NaOH/PEG-400: An eloquent system for the synthesis of new thienyl benzo[b]1,4-diazepines European Journal of Chemistry 11 (4) (2020) 276-279 European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2020 The Authors – Atlanta Publishing House LLC – Printed in the USA. This work is published and licensed by Atlanta Publishing House LLC – CC BY NC – Some Rights Reserved. http://dx.doi.org/10.5155/eurjchem.11.4.276-279.2009 European Journal of Chemistry View Journal Online View Article Online NaOH/PEG-400: An eloquent system for the synthesis of new thienyl benzo[b]1,4-diazepines Gajanan Gopinath Mandawad 1, Baseer Mubeen Shaikh 2, Santosh Subhash Chobe 3 and Shankaraiah Guruvaiah Konda 1,4,* 1 Department of Chemistry, Maharashtra Udayagiri College, Udgir-413517, Maharashtra, India mandawadgajanan@rediffmail.com (G.G.M.), kondasg@rediffmail.com (S.G.K.) 2 Department of Chemistry, Sir Sayyed College, Aurangabad-431001, Maharashtra, India baseershaikh@gmail.com (B.M.S.) 3 Organic Research Laboratory, Loknete Vyankatrao Hirey College, Nashik-422003, Maharashtra, India chobesantosh@rediffmail.com (S.S.C.) 4 Department of Chemistry, Karamsibhai Jethabhai Somaiya College, Kopargaon-423601, Maharashtra, India * Corresponding author at: Department of Chemistry, Karamsibhai Jethabhai Somaiya College, Kopargaon-423601, Maharashtra, India. e-mail: kondasg@rediffmail.com (S.G. Konda). 10.5155/eurjchem.11.4.276-279.2009 Received: 19 July 2020 Received in revised form: 05 September 2020 Accepted: 14 September 2020 Published online: 31 December 2020 Printed: 31 December 2020 A simple and eloquent procedure for the synthesis of a new series of thienyl benzo[b]1,4- diazepines is reported. They were synthesized by the condensation of o-phenylenediamine (o-PDA) with distinct hetero chalcones using NaOH in polyethylene glycol (PEG-400) as green and alternative reaction solvent. The significances of this present method are shorter reaction time, easy work-up, high yields, and mild reaction conditions. Furthermore, this method is environment friendly and without use of an expensive catalyst. The all newly synthesized compounds are characterized by the spectroscopic methods. Chalcones Green synthesis NaOH/PEG-400 o-Phenylenediamine Operational simplicity Benzo[b]1,4-diazepines Cite this: Eur. J. Chem. 2020, 11(4), 276-279 Journal website: www.eurjchem.com 1. Introduction Benzodiazepines and their derivatives are a very significant class of bioactive compounds because of their diverse pharma- ceutical properties. They are widely used as antidepressants, anticonvulsant, analgesic, hypnotic, and sedative [1]. This compound possesses antimicrobial [2], antioxidant [3], and anticancer activity [4]. It acts as an inhibitor of respiratory syncytial virus [5]. 1,4-Benzodiazepine analogs have been demonstrated as anticonvulsants, muscle relaxants, blood pressure lowering, and Central Nervous System (CNS) depres- sant agents [6]. In addition to this, 1,5-benzodiazepines are also useful synthons for the preparation of various fused ring compounds such as triazolo, oxazino, oxadiazolo and furano benzodiazepines [7,8]. On the other hand, sulfur and nitrogen heterocycles having pharmaceutical activities are widely found in nature in the form of alkaloids, vitamins, pigments, and as constituents of plant and animal cells [9]. They are commonly prepared by the classical condensation reaction of o-phenylenediamine and α,β-unsaturated carbonyl compounds, β-haloketones. There are various methods for the preparation of 1,5-benzodiazepines reported in the literature such as BF3-etherate [10], NaBH4 [11], SiO2 [12], Amberlyst-15 [13], Yb(Otf)3 [14], MgO/POCl3 [15], Al2O3/P2O5 [16], CH3COOH in MWI, TiCl4/THF [17], [bbim] ionic liquid [18] Silica-gel [19], and CeCl3/Silica-gel [20]. Recently, the synthesis of benzo- diazepines has also been reported using different solid acid catalysts such as sulfated zirconia, Al2O3/P2O5, Ag3 PW12O40, PVPFeCl3, and zeolite catalysts [21-25]. However, many of these reported methods have some limitations such as use of expensive catalysts, long reaction time, high catalyst loading, low selectivity, requirement of special apparatus, and side reactions. These factors stimulate us for the search of new methodology with simple catalyst under the framework of green chemistry at mild reaction conditions. ABSTRACT RESEARCH ARTICLE KEYWORDS http://dx.doi.org/10.5155/eurjchem.11.4.276-279.2009 http://www.eurjchem.com/ http://dx.doi.org/10.5155/eurjchem.11.4.276-279.2009 mailto:mandawadgajanan@rediffmail.com mailto:kondasg@rediffmail.com mailto:baseershaikh@gmail.com mailto:chobesantosh@rediffmail.com mailto:kondasg@rediffmail.com http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.11.4.276-279.2009&domain=pdf&date_stamp=2020-12-31 Mandawad et al. / European Journal of Chemistry 11 (4) (2020) 276-279 277 2020 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.11.4.276-279.2009 Scheme 1. Synthetic route for preparation of hetero chalcones. Scheme 2. Synthetic route for the preparation of thienyl benzo[b]1,4-diazepines. 2. Experimental 2.1. Instrumentation The melting points were uncorrected and determined by an open capillary method. IR spectra were recorded (in KBr pellets) on Shimadzu FTIR-8400S spectrophotometer. 1H NMR spectra were recorded (in DMSO-d6) on Bruker Avance-300 MHz spectrometer using tetramethylsilane (TMS) as an internal standard. The mass was recorded on EI-Shimadzu QP 2010 Plus GC-MS spectrometer. The elemental analyses were performed on a Carlo Erba 106 Perkin-Elmer model 240 analyzer. The required chemicals and solvents used were purified and labora- tory grade. 2.2. General procedure for the synthesis of benzo[b] 1,4- diazepines (2a-h) A mixture of substituted chalcone 1 (1 mmol), o-phenyl- enediamine (1.5 mmol), and solid NaOH (0.1 g) in polyethylene glycol (PEG-400) (15 mL) was stirred on a magnetic stirrer at 80 °C for the time period as shown in Table 1. After completion of the reaction (monitored by thin layer chromatography, TLC), the reaction mixture was cooled and poured in 100 mL ice-cold water. The obtained solid crude product was filtered and washed with 2×5 mL water. The crude product was recrystallized by the suitable solvent to give pure product (Schemes 1 and 2). 4-(5-(Benzylthio)-2-chlorothiophen-3-yl)-2- (4-chlorophenyl)- 2,3-dihydro-1H-benzo[b][1,4]diazepine (2a): Color: Pale yellow. Yield: 90%. M.p.: 132-134 °C. FT-IR (KBr, ν, cm-1): 1608 (C=N), 3065 (Ar-CH), 3272 (NH). 1H NMR (300 MHz, DMSO-d6, δ, ppm): 3.10-3.35 (m, 2H, Ha and Hb), 4.09 (s, 2H, -SCH2-Ph), 4.3 (m, 1H, Hx), 4.8 (s, 1H, NH) 6.95 -7.40 (m, 14H, Ar-H). MS (EI, m/z (%)): 494 (M+, 100), 496 (M+2), 499 (M+4). Anal. calcd. for C26H20N2S2Cl2: C, 63.03; H, 4.07; N, 5.65. Found: C, 63.13; H, 4.11; N, 5.56%. 4-(5-(Benzylthio)-2-chlorothiophen-3-yl)-2- (4-fluorophenyl)- 2,3-dihydro-1H-benzo[b][1,4]diazepine (2b): Color: Yellow. Yield: 86%. M.p.: 150-152 °C. FT-IR (KBr, ν, cm-1): 1610 (C=N), 3061 (Ar-CH), 3265 (NH). 1H NMR (300 MHz, DMSO-d6, δ, ppm): 3.15-3.38 (m, 2H, Ha and Hb), 4.15 (s, 2H, -SCH2-Ph), 4.36 (m, 1H, Hx), 4.86 (s, 1H, NH) 7.05-7.51 (m, 14H, Ar-H). MS (EI, m/z (%)): 478 (M+, 100), 480 (M+2). Anal. calcd. for C26H20N2S2FCl: C, 65.19; H, 4.21; N, 5.85. Found: C, 65.11; H, 4.28; N, 5.74%. 4-(4-(5-(Benzylthio)-2-chlorothiophen-3-yl)-2, 3-dihydro-1H- benzo[b][1, 4]diazepin-2-yl)-N, N-dimethylaniline (2c): Color: Yellow. Yield: 85%. M.p.: 138-140 °C. FT-IR (KBr, ν, cm-1): 1615 (C=N), 2998 (Ar-CH), 3268 (NH). 1H NMR (300 MHz, DMSO-d6, δ, ppm): 2.89 (s, 6H, N(CH3)2), 3.15-3.36 (m, 2H, Ha and Hb), 4.11 (s, 2H, -SCH2-Ph), 4.31 (m, 1H, Hx), 4.78 (s, 1H, NH) 7.11- 7.65 (m, 14H, Ar-H). MS (EI, m/z (%)): 503 (M+, 100), 505 (M+2); Anal. calcd. for C28H26N3S2Cl: C, 66.71; H, 5.21; N, 8.34. Found: C, 66.62; H, 5.12; N, 8.43%. 4-(5-(Benzylthio)-2-chlorothiophen-3-yl)-2- (4-methoxyphen yl)-2,3-dihydro-1H-benzo[b][1,4]diazepine (2d): Color: Pale Yellow. Yield: 90%. M.p.: 146-148 °C. FT-IR (KBr, ν, cm-1): 1612 (C=N), 3026 (Ar-CH), 3276 (NH). 1H NMR (300 MHz, DMSO-d6, δ, ppm): 3.11-3.34 (m, 2H, Ha and Hb), 3.41 (s, 3H, OCH3), 4.16 (s, 2H, SCH2-Ph), 4.38 (m, 1H, Hx), 4.82 (s, 1H, NH) 7.09-7.68 (m, 14H, Ar-H). MS (EI, m/z (%)): 490 (M+, 100), 492 (M+2). Anal. calcd. for C27H23N2OS2Cl: C, 66.04; H, 4.72; N, 5.70. Found: C, 66.13; H, 4.81; N, 5.62%. 5-Chloro-4-(2-(4-chlorophenyl)-2, 3-dihydro-1H-benzo[b][1,4] diazepin-4-yl)thiophene-2-sulfonamide (2e): Color: Light Brown. Yield: 86%. M.p.: 157-159 °C. FT-IR (KBr, ν, cm-1): 1610 (C=N), 3051 (Ar-CH), 3245 (NH2), 3326 (NH2). 1H NMR (300 MHz, DMSO-d6, δ, ppm): 3.09-3.35 (m, 2H, Ha and Hb), 4.31 (m, 1H, Hx), 4.76 (s, 1H, NH), 5.26 (s, 2H, NH2), 7.05-7.76 (m, 9H, Ar- H). MS (EI, m/z (%)): 451 (M+, 100), 453 (M+2), 455 (M+4). Anal. calcd. for C19H15N3O2S2Cl2: C, 50.45; H, 3.34; N, 9.29. Found: C, 50.52; H, 3.46; N, 9.21%. 5-Chloro-4-(2-(4-fluorophenyl)-2, 3-dihydro-1H-benzo[b][1, 4] diazepin-4-yl)thiophene-2-sulfonamide (2f): Color: Light Brick red. Yield: 88%. M.p.: 173-175 °C. FT-IR (KBr, ν, cm-1): 1615 (C=N), 3038 (Ar-CH), 3238 (NH2), 3315 (NH2). 1H NMR (300 MHz, DMSO-d6, δ, ppm): 3.05-3.28 (m, 2H, Ha and Hb), 4.36 (m, 1H, Hx), 4.68 (s, 1H, NH), 5.28 (s, 2H, NH2), 7.09-7.86 (m, 9H, Ar- H). MS (EI, m/z (%)): 435 (M+, 100), 437 (M+2). Anal. calcd. for C19H15N3O2S2FCl: C, 52.35; H, 3.47; N, 9.64. Found: C, 52.28; H, 3.56; N, 9.55%. 5-Chloro-4-(2-(4-(dimethylamino)phenyl)-2, 3-dihydro-1H- benzo[b][1,4]diazepin-4-yl)thiophene-2-sulfonamide (2g):Color: Brick red. Yield: 82%. M.p.: 154-156 °C. FT-IR (KBr, ν, cm-1): 1610 (C=N), 3051 (Ar-CH), 3246 (NH2), 3309 (NH2). 1H NMR (300 MHz, DMSO-d6, δ, ppm): 2.85 (s, 6H, N(CH3)2), 3.09-3.35 (m, 2H, Ha and Hb), 4.31 (m, 1H, Hx), 4.75 (s, 1H, NH), 5.19 (s, 2H, NH2), 7.05-7.81 (m, 9H, Ar-H). MS (EI, m/z (%)): 460 (M+, 100), 462 (M+2). Anal. calcd. for C21H21N4O2S2Cl: C, 54.71; H, 4.59; N, 12.15. Found: C, 54.78; H, 4.66; N, 12.06%. 5-Chloro-4-(2-(4-methoxyphenyl)-2, 3-dihydro-1H-benzo[b] [1, 4] diazepin-4-yl)thiophene-2-sulfonamide (2h): Color: Brown. Yield: 89%. M.p.: 160-162 °C. FT-IR (KBr, ν, cm-1): 1612 (C=N), 3046 (Ar-CH), 3262 (NH2), 3312 (NH2). 1H NMR (300 MHz, DMSO-d6, δ, ppm): 3.11-3.38 (m, 2H, Ha and Hb), 3.51 (s, 3H, OCH3), 4.38 (m, 1H, Hx), 4.82 (s, 1H, NH), 5.25 (s, 2H, NH2), 7.09 -7.91 (m, 9H, Ar-H). MS (EI, m/z (%)): 447 (M+,100), 449 (M+2). Anal. calcd. for C20H18N3O3S2Cl: C, 53.63; H, 4.05; N, 9.38. Found: C, 53.51; H, 4.14; N, 9.31%. 278 Mandawad et al. / European Journal of Chemistry 11 (4) (2020) 276-279 2020 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.11.4.276-279.2009 Table 1. Physico-chemical data of synthesized thienyl benzo[b]1,4-diazepines 2a-h. Entry R Ar Time (h) Yield (%) M.p. (°C) 2a SCH2-Ph 4-Cl-C6H4 2.5 90 132-134 2b SCH2-Ph 4-F-C6H4 3 86 150-152 2c SCH2-Ph 4-N-(CH3)2-C6H4 3 85 138-140 2d SCH2-Ph 4-OMe-C6H4 2.5 90 146-148 2e SO2NH2 4-Cl-C6H4 2.5 86 157-159 2f SO2NH2 4-F-C6H4 2.5 88 173-175 2g SO2NH2 4-N-(CH3)2-C6H4 3 82 154-156 2h SO2NH2 4-OMe-C6H4 2.5 89 160-162 Table 2. Physical-chemical data of synthesized chalcone derivatives 1a-h [40]. Entry R Ar Time (h) Yield (%) M.p. (°C) 1a SCH2-Ph 4-Cl-C6H4 1.5 92 148 1b SCH2-Ph 4-F-C6H4 1.0 92 142 1c SCH2-Ph 4-N-(CH3)2-C6H4 1.5 88 156 1d SCH2-Ph 4-OMe-C6H4 1.5 90 134 1e SO2NH2 4-Cl-C6H4 1.5 89 127 1f SO2NH2 4-F-C6H4 1.5 90 168 1g SO2NH2 4-N-(CH3)2-C6H4 1.5 89 130 1h SO2NH2 4-OMe-C6H4 1.0 90 126 Table 3. Effect of solvent on the reaction of 1-(2-(benzylthio)-5-chlorothiophen-3-yl)-3-(4-chlorophenyl) prop-2-en-1-one (1a) with o-phenylenediamine (o- PDA) using NaOH. Entry Solvent Time (h) Yield (%) 1 EtOH 10 55 2 DCM 9 58 3 CH3CN 8 62 4 Acetic acid 9 58 5 PEG-400 2.5 90 3. Results and discussion The replacement of toxic solvents with environmentally benign solvents is the broad focus area of green chemistry. The utility of alternative reaction solvents includes water [26], ionic liquid [27], flourous [28], supercritical media [29], and polyethylene glycol (PEG) [30] is rapidly growing. Liquid polymers have emerged as an alternative green reaction media in organic synthesis. Polyethylene glycol (PEG-400) competed reactions [31-35] have attracted attention towards organic chemists due to their solvating ability and aptitude to act as a phase transfer catalyst, negligible vapor pressure, easy recyclability, ease of work-up, eco-friendly nature and low cost. As a part of our continuous work towards the exploration of polyethylene glycol (PEG-400) [36-39] as a green reaction solvent for the preparation of biologically active compounds, herein we report the synthesis of some new thienyl benzo[b]1,4-diazepines 2a-h by the condensation reaction of o- phenylenediamine (o-PDA) with distinct hetero chalcones using NaOH in polyethylene glycol (PEG-400) as green reaction solvent. The starting compounds (hetero chalcones) 1a-h were prepared by our previously reported method (Scheme 1, Table 2) [40]. Initially, we started the reaction of 1-(2-(benzylthio)-5- chlorothiophen-3-yl)-3-(4-chlorophenyl) prop-2-en-1-one (1a) with o-phenylenediamine (o-PDA) using NaOH (catalyst) in polyethylene glycol (PEG-400) as green reaction solvent. The reaction was completed within 2.5 hours and the corresponding product (2a) was obtained in 90% yield. To optimize the reaction conditions, we studied out the same above reaction in different solvents such as ethanol, dichloromethane, acetonitrile, acetic acid, and PEG-400 (Table 3). We found that PEG-400 as an efficient reaction medium in terms of reaction time as well as yield (90%). Next, we moved our attention towards the different substituted chalcones. In all cases, the reaction was smoothly proceeded in high yields at 80 °C using PEG-400 as an alternative reaction solvent (Scheme 2, Table 1). Furthermore, these newly synthesized compounds were characterized by the IR, 1H NMR, and Mass spectroscopic methods. The IR spectra of benzo[b]1,4-diazepines were showed disappearance of bands at 1660-1640 cm-1 due to transformation of >C=O of 3,5-diaryl prop-2-en-1-ones (chalcones) into products. The characteristic bands at near 1600-1610 and 3100-3330 cm-1 due to -C=N and –NH stretching, respectively, in products. Besides these bands, 1050-1150 cm-1 are observed due to C-S and 680-800 cm-1 due to C-Cl stretching. In the 1H NMR spectra of the products, the three hydrogen atoms attached to the C-2 and C-3 carbon atoms of the heterocyclic ring gave an ABX spin system proved the benzodiazepines structure. The CH2 protons of the benzodiazepines showed as multiplate at δ 3.09-3.21 (Ha), δ 3.41-3.54 (Hb) and δ 4.0-4.3 ppm triplet 1H of Hx. A characteristic singlet of NH was observed at δ 4.7-4.8 ppm. The singlet observed at 4.1-4.2 ppm due to -SCH2-Ph moiety, while the corresponding aromatic and aliphatic protons were observed at excepted regions. These findings are in agreements with those observed by different researchers. The mass spectra (EI-MS) of the synthesized benzo[b]1,4-diazepines were in agreement with their molecular formula weight. 4. Conclusion In conclusion, we have developed a new, efficient and environmentally benign reaction methodology towards the synthesis of novel thienyl benzo[b]1,4-diazepines derivatives by the treatment of chalcones with o-phenylenediamine using solid NaOH as catalyst in polyethylene glycol as green reaction solvent is described. The advantages of the present protocol are the shorter reaction time, simple reaction workup, high yields of products, and avoidance of expensive catalysts. Therefore, the present study is more beneficial in the synthesis of some new benzo[b]1,4-diazepines derivatives as medicinal drugs. In the future, these synthesized compounds can be used for medicinal investigation against bacterial and fungal diseases as drug molecules. Acknowledgements The authors are thankful to Prof. Dr Bhaskar Sadashiv Dawane, Director, School of Chemical Sciences Swami Ramanand Teerth Marathwada University, Nanded for his continuous support and encouragement. Mandawad et al. / European Journal of Chemistry 11 (4) (2020) 276-279 279 2020 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.11.4.276-279.2009 Disclosure statement Conflict of interests: The authors declare that they have no conflict of interest. Author contributions: All authors contributed equally to this work. Ethical approval: All ethical guidelines have been adhered. Sample availability: Samples of the compounds are available from the author. ORCID Gajanan Gopinath Mandawad http://orcid.org/0000-0002-5317-2637 Baseer Mubeen Shaikh http://orcid.org/0000-0001-8073-3332 Santosh Subhash Chobe http://orcid.org/0000-0001-5522-2522 Shankaraiah Guruvaiah Konda http://orcid.org/0000-0002-1939-6784 References [1]. Mallinath, M. L. 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Permissions for commercial use of this work beyond the scope of the License (http://www.eurjchem.com/index.php/eurjchem/pages/view/terms) are administered by Atlanta Publishing House LLC (European Journal of Chemistry). http://orcid.org/0000-0002-5317-2637 http://orcid.org/0000-0001-8073-3332 http://orcid.org/0000-0001-5522-2522 http://orcid.org/0000-0002-1939-6784 http://www.eurjchem.com/index.php/eurjchem/pages/view/terms http://creativecommons.org/licenses/by-nc/4.0 http://www.eurjchem.com/index.php/eurjchem/pages/view/terms 1. Introduction 2. Experimental 2.1. Instrumentation 2.2. General procedure for the synthesis of benzo[b] 1,4-diazepines (2a-h) 3. Results and discussion 4. Conclusion Acknowledgements Disclosure statement ORCID References PrintField10: PrintField11: PrintField12: PrintField13: PrintField20: PrintField21: PrintField22: PrintField23: