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Zinc Chloride Catalyzed Multicomponent Synthesis of Pyrazolopyridocoumarin Scaffolds

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Zinc Chloride Catalyzed Multicomponent Synthesis of Pyrazolopyridocoumarin Scaffolds View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by ePrints@Bangalore University J. Chem. Sci. (2019) 131:29 © Indian Academy of Sciences https://doi.org/10.1007/s12039-019-1610-0 REGULAR ARTICLE Zinc chloride catalyzed multicomponent synthesis of pyrazolopyridocoumarin scaffolds DEVADAS SHAMALAa, KALEGOWDA SHIVASHANKARa,∗ , CHANDRAb and MADEGOWDA MAHENDRAb aP. G. Department of Chemistry, Bangalore University, Central College Campus, Bangalore, Karnataka 560 001, India bDepartment of Studies In Physics, Manasagangotri, University of Mysore, Mysore, Karnataka 570 006, India E-mail: [email protected] MS received 4 October 2018; revised 20 February 2019; accepted 27 February 2019; published online 22 March 2019 Abstract. An efficient synthesis of a series of pyrazolopyridocoumarins is reported by condensation of 4- hydroxycoumarin, benzaldehydes and 1-alkyl-5-amino-pyrazoles in the presence of 10 mol% zinc chloride in ethanol under reflux conditions through one-pot reaction. The significant attraction of this protocol is being a simple procedure, mild reaction condition, and excellent yield. The molecular structure of the compound (4e) is established by single crystal X-ray structure determination. Keywords. Coumarins; pyridine; pyrazole; zinc chloride; multicomponent reactions; one-pot synthesis. 1. Introduction have been developed for the preparation of pyra- zolopyridocoumarin derivatives with the use of various Multicomponent reactions (MCRs) efficiently combine catalysts such as n-tetrabutylammonium tribromide, 28 29 30 three or more reactants simultaneously in one pot that do Zn(OTf)2, glacial acetic acid, piperidine in acetic not need the isolation, purification and characterization acid, 31 and iodine. 19,32 However, these methodologies of intermediate products. The MCRs have additional suffer from one or more shortcomings such as long benefits of being selective, time-saving, convergent, reaction time, low yields and use of excess amounts atom economy and playing an important role in modern of expensive and toxic catalysts. Therefore, the devel- synthetic methodology. 1–13 opment of an efficient and low-cost method for the Fused polyheterocycles are an important class of synthesis of fused tetracyclic pyrazolopyridocoumarins organic molecules 14–18 because of their widespread is still in great demand. applications (Figure 1) as pharmaceuticals (A, B, C Based on the literature survey and in continuation &D), 19–21 photosensitizer (E) 20,21 and fluorescent dye with our ongoing research work on the preparation (F). 22 Coumarin nucleus fused with pyridine rings of biologically active heterocycles, 33–52 we desire to have received increasing attention due to their pho- report a novel method for synthesis of pyrazolopyrido- tophysical properties 23 and potential biological activ- coumarins from simple and readily available starting ities such as antimicrobial, 24 antiosteoporotic, 25 anti- materials, which went through the simultaneous con- inflammatory 21 and analgesic. 26 struction of pyrazole and pyridine rings. The synthesis of fused tetracyclic pyrazolopyrido- coumarins has evoked much attention as a result of which a variety of synthetic methodologies are reported. Among them, the reaction of 4-hydroxycoumarin, aro- 2. Experimental matic aldehydes and 5-amino-3-methyl-1-phenyl- 2.1 General pyrazole is of particular interest. 27 A few protocols The melting points were determined by an open capillary *For correspondence method using electric melting point apparatus and were not Electronic supplementary material: The online version of this article (https:// doi.org/ 10.1007/ s12039-019-1610-0) contains supplementary material, which is available to authorized users. 1 29 Page 2 of 8 J. Chem. Sci. (2019) 131:29 (A) (B) (C) (D) (E) (F) Figure 1. Pyridocoumarins in pharmaceuticals, photosensitizer and dye. corrected. The IR spectra (KBr disc) were measured with a was added zinc chloride (10 mol%). The reaction flask was Shimadzu-8400S FT-IR spectrophotometer. 1H NMR (400 refluxed in an oil bath for 6–7 h. After completion of the 13 MHz) and C NMR (100 MHz) spectra in CDCl3/DMSO- reaction (monitored by TLC), the solvent was removed under d6were recorded using a Bruker spectrometer at IISc, Banga- reduced pressure. The residue left out was dissolved with ethyl lore. Chemical shifts were given in parts per million (ppm) acetate and added aqueous Na2S2O3 solution. The organic relative to tetramethylsilane. The mass spectrum (ESI-MS) layer was separated, and the aqueous layer was extracted with was obtained at IISc, Bangalore. The purity of the compounds ethyl acetate (15 mL x 3). The combined organic phase was was checked by TLC. The elemental analyses were carried out washed with water and dried over anhydrous Na2SO4.The using Elemental Vario Micro Cube CHN Rapid Analyzer. All solvent was removed under reduced pressure. The residue the compounds gave satisfactory elemental analyses. was purified by column chromatography on silica gel [elu- ent: hexane and ethyl acetate (7:3)] provided the pure title compounds. 2.2 General procedure for the zinc chloride catalysed the multicomponent synthesis of 2.2a 10-Ethyl-7-phenyl-10,11-dihydro-7H-5-oxa-9,10, pyrazolopyridocoumarins 11-triaza-cyclo-penta[b]phenanthren-6-one (4a): Yield: 86%; Colorless solid; M.p. 301–303 ◦C; IR (KBr, cm−1): To a stirring solution of 4-hydroxycoumarin (1) (0.5 g, 1725 (C=O), 3082, 3173 (NH); 1H NMR (400 MHz, DMSO- 0.003 mol), benzaldehydes 2(a–h) (0.003 mol) and 1-alkyl- d6): δ 1.45 (t, 3H, CH3 of C2H5 group, J1,2 = 7.6 Hz), 3.54 5-amino-pyrazoles 3(a–b) (0.003 mol) in ethanol (15 mL) (s, 1H, methine proton), 4.19 (q, 2H, CH2 of C2H5 group, J. Chem. Sci. (2019) 131:29 Page 3 of 8 29 J1,2 = 7.6 Hz), 6.88–8.74 (m, 10H, Ar-H), 10.67 (s, 1H, NH); 60.0, 109.6, 113.3, 116.6, 119.2, 120.3, 123.8, 124.5, 125.1, 13 C NMR (100 MHz, DMSO-d6): δ 14.0, 45.9, 48.1, 101.1, 130.6, 132.7, 134.0, 144.8, 147.9, 149.7, 150.6, 151.9, 152.0, 104.5, 108.0, 114.5 (2C), 120.9, 121.8, 127.5, 127.7 (2C), 158.7; ESI-MS: [M+H] 404.1. Anal. C23H21N3O4. Cald For: 128.3 (2C), 137.0, 137.2, 147.9, 152.0, 157.4, 159.9; Anal. C, 68.47; H, 5.25; N, 10.42. Found: C, 68.38; H, 5.16; N, C21H17N3O2. Cald for: C, 73.45; H, 4.99; N, 12.24. Found: 10.35. C, 73.36; H, 4.93; N, 12.19. 2.2f 10-Ethyl-7-(3,4,5-trimethoxy-phenyl)-10,11-di- 2.2b 7-(4-Bromo-phenyl)-10-ethyl-10,11-dihydro-7H- hydro-7H-5-oxa-9,10,11-triaza-cyclopenta[b]phenan- 5-oxa-9,10,11-triaza-cyclo-penta[b]phenanthren-6-one thren-6-one (4f): Yield: 93%; Colorless solid; M.p. 297– ◦ −1 1 (4b): Yield: 89%; Brown solid; M.p. 311–313 ◦C; IR (KBr, 299 C; IR (KBr, cm ): 1718 (C=O), 3275, 3337 (NH); H − ) δ cm 1): 1721 (C=O), 3068, 3192 (NH); 1H NMR (400 MHz, NMR (400 MHz, DMSO-d6 : 1.55 (t, 3H, CH3 of C2H5 , DMSO-d6): δ 1.44 (t, 3H, CH3 of C2H5 group, J1,2 =7.6 group, J1 2 = 7.6 Hz), 2.34 (s, 1H, methine proton), 2.42 (s, ) ) ) Hz), 3.47 (s, 1H, methine proton), 4.44 (q, 2H, CH2 of C2H5 3H, OCH3 , 3.48 (s, 3H, OCH3 ,3.60(s,3H,OCH3 ,4.19(q, , group, J1,2 = 7.6 Hz), 7.15–8.92 (m, 9H, Ar-H), 10.50 (s, 1H, 2H, CH2 of C2H5 group, J1 2 = 7.6 Hz), 6.97–8.44 (m, 7H, 13 13 ) NH); C NMR (100 MHz, DMSO-d6): δ 14.0, 45.3, 49.8, Ar-H), 10.52 (s, 1H, NH); C NMR (100 MHz, DMSO-d6 : 102.8, 103.7, 113.0, 115.9, 119.9, 124.0, 125.5 (2C), 132.9 δ 13.9, 44.1, 49.3, 55.7, 59.0 (2C), 102.1, 108.0, 111.4, 113.7 (3C), 133.1, 142.1, 148.2, 149.2, 151.3, 152.0, 160.15; Anal. (2C), 121.3, 123.6, 126.8, 129.8, 131.1, 134.2, 142.9 (2C), C21H16BrN3O2. Cald for: C, 59.73; H, 3.61; N, 9.95. Found: 143.1, 149.1, 151.8, 155.9, 160.1; Anal. C24H23N3O5.Cald C, 59.69; H, 3.60; N, 9.88. for: C, 66.50; H, 5.35; N, 9.69. Found: C, 66.44; H, 5.31; N, 9.62. 2.2c 10-Ethyl-7-(2-hydroxy-phenyl)-10,11-dihydro-7H -5-oxa-9,10,11-triaza-cyclo-penta[b]phenanthren-6- 2.2g 7-(4-Chloro-phenyl)-10-methyl-10,11-dihydro- ◦ 7H-5-oxa-9,10,11-triaza-cyclopenta[b]phenanthren-6- one (4c): Yield: 87%; Colorless solid; M.p. 309–311 C; ◦ −1) one (4g): Yield: 88%; Colorless solid; M.p. 248–250 C; IR IR (KBr, cm : 1722 (C=O), 3076 (OH), 3209, 3447 (NH); −1 1 1 (KBr, cm ): 1721 (C=O), 3184, 3297 (NH); H NMR (400 H NMR (400 MHz, DMSO-d6): δ 1.53 (t, 3H, CH3 of C2H5 MHz, CDCl3): δ 3.82 (s, 3H, CH3), 4.27 (s, 1H, methine pro- group, J1,2 = 7.6 Hz), 3.61 (s, 1H, methine proton), 4.45 (q, ton), 6.88–8.10 (m, 9H, Ar-H), 10.33 (s, 1H, NH); 13CNMR 2H, CH of C H group, J , = 7.6 Hz), 7.09–8.33 (m, 9H, 2 2 5 1 2 ) δ Ar-H), 9.85 (s, 1H, OH), 10.70 (s, 1H, NH); 13C NMR (100 (100 MHz, CDCl3 : 36.3, 39.2, 98.9, 106.5, 113.3, 117.5, 121.6, 124.3, 128.5, 128.7, 128.8, 129.1, 131.3, 132.0, 132.6, MHz, DMSO-d6): δ 14.1, 45.9, 48.0, 102.4, 107.6, 108.3, 112.9 (2C), 114.7, 122.2, 123.9, 127.8, 129.7, 133.9, 139.1, 143.5, 144.3, 146.9, 152.7, 159.0; Anal.
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