Scholarly article on topic 'Phthalimide-N-sulfonic acid as a recyclable organocatalyst for an efficient and eco-friendly synthesis of 2-(2-oxo-2H-chromen-3-yl)-4-aryl-indeno[1,2-b]pyridine-5-one derivatives'

Phthalimide-N-sulfonic acid as a recyclable organocatalyst for an efficient and eco-friendly synthesis of 2-(2-oxo-2H-chromen-3-yl)-4-aryl-indeno[1,2-b]pyridine-5-one derivatives Academic research paper on "Chemical sciences"

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{"2-(2-Oxo-2H-chromen-3-yl)-4-aryl-indeno[1 / 2-b]pyridine-5-one" / "Phthalimide-N-sulfonic acid" / "1 / 3-Indandione" / 3-Acetylcoumarin}

Abstract of research paper on Chemical sciences, author of scientific article — Prasanna Nithiya Sudhan, Majid Ghashang, Syed Sheik Mansoor

Abstract A facile and environmentally benign synthesis of some 2-(2-oxo-2H-chromen-3-yl)-4-aryl-indeno[1,2-b]pyridine-5-one derivatives from the reaction of aromatic aldehydes, 3-acetylcoumarin, 1,3-indandione and ammonium acetate using phthalimide-N-sulfonic acid (PISA) as a catalyst is described. The present method has some important features such as mild reaction conditions, short reaction times, less catalyst dosage and high yields with the green aspects by avoiding toxic catalysts and solvents. Further, the catalyst can be reused for four times without any noticeable decrease in the catalytic activity.

Academic research paper on topic "Phthalimide-N-sulfonic acid as a recyclable organocatalyst for an efficient and eco-friendly synthesis of 2-(2-oxo-2H-chromen-3-yl)-4-aryl-indeno[1,2-b]pyridine-5-one derivatives"

King Saud University Journal of Saudi Chemical Society

www.ksu.edu.sa www.sciencedirect.com

ORIGINAL ARTICLE

Phthalimide-N-sulfonic acid as a recyclable organocatalyst for an efficient and eco-friendly synthesis of 2-(2-oxo-2H-chromen-3-yl)-4-aryl-indeno[1,2-b]pyridine-5-one derivatives

Prasanna Nithiya Sudhana, Majid Ghashangb, Syed Sheik Mansoora*

aResearch Department of Chemistry, Bioactive Organic Molecule Synthetic Unit, C. Abdul Hakeem College (Autonomous), Melvisharam 632 509, Tamil Nadu, India

b Faculty of Sciences, Najafabad Branch, Islamic Azad University, P.O. Box: 517, Najafabad, Esfahan, Iran Received 9 July 2015; revised 8 September 2015; accepted 29 September 2015

KEYWORDS

2-(2-Oxo-2H-chromen-3-yl)-

4-aryl-indeno[1,2-b]pyridine-

5-one;

Phthalimide-N-sulfonic acid; 1,3-Indandione;

3-Acetylcoumarin

Abstract A facile and environmentally benign synthesis of some 2-(2-oxo-2H-chromen-3-yl)-4-aryl-indeno[1,2-b]pyridine-5-one derivatives from the reaction of aromatic aldehydes, 3-acetylcoumarin, 1,3-indandione and ammonium acetate using phthalimide-N-sulfonic acid (PISA) as a catalyst is described. The present method has some important features such as mild reaction conditions, short reaction times, less catalyst dosage and high yields with the green aspects by avoiding toxic catalysts and solvents. Further, the catalyst can be reused for four times without any noticeable decrease in the catalytic activity.

© 2015 King Saud University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction

Coumarins and their derivatives are very important structural motifs that occur widely in different parts of plants, such as roots, seeds, nuts, flowers and fruits [1]. According to their chemical structure, they belong to the family of benzopyrones. So far, more than 1300 different coumarins have been

* Corresponding author. Tel.: +91 9944093020.

E-mail address: smansoors2000@yahoo.co.in (S.S. Mansoor).

Peer review under responsibility of King Saud University.

identified. The most representative molecule, that is coumarin, has been extensively studied both in biochemical and pharmaceutical fields [2-4]. A novel series of substituted 2-oxo-2H-chromenyl-pyrazole carboxylates were synthesized and screened for anticancer activity against three human cancer cell lines such as prostate (DU-145), lung adenocarcinoma (A549), and cervical (HeLa) by standard MTT assay method [5]. A cascade operation was designed to synthesize nine coumarin-substituted dihydropyrazoles with only one or two phenolic hydroxyl groups contained. Antioxidant abilities of the obtained compounds were evaluated [6]. A new series of coumarin substituted dihydrobenzo[4,5]imidazo[1,2-a]pyrimi din-4-ones were synthesized and screened for their in vitro antimicrobial activity. In general, all the compounds possess better antifungal properties than antibacterial properties [7].

http://dx.doi.org/10.1016/jjscs.2015.09.005

1319-6103 © 2015 King Saud University. Production and hosting by Elsevier B.V.

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Various 7-substituted carboxycoumarins and quinolinone derivatives were synthesized and pharmacological evaluation as a new antitumor treatment targeting lactate transport in cancer cells was studied [8].

The indenopyridine nucleus is present in the 4-azafluorenone group of the naturally occurring alkaloids, isolated from the root of the plant Polyalthia debilis (Pierre) belonging to the family of Annonaceae. Many indenopyridine derivatives being the core structural unit in a wide range of natural products, has attracted much research in recent times

[9]. They are useful inhibitors of spermatogenesis in animals

[10] and some also show fungicidal activity [11]. Hydrogenated indenopyridines have potential antidepressant activity [12]. A series of novel 4-[2-amino-3-cyano-5-oxo-4-substitutedaryl-4H-indeno[1,2-b]pyridin-1-(5H)-yl]benzene sulfonamide derivatives were synthesized and they were subjected to in vitro anticancer activity against the breast cancer cell line (MCF7) [13]. Therefore, these compounds have distinguished themselves as heterocycles of profound chemical and biological significance.

In view of the pharmaceutical importance of heterocyclic compounds, various methods have been developed for the synthesis of indeno[1,2-b]pyridines [14-18]. On the other hand many techniques have been employed in the synthesis of cou-marin frameworks [19-23]. In the design of new bioactive molecules, the development of hybrid molecules through the combination of different pharmacophores may lead to compounds with interesting biological profiles. Therefore, a single molecule containing more than one pharmacophore, each with different biological activities could be beneficial in modern drug discovery. Therefore, we have designed and synthesized a series of novel compounds that have both coumarin and indeno[1,2-b]pyridine entities in one molecule.

Multicomponent reactions have gained significant importance as a tool for the synthesis of a wide variety of useful compounds, including pharmaceuticals. In this context, the multiple component approach is especially appealing in view of the fact that products are formed in a single step, and the diversity can be readily achieved simply by varying the reacting components [24-26]. The chemo-, regio- or stereoselective synthesis of high-value chemical entities and parallel synthesis to generate a library of small molecules will add to the growth of multicomponent solvent-free reactions in the near future. It is quite clear from the growing number of emerging publications in this field that the possibility to utilize multicomponent technology allows reaction conditions to be accessed that are very valuable for organic synthesis. Therefore, diversity oriented synthesis (DOS) is rapidly becoming one of the paradigms in the process of modern drug discovery. This has spurred research in those fields of chemical investigation that lead to the rapid assembly of not only molecular diversity, but also molecular complexity. As a consequence multicompo-nent and other related reactions are witnessing a new spring [27].

In recent years, the discovery of catalysis by small organic molecules termed as organocatalysts has become a break-through, which offers numerous advantages including lower activation energy, high stability, metal free environment, reduced toxicity, and mild reaction conditions [28].

Organocatalytic strategies have attracted attention for their application in organic synthesis due to their ability to facilitate chemical transformations with a substoichiometric amount of an organic compound [29].

Green chemistry with its 12 principles would like to increase the efficiency of synthetic methods, to use less toxic solvents, reduce the stages of the synthetic routes and minimize waste as far as practically possible. One of the key areas of green chemistry is the replacement of hazardous solvents with environmentally benign ones or the elimination of solvents altogether [30].

The eco-friendly, solvent-free multicomponent approach opens up numerous possibilities for conducting rapid organic synthesis and functional group transformations more efficiently. Implementation of organic transformations under solvent-free reaction conditions have gained in popularity in recent years because of their simple workup procedure, high efficiency, mild conditions, environmental friendliness, cleanliness, low cost, handling, and economical friendliness [31,32].

Recently, phthalimide-N-sulfonic acid (PISA) has been used as an efficient organocatalyst in organic transformations [33,34]. PISA has been used as a catalyst for the solvent-free synthesis of 5-alkenyl-2,2-butylidene-1,3-dioxane-4,6-diones under ultrasonic irradiation [33] and for Biginelli reaction under solvent-free conditions [34].

As a part of our ongoing programed synthesis of biologically active heterocyclic molecules [35-39], an efficient and convenient synthesis of 2-(2-oxo-2H-chromen-3-yl)-4-aryl-indeno [1,2-b]pyridine-5-one derivatives have been accomplished by the multi-component reaction of aromatic aldehydes, 3-acetylcoumarin, 1,3-indanedione and ammonium acetate using phthalimide-N-sulfonic acid as an efficient catalyst in good yields (Scheme 1).

2. Experimental

2.1. Apparatus and analysis

Commercially available chemicals with high purity were purchased from Merck, Fluka and Aldrich Chemical Companies. Potassium phthalimide and chlorosulfonic acid were used for the preparation of catalyst. The benzaldehydes used were with substituents H, 4-Cl, 4-F, 4-CH3, 4-OCH3, 4-NO2, 3-Cl, 3-NO2, 3-Br, 2-F, 2-Cl, 2-CH3, 2,4-dichloro and 3,4-dichloro benzaldehydes. In addition to aldehydes, 3-acetylcoumarin,

1.3-indandione and ammonium acetate were used in the synthesis of various 2-(2-oxo-2H-chromen-3-yl)-4-aryl-indeno[1,2 -b]pyridine-5-ones. The solid aldehydes were used as such and the liquid aldehydes were used after vacuum distillation. Solvents like CH3CN, DMF, CHCl3, EtOH, MeOH and

1.4-dioxane were used to study the optimization of solvent. All yields refer to isolated products unless otherwise stated. *H NMR (500 MHz) and 13C NMR (125 MHz) spectra were obtained using Bruker DRX-500 Avance at ambient temperature, using TMS as internal standard. FT-IR spectra were obtained as KBr disks on a Shimadzu spectrometer. Mass spectra were determined on a Varion-Saturn 2000 GC-MS instrument. Elemental analysis was measured by means of Perkin Elmer 2400 CHN elemental analyzer flowchart.

+ NH4OAc

N-SO3H O

Solvent-free, 80 oC

Scheme 1 Synthesis of various 2-(2-oxo-2H-chromen-3-yl)-4-aryl-indeno[1,2-b]pyridine-5-one derivatives.

2.2. Preparation of the phthalimide-N-sulfonic acid (PISA)

Phthalimide-N-sulfonic acid (PISA) was easily prepared according to the previously reported method [34] (Scheme 2).

2.3. General procedure for the preparation of 2-(2-oxo-2H-chromen-3-yl)-4-aryl-indeno[1,2-b]pyridine-5-one derivatives

In a 25 mL round-bottomed flask, aldehydes (1 mmol), 3-acetylcoumarin (1 mmol), 1,3-indandione (1 mmol) and ammonium acetate (1.3 mmol) were stirred in the presence of 10 mol% of PISA under solvent-free condition at 80 0C for the stipulated time. After completion of the reaction, as indicated by TLC analysis, the system was cooled to room temperature. Ethanol (5 mL) was added to the reaction mixture, and the mixture was heated until a homogeneous solution was obtained. Next, ethyl acetate was added to the resulting mixture and then cooled to room temperature, and the catalyst was recovered by filtration and washed thoroughly with ethyl acetate and then diethyl ether. The recovered catalyst was then reused under the same conditions as above for at least four reactions. After this, the organic phase was concentrated by evaporation, distilled water was added to the residue, and the solid thus obtained. The resulting solid product was filtered off, washed with cold water, and recrystallised from hot ethanol to afford pure product. The IR, гИ NMR, 13C NMR, mass and elemental analysis data of the synthesized compounds are given below.

2.4. Spectral date for the synthesized indeno[1 ,2-b]pyridine -5-one derivatives

2.4.1. 2-(2-Oxo-2H-chromen-3yl)-4-phenyl-indeno[1,2-b] pyridine-5-one (4a)

IR (KBr, cm-1): 3136, 1706, 1669, 1633, 1581, 1200, 1066, 804; гИ NMR (500 MHz, DMSO-d6) Ô: 7.11-7.32 (m, 5И, Ar-H),

ClSO3H

Potassium phthalimide

CH2Cl2

0oC, r.t., 2.5 h

O=S=O I

Phthalimide-W-sulfonic acid (PISA)

Scheme 2 Preparation of phthalimide-N-sulfonic acid.

7.49-7.63 (m, 4H, Ar-H), 7.73-7.81 (m, 2H, Ar-H), 7.94 (s, 1H, Py-H), 8.26-8.37 (m, 2H, Ar-H), 8.73 (s, 1H, coumarin 4-H) ppm; 13C NMR (125 MHz, DMSO-d6) S: 116.0, 122.0, 125.3, 125.7, 126.1, 126.5, 126.9, 127.2, 127.5, 128.7, 129.2,

129.3, 129.8, 130.2, 131.2, 132.2, 133.7, 139.6, 140.4, 141.5,

150.4, 151.7, 160.7, 162.2, 189.2 ppm; MS(ESI): m/z 402 (M + H) + ; Anal. Calcd. for C27H15NO3: C, 80.80; H, 3.74; N, 3.49%. Found: C, 80.70; H, 3.71; N, 3.44%.

2.4.2. 2-(2-Oxo-2H-chromen-3yl)-4-(4-fluorophenyl)-indeno [1,2-b]pyridine-5-one (4b)

IR (KBr, cm-1): 3133, 1714, 1668, 1628, 1586, 1198, 1064, 811 1H NMR (500 MHz, DMSO-d6) S: 7.05 (d, J = 8.2 Hz, 2H Ar-H), 7.27 (d, J = 8.2 Hz, 2H, Ar-H), 7.40-7.59 (m, 4H Ar-H), 7.69-7.81 (m, 2H, Ar-H), 7.88 (s, 1H, Py-H) 8.30-8.41 (m, 2H, Ar-H), 8.80 (s, 1H, coumarin 4-H) ppm 13C NMR (125 MHz, DMSO-d6) S: 115.7, 121.6, 125.5 125.8, 126.0, 126.4, 126.8, 127.1, 127.4, 128.5, 129.2, 129.5

129.7, 130.4, 131.6, 132.6, 133.5, 139.4, 140.6, 141.7, 150.2

151.8, 160.8, 162.4, 190.3 ppm; MS(ESI): m/z 420 (M + H) + Anal. Calcd. for C27H14FNO3: C, 77.33; H, 3.34; N, 3.34%. Found: C, 77.25; H, 3.28; N, 3.30%.

2.4.3. 2-(2-Oxo-2H-chromen-3yl)-4-(3-bromophenyl)-indeno [1 ,2-b]pyridine-5-one (4c)

IR (KBr, cm-1): 3128, 1711, 1674, 1627, 1588, 1202, 1070, 800; 1H NMR (500 MHz, DMSO-d6) S: 7.03-7.21 (m, 4H, Ar-H), 7.39-7.59 (m, 4H, Ar-H), 7.70-7.80 (m, 2H, Ar-H), 7.90 (s, 1H, Py-H), 8.24-8.33 (m, 2H, Ar-H), 8.84 (s, 1H, coumarin 4-H) ppm; 13C NMR (125 MHz, DMSO-d6) S: 116.1, 121.5, 125.7, 126.0, 126.2, 126.5, 126.9, 127.0, 127.4, 128.7, 129.1,

129.5, 129.9, 130.6, 131.3, 132.5, 133.4, 139.8, 140.2, 141.6,

150.3, 151.3, 160.5, 162.6, 189.5 ppm; MS(ESI): m/z 480.2 (M + H) + ; Anal. Calcd. for C27H14BrNO3: C, 67.51; H, 2.92; N, 2.92%. Found: C, 67.44; H, 2.90; N, 2.89%.

2.4.4. 2-(2-Oxo-2H-chromen-3yl)-4-(2-chlorophenyl)-indeno [1 ,2-b]pyridine-5-one (4d)

IR (KBr, cm-1): 3124, 1720, 1660, 1629, 1590, 1190, 1072, 799; 1H NMR (500 MHz, DMSO-d6) S: 7.12-7.27 (m, 4H, Ar-H), 7.41-7.57 (m, 4H, Ar-H), 7.68-7.79 (m, 2H, Ar-H), 7.87 (s, 1H, Py-H), 8.31-8.40 (m, 2H, Ar-H), 8.80 (s, 1H, coumarin 4-H) ppm; 13C NMR (125 MHz, DMSO-d6) S: 115.5, 121.3, 125.2, 125.7, 126.1, 126.6, 126.7, 127.2, 127.7, 128.6, 129.1, 129.4, 129.8, 130.3, 131.5, 132.3, 133.3, 139.7, 140.4, 140.7, 150.2, 151.7, 160.1, 162.5, 189.4 ppm; MS(ESI): m/z 436.1

(M + H) + ; Anal. Calcd. for C27H14ClNO3: C, 74.40; H, 3.21; N, 3.21%. Found: C, 74.33; H, 3.15; N, 3.17%.

2.4.5. 2-(2-Oxo-2H-chromen-3yl)-4-(4-methylphenyl)-indeno [1,2-b]pyridine-5-one (4e)

IR (KBr, cm-1): 3121, 1713, 1676, 1632, 1579, 1194, 1068, 792; 1H NMR (500 MHz, DMSO-d6) d: 2.21 (s, 3H, CH3), 7.13 (d, J = 8.2 Hz, 2H, Ar-H), 7.24 (d, J = 8.2 Hz, 2H, Ar-H), 7.43-7.64 (m, 4H, Ar-H), 7.78-7.85 (m, 2H, Ar-H), 7.96 (s, 1H, Py-H), 8.24-8.38 (m, 2H, Ar-H), 8.77 (s, 1H, coumarin 4-H) ppm; 13C NMR (125 MHz, DMSO-d6) d: 17.2, 115.7, 122.2, 125.4, 125.9, 126.3, 126.6, 126.9, 127.2, 127.8, 128.4, 129.2, 129.4, 129.8, 130.5, 131.7, 132.4, 133.5, 139.5, 140.3, 140.8, 150.6, 151.9, 160.3, 162.3, 190.0 ppm; MS(ESI): m/z 416 (M + H) + ; Anal. Calcd. for C28H17NO3: C, 80.96; H, 4.09; N, 3.37%. Found: C, 80.88; H, 4.02; N, 3.33%.

2.4.6. 2-(2-Oxo-2H-chromen-3yl)-4-(4-methoxyphenyl)-indeno [1,2-b]pyridine-5-one (4f)

IR (KBr, cm-1): 3130, 1712, 1677, 1633, 1582, 1196, 1072, 788; 1H NMR (500 MHz, DMSO-d6) d: 3.59 (s, 3H, OCH3), 7.17 (d, J = 8.2 Hz, 2H, Ar-H), 7.31 (d, J = 8.2 Hz, 2H, Ar-H), 7.51-7.62 (m, 4H, Ar-H), 7.72-7.82 (m, 2H, Ar-H), 7.89 (s, 1H, Py-H), 8.21-8.35 (m, 2H, Ar-H), 8.83 (s, 1H, coumarin 4-H) ppm; 13C NMR (125 MHz, DMSO-d6) d: 54.3, 115.9,

121.6, 125.6, 125.8, 126.2, 126.5, 126.7, 127.3, 127.8, 128.6, 129.0, 129.5, 129.9, 130.7, 131.2, 132.7, 133.7, 139.3, 140.3,

140.7, 150.2, 151.5, 160.8, 162.1, 190.3 ppm; MS(ESI): m/z 432 (M + H) + ; Anal. Calcd. for C28H17NO4: C, 77.96; H, 3.94; N, 3.25%. Found: C, 77.90; H, 3.91; N, 3.22%.

2.4.7. 2-(2-Oxo-2H-chromen-3yl)-4-(3, 4-dichlorophenyl)-indeno[1,2-b]pyridine-5-one (4g)

IR (KBr, cm-1): 3125, 1705, 1663, 1624, 1584, 1199, 1073, 806; 1H NMR (500 MHz, DMSO-d6) d: 7.19-7.32 (m, 3H, Ar-H),

7.48-7.64 (m, 4H, Ar-H), 7.73-7.83 (m, 2H, Ar-H), 7.93 (s, 1H, Py-H), 8.33-8.42 (m, 2H, Ar-H), 8.78 (s, 1H, coumarin 4-H) ppm; 13C NMR (125 MHz, DMSO-d6) d: 115.2, 121.8,

125.5, 125.9, 126.1, 126.6, 126.8, 127.3, 127.7, 128.5, 129.1,

129.6, 129.9, 130.5, 131.4, 132.6, 133.4, 139.5, 140.5, 140.8,

150.7, 151.7, 160.9, 162.5, 189.7 ppm; MS(ESI): m/z 470.2 (M + H) + ; Anal. Calcd. for C27H13Cl2NO3: C, 68.95; H, 2.77; N, 2.99%. Found: C, 68.88; H, 2.75; N, 2.97%.

2.4.8, 2-(2-Oxo-2H-chromen-3yl)-4-(2, 4-dichlorophenyl)-indeno[1,2-b]pyridine-5-one (4h)

IR (KBr, cm-1): 3132, 1702, 1667, 1639, 1586, 1202, 1071, 803; 1H NMR (500 MHz, DMSO-d6) d: 7.12-7.31 (m, 3H, Ar-H), 7.40-7.61 (m, 4H, Ar-H), 7.71-7.82 (m, 2H, Ar-H), 7.95 (s, 1H, Py-H), 8.27-8.38 (m, 2H, Ar-H), 8.83 (s, 1H, coumarin 4-H) ppm; 13C NMR (125 MHz, DMSO-d6) d: 116.0, 121.3, 124.2, 125.3, 126.0, 126.4, 126.9, 127.0, 127.6, 128.7, 129.2,

129.5, 129.7, 130.3, 131.2, 132.0, 133.4, 138.9, 140.0, 140.6,

149.9, 151.6, 161.0, 163.0, 188.9 ppm; MS(ESI): 470.2 (M + H) + ; Anal. Calcd. for C27H13Cl2NO3: C, 68.95; H, 2.77; N, 2.99%. Found: C, 68.86; H, 2.77; N, 2.94%.

2.4.9. 2-(2-Oxo-2H-chromen-3yl)-4-(2-fluorophenyl)-indeno [1, 2-b]pyridine-5-one (4i)

IR (KBr, cm-1): 3138, 1720, 1661, 1636, 1592, 1204, 1068, 797; 1H NMR (500 MHz, DMSO-d6) d: 7.17-7.36 (m, 4H, Ar-H), 7.47-7.63 (m, 4H, Ar-H), 7.78-7.87 (m, 2H, Ar-H), 7.96 (s, 1H, Py-H), 8.30-8.41 (m, 2H, Ar-H), 8.82 (s, 1H, coumarin 4-H) ppm; 13C NMR (125 MHz, DMSO-d6) d: 116.2, 121.5,

124.6, 125.6, 126.2, 126.5, 126.8, 127.1, 127.5, 128.5, 129.4,

129.7, 129.9, 130.5, 131.4, 132.0, 133.7, 138.8, 140.0, 140.5,

149.8, 151.8, 161.0, 163.2, 189.7 ppm; MS(ESI): m/z 420 (M + H) + ; Anal. Calcd. for C27H14FNO3: C, 77.33; H, 3.34; N, 3.34%. Found: C, 77.29; H, 3.30; N, 3.32%.

Table 1 Optimizing the reaction conditions for the synthesis of 2-(2-oxo-2H-chromen-3-yl)-4-aryl-indeno[1,2-b]pyridine-5-one in the presence of PISA as catalyst.a

Entry catalyst Amount (mol%) Solvent Temperature (°C) Time (min) Yield (%)b

1 PISA 10 CH3CN Reflux 180 41

2 PISA 10 DMF Reflux 180 34

3 PISA 10 CHCl3 Reflux 180 44

4 PISA 10 EtOH Reflux 150 67

5 PISA 10 MeOH Reflux 150 55

6 PISA 10 1,4-Dioxane Reflux 150 68

7 PISA 10 Solvent-free 80 60 95

8 PISA 10 Solvent-free RT 150 41

9 PISA 10 Solvent-free 50 150 56

10 PISA 10 Solvent-free 60 120 74

11 PISA 10 Solvent-free 70 90 86

12 PISA 10 Solvent-free 90 60 95

13 PISA 0 Solvent-free 80 150 22

14 PISA 5 Solvent-free 80 90 61

15 PISA 15 Solvent-free 80 60 95

16 CH3SO3H 10 Solvent-free 80 90 66

17 p-TSA 10 Solvent-free 80 90 57

18 SA 10 Solvent-free 80 90 61

19 ZrOCl2 10 Solvent-free 80 120 44

a Reaction conditions: 4-fluorobenzaldehyde (1 mmol), 3-acetylcoumarin (1 mmol), 1,3-indandione (1 mmol) and ammonium acetate (1.3 mmol) were refluxed in the presence of PISA with various solvents (5 ml) and also heated at 80 °C under solvent-free conditions. b Isolated yield.

Table 2 Synthesis of various 2-(2-oxo-2H-chromen-3-yl)-4-aryl-indeno[1,2-b]pyridine-5-ones in the presence of PISA (10mol%).a

Aldehyde

Product

Time (min)

Yield (%)b

M.p (oC)

217-219

199-201

190-192

207-209

233-234

189-191

242-244

(continued on next page)

Table 2 (continued)

Entry Aldehyde Product Time (min) Yield (%)b M.p (oC)

Cly\ Cl

14 O 60 90 231-233

A^O^O 4n

a Reaction conditions: benzaldehyde (1 mmol), 3-acetylcoumarin (1 mmol), 1,3-indandione (1 mmol) and ammonium acetate (1.3 mmol) were heated at 80 °C under solvent-free conditions in the presence of PISA (10 mol%). b Isolated yield.

2.4.10. 2-(2-Oxo-2H-chromen-3yl)-4-(2-methylphenyl)-indeno [l,2-b]pyridine-5-one (4j)

IR (KBr, cm-1): 3127, 1714, 1672, 1629, 1590, 1194, 1071, 794; 1H NMR (500 MHz, DMSO-d6) d: 2.26 (s, 3H, CH3), 7.09-7.33 (m, 4H, Ar-H), 7.45-7.57 (m, 4H, Ar-H), 7.68-7.80 (m, 2H, Ar-H), 7.88 (s, 1H, Py-H), 8.34-8.42 (m, 2H, Ar-H), 8.75 (s, 1H, coumarin 4-H) ppm; 13C NMR (125 MHz, DMSO-d6) d: 17.8, 115.7, 121.7, 124.3, 125.4, 126.4, 126.6, 126.8, 127.1, 127.5, 128.3, 129.4, 129.7, 129.8, 130.5, 131.6, 132.5, 133.7, 139.3, 140.5, 140.6, 150.2, 151.7, 160.7, 162.7, 190.4 ppm; MS(ESI): m/z 416 (M + H) + ; Anal. Calcd. for C28H17NO3: C, 80.96; H, 4.09; N, 3.37%. Found: C, 80.91; H, 4.00; N, 3.31.

2.4.11. 2-(2-Oxo-2H-chromen-3yl)-4-(3-nitrophenyl)-indeno [1,2-b]pyridine-5-one (4k)

IR (KBr, cm-1): 3125, 1717, 1668, 1631, 1591, 1192, 1073, 799; 1H NMR (500 MHz, DMSO-d6) d: 7.16-7.39 (m, 4H, Ar-H), 7.46-7.61 (m, 4H, Ar-H), 7.73-7.84 (m, 2H, Ar-H), 7.95

(s, 1H, Py-H), 8.27-8.36 (m, 2H, Ar-H), 8.83 (s, 1H, coumarin 4-H) ppm; 13C NMR (125 MHz, DMSO-d6) d: 115.6, 121.2,

124.7, 125.8, 126.3, 126.7, 126.9, 127.3, 127.9, 128.4, 129.3,

129.8, 129.9, 130.2, 131.5, 132.3, 133.9, 139.5, 140.6, 140.5, 150.4, 151.5, 160.7, 162.8, 190.2 ppm; MS(ESI): m/z 447 (M + H) + ; Anal. Calcd. for C27H14N2O5: C, 72.65; H, 3.14; N, 6.28%. Found: C, 72.61; H, 3.11; N, 6.25%.

2.4.12. 2-(2-Oxo-2H-chromen-3yl)-4-(4-chlorophenyl)-indeno [1,2-b]pyridine-5-one (4l)

IR (KBr, cm-1): 3119, 1709, 1664, 1634, 1588, 1197, 1075, 805; 1H NMR (500 MHz, DMSO-d6) d: 7.15 (d, J = 8.2 Hz, 2H, Ar-H), 7.29 (d, J = 8.2 Hz, 2H, Ar-H), 7.39-7.60 (m, 4H, Ar-H), 7.68-7.77 (m, 2H, Ar-H), 7.81 (s, 1H, Py-H), 8.29-8.40 (m, 2H, Ar-H), 8.82 (s, 1H, coumarin 4-H) ppm; 13C NMR (125 MHz, DMSO-d6) d: 115.4, 121.4, 125.0, 125.2, 126.0, 126.3, 126.9, 127.3, 127.9, 128.6, 129.3, 129.7,

129.9, 130.4, 131.5, 132.5, 133.9, 139.7, 140.2, 140.7, 150.6, 151.2, 160.4, 162.9, 190.0 ppm; MS(ESI): m/z 436.1

100 98969492-

sj: 8886 84 82 80

Recyclability of the catalyst

Number of runs

Figure 1 Recyclability of the catalyst: the catalyst PISA could be reused four times without any loss of its activity toward the synthesis of 2-(2-oxo-2H-chromen-3-yl)-4-(4-fluorophenyl)-indeno[1,2-b]pyridine-5-one.

(M + H) + ; Anal. Calcd. for C27H14ClNO3: C, 74.40; H, 3.21; N, 3.21%. Found: C, 74.35; H, 3.17; N, 3.19%.

2.4.13. 2-(2-Oxo-2H-chromen-3yl)-4-(4-nitrophenyl)-indeno [l,2-b]pyridine-5-one (4m)

IR (KBr, cm-1): 3122, 1710, 1665, 1637, 1589, 1203, 1072, 795; 1H NMR (500 MHz, DMSO-d6) d: 7.18 (d, J = 8.2 Hz, 2H, Ar-H), 7.36 (d, J = 8.2 Hz, 2H, Ar-H), 7.48-7.67 (m, 4H, Ar-H), 7.77-7.85 (m, 2H, Ar-H), 7.95 (s, 1H, Py-H), 8.30-8.42 (m, 2H, Ar-H), 8.77 (s, 1H, coumarin 4-H) ppm; 13C NMR (125 MHz, DMSO-d6) d: 115.8, 121.2, 125.1, 125.2, 126.1, 126.5, 126.8, 127.2, 127.8, 128.1, 129.3, 129.7, 130.0, 130.4, 131.7, 132.2, 133.5, 139.2, 140.2, 140.3, 150.7, 151.4, 160.4, 162.6, 189.7 ppm; MS(ESI): m/z 447 (M + H) + ;

Anal. Calcd. for C27H14N2O5: C, 72.65; H, 3.14; N, 6.28%. Found: C, 72.58; H, 3.09; N, 6.24%.

2.4.14. 2-(2-Oxo-2H-chromen-3yl)-4-(3-chlorophenyl)-indeno [l,2-b]pyridine-5-one (4n)

IR (KBr, cm-1): 3129, 1714, 1664, 1628, 1590, 1193, 1069, 790; 1H NMR (500 MHz, DMSO-d6) d: 7.19-7.40 (m, 4H, Ar-H), 7.51-7.65 (m, 4H, Ar-H), 7.76-7.82 (m, 2H, Ar-H), 7.92 (s, 1H, Py-H), 8.31-8.42 (m, 2H, Ar-H), 8.88 (s, 1H, coumarin 4-H) ppm; 13C NMR (125 MHz, DMSO-d6) d: 115.2, 121.6, 124.9, 125.3, 126.2, 126.4, 126.6, 127.3, 127.7, 128.2, 129.4, 129.8, 130.0, 130.3, 131.7, 132.6, 133.5, 139.4, 140.2, 140.7, 150.8, 151.6, 160.3, 162.6, 190.4 ppm; MS(ESI): m/z 436.1 (M + H) + ; Anal. Calcd. for C27H14ClNO3: C, 74.40; H, 3.21; N, 3.21%. Found: C, 74.30; H, 3.13; N, 3.15%.

- H2O Ar

Oxidation

one-pot synthesis of various 2-(2-oxo-2H-chromen-3-yl)-4-aryl-

Ar^-H 1

N-SO3H O

+ NH4OAc

Nn-so3h

-AcOH -H2O

NH2 CH2 O 'O (b)

Scheme 3 Mechanism for the phthalimide-N-sulfonic acid catalyzed indeno[1,2-b]pyridine-5-one derivatives.

3. Results and discussion

To find out the suitable conditions for the reaction, a series of experiments were performed with the standard reaction of 4-fluorobenzaldehyde (1b), 3-acetylcoumarin (2), 1,3-indandione (3) and ammonium acetate in the presence of catalytic amount of PISA (10mol%) on the synthesis of 2-(2-oxo-2H-chromen-3yl)-4-(4-fluorophenyl)-indeno[1,2-b]pyridine-5-one (4b) as a model reaction.

Our initial work started with screening of solvent and catalyst loading so as to identify optimal reaction conditions for the synthesis of 2-(2-oxo-2H-chromen-3-yl)-4-aryl-indeno[1,2-b]pyridine-5-one derivatives. A range of solvents like acetoni-trile, DMF, CHCl3, EtOH, MeOH and 1,4-dioxane were examined (Table 1, entries 1-6). The reaction was more facile and proceeded to give highest yield without any solvent at 80 °C (Table 1, entry 7).

Furthermore, the model reaction was conducted in a range of different temperatures, including room temperature, 50, 60, 70, 80 and 90 °C, in the presence of 10mol% PISA catalyst under solvent-free condition (Table 1, entries 7-12). As can be concluded from Table 1, the reaction proceeded slowly at room temperature. With increasing temperature to 80 °C, reaction yield was increased and time of reaction was decreased, when the reaction was heated above 80 °C, so high temperatures did not further improve the yield and decrease the time of reaction. The greatest yield in the shortest reaction time was obtained in water at 80 °C (Table 1, entry 7). We also evaluated the amount of PISA required for the reaction. Catalyst loadings in the range of 0-15 mol% were tested (Table 1, entry 7 and entries 13-15). The best result was obtained with 10 mol % of PISA in water at 80 °C (Table 1, entry 7). Among the different catalysts tested, including methane sulfonic acid (CH3-SO3H), p-toluene sulfonic acid (p-TSA), sulfamic acid (SA), zirconyl(IV) chloride (ZrOCl2) and PISA, PISA was found to be the most efficient in terms of the reaction time and yield of the product (Table 1, entry 7 and entries 16-19).

In order to investigate the scope of these conditions, we have undertaken the synthesis of different derivatives of 2-(2-oxo-2H-chromen-3-yl)-4-aryl-indeno[1,2-b]pyridine-5-ones from a variety of substrates from aldehydes, 3-acetylcoumarin, 1,3-indandione and ammonium acetate in the presence of 10 mol % of PISA as catalyst. The results are presented in Table 2. All the reactions, consisting of those involving ortho-, meta-, and para-substituted benzaldehydes, proceeded smoothly and afforded the corresponding 2-(2-oxo-2H-chromen-3-yl)-4-aryl-indeno[1,2-b]pyridine-5-ones in moderate to high yields. Electronic effects can be observed. The electron-donating group substituted benzaldehydes required prolonged reaction time to give the yields, while electron-withdrawing group substituted ones gave evidently increasing yields. The ortho-substituted benzaldehydes, whether the substituent is an electron-donating group or electron-withdrawing group, afforded the corresponding 2-(2-oxo-2H-chromen-3-yl)-4-aryl-indeno[1,2-b]pyridine-5-ones in relatively lower yields, indicating an obvious steric effect.

Ease of recycling of the catalyst is a valuable advantage of our method. After completion of the reaction, as indicated by TLC analysis, the system was cooled to room temperature. The catalyst was recovered by filtration as described in the experimental section and washed thoroughly with ethyl acetate

and then diethyl ether. The recovered catalyst was then reused under the same conditions as above for at least four reactions. As shown in Fig. 1, the solid acid PISA can be recycled at least four times without a significant decrease in catalytic activity, the yields ranged from 95% to 89%.

A possible mechanism for the formation of various 2-(2-oxo-2H-chromen-3-yl)-4-aryl-indeno[1,2-b]pyridine-5-ones is shown in Scheme 3. The first step of the reaction included the formation of 2-benzylidene-2H-indene-1,3-dione (a) from the condensation reaction of protonated benzaldehyde with the enol form of 1,3-indandione. The next intermediate is an enam-ine (b) which is resulted from the reaction of 3-acetylcoumarin with ammonium acetate. In the next step, the prepared 2-benzylidene-2H-indene-1,3-dione (a) is reacted with enamine (b) which undergoes the preparation of intermediate (c). The later stages including enol-keto and imine-enamine tautomer-ization lead to the formation of intermediate (d) which was transferred into the targeted molecule via cyclo-addition and oxidation processes respectively.

As mentioned above aromatic aldehydes bearing electron withdrawing groups have lower reaction times than those with electron-donating groups. A reasonable explanation for this result can be given by considering the nucleophilic addition to 2-benzylidene-2H-indene-1,3-dione (a) intermediate favorable via conjugate addition on a,b-unsaturated carbonyl group of this intermediate. When electron withdrawing groups are substituted on the aromatic ring of 2-benzylidene-2H-indene-1,3-dione (a) intermediate, the LUMO of alkene is at lower energy than the substitution of electron donating groups. Thus the rate of 1,4-nucleophilic addition reaction increased with the substitution of electron withdrawing groups on the aromatic ring [40].

4. Conclusions

In summary, we have developed a straightforward and efficient method for the preparation of 2-(2-oxo-2H-chromen-3-yl)-4-ar yl-indeno[1,2-b]pyridine-5-one derivatives by the condensation of aromatic aldehydes, 3-acetylcoumarin, 1,3-indandione and ammonium acetate using phthalimide-N-sulfonic acid (PISA) as a catalyst. A mechanistic rationale portraying the probable sequence of events for the formation of various 2-(2-oxo-2H-chromen-3-yl)-4-aryl-indeno[1,2-b]pyridine-5-ones from the condensation reaction of 2-benzylidene-2H-indene-1,3-dione (a) with enamine (b) using PISA is described. This method tolerates most of the substrates, and the catalyst can be reused at least four times without a significant loss of activity.

Acknowledgement

The author Mansoor is grateful to C. Abdul Hakeem College Management for the facilities and support.

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