CN111944539A - Fluropiperazine-based benzoxazole liquid crystal compound and preparation method thereof - Google Patents
Fluropiperazine-based benzoxazole liquid crystal compound and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a liquid crystal compound based on fluoropiperazine benzoxazole, which belongs to the technical field of organic synthesis and has a structure shown as a formula (I), wherein in the formula (I), Fm、FnThe hydrogen on the benzene ring is replaced by fluorine atoms, m and n are the replacing numbers of the fluorine atoms, and the values are both 1 or 2; m is-NO2、‑Cl、‑CH3or-H; r is C3-16 straight-chain alkyl. The invention also provides a preparation method of the liquid crystal compound based on the fluoropiperazine benzoxazole. The liquid crystal compound provided by the invention takes biphenyl-benzoxazole as a crystal-forming unit, an alkyl chain as a flexible group, fluorine atoms as lateral substituents, and different substituents (methyl and NO) are introduced into a terminal group2Cl, H) with liquid crystal state, showing smectic phase, and can be used for special liquid crystal materialMeanwhile, the preparation method of the liquid crystal compound based on the fluoropiperazine benzoxazole is simple to operate and high in product yield and purity. The structure is shown as the following formula (I):
Description
Technical Field
The invention belongs to the technical field of organic synthesis, and particularly relates to a fluoropiperazine-based benzoxazole liquid crystal compound and a preparation method thereof.
Background
With the rapid development of liquid crystal displays, liquid crystal materials have been studied in depth. Among many research fields, polar aromatic heterocyclic liquid crystal materials are one of the important fields of liquid crystal research. The polar aromatic heterocyclic compound has polar hetero atoms, so that the molecular polarity can be changed, and the introduction of the piperazine ring can change the phase transition temperature range, the electrical anisotropy, the optical anisotropy and the like of liquid crystal molecules, and is always an important aspect in the field of liquid crystal research, so that the functional modification is carried out on liquid crystal materials.
Disclosure of Invention
In order to solve the problems, the invention provides a compound based on fluoropiperazine and benzoxazole and a preparation method thereof. The compound takes biphenyl-benzoxazole as a crystal-forming unit, an alkyl chain as a flexible group, fluorine atoms as lateral substituents, and different substituents (methyl and NO) are introduced into an end group2Cl and H) has a liquid crystal state, shows a smectic phase, can be used for special liquid crystal materials, and simultaneously, synthesizes the lateral fluorine substituted biphenyl compound containing the benzoxazole end group, and has simple operation, high product yield and high purity.
The invention provides a fluoropiperazine-based benzoxazole liquid crystal compound, which has a structure shown as a formula (I),
in the formula (I), the compound is shown in the specification,
Fm、Fnall hydrogen on the benzene ring is replaced by fluorine atoms, m and n are the number of fluorine atoms, and the values are both 1 or 2;
m is-NO2、-Cl、-CH3or-H;
r is C3-16 straight-chain alkyl.
Preferably, the liquid crystal compound specifically includes any one of the following compounds,
the second purpose of the invention is to provide a preparation method of the fluoropiperazine-based benzoxazole liquid crystal compound, which comprises the following preparation steps:
s1, uniformly dispersing the compound of the formula (II), alkali and RX as raw materials in DMF, and reacting at 60-110 ℃ for 4-10 h to obtain a compound of the formula (III);
s2, uniformly dispersing the compound of the formula (III) and N-bromosuccinimide serving as raw materials in a solvent, and reacting at 40-80 ℃ for 4-10 hours to obtain a compound of the formula (IV);
s3, under the protection of nitrogen or inert gas, adding a compound of formula (IV), a compound of formula (V) and alkali serving as raw materials into a certain amount of solvent by taking Pd as a catalyst, and reacting at 40-80 ℃ for 4-10 h to obtain a compound of formula (VI);
s4, dispersing the compound of the formula (VI) and the compound of the formula (VII) into a solvent, reacting at 40-80 ℃ for 4-10 h, adding an epoxy reagent, and continuing to react for 4-8 h to obtain the liquid crystal compound based on the fluoropiperazine benzoxazole as shown in the formula (I);
the preparation route is as follows:
in the formulae (II), (III), (IV), (V), (VI), (VII), (I) and RX,
Fm、Fnall hydrogen on the benzene ring is replaced by fluorine atoms, m and n are the number of fluorine atoms, and the values are both 1 or 2;
m is-NO2、-Cl、-CH3or-H;
r is C3-16 straight-chain alkyl;
x is Br or I;
w is O or S.
Preferably, the compound of formula (II) is 1- (3-fluorophenyl) piperazine or 1- (2, 3-difluorophenyl) piperazine.
Preferably, in S1 and S3, the base comprises one or more of potassium carbonate, sodium tert-butoxide and potassium tert-butoxide; wherein, in S1, the molar ratio of the compound of formula (II) to the base is 1: 1-2; s3, wherein the molar ratio of the compound of formula (iv) to the base is 1:1 to 2.
Preferably, the molar ratio of the compound of formula (iii) to the N-bromosuccinimide is 1: 1.
preferably, the molar ratio of the compound of formula (iv) to the compound of formula (v) is 1: 1.
preferably, the Pd catalyst is tetrakis (triphenylphosphine) palladium, palladium acetate or tris-dibenzylideneacetone dipalladium; the molar ratio of the compound of the formula (IV) to the Pd catalyst is 1: 1-2.
Preferably, the epoxidizing agent is 2, 3-dichloro-5, 6-dicyanobenzoquinone, iodobenzene acetate or lead tetraacetate; the molar ratio of the compound of the formula (VI), the compound of the formula (VII) and the epoxidation reagent is 1: 1: 2-4.
Preferably, the solvent is one or more of chloroform, dichloroethane and chloroform.
Compared with the prior art, the invention has the beneficial effects that:
the liquid crystal compound provided by the invention takes biphenyl-benzoxazole as a crystal-forming unit, an alkyl chain as a flexible group, fluorine atoms as lateral substituents, and different substituents (methyl and NO) are introduced into a terminal group2Cl and H) has a liquid crystal state, shows a smectic phase, can be used for special liquid crystal materials, and simultaneously, the preparation method based on the fluoropiperazine benzoxazole liquid crystal compound has the advantages of simple operation, high product yield and high purity.
Drawings
FIG. 1 is a differential scanning calorimetry trace of a liquid crystal compound prepared in example 1 of the present invention.
FIG. 2 is a liquid crystal texture pattern of the liquid crystal compound prepared in example 1 of the present invention at a temperature of 136 ℃ during temperature rise.
FIG. 3 is a liquid crystal texture pattern of the liquid crystal compound prepared in example 1 of the present invention at a temperature of 130 ℃ during cooling.
Detailed Description
In order to make the technical solutions of the present invention better understood and implemented by those skilled in the art, the present invention is further described below with reference to the following specific embodiments and the accompanying drawings, but the embodiments are not meant to limit the present invention.
The experimental methods and the detection methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials are commercially available, unless otherwise specified.
The compound provided by the invention takes biphenyl-benzoxazole as a crystal-forming unit, an alkyl chain as a flexible group, fluorine atoms as lateral substituents, and different substituents (methyl and NO) are introduced into an end group2Cl and H) has a liquid crystal state, shows a smectic phase, can be used for special liquid crystal materials, and simultaneously, synthesizes the lateral fluorine substituted biphenyl compound containing the benzoxazole end group, and has simple operation, high product yield and high purity.
The invention provides a fluoropiperazine-based benzoxazole liquid crystal compound which has a structure shown as a formula (I),
in the formula (I), the compound is shown in the specification,
Fm、Fnall hydrogen on the benzene ring is replaced by fluorine atoms, m and n are the number of fluorine atoms, and the values are both 1 or 2;
m is-NO2、-Cl、-CH3or-H;
r is C3-16 straight-chain alkyl.
The compound provided by the invention takes biphenyl-benzoxazole as a crystal-forming unit, an alkyl chain as a flexible group, a fluorine atom as a lateral substituent, and the terminal groupIntroduction of different substituents (methyl, NO)2Cl and H) has a liquid crystal state, shows a smectic phase, can be used for special liquid crystal materials, and simultaneously, synthesizes the lateral fluorine substituted biphenyl compound containing the benzoxazole end group, and has simple operation, high product yield and high purity.
Specific examples of the fluoropiperazine-based benzoxazole liquid crystal compound of the present invention are shown below:
in the following, we provide specific synthetic methods for preparing the above compounds.
Example 1
A liquid crystal compound based on fluoropiperazine benzoxazole has a structure shown as a formula (Ib),
the preparation method of the fluoropiperazine benzoxazole-based liquid crystal compound shown as the formula (Ib) specifically comprises the following steps:
(1) preparation of 1- (3-fluorophenyl) -4-pentylpiperazine:
adding 18g of 1- (3-fluorophenyl) piperazine, 15g of 1-bromopentane and 20.7g of potassium carbonate into DMF, stirring, heating to 80 ℃, reacting for 8 hours, filtering, pouring into petroleum ether, filtering, and drying to obtain 20g of 1- (3-fluorophenyl) -4-pentylpiperazine, wherein the yield is 80%, and the purity is 97.8%;
1H-NMR(CDCl3,300MHz)(ppm):6.91(m,2H),6.71(m,1H),6.51(m,1H),3.4～3.5(m,4H),3.01(m,2H),1.3～1.4(m,6H),0.92(t,J＝6.6Hz,3H).MALDI-MS m/z(rel.int.):calcd 250.18found 250.13；
the reaction equation is as follows:
(2) preparation of 1- (4-bromo-3-fluorophenyl) -4-pentylpiperazine:
20g of 1- (3-fluorophenyl) -4-pentylpiperazine, 14.2g of NBS (N-bromosuccinimide) and 150ml of chloroform were stirred, the temperature was raised to 60 ℃ to react for 6 hours, the chloroform was distilled off and recrystallized from ethanol to obtain 22.3g of 1- (4-bromo-3-fluorophenyl) -4-pentylpiperazine with the yield: 83 percent and the purity is 98.3 percent;
1H-NMR(CDCl3,300MHz)(ppm):7.23(d,J＝8.4Hz,1H),6.25(d,J＝8.4Hz,1H),6.19(s,1H),3.4～3.5(m,4H),3.01(m,2H),1.3～1.4(m,6H),0.89(t,J＝6.6Hz,3H).MALDI-MS m/z(rel.int.):calcd 328.10found 328.12；
the reaction equation is as follows:
(3) preparation of 2,3' -difluoro-4 ' - (4-pentylpiperazin-1-yl) - [1,1' -biphenyl ] -4-carbaldehyde:
under the protection of nitrogen, 22.3g of 1- (4-bromo-3-fluorophenyl) -4-pentylpiperazine, 32.4g of potassium carbonate, 12.6g of 2, 3-difluorobenzaldehyde-4-borate and 0.6g of dipalladium tris-dibenzylideneacetone were added to 200ml of toluene, and after 4 hours of reaction, the mixture was filtered and recrystallized from ethanol and toluene to obtain 19.1g of 2,3' -difluoro-4 ' - (4-pentylpiperazin-1-yl) - [1,1' -biphenyl ] -4-carbaldehyde, with the yield: 72 percent and the purity is 97.6 percent;
1H-NMR(CDCl3,300MHz)(ppm):10.23(s,1H),7.65(d,J＝8.4Hz,1H),7.59(d,J＝8.4Hz,1H),7.52(s,1H),7.10(d,J＝8.4Hz,1H),7.03(s,1H),6.65(d,J＝8.4Hz,1H),3.4～3.5(m,4H),3.01(m,2H),1.28～1.35(m,6H),0.87(t,J＝6.6Hz,3H).MALDI-MS m/z(rel.int.):calcd 372.20 found 372.23；
the reaction equation is as follows:
(4) preparation of 5-methyl-2- (2,3' -difluoro-4 ' - (4-pentylpiperazin-1-yl) - [1,1' -biphenyl ] -4-yl) benzo [ d ] oxazole:
adding 19.1g of 2,3 '-difluoro-4' - (4-pentylpiperazin-1-yl) - [1,1 '-biphenyl ] -4-formaldehyde and 9.1g of 4-methyl-2-aminophenol into 300ml of dichloroethane, heating to 80 ℃, reacting for 6h, adding 11.1g of 2, 3-dichloro-5, 6-dicyanobenzoquinone, continuing to react, after the reaction is completed, adding 300ml of water, washing with water, separating, concentrating, recrystallizing, and obtaining 15.7g of 5-methyl-2- (2,3' -difluoro-4 '- (4-pentylpiperazin-1-yl) - [1,1' -biphenyl ] -4-yl) benzo [ d ] oxazole, namely the fluoropiperazine-based benzoxazole liquid crystal compound shown in the formula (Ib), the yield is 65 percent, and the purity is 98.7 percent;
1H-NMR(CDCl3,300MHz)(ppm):7.95(d,J＝8.4Hz,1H),7.78(d,J＝8.4Hz,1H),7.74(s,1H),7.69(d,J＝8.4Hz,1H),7.62(s,1H),7.34(s,1H),7.18(d,J＝8.4Hz,1H),7.15(d,J＝8.4Hz,1H),6.91(d,J＝8.4Hz,1H),3.4～3.5(m,4H),3.05(m,2H),2.45(S,3H)1.28～1.38(m,6H),0.87(t,J＝6.6Hz,3H).MALDI-MS m/z(rel.int.):calcd 475.24 found 475.21；
the reaction equation is as follows:
the 5-methyl-2- (2,3 '-difluoro-4' - (4-pentylpiperazin-1-yl) - [1,1 '-biphenyl ] -4-yl) benzo [ d ] oxazole obtained in the example was characterized by DSC-60 type differential scanning calorimeter and XPN-300E type hot stage polarization microscope, and the results are shown in FIGS. 1-3, as can be seen from FIG. 1, the prepared 5-methyl-2- (2,2', 3-trifluoro-4 '- (4-pentylpiperazin-1-yl) - [1,1' -biphenyl ] -4-yl) benzo [ d ] oxazole had liquid crystal phase during the temperature raising and lowering processes, and the liquid crystal phase interval is melting point: 56 ℃; clearing the bright spots: at 150 ℃. As can be seen from fig. 2 and 3, the compound has a typical smectic grain texture.
Example 2
A liquid crystal compound based on fluoropiperazine benzoxazole has a structure shown as the following formula (IC),
the preparation method of the fluoropiperazine-based benzoxazole liquid crystal compound shown as the formula (ic) specifically comprises the following steps:
(1) preparation of 1- (2, 3-difluorophenyl) -4-heptylpiperazine:
adding 19.8g of 1- (2, 3-fluorophenyl) piperazine, 17.9g of 1-bromoheptane and 20.7g of potassium carbonate into DMF, stirring, heating to 60 ℃, reacting for 6h, filtering, pouring into petroleum ether, filtering, and drying to obtain 24.3g of 1- (2, 3-difluorophenyl) -4-heptylpiperazine, wherein the yield is 82% and the purity is 98.1%;
1H-NMR(CDCl3,300MHz)(ppm):6.89(m,1H),6.52(d,J＝8.4Hz,1H),6.48(d,J＝8.4Hz,1H),3.4～3.5(m,4H),3.01(m,2H),1.36(m,2H),1.26～1.3(m,8H),0.90(t,J＝6.6Hz,3H).MALDI-MS m/z(rel.int.):calcd 296.21，found296.17；
the reaction equation is as follows:
(2) preparation of 1- (4-bromo-2, 3-difluorophenyl) -4-heptylpiperazine:
24.3g of 1- (2, 3-fluorophenyl) -4-heptylpiperazine, 14.6g of NBS and 150ml of chloroform were stirred, the temperature was raised to 70 ℃ to react for 5 hours, the chloroform was distilled off, and recrystallization was performed with ethanol to obtain 23.0g of 1- (4-bromo-2, 3-difluorophenyl) -4-heptylpiperazine, yield: 75 percent and the purity is 97.6 percent;
1H-NMR(CDCl3,300MHz)(ppm):7.11(d,J＝8.4Hz,1H),6.48(d,J＝8.4Hz,1H),3.4～3.5(m,4H),3.0(m,2H),1.35(m,2H),1.25～1.3(m,8H),0.89(t,J＝6.6Hz,3H).MALDI-MS m/z(rel.int.):calcd 374.12，found 374.15；
the reaction equation is as follows:
(3) preparation of 2',2, 3' -trifluoro-4 '- (4-heptylpiperazin-1-yl) - [1,1' -biphenyl ] -4-carbaldehyde:
under the protection of argon, 23.0g of 1- (4-bromo-3-fluorophenyl) -4-heptylpiperazine, 13g of sodium carbonate, 10.3g of 2, 3-difluorobenzaldehyde-4-borate and 0.6g of dipalladium tris (dibenzylideneacetone) are added to 200ml of toluene, reacted for 6 hours, filtered and recrystallized from ethanolic toluene to obtain 21.8g of 2',2, 3' -trifluoro-4 '- (4-heptylpiperazin-1-yl) - [1,1' -biphenyl ] -4-carbaldehyde, and the yield: 85 percent and the purity is 98.2 percent;
1H-NMR(CDCl3,300MHz)(ppm):10.36(s,1H)，8.01(d,J＝8.4Hz,1H),7.71(s,1H)，7.61(d,J＝8.4Hz,1H),7.34(d,J＝8.4Hz,1H),6.68(d,J＝8.4Hz,1H),3.4～3.5(m,4H),2.99(m,2H),1.36(m,2H),1.25～1.3(m,8H),0.88(t,J＝6.6Hz,3H).MALDI-MS m/z(rel.int.):calcd 418.22，found 418.25；
the reaction equation is as follows:
(4) preparation of 5-chloro-2- (2', 3,3' -trifluoro-4 '- (4-heptapiperazin-1-yl) - [1,1' -biphenyl ] -4-yl) benzo [ d ] oxazole:
adding 21.8g of 2',2, 3' -trifluoro-4 '- (4-heptylpiperazin-1-yl) - [1,1' -biphenyl ] -4-formaldehyde and 7.5g of 4-chloro-2-aminophenol into 300ml of dichloroethane, heating to 80 ℃, reacting for 6h, adding 11.8g of 2, 3-dichloro-5, 6-dicyanobenzoquinone, continuing to react, after the reaction is completed, adding 300ml of water, washing with water, separating liquid, concentrating and recrystallizing to obtain 16.7g of 5-chloro-2- (2', 3,3' -trifluoro-4 '- (4-heptylpiperazin-1-yl) - [1,1' -biphenyl ] -4-yl) benzo [ d ] oxazole, namely the liquid crystal compound based on the fluoropiperazine benzoxazole shown in the formula (IC), the yield is 56.2 percent, and the purity is 98.2 percent;
1H-NMR(CDCl3,300MHz)(ppm):7.94(d,J＝8.4Hz,1H),7.81(s,1H)，8.75(d,J＝8.4Hz,1H),7.70(s,1H)，7.40(d,J＝8.4Hz,1H),7.32(d,J＝8.4Hz,1H),7.02(d,J＝8.4Hz,1H),6.67(d,J＝8.4Hz,1H),3.4～3.5(m,4H),3.00(m,2H),1.35(m,2H),1.25～1.31(m,8H),0.89(t,J＝6.6Hz,3H).MALDI-MS m/z(rel.int.):calcd418.22，found 418.25。
the reaction equation is as follows:
example 3
A liquid crystal compound based on fluoropiperazine benzoxazole has a structure shown as the following formula (Id),
the preparation method of the fluoropiperazine-based benzoxazole liquid crystal compound shown as the formula (id) specifically comprises the following steps:
(1) preparation of 1- (3-fluorophenyl) -4-propylpiperazine:
adding 18g of 1- (3-fluorophenyl) piperazine, 124.6g of 1-bromopentane and 13.8g of potassium carbonate into DMF, stirring, heating to 70 ℃, reacting for 5 hours, filtering, pouring into petroleum ether, filtering, and drying to obtain 18.6g of 1- (3-fluorophenyl) -4-propylpiperazine, wherein the yield is 84%, and the purity is 98.4%;
1H-NMR(CDCl3,300MHz)(ppm):6.92(m,2H),6.71(m,1H),6.51(m,1H),3.4～3.5(m,4H),2.46(m,2H),1.44(m,2H),0.87(t,J＝6.6Hz,3H).MALDI-MS m/z(rel.int.):calcd 222.15，found 222.13；
the reaction equation is as follows:
(2) preparation of 1- (4-bromo-3-fluorophenyl) -4-propylpiperazine:
stirring 18.6g of 1- (3-fluorophenyl) -4-propylpiperazine, 14.9g of NBS and 150ml of trichloromethane, heating to 60 ℃, reacting for 6 hours, evaporating the trichloromethane, and recrystallizing with ethanol to obtain 20.4g of 1- (4-bromo-3-fluorophenyl) -4-propylpiperazine with the yield: 80.3 percent and the purity is 98.1 percent;
1H-NMR(CDCl3,300MHz)(ppm):7.20(s,1H),7.01(d,J＝8.4Hz,1H),6.60(d,J＝8.4Hz,1H),3.4～3.5(m,4H),2.45(m,2H),1.43(m,2H),0.89(t,J＝6.6Hz,3H).MALDI-MS m/z(rel.int.):calcd 300.06，found 300.10；
the reaction equation is as follows:
(3) preparation of 3,3' -difluoro-4 ' - (4-propylpiperazin-1-yl) - [1,1' -biphenyl ] -4-carbaldehyde:
under the protection of nitrogen, 20.4g of 1- (4-bromo-3-fluorophenyl) -4-propylpiperazine, 14.1g of potassium carbonate, 11.4g of 4-boronic acid-3-fluorobenzaldehyde and 0.8g of tetrakis (triphenylphosphine) palladium are added into 200ml of toluene, reacted for 8 hours, filtered and recrystallized from ethanol and toluene to obtain 17.1g of 3,3' -difluoro-4 ' - (4-propylpiperazin-1-yl) - [1,1' -biphenyl ] -4-carbaldehyde, and the yield is as follows: 73 percent and the purity is 97.9 percent;
1H-NMR(CDCl3,300MHz)(ppm):10.08(s,1H),8.01(d,J＝8.4Hz,1H),7.70(s,1H),7.61(d,J＝8.4Hz,1H),7.33(s,1H),7.17(d,J＝8.4Hz,1H),6.90(d,J＝8.4Hz,1H),3.4～3.5(m,4H),2.44(m,2H),1.45(m,2H),0.89(t,J＝6.6Hz,3H).MALDI-MS m/z(rel.int.):calcd 344.17，found 344.21；
the reaction equation is as follows:
(4) preparation of 5-nitro-2- (3,3' -difluoro-4 ' - (4-propylpiperazin-1-yl) - [1,1' -biphenyl ] -4-yl) benzo [ d ] oxazole:
adding 17.1g of 3,3 '-difluoro-4' - (4-propylpiperazin-1-yl) - [1,1 '-biphenyl ] -4-formaldehyde and 7.7g of 4-nitro-2-aminophenol into 300ml of dichloroethane, heating to 80 ℃, reacting for 6h, adding 11.3g of 2, 3-dichloro-5, 6-dicyanobenzoquinone, continuing to react, after the reaction is completed, adding 300ml of water, washing with water, separating, concentrating, recrystallizing, and obtaining 12.4g of 5-nitro-2- (3,3' -difluoro-4 '- (4-propylpiperazin-1-yl) - [1,1' -biphenyl ] -4-yl) benzo [ d ] oxazole, namely the liquid crystal compound based on the fluoropiperazine benzoxazole shown in the formula (Id), the yield is 52.2 percent, and the purity is 98.0 percent;
1H-NMR(CDCl3,300MHz)(ppm):8.17(d,J＝8.4Hz,1H),8.01(d,J＝8.4Hz,1H),7.94(d,J＝8.4Hz,1H),7.86(s,1H),7.71(s,1H),7.34(s,1H),7.18(d,J＝8.4Hz,1H),7.02(d,J＝8.4Hz,1H),6.90(d,J＝8.4Hz,1H),3.4～3.5(m,4H),2.44(m,2H),1.44(m,2H),0.88(t,J＝6.6Hz,3H).MALDI-MS m/z(rel.int.):calcd 478.18，found 478.23。
the reaction equation is as follows:
it will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, it is intended that such changes and modifications be included within the scope of the appended claims and their equivalents.
Claims (10)
1. A flupiperazines-based benzoxazole liquid crystal compound is characterized by having a structure shown as a formula (I),
in the formula (I), the compound is shown in the specification,
Fm、Fnthe hydrogen on the benzene ring is replaced by fluorine atoms, m and n are the number of the fluorine atoms, and the value is 1 or 2;
m is-NO2、-Cl、-CH3or-H;
r is C3-16 straight-chain alkyl;
w is O or S.
2. The fluoropiperazine benzoxazole based liquid crystal compound according to claim 1, wherein the liquid crystal compound specifically comprises any one of the following compounds,
3. a preparation method of the fluoropiperazine benzoxazole-based liquid crystal compound according to claim 1 or 2, comprising the following preparation steps:
s1, uniformly dispersing the compound of the formula (II), alkali and RX as raw materials in DMF, and reacting at 60-110 ℃ for 4-10 h to obtain a compound of the formula (III);
s2, uniformly dispersing the compound of the formula (III) and N-bromosuccinimide serving as raw materials in a solvent, and reacting at 40-80 ℃ for 4-10 hours to obtain a compound of the formula (IV);
s3, under the protection of nitrogen or inert gas, adding a compound of formula (IV), a compound of formula (V) and alkali serving as raw materials into a certain amount of solvent by taking Pd as a catalyst, and reacting at 40-80 ℃ for 4-10 h to obtain a compound of formula (VI);
s4, dispersing the compound of the formula (VI) and the compound of the formula (VII) into a solvent, reacting at 40-80 ℃ for 4-10 h, adding an epoxy reagent, and continuing to react for 4-8 h to obtain the liquid crystal compound based on the fluoropiperazine benzoxazole as shown in the formula (I);
the preparation route is as follows:
in the formulae (II), (III), (IV), (V), (VI), (VII), (I) and RX,
Fm、Fnall hydrogen on the benzene ring is replaced by fluorine atoms, m and n are the number of fluorine atoms, and the value is 1 or 2;
m is-NO2、-Cl、-CH3or-H;
r is C3-16 straight-chain alkyl;
x is Br or I;
w is O or S.
4. The method for preparing a fluoropiperazine-based benzoxazole liquid crystal compound according to claim 3, wherein the compound of formula (II) is 1- (3-fluorophenyl) piperazine or 1- (2, 3-difluorophenyl) piperazine.
5. The method for preparing a fluoropiperazine-based benzoxazole liquid crystal compound according to claim 3, wherein in S1 and S3, the base comprises one or more of potassium carbonate, sodium tert-butoxide and potassium tert-butoxide; wherein, in S1, the molar ratio of the compound of formula (II) to the base is 1: 1-2; s3, wherein the molar ratio of the compound of formula (iv) to the base is 1:1 to 2.
6. The method for preparing a fluoropiperazine-based benzoxazole liquid crystal compound according to claim 3, wherein the molar ratio of the compound of formula (III) to the N-bromosuccinimide is 1: 1.
7. the preparation method of the fluoropiperazine-based benzoxazole liquid crystal compound according to claim 3, wherein a molar ratio of the compound of formula (IV) to the compound of formula (V) is 1: 1.
8. the method for preparing a fluoropiperazine-based benzoxazole liquid crystal compound according to claim 3, wherein the Pd catalyst is tetrakis (triphenylphosphine) palladium, palladium acetate, or tris-dibenzylideneacetone dipalladium; the molar ratio of the compound of the formula (IV) to the Pd catalyst is 1: 1-2.
9. The method for preparing a fluoropiperazine-based benzoxazole liquid crystal compound according to claim 3, wherein the epoxidizing agent is 2, 3-dichloro-5, 6-dicyanobenzoquinone, iodobenzene acetate, or lead tetraacetate; the molar ratio of the compound of the formula (VI), the compound of the formula (VII) and the epoxidation reagent is 1: 1: 2-4.
10. The method for preparing a fluoropiperazine-based benzoxazole liquid crystal compound according to claim 3, wherein the solvent is one or more of chloroform, dichloroethane, and chloroform.
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