A Simple Synthesis of 1,3-Diphenylpropene

Abstract

Abstract-A simple approach to the synthesis of 1,3-diphenylpropene isomers was developed based on Fe(acac) 3 -catalyzed cross-coupling of (E)-and (Z)-1,3-dichloropropenes with phenylmagnesium bromide.Keywords: 1,3-diphenylpropene, cross-coupling, Fe-catalyzed cross-coupling, Fe(acac) 3 ISSN 1070-3632, Russian Journal of General Chemistry, 2018, Vol. 88, No. 2, pp. 342-344. © Pleiades Publishing, Ltd., 2018. Original Russian Text © R.N. Shakhmaev, A.Sh. Sunagatullina, A.N. Vasilyeva, V.V. Zorin, 2018, published in Zhurnal Obshchei Khimii, 2018 1,3-Diphenylpropene isomers are used in organic synthesis as the starting substrates and model compounds [1][2][3][4]. The specific reactivity of 1,3-diphenylpropene is due to the presence of methylene group, being simultaneously in the allyl and benzyl positions. (E)-1,3-Diphenylpropene is usually obtained by treating a not easily accessible phenylacetaldehyde with a KOH alcohol solution [5,6], while the synthesis of less thermodynamically stable (Z)-isomer with an acceptable stereochemical purity is very problematic [7,8]. LETTERS TO THE EDITORWe investigated the possibility of obtaining 1,3-diphenylpropene 2 by Fe(acac) 3 -catalyzed crosscoupling of 1,3-dichloropropene 1 with phenylmagnesium bromide. It is known that available iron(III) salts are effective catalysts in cross-coupling reactions of Grignard reagents with vinyl [9--12] and allyl halides [13,14]. Fe(acac) 3 the most commonly used in the synthesis of natural compounds [15,16] and drugs [17][18][19][20] is advantageously characterized by low hygroscopicity, good solubility, and ease of handling [21].The reaction of (E)-1,3-dichloropropene la with 3 equiv of PhMgBr in tetrahydrofuran in the presence of 3 mol % of Fe(acac) 3 afforded a mixture of (E)-and (Z)-isomers of 1,3-diphenylpropene 2a and 2b (E : Z = 92 : 8) in a 52% yield. The introduction of the most frequently used ligands like N,N,N,N-tetramethylethylenediamine (TMEDA) [22] or N-methylpyrrolidone (NMP) [10], the replacement of THF by diethyl ether and the use of FeCl 3 as the catalyst did not substantially increase the yield of the reaction product. However, a decrease in the reaction temperature to -35°C results in an increase in the yield of 1,3-diphenylpropene to 80% with the same isomeric composition.The cross-coupling with (Z)-1,3-dichloropropene under similar conditions resulted in an isomeric mixture of 1,3-diphenylpropene (E : Z = 55 : 45) with 72% yield, while at room temperature the reaction direction shifted toward the formation of (E)-isomer (E : Z = 76 : 24). (E)-and (Z)-isomers of 1,3-diphenylpropene and diphenyl formed by homocoupling reaction were separated by column chromatography (Scheme 1).Structure and purity of the obtained compounds was confirmed by high-performance GLC analysis, NMR spectroscopy and chromato-mass spectrometry. A reliable evidence of the stereochemical configuration of isomers 2a and 2b was the values of spin-spin coupling constant of vinyl hydrogen atoms (J = 15.6 and 11.3 Hz), characteristic of the E-and Z-con...