Novel synthetic approach to pyrrolo[1,2- b ]cinnolines
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Novel synthetic approach to pyrrolo[1,2-b]cinnolines Anastasia T. Plieva1*, Petrakis N. Chalikidi1, Andrey V. Gutnov1, Anatolij M. Turiev1, Oleg P. Demidov2, Nicolai A. Aksenov2, Taimuraz T. Magkoev1, Vladimir T. Abaev1* 1
Department of Chemistry, North Ossetian State University named after K. L. Khetagurov, 46 Vatutina St., Vladikavkaz 362025, Russia; e-mail: [email protected], [email protected] 2 Department of Chemistry, North Caucasus Federal University, 1a Pushkina St., Stavropol 355009, Russia Submitted March 20, 2020 Accepted after revision July 15, 2020
Published in Khimiya Geterotsiklicheskikh Soedinenii, 2020, 56(8), 1030–1041
Straightforward method for the synthesis of pyrrolo[1,2-b]cinnolines starting from 2-nitrobenzaldehydes and 2-methylfurans has been elaborated. The key steps of the process are oxidative furan ring opening with diazonium cation and intramolecular alkylation of azo group of the resulted cinnoline with secondary allyl alcohol. Keywords: aza-heterocycles, cinnolines, pyrrolo[1,2-b]cinnolines, furan ring opening.
In the last decade, pyrrolo[1,2-b]pyridazines enjoy evergrowing use in medicine due to the wide spectrum of biological activity they possess including anticancer,1 antibacterial,2 antioxidant,3–5 anti-inflammatory,6 Janus kinase (JAKs)7–9 and IRAK4 inhibiting activity.10 No less attention is paid to the photophysical properties of this class of compounds. Their fluorescent properties made them popular materials in the constructing different optical devices, lasers, OLED screens.11–15 Some representatives of pyrrolo[1,2-b]cinnolines display prominently high luminescence level with quantum efficiencies up to 90%.12 General methods of assembling pyrrolo[1,2-b]pyridazine framework are numerous and mainly based on condensation and cycloaddition approaches.16,17 The number of synthetic routes to access pyrrolo[1,2-b]cinnolines is considerably lower. Thus, the first derivative of rare pyrrolo[1,2-b]cinnoline ring system was reported by Ames in 1975.18 The corresponding 2-aminovalerophenone was diazotized under conditions of Borsche–Koelsch cinnoline synthesis, and resulting 3-methoxypropylcinnolinone was refluxed with concentrated HBr (Scheme 1). Later on pyrrolo[1,2-b]cinnolinone derivative was prepared from 2-benzoyl-1H-pyrrol-1-ylcarbamate employing aromatic nucleophilic substitution.19 Methylation with diazomethane produced O-methyl ether and further reaction with 0009-3122/20/56(8)-1030©2020 Springer Science+Business Media, LLC
benzylamine allowed for obtaining 10-amino derivative of pyrrolo[1,2-b]cinnoline. Pyrrolo[1,2-b]cinnoline derivative accompanied anticipated product of the Hantzsch 1,4-dihydropyridine Vilsmeier formylation. Its formation was rationalized by unusual dihydropyridine ring recyclization (Scheme 1).20 In 2003, the synthesis of pyrrolo[1,2-b]cinnolines directly from cinnolines under the action of dimethyl acetylenedicarboxylate (DMAD) in MeOH at low temperature was developed. Alternatively, cinnolines were N-alkylated with tert-butyl bromoacetate before t
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