Alkyl 3-Nitroacrylates in the Reactions with Heterocyclic CH Acids
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Alkyl 3-Nitroacrylates in the Reactions with Heterocyclic CH Acids V. V. Pelipkoa, M. A. Kuritsynаa, R. I. Baichurina, and S. V. Makarenkoa,* a Herzen
State Pedagogical University of Russia, St. Petersburg, 191186 Russia *e-mail: [email protected] Received May 6, 2020; revised May 6, 2020; accepted May 16, 2020
Abstract—The reactions of alkyl 3-nitroacrylates with certain heterocyclic CH acids such as 1,3-dimethylpyrimidine2,4,6(1Н,3Н,5Н)-trione, 5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one, 4-hydroxy-6-methyl-2H-pyran-2-one, and 4-hydroxy-2H-chromen-2-one occur in the presence of the Rodionov catalyst to form the Michael adducts. The products structure has been confirmed by 1H, 13C{1H}, and 1Н-15N HMBC NMR as well as IR spectroscopy methods. Keywords: nitroacrylates, CH-acids, Rodionov catalyst, nucleophilic addition, Michael adducts
DOI: 10.1134/S1070363220080034 The ongoing research of unsaturated nitro compounds have demonstrated the importance of these substances in the fields of fundamental and applied organic chemistry [1–6]. Alkyl 3-nitroacrylates are peculiar representatives of the conjugated nitroalkenes [6, 7]. High electrophilicity of the С=С bond makes them efficient substrates in the reactions with nucleophiles [8–10]. The data on the interactions of alkyl 3-nitroacrylates with СН acids have been scarce. 2-Phenylindane-1,3dione [11], tert-butyl-1-methyl-3,5-dioxocyclohexane1-carboxylate [12], and dihydroresorcinol [13] can be added at alkyl 3-nitroacrylates in the presence of triethylamine. Hexahydro-1H-indene-1,3(2H)-dione [14] and 2-isopropyl-3,6-dimethoxy-2,5-dihydropyrazine [15] can be involved in this reaction in the presence of sodium methylate and butyllithium, respectively. We have demonstrated the use of the Rodionov catalyst [16] in the reactions of alkyl 3-nitroacrylates with cyclohexane-1,3-diones and Meldrum’s acid (2,2-dimethyl-1,3-dioxane-4,6-dione) [17]. The Rodionov catalyst (alcoholic solution of trimethylphenylammonium hydroxide [16]) as well as other quaternary analogs [18–21] have been used in the Michael reactions in the mid-twentieth century. It was therefore appropriate to investigate the use of that commercially available catalyst in the reactions of alkyl 3-nitroacrylates with a broader range of cyclic CH acids.
The use of the Rodionov catalyst (10 mol %) in the reactions of alkyl 3-nitroacrylates 1a, 1b with 1,3-dimethylpyrimidine-2,4,6(1Н,3Н,5Н)-trione, 5-methyl-2phenyl-2,4-dihydro-3Н-pyrazol-3-one, 4-hydroxy-6methyl-2Н-pyran-2-one, and 4-hydroxy-2Н-chromen2-one (room temperature, anhydrous methanol) gave the Michael adducts 2‒5 in 58‒93% yield (Scheme 1). Regioselectivity of the nucleophilic addition at the C=C bond was determined by strong electron-accepting properties of the nitro group. The 1Н NMR spectra of adducts 2a, 2b manifested the АВСМ (2JAB = 15.0‒15.3, 3J 3 3 AC = 5.3‒5.5, JBC = 7.2‒7.8, JCM = 2.1‒2.3 Hz) spin system of the CH2NO2 (4.75‒5.08 ppm) and two methine HC (4.39–4.45 ppm; HМ (4.02‒4.24 ppm) protons thus
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