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Photooxidative cyclization of 3-aryl/heteroaryl-4-heteroaryl coumarins: an experimental and semi-empirical study

  • T.U. Kumari , G.L.D. Krupadanam , G. Srimannarayana , D.A. Padmavathi , A.K.D. Bhavani EMAIL logo and S. Veeresham
Published/Copyright: December 8, 2012
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Heterocyclic Communications
From the journal Heterocyclic Communications Volume 18 Issue 5-6

Abstract

Photochemical oxidation of substituted coumarins 1, 3 and 5 in benzene solution containing iodine gave the respective products 2, 4 and 6. The structures of the photoproducts have been confirmed by analyses of analytical and spectral data. The experimental results are further strengthened by their agreement with computationally calculated dipole moments (μ), minimum-energy values and heats of formations.

Keywords: benzopyranone derivatives; coumarins; heats of formation; NDDO; parametric method 3 (PM3); photooxidative cyclization

Introduction

Diarylethenes, the photochromic molecules, have been the focus of attention because of their medicinal importance (Wood and Mallory, 1964; Carruthers and Stewart, 1965; Blackburn and Timmons, 1969; Blackburn et al., 1970). Their potential applications also extend to photochromic devices such as molecular level switches (Irie, 2000; Browne and Feringa, 2011), optical memory display devices (Irie, 2000; Rudzinski et al., 2001) and photochromic fluorescent proteins (Ando et al., 2004; Irie et al., 2007).

Diarylethenes and related diheteroaryl analogs undergo photo-induced ring closure. This is exploited as a tool to synthesize fused aromatic and heterocyclic ring systems. Diaryl/diheteroarylethene derivatives can undergo UV light-induced photocyclization in single crystalline phase or in solution. The corresponding cyclized products undergo cycloreversion upon irradiation with visible light (Irie and Yamaguchi, 2006; Uno et al., 2011; Kose et al., 2011). Substituted coumarins have also been used in this type of photochromic reactions (Traven et al., 2008; Yokoyama et al., 2012).

In the presence of an oxidizing agent, such as iodine, upon irradiation with UV light diaryl/diheteroarylethene derivatives and vicinal diarylheterocycles undergo photooxidative reactions (Buckles, 1955; Padwa and Hartman, 1966; Moriarty et al., 1967; Cooper and Wasserman, 1969; Gilbert, 2003; Jørgensen, 2010; Miya et al., 2012). It has been reported that 3,4-diarylcoumarins undergo photooxidative cyclization reactions to form heterocycles (Sabitha et al., 1988). Our interest in biologically active heterocyclic compounds prompted us to synthesize novel fused benzopyranones 2a–c, 4a–c and 6a–c by photooxidative cyclization of the corresponding substituted coumarins 1a–c, 3a–c and 5a–c (Scheme 1 and Eqs. 1–3).

These reactions were also studied using semi-empirical methods belonging to NDDO (neglect of double differential overlap) approximation. Molecular orbital calculations were performed using parametric method 3 (PM3) (Komornicki and McIver, 1971; Stewart, 1989a,b; Young, 2001; Matthew et al., 2002; Thomas and Karl, 2005). Minimum-energy values and heats of formations of the optimized geometries were computed.

Results and discussion

Synthesis

The starting compounds 1 and 3 were prepared by the reaction of 5-substituted 2-hydroxyphenyl-2-thienyl/2-furyl ketones with phenyl acetyl chloride under phase transfer catalytic (PTC) conditions as reported by us previously (Kumari et al., 2000). In a similar manner, 3,4-di(2′-thienyl)coumarins 5 were prepared by the condensation of 5-substituted 2-hydroxyphenyl-2-thienyl ketones with 2-(2′-thienyl)acetyl chloride under PTC conditions.

In a typical experiment, a solution of coumarin 1a–c (Eq. 1) in benzene containing a catalytic amount of iodine as oxidant was placed in a quartz flask and irradiated with UV light using a medium pressure mercury arc lamp for 20–34 h under atmospheric conditions. Product 2a–c was purified by chromatography. The analytical and spectral data are consistent with the formation of the cyclized product. Similarly, the photooxidative cyclizations of 6-substituted-3-phenyl-4-(2′-furyl)coumarins 3a–c and 3,4-di(2′-thienyl) coumarins 5a–c furnished the photoproducts 4a–c and 6a–c, respectively (Eqs. 2 and 3). The structures of these products were assigned based on analytical and spectral data that are given in the experimental section.

Computations

Semi-empirical methods belonging to NDDO approximation were used to study the stabilities of 8H-thieno[2′,3′:3,4]-naphtho[1,2-c][1]benzopyran-8-ones 2a–c, 8H-furo[2′,3′:3,4]naphtho[1,2-c][1]benzo-pyran-8-ones 4a–c and 7H-dithieno[2′,3′:3,4:3″,2″:5,6]benzo[1,2-c][1]benzopyran-7-ones 6a–c along with their corresponding acyclic analogs 1a–c, 3a–c and 5a–c. All molecules were geometrically optimized and the molecular orbital calculations were performed using PM3. The general ball and stick model, distribution of electron density mapped with electrostatic potential for the ground state and the structures of HOMO and LUMO of cyclic compounds 2a and those of acyclic compounds 1a are displayed in Figures 1–6. Minimum-energy values Emin, binding energies, heats of formation ΔHf, dipole moments (μ), IR and UV data of the optimized geometries were calculated for both cyclic and acyclic systems. These are shown in Tables 1 and 2. The energy difference between the molecular orbitals HOMO and LUMO is comparable with the UV spectral data for both cyclic and acyclic sets of compounds. The electrostatic potential density maps reveal the reactive sites on the molecules, portraying the potential donor atoms.

Figure 1 Compound 2a.
Figure 1

Compound 2a.

Figure 2 Electron density of 2a mapped with electrostatic potential.
Figure 2

Electron density of 2a mapped with electrostatic potential.

Figure 3 Compound 2a (HOMO→LUMO).
Figure 3

Compound 2a (HOMO→LUMO).

Figure 4 Compound 1a.
Figure 4

Compound 1a.

Figure 5 Electron density of 1a mapped with electrostatic potential.
Figure 5

Electron density of 1a mapped with electrostatic potential.

Figure 6 Compound 1a (HOMO→LUMO).
Figure 6

Compound 1a (HOMO→LUMO).

Table 1

Calculated energies, heats of formation ΔHf, UV (λmax), dipole moments (μ), IR (C = O stretch) and log P values obtained using PM3 for cyclic systems.

Compd. no.Total energy (kcal/mol)Binding energy (kcal/mol)ΔHf (kcal/mol)HOMO→LUMO (λmax)μ (Debye)Carbonyl stretchaLog P
2a-80213.09-3918.9911.3435351.3 nm3.3751773.76-0.95
2b-81057.70-3902.4025.682352.3 nm3.3121773.59-0.67
2c-76715.15-4220.298.2788353.3 nm4.1381771.00-0.57
4a-82682.42-3946.44-22.955355.1 nm3.7771774.36-1.29
4b-83527.11-3929.93-8.6815355.5 nm3.6871774.14-1.02
4c-79178.45-4247.69-25.986356.3 nm4.6401771.34-0.91
6a-78323.84-3532.2218.533353.2 nm4.2651794.94-2.34
6b-79168.42-3515.5932.9105354.2 nm4.2081795.11-2.06
6c-74825.91-3833.5015.4552355.1 nm4.9891791.94-1.96

aScaled vibrational frequencies.

Table 2

Calculated energies, heats of formation ΔHf, UV (λmax), dipole moments (μ), IR (C = O stretch) and log P values obtained using PM3 for acyclic systems.

Compd. no.Total energy (kcal/mol)Binding energy (kcal/mol)ΔHf (kcal/mol)HOMO→LUMO (λmax)μ (Debye)Carbonyl stretchaLog P
1a-80911.11-4014.0620.4714327.9 nm3.8511777.520.04
1b-81755.77-3997.5134.774321.8 nm3.7371778.390.32
1c-77413.05-4315.2217.529333.9 nm4.8811774.390.42
3a-83381.59-4042.67-14.9674335.8 nm3.611779.78-0.30
3b-84226.24-4026.11-0.6568332.9 nm3.4941785.08-0.03
3c-79883.66-4343.94-18.0408340.7 nm4.6471776.820.08
4a-79018.81-3624.2430.7167324.3 nm4.1861798.58-1.35
4b-79863.46-3607.6745.0294317.5 nm4.0761798.97-1.07
4c-75521.00-3925.6427.5275327.9 nm5.1471795.73-0.97

aScaled vibrational frequencies.

The calculated low energies of coumarin compounds suggest that they are fairly stable. Total energy, binding energy and heats of formation indicate that coumarin compounds containing furan moiety appear to be more stable. The energy gap between HOMO and LUMO is in accordance with electronic transitions. A bathochromic shift of ˜20 nm in λmax is consistent with extended conjugation in the planar cyclic system when compared with the nonplanar acyclic system. The calculated characteristic IR absorption for the carbonyl group is in the range from 1770 cm-1 to 1790 cm-1 for both cyclic and acyclic compounds. Theoretical carbonyl vibrational absorption frequencies show an acceptable deviation of ˜10% from experimental data as reported in Tables 1 and 2 (Repasky et al., 2002). Thus, computationally evaluated IR and UV data are in good agreement with experimental results.

Compounds 2a–c, 4a–c and 6a–c were tested at 1000 ppm concentration in acetone for their insect antifeedant activity on 6–8 h prestarted larva of IV instar Spodoptera litura F., on castor leaf disc, by the non-choice test method (Ascher and Rones, 1964), and the percentage of antifeedant activity was calculated (Singh and Pant, 1980). Compounds 4b and 6c showed high antifeedant activity (>75%). The rest of the compounds showed moderate antifeedant activity. Compounds which showed high antifeedant activity will be studied further for their practical utility as antifeedants to control insect population in agriculture.

Conclusions

Photooxidative cyclization of coumarins 1, 3 and 5 is a convenient and eco-friendly route to benzopyranone derivatives 2, 4 and 6. Computational energies and spectroscopic data obtained using the semi-empirical method PM3 are comparable with the experimental results.

Experimental section

IR spectra were recorded in KBr pellets on an Infracold Model 337 Perkin-Elmer instrument. UV spectra were recorded on a Shimadzu UV 200 spectrometer in methanol. Owing to solubility problems, 1H NMR spectra for 2a, 2b and 4b only were taken. The spectra were taken in DMSO-d6 on a Bruker AC-200 spectrometer. Electron impact mass spectra were recorded on a Hitachi RMU-6L MS.30 instrument with a D55 data system.

General procedure for synthesis of compounds 2, 4 and 6

A solution of coumarin 1, 3 or 5 (1 mmol), iodine (0.5 mmol) in benzene (250 mL) was placed in a quartz flask and irradiated with a medium pressure mercury arc lamp (OMEGA long wave length model, 300 W) for 30 h. Progress of the photoreaction was monitored by TLC. The solution was concentrated under reduced pressure. The crude product was subjected to chromatography on silica gel (ACME 200 mesh) eluting successively with petroleum ether, benzene and chloroform. The petroleum ether fractions contained iodine. The benzene fractions contained product 2, 4 or 6. Crystallization from methanol furnished the photoproduct as a dark yellow to light yellow crystalline solid.

12-Chloro-8H-thieno[2′,3′:3,4]naphtho[1,2-c][1]benzopyran-8-one (2a)

Yield 0.25 g (75%); mp 293–295°C; IR: 1720 cm-1; UV: 210 nm (log є 4.66), 280 nm (log є 4.60), 360 nm (log є 4.22); 1H NMR: δ 10.00 (d, 1H, J7H,6H = 9 Hz, H-7), 8.55 (d, 1H, J2H,3H = 5Hz, H-2), 8.45 (d, 1H, J3H,2H = 5Hz, H-3), 8.80 (m, 2H, H-4 and 13), 7.90 (m, 2H, H-5 and H-6), 7.5 (d, 1H, J10H,11H = 9 Hz, H-10), 7.70 (d, 1H, J11H,10H = 9Hz, H-11); MS: m/z 336 (M+). Anal. Calcd for C19H9O2SCl: C, 67.85; H, 2.67. Found: C, 67.6; H, 2.4.

12-Bromo-8H-thieno[2′,3:3,4]naphtho[1,2-c][1]benzopyran-8-one (2b)

Yield 0.26 g (70%); mp 255–257°C; IR: 1720 cm-1; UV: 220 nm (log є 4.01), 280 nm (log є 4.48), 360 nm (log є 3.88); 1H NMR: δ 9.80 (d, 1H, J7H,6H = 9 Hz, H-7), 8.43 (d, 1H, J2H,3H = 5 Hz, H-2), 8.25 (d, 1H, J3H,2H = 5 Hz, H-3), 7.80 (m, 1H, H-4), 7.85 (m, 2H, H-5 and H-6), 7.23 (d, 1H, J10H,11H = 9 Hz, H-10), 7.27(m, 1H, H-11), 8.00 (m,1H, H-13); MS: m/z 380 (M+). Anal. Calcd for C19H9O2SBr: C, 60.0; H, 2.36. Found: C, 60.0; H, 2.1.

12-Methyl-8H-thieno[2′,3′:3,4]naphtho[1,2-c][1]benzopyran-8-one (2c)

Yield 0.26 g (82%); mp 256–258°C; IR: 1710 cm-1; UV: 230 nm (log є 3.93), 280 nm (log є 4.27) and 380 nm (log є 3.87); MS: m/z 316 (M+). Anal. Calcd for C20H22O2S: C, 75.94; H, 3.73. Found: C, 75.8; H, 3.6.

12-Chloro-8H-furo[2′,3′:3,4]naphtho[1,2-c][1]benzopyran-8-one (4a)

Yield 0.27 g (80%); mp > 290°C; IR: 1710 cm-1; UV: 210 nm (log є 4.68), 270 nm (log є 4.66), 370 nm (log є 4.20); MS: m/z 320 (M+). Anal. Calcd for C19H9O3Cl: C, 71.25; H, 2.8. Found: C, 71.0; H, 3.01.

12-Bromo-8H-furo[2′,3′:3,4]naphtho[1,2-c][1]benzopyran-8-one (4b)

Yield 0.28 g (78%); mp 243–245°C; IR: 1720 cm-1; UV: 220 nm (log є 4.99), 270 nm (log є 4.51), 370 nm (log є 3.95); 1H NMR: δ 9.10 (d, 1H, J7H,6H = 9Hz, H-7), 7.3–8.2 (m, 8H, H-2, 3.4, 5, 6, 10, 11, 13) MS: m/z 364 (M+). Anal. Calcd for C19H9O3Br: C, 62.63; H, 2.4. Found: C, 62.4; H, 2.2.

12-Methyl-8H-furo[2′,3′:3,4]naphtho[1,2-c][1]benzopyran-8-one (4c)

Yield 0.24 g (80%); mp > 290°C; IR: 1720 cm-1; UV: 220 nm (log є 4.80), 370 nm (log є 4.68); MS: m/z, 300 (M+). Anal. Calcd for C20H12O3: C, 80.0; H, 4.0. Found: C, 79.8; H, 3.8.

11-Chloro-7H-dithieno[2′,3′:3,4:3″,2″:5,6]benzo[1,2-c][1]benzopyran-7-one (6a)

Yield 0.26 g (82%); mp 288–290°C; IR: 1710 cm-1; UV: 280 nm (log є 4.28), 370 nm (log є 3.73); MS: m/z 322 (M+). Anal. Calcd for C17H7O2S2Cl: C, 63.35; H, 2.17. Found: C, 63.2; H, 2.0.

11-Bromo-7H-dithieno[2′,3′:3,4:3″,2″:5,6]benzo[1,2-c][1]benzopyran-7-one (6b)

Yield 0.30 g (82%); mp > 290°C; IR: 1710 cm-1; UV: 270 nm (log є 4.47), 370 nm (log є 4.04); MS: m/z 366 (M+). Anal. Calcd for C17H7O2S2Br: C, 55.73; H, 1.91. Found: C, 55.6; H, 1.8.

11-Methyl-7H-dithieno[2′,3′:3,4:3″,2″:5,6]benzo[1,2-c][1]benzopyran-7-one (6c)

Yield 0.23 g (78%); mp 235–237°C; IR: 1700 cm-1; UV: 270 nm (log є 4.43), 370 nm (log є 3.87); MS: m/z 302 (M+). Anal. Calcd for C18H12O2S2: C, 71.52; H, 3.97. Found: C, 71.4; H, 3.7.

Corresponding author: A.K.D. Bhavani, Department of Chemistry, University College of Science, Saifabad, Osmania University, Hyderabad, 500004, India

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Received: 2012-8-19
Accepted: 2012-11-2
Published Online: 2012-12-08
Published in Print: 2012-12-01

©2012 by Walter de Gruyter Berlin Boston

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https://doi.org/10.1515/hc-2012-0128
Keywords for this article
benzopyranone derivatives; coumarins; heats of formation; NDDO; parametric method 3 (PM3); photooxidative cyclization
Creative Commons
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Articles in the same Issue

  1. Masthead
  2. Masthead
  3. Research Articles
  4. Sequential amination of heteroaromatic halides with aminopyridine 1 - oxides and their N-protected derivatives based on novel aza-Smiles rearrangement
  5. Convenient synthetic route to 3-cyanopyridine-2(1H)-one derivatives with aromatic substituents
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