Fluorescent Pyranoindole Congeners: Synthesis and Photophysical Properties of Pyrano[3,2-f], [2,3-g], [2,3-f], and [2,3-e]Indoles

This paper reports the synthesis of four types of annulated pyranoindole congeners: pyrano[3,2-f]indole, pyrano[2,3-g]indole, pyrano[2,3-f]indole, and pyrano[2,3-e]indole and photophysical studies in this series. The synthesis of pyrano[3,2-f], [2,3-g], and [2,3-e]indoles involve a tandem of Bischler–Möhlau reaction of 3-aminophenol with benzoin to form 6-hydroxy- or 4-hydroxyindole followed by Pechmann condensation of these hydroxyindoles with β-ketoesters. Pyrano[2,3-f]indoles were synthesized through the Nenitzescu reaction of p-benzoquinone and ethyl aminocrotonates and subsequent Pechmann condensation of the obtained 5-hydroxyindole derivatives. Among the pyranoindoles studied, the most promising were pyrano[3,2-f] and [2,3-g]indoles. These compounds were characterized by moderate to high quantum yields (30–89%) and a large (9000–15,000 cm−1) Stokes shift. More detailed photophysical studies were carried out for a series of the most promising derivatives of pyrano[3,2-f] and [2,3-g]indoles to demonstrate their positive solvatochromism, and the data collected was analyzed using Lippert-Mataga equation. Quantum chemical calculations were performed to deepen the knowledge of the absorption and emission properties of pyrano[3,2-f] and [2,3-g]indoles as well as to explain their unusual geometries and electronic structures.

Authors
Sharapov Ainur D.1 , Fatykhov Ramil F.1 , Khalymbadzha Igor A.1 , Valieva Maria I.1, 2 , Nikonov Igor L.1, 2 , Taniya Olga S.1 , Kopchuk Dmitry S.1, 2 , Zyryanov Grigory V.1, 2 , Potapova Anastasya P.1 , Novikov Alexander S. 3, 4 , Sharutin Vladimir V.5 , Chupakhin Oleg N.1
Journal
Publisher
MDPI AG
Number of issue
24
Language
English
Pages
8867
Status
Published
Volume
27
Year
2022
Organizations
  • 1 Department of Organic and Biomolecular Chemistry, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
  • 2 Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences, Kovalevskoy Street 22, 620219 Ekaterinburg, Russia
  • 3 Institute of Chemistry, Saint Petersburg State University, Universitetskaya Emb., 7/9, 199034 Saint Petersburg, Russia
  • 4 Research Institute of Chemistry, Peoples’ Friendship University of Russia (RUDN University), Miklukho-Maklaya Street, 6, 117198 Moscow, Russia
  • 5 Department of Chemistry, Institute of Natural Sciences, South Ural State University (National Research University), Lenin Avenue 76, 454080 Chelyabinsk, Russia
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