was separated by TLC (dichloromethane/MeOH = 97:3) to give 9.

N-(2-(1-Methyl-1H-benzo[d]imidazol-2-yl)phenyl)benzamide (9)

Pale yellow solid (69 mg, 70%). Mp 267–269 °C. 1H NMR (500 MHz, n class="Chemical">CDCl3): δ 3.87 (s, 3H), 7.30–7.38 (m, 3H), 7.39–7.43 (m, 2H), 7.46–7.59 (m, 5H), 7.76–7.78 (m, 2H), 7.82–7.84 (m, 1H), 12.18 (s, 1H). 13C NMR (125 MHz, CDCl3): δ 31.7, 109.6, 119.9, 122.5, 122.8, 123.0, 127.0, 127.5, 128.6, 128.7, 129.5, 129.7, 130.3, 131.3, 132.5, 136.6, 143.0, 153.8, 165.4. HRMS (EI) calcd for C21H17N3O (M+): 327.1372. Found: 327.1372.