Synthetic approaches to pyrido[1,2- a ]indoles (microreview)
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Dedicated to Proffesor Vasiliy A. Bakulev on the occasion of his 70th birthday
Synthetic approaches to pyrido[1,2-a]indoles (microreview) Igor L. Nikonov1,2, Dmitry S. Kopchuk1,2*, Grigory V. Zyryanov1,2, Oleg N. Chupakhin1,2 1
Department of Organic and Biomolecular Chemistry, Chemical Engineering Institute, Ural Federal University named after the first President of Russia B. N. Yeltsin, 19 Mira St., K-2, Yekaterinburg 620002, Russia; е-mail: [email protected] 2 Postovsky Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences, 22 S. Kovalevskoi / 20 Akademicheskaya St., Yekaterinburg 620108, Russia Submitted April 16, 2020 Accepted after revision May 19, 2020
Published in Khimiya Geterotsiklicheskikh Soedinenii, 2020, 56(9), 1155–1157
The review presents the main methods for the synthesis of pyrido[1,2-a]indoles and their annulated and conjugated derivatives over the past 10 years. The approaches are divided into three groups depending on the starting compounds: construction of the pyridine nucleus on the indole fragment, cyclization using benzylsubstituted pyridines, and formally one-step process via aryne intermediates. Introduction Pyrido[1,2-a]indole is a structural part of many natural alkaloids. Compounds of this class were isolated from various living organisms, for example, from the bark of flowering plants of the Gonioma malagasy species,1 as well as from the surface of deep-sea sponges of the Fascaplysinopsis genus.2 Pyrido[1,2-a]indoles are of significant interest primarily due to the wide range of their biological activities, in particular
cytostatic,3 antiviral,4 tuberculostatic,5 immunosuppressive,6 antitumor,7 etc. In addition, due to their unique fluorescent properties, they are widely used for creating organic luminescent materials.8 The different synthetic approaches to pyrido[1,2-a]indole derivatives have been very widely developed over the past 10 years. The main methods for the synthesis of such heterocycles are summarized in this review.
Construction of the pyridine nucleus on the basis of indole The first group of methods for the preparation of substituted pyrido[1,2-a]indoles, as well as indolo[2,1-a]isoquinolines, is the construction of the pyridine ring on the indole one. For example, the three-component reaction of indole2-carbaldehyde (1) with alkynes 2 and 2-bromoacetophenones 3 in DMF at 110°С was described as a method for the synthesis of pyrido[1,2-a]indole esters 4 in 40–58% yields.9 Igor L. Nikonov works at the Postovsky Institute of Organic Synthesis of the Ural Branch of the Russian Academy of Sciences and at the Department of Organic and Biomolecular Chemistry of the Ural Federal University. His research interests include the study of new synthetic approaches to nitrogenous heterocycles, in particular 1,2,4-triazines, including their reactions with 1,2-dehydrobenzenes. Dmitry S. Kopchuk earned his PhD (Organic Chemistry) in 2010 and Dr. Sc. (Organic Chemistry) in 2019 from the Ural Federal University and Postovsky Institute of Organic Synthesis of the
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