CC BY ND NC 4.0 · SynOpen 2017; 01(01): 0129-0137
DOI: 10.1055/s-0036-1591503
paper
Copyright with the author

Pd/C-Catalyzed Intramolecular C–H Arylation for the Synthesis of Phenanthridinones and Dibenzo-α-pyrones

Lingyu Zhao*
,
Guodong Shen*
,
Tongxin Zhang
,
Zhen Wang
,
Yuhua Liang
This work was financially supported by the National Natural Science Foundation of China (No. 21402079) and the Research Fund for the Doctoral Program of Liaocheng University (No. 318051403 and 318051419).
Further Information

Publication History

Received: 06 September 2017

Accepted: 04 October 2017

Publication Date:
20 October 2017 (online)

 

Abstract

Pd/C was found to be an efficient and convenient metal catalyst for intramolecular C–H arylation reactions in the synthesis of phenanthridinones and dibenzo-α-pyrones. A variety of phenanthridinones and dibenzo-α-pyrones were synthesized under the highly active catalytic system of Pd/C-KOAc-DMA in moderate to excellent yields. The high catalytic activity, high recyclability, low costs, and ease of removal of Pd/C, combined with its commercial availability, render this protocol attractive for both synthetic and industrial applications.


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Phenanthridinones[1] and dibenzo-α-pyrones[2] are important classes of molecules in natural products because of their biological and pharmaceutical activities. For example (Figure [1]), 5-methyl-8H-benzo[h]chromeno[2,3-b][1,6]naphthyridine-6(5H),8-dione (A) is a novel derivative of a chromeno[2,3-b]pyridine fused quinolinone moiety, which possess significant biological activity.[3] The fluorescent dye (B) is a polymerizable anthrapyridone dye containing an acryloyl-group, it can copolymerize with methyl methacrylate and 4-chloromethyl styrene, providing fluorescent nanoparticles with reactive chloromethyl groups (Figure [1]).[4] Arnottion I (C) and WS-5995A (D) are natural products and display important biological activities such as antitumor, antibacterial and antivirus action.[5]

Common synthetic methods used for the construction of phenanthridinones are homolytic aromatic substitution and palladium-catalyzed direct C–H activation. In 2005, Fagnou et al. reported the intramolecular and intermolecular direct arylation reactions of aryl iodides and bromides for the synthesis of 6H-benzo[c]chromenes and 5-methylphenanthridin-6(5H)-one by using Pearlman’s catalyst (Pd(OH)2/C/KOAc/DMA/130 °C).[6] In 2008, Itami et al. first reported the t-BuOK mediated homolytic aromatic substitution of electron-deficient heteroarenes with aryl halides.[7] After these reports, several methodologies have emerged that demonstrated different N/O-based ligand promoted biaryl synthesis methods, which proceed through homolytic aromatic substitution mechanisms.[8] There are also many methodologies for the synthesis of dibenzo-α-pyranones[9] and the strategies mainly focus on palladium-catalyzed reactions. For example, the Suzuki–Miyaura cross-coupling of o-bromoarylcarboxylates and o-hydroxyarylboronic acids,[10] the Pd-catalyzed CO insertion into 2-arylphenols[11] and 10-hydroxy-10,9-boroxarophenanthrenes,[12] and the new [N,P]-pyrrole PdCl2 complexes catalyzed the formation of dibenzo-α-pyrones via phenyl 2-iodobenzoates.[13]

Zoom Image
Figure 1 Some useful phenanthridinone and dibenzo-α-pyrone derivatives

In recent years, palladium-catalyzed direct C–H bond activation (sp2-C and sp3-C),[14] particularly the heterogeneous palladium-catalyzed C–H bond activation,[15] has drawn considerable attention because of their convenience and efficiency both on laboratory and industrial scales. Among palladium catalysts, Pd/C is one of the most commonly used catalysts in organic synthesis because of its large surface area, good pore structure, good load performance and reduction property.[16] It is also attractive for industrial applications because of its high catalytic activity, low costs, ease of removal and commercial availability.[17] In a continuation of our ongoing efforts to assemble these heterocycles,[18] here we report two efficient and convenient Pd/C catalyzed intramolecular C–H arylation reactions for the synthesis of phenanthridinones and dibenzo-α-pyrones, which might be applicable in industrial areas.

Initially, 2-iodo-N-methyl-N-phenylbenzamide 1a was selected as the model substrate to identify and optimize the reaction parameters including reaction temperature, base, and solvent. When the reaction was carried out with 10% Pd/C (10% wt% of 1a, 10 mg), 2-iodo-N-methyl-N-phenylbenzamide 1a (0.3 mmol) and KOAc (0.6 mmol) in toulene (2.0 mL) at 130 °C under N2 atmosphere for 24 h, the desired product 5-methylphenanthridin-6(5H)-one 1b could be isolated in 56% yield (Table [1], entry 1). The reaction was investigated in other solvents (DMSO, DMF, dioxane and DMA) and DMA was found to be the best choice (entries 2–5). The reaction at lower temperature (120 °C) reduced the reaction yields and 125 °C was the optimal temperature (entries 6 and 7). Other economical bases such as K2CO3 were also used and the yield was clearly reduced (entry 8). From the experiments we can conclude that both the 10% Pd/C catalyst and the base are important for the reaction (entries 9 and 10). When we reduced the amount of 10% Pd/C, the product was obtained in lower yield (entry 11). We also bought several Pd/C sources from different companies and the results did not change sognificantly (see the Supporting Information for experimental data). Table [1], entry 6 summarizes the best reaction conditions.

Table 1 Optimization of the Reaction Conditionsa

Entry

Base

Solvent

T (°C)

Yield (%)b

1

KOAc

toluene

130

56

2

KOAc

DMSO

130

75

3

KOAc

DMF

130

82

4

KOAc

dioxane

130

49

5

KOAc

DMA

130

98

6

KOAc

DMA

125

98

7

KOAc

DMA

120

96

8

K2CO3

DMA

125

80

9

DMA

125

0c

10

KOAc

DMA

125

0d

11

KOAc

DMA

125

89e

a Reaction conditions: 10% Pd/C (10% wt% of 1a, 10 mg), 2-iodo-N-methyl-N-phenylbenzamide 1a (0.3 mmol), base (0.6 mmol), solvent (2.0 mL) under N2 atmosphere for 24 h.

b Isolated yield after flash chromatography based on 1a.

c No base was used.

d No 10% Pd/C was used.

e 10% Pd/C (5% wt% of 1a) was used.

Table 2 Optimization of the Reaction Conditionsa

Entry

A

b

Yield (%)b

1

1a

1b

98

2

2a

2b

85

3

3a

3b+3b′

90c

4

4a

4b

93

5

5a

5b

91

6

6a

6b

99

7

7a

7b

96

8

8a

8b

56

9

9a

9b

90

10

10a

10b

90

11

11a

11b

96

12

12a

12b

97

13

13a

1b

76

14

14a

4b

73

15

15a

1b

0

a Reaction conditions: 10% Pd/C (10% wt% of a), 2-halo-N-methyl-N-phenylbenzamides a (0.3 mmol), KOAc (0.6 mmol) in DMA (2.0 mL) at 125 °C under N2 atmosphere for 24 h.

b Isolated yield after flash chromatography based on a.

c A mixture of two isomers was obtained, and the isomeric ratio based on 1H NMR analysis was ca. 1:1.

With the optimized reaction conditions in hand, the scope of the reaction with respect to substrates was further investigated (Table [2]). The substrates of 2-halo-N-methyl-N-phenylbenzamides a could generate the desired products b in moderate to excellent yields (entries 1–15). When the group R2 was a mono-substituted electron-donating group (CH3 and t-Bu) and electron-withdrawing group substituted (F, Cl, and OCF3), the products were obtained in excellent yield (entries 1–7). When N-(2,4-dichlorophenyl)-2-iodo-N-methylbenzamide 8a was used, the desired product 8b was obtained only in 56% yield (entry 8). The reaction of N-ethyl-2-iodo-N-phenylbenzamide 9a was also investigated and excellent yield was achieved (entry 9). When the group R1 of 2-halo-N-methyl-N-phenylbenzamides a was an electron-donating group (CH3) and electron-withdrawing group (F), the corresponding products were also isolated in excellent yields (entries 10–12). 2-Bromo-N-methyl-N-phenylbenzamide 13a and 2-bromo-N-methyl-N-(p-tolyl)benzamide 14a were used to repeat the reaction, but only moderate yields were obtained (entries 13 and 14). When 2-chloro-N-methyl-N-phenylbenzamide 15a was used, the reaction did not proceed (entry 15). Then the scope of Pd/C catalyzed cross-coupling reaction for the synthesis of dibenzo-α-pyrones was also investigated. The ­substrates of phenyl 2-iodobenzoates c could react well under the reaction conditions, and generated the corresponding products d in moderate yields (1d5d).

Table 3 Scope of the Pd/C-Catalyzed Cross-Coupling Reaction for the Synthesis of Dibenzo-α-pyronesa

Entry

c

d

Yield (%)b

1

1c

1d

62

2

2c

2d

59

3

3c

3d

60

4

4c

4d

64

5

5c

5d

51

a Reaction conditions: 10% Pd/C (20% wt% of c), phenyl 2-iodobenzoates c (0.3 mmol), KOAc (0.6 mmol) in DMA (2.0 mL) at 125 °C under N2 atmosphere for 24 h.

b Isolated yield after flash chromatography based on c.

Table 4 Pd/C Recycling Experiments for the Synthesis of 5-Methylphenanthridin-6(5H)-onea

Cycle

1

2

3

4

Yield (%)b

98

98

97

95

a Reaction conditions: 10% Pd/C (10% wt% of 1a), 2-halo-N-methyl-N-phenylbenzamide 1a (5 mmol), KOAc (10 mmol) in DMA (10 mL) at 125 °C under N2 atmosphere for 24 h.

b Isolated yield after flash chromatography based on 1a.

From an economic and industrial point of view, the recyclability of the Pd/C catalyst was studied. Taking advantage of the insolubility of Pd/C in H2O and EtOAc, the simple operations of filtration and washing were sufficient to recover the catalyst. The results of the recycling experiment are shown in Table [4]. The catalyst could be reused under the same reaction conditions after separation and washing with water. Notably, the Pd/C catalyst remained highly catalytically active after being reused four times. The coupling reaction at the fourth run gave the desired product 1b in 95% yield.

In summary, we have developed two Pd/C catalyzed intramolecular C–H arylation reactions for the synthesis of phenanthridinones and dibenzo-α-pyrones. The reactions exhibit some functional group tolerance and allows for the preparation of a number of phenanthridinones and dibenzo-α-pyrones in moderate to excellent yields. The high catalytic activity, high recyclability, low costs, ease of removal, and commercial availability of Pd/C render this protocol attractive for both synthetic and industrial applications.

All reagents and solvents were pure analytical grade materials purchased from commercial sources and were used without further purification, if not stated otherwise. All melting points are uncorrected. All starting substrates were prepared according to reported procedures. NMR spectra were recorded in CDCl3 with an Agilent 400 MHz instrument with TMS as internal standard. High-resolution mass spectra (HRMS) were obtained with a G2-X5 Q-TOF Premier (ESI). TLC was carried out with 0.2 mm thick silica gel plates (GF254). Visualization was accomplished under UV light. Columns for chromatography were hand packed with silica gel (200–300 mesh). All reactions were carried out in an over-dried Schlenk tube equipped with a magnetic stir bar.


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Synthesis of Phenanthridinones; General Procedure

An oven-dried Schlenk tube equipped with a Teflon valve was charged with a magnetic stir bar, 10% Pd/C (10 wt% of a), 2-halo-N-methyl-N-phenylbenzamides a (0.3 mmol) and KOAc (0.6 mmol). The tube was placed under vacuum for 20 min and backfilled with N2. Then DMA (2.0 mL) was added through a syringe. The reaction mixture was stirred at 125 °C for 24 h. The reaction was monitored by TLC. When 2-halo-N-methyl-N-phenylbenzamides a was consumed completely, the reaction was stopped and cooled to r.t., EtOAc (40 mL) was added and the mixture was washed with brine (3 × 20 mL). The organic phase was dried over Na2SO4 and concentrated. The residue was purified directly by column chromatography on silica gel (petroleum ether/EtOAc = 5:1 v/v) to give the pure products b.


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Synthesis of Dibenzo-α-pyrones; General Procedure

An oven-dried Schlenk tube equipped with a Teflon valve was charged with a magnetic stir bar, 10% Pd/C (20 wt% of c), phenyl 2-iodobenzoates c (0.3 mmol) and KOAc (0.6 mmol). The tube was placed under vacuum for 20 min and backfilled with N2. Then DMA (2.0 mL) was added through a syringe. The reaction mixture was stirred at 125 °C for 24 h. The reaction was monitored by TLC. When phenyl 2-iodobenzoates c was consumed completely, the reaction was stopped and cooled to r.t., EtOAc (40 mL) was added and the mixture was washed with brine (3 × 20 mL). The organic phase was dried over Na2SO4 and concentrated. The residue was purified directly by column chromatography on silica gel (petroleum ether/Et3N = 20:1 v/v) to give the pure products d.


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Synthesis of 5-Methylphenanthridin-6(5H)-one with Pd/C Recycling

A 100 mL oven-dried Schlenk tube equipped with a Teflon valve was charged with a magnetic stir bar, 10% Pd/C (10 wt% of 1a, 0.169 g), 2-iodo-N-methyl-N-phenylbenzamide 1a (5 mmol) and KOAc (10 mmol). The tube was placed under vacuum for 20 min and backfilled with N2. Then DMA (20 mL) was added through a syringe. The reaction mixture was stirred at 125 °C for 24 h. The reaction was monitored by TLC. When 2-iodo-N-methyl-N-phenylbenzamide 1a was consumed completely, the reaction was stopped and cooled to r.t., H2O (50 mL) was added and the mixture was filtrated, the black solid residue was washed with EtOAc (3 × 20 mL), then the black solid residue of Pd/C was collected to repeat the next recycling experiment without purification. The organic phase of the filtrate was separated and the organic phase was washed with brine (3 × 20 mL). The organic phase was dried over Na2SO4 and concentrated. The residue was purified directly by column chromatography on silica gel (petroleum ether/EtOAc = 5:1 v/v) to give the pure product 1b.


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5-Methylphenanthridin-6(5H)-one (1b)

Synthesized according to the general procedure. The procedure was followed starting from 10% Pd/C (10 wt% of 1a, 10 mg), 1a (0.3 mmol), KOAc (0.6 mmol) in DMA (2.0 mL) at 125 °C under N2 atmosphere for 24 h. Flash chromatography [silica gel; petroleum ether/EtOAc = 5:1 v/v; Rf = 0.45] gave a white solid (61.4 mg, 98% yield); mp 104–106 °C.

1H NMR (400 MHz, CDCl3): δ = 8.55 (d, J = 8.0 Hz, 1 H), 8.27 (d, J = 7.6 Hz, 1 H), 8.26 (d, J = 8.0 Hz, 1 H), 7.75 (t, J = 7.6 Hz, 1 H), 7.60–7.53 (m, 2 H), 7.41 (d, J = 8.4 Hz, 1 H), 7.32 (t, J = 7.6 Hz, 1 H), 3.81 (s, 3 H).

13C NMR (100 MHz, CDCl3): δ = 161.76, 138.14, 133.65, 132.50, 129.67, 129.01, 128.06, 125.70, 123.33, 122.58, 121.72, 119.40, 115.16, 30.10.


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4,5-Dimethylphenanthridin-6(5H)-one (2b)

Synthesized according to the general procedure. The procedure was followed starting from 10% Pd/C (10 wt% of 2a, 11 mg), 2a (0.3 mmol), KOAc (0.6 mmol) in DMA (2.0 mL) at 125 °C under N2 atmosphere for 24 h. Flash chromatography [silica gel; petroleum ether/EtOAc = 5:1 v/v; Rf = 0.49] gave a white solid (56.9 mg, 85% yield); mp 57–58 °C.

1H NMR (400 MHz, CDCl3): δ = 8.48 (d, J = 8.0 Hz, 1 H), 8.17 (d, J = 8.8 Hz, 1 H), 8.06 (d, J = 8.0 Hz, 1 H), 7.69 (t, J = 8.0 Hz, 1 H), 7.53 (t, J = 7.2 Hz, 1 H), 7.27 (d, J = 7.2 Hz, 1 H), 7.18 (t, J = 7.6 Hz, 1 H), 3.77 (s, 3 H), 2.63 (s, 3 H).

13C NMR (100 MHz, CDCl3): δ = 164.19, 139.52, 133.98, 133.80, 132.49, 128.50, 127.86, 126.21, 125.42, 122.91, 121.89, 121.30, 121.05, 38.42, 23.16.


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1,5-Dimethylphenanthridin-6(5H)-one (3b) and 3,5-Dimethylphenanthridin-6(5H)-one (3b′)

Synthesized according to the general procedure. The procedure was followed starting from 10% Pd/C (10 wt% of 3a, 11 mg), 3a (0.3 mmol), KOAc (0.6 mmol) in DMA (2.0 mL) at 125 °C under N2 atmosphere for 24 h. Flash chromatography [silica gel; petroleum ether/EtOAc = 5:1 v/v; Rf = 0.50] gave a mixture of two isomers as a brown oil (60.2 mg, 90% yield, ratio = 1:1).

1H NMR (400 MHz, CDCl3): δ = 8.63 (d, J = 8.0 Hz, 1 H), 8.52 (d, J = 8.0 Hz, 1 H), 8.42 (d, J = 8.4 Hz, 1 H), 8.20 (d, J = 8.0 Hz, 1 H), 8.13 (d, J = 8.0 Hz, 1 H), 7.75–7.70 (m, 2 H), 7.60–7.52 (m, 2 H), 7.41 (t, J = 8.0 Hz, 1 H), 7.32 (d, J = 8.4 Hz, 1 H), 7.19–7.11 (m, 3 H), 3.80 (s, 3 H), 3.79 (s, 3 H), 2.93 (s, 3 H), 2.50 (s, 3 H).

13C NMR (100 MHz, CDCl3): δ = 161.91, 161.74, 139.99, 139.16, 138.08, 136.43, 134.73, 133.74, 132.43, 131.51, 128.97, 128.94, 128.40, 127.55, 127.38, 127.29, 126.73, 125.23, 123.72, 123.19, 121.47, 119.32, 116.92, 115.51, 113.40, 110.11, 30.96, 30.05, 26.61, 22.08.


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2,5-Dimethylphenanthridin-6(5H)-one (4b)

Synthesized according to the general procedure. The procedure was followed starting from 10% Pd/C (10 wt% of 4a, 11 mg), 4a (0.3 mmol), KOAc (0.6 mmol) in DMA (2.0 mL) at 125 °C under N2 atmosphere for 24 h. Flash chromatography [silica gel; petroleum ether/EtOAc = 5:1 v/v; Rf = 0.49] gave a white solid (62.2 mg, 93% yield); mp 130–131 °C.

1H NMR (400 MHz, CDCl3): δ = 8.51 (d, J = 8.0 Hz, 1 H), 8.18 (d, J = 8.0 Hz, 1 H), 7.97 (s, 1 H), 7.69 (t, J = 8.0 Hz, 1 H), 7.53 (t, J = 7.6 Hz, 1 H), 7.29 (d, J = 8.4 Hz, 1 H), 7.22 (t, J = 8.4 Hz, 1 H), 3.73 (s, 3 H), 2.44 (s, 3 H).

13C NMR (100 MHz, CDCl3): δ = 161.49, 135.88, 133.47, 132.25, 131.87, 130.54, 128.88, 127.79, 125.63, 123.34, 121.58, 119.06, 114.94, 29.98, 21.04.


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2-(tert-Butyl)-5-methylphenanthridin-6(5H)-one (5b)

Synthesized according to the general procedure. The procedure was followed starting from 10% Pd/C (10 wt% of 5a, 12 mg), 5a (0.3 mmol), KOAc (0.6 mmol) in DMA (2.0 mL) at 125 °C under N2 atmosphere for 24 h. Flash chromatography [silica gel; petroleum ether/EtOAc = 5:1 v/v; Rf = 0.47] gave a white solid (72.3 mg, 91% yield); mp 164–167 °C.

1H NMR (400 MHz, CDCl3): δ = 8.54 (d, J = 8.4 Hz, 1 H), 8.31–8.27 (m, 2 H), 7.45 (t, J = 7.6 Hz, 1 H), 7.60–7.54 (m, 2 H), 7.35 (d, J = 8.4 Hz, 1 H), 3.79 (s, 3 H), 1.43 (s, 9 H).

13C NMR (100 MHz, CDCl3): δ = 161.64, 145.27, 135.90, 133.85, 132.33, 129.00, 127.81, 127.22, 125.71, 121.56, 119.53, 118.73, 114.93, 34.62, 31.56, 30.01.

HRMS (ESI): m/z calcd for [C18H19NO+H+]: 266.1545; found: 266.1548.


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2-Fluoro-5-methylphenanthridin-6(5H)-one (6b)

Synthesized according to the general procedure. The procedure was followed starting from 10% Pd/C (10% wt% of 6a, 11 mg), 6a (0.3 mmol), KOAc (0.6 mmol) in DMA (2.0 mL) at 125 °C under N2 atmosphere for 24 h. Flash chromatography [silica gel; petroleum ether/EtOAc = 5:1 v/v; Rf = 0.52] gave a white solid (67.4 mg, 99% yield); mp 168–171 °C.

1H NMR (400 MHz, CDCl3): δ = 8.51 (d, J = 8.0 Hz, 1 H), 8.09 (d, J = 8.0 Hz, 1 H), 7.85 (dd, J 1 = 2.4 Hz, J 2 = 9.6 Hz, 1 H), 7.74 (t, J = 7.6 Hz, 1 H), 7.59 (t, J = 8.0 Hz, 1 H), 7.34–7.21 (m, 2 H), 3.76 (s, 3 H).

13C NMR (100 MHz, CDCl3): δ = 161.28, 158.55 (d, J = 240.1 Hz), 134.51, 132.67 (d, J = 2.8 Hz), 132.59, 129.10, 128.71, 125.87, 121.87, 120.69 (d, J = 7.7 Hz), 116.83 (d, J = 23.2 Hz), 116.58 (d, J = 8.1 Hz), 109.28 (d, J = 23.6 Hz), 30.30.


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5-Methyl-2-(trifluoromethoxy)phenanthridin-6(5H)-one (7b)

Synthesized according to the general procedure. The procedure was followed starting from 10% Pd/C (10 wt% of 7a, 13 mg), 7a (0.3 mmol), KOAc (0.6 mmol) in DMA (2.0 mL) at 125 °C under N2 atmosphere for 24 h. Flash chromatography [silica gel; petroleum ether/EtOAc = 5:1 v/v; Rf = 0.45] gave a white solid (84.4 mg, 96% yield); mp 145–147 °C.

1H NMR (400 MHz, CDCl3): δ = 8.51 (d, J = 8.0 Hz, 1 H), 8.14 (d, J = 8.0 Hz, 1 H), 8.04 (s, 1 H), 7.76 (t, J = 7.6 Hz, 1 H), 7.61 (t, J = 7.6 Hz, 1 H), 7.39 (m, 2 H), 3.78 (s, 3 H).

13C NMR (100 MHz, CDCl3): δ = 161.38, 144.37 (d, J = 2.2 Hz), 136.66, 132.77, 132.49, 129.13, 128.92, 125.83, 122.42, 121.84, 120.70 (q, J = 255.6 Hz), 120.47, 116.42, 115.95, 30.31.

HRMS (ESI): m/z calcd for [C15H10F3NO2+H+]: 294.0742; found: 294.0740.


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2,4-Dichloro-5-methylphenanthridin-6(5H)-one (8b)

Synthesized according to the general procedure. The procedure was followed starting from 10% Pd/C (10 wt% of 8a, 12 mg), 8a (0.3 mmol), KOAc (0.6 mmol) in DMA (2.0 mL) at 125 °C under N2 atmosphere for 24 h. Flash chromatography [silica gel; petroleum ether/EtOAc = 5:1 v/v; Rf = 0.50] gave a yellow solid (46.5 mg, 56% yield); mp 156–159 °C.

1H NMR (400 MHz, CDCl3): δ = 8.50 (d, J = 7.6 Hz, 1 H), 8.15–8.12 (m, 2 H), 7.78 (t, J = 7.6 Hz, 1 H), 7.63 (t, J = 7.6 Hz, 1 H), 7.53 (s, 1 H), 3.92 (s, 3 H).

13C NMR (100 MHz, CDCl3): δ = 163.47, 135.77, 133.13, 132.06, 131.98, 129.42, 128.97, 128.53, 125.82, 124.13, 122.82, 122.11, 121.91, 38.73.

HRMS (ESI): m/z calcd for [C14H9Cl2NO+H+]: 278.0139; found: 278.0144.


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5-Ethylphenanthridin-6(5H)-one (9b)

Synthesized according to the general procedure. The procedure was followed starting from 10% Pd/C (10 wt% of 9a, 11 mg), 9a (0.3 mmol), KOAc (0.6 mmol) in DMA (2.0 mL) at 125 °C under N2 atmosphere for 24 h. Flash chromatography [silica gel; petroleum ether/EtOAc = 5:1 v/v; Rf = 0.46] gave a yellow solid (60.2 mg, 90% yield); mp 81–84 °C.

1H NMR (400 MHz, CDCl3): δ = 8.55 (d, J = 8.0 Hz, 1 H), 8.28 (t, J = 8.8 Hz, 2 H), 7.75 (t, J = 7.6 Hz, 1 H), 7.60–7.53 (m, 2 H), 7.43 (d, J = 8.8 Hz, 1 H), 7.31 (t, J = 7.6 Hz, 1 H), 4.47 (q, J = 7.2 Hz, 2 H), 1.42 (t, J = 7.2 Hz, 3 H).

13C NMR (100 MHz, CDCl3): δ = 161.25, 136.99, 133.65, 132.48, 129.68, 128.87, 128.02, 125.69, 123.61, 122.38, 121.68, 119.65, 115.08, 37.81, 12.85.


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5,9-Dimethylphenanthridin-6(5H)-one (10b)

Synthesized according to the general procedure. The procedure was followed starting from 10% Pd/C (10 wt% of 10a, 11 mg), 10a (0.3 mmol), KOAc (0.6 mmol) in DMA (2.0 mL) at 125 °C under N2 atmosphere for 24 h. Flash chromatography [silica gel; petroleum ether/EtOAc = 5:1 v/v; Rf = 0.46] gave a white solid (60.2 mg, 90% yield); mp 127–128 °C.

1H NMR (400 MHz, CDCl3): δ = 8.33 (s, 1 H), 8.22 (d, J = 7.6 Hz, 1 H), 8.14 (d, J = 8.4 Hz, 1 H), 7.48–7.56 (m, 2 H), 7.38 (d, J = 8.4 Hz, 1 H), 7.27 (t, J = 7.6 Hz, 1 H), 3.80 (s, 3 H), 2.51 (s, 3 H).

13C NMR (100 MHz, CDCl3): δ = 161.78, 138.18, 137.72, 133.82, 131.13, 129.14, 128.69, 125.47, 123.04, 122.49, 121.71, 119.48, 115.08, 30.09, 21.51.


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9-Fluoro-5-methylphenanthridin-6(5H)-one (11b)

Synthesized according to the general procedure. The procedure was followed starting from 10% Pd/C (10 wt% of 11a, 11 mg), 11a (0.3 mmol), KOAc (0.6 mmol) in DMA (2.0 mL) at 125 °C under N2 atmosphere for 24 h. Flash chromatography [silica gel; petroleum ether/EtOAc = 5:1 v/v; Rf = 0.48] gave a yellow solid (65.4 mg, 96% yield); mp 153–155 °C.

1H NMR (400 MHz, CDCl3): δ = 8.53 (dd, J 1 = 6.0 Hz, J 2 = 8.8 Hz, 1 H), 8.11 (d, J = 8.0 Hz, 1 H), 7.83 (d, J = 10.0 Hz, 1 H), 7.56 (t, J = 8.0 Hz, 1 H), 7.39 (d, J = 8.4 Hz, 1 H), 7.33–7.23 (m, 2 H), 3.77 (s, 3 H).

13C NMR (100 MHz, CDCl3): δ = 165.59 (d, J = 250.3 Hz), 160.99, 138.46, 136.15 (d, J = 9.4 Hz), 132.17 (d, J = 9.8 Hz), 130.40, 123.55, 122.67, 122.16, 118.55 (d, J = 3.0 Hz), 116.29 (d, J = 22.7 Hz), 115.31, 107.63 (d, J = 21.3 Hz), 30.04.

HRMS (ESI): m/z calcd for [C14H10FNO+H+]: 228.0825; found: 228.0826.


#

8-Fluoro-5-methylphenanthridin-6(5H)-one (12b)

Synthesized according to the general procedure. The procedure was followed starting from 10% Pd/C (10 wt% of 12a, 11 mg), 12a (0.3 mmol), KOAc (0.6 mmol) in DMA (2.0 mL) at 125 °C under N2 atmosphere for 24 h. Flash chromatography [silica gel; petroleum ether/EtOAc = 5:1 v/v; Rf = 0.50] gave a yellow solid (66.1 mg, 97% yield); mp 172–173 °C.

1H NMR (400 MHz, CDCl3): δ = 8.24 (dd, J 1 = 4.8 Hz, J 2 = 8.8 Hz, 1 H), 8.20–7.16 (m, 2 H), 7.54 (t, J = 7.2 Hz, 1 H), 7.46 (dt, J 1 = 2.8 Hz, J 2 = 8.8 Hz, 1 H), 7.41 (d, J = 8.4 Hz, 1 H), 7.33 (t, J = 7.6 Hz, 1 H), 3.80 (s, 3 H).

13C NMR (100 MHz, CDCl3): δ = 162.34 (d, J = 246.9 Hz), 160.80 (d, J = 3.1 Hz), 137.53, 130.07 (d, J = 2.6 Hz), 129.56, 127.48 (d, J = 7.9 Hz), 124.31 (d, J = 7.8 Hz), 123.16, 122.85, 120.90 (d, J = 23.0 Hz), 118.77, 115.28, 114.34 (d, J = 22.8 Hz), 30.27.

HRMS (ESI): m/z calcd for [C14H10FNO+H+]: 228.0825; found: 228.0822.


#

6H-Benzo[c]chromen-6-one (1d)

Synthesized according to the general procedure. The procedure was followed starting from 10% Pd/C (20 wt% of 1c, 19 mg), 1c (0.3 mmol), KOAc (0.6 mmol) in DMA (2.0 mL) at 125 °C under N2 atmosphere for 24 h. Flash chromatography [silica gel; petroleum ether/Et3N = 20:1 v/v; Rf = 0.40] gave a white solid (36.5 mg, 62% yield); mp 92–94 °C.

1H NMR (400 MHz, CDCl3): δ = 8.40 (d, J = 8.0 Hz, 1 H), 8.12 (d, J = 8.8 Hz, 1 H), 8.06 (d, J = 7.6 Hz, 1 H), 7.83 (t, J = 8.0 Hz, 1 H), 7.58 (t, J = 8.0 Hz, 1 H), 7.48 (t, J = 8.0 Hz, 1 H), 7.38–7.32 (m, 2 H).

13C NMR (100 MHz, CDCl3): δ = 161.31, 151.42, 134.97, 134.90, 130.71, 130.57, 129.01, 124.67, 122.89, 121.81, 121.40, 118.17, 117.92.


#

2-Methyl-6H-benzo[c]chromen-6-one (2d)

Synthesized according to the general procedure. The procedure was followed starting from 10% Pd/C (20 wt% of 2c, 20 mg), 2c (0.3 mmol), KOAc (0.6 mmol) in DMA (2.0 mL) at 125 °C under N2 atmosphere for 24 h. Flash chromatography [silica gel; petroleum ether/Et3N = 20:1 v/v; Rf = 0.45] gave a white solid (37.2 mg, 59% yield); mp 118–120 °C.

1H NMR (400 MHz, CDCl3): δ = 8.37 (d, J = 8.0 Hz, 1 H), 8.08 (d, J = 8.0 Hz, 1 H), 8.01–7.77 (m, 2 H), 7.55 (t, J = 8.0 Hz, 1 H), 7.27–7.21 (m, 2 H), 2.45 (s, 3 H).

13C NMR (100 MHz, CDCl3): δ = 161.47, 149.46, 134.92, 134.82, 134.21, 131.44, 130.66, 128.79, 122.84, 121.70, 121.38, 117.72, 117.57, 21.23.


#

1,3-Dimethyl-6H-benzo[c]chromen-6-one (3d)

Synthesized according to the general procedure. The procedure was followed starting from 10% Pd/C (20 wt% of 3c, 21 mg), 3c (0.3 mmol), KOAc (0.6 mmol) in DMA (2.0 mL) at 125 °C under N2 atmosphere for 24 h. Flash chromatography [silica gel; petroleum ether/Et3N = 20:1 v/v; Rf = 0.40] gave a white solid (40.3 mg, 60% yield); mp 133–135 °C.

1H NMR (400 MHz, CDCl3): δ = 8.45 (d, J = 7.6 Hz, 1 H), 8.31 (d, J = 7.6 Hz, 1 H), 7.78 (t, J = 7.6 Hz, 1 H), 7.54 (t, J = 7.6 Hz, 1 H), 7.04 (s, 1 H), 6.96 (s, 1 H), 2.82 (s, 3 H), 2.38 (s, 3 H).

13C NMR (100 MHz, CDCl3): δ = 161.60, 152.30, 140.01, 136.36, 135.95, 134.35, 130.89, 130.11, 127.69, 125.94, 121.80, 116.48, 114.92, 25.56, 21.16.


#

2,4-Di-tert-butyl-6H-benzo[c]chromen-6-one (4d)

Synthesized according to the general procedure. The procedure was followed starting from 10% Pd/C (20 wt% of 4c, 26 mg), 4c (0.3 mmol), KOAc (0.6 mmol) in DMA (2.0 mL) at 125 °C under N2 atmosphere for 24 h. Flash chromatography [silica gel; petroleum ether/Et3N = 20:1 v/v; Rf = 0.44] gave a white solid (59.2 mg, 64% yield); mp 135–137 °C.

1H NMR (400 MHz, CDCl3): δ = 8.42 (d, J = 7.6 Hz, 1 H), 8.19 (d, J = 8.8 Hz, 1 H), 7.96 (d, J = 2.0 Hz, 1 H), 7.82 (dt, J 1 = 1.2 Hz, J 2 = 7.6 Hz,1 H), 7.58–7.55 (m, 2 H), 1.56 (s, 9 H), 1.42 (s, 9 H).

13C NMR (100 MHz, CDCl3): δ = 160.88, 148.20, 146.42, 137.98, 135.90, 134.59, 130.29, 128.39, 125.69, 121.94, 120.94, 115.53, 117.17, 31.62, 30.21.


#

4-Phenyl-6H-benzo[c]chromen-6-one (5d)

Synthesized according to the general procedure for the dibenzo-α-pyrones. The procedure was followed starting from 10% Pd/C (20 wt% of 5c, 24 mg), 5c (0.3 mmol), KOAc (0.6 mmol) in DMA (2.0 mL) at 125 °C under N2 atmosphere for 24 h. Flash chromatography [silica gel; petroleum ether/Et3N = 20:1 v/v; Rf = 0.45] gave a yellow solid (41.6 mg, 51% yield); mp 126–128 °C.

1H NMR (400 MHz, CDCl3): δ = 8.41 (d, J = 7.6 Hz, 1 H), 8.19 (d, J = 8.8 Hz, 1 H), 8.09 (d, J = 8.0 Hz, 1 H), 7.85 (t, J = 8.0 Hz,1 H), 7.65–7.58 (m, 3 H), 7.54–7.48 (m, 3 H), 7.43–7.39 (m, 2 H).

13C NMR (100 MHz, CDCl3): δ = 160.85, 148.28, 136.44, 135.10, 134.95, 132.05, 131.32, 130.65, 129.77, 129.05, 128.54, 127.97, 124.48, 122.13, 122.08, 121.28, 118.57.


#
#
  • References

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    • 1b Ghosal S. Rao PH. Jaiswal DK. Kumar Y. Frahm AW. Phytochemistry 1981; 20: 2003
    • 1c Patil S. Kamath S. Sanchez T. Neamati N. Schinazi RF. Buolamwini JK. Bioorg. Med. Chem. 2007; 15: 1212
    • 1d Holl V. Coelho D. Weltin D. Hyun JW. Dufour P. Bischoff P. Anticancer Res. 2000; 20: 3233
    • 2a Aly AH. Edrada-Ebel R. Indriani ID. Wray V. Müller WE. G. Totzke F. Zirrgiebel U. Schächtele C. Kubbutat MH. G. Lin WH. Proksch P. Ebel R. J. Nat. Prod. 2008; 71: 972
    • 2b Mao Z. Sun W. Fu L. Luo H. Lai D. Zhou L. Molecules 2014; 19: 5088
    • 2c Bialonska D. Kasimsetty SG. Khan SI. Ferreira D. J. Agric. Food Chem. 2009; 57: 10181
    • 2d Griffin GF. Chu FS. Appl. Environ. Microbiol. 1983; 46: 1420
    • 2e Chu FS. J. Am. Oil Chem. Soc. 1981; 58: 1006
    • 2f Maeda N. Kokai Y. Ohtani S. Sahara H. Kuriyama I. Kamisuki S. Takahashi S. Sakaguchi K. Sugawara F. Yoshida H. Biochem. Biophys. Res. Commun. 2007; 352: 390
  • 3 Halim SA. Ibrahim MA. J. Mol. Struct. 2017; 1130: 543
  • 4 Qiang XX. Wu T. Fan JL. Wang JY. Song FL. Sun SG. Jiang JY. Peng XJ. J. Mater. Chem. 2012; 22: 16078
    • 5a Harayama T. Yasuda H. Heterocycles 1997; 46: 61
    • 5b Harayama T. Yasuda H. Akiyama T. Takeuchi Y. Abe H. Chem. Pharm. Bull. 2000; 48: 861
    • 5c Qabaja G. Jones GB. J. Org. Chem. 2000; 65: 7187
  • 6 Parisien M. Valette D. Fagnou K. J. Org. Chem. 2005; 70: 7578
  • 7 Yanagisawa S. Ueda K. Taniguchi T. Itami K. Org. Lett. 2008; 10: 4673
    • 8a Sun CL. Li H. Yu DG. Yu M. Lu XY. Haung K. Zheng SF. Li BJ. Shi ZJ. Nat. Chem. 2010; 2: 1044
    • 8b Liu W. Cao H. Zhang H. Zhang H. Chung KH. He C. Wang H. Kwong FY. Lei A. J. Am. Chem. Soc. 2010; 132: 16737
    • 8c Shirakawa E. Itoh K. Higashino T. Hayashi T. J. Am. Chem. Soc. 2010; 132: 15537
    • 8d Bhakuni BS. Kumar A. Balkrishna SJ. Sheikh JA. Konar S. Kumar S. Org. Lett. 2012; 14: 11
    • 8e Sharma S. Kumar M. Sharma S. Nayal OS. Kumar N. Singh B. Sharma U. Org. Biomol. Chem. 2016; 14: 8536
    • 9a Nandaluru PR. Bodwell GJ. Org. Lett. 2012; 14: 310
    • 9b Hussain I. Nguyen VT. H. Yawer MA. Dang TT. Fischer C. Reinke H. Langer P. J. Org. Chem. 2007; 72: 6255
    • 9c Prust EE. Carlson EJ. Dahl BJ. Tetrahedron Lett. 2012; 53: 6433
    • 9d Wang Y. Gulevich AV. Gevorgyan V. Chem. Eur. J. 2013; 19: 15836
    • 9e Sun CL. Gu YF. Huang WP. Shi ZJ. Chem. Commun. 2011; 9813
    • 9f Hager A. Mazunin D. Mayer P. Trauner D. Org. Lett. 2011; 13: 1386
    • 9g Thasana N. Worayuthakarn R. Kradanrat P. Hohn E. Young L. Ruchirawat S. J. Org. Chem. 2007; 72: 9379
    • 9h Ceylan S. Klande T. Vogt C. Friese C. Kirschning A. Synlett 2010; 2009
    • 10a Kemperman GJ. Horst BT. Van de Goor D. Roeters T. Bergwerff J. Van der Eem R. Basten J. Eur. J. Org. Chem. 2006; 3169
    • 10b Vishnumurthy K. Makriyannis A. J. Comb. Chem. 2010; 12: 664
    • 10c Luo J. Lu Y. Liu S. Liu J. Deng GJ. Adv. Synth. Catal. 2011; 353: 2604
    • 10d Singha R. Roy S. Nandi S. Ray P. Ray JK. Tetrahedron Lett. 2013; 54: 657
    • 11a Luo S. Luo FX. Zhang XS. Shi ZJ. Angew. Chem. Int. Ed. 2013; 52: 10598
    • 11b Lee TH. Jayakumar J. Cheng CH. Chuang SC. Chem. Commun. 2013; 11797
  • 12 Zhou QJ. Worm K. Dolle RE. J. Org. Chem. 2004; 69: 5147
  • 13 Suárez-Meneses JV. Oukhrib A. Gouygou M. Urrutigoïty M. Daran JC. Cordero-Vargas A. Ortega-Alfarod MC. López-Cortés JG. Dalton Trans. 2016; 9621
    • 14a Hassan J. Sevignon M. Gozzi C. Schulz E. Lemaire M. Chem. Rev. 2002; 102: 1359
    • 14b Yu JQ. Shi ZJ. Topics in Current Chemistry . Springer; Berlin: 2010
    • 14c Wu XF. Neumann H. Beller M. Chem. Rev. 2013; 113: 1
    • 14d Yin LX. Liebscher J. Chem. Rev. 2007; 107: 133
    • 15a Djakovitch L. Felpin FX. ChemCatChem 2014; 6: 2175
    • 15b Reay AJ. Fairlamb IJ. S. Chem. Commun. 2015; 16289
    • 15c Santoro S. Kozhushkov SI. Ackermann L. Vaccaro L. Green Chem. 2016; 18: 3471
    • 15d Jafarpour F. Rahiminejadan S. Hazrati H. J. Org. Chem. 2010; 75: 3109
    • 16a Midgley PA. Weyland M. Thomas JM. Gai PL. Boyes ED. Angew. Chem. 2002; 114: 3958
    • 16b Jansson AM. Grøtli M. Halkes KM. Meldal M. Org. Lett. 2002; 4: 27
    • 16c Yuan G. Keane MA. Appl. Catal., B 2004; 52: 301
    • 16d Liebeskind LS. Peña-Cabrera E. Org. Synth. 2000; 77: 138
    • 16e Yu K. Sommer W. Richardson JM. Weck M. Jones CW. Adv. Synth. Catal. 2005; 347: 161
    • 16f Chen JS. Vasiliev AN. Panarello AP. Khinast JG. Appl. Catal., A 2007; 325: 76
    • 17a Heidenreich RG. Kohler K. Krauter JG. E. Pietsch J. Synlett 2002; 1118
    • 17b Conlon DA. Pipik B. Ferdinand S. Leblond CR. Sowa Jr. JR. Izzo B. Collin P. Ho GJ. Williams JM. Shi YJ. Sun Y. Adv. Synth. Catal. 2003; 345: 931
    • 18a Sun MM. Shen GD. Bao WL. Adv. Synth. Catal. 2012; 354: 3468
    • 18b Shen GD. Zhao LY. Wang YC. Xia WF. Yang MS. Zhang TX. RSC Adv. 2016; 6: 84748
    • 18c Shen GD. Yang BC. Huang XQ. Hou YX. Gao H. Cui JC. Cui CS. Zhang TX. J. Org. Chem. 2017; 82: 3798

  • References

    • 1a Nakamura M. Aoyama A. Salim MT. A. Okamoto M. Baba M. Miyachi H. Hashimoto Y. Aoyam H. Bioorg. Med. Chem. 2010; 18: 2402
    • 1b Ghosal S. Rao PH. Jaiswal DK. Kumar Y. Frahm AW. Phytochemistry 1981; 20: 2003
    • 1c Patil S. Kamath S. Sanchez T. Neamati N. Schinazi RF. Buolamwini JK. Bioorg. Med. Chem. 2007; 15: 1212
    • 1d Holl V. Coelho D. Weltin D. Hyun JW. Dufour P. Bischoff P. Anticancer Res. 2000; 20: 3233
    • 2a Aly AH. Edrada-Ebel R. Indriani ID. Wray V. Müller WE. G. Totzke F. Zirrgiebel U. Schächtele C. Kubbutat MH. G. Lin WH. Proksch P. Ebel R. J. Nat. Prod. 2008; 71: 972
    • 2b Mao Z. Sun W. Fu L. Luo H. Lai D. Zhou L. Molecules 2014; 19: 5088
    • 2c Bialonska D. Kasimsetty SG. Khan SI. Ferreira D. J. Agric. Food Chem. 2009; 57: 10181
    • 2d Griffin GF. Chu FS. Appl. Environ. Microbiol. 1983; 46: 1420
    • 2e Chu FS. J. Am. Oil Chem. Soc. 1981; 58: 1006
    • 2f Maeda N. Kokai Y. Ohtani S. Sahara H. Kuriyama I. Kamisuki S. Takahashi S. Sakaguchi K. Sugawara F. Yoshida H. Biochem. Biophys. Res. Commun. 2007; 352: 390
  • 3 Halim SA. Ibrahim MA. J. Mol. Struct. 2017; 1130: 543
  • 4 Qiang XX. Wu T. Fan JL. Wang JY. Song FL. Sun SG. Jiang JY. Peng XJ. J. Mater. Chem. 2012; 22: 16078
    • 5a Harayama T. Yasuda H. Heterocycles 1997; 46: 61
    • 5b Harayama T. Yasuda H. Akiyama T. Takeuchi Y. Abe H. Chem. Pharm. Bull. 2000; 48: 861
    • 5c Qabaja G. Jones GB. J. Org. Chem. 2000; 65: 7187
  • 6 Parisien M. Valette D. Fagnou K. J. Org. Chem. 2005; 70: 7578
  • 7 Yanagisawa S. Ueda K. Taniguchi T. Itami K. Org. Lett. 2008; 10: 4673
    • 8a Sun CL. Li H. Yu DG. Yu M. Lu XY. Haung K. Zheng SF. Li BJ. Shi ZJ. Nat. Chem. 2010; 2: 1044
    • 8b Liu W. Cao H. Zhang H. Zhang H. Chung KH. He C. Wang H. Kwong FY. Lei A. J. Am. Chem. Soc. 2010; 132: 16737
    • 8c Shirakawa E. Itoh K. Higashino T. Hayashi T. J. Am. Chem. Soc. 2010; 132: 15537
    • 8d Bhakuni BS. Kumar A. Balkrishna SJ. Sheikh JA. Konar S. Kumar S. Org. Lett. 2012; 14: 11
    • 8e Sharma S. Kumar M. Sharma S. Nayal OS. Kumar N. Singh B. Sharma U. Org. Biomol. Chem. 2016; 14: 8536
    • 9a Nandaluru PR. Bodwell GJ. Org. Lett. 2012; 14: 310
    • 9b Hussain I. Nguyen VT. H. Yawer MA. Dang TT. Fischer C. Reinke H. Langer P. J. Org. Chem. 2007; 72: 6255
    • 9c Prust EE. Carlson EJ. Dahl BJ. Tetrahedron Lett. 2012; 53: 6433
    • 9d Wang Y. Gulevich AV. Gevorgyan V. Chem. Eur. J. 2013; 19: 15836
    • 9e Sun CL. Gu YF. Huang WP. Shi ZJ. Chem. Commun. 2011; 9813
    • 9f Hager A. Mazunin D. Mayer P. Trauner D. Org. Lett. 2011; 13: 1386
    • 9g Thasana N. Worayuthakarn R. Kradanrat P. Hohn E. Young L. Ruchirawat S. J. Org. Chem. 2007; 72: 9379
    • 9h Ceylan S. Klande T. Vogt C. Friese C. Kirschning A. Synlett 2010; 2009
    • 10a Kemperman GJ. Horst BT. Van de Goor D. Roeters T. Bergwerff J. Van der Eem R. Basten J. Eur. J. Org. Chem. 2006; 3169
    • 10b Vishnumurthy K. Makriyannis A. J. Comb. Chem. 2010; 12: 664
    • 10c Luo J. Lu Y. Liu S. Liu J. Deng GJ. Adv. Synth. Catal. 2011; 353: 2604
    • 10d Singha R. Roy S. Nandi S. Ray P. Ray JK. Tetrahedron Lett. 2013; 54: 657
    • 11a Luo S. Luo FX. Zhang XS. Shi ZJ. Angew. Chem. Int. Ed. 2013; 52: 10598
    • 11b Lee TH. Jayakumar J. Cheng CH. Chuang SC. Chem. Commun. 2013; 11797
  • 12 Zhou QJ. Worm K. Dolle RE. J. Org. Chem. 2004; 69: 5147
  • 13 Suárez-Meneses JV. Oukhrib A. Gouygou M. Urrutigoïty M. Daran JC. Cordero-Vargas A. Ortega-Alfarod MC. López-Cortés JG. Dalton Trans. 2016; 9621
    • 14a Hassan J. Sevignon M. Gozzi C. Schulz E. Lemaire M. Chem. Rev. 2002; 102: 1359
    • 14b Yu JQ. Shi ZJ. Topics in Current Chemistry . Springer; Berlin: 2010
    • 14c Wu XF. Neumann H. Beller M. Chem. Rev. 2013; 113: 1
    • 14d Yin LX. Liebscher J. Chem. Rev. 2007; 107: 133
    • 15a Djakovitch L. Felpin FX. ChemCatChem 2014; 6: 2175
    • 15b Reay AJ. Fairlamb IJ. S. Chem. Commun. 2015; 16289
    • 15c Santoro S. Kozhushkov SI. Ackermann L. Vaccaro L. Green Chem. 2016; 18: 3471
    • 15d Jafarpour F. Rahiminejadan S. Hazrati H. J. Org. Chem. 2010; 75: 3109
    • 16a Midgley PA. Weyland M. Thomas JM. Gai PL. Boyes ED. Angew. Chem. 2002; 114: 3958
    • 16b Jansson AM. Grøtli M. Halkes KM. Meldal M. Org. Lett. 2002; 4: 27
    • 16c Yuan G. Keane MA. Appl. Catal., B 2004; 52: 301
    • 16d Liebeskind LS. Peña-Cabrera E. Org. Synth. 2000; 77: 138
    • 16e Yu K. Sommer W. Richardson JM. Weck M. Jones CW. Adv. Synth. Catal. 2005; 347: 161
    • 16f Chen JS. Vasiliev AN. Panarello AP. Khinast JG. Appl. Catal., A 2007; 325: 76
    • 17a Heidenreich RG. Kohler K. Krauter JG. E. Pietsch J. Synlett 2002; 1118
    • 17b Conlon DA. Pipik B. Ferdinand S. Leblond CR. Sowa Jr. JR. Izzo B. Collin P. Ho GJ. Williams JM. Shi YJ. Sun Y. Adv. Synth. Catal. 2003; 345: 931
    • 18a Sun MM. Shen GD. Bao WL. Adv. Synth. Catal. 2012; 354: 3468
    • 18b Shen GD. Zhao LY. Wang YC. Xia WF. Yang MS. Zhang TX. RSC Adv. 2016; 6: 84748
    • 18c Shen GD. Yang BC. Huang XQ. Hou YX. Gao H. Cui JC. Cui CS. Zhang TX. J. Org. Chem. 2017; 82: 3798

Zoom Image
Figure 1 Some useful phenanthridinone and dibenzo-α-pyrone derivatives