Reactions of perfluoroacylchromenes with aromatic amines: synthesis of perfluoroalkylchromene carbaldehydes
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Reactions of perfluoroacylchromenes with aromatic amines: synthesis of perfluoroalkylchromene carbaldehydes Dmitry V. Osipov1, Irina V. Melnikova1, Kirill S. Korzhenko1, Vitaly A. Osyanin1*, Yuri N. Klimochkin1 1
Samara State Technical University, 244 Molodogvardeiskaya St., Samara 443100, Russia; е-mail: [email protected] Submitted February 12, 2020 Accepted after revision April 22, 2020
Translated from Khimiya Geterotsiklicheskikh Soedinenii, 2020, 56(8), 990–996
The reactions of 3-perfluoroacyl-4Н-chromenes and 2-perfluoroacyl-1Н-benzo[f]chromenes with primary aromatic amines resulted in pyran ring cleavage, which was initiated by an aza-Michael reaction. The obtained enamino ketones underwent rearrangements in the presence of superacids, giving 2-perfluoroalkyl-4Н-chromene-3-carbaldehydes and 3-perfluoroalkyl-1Н-benzo[f]chromene2-carbaldehydes, respectively. Keywords: chromene carbaldehyde, enamino ketone, 2-perfluoroacyl-1Н-benzo[f]chromene, 3-perfluoroacyl-4Н-chromene, aza-Michael reaction, rearrangement.
Polyfluoroalkyl groups are known to significantly enhance the reactivity of electrophilic substrates, while also affecting the regioselective outcomes of reactions involving nucleophiles. The introduction of CnF2n+1 groups in heterocycles often enables reactions that would not occur without such groups.1 The presence of a perfluoroacyl group at position 3 of 4Н-chromenes markedly increased the reactivity of pyran ring toward the action of various nucleophiles, making these compounds valuable as building blocks for the synthesis of various heterocyclic compounds.2 Examples of such synthetic routes include the preparation of 3-carbethoxypyridones and 3-(benzimidazol2-yl)pyridin-2-ones from trifluoroacetylchromenes and nitriles containing active methylene groups,3 the preparation of benzo[f]coumarins from 2-trifluoroacetyl1Н-benzo[f]chromenes and 2-naphthols,4 as well as the synthesis of trifluoromethylchromenols from trifluoroacetylchromenes.5 0009-3122/20/56(8)-0990©2020 Springer Science+Business Media, LLC
3-Perfluoroacyl-4Н-chromenes and 2-perfluoroacyl-1Нbenzo[f]chromenes 1a–g containing bromo, nitro, or methyl substituents in the aromatic ring reacted with anilines via an aza-Michael reaction as the first step,6 which can serve as a convenient model process for studying the addition of various N-nucleophiles to acylchromenes. We showed that the interaction of primary arylamines 2a–d with perfluoroacylchromenes 1a–g provided high yields of β-aminoperfluoroalkylvinyl ketones 3a–j (Scheme 1), which have been used as valuable starting materials for the assembly of various heterocycles.7 The reaction was performed in MeOH or a mixture of MeOH–MeCN at room temperature or by brief heating. The given transformation can be viewed as a nucleophilic substitution at the vinyl carbon atom (SNVin), consisting of two steps: an aza-Michael reaction and a retrooxa-Michael reaction (addition–elimination).8 The formation of products due to 1,2-addition at the C=O group 990
Chemistry of Heterocyclic Compounds 2020, 56(8)
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