Synthesis of 5H-Chromeno[4,3-b]pyridin-5-one derivatives as a backbone of natural product polyneomarline C scaffolds in presence of Et3N and NH4OAc in EtOH Chimica Techno Acta ARTICLE published by Ural Federal University 2022, vol. 9(2), No.20229211 eISSN 2411-1414; chimicatechnoacta.ru DOI: 10.15826/chimtech.2022.9.2.11 1 of 5 Synthesis of 5H-Chromeno[4,3-b]pyridin-5-one derivatives as a backbone of natural product polyneomarline C scaffolds in presence of Et3N and NH4OAc in EtOH Shrishnu Kumar Kundu a*, Susanta Patra b, Chayan Sardar c, Sunil Kumar Bhanja d, Prasanta Patra b* a: Department of Chemistry, Acharya Prafulla Chandra Roy Government College, Siliguri 734 010, India b: Department of Chemistry, Jhargram Raj College, Jhargram 721507, India c: Techno-India University, Kolkata 700091, India d: Government General Degree College, Kharagpur-II, Paschim Medinipur, India * Corresponding authors: shrishnuk@gmail.com (S.K. Kundu); prasantaanupama1983@gmail.com (P. Patra) This paper belongs to a Regular Issue. © 2022, the Authors. This article is published open access under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Abstract A green one-pot synthesis of 5H-Chromeno[4,3-b]pyridin-5-one deriv- atives which are the main core of the natural product of Polyneomar- line C is described by the reaction of 4-chloro-3-formyl coumarin and different cyclic and acyclic compounds having active methylene group in presence of Et3N and NH4OAc in EtOH. The advantages of this strat- egy are good yields, no need for the chromatographic separation and the absence of heavy metal catalysts and toxic by-products. The 4- chloro-3-formyl coumarin is obtained by Vilsmeier Heck reaction of 4- hydroxy coumarin. Keywords 5H-Chromeno[4,3-b]pyridin- 5-one green synthesis 4-chloro-3-formyl coumarin active methylene group Polyalthia nemoralis C Received: 21.04.22 Revised: 07.06.22 Accepted: 07.06.22 Available online: 14.06.22 1. Introduction In the last one or two decades, one-pot tandem chemical transformation without metal catalysts has been widely used for the synthesis of complex organic molecules. A variety of chemical conversion processes, such as oxidation, reduction, substitution, condensation, etc., has been developed using this principle [1–3]. A reaction undergoing without using toxic reagents (catalysts and solvents) has many advantages: a decrease of wastes, lower toxicity, maximum efficacy, a de- crease in the energy requirements of the reactions, a possi- bility of designing biodegradable products, economic and time factors. Hence, heterocyclic ring formation using this green protocol is an active and attractive field. Coumarin de- rivatives represent the core structure of many naturally oc- curring compounds with significant biological activities [4– 7]. Lamellarins and related pyrrole derived alkaloids isolated from diverse marine organisms are well known for their re- markable biological activities [8, 9]. The coumarin deriva- tives fused with azaheterocycles specially the pyridine nu- cleus have been reported to possess antiallergic, antidiabetic and analgesic properties [10–12]. Santiagonamine is a natu- rally occurring pyridine fused coumarin derivatives found in the stems and branches of Berberisdarwinii Hook, which is a shrub that abounds in South America having wound-healing properties [13, 14]. Goniothaline [15] is another a natural pyridocoumarin alkaloid, isolated from the Australian rain- forest plant Goniothalamusaustralis, having antimalarial ac- tivity against a chloroquine-sensitive Plasmodium falcipa- rum line (3D7). Polyneomarline C [16] is also a natural 6H- chromeno[4,3-b]quinolin-6-one derivative, isolated from the Polyalthia nemoralis A. DC, used as Chinese herbal medicine. Coumarin fused pyridine [17–19] derivatives have been re- ported to possess anti-hypertensive activities, anti-HIV activ- ity, androgen receptor antagonist activity, and optoelec- tronic activity; they can also act as fluorescent dyes. All these observations highlight the importance and bioactivity of pyr- idine fused coumarin derivatives. So the interest towards the synthesis of pyridine fused comarin is trending among the organic chemists. Many methods [20–30] have been devel- oped to synthesize these types of compounds using different types of Lewis acids/bases and metal catalysts with different solvents. The 5H-Chromeno[4,3-b]pyridin-5-one skeleton constitutes the backbone of Polyneomarline C. We were in- terested in the preparation of some non-natural analogs of this type of compounds by an easy process. Many synthese of 5H-Chromeno[4,3-b]pyridin-5-one derivatives have been de- http://chimicatechnoacta.ru/ https://dx.doi.org/10.15826/chimtech.2022.9.2.11 mailto:shrishnuk@gmail.com mailto:prasantaanupama1983@gmail.com http://creativecommons.org/licenses/by/4.0/ https://orcid.org/0000-0002-2738-1216 https://crossmark.crossref.org/dialog/?doi=https://dx.doi.org/10.15826/chimtech.2022.9.2.11&domain=pdf&date_stamp=2022-6-14 Chimica Techno Acta 2022, vol. 9(2), No. 20229211 ARTICLE 2 of 5 scribed in the literature [31, 32] using different reagents, cat- alyst, solvents and ultrasound irradiation. In our present work, we reported a modified green approach for the synthe- sis of 5H-Chromeno[4,3-b]pyridin-5-one derivatives from 4- chloro-3-formyl coumarin and various compounds having an active methylene group. In this method there is no need for the chromatographic separation. 2. Experimental 2.1. Preparation of substituted pyridocoumarin deriv- atives A mixture of chloroaldehyde 1 of 4-hydroxy coumarin (1 mmol), 2 (1.2 mmol), Et3N (1–2 drops) and NH4OAc (2 mol%) with 10 ml EtOH was taken in 50 mL r.b. The mix- ture was then heated on an oil bath at 60 °C for 2 h. It was then cooled to room temperature. Then solvent was distilles out and residue was mixed with 20 mL water and filtered and washed with water and dried. The crude product which was purified by recrystalisation with EtOH to furnish compound 3. 2.1.1. 3-acetyl-2-methyl-5H-chromeno[4,3-b]pyridin-5-one (3a) Light pink solid, yield, 90%; mp 220–221 °C (EtOH); 1H NMR (400 MHz, DMSO-d6): 2.62 (s, 3H), 2.68 (s, 3H), 7.42 (m, 1H), 7.52 (d, 1H, J = 7.8 Hz), 7.65 (d, 1H, J = 7.8 Hz), 7.79 (m, 1H), 9.33 (s, 1H); HRMS (ESI, 70 eV): m/z = 254.0820 (M++H) [Calcd mass for C15H12NO3: 254.0817 (M++H)]. 2.1.2. Ethyl 2-methyl-5-oxo-5H-chromeno[4,3-b]pyridine-3- carboxylate (3b) Light pink solid, yield, 82%; mp 230–231 °C (EtOH); 1H NMR (400 MHz, DMSO-d6): 1.3 (t, 3H, J = 7.2 Hz) 2.62 (s, 3H), 4.8 (m, 2H), 7.30–7.33 (m, 1H), 7.65 (m, 1H), 7.92 (d, 1H, J = 7.2 Hz), 7.78–7.80 (m, 1H), 8.90 (s, 1H); HRMS (ESI, 70 eV): m/z = 284.0929 (M++H) [Calcd mass for C16H14NO4: 284.0923 (M++H)]. 2.1.3. 10,11-Dihydro-9H-chromeno[4,3-b]quinoline-6,8-di- one (3c) Light yellow solid, yield, 92%; mp 221–222 °C (EtOH); 1H NMR (400 MHz, DMSO-d6): 1.98 (m, 2H), 2.45 (t, 2H, J = 7.2 Hz) 2.95 (m, 2H), 7.35 (m, 2H), 7.65–7.80 (m, 1H), 8.03 (d, 1H, J = 7.5 Hz), 9.22 (s, 1H) ppm; HRMS (ESI, 70 eV): m/z = 266.0821 (M++H) [Calcd mass for C16H12NO3: 266.0817 (M++H)]. 2.1.4. 9,9-Dimethyl-10,11-dihydro-9H-chromeno[4,3-b]quin- oline-6,8-dione (3d) Light yellow solid, yield, 85%; mp 239–240 °C (EtOH); 1H NMR (400 MHz, DMSO-d6): 1.38 (s, 6H), 1.91 (t, 2H, J = 7.8 Hz), 2.92–2.95 (m, 2H), 7.45 (t, 2H, J = 8.0 Hz), 7.7 (t, 1H, J = 7.7 Hz), 8.13 (dd, 1H, J = 2.2 and 9.0 Hz), 9.33 (s, 1H) ppm; 13C NMR (13C NMR 100 MHz, DMSO-d6): 23.2 (2), 28.2, 32.9, 113.3, 117.2, 117.9, 123.8, 125.32, 125.6, 125.7, 127.3, 136.33, 153.0, 154.0, 160.5, 169.8, 196.7; HRMS (ESI, 70 eV): m/z = 294.1121 (M++H) [Calcd mass for C18H16NO3: 294.1130 (M++H)]. 3. Results and discussion Our first task was to find out an optimal condition to pre- pare the 5H-Chromeno[4,3-b]pyridin-5-one derivatives in the best possible yield using different methodologies. A re- action between 4-chloro-3-formyl coumarin (1 equivalent) and acetyl acetone (1.2 equivalent) (Scheme 1) was studied under different conditions with different temperatures and times (Table 1). When 3-formyl 4-chloro coumarin, which was obtained from 4-hydroxy coumarins [33], was treated with different cyclic and acyclic compounds having active methylene group in the presence of Et3N and NH4OAc in EtOH at 60 °C, within 2 h the corresponding 5H- Chromeno[4,3-b]pyridin-5-one derivatives were obtained. The 1H-NMR (400 MHz, DMSO-d6) data is in conformity with the assigned structure for the 5H-Chromeno[4,3- b]pyridin-5-one derivatives. A reaction of the other cyclic and acyclic compounds having an active methylene group 2(b-d) and 4-chloro 3-formyl coumarin (1 equivalent) under identical condition produced the 5H-Chromeno[4,3-b]pyri- din-5-one derivatives 3(a-d), respectively, in excellent yields (Scheme 2). Scheme 1 Synthesis of pyridocoumarin by condensation followed by cyclization reaction. Table 1 Optimization Studies in the formation of pyridocoumarin derivatives.a Entry Reactant propor- tions (1:2a) Solvent Catalysts Additives Temp. (°C) Time (h) Yields (%) 1 1:1 H2O – – 100 10 -- 2 1:2 H2O Et3N NH4OAc 100 10 trace 3 1:1 EtOH Et3N NH4OAc 100 3 75 4 1:1 EtOH Et3N NH4OAc 60 2 90 5 1:1 EtOH Et3N NH4OAc 60 1 80 6 1:1 MeOH Et3N NH4OAc 80 5 40 7 1:1 EtOH NaHCO3 NH4OAc 100 5 trace 8 1:1 DMF Et3N NH4OAc 100 2 trace 9 1:1 EtOH/H2O Et3N NH4OAc 100 2 45 10 1:1 – – NH4OAc 100 1 trace a Reaction conditions: 4-Chloro 3-formyl coumarin 1 (1 mmol), 2a (1.2 mmol), solvent (10 ml); Et3N (cat), NH4OAc (2 mmol), 60 °C. Chimica Techno Acta 2022, vol. 9(2), No. 20229211 ARTICLE 3 of 5 Scheme 2 Substrate scope of for the synthesis of 3(a-d). Unfortunately, we did not have access to any other cou- marin derivatives, but we believe our method will be appli- cable for other derivatives. A probable mechanism for the formation of compounds 3a is given in Scheme 3. In general, the reactions are very clean, proceeding without any side product, with remarkable yields, and do not requiring any chromatographic separation. Recrys- tallization from EtOH provides an analytically pure sample. We believe that it is the first green approach reported for the synthesis of fused 5H-Chromeno[4,3-b]pyridin-5-one deriva- tives. 4. Conclusions In conclusion, we achieved the synthesis of poly-substituted pyridocoumarin derivative in one-pot three-component condensation and cyclization via an efficient, short and easy method. The method has a number of advantages: easy availability of the starting material, short time of the reac- tion, and the use of simple and inexpensive catalyst. We are planning a collaborative study into the photophysical and biological properties of the synthesized compounds in the near future. Supplementary materials No supplementary materials are available. Funding This work was financially supported by the Department of Science & Technology and Biotechnology (DSTBT) of West Bengal (34(Sanc.)-ST/P/S&T/15G-1/2018 Date: 31/01/2019). Acknowledgments P. Patra is grateful to his supervisor Prof. Gandhi Kumar Kar, Dean of Science, Presidency University, Kolkata and Dept. of Chemistry, Jhargram Raj College. Author contributions Conceptualization: S.K.K., P.P. Data curation: S.P., C.S., S.K.B. Formal Analysis: S.K.K., C.S. Funding acquisition: P.P. Investigation: S.K.K., P.P. Methodology: S.P., C.S., S.K.B. Project administration: P.P. Resources: S.K.K. Software: S.P. Supervision: S.K.K., P.P. Validation: S.K.K. Visualization: P.P. Writing – original draft: S.P. Writing – review & editing: S.K.K., P.P. Conflict of interest The authors declare no conflict of interest. Additional information Author IDs: Shrishnu Kumar Kundu, Scopus ID 15128586000; Prasanta Patra, Scopus ID 36182642900. Scheme 3 Probable mechanism for the formation of pyridocoumarin derivatives. https://www.scopus.com/authid/detail.uri?authorId=15128586000 https://www.scopus.com/authid/detail.uri?authorId=36182642900 Chimica Techno Acta 2022, vol. 9(2), No. 20229211 ARTICLE 4 of 5 Websites: Acharya Prafulla Chandra Roy Government College, http://apcrgc.org/dept_chemistry/; Jhargram Raj College, https://jrc.ac.in/; Techno-India University, https://technoindia- group.com/; Government General Degree College, http://singur- govtcollege.org/. References 1. Sarkar A, Santra S, Kundu SK, Hajra A, Zyryanov GV, Chupakhin ON, Charushin VN, Majee A. 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