A method for preparing polysubstituted propenyl aromatic compounds

Abstract

The present invention belongs to the field of fine chemicals and related chemical technologies and provides a method for preparing polysubstituted propenyl aromatic compounds. Using halomethyl aromatic hydrocarbons and allyltributyltin as raw materials, in the presence of palladium and phosphine catalysts, the reaction is carried out in an anhydrous organic solvent at room temperature for 12 hours. Acid is then added, and the reaction is continued at 40°C for 12 hours to obtain the corresponding polysubstituted propenyl aromatic compounds. The preparation method of the present invention is a one-pot process characterized by mild reaction conditions, simple operation, high yield, and good regioselectivity. The polysubstituted propenyl aromatic compounds synthesized using this method can be further functionalized to obtain various compounds for application in the development and research of natural products, functional materials, and fine chemicals.

Description

Technical Field

[0001] The invention belongs to the field of fine chemicals and related chemical technologies, and provides a highly efficient preparation method of polysubstituted propenyl aromatic compounds. Background Art

[0002] Propylene aromatic compounds are widely found in natural products, pharmaceuticals, and pesticide intermediates. Furthermore, the methyl group and carbon-carbon double bond of the propenyl group are easily functionalized, offering opportunities for further modification. Therefore, developing a simple and efficient synthetic method to obtain polysubstituted propenyl aromatic compounds is gaining increasing attention.

[0003] Traditional methods for synthesizing polysubstituted propenyl aromatic compounds primarily involve chemical modification of the original structure. In addition to the common Suzuki-Miyaura coupling reaction of aromatic halides with propenylboronic acid pinacol esters (Tetrahedron Lett., 2008, 49, 5605-5607), a range of methods for introducing propenyl groups into aromatic compounds also include the semi-reduction of aromatic alkynes (J. Am. Chem. Soc., 2016, 138, 8588-94), the Wittig reaction of benzaldehyde with ethyltriphenylphosphonium bromide (J. Org. Chem., 2008, 73, 801-812), the dehydration of aromatic alcohols (Eur. J. Org. Chem., 2008, 5577-5582), and the double bond isomerization of allylbenzenes (Org. Lett., 2012, 14, 3716-3719). However, these methods are limited by poor functional group compatibility, the need for pre-functionalization, and harsh reaction conditions.

[0004] In contrast, direct C-H allylation catalyzed by transition metals is a more ideal method. So far, there are two types of substrates that can be used for direct C-H allylation. One is an aromatic compound containing a directing group (Adv. Synth. Catal., 2016, 358, 3932-3937), and the other is an aromatic compound containing multiple electron-withdrawing groups (Angew. Chem. Int. Ed., 2016, 55, 1876-1880). However, these methods sometimes produce a mixture of allylic and propylene products, and most of them require high temperatures (over 100°C) to generate.

[0005] Therefore, in order to obtain a richer variety of polysubstituted propenyl aromatic compounds, it is necessary to develop a synthetic method with wide substrate applicability, mild reaction conditions, good functional group compatibility and high regioselectivity. Summary of the Invention

[0006] The invention provides a novel preparation method of a polysubstituted propenyl aromatic compound. The synthesis method is a one-pot process with mild reaction conditions, simple operation, high yield and good regioselectivity.

[0007] The technical solution of the present invention:

[0008] A highly efficient method for preparing polysubstituted propenyl aromatic compounds comprises using halomethyl aromatic hydrocarbons and their derivatives, and allyltributyltin as raw materials. In the presence of palladium and phosphine catalysts, the reaction is carried out in an anhydrous organic solvent at room temperature for 12 hours. An acid is then added, and the reaction is carried out at 40°C for 12 hours to obtain the corresponding polysubstituted propenyl aromatic compounds. The synthetic route is as follows:

[0009]

[0010] Where R 1 Select aryl, methyl, 2-naphthyl, heteroaryl;

[0011] The molar ratio of halomethyl aromatic hydrocarbons and their derivatives to allyltributyltin is 1:1;

[0012] The molar ratio of methyl halide aromatic hydrocarbons and their derivatives to the catalyst is 1:0.05;

[0013] The molar ratio of the halogenated methyl aromatic hydrocarbon and its derivatives to the acid is 1:2;

[0014] The molar ratio of halogenated methyl aromatic hydrocarbons and their derivatives to palladium is 1:0.05;

[0015] The molar concentration of halogenated methyl aromatic hydrocarbons and their derivatives in the system is 0.15 mmol / mL.

[0016] The palladium is one or a mixture of two or more selected from trisdibenzylideneacetone dipalladium, palladium acetate, palladium chloride, bis(dibenzylideneacetone) palladium, palladium pivalate, palladium acetylacetonate, ditriphenylphosphine palladium diacetate, ethylenediamine palladium chloride, bis(tricyclohexylphosphine) palladium dichloride, and palladium trifluoroacetate. Preferably, the palladium is one or a mixture of two or more selected from trisdibenzylideneacetone dipalladium, palladium acetate, and palladium chloride.

[0017] The phosphine catalyst is triphenylphosphine, tri-p-tolylphosphine, tri-p-methoxyphenylphosphine, tri-p-fluorophenylphosphine, tert-butyldiphenylphosphine, tricyclohexylphosphine, tri(2-furyl)phosphine, 1,4-bis(diphenylphosphino)butane, 1,1'-bis(diphenylphosphino)ferrocene. Triphenylphosphine, tri-p-tolylphosphine, and tert-butyldiphenylphosphine are preferred.

[0018] The anhydrous organic solvent is one or a mixture of two or more of dichloromethane, tetrahydrofuran, 1,4-dioxane, ether, methyl tert-butyl ether, toluene, acetonitrile, methyl cyclopentyl ether, and 1,2-dichloroethane, preferably dichloromethane, tetrahydrofuran, and 1,4-dioxane.

[0019] The acid is one or a mixture of two or more of p-toluenesulfonic acid monohydrate, trifluoroacetic acid, acetic acid, fluoroboric acid, methanesulfonic acid, and trifluoromethanesulfonic acid, preferably p-toluenesulfonic acid monohydrate, trifluoroacetic acid, and acetic acid.

[0020] The separation method is column chromatography.

[0021] When using column chromatography to separate products, silica gel or neutral alumina can be used as the stationary phase, and the developing solvent is generally a mixed solvent of polar and non-polar solvents, such as ethyl acetate-petroleum ether, ethyl acetate-n-hexane, dichloromethane-petroleum ether, and methanol-petroleum ether.

[0022] The beneficial effects of the present invention are that the synthesis method is a one-pot process, the reaction conditions are mild, the operation is simple, and the yield and regioselectivity are high; the polysubstituted propenyl aromatic compounds synthesized by this method can be further functionalized to obtain various compounds, which can be applied to the development and research of natural products, functional materials and fine chemicals. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Example 1 (E) -2,5-dimethyl-4-propenyl-1,1'-biphenyl 1 H NMR spectrum.

[0024] Figure 2 is (E)-2,5-dimethyl-4-propenyl-1,1'-biphenyl in Example 1 13 C NMR spectrum.

[0025] Figure 3 is (E)-4'-fluoro-2,5-dimethyl-4-propenyl-1,1'-biphenyl in Example 2 1 H NMR spectrum.

[0026] Figure 4 is (E)-4'-fluoro-2,5-dimethyl-4-propenyl-1,1'-biphenyl in Example 2 13 C NMR spectrum.

[0027] Figure 5 is (E)-4'-chloro-2,5-dimethyl-4-propenyl-1,1'-biphenyl in Example 3 1 H NMR spectrum.

[0028] Figure 6is (E)-4'-chloro-2,5-dimethyl-4-propenyl-1,1'-biphenyl in Example 3 13 C NMR spectrum.

[0029] Figure 7 is (E)-4'-bromo-2,5-dimethyl-4-propenyl-1,1'-biphenyl in Example 4 1 H NMR spectrum.

[0030] Figure 8 is (E)-4'-bromo-2,5-dimethyl-4-propenyl-1,1'-biphenyl in Example 4 13 C NMR spectrum.

[0031] Figure 9 is (E)-2,4',5-trimethyl-4-propenyl-1,1'-biphenyl in Example 5 1 H NMR spectrum.

[0032] Figure 10 is (E)-2,4',5-trimethyl-4-propenyl-1,1'-biphenyl in Example 5 13 C NMR spectrum.

[0033] Figure 11 is (E)-2,5-dimethyl-4-propenyl-4'-trifluoromethoxy-1,1'-biphenyl in Example 6 1 H NMR spectrum.

[0034] Figure 12 is (E)-2,5-dimethyl-4-propenyl-4'-trifluoromethoxy-1,1'-biphenyl in Example 6 13 C NMR spectrum.

[0035] Figure 13 is (E)-1,2,4-trimethyl-5-propenylbenzene in Example 7 1 H NMR spectrum.

[0036] Figure 14 is (E)-1,2,4-trimethyl-5-propenylbenzene in Example 7 13 C NMR spectrum.

[0037] Figure 15 is (E)-2-(2,5-dimethyl-4-propenylphenyl)naphthalene in Example 8 1 H NMR spectrum.

[0038] Figure 16 is (E)-2-(2,5-dimethyl-4-propenylphenyl)naphthalene in Example 8 13 C NMR spectrum.

[0039] Figure 17 is (E)-2-(2,5-dimethyl-4-propenylphenyl)thiophene in Example 9 1 H NMR spectrum.

[0040] Figure 18 is (E)-2-(2,5-dimethyl-4-propenylphenyl)thiophene in Example 9 13 C NMR spectrum. DETAILED DESCRIPTION

[0041] The method for preparing the polysubstituted propenyl aromatic compound of the present invention has the advantages of a one-pot process, mild reaction conditions, simple operation, high yield and regioselectivity, and the like.

[0042] The present invention will be further described below in conjunction with specific examples. These examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. Simple substitutions or improvements made by those skilled in the art to the present invention fall within the technical solutions protected by the present invention.

[0043] Example 1: Synthesis of (E)-2,5-dimethyl-4-propenyl-1,1'-biphenyl

[0044] In a 25 mL reactor, 2-phenyl-4-methylbenzyl chloride (0.064 g, 0.3 mmol), allyltributyltin (0.100 mg), trisdibenzylideneacetone dipalladium (0.014 g, 0.015 mmol), and triphenylphosphine (0.016 g, 0.06 mmol) were added. 2 mL of anhydrous dichloromethane was added and the mixture was stirred at room temperature under nitrogen for 24 hours. p-Toluenesulfonic acid monohydrate (0.142 mg, 0.6 mmol) was added and stirred at 40°C for 12 hours. Column chromatography (basic alumina, 200-300 mesh; developing solvent: petroleum ether) afforded 0.040 g of (E)-2,5-dimethyl-4-propenyl-1,1'-biphenyl in a 60% yield.

[0045]

[0046] Yellow solid; melting point 59-60℃; 1 H NMR (400MHz, CDCl3) δ7.48–7.39(m,2H),7.37–7.33(m,4H),7.05(s,1H),6.63(dd,J=15.8,2. 0Hz,1H),6.19(dq,J=15.4,6.5Hz,1H),2.36(s,3H),2.28(s,3H),1.96(dd,J=6.7,1.7Hz,3H); 13 C{ 1H}NMR(100MHz, CDCl3)δ141.9,140.4,136.0,132.7,132.2,131.7,129.2,128.6,128.1,127.4,126.9,126.7,20.1,19.3,18.9; IR(KBr):ν max 2925,1618,1447,1325,1166,1127,1068,963,847,696cm -1 ;HRMS(EI)m / z:[M] + Calcd for C 17 H 18 222.1409; Found 222.1402.

[0047] Example 2: Synthesis of (E)-4'-fluoro-2,5-dimethyl-4-propenyl-1,1'-biphenyl

[0048] In a 25 mL reactor, 2-(chloromethyl)-4'-fluoro-5-methyl-1,1'-biphenyl (0.072 g, 0.3 mmol), allyltributyltin (0.100 mg), palladium acetate (0.004 g, 0.015 mmol), and tri-p-tolylphosphine (0.018 g, 0.06 mmol) were added. Anhydrous tetrahydrofuran (2 mL) was then added and stirred at room temperature under nitrogen for 24 h. Trifluoroacetic acid (0.068 mg, 0.6 mmol) was then added and stirred at 40°C for 12 h. Column chromatography (silica gel, 200-300 mesh; developing solvent: petroleum ether) afforded 0.043 g of (E)-4'-fluoro-2,5-dimethyl-4-propenyl-1,1'-biphenyl in a 60% yield.

[0049]

[0050] Brown oily liquid; 1 H NMR (400MHz, CDCl3) δ7.39–7.27(m,3H),7.18–7.07(m,2H),7.01(s,1H),6.63(dd,J=15.6,1. 8Hz,1H),6.19(dq,J=15.6,6.6Hz,1H),2.36(s,3H),2.25(s,3H),1.96(dd,J=6.6,1.8Hz,3H); 13 C{ 1H}NMR(100MHz, CDCl3)δ161.9(d,J=245.2Hz),139.3,137.8(d,J=3.2Hz),136.1,132.7,132 .3,131.7,130.7(d,J=7.9Hz),128.4,127.4,127.0,114.9(d,J=21.2Hz),20.0,19.3,18.9; 19 FNMR(376MHz, CDCl3)δ-116.34; IR(neat):ν max 2925,1652,1605,1509,1489,1447,1222,1157,963,839,699cm -1 ;HRMS(EI)m / z:[M] + Calcd for C 17 H 17 F240.1314; Found 240.1308.

[0051] Example 3: Synthesis of (E)-4'-chloro-2,5-dimethyl-4-propenyl-1,1'-biphenyl

[0052] The operation was the same as that in Example 1 to obtain 0.045 g of (E)-4'-chloro-2,5-dimethyl-4-propenyl-1,1'-biphenyl from 2-(chloromethyl)-4'-chloro-5-methyl-1,1'-biphenyl with a yield of 58%.

[0053]

[0054] White solid; melting point 60-61°C; 1 H NMR (400MHz, CDCl3) δ7.38–7.33(m,2H),7.29(s,1H),7.26–7.20(m,2H),6.96(s,1H),6.58(dd,J=15 .7,1.9Hz,1H),6.15(dq,J=15.6,6.6Hz,1H),2.31(s,3H),2.21(s,3H),1.92(dd,J=6.6,1.8Hz,3H); 13 C{ 1 H}NMR(100MHz, CDCl3)δ140.3,139.1,136.3,132.7,132.6,132.3,131.5,130.5,128.5,128.2,127.5,127.1,20.0,19.2,18.8; IR(KBr):ν max2922,2069,1652,1483,1445,1266,1090,1013,962,834,747,692cm -1 ;HRMS(EI)m / z:[M] + Calcd for C 17 H 17 Cl256.1019; Found 256.1012.

[0055] Example 4: Synthesis of trans-4,4'-dimethyl dicarboxylate-1,2-phenylethylene

[0056] The operation was the same as that in Example 2 to obtain 0.051 g of (E)-4'-bromo-2,5-dimethyl-4-propenyl-1,1'-biphenyl from 2-(chloromethyl)-4'-bromo-5-methyl-1,1'-biphenyl with a yield of 57%.

[0057]

[0058] White solid; melting point 73-74°C; 1 H NMR (400MHz, CDCl3) δ7.58–7.51(m,2H),7.33(s,1H),7.24–7.18(m,2H),6.99(s,1H),6.61(dd,J=15 .6,1.8Hz,1H),6.19(dq,J=15.6,6.6Hz,1H),2.34(s,3H),2.25(s,3H),1.95(dd,J=6.6,1.8Hz,3H); 13 C{ 1 H}NMR(100MHz, CDCl3)δ140.7,139.0,136.3,132.5,132.3,131.4,131.2,130.9,128.4,127.5,127.2,120.8,20.0,19.2,18.9; IR(KBr):ν max 2925,1646,1480,1442,1267,1070,1011,962,698cm -1 ;HRMS(EI)m / z:[M] + Calcd for C 17 H 17 79 Br,C 17 H 17 81 Br300.0514,302.0493; Found 300.0506,302.0485.

[0059] Example 5: Synthesis of (E)-2,4',5-trimethyl-4-propenyl-1,1'-biphenyl

[0060] In a 25 mL reactor, 2-(chloromethyl)-4',5-dimethyl-1,1'-biphenyl (0.069 g, 0.3 mmol), palladium chloride (0.003 g, 0.015 mmol), tert-butyldiphenylphosphine (0.015 g, 0.06 mmol), and 2 mL of anhydrous 1,4-dioxane were added. The mixture was stirred at room temperature under nitrogen for 24 hours. Acetic acid (0.036 mg, 0.6 mmol) was added, and the mixture was stirred at 40°C for 12 hours. Column chromatography (silica gel, 200-300 mesh; developing solvent: petroleum ether) yielded 0.062 g of (E)-2,4',5-trimethyl-4-propenyl-1,1'-biphenyl in a 54% yield.

[0061]

[0062] White solid; melting point 59-60℃; 1 H NMR(400MHz, CDCl3)δ7.32(s,1H),7.25–7.19(m,4H),7.02(s,1H),6.62(dd,J=15.7,2.0Hz,1H), 6.17(dq,J=15.6,6.6Hz,1H),2.41(s,3H),2.34(s,3H),2.26(s,3H),1.94(dd,J=6.6,1.8Hz,3H); 13 C{ 1 H}NMR(100MHz, CDCl3)δ140.3,138.9,136.2,135.8,132.7,132.1,131.7,129.1,128.7,128.6,127.4,126.8,21.2,20.1,19.3,18.9; IR(KBr):ν max 3020,2922,2853,1650,1489,1446,1377,962,889,815cm -1 ;HRMS(EI)m / z:[M] + Calcd for C 18 H 20 236.1565; Found 236.1556.

[0063] Example 6: Synthesis of (E)-2,5-dimethyl-4-propenyl-4'-trifluoromethoxy-1,1'-biphenyl

[0064] The operation was the same as that in Example 5. 2-(chloromethyl)-5-methyl-4'-(trifluoromethoxy)-1,1'-biphenyl was reacted to obtain 0.051 g of (E)-2,5-dimethyl-4-propenyl-4'-trifluoromethoxy-1,1'-biphenyl with a yield of 55%.

[0065]

[0066] Brown oily liquid; 1 H NMR (400MHz, CDCl3) δ7.37–7.29(m,3H),7.25–7.21(m,2H),6.98(s,1H),6.59(dd,J=15.6,1. 9Hz,1H),6.16(dq,J=15.6,6.6Hz,1H),2.32(s,3H),2.22(s,3H),1.92(dd,J=6.6,1.8Hz,3H); 13 C{ 1 H}NMR (100MHz, CDCl3) δ148.1,140.6,138.9,136.4,132.6,132.3,131.6,130.5,128.4,127.5,127.2,120.5,19.9,19.2,18.8; 19 F NMR(376MHz, CDCl3)δ-57.79; IR(neat):ν max 2923,2855,1636,1490,1444,1258,1222,1165,964,750,696cm -1 ;HRMS(EI)m / z:[M] + Calcd for C 18 H 17 F3O306.1231;Found 306.1222.

[0067] Example 7: Synthesis of (E)-1,2,4-trimethyl-5-propenylbenzene

[0068] The operation was the same as in Example 5, and 0.027 g of (E)-1,2,4-trimethyl-5-propenylbenzene was obtained from 1-(chloromethyl)-2,4-dimethylbenzene with a yield of 56%.

[0069]

[0070] Brown oily liquid; 1H NMR (400MHz, CDCl3) δ7.17 (s, 1H), 6.89 (s, 1H), 6.53 (dd, J = 15.6, 1.9Hz, 1H), 6.06 (dq, J=15.6,6.6Hz,1H),2.26(s,3H),2.21(s,3H),2.20(s,3H),1.88(dd,J=6.6,1.8Hz,3H); 13 C{ 1 H}NMR(100MHz, CDCl3)δ135.0,134.4,133.9,132.1,131.5,128.7,126.7,125.8,19.31,19.27,19.1,18.8.IR(neat):ν max 2919,2862,1647,1502,1459,1377,963,870,840,803cm -1 ;HRMS(EI)m / z:[M] + Calcd for C 12 H 16 160.1252; Found 160.1243.

[0071] Example 8: Synthesis of (E)-2-(2,5-dimethyl-4-propenylphenyl)naphthalene

[0072] The operation was the same as in Example 5, and 0.051 g of (E)-2-(2,5-dimethyl-4-propenylphenyl)naphthalene was obtained from 2-(2-(chloromethyl)-5-methylphenyl)naphthalene with a yield of 62%.

[0073]

[0074] Brown oily liquid; 1 H NMR (400MHz, CDCl3) δ7.89–7.82(m,3H),7.76(s,1H),7.50–7.44(m,3H),7.34(s,1H),7.10(s,1H),6.62(d d,J=15.6,1.8Hz,1H),6.17(dq,J=15.6,6.6Hz,1H),2.34(s,3H),2.27(s,3H),1.93(dd,J=6.6,1.8Hz,3H); 13 C{ 1H}NMR (100MHz, CDCl3) δ140.3,139.5,136.1,133.4,132.9,132.3,131.9,128.6,128.0,127 .8,127.73,127.69,127.5,127.4,127.0,126.1,125.8,77.3,20.1,19.3,18.9;IR(neat):ν max 3053,3016,2923,2852,1631,1495,1445,1377,1267,1131,963,857,820,749cm -1 ;HRMS(EI)m / z:[M] + Calcd for C 21 H 20 272.1565; Found 272.1558.

[0075] Example 9: Synthesis of ((E)-2-(2,5-dimethyl-4-propenylphenyl)thiophene

[0076] The operation was the same as in Example 5, and 0.039 g of (E)-2-(2,5-dimethyl-4-propenylphenyl)thiophene was obtained from 2-(2-(chloromethyl)-5-methylphenyl)thiophene with a yield of 57%.

[0077]

[0078] Brown oily liquid; 1 H NMR (400MHz, CDCl3) δ7.28–7.25(m,1H),7.22(s,1H),7.14–7.10(m,1H),7.09–7.06(m,1H),7.01(s,1H),6. 50(dd,J=15.6,1.8Hz,1H),6.07(dq,J=15.8,6.7Hz,1H),2.23(d,J=3.2Hz,6H),1.84(dd,J=6.6,1.8Hz,3H); 13 C{ 1 H}NMR(100MHz, CDCl3)δ142.1,136.0,134.9,133.0,132.2,131.5,129.0,128.5,127.5,126.9,124.8,122.3,20.4,19.2,18.9; IR(neat):ν max 2923,1691,1607,1448,1377,1080,1035,964,889,857,789,723cm -1;HRMS(EI)m / z:[M] + Calcd forC 15 H 16 S228.0973;Found 228.0966.

Claims

1. A method for preparing a polysubstituted propenyl aromatic compound, characterized in that: Using halogenated methyl aromatic hydrocarbons and their derivatives, and allyl tributyltin as raw materials, in the presence of palladium and phosphine catalysts, in an anhydrous organic solvent, react at room temperature for 24 hours, then add acid and react at 40°C for 12 hours to obtain the corresponding polysubstituted propenyl aromatic compounds. The synthetic route is as follows: Where R 1 Select methyl, 2-naphthyl; The molar ratio of halomethyl aromatic hydrocarbons and their derivatives to allyltributyltin is 1:1; The molar ratio of halomethyl aromatic hydrocarbons and their derivatives to the phosphine catalyst is 1:0.05; The molar ratio of the halogenated methyl aromatic hydrocarbon and its derivatives to the acid is 1:2; The molar ratio of halogenated methyl aromatic hydrocarbons and their derivatives to palladium is 1:0.05; The molar concentration of halogenated methyl aromatic hydrocarbons and their derivatives in the system is 0.15 mmol / mL.

2. The preparation method according to claim 1, characterized in that The palladium is one or a mixture of two or more of trisdibenzylideneacetone palladium, palladium acetate, palladium chloride, bis(dibenzylideneacetone) palladium, palladium pivalate, palladium acetylacetonate, ditriphenylphosphine palladium diacetate, ethylenediaminepalladium chloride, bis(tricyclohexylphosphine)palladium dichloride, and palladium trifluoroacetate.

3. The preparation method according to claim 1, characterized in that The phosphine catalyst is triphenylphosphine, tri-p-tolylphosphine, tri-p-methoxyphenylphosphine, tri-p-fluorophenylphosphine, tert-butyldiphenylphosphine, tricyclohexylphosphine, tri(2-furyl)phosphine, 1,4-bis(diphenylphosphino)butane, and 1,1'-bis(diphenylphosphino)ferrocene.

4. The preparation method according to claim 1, characterized in that The anhydrous organic solvent is one or a mixture of two or more of dichloromethane, tetrahydrofuran, 1,4-dioxane, ether, methyl tert-butyl ether, toluene, acetonitrile, methyl cyclopentyl ether, and 1,2-dichloroethane.

5. The preparation method according to claim 1, characterized in that The acid is one or a mixture of two or more of p-toluenesulfonic acid monohydrate, trifluoroacetic acid, acetic acid, fluoroboric acid, methanesulfonic acid and trifluoromethanesulfonic acid.

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