HPW-Catalyzed environmentally benign approach to imidazo[1,2-a]pyridines

• Luan A. Martinho and
• Carlos Kleber Z. Andrade

Beilstein J. Org. Chem. 2024, 20, 628–637, doi:10.3762/bjoc.20.55

• ], pyrazolo-fused benzophenazines [45], 4,5-dioxopyrrolidines [46], 1,2-dihydropyridine (1,2-DHPs) [47], pyrimido[4,5-b]quinoline-tetraones [48], tetrahydrobenzo[b]pyrans and indazolo[2,1-b]phthalazinetriones [49]. Herein, we report the synthesis of imidazo[1,2-a]pyridines via the GBB-3CR using HPW as

• % yield (compared to the expected 91% yield) was obtained (Scheme 1b). This reaction was carried out in triplicate with the same outcome. Therefore, the search for a broader and more reliable methodology to obtain imidazo[1,2-a]pyridines using heteropolyacids became necessary. Due to its already mentioned

• obtained. Meta,para-substituted aromatic aldehydes showed a high reactivity with yields greater than 84% for products 4s–w. Notably, the use of tri-substituted aromatic aldehydes gave imidazo[1,2-a]pyridines 4x–z in moderate to excellent yields (35–99%), though the hydroxy substituent at the ortho position

Non-noble metal-catalyzed cross-dehydrogenation coupling (CDC) involving ether α-C(sp³)–H to construct C–C bonds

• Hui Yu and
• Feng Xu

Beilstein J. Org. Chem. 2023, 19, 1259–1288, doi:10.3762/bjoc.19.94

• esters. Co-catalyzed construction of C(sp2)–C(sp3) bonds. Co-catalyzed CDC of imidazo[1,2-a]pyridines with isochroman. Co-catalyzed C–H alkylation of (benz)oxazoles with ethers. Cobalt-catalyzed CDC between unactivated C(sp2)–H and C(sp3)–H bonds. MnO2-catalyzed CDC of the inactive C(sp3)-H. Oxidative

Photocatalytic sequential C–H functionalization expediting acetoxymalonylation of imidazo heterocycles

• Deepak Singh,
• Shyamal Pramanik and
• Soumitra Maity

Beilstein J. Org. Chem. 2023, 19, 666–673, doi:10.3762/bjoc.19.48

• investigation revealed a sequential sp2 and sp3 C–H activation, followed by functionalization driven by zinc acetate coupled with the photocatalyst PTH. A variety of imidazo[1,2-a]pyridines and related heterocycles were explored as substrates along with several active methylene reagents, all generating the

• products with excellent yields and regioselectivity, thus confirming excellent functional group tolerability. Keywords: C–H functionalization; imidazo heterocycles; photoredox; regioselective; relay catalysis; Introduction Among all N-fused heterocycles, imidazo[1,2-a]pyridines (IPs) are the prevalent

• moieties in several bioactive pharmaceuticals and natural products [1][2][3][4]. Moreover, due to their susceptibility towards 'exited-state intramolecular proton transfer' phenomena, IPs are also effective in optoelectronics and materials sciences [5][6]. C-3-functionalized imidazo[1,2-a]pyridines are

Synthesis of novel alkynyl imidazopyridinyl selenides: copper-catalyzed tandem selenation of selenium with 2-arylimidazo[1,2-a]pyridines and terminal alkynes

• Mio Matsumura,
• Kaho Tsukada,
• Kiwa Sugimoto,
• Yuki Murata and
• Shuji Yasuike

Beilstein J. Org. Chem. 2022, 18, 863–871, doi:10.3762/bjoc.18.87

• reaction between terminal alkynes and diimidazopyridinyl diselenides, generated from imidazo[1,2-a]pyridines and Se powder, using 10 mol % of CuI and 1,10-phenanthroline as the catalytic system under aerobic conditions. The C(sp2)–Se and C(sp)–Se bond-formation reaction can be performed in one-pot by using

• reagents and 1,3-dipolar azide–alkyne cycloaddition based on the alkyne moiety. Keywords: alkynyl imidazopyridinyl selenide; copper catalyst; imidazo[1,2-a]pyridine; selenium; tandem reaction; terminal alkyne; Introduction Imidazo[1,2-a]pyridines are important heterocycles that serve as key functional

• groups in many biologically active substances and pharmaceuticals, such as zolpidem, alpidem, and GSK812397 [1][2][3]. Therefore, the development of multiple chemical modification methods, at the 3-position of the imidazo[1,2-a]pyridine skeleton, for the synthesis of 3-substituted-imidazo[1,2-a]pyridines

Synthesis of novel [1,2,4]triazolo[1,5-b][1,2,4,5]tetrazines and investigation of their fungistatic activity

• Anna V. Korotina,
• Svetlana G. Tolshchina,
• Rashida I. Ishmetova,
• Natalya P. Evstigneeva,
• Natalya A. Gerasimova,
• Natalya V. Zilberberg,
• Nikolay V. Kungurov,
• Gennady L. Rusinov,
• Oleg N. Chupakhin and
• Valery N. Charushin

Beilstein J. Org. Chem. 2022, 18, 243–250, doi:10.3762/bjoc.18.29

• particular, imidazo[1,2-a]pyridines and imidazo[1,2-a]pyrimidines exhibit a wide spectrum of biological activity, including antiviral and antibacterial ones [1][2]. A promising approach for the development of new drugs is the synthesis and bioscreening of high nitrogen-containing azoloazines, including azolo

Microwave-assisted multicomponent reactions in heterocyclic chemistry and mechanistic aspects

• Shivani Gulati,
• Stephy Elza John and
• Nagula Shankaraiah

Beilstein J. Org. Chem. 2021, 17, 819–865, doi:10.3762/bjoc.17.71

• -imidazo[1,2-a]pyridines 136 (Scheme 51). The method developed employs a Groebke−Blackburn−Bienaymé reaction as the key transformation and facilitates the integration of two pharmacophores in one framework further enhancing the applicability in drug discovery with increased chemical space. The efficiency

Synthesis and anticancer activity of bis(2-arylimidazo[1,2-a]pyridin-3-yl) selenides and diselenides: the copper-catalyzed tandem C–H selenation of 2-arylimidazo[1,2-a]pyridine with selenium

• Mio Matsumura,
• Tsutomu Takahashi,
• Hikari Yamauchi,
• Shunsuke Sakuma,
• Yukako Hayashi,
• Tadashi Hyodo,
• Tohru Obata,
• Kentaro Yamaguchi,
• Yasuyuki Fujiwara and
• Shuji Yasuike

Beilstein J. Org. Chem. 2020, 16, 1075–1083, doi:10.3762/bjoc.16.94

• medicinal chemistry [19][20]. A number of clinically used drugs and clinical candidates, such as zolpidem, alpidem, saripidem, zolimidine, necopidem, and GSK812397 contain the imidazo[1,2-a]pyridine scaffold [21][22][23][24][25][26]. 3-(Arylselanyl)imidazo[1,2-a]pyridines IV were reported to act as

• ]pyridines, which are isomers of imidazo[1,2-a]pyridines, with Se powder [34]. However, in this reaction, selenides and diselenides were generated in ratios of approximately 1:1; hence, an efficient selective synthesis has not yet been achieved. Inspired by the aforementioned reports and our continuing

• diselenide 2f may possibly be highly cytotoxic toward various cancer cell lines and relatively low cytotoxic against noncancer cells. Conclusion The Cu-catalyzed double C–H selenations of imidazo[1,2-a]pyridines with Se powder afforded novel bis(2-arylimidazopyridin-3-yl) diselenides in satisfactory yields

Synthesis of benzo[d]imidazo[2,1-b]benzoselenoazoles: Cs₂CO₃-mediated cyclization of 1-(2-bromoaryl)benzimidazoles with selenium

• Mio Matsumura,
• Yuki Kitamura,
• Arisa Yamauchi,
• Yoshitaka Kanazawa,
• Yuki Murata,
• Tadashi Hyodo,
• Kentaro Yamaguchi and
• Shuji Yasuike

Beilstein J. Org. Chem. 2019, 15, 2029–2035, doi:10.3762/bjoc.15.199

• constructing tetracyclic aromatic heterocycles containing selenium. For example, the reaction of 2-(2-iodophenyl)indoles with selenium powder in the presence of CuO as catalyst resulted in benzoselenopheno[3,2-b]indole derivatives [14]. The reaction of 2-(2-haloaryl)imidazo[1,2-a]pyridines with selenium using

• a CuI catalyst for the synthesis of benzo[b]selenophene-fused imidazo[1,2-a]pyridines occurred smoothly [15][16]. Performing these types of reactions without the addition of a transition metal catalyst is more challenging, but would alleviate the environmental burden of removing and disposing of the

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

• been given much attention in various research fields, such as the discovery of lead compounds in medicinal chemistry, or combinatorial chemistry [95][96]. Copper-catalyzed synthetic protocols Ghosh and Mishra [97] have successfully reported the synthesis of imidazo[1,2-a]pyridines in a three-component

• -benzenedicarboxylate), Puthiaraj and co-workers have unprecedently discovered the catalytic activity of this metal-organic framework (MOF) for the synthesis of imidazo[1,2-a]pyridines [100]. The three-component, one-pot reaction between 1, 3 and nitromethane (10, Scheme 5) involved an intermolecular aza-Michael

• heterogeneously catalyzed synthesis of imidazo[1,2-a]pyridines from 3 and ketones 20 has been reported (Scheme 7) [101]. Titania-supported CuCl2 (CuCl2/nano TiO2) played the role of catalyst in this transformation under aerobic conditions. Titania support helped in recyclability of the copper salt to four

Synthesis of ([1,2,4]triazolo[4,3-a]pyridin-3-ylmethyl)phosphonates and their benzo derivatives via 5-exo-dig cyclization

• Aleksandr S. Krylov,
• Artem A. Petrosian,
• Julia L. Piterskaya,
• Nataly I. Svintsitskaya and
• Albina V. Dogadina

Beilstein J. Org. Chem. 2019, 15, 1563–1568, doi:10.3762/bjoc.15.159

• imidazo[1,2-a]pyridines [4]. In continuation of this study, herein we report an effective approach to the synthesis of new phosphonylated triazolopyridine derivatives by reacting chloroethynylphosphonates with 2-hydrazinylpyridines. The triazolopyridine ring is a structural fragment that is present in a

Mn-mediated sequential three-component domino Knoevenagel/cyclization/Michael addition/oxidative cyclization reaction towards annulated imidazo[1,2-a]pyridines

• Olga A. Storozhenko,
• Alexey A. Festa,
• Delphine R. Bella Ndoutoume,
• Alexander V. Aksenov,
• Alexey V. Varlamov and
• Leonid G. Voskressensky

Beilstein J. Org. Chem. 2018, 14, 3078–3087, doi:10.3762/bjoc.14.287

• annulation patterns. Biologically relevant imidazo[1,2-a]pyridines and chromenes. General view of the molecule 7b in the crystal state (CCDC 1849215). Anisotropic displacement parameters are drawn at 50% probability. Domino formation of imidazopyridines and current work. Scope of the reaction between N

Applications of organocatalysed visible-light photoredox reactions for medicinal chemistry

• Michael K. Bogdos,
• Emmanuel Pinard and
• John A. Murphy

Beilstein J. Org. Chem. 2018, 14, 2035–2064, doi:10.3762/bjoc.14.179

• compatibility. Hajra et al. have reported the direct C–H thiocyanation of substituted imidazo[1,2-a]pyridines, using ammonium thiocyanate, in combination with Eosin Y under irradiation by blue LEDs (Scheme 9) [52]. This is another photoredox example of C–S bond formation, in this case to a highly versatile

• the modified substituted imidazo[1,2-a]pyridines contains scaffolds commonly found in pharmaceuticals, such as sulfones 9a and trifluoromethyl groups 9b. Hence, this publication provides an easy route to access scaffolds with diverse aromatic systems, allowing for the construction of interesting

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation. Part 1: Use of CF₃SO₂Na

• Hélène Guyon,
• Hélène Chachignon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2764–2799, doi:10.3762/bjoc.13.272

• ]BF4) and water [66]. The substrate scope was investigated on 11 imidazothiazoles, 13 imidazo[1,2-a]pyridines and 6 imidazoles (Scheme 43). The reaction was simple, achieved at room temperature and had a good tolerance for various functional groups. However, for the trifluoromethylation of imidazoles

Reagent-controlled regiodivergent intermolecular cyclization of 2-aminobenzothiazoles with β-ketoesters and β-ketoamides

• Irwan Iskandar Roslan,
• Kian-Hong Ng,
• Gaik-Khuan Chuah and
• Stephan Jaenicke

Beilstein J. Org. Chem. 2017, 13, 2739–2750, doi:10.3762/bjoc.13.270

• -efficient protocols, we have employed transition-metal-free approaches for the one-pot synthesis of imidazo[1,2-a]pyridines and thiazolamines by coupling β-ketoesters or their derivatives, phenylacetones and phenylacetophenones, with aminopyridines [20][21] and thioureas [22]. The strategy involves in situ

• bromination of the α-carbon using CBrCl3 as the Br source. This in situ halogenation strategy has been employed for the synthesis of quinoxalines [23], oxazoles [24][25], pyrido[1,2-a]benzimidazoles [26], imidazo[1,2-a]pyridines [27][28][29][30], thiazoles [31][32] and benzothiazoles [33][34]. With weak

Preparation of imidazo[1,2-a]-N-heterocyclic derivatives with gem-difluorinated side chains

• Layal Hariss,
• Kamal Bou Hadir,
• Mirvat El-Masri,
• Thierry Roisnel,
• René Grée and
• Ali Hachem

Beilstein J. Org. Chem. 2017, 13, 2115–2121, doi:10.3762/bjoc.13.208

• formation inhibitors, GABA and benzodiazepine receptor agonists, and cardiotonic agents [7][8][9][10]. Further, the biological activities of imidazo[1,2-a]pyridines proved to be strongly depending upon the nature of substituents at C2 and C3 positions. For instance, the 3-aroylimidazo[1,2-a]pyridines 1c

• [24]. Herein, we report the synthesis of imidazo[1,2-a]pyridines, imidazo[1,2-a]pyrimidines, and imidazopyridazines with fluorinated side chains following an efficient strategy developed by Hajra et al. [25]. This methodology, developed for the synthesis of 3-aroylimidazopyridines, involves a copper

• was purified by column chromatography on silica gel, using petroleum ether/ethyl acetate as eluent. Imidazopyridine 7a was isolated in 33% yield. Representative examples of bioactive imidazo[1,2-a]pyridines, imidazo[1,2-a]pyrimidines, imidazopyridazines and our target molecules. Structures of 7a and

Automating multistep flow synthesis: approach and challenges in integrating chemistry, machines and logic

• Chinmay A. Shukla and
• Amol A. Kulkarni

Beilstein J. Org. Chem. 2017, 13, 960–987, doi:10.3762/bjoc.13.97

• drug candidates. For example, Guetzoyan et al. have demonstrated the use of automation for synthesizing imidazo[1,2-a]pyridines, potential GABAA agonists [12]. II) Optimization: For a set synthesis protocol usually an optimization of conditions to maximize the yield of the desired product brings the

A practical and efficient approach to imidazo[1,2-a]pyridine-fused isoquinolines through the post-GBB transformation strategy

• Taofeng Shao,
• Zhiming Gong,
• Tianyi Su,
• Wei Hao and
• Chao Che

Beilstein J. Org. Chem. 2017, 13, 817–824, doi:10.3762/bjoc.13.82

• conditions and a broad substrate scope, allowing for the rapid construction of structurally complex and diverse heterocycles in moderate to good yields. Keywords: Groebke–Blackburn–Bienaymé reaction; imidazo[1,2-a]pyridines; isoquinolines; multicomponent reaction; Ugi reaction; Introduction Imidazo[1,2-a

• ]pyridines have been reported to display a wide range of biological activities [1][2][3][4][5], and these skeletons are found in various clinical drugs such as zolpidem (I), alpidem (II), and olprinone (III), which were approved for the treatment of insomnia, anxiety and acute heart failure, respectively

One-pot synthesis of tetracyclic fused imidazo[1,2-a]pyridines via a three-component reaction

• Bo Yang,
• Chuanye Tao,
• Taofeng Shao,
• Jianxian Gong and
• Chao Che

Beilstein J. Org. Chem. 2016, 12, 1487–1492, doi:10.3762/bjoc.12.145

• -component reaction has been developed to assemble biologically and pharmaceutically important tetracyclic fused imidazo[1,2-a]pyridines in a one-pot fashion utilizing readily available 2-aminopyridines, isatins and isocyanides. The three-component coupling proceeds through the Groebke–Blackburn–Bienaymé

• reaction followed by a retro-aza-ene reaction and subsequent nucleophilic reaction of the in-situ generated imidazo[1,2-a]pyridines bearing an isocyanate functional group. Keywords: Groebke–Blackburn–Bienaymé reaction; imidazo[1,2-a]pyridines; multi-component reaction; one-pot reaction; Introduction

• development of new GBB-based methods for the efficient synthesis of novel polycyclic fused imidazo[1,2-a]pyridines is highly desirable. In an earlier study, we have developed a GBB/lactamization MCR strategy, which provided the rapid access to isoquinolinone-fused imidazo[1,2-a]pyridines with potent and

A convenient route to symmetrically and unsymmetrically substituted 3,5-diaryl-2,4,6-trimethylpyridines via Suzuki–Miyaura cross-coupling reaction

• Dariusz Błachut,
• Joanna Szawkało and
• Zbigniew Czarnocki

Beilstein J. Org. Chem. 2016, 12, 835–845, doi:10.3762/bjoc.12.82

• teams in the construction of polyarylated benzenes [56], pyridines [57][58][59][60], thiophenes [61][62], quinoxalines [63], pyrazoles [64] pyrroles [65], pyrimidines [66][67], benzofuranes [68], imidazo[1,2-a]pyridines [69], diaryl/heteroaryl methanes [70], and indoles [71], bearing differently

The synthesis of active pharmaceutical ingredients (APIs) using continuous flow chemistry

• Marcus Baumann and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2015, 11, 1194–1219, doi:10.3762/bjoc.11.134

• small collection of 22 imidazo[1,2-a]pyridines 136 was prepared within four working days. The synthetic route consisted of an aldol condensation between various acetophenones 137 and ethyl glyoxylate (138). This was followed by an HBF4-catalysed cyclocondensation of the resulting Michael acceptor 139