CC BY-ND-NC 4.0 · SynOpen 2019; 03(01): 11-15
DOI: 10.1055/s-0037-1611667
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Palladium-Catalysed Intramolecular C–N versus C–C Coupling: The Effect of 1,8-peri-Interaction in the Naphthalene System

Sudarshan Debnath
,
Department of Chemistry, Syamsundar College, Shyamsundar 713424, India   Email: shovanku@gmail.com
› Author Affiliations
The Science and Engineering Research Board of the Department of Science and Technology under the Government of India is gratefully acknowledged for an Early Career Research Award to S. M. (Sanction no. ECR/2017/000537).
Further Information

Publication History

Received: 22 December 2018

Accepted after revision: 02 January 2019

Publication Date:
31 January 2019 (online)

 

Abstract

Palladium-catalysed competitive intramolecular C–N and C–C coupling of 2-amino-2′-bromodiarylsulfones has been carried out based on 1,8-peri-interactions for the synthesis of phenothiazinedioxide and benzonaphthathiophenedioxide derivatives. A DFT study has been performed that provides support for the influence of the 1,8-peri-interaction.


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Due to the rigidity of the naphthalene skeleton, the substituents on 1- and 8-positions are forced to be relatively close, at 2.5 Å, which is within the van der Waals radius for many atoms. In contrast, ortho-substituents on a benzene ring are separated by 3.3 Å.[1] This 1,8-interaction of naphthalenes, also known as a peri-interaction, results in some unique reactivity compared with substituted benzene derivatives.

During our continuing studies on developing novel synthetic routes to heterocycles,[2] we have prepared phenothiazine dioxides and benzonaphthathiophene dioxides via Pd-catalysed intramolecular C–N and C–C coupling and we have studied the effect of the 1,8-peri-interaction on the ­reactivity of the naphthalene moiety. Arylthiazine dioxides and arylthiophene dioxides are important classes of heterocycles because of their applications in medicinal and materials chemistry (Figure [1]).[3] Moreover thiazine and thiophene cores are also found in various biologically active natural products and synthetic drugs.[4]

Zoom Image
Figure 1 Examples of some useful arylthiazinedioxides and arylthiophenedioxides

We began this work with 2-amino-2′-bromodiarylsulfones 7, which were prepared from the corresponding 2-bromo-N-alkyl-N-arylbenzenesulfonamide derivatives 6 according to our reported procedure (Scheme [1]).[5]

Zoom Image
Scheme 1 Regioselective Fries type rearrangement for 2-amino-2′-bromodiarylsulfones synthesis

2-Amino-2′-bromodiarylsulfone 7a was treated with Pd(OAc)2 catalyst in DMF using Cs2CO3 as base at 100 °C for 1 h to effect intramolecular C–N coupling, leading to phenothiazine dioxide 8a in 78% yield. We then optimised the reaction conditions by varying the Pd catalyst, base, solvent, additive, temperature and time. The summarised results are presented in Table [1]. Among the three Pd catalysts examined, Pd(OAc)2 provided the best result. Changing base from Cs2CO3 to K2CO3 led to a notable decrease in yield; whereas KOAc proved more effective. Among different solvents, DMF showed the best results compared with toluene and DMA. The addition of TBAB did not show any improvement in yield. Increasing time or temperature led to little a slight lowering of reaction yields. At low temperatures (50–70 °C), the reaction did not proceed even with extended reaction periods (entries 15 and 16). Increasing the temperature to 85 °C led to a 30% yield of product. The effect of catalyst loading was also studied and we observed the best result using 5 mol% Pd(OAc)2 as catalyst, 2.5 equivalents KOAc as base, DMF as solvent at 100 °C for 1 h, obtaining phenothiazine dioxide in 96% yield (entry 10).

Table 1 Optimisation of Reaction Conditions for Pd-Catalysed ­Intramolecular C–N couplinga

Entry

Cat. System (mol%)

Baseb

Solvent

Additive

Time (h)

Temp. (°C)

Yield (%)c

1

Pd(OAc)2 (10)

Cs2CO3

DMF

1

100

78

2

Pd(PPh3)2Cl2 (10)

Cs2CO3

DMF

1

100

67

3

Pd2dba3 (10)

Cs2CO3

DMF

1

100

65

4

Pd(OAc)2 (10)

Cs2CO3

DMF

TBAB

1

100

75

5

Pd(OAc)2 (10)

Cs2CO3

toluene

1

100

52

6

Pd(OAc)2 (10)

K2CO3

DMF

1

100

55

7

Pd(OAc)2 (10)

KOAc

DMF

1

100

92

8

Pd(OAc)2 (10)

KOAc

DMF

2

100

81

9

Pd(OAc)2 (10)

KOAc

DMF

1

120

79

10

Pd(OAc)2 (5)

KOAc

DMF

1

100

96

11

Pd(OAc)2 (5)

KOAc

DMF

TBAB

1

100

92

12

Pd(OAc)2 (5)

KOAc

DMA

2

100

78

13

Pd(OAc)2 (3)

KOAc

DMF

1

120

64

14

Pd(OAc)2 (5)

KOAc

DMF

0.5

100

70

15

Pd(OAc)2 (5)

KOAc

DMF

4

50

np

16

Pd(OAc)2 (5)

KOAc

DMF

4

70

np

17

Pd(OAc)2 (5)

KOAc

DMF

4

85

30

a All reactions were carried out in a sealed tube under nitrogen.

b In every case 2.5 equivalents of base were used.

c np = no product

After optimising the reaction conditions, 2-amino-2′-bromodiarylsulfone derivatives 7bg were used for the preparation of the corresponding phenothiazine dioxide derivatives 8bg. For compounds 7be the corresponding phenothiazine dioxides 8be were formed in excellent yields under the optimised reaction conditions (Scheme [2]); however, for substrates 7f and 7g a different reaction course took place. The 1H NMR spectra of the products obtained from precursors 7f and 7g showed the N-H proton to be present and one aromatic proton was absent; whilst the 13C NMR spectra revealed the presence of two additional fully substituted aromatic carbon atoms. These data indicate that, for precursors 7f and 7g, intramolecular C–C ­coupling had occurred instead of intramolecular C–N coupling, leading to the corresponding benzonaphthathiophene dioxide derivatives 8f and 8g. Finally we confirmed the structures of compound 8a [6] and 8f [7] by single-crystal X-ray analysis (Figure [2]).

Zoom Image
Figure 2 ORTEP diagrams of (a) phenothiazine dioxide 8a and (b) benzonaphthathiophene dioxide 8f (the thermal ellipsoids are drawn at the 50% probability level).
Zoom Image
Scheme 2 Synthesis of phenothiazine dioxide derivatives

During cyclisation of compounds 7af, two different modes of cyclisation, C–N and C–C, are possible. However, between these two possibilities, C–N coupling is preferred for compounds 7ae. A plausible mechanism for the formation of compounds 8ae is shown in Scheme [3]. Initially, Pd(OAc)2 is reduced to give the active Pd(0) species,[8] which complexes with 7ae via coordination with nitrogen to form aryl palladium intermediates 9ae. The intermediate then leads to the phenothiazine dioxide derivatives 8ae via oxidative addition followed by reductive elimination.

Zoom Image
Scheme 3 Plausible mechanism for Pd-catalysed C–N coupling

When compounds 7f and 7g were treated under the same reaction conditions, C–C coupling was observed instead of C–N coupling, leading to benzonaphthathiophene dioxide derivatives 8f and 8g (Scheme [4]). A plausible mechanism for the formation of 8f and 8g is shown in Scheme [5]. Here N-Pd complex 11 is not formed, which may be due to the peri-interaction between H-8 and the 1-alkyl-NPd group. Instead, Pd(0) first undergoes oxidative addition to form intermediates 12f and 12g, which then lead to the benzonaphthathiophene dioxide derivatives 8f and 8g via carbopalladation followed by elimination of PdBr.

Zoom Image
Scheme 4 Synthesis of benzonaphthathiophene dioxide derivatives

We performed DFT calculations to investigate the 1,8-peri-interaction in naphthalene systems and the results support the mechanism depicted in Scheme [5] for C–C coupling. All calculations were performed with the Gaussian09 program package[9] using hybrid density functional (B3LYP) theory and the 6-31G(d) basis set. For Pd, the LanL2DZ basis set was used with LanL2 effective core potential. This DFT study shows that the formation energy of complex 11 from the anion of 7f is –420.48 kcal mol–1; whereas the formation energy of intermediate 12 is –490.33 kcal mol–1. This indicates that the formation of intermediate 12 is more energetically favourable than that of complex 11 by 69.85 kcal mol–1. This could explain why the reaction passes through the successive oxidative addition of Pd(0) to the C–Br bond, carbopalladation and elimination of PdBr to give the corresponding benzonaphthathiophene dioxides 8f and 8g instead of phenothiazine dioxides 8′f and 8′g.

Zoom Image
Scheme 5 Plausible mechanism for Pd-catalysed C–C coupling.

In conclusion we have synthesised phenothiazine di­oxides 8ae and benzonaphthathiophene dioxides 8f and 8g by Pd-catalysed intramolecular C–N and C–C coupling reactions, respectively. The effect of the 1,8-peri-interaction in the naphthalene system was investigated by DFT calculations and the results support the observed outcomes.

Synthesis of 7e

Compound 7e was prepared according to the previously reported procedure.[5]

IR (KBr): 3420, 2915, 1617, 1531, 1302, 1135, 708, 580 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 8.13 (d, J = 7.8 Hz, 1 H), 7.64 (d, J = 7.7 Hz, 1 H), 7.49–7.43 (m, 2 H), 7.38–7.34 (m, 1 H), 6.45 (s, 1 H), 5.99 (br s, 1 H), 2.80 (s, 3 H), 2.23 (s, 3 H), 2.13 (s, 3 H).

13C NMR (CDCl3, 100 MHz): δ = 146.9, 145.5, 140.6, 135.6, 133.8, 132.1, 127.3, 123.8, 120.7, 115.7, 112.8, 30.1, 20.6, 18.5.

LCMS (ES+): m/z [M + H]+ calcd for C15H17BrNO2S+: 354.02; found: 354.

Synthesis of Phenothiazine Dioxides 8a–e and Benzonaphthathiophene Dioxides 8f and 8g; General Procedure

3,10-Dimethyl-10H-phenothiazine 5,5-dioxide (8a)

A solution of 7a (200 mg, 0.59 mmol) in anhydrous DMF (2 mL) and KOAc (115 mg, 1.17 mmol) was purged with nitrogen for 10 min. Pd(OAc)2 (7 mg, 5 mol%) was then added and the mixture was heated to 100 °C for 1 h in a sealed tube. The reaction mixture was cooled, H2O (10 mL) was added, and the mixture was extracted with EtOAc (3 × 10 mL). The combined EtOAc extracts were washed with H2O (10 mL), brine (10 mL), and dried (Na2SO4). The solvent was distilled off to furnish a viscous residue that was purified by column chromato­graphy (EtOAc/petroleum ether, 1:4) on silica gel to yield compound 8a (146 mg, 96%) as a white solid; mp 149–151 °C.

IR (KBr): 2975, 1597, 1477, 1273, 1154, 748, 577 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 8.12 (d, J = 7.8 Hz, 1 H), 7.94 (s, 1 H), 7.66–7.60 (m, 1 H), 7.44 (d, J = 8.6 Hz, 1 H), 7.33–7.20 (m, 3 H), 3.67 (s, 3 H), 2.46 (s, 3 H).

13C NMR (CDCl3, 100 MHz): δ = 142.1, 139.9, 134.2, 133.1, 131.9, 124.2, 123.4, 123.0, 121.5, 115.6, 115.5, 35.7, 20.5.

HRMS (ESI): m/z [M + H]+ calcd for C14H14NO2S+: 260.0740; found: 260.0743.

10-Ethyl-3-methyl-10H-phenothiazine 5,5-dioxide (8b)

Yield: 92%; white solid; mp 136–138 °C.

IR (KBr): 2979, 1584, 1471, 1273, 1155, 746, 560 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 8.09 (dd, J = 7.8, 1.5 Hz, 1 H), 7.92–7.89 (m, 1 H), 7.59–7.54 (m, 1 H), 7.39 (dd, J = 8.7, 1.9 Hz, 1 H), 7.32 (d, J = 8.6 Hz, 1 H), 7.27–7.17 (m, 2 H), 4.19 (q, J = 7.1 Hz, 2 H), 2.39 (s, 3 H), 1.49 (t, J = 7.1 Hz, 3 H).

13C NMR (CDCl3, 100 MHz): δ = 140.6, 138.3, 134.4, 133.3, 131.8, 123.8, 123.7, 123.2, 121.4, 115.8, 115.6, 43.1, 20.5, 12.6.

HRMS (ESI): m/z [M + H]+ calcd for C15H16NO2S+: 274.0896; found: 274.0898.

3-Methoxy-10-methyl-10H-phenothiazine 5,5-dioxide (8c)

Yield: 95%; white solid; mp 168–170 °C.

IR (KBr): 2929, 1584, 1479, 1275, 1150, 835, 746, 579 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 8.11 (dd, J = 7.8, 1.4 Hz, 1 H), 7.65–7.58 (m, 2 H), 7.30–7.24 (m, 3 H), 7.24–7.20 (m, 1 H), 3.91 (s, 3 H), 3.70 (s, 3 H).

13C NMR (CDCl3, 100 MHz): δ = 154.8, 142.3, 136.4, 133.2, 124.8, 123.6, 123.5, 121.8, 121.5, 117.4, 115.3, 105.4, 56.1, 35.8.

HRMS (ESI): m/z [M + H]+ calcd for C14H14NO3S+: 276.0689; found: 276.0690.

10-Ethyl-3-methoxy-10H-phenothiazine 5,5-dioxide (8d)

Yield: 97%; white solid; mp 158–160 °C.

IR (KBr): 2934, 1578, 1478, 1269, 1145, 832, 752, 568 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 8.09 (dd, J = 7.9, 1.4 Hz, 1 H), 7.61–7.54 (m, 2 H), 7.34–7.29 (m, 2 H), 7.24–7.17 (m, 2 H), 4.21 (q, J = 7.0 Hz, 2 H), 3.86 (s, 3 H), 1.50 (t, J = 7.0 Hz, 3 H).

13C NMR (CDCl3, 100 MHz): δ = 154.6, 140.7, 134.7, 133.2, 124.3, 123.7, 122.9, 122.1, 121.3, 117.6, 115.4, 105.2, 56.1, 43.1, 12.7.

HRMS (ESI): m/z [M + H]+ calcd for C15H16NO3S+: 290.0845; found: 290.0849.

2,4,10-Trimethyl-10H-phenothiazine 5,5-dioxide (8e)

Yield: 94%; white solid; mp 152–154 °C.

IR (KBr): 2973, 1594, 1465, 1273, 1148, 745, 570 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 8.08 (d, J = 7.7 Hz, 1 H), 7.83 (s, 1 H), 7.60–7.56 (m, 1 H), 7.25–7.21 (m, 2 H), 7.05 (s, 1 H), 3.66 (s, 3 H), 2.37 (s, 3 H), 2.31 (s, 3 H).

13C NMR (CDCl3, 100 MHz): δ = 142.9, 142.1, 140.1, 132.9, 130.9, 124.3, 123.4, 123.3, 121.8, 121.4, 116.4, 115.3, 35.6, 20.7, 18.9.

LCMS (ES+): m/z [M + H]+ calcd for C15H16NO2S+: 274.09; found: 274.1.

N-Methylbenzo[d]naphtho[2,3-b]thiophen-6-amine-5,5-dioxide (8f)

Yield: 82%; white solid; mp 183–185 °C.

IR (KBr): 3404, 2967, 1554, 1280, 1135, 758, 542 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 7.92 (d, J = 8.4 Hz, 1 H), 7.87–7.80 (m, 2 H), 7.77 (d, J = 7.9 Hz, 1 H), 7.60 (td, J = 7.5, 0.9 Hz, 1 H), 7.56–7.41 (m, 4 H), 5.25 (m, 1 H), 3.58 (d, J = 5.2 Hz, 3 H).

13C NMR (CDCl3, 100 MHz): δ = 144.6, 138.4, 136.5, 133.4, 132.3, 130.0, 129.6, 129.2, 129.0, 126.7, 126.1, 122.6, 121.6, 121.6, 114.7, 110.9, 34.9.

DEPT-135 (CDCl3, 100 MHz): δ = 133.4, 130.0, 129.6, 129.0, 126.7, 122.6, 121.6, 121.6, 110.9, 34.9.

HRMS (ESI): m/z [M + H]+ calcd for C17H14NO2S+: 296.0740; found: 296.0742.

N-Ethylbenzo[d]naphtho[2,3-b]thiophen-6-amine-5,5-dioxide (8g)

Yield: 93%; white solid; mp 177–179 °C.

IR (KBr): 3407, 2968, 1549, 1272, 1136, 750, 537 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 7.93 (d, J = 8.4 Hz, 1 H), 7.81 (t, J = 7.7 Hz, 2 H), 7.74 (d, J = 8.0 Hz, 1 H), 7.58 (td, J = 7.6, 0.8 Hz, 1 H), 7.54–7.38 (m, 4 H), 4.81 (br s, 1 H), 3.89 (q, J = 7.1 Hz, 2 H), 1.45 (t, J = 7.1 Hz, 3 H).

13C NMR (CDCl3, 100 MHz): δ = 143.9, 138.5, 136.7, 133.5, 132.3, 130.0, 129.6, 129.0, 126.7, 123.2, 121.6, 116.4, 111.6, 43.2, 16.2.

DEPT-135 (CDCl3, 100 MHz): δ = 133.5, 130.0, 129.6, 129.0, 126.7, 123.2, 121.7, 121.6, 111.6, 43.2, 16.2.

HRMS (ESI): m/z [M + H]+ calcd for C18H16NO2S+: 310.0896; found: 310.0899.


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Acknowledgment

We are very grateful to Professor S. K. Chandra, Department of Chemistry, Visva-Bharati for assistance with the X-ray analyses.

Supporting Information

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  • References

    • 1a Balasubramaniyan V. Chem. Rev. 1966; 66: 567
    • 1b Robert J.-B, Sherfinski JS, Marsh RE, Roberts JD. J. Org. Chem. 1974; 39: 1152
    • 1c Banoglu E, Duffel MW. Chem. Res. Toxicol. 1999; 12: 278
    • 1d Hoefelmeyer JD, Gabbaï FP. Organometallics 2002; 21: 982
    • 1e Mallinson PR, Smith GT, Wilson CC, Grech E, Wozniak K. J. Am. Chem. Soc. 2003; 125: 4259
    • 1f Kilian P, Knight FR, Woollins JD. Coord. Chem. Rev. 2011; 255: 1387
    • 2a Mondal S, Debnath S. Synthesis 2014; 46: 368
    • 2b Mondal S, Debnath S. Tetrahedron Lett. 2014; 55: 1577
    • 2c Mondal S, Debnath S, Das B. Tetrahedron 2015; 71: 476
    • 2d Mondal S, Debnath S, Pal S, Das A. Synthesis 2015; 47: 3423
    • 2e Debnath S, Mondal S. J. Org. Chem. 2015; 80: 3940
    • 2f Debnath S, Mondal S. Synthesis 2016; 48: 710
    • 2g Debnath S, Malakar S, Mondal S. ChemistrySelect 2017; 2: 3147
    • 2h Debnath S, Mondal S. Tetrahedron Lett. 2018; 59: 2260
    • 3a Carbone A, Lucas CL, Moody CJ. J. Org. Chem. 2012; 77: 9179
    • 3b Hunt CA, Mallorga PJ, Michelson SR, Schwam H, Sondey JM, Smith RL, Sugrue MF, Shepard KL. J. Med. Chem. 1994; 37: 240
    • 3c Kim G, Yeom HR, Cho S, Seo JH, Kim JY, Yang C. Macromolecules 2012; 45: 1847
    • 3d Prinz H, Chamasmani B, Vogel K, Böhm KJ, Aicher B, Gerlach M, Günther EG, Amon P, Ivanov I, Müller K. J. Med. Chem. 2011; 54: 4247
    • 3e Encío I, Morré DJ, Villar R, Gil MJ, Martínez-Merino V. Br. J. Cancer 2005; 92: 690
    • 3f Chandrasekera NS, Bailey MA, Files M, Alling T, Florio SK, Ollinger J, Odingo JO, Parish T. PeerJ 2 e612 DOI: 10.7717/peerj.612.
    • 3g Svoboda J, Štádler M, Jandera A, Panajotová V, Kuchař M. Collect. Czech. Chem. Commun. 2000; 65: 1082
    • 4a Das B, Madhusudhan P, Venkataiah B. J. Chem. Res. Synop. 2000; 200
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    • 4c Cecchetti V, Calderone V, Tabarrini O, Sabatini S, Filipponi E, Testai L, Spogli R, Martinotti E, Fravolini A. J. Med. Chem. 2003; 46: 3670
    • 4d Sabatini S, Kaatz GW, Rossolini GM, Brandini D, Fravolini A. J. Med. Chem. 2008; 51: 4321
    • 4e Calderone V, Spogli R, Martelli A, Manfroni G, Testai L, Sabatini S, Tabarrini O, Cecchetti V. J. Med. Chem. 2008; 51: 5085
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  • 6 The CCDC reference number for the CIF file of compound 8a is CCDC 1481104. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif
  • 7 The CCDC reference number for the CIF file of compound 8f is CCDC 1481105. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif
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Figure 1 Examples of some useful arylthiazinedioxides and arylthiophenedioxides
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Scheme 1 Regioselective Fries type rearrangement for 2-amino-2′-bromodiarylsulfones synthesis
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Figure 2 ORTEP diagrams of (a) phenothiazine dioxide 8a and (b) benzonaphthathiophene dioxide 8f (the thermal ellipsoids are drawn at the 50% probability level).
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Scheme 2 Synthesis of phenothiazine dioxide derivatives
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Scheme 3 Plausible mechanism for Pd-catalysed C–N coupling
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Scheme 4 Synthesis of benzonaphthathiophene dioxide derivatives
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Scheme 5 Plausible mechanism for Pd-catalysed C–C coupling.