Synthesis of 2,3-Diphenylacrolein Acetals
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Synthesis of 2,3-Diphenylacrolein Acetals G. N. Sakhabutdinovaa, G. Z. Raskilʼdinaa,*, and S. S. Zlotskiia a
Ufa State Petroleum Technological University, Ufa, 450062 Russia *e-mail: [email protected] Received April 23, 2020; revised April 23, 2020; accepted April 30, 2020
Abstract—Linear acetals have been synthesized by decomposition trans- and cis-1,1-dichloro-2,3-diphenylcyclopropanes in the presence of aliphatic alcohols (ethanol and butan-1-ol). The reactivities of pure trans- and cis-stilbenes and styrene toward dichlorocarbene have been compared. The structure of the isolated compounds was determined by NMR and GC/MS. Keywords: trans- and cis-stilbenes, dichlorocarbene, anion exchanger, gem-dichlorocyclopropane
DOI: 10.1134/S1070363220090248 Compounds containing a gem-dichlorocyclopropane fragment are widely used in the synthesis of polyfunctionalized unsaturated compounds as intermediate products for the preparation of inhibitors, biologically active agents, and fuel, oil, and polymer additives [1–7]. Alcohoysis of aryl-gem-dichlorocyclopropanes in alkaline medium gives acrolein acetals and their derivatives [8, 9]. By dichlorocarbenation [10] of pure trans- and cis-stilbenes 1a and 1b we obtained the corresponding trans- and cis-1,1-dichloro-2,3diphenylcyclopropanes 2a and 2b in quantitative yield (Scheme 1). Using the competitive reaction method we found that the reactivities of trans and cis isomers 1a and 1b under the given conditions are similar and that they
are an order of magnitude less reactive than styrene. Presumably, this is related to sterically hindered approach of dichlorocarbene(:CCl2) to the C=C double bond shielded by bulky phenyl groups. Pure trans- and cis-1,1-dichloro-2,3-diphenylcyclopropanes 2a and 2b in boiling ethanol (75‒80°C) in the presence of NaOH in 20 h were converted by 56% to the corresponding acetals 3a and 3b. The reactivities of isomers 2a and 2b in this transformation were similar and were 8 times higher than the reactivity of 1,1-dichloro2-phenylcyclopropane. This is likely to be related to the presence of two benzylic hydrogen atoms in the 2- and 3-positions of 2a and 2b, which are capable of undergoing 1,2-migration. As a drawback, this method of synthesis of acetals 3a and 3b is characterized by high consumption
Scheme 1.
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SYNTHESIS OF 2,3-DIPHENYLACROLEIN ACETALS
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Scheme 2.
of alkali (NaOH‒2 molar ratio 1 : 1) and long reaction time (> 20 h). We modified the reaction conditions and used butan-1ol instead of low-boiling ethanol and commercial AV-17 anion exchanger instead of sodium hydroxide, and the reaction mixtures were heated at 115‒120°C. Under these conditions, the conversion of 2a and 2b in 8 h exceeded 80%, and the yields of 4a and 4b were 87%. However, the reactions at elevated temperature (>100°C) were less stereoselective, and both isomers 4a and 4b were formed in each case (Scheme 2). The structure of compounds 3a, 3b, 4a, and 4b was determined on the basis of their 1H and 13C NMR and mass spectra. The 1H NMR spectr
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