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Synthesis of pyrimido[4′,5′:2,3][1,4]thiazepino[7,6-b]quinolines, derivatives of a novel ring system

  • Azam Karimian , Hossein Eshghi EMAIL logo , Mehdi Bakavoli and Ali Shiri
Published/Copyright: September 24, 2014
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Heterocyclic Communications
From the journal Heterocyclic Communications Volume 20 Issue 5

Abstract

Several derivatives of the novel pyrimido[4′,5′:2,3][1,4]thiazepino[7,6-b]quinoline ring system have been synthesized through cyclocondensation of 5-amino-6-methylpyrimidine-4-thiols 5a,b and 2-chloroquinoline-3-carbaldehydes 6a–c in the presence of K2 CO3 in DMF.

Keywords: heterocyclization; pyrimidothiazepinoquinoline; quinoline; thiazepine

Introduction

Heterocycles containing a 1,4-thiazepine moiety are important targets in synthetic and medicinal chemistry because of their presence in a wide range of natural and synthetic active agents [1–4]. Among them, fused derivatives represent interesting pharmaceutical properties. For example, different alkyl derivatives of dihydro-1,4-benzothiazepine are HIV-1 enzyme integrase inhibitor [5] and antitumor agents [6]. Several heteroannulated analogues of this core fragment are also potent inhibitors of herpes simplex virus type 1 replication [7], show antihistamine activity [8], and are vasoconstrictor agents [9]. Various methods for the synthesis of fused 1,4-thiazepine derivatives have been reported in recent years with respect to their different structures [10–18]. Synthetic approaches to these compounds involve addition [19], condensation [20], coupling [21], rearrangement [22], and thermolysis [23] reactions in multistep syntheses. These compounds have also been prepared through the treatment of thioxanthen-9-ol with o-mesitylene sulfonyl hydroxylamine [4] or cyclization of o-nitrobenzene halides with o-thiosalicylic acid esters as well as reduction and dehydration of the resulting products [5].

As part of our ongoing studies dealing with the synthesis of new biologically active heterocyclic compounds [24–27], herein, we wish to report on the synthesis and structural elucidations of various pyrimido[4′,5′:2,3][1,4]thiazepino[7,6-b]quinoline derivatives as a novel heterocyclic system.

Results and discussion

2,4-Dichloro-6-methyl-5-nitropyrimidine (1) was conveniently synthesized according to the published procedure [28]. The nitro group of this compound was reduced by treatment with iron powder in acetic acid at room temperature to give 2,4-dichloro-6-methylpyrimidin-5-amine (2). Further treatment of compound 2 with KSCN in boiling dimethyl formamide (DMF) gave 5-chloro-7-methylthiazolo[5,4-d]pyrimidin-2-amine (3). Nucleophilic displacement of chlorine atom in 2-position of the pyrimidine ring in compound 3 with morpholine and piperidine as typical secondary amines furnished the respective substituted derivatives 7-methyl-5-morpholinothiazolo[5,4-d]pyrimidin-2-amine (4a) and 7-methyl-5-piperidinothiazolo[5,4-d]pyrimidin-2-amine (4b). The synthesized compounds 4a,b were hydrolyzed in aqueous KOH solution to produce the respective 5-amino-6-methylpyrimidine-4-thiols 5a,b. Meanwhile, chloroquinoline-3-carbaldehydes 6a–c were conveniently prepared according to the reported procedure [29]. Potassium carbonate catalyzed cyclocondensation reaction of compounds 6a–c with compounds 5a,b in DMF under reflux proceeded smoothly and gave the first members of the hitherto unknown 4-methylpyrimido[4′,5′:2,3][1,4]thiazepino[7,6-b]quinolines 7a–f. The progress of these reactions was monitored by thin layer chromatography (TLC) using n-hexane/ethyl acetate (EtOAc) (8:1) as eluent (Scheme 1).

Scheme 1 Reagents and conditions: (i) Fe powder, HOAc, rt, 2 h; (ii) KSCN, DMF, reflux, 3 h; (iii) morpholine or piperidine, EtOH, reflux, 6 h; (iv) KOH(aq), reflux, 10 h; (v) K2 CO3, DMF, reflux, 8–12 h.
Scheme 1

Reagents and conditions: (i) Fe powder, HOAc, rt, 2 h; (ii) KSCN, DMF, reflux, 3 h; (iii) morpholine or piperidine, EtOH, reflux, 6 h; (iv) KOH(aq), reflux, 10 h; (v) K2 CO3, DMF, reflux, 8–12 h.

All synthesized products were characterized by spectroscopic and microanalytical data. For instance, the IR spectrum of compound 7a did not show the stretching vibration bands of compounds 5a and 6a at 3336 and 3248 cm-1 for the amino group, 2666 cm-1 for the thiol, and at 1690 cm-1 belonging to a carbonyl group. The 1H NMR spectrum of 7a does not show the signal for an aldehydic proton found in the spectrum of compound 6a at 9.20 ppm. There are no D2 O exchangeable signals, which indicates the absence of SH and NH2 groups present in the starting material 5a. The spectrum shows a new sharp singlet signal at 8.71 ppm corresponding to the imino proton of the thiazepine ring of 7a. Elimination of HCl is observed in the mass spectrum of 7a. The molecular ion peak of 7a is observed at m/z 363 (M+), which, together with the results of elemental analysis, fully support the molecular formula of C19 H17 N5 OS. Analogous results were obtained for the remaining products 7b–f. A self-explanatory mechanism for the synthesis of 4-methylpyrimido[4′,5′:2,3][1,4]thiazepino[7,6-b]quinoline derivatives 7a–f is proposed in Scheme 2.

Scheme 2
Scheme 2

Conclusion

Compounds 7a–f containing the previously unknown pyrimido[4′,5′:2,3][1,4]thiazepino[7,6-b]quinoline ring system were synthesized for the first time by cyclocondensation of 2-chloroquinoline-3-carbaldehydes and 5-amino-6-methylpyrimidine-4-thiols in the presence of K2 CO3 in boiling DMF. Products 7a–f were obtained in high yields.

Experimental

Melting points were recorded on an Electrothermal 9100 melting point apparatus. The IR spectra were obtained in KBr pellets on an Avatar 370 FT-IR Thermo Nicolet spectrometer. The 1H NMR (400 MHz) and the 13C NMR (100 MHz) spectra were recorded on a Bruker Avance DRX-400 spectrometer. The mass spectra were scanned on a Varian Mat CH-7 instrument operating at 70 eV. Elemental analyses were performed on a Thermo Finnigan Flash EA microanalyzer.

2,4-Dichloro-6-methylpyrimidin-5-amine (2)

A mixture of 2,4-dichloro-6-methyl-5-nitropyrimidine (1, 10 mmol, 2.1 g) and iron powder (2.5 g) in acetic acid (50 mL) was stirred at room temperature for 2 h. After completion of the reaction, the mixture was filtered off and the filtrate was concentrated in vacuo. The resulting solid was crystallized from ethyl acetate: yield 70% of a red powder; mp 101–103°C; 1H NMR (CDCl3): δ 2.32 (s, 3H, CH3), 6.08 (s, 2H, NH2, D2 O exchangeable); 13C NMR (CDCl3): δ 22.6, 115.2, 155.6, 159.6, 168.2; IR: ν 3472, 3371, 1621, 1555 cm-1; MS (m/z) 178 (M+), 180 (M++2). Anal. Calcd for C5 H5 Cl2 N3: C, 33.73; H, 2.83; N, 23.60. Found: C, 33.70; H, 2.81; N, 23.57.

5-Chloro-7-methylthiazolo[5,4-d]pyrimidin-2-amine (3)

A mixture of 2,4-dichloro-6-methylpyrimidin-5-amine (2, 10 mmol, 1.7 g) and KSCN (10 mmol, 0.97 g) in DMF (15 mL) was heated under reflux for 3 h. After completion of the reaction, the mixture was cooled and the resulting precipitate was collected by filtration and crystallized from ethanol: yield 85% of a brown powder; mp 255–257°C; 1H NMR (DMSO-d6): δ 2.56 (s, 3H, CH3), 6.88 (s, 2H, NH2, D2 O exchangeable); 13C NMR (DMSO-d6): δ 22.6, 115.2, 145.6, 159.6, 166.5 167.2; IR: ν 3195, 3288, 2961, 1618 cm-1; MS (m/z) 200 (M+), 202 (M++2), 170 (M+-S), 126 (M+-thiourea). Anal. Calcd for C6 H5 ClN4 S: C, 35.92; H, 2.51; N, 27.92; S, 15.98. Found: C, 35.85; H, 2.47; N, 27.88; S, 15.93.

General procedure for the preparation of compounds 4a,b

A mixture of 5-chloro-7-methylthiazolo[5,4-d]pyrimidin-2-amine (3, 10 mmol, 2.0 g) and the appropriate secondary amine (30 mmol) in ethanol (20 mL) was heated under reflux for 6 h. The progress of the reaction was monitored by TLC using n-hexane/EtOAc (6:1) as eluent. Then, the solvent was removed under reduced pressure using rotary evaporator. The crude residue was washed with ethanol (2×20 mL) and dried.

7-Methyl-5-morpholinothiazolo[5,4-d]pyrimidin-2-amine (4a)

This compound was obtained in 90% yield as a gray powder; mp 235–237°C; 1H NMR (DMSO-d6): δ 2.36 (s, 3H, CH3), 3.65 (t, 4H, CH2 N, J= 5.2 Hz), 3.76 (t, 4H, CH2 O, J= 5.2 Hz), 6.9 (br s, 2H, NH2, D2 O exchangeable); 13C NMR (DMSO-d6): δ 22.6, 44.5, 62.3, 115.1, 145.4, 159.6, 166.8 167.1; IR: ν 3145, 3230, 2953, 2859, 1654 cm-1; MS (m/z) 251 (M+), 221 (M+-S), 177 (M+-thiourea), 166 (M+-morpholine). Anal. Calcd for C10 H13 N5 OS: C, 47.79; H, 5.21; N, 27.87; S, 12.76. Found: C, 47.74; H, 5.18; N, 27.84; S, 12.72.

7-Methyl-5-piperidinothiazolo[5,4-d]pyrimidin-2-amine (4b)

This compound was obtained in 90% yield as a gray powder; mp 207–210°C; 1H NMR (DMSO-d6): δ 1.50–1.56 (m, 6H, 3CH2), 2.44 (s, 3H, CH3), 3.73–3.75 (m, 4H, 2-CH2 N), 6.92 (br s, 2H, NH2, D2 O exchangeable); 13C NMR (DMSO-d6): δ 22.6, 24.3, 26.4, 54.8, 125.1, 143.4, 160.5, 165.8, 168.1; IR: ν 3135, 3245, 2940, 2865, 1615 cm-1; MS (m/z) 249 (M+) 219 (M+-S), 166 (M+-piperidine). Anal. Calcd for C11 H15 N5 S: C, 52.99; H, 6.06; N, 28.09; S, 12.86. Found: C, 52.90; H, 6.04; N, 27.99; S, 12.82.

General procedure for the preparation of compounds 5a,b

A mixture of 4a or 4b (10 mmol) in aqueous 15% KOH solution (20 mL) was heated in a water bath for 10 h. The reaction mixture was then neutralized with acetic acid, and the separated solid was collected by filtration and crystallized from water.

5-Amino-6-methyl-2-morpholinopyrimidine-4-thiol (5a)

This compound was obtained in 86% yield as yellow solid; mp 215–217°C; 1H NMR (DMSO-d6): δ 2.33 (s, 3H, CH3), 3.65 (t, 4H, CH2 N, J= 4.8 Hz), 3.75 (t, 4H, CH2 O, J= 4.8 Hz), 6.56 (br s, 2H, NH2, D2 O exchangeable), 5.50 (br s, 1H, SH, D2 O exchangeable); 13C NMR (DMSO-d6): δ 23.6, 46.5, 66.3, 115.8, 133.0, 147.9, 167.2; IR: ν 3336, 3248, 2940, 2865, 2666, 1610 cm-1; MS (m/z) 226 (M+), 194 (M+-SH), 141 (M+-morpholine). Anal. Calcd for C9 H14 N4 OS: C, 47.77; H, 6.24; N, 24.76; S, 14.17. Found: C, 47.70; H, 6.21; N, 24.72; S, 14.14.

5-Amino-6-methyl-2-piperidinopyrimidine-4-thiol (5b)

This compound was obtained in 80% yield as yellow solid; mp 187–190°C; 1H NMR (DMSO-d6): δ 1.51–1.56 (m, 6H, 3CH2), 2.45 (s, 3H, CH3), 3.75–3.77 (m, 4H, 2CH2 N), 6.81 (br s, 2H, NH2, D2 O exchangeable), 6.40 (br s, 1H, SH, D2 O exchangeable); 13C NMR (DMSO-d6): δ 22.6, 24.3, 25.4, 56.8, 128.1, 162.5, 168.8, 170.1; IR: ν 3348, 3256, 2924, 2853, 2668, 1615 cm-1; MS (m/z) 224 (M+), 192 (M+-SH), 141 (M+-piperidine). Anal. Calcd for C10 H16 N4 S: C, 53.54; H, 7.19; N, 24.98; S, 14.29. Found: C, 53.51; H, 7.14; N, 24.92; S, 14.25.

General procedure for the preparation of 4-methylpyrimido[4′,5′:2,3][1,4]thiazepino[7,6-b]quinolines 7a-f

To a mixture of 2-chloroquinoline-3-carbaldehyde (6a–c, 1 mmol) and K2 CO3 (2 mmol, 0.13 g) in DMF (50 mL), the appropriate 5-amino-6-methylpyrimidine-4-thiol (5a,b, 1 mmol) was added, and the mixture was heated under reflux for 8–12 h according to the TLC monitoring using n-hexane/EtOAc (8:1) as eluent. After the completion of the reaction, water was added and the resulting solid was filtered off and purified by column chromatography using n-hexane/EtOAc (8:1) as mobile phase.

4-(4-Methylpyrimido[4′,5′:2,3][1,4]thiazepino[7,6-b]quinolin-2-yl)morpholine (7a)

This compound was obtained in 65% yield as a pale yellow powder; mp 245–247°C; 1H NMR (CDCl3): δ 2.53 (s, 3H, CH3), 3.75 (t, 4H, CH2 N, J= 5.2 Hz), 3.86 (t, 4H, CH2 O, J= 5.2 Hz), 7.61 (t, 1H, ArH, J= 8 Hz), 7.79 (t, 1H, ArH, J= 8 Hz), 7.88 (d, 1H, ArH, J= 8 Hz), 8.12 (d, 1H, ArH, J= 8 Hz), 8.22 (s, 1H, ArH), 8.71 (s, 1H, HC=N); 13C NMR (CDCl3): δ 22.0, 44.8, 66.8, 117.3, 127.0, 127.9, 128.1, 129.2, 130.2, 131.7, 138.2, 148.6, 149.0, 154.0, 155.1, 159.5, 166.1; IR: ν 3047, 3023, 2961, 2864, 1605, 1561, 1447 cm-1; MS (m/z) 363 (M+), 365 (M++2), 333 (M+-S), 277 (M+-morpholine). Anal. Calcd for C19 H17 N5 OS: C, 62.79; H, 4.71; N, 19.27; S, 8.82. Found: C, 62.75; H, 4.67; N, 19.24; S, 8.85.

4-(10-Chloro-4-methylpyrimido[4′,5′:2,3][1,4]thiazepino[7,6-b]quinolin-2-yl)morpholine (7b)

This compound was obtained in 70% yield as a yellow powder; mp 305–307°C; 1H NMR (CDCl3): δ 2.51 (s, 3H, CH3), 3.74 (t, 4H, 2CH2 N, J= 5.2 Hz), 3.85 (t, 4H, 2CH2 O, J= 5.2 Hz), 7.71 (dd, 1H, ArH, J= 8 Hz, J= 2.0 Hz), 7.85 (d, 1H, J= 2.0 Hz, ArH), 8.04 (d, 1H, ArH, J= 8 Hz), 8.12 (s, 1H, ArH), 8.71 (s, 1H, HC=N); 13C NMR (CDCl3): δ 22.0, 44.4, 66.8, 126.6, 127.0, 130.7, 131.0, 132.5, 133.8, 137.0, 147.3, 151.7, 152.0, 153.6, 154.5, 159.6, 166.4; IR: ν 3076, 3019, 2953, 2868, 2839, 1607, 1555, 1491, 1449, 1311 cm-1; MS (m/z) 397 (M+), 362 (M+-Cl), 367 (M+-S), 311 (M+-morpholine). Anal. Calcd for C19 H16 ClN5 OS: C, 57.35; H, 4.05; N, 17.60; S, 8.06. Found: C, 57.31; H, 4.02; N, 17.56; S, 8.01.

4-(4,10-Dimethylpyrimido[4′,5′:2,3][1,4]thiazepino[7,6-b]quinolin-2-yl)morpholine (7c)

This compound was obtained in 55% yield as a yellow powder; mp 256–258°C; 1H NMR (CDCl3): δ 2.45 (s, 3H, CH3), 2.61 (s, 3H, CH3), 3.66 (t, 4H, 2CH2 N, J= 4.4 Hz), 3.73 (t, 4H, 2CH2 O, J= 4.4 Hz), 7.47 (d, 1H, ArH, J= 8Hz), 7.84 (s, 1H, ArH), 7.88 (d, 1H, ArH, J= 8 Hz), 8.29 (s, 1H, ArH), 8.92 (s, 1H, HC=N); 13C NMR (CDCl3): δ 21.3, 22.8, 45.1, 66.3, 117.4, 127.0, 127.5, 128.9, 129.2, 130.2, 131.2, 137.3, 148.9, 150.7, 154.0, 155.2, 160.3, 165.4; IR: ν 3030, 2962, 2904, 2855, 1617, 1579, 1538, 1507, 1494, 1444 cm-1; MS (m/z) 377 (M+), 347 (M+-S), 291 (M+-morpholine). Anal. Calcd for C20 H19 N5 OS: C, 63.64; H, 5.07; N, 18.55; S, 8.49. Found: C, 63.61; H, 5.01; N, 18.51; S, 8.45.

4-Methyl-2-piperidinopyrimido[4′,5′:2,3][1,4]thiazepino[7,6-b]quinoline (7d)

This compound was obtained in 65% yield as an orange powder; mp 305–307°C; 1H NMR (CDCl3): δ 1.52–1.59 (m, 6H, 3CH2), 2.44 (s, 3H, CH3), 3.71–3.73 (m, 4H, 2-CH2 N), 7.61 (t, 1H, ArH, J= 7.8 Hz), 7.80 (t, 1H, ArH, J= 7.8 Hz), 7.9 (d, 1H, ArH, J= 8.0 Hz), 8.14 (d, 1H, ArH, J= 8.0 Hz), 8.23 (s, 1H, ArH), 8.74 (s, 1H, HC=N); 13C NMR (CDCl3): δ 23.5, 24.7, 26.4, 54.8, 118.6, 126.3, 127.3, 127.8, 128.5, 129.1, 130.2, 137.1, 148.5, 160.8, 160.9, 161.4, 163.1, 163.6; IR: ν 3007, 2937, 2855, 1620, 1569, 1506, 1445 cm-1; MS (m/z) 361 (M+), 331 (M+-S), 377 (M+-piperidine). Anal. Calcd for C20 H19 N5 S: C, 66.46; H, 5.30; N, 19.37; S, 8.87. Found: C, 66.50; H, 5.12; N, 19.4; S, 8.9.

10-Chloro-4-methyl-2-piperidinopyrimido[4′,5′:2,3][1,4]thiazepino[7,6-b]quinoline (7e)

This compound was obtained in 72% yield as a yellow powder; mp 272–274°C; 1H NMR (CDCl3): δ 1.56–1.61 (m, 6H, 3CH2), 2.50 (s, 3H, CH3), 3.79–3.82 (m, 4H, 2CH2 N), 7.16–7.21 (m, 1H, ArH), 7.83 (d, 1H, ArH, J= 4 Hz), 8.1 (d, 1H, ArH, J= 4 Hz), 8.23 (s, 1H, ArH), 8.74 (s, 1H, HC=N); 13C NMR (CDCl3): δ 25.8, 27.3, 27.6, 37.2, 125.6, 127.3, 131.1, 131.8, 132.5, 135.2, 137.0, 147.5, 150.3, 152.1, 153.6, 155.5, 159.4, 166.0; IR: ν 3024, 2990, 2926, 2831, 1629, 1611, 1593, 1500, 1395, 1337 cm-1; MS (m/z) 395 (M+), 397 (M++2), 360 (M+-Cl), 365 (M+-S), 311 (M+-piperidine). Anal. Calcd for C20 H18 ClN5 S: C, 60.67; H, 4.58; N, 17.69; S, 8.10. Found: C, 60.65; H, 4.45; N, 17.50; S, 8.16.

4,10-Dimethyl-2-piperidinopyrimido[4′,5′:2,3][1,4]thiazepino[7,6-b]quinoline (7f)

This compound was obtained in 70% yield as a yellow powder; mp 294–295°C; 1H NMR (CDCl3): δ 1.55–1.61 (m, 6H, 3CH2), 2.35 (s, 3H, CH3), 2.47 (s, 3H, CH3), 3.63–3.67 (m, 4H, 2CH2 N), 7.40 (d, 1H, ArH, J= 8 Hz), 7.84 (s, 1H, ArH), 7.92 (d, 1H, ArH, J= 8 Hz), 8.3 (s, 1H, ArH), 8.81 (s, 1H, HC=N); 13C NMR (CDCl3): δ 21.9, 23.7, 28.4, 33.9, 66.1, 117.1, 124.2, 125.9, 127.3, 128.3, 129.2, 130.8, 131.2, 136.3, 148.7, 150.7, 154.1, 162.3, 165.2; IR: ν 3020, 2940, 2835, 1616, 1562, 1501, 1445, 1363 cm-1; MS (m/z) 375 (M+), 377 (M++2), (M+-Cl), 345 (M+-S), 391 (M+-piperidine). Anal. Calcd for C21 H21 N5 S: C, 67.17; H, 5.64; N, 18.65; S, 8.54. Found: C, 67.20; H, 5.70; N, 18.63; S, 8.78.

Dedication: In memory of Professor Mohammad Rahimizadeh.

Corresponding author: Hossein Eshghi, Department of Chemistry, School of Sciences, Ferdowsi University of Mashhad, 91775-1436 Mashhad, Iran, e-mail:

Acknowledgments

The authors gratefully acknowledge the Research Council of Ferdowsi University of Mashhad for financial support of this project 25422/3.

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Received: 2014-6-2
Accepted: 2014-8-28
Published Online: 2014-9-24
Published in Print: 2014-10-1

©2014 by De Gruyter

This article is distributed under the terms of the Creative Commons Attribution Non-Commercial License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Articles in the same Issue

  1. Frontmatter
  2. Reviews
  3. Recent advances in dibenzo[b,f][1,4]oxazepine synthesis
  4. Recent trends in synthesis of five- and six-membered heterocycles using dimethyl N-cyanodithioiminocarbonate
  5. Preliminary Communication
  6. 12T061C, a new Julichrome family radical scavenger from Streptomyces species
  7. Research Articles
  8. Synthesis of pyrimido[4′,5′:2,3][1,4]thiazepino[7,6-b]quinolines, derivatives of a novel ring system
  9. Solvent-free multicomponent assembling of aldehydes, N,N′-dialkyl barbiturates and malononitrile: fast and efficient approach to pyrano[2,3-d]pyrimidines
  10. One-pot, three-component synthesis of pyranocoumarins containing an aroyl group
  11. Selective fluorescence sensor for Cu2+ with a novel triazole Schiff-base derivative with coumarin units
  12. Microwave-assisted synthesis of (E)-7-[(1-benzyl-1H-1,2,3-triazol-4-yl)methoxy]-8-(3-arylacryloyl)-4-methyl-2H-chromen-2-ones and their antimicrobial activity
  13. One-pot synthesis of 3,4-dihydro-3-hydroxyisochroman-1-one and evaluation of acetal derivatives as antibacterial and antifungal agents
  14. Copper-mediated ligand-free Ullmann reaction approach to substituted s-triazines: rationale, synthesis, and biological evaluation
https://doi.org/10.1515/hc-2014-0095
Keywords for this article
heterocyclization; pyrimidothiazepinoquinoline; quinoline; thiazepine
Creative Commons
BY-NC-ND 3.0

Articles in the same Issue

  1. Frontmatter
  2. Reviews
  3. Recent advances in dibenzo[b,f][1,4]oxazepine synthesis
  4. Recent trends in synthesis of five- and six-membered heterocycles using dimethyl N-cyanodithioiminocarbonate
  5. Preliminary Communication
  6. 12T061C, a new Julichrome family radical scavenger from Streptomyces species
  7. Research Articles
  8. Synthesis of pyrimido[4′,5′:2,3][1,4]thiazepino[7,6-b]quinolines, derivatives of a novel ring system
  9. Solvent-free multicomponent assembling of aldehydes, N,N′-dialkyl barbiturates and malononitrile: fast and efficient approach to pyrano[2,3-d]pyrimidines
  10. One-pot, three-component synthesis of pyranocoumarins containing an aroyl group
  11. Selective fluorescence sensor for Cu2+ with a novel triazole Schiff-base derivative with coumarin units
  12. Microwave-assisted synthesis of (E)-7-[(1-benzyl-1H-1,2,3-triazol-4-yl)methoxy]-8-(3-arylacryloyl)-4-methyl-2H-chromen-2-ones and their antimicrobial activity
  13. One-pot synthesis of 3,4-dihydro-3-hydroxyisochroman-1-one and evaluation of acetal derivatives as antibacterial and antifungal agents
  14. Copper-mediated ligand-free Ullmann reaction approach to substituted s-triazines: rationale, synthesis, and biological evaluation
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