下文更詳細地解釋本發明且揭示較佳實施例。 式I之參數m及n之總和m + n較佳具有1、2或3、尤佳2之值。因此，m較佳為0或1、尤佳1，且n較佳為1。 R1
較佳表示分別具有1至7個或2至7個碳原子之烷氧基、烷基或烯基。 R2
較佳表示具有1至15個碳原子之未經取代之烷基、S-烷基(烷基硫基)、S-烯基(烯基硫基)或烷氧基或具有2至15個C原子之烯基、烯基氧基或炔基，其各自視情況經單鹵化或多鹵化。通式I中之R2
尤佳係具有1至7個C原子、尤佳具有2至5個C原子且極特別具有2個C原子之烷氧基或烷基硫基。 R1
及R2
中碳原子數之總和一起較佳為3、4、5、6、7、8、9或10，尤佳4、5、6、7、8或9。 若式I中之R1
及R2
各自彼此獨立地代表烷基，則該等為直鏈或具支鏈。較佳地，該等基團中每一者為直鏈，且除非另外指示，否則具有1、2、3、4、5、6或7個C原子且因此較佳為甲基、乙基、丙基、丁基、戊基、己基或庚基。 若式I中之R1
及R2
各自彼此獨立地代表烷氧基，則該等為直鏈或具支鏈。較佳地，該等基團中每一者為直鏈，且除非另外指示，否則具有1、2、3、4、5、6或7個C原子且因此較佳為甲氧基、乙氧基、丙氧基、丁氧基、戊氧基、己氧基或庚氧基。 若式I中之R2
在每一情形中彼此都獨立地代表烷基硫基(與S-烷基同義)，則此為直鏈或具支鏈。較佳地，此基團為直鏈，且除非另外指示，否則具有1、2、3、4、5、6或7個C原子且因此較佳為甲基硫基、乙基硫基、丙基硫基、丁基硫基、戊基硫基、己基硫基或庚基硫基。 此外，式I中之R1
及R2
可各自彼此獨立地為具有2至15個C原子之烯基，其為直鏈或具支鏈且具有至少一個C-C雙鍵。其較佳係直鏈且具有2至7個C原子。因此，其較佳係乙烯基、丙-1-或-2-烯基、丁-1-、-2-或-3-烯基、戊-1-、-2-、-3-或-4-烯基、己-1-、-2-、-3-、-4-或-5-烯基或庚-1-、-2-、-3-、-4-、-5-或-6-烯基。若C-C雙鍵之兩個C原子經取代，則烯基可呈E及/或Z異構物(反式/順式)之形式。一般而言，各別E異構物較佳。在烯基中，尤佳者係丙-2-烯基、丁-2-或-3-烯基及戊-3-或-4-烯基。 式I中之R1
及R2
亦可彼此獨立地為具有2至15個C原子之炔基，其係直鏈或具支鏈且具有至少一個C-C三鍵。炔基較佳為1-或2-丙炔基或1-、2-或3-丙炔基。 基團A1
較佳獨立地表示選自下式之二取代環狀基團 及尤其式。 基團A2
較佳在每一情形中獨立地表示選自下式之二取代環狀基團 及尤佳下式之基團。 基團L較佳表示F、Cl、-CF3
或具有1、2或3個碳原子之烷基或烷氧基。 鹵素在本發明上下文中表示氟、氯、溴或碘，特定而言氟或氯。 與本發明結合，除非在本說明書中或申請專利範圍中其他地方另外定義，否則術語「烷基」表示具有1至15個(即1、2、3、4、5、6、7、8、9、10、11、12、13、14或15個)碳原子之直鏈或具支鏈、飽和、脂肪族烴基團。 本發明之式I化合物尤佳選自子式IA、IB、IC及ID，其中R1
、R2
、A1
及A2
具有如針對式I所定義之含義。 式IA、IB、IC及ID之較佳化合物係下式之化合物： 其中「烷基」及「烷基*」各自彼此獨立地表示具有1-7個C原子之直鏈烷基。「烷基」尤佳表示具有2、3、4、5或6個、尤其具有3或5個C原子之烷基。烷基*較佳表示具有1、2、3或4個C原子之烷基。 式I之尤佳化合物係選自下式之彼等： 其中「烷基」係如上文針對IA-1、IB-1等所定義。在該等中，尤佳者係式IB-1-1及IB-2-1、尤其其中烷基表示正丙基之化合物。 若本發明化合物之基團或取代基或本發明化合物本身由於具有(例如)不對稱中心而呈光學活性或立體異構物基團、取代基或化合物之形式，則該等同樣涵蓋於本發明中。此處不言而喻，本發明之通式I化合物可以異構純形式(例如純鏡像異構物、非鏡像異構物、E或Z異構物、反式或順式異構物)存在，或以任何期望比率之複數種異構物之混合物形式(例如外消旋物、E/Z異構物混合物或順式/反式異構物混合物)存在。 針對液晶介質所揭示化合物中之式或-Cyc-之1,4-經取代環己基環較佳具有反式構形，即兩個取代基皆處於熱力學上較佳之椅形構象之赤道位。此類似地應用於四氫吡喃及二噁烷環之較佳構象。 式之1,4-經取代之1-氟環己基環表示式之環，即，在軸向位置經F取代且呈熱力學較佳構象之1,4-反式構形之環己烷環。 通式I化合物可藉由本身已知之方法，如文獻(例如標準著作，例如Houben-Weyl, Methoden der organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart)中所述、確切而言在已知且適於該等反應之反應條件下製備。此處亦可使用其本身已知之變化形式，此處不提及更多細節。 若期望，起始材料亦可不自反應混合物分離、而是立即將其進一步轉化成通式I化合物來原位形成。 在實例中以實例的方式闡述本發明通式I化合物之合成。起始物質可藉由一般可獲得文獻程序獲得或市售可得。 本發明化合物之尤其適宜合成途徑於以下方案中解釋。以下方案中之取代基R1
、R2
及下標m及n具有如針對式I所指示之含義。 式I化合物之合成有利地藉由以下實施：將環己酮5
使用硫偶極體親核試劑(Corey)環氧化，使用HF使環氧化物6
開環，且隨後使用酚化合物(參見方案1)使醇7
酯化，以獲得標題化合物8
(參見式I)。 方案 1
. 式I化合物之說明性合成。R對應於基團R1
-[A1
]n
-。 所繪示反應應視為說明性的。部分反應對於熟習此項技術者而言係基本熟悉的。含有不同環及取代基之化合物係根據所概述合成來製備。方案1中之基團R代表通式I中之一般基團-[A1
]n
-R1
。熟習此項技術者將能夠實施所示合成之相應變化形式以及遵循其他適宜合成途徑以獲得式I化合物。 根據上文所繪示之合成，本發明在一個實施例中亦涵蓋式I化合物之一或多個製備製程。 因此，本發明涵蓋製備式I化合物之製程，其特徵在於其包括如下製程步驟：其中式(A)化合物其中m、A1
及R1
獨立地如式I中所定義， 與式(B)化合物反應其中獨立地 A2
、n及R2
係如式I中所定義。 A與B之反應視情況接著其他製程步驟，此最終產生式I化合物。反應較佳直接產生式I化合物。 本發明之一個態樣亦係式(A)之中間體化合物。出現類似於此處上下文所揭示式I化合物之較佳實施例的化合物之較佳物種。 式(A)化合物可有利地藉由使用HF自相應的環氧乙烷進行環氧化物開環來製備，該等相應的環氧乙烷進而係直接自環己酮獲得。式(A)之中間體化合物可直接轉化為式I之最終化合物。因此，其代表有價值的中間體。 本發明之製程使取代基及參數A1
、A2
、m、n、R1
及R2
能夠簡單且獨立的變化，此乃因兩個環A1
及A2
僅在會聚合成結束時組合於式I化合物中。 製程、在先反應步驟及反應混合物之後續處理基本上可以分批反應或在連續反應程序中實施。連續反應程序涵蓋(例如)在連續攪拌槽反應器、攪拌反應器級聯、環流或交叉流反應器、流管或微型反應器中之反應。反應混合物視情況藉由經由固相過濾、層析、不混溶相間之分離(例如萃取)、吸附至固體支撐物上、藉由蒸餾去除溶劑及/或共沸混合物、選擇性蒸餾、昇華、結晶、共結晶或藉由在膜上奈米過濾來視需要進行處理。 如已提及，通式I化合物可用於液晶介質中。因此，本發明亦係關於包含至少兩種液晶化合物、包含至少一種通式I化合物之液晶介質。 本發明亦係關於除一或多種本發明之式I化合物以外包含2至40種、較佳地4至30種組分作為其他成分之液晶介質。該等介質尤佳地除一或多種本發明化合物以外包含7至25種組分。該等其他成分較佳選自向列型或致向列態(單變型或各向同性)物質，特定而言來自以下類別之物質：氧偶氮苯、亞苄基苯胺、聯苯、聯三苯、1,3-二噁烷、2,5-四氫吡喃、苯甲酸苯基酯或苯甲酸環己基酯、環己烷甲酸之苯基酯或環己基酯、環己基苯甲酸之苯基酯或環己基酯、環己基環己烷甲酸之苯基酯或環己基酯；苯甲酸、環己烷甲酸或環己基環己烷甲酸之環己基苯基酯；苯基環己烷、環己基聯苯、苯基環己基環己烷、環己基環己烷、環己基環己基環己烯、1,4-雙環己基苯、4',4'-雙環己基聯苯、苯基嘧啶或環己基嘧啶、苯基吡啶或環己基吡啶、苯基二噁烷或環己基二噁烷、苯基-1,3-二噻𠮿或環己基-1,3-二噻𠮿、1,2-二苯基乙烷、1,2-二環己基乙烷、1-苯基-2-環己基乙烷、1-環己基-2-(4-苯基環己基)乙烷、1-環己基-2-聯苯乙烷、1-苯基-2-環己基苯基乙烷、視情況鹵化之二苯乙烯、苄基苯基醚、二苯乙炔及經取代肉桂酸。該等化合物中之1,4-伸苯基亦可經單氟化或多氟化。 適宜作為本發明介質之其他成分之最重要化合物可由式(II)、(III)、(IV)、(V)及(VI)來表徵： R'-L-E-R'' (II) R'-L-COO-E-R'' (III) R'-L-OOC-E-R'' (IV) R'-L-CH2
CH2
-E-R'' (V) R'-L-CF2
O-E-R'' (VI) 在式(II)、(III)、(IV)、(V)及(VI)中，L及E可相同或不同，其各自彼此獨立地表示來自由-Phe-、-Cyc-、-Phe-Phe-、-Phe-Cyc-、-Cyc-Cyc-、-Pyr-、-Dio-、-Thp-、-G-Phe-及-G-Cyc-及其鏡像形成之基團之二價基團，其中Phe表示未經取代或氟取代之1,4-伸苯基，Cyc表示反式-1,4-伸環己基或1,4-伸環己烯基，Pyr表示嘧啶-2,5-二基或吡啶-2,5-二基，Dio表示1,3-二噁烷-2,5-二基，Thp表示四氫吡喃-2,5-二基，且G表示2-(反式-1,4-環己基)乙基、嘧啶-2,5-二基、吡啶-2,5-二基、1,3-二噁烷-2,5-二基或四氫吡喃-2,5-二基。 基團L及E中之一者較佳為Cyc或Phe。E較佳為Cyc、Phe或Phe-Cyc。本發明介質較佳包含一或多種選自式(II)、(III)、(IV)、(V)及(VI)之化合物之組分，其中L及E係選自由Cyc及Phe組成之群；且同時一或多種選自式(II)、(III)、(IV)、(V)及(VI)之化合物之組分，其中基團L及E中之一者係選自由Cyc及Phe組成之群且另一基團係選自由-Phe-Phe-、-Phe-Cyc-、-Cyc-Cyc-、-G-Phe-及-G-Cyc-組成之群；且視情況一或多種選自式(II)、(III)、(IV)、(V)及(VI)之化合物之組分，其中基團L及E係選自由-Phe-Cyc-、-Cyc-Cyc-、-G-Phe-及-G-Cyc-組成之群。 在式(II)、(III)、(IV)、(V)及(VI)之化合物之較小子群中，R'及R"各自彼此獨立地表示具有最多8個C原子之烷基、烯基、烷氧基、烷氧基烷基(氧雜烷基)、烯基氧基或烷醯基氧基。此較小子群在下文中稱為群A，且該等化合物係由子式(IIa)、(IIIa)、(IVa)、(Va)及(VIa)提及。在大多數該等化合物中，R'及R"彼此不同，該等基團中之一者通常為烷基、烯基、烷氧基或烷氧基烷基(氧雜烷基)。 在式(II)、(III)、(IV)、(V)及(VI)之化合物之另一較小子群(其稱為群B)中，E表示。 在由子式(IIb)、(IIIb)、(IVb)、(Vb)及(VIb)提及之群B之化合物中，R'及R"係如針對子式(IIa)至(VIa)之化合物所定義且較佳係烷基、烯基、烷氧基或烷氧基烷基(氧雜烷基)。 在式(II)、(III)、(IV)、(V)及(VI)之化合物之進一步較小子群中，R"表示-CN。此子群在下文中稱為群C，且此子群之化合物相應地由子式(IIc)、(IIIc)、(IVc)、(Vc)及(VIc)闡述。在子式(IIc)、(IIIc)、(IVc)、(Vc)及(VIc)之化合物中，R'係如針對子式(IIa)至(VIa)之化合物所定義且較佳為烷基、烯基、烷氧基或烷氧基烷基(氧雜烷基)。 除群A、B及C之較佳化合物以外，具有所建議取代基之其他變體之式(II)、(III)、(IV)、(V)及(VI)之其他化合物亦常見。所有該等物質可藉由自文獻已知之方法或以與其類似之方式獲得。 除本發明之通式I化合物以外，本發明介質較佳包含來自群A、B及/或C之一或多種化合物。本發明介質中來自該等群之化合物之重量比例為： 群A： 0%至90%、較佳20%至90%、特定而言30%至90%。 群B： 0%至80%、較佳10%至80%、特定而言10%至70%。 群C： 0%至80%、較佳5%至80%、特定而言5%至50%。 本發明介質較佳包含1%至40%、尤佳5%至30%之本發明式I化合物。該等介質較佳地包含一種、兩種、三種、四種或五種本發明之式I化合物。 本發明介質係以本身習用之方式製備。通常，較佳在高溫下將組分互相溶解。藉助適宜添加劑，本發明之液晶相可經改良以使得其可用於迄今已揭示所有類型之液晶顯示元件中。此類型之添加劑為熟習此項技術者已知且詳細闡述於文獻(H. Kelker/R. Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980)中。例如，可添加多色染料用於產生彩色客體-主體系統或可添加物質以改良介電各向異性、黏度及/或向列相之配向。 由於其負性Δε，式I化合物尤其適於用於VA-TFT顯示器或被動VA顯示器。 因此，本發明亦係關於含有本發明液晶介質之電光顯示元件。顯示元件較佳係VA-TFT顯示元件(VA：垂直配向(vertical alignment)；TFT：薄膜電晶體)。 根據說明書之本發明實施例之其他組合及變化形式可自技術方案及該等技術方案中之兩個或更多個之組合得出。 在下文中參照工作實例更詳細地解釋本發明，但並不意欲由此受限。熟習此項技術者將能夠自該等實例發現在一般說明中並未詳細給出之工作細節，依照一般專業知識對其進行歸納並將其應用至具體問題中。 除慣用及熟知之縮寫以外，使用以下縮寫：m.p.：熔點；C：液晶相；N：向列相；Sm：層列相(在適當情形中更詳細指定)；I：各向同性相。該等符號間之數字顯示有關物質之轉變溫度。 除非另外指示，否則溫度數據係以℃(攝氏度)表示。 物理、物理化學或電光參數係藉由眾所周知之方法測定，如尤其在手冊「Merck Liquid Crystals - Licristal® - Physical Properties of Liquid Crystals - Description of the Measurement Methods」, 1998, Merck KGaA, Darmstadt中所述。 在上下文中，Δn表示光學各向異性(589 nm, 20℃)且Δε表示介電各向異性(1 kHz, 20℃)。介電各向異性Δε係在20℃及1 kHz下測定。光學各向異性∆n係在20℃及589.3 nm之波長下測定。 本發明化合物之Δε及Δn值、外推澄清點(cl. p.)及旋轉黏度(γ1
)係藉由自由5%至10%各別本發明化合物及90%至95%市售液晶混合物ZLI-2857 (針對Δε、cl. p.)或ZLI-4792 (針對Δn、γ1
) (混合物，Merck KGaA，Darmstadt)組成之液晶混合物直線外推來獲得。實例
起始物質可藉由一般可獲得文獻程序獲得或市售可得。 實例1：步驟 1 於室溫下將第三丁醇鉀(21.9 g, 195.6 mmol)於二甲亞碸(90 ml)中之溶液逐滴添加至酮9
(29.0 g, 130.4 mmol)及三甲基碘化硫鎓(43.0 g, 195.6 mmol)於二甲亞碸(210 ml)中之混合物中。將所得混合物攪拌36 h，隨後添加庚烷(500 ml)，並將混合物再攪拌0.5 h。將庚烷相分離，藉助Celite®過濾，用水洗滌，經Na2
SO4
乾燥並在真空中蒸發。殘餘物(16.7 g)借助Puriflash (300 g SiO2
, 庚烷/甲基第三丁基醚 9:1)純化，獲得呈無色晶體之環氧化物10
(95.8% HPLC)。步驟 2 於-5℃將HF於吡啶中之溶液(65%, 5.0 ml, 185.5 mmol)逐滴添加至環氧化物10
(15.6 g, 61.8 mmol, HPLC: 93.7%)於二氯甲烷(275 ml)中之溶液。將所得混合物於-5℃攪拌1 h且隨後藉助SiO2
層(1 l, 用二氯甲烷洗滌)過濾，獲得呈無色油狀物之醇11
(HPLC: 31.9%)。步驟 3 於10℃將偶氮二甲酸二異丙酯(DIAD, 10.9 ml, 55.5 mmol)逐滴添加至醇11
(10.2 g, 12.6 mmol, HPLC: 31.9%)、酚12
(6.9 g, 47.8 mmol)及三苯基膦(12.5 g, 47.6 mmol)於四氫呋喃(THF, 161 ml)中之攪拌溶液中。將所得混合物於室溫攪拌7天並在45℃攪拌1天，隨後藉助SiO2
層(100 g)過濾並藉由急驟層析(庚烷/甲基第三丁基醚)純化兩次。自異丙醇再結晶兩次，獲得呈無色晶體之最終化合物2
(1.2 g, 25%, HPLC: 99.7%)。1
H NMR: 0.81-1.87 (m, 24H), 2.03-2.15 (m, 2H), 2.25 (d,J
= 2.1 Hz, 3H), 3.98 (d,J
= 16.4 Hz, 2H), 6.68 (ddd,J
= 8.7, 8.1, 1.9 Hz, 1H), 6.82 (ddd,J
= 8.2, 8.2, 2.1 Hz, 1H)；19
F NMR: -140.6 (ddt,J
= 19.3, 7.8, 1.8 Hz, 1F), −159.0 (ddd,J
= 19.4, 7.4, 2.4 Hz, 1F), -165.8 (qt,J
= 24.3, 9.3 Hz, 1F)；EI-MS: 382.3 相：C 91 N 118 I (m.p. 91℃)， Δε = -6.73, Δn=0.0792；γ1
=454 mPa∙s。 類似於實例1製備以下化合物：相：C 72 SmB (61) N 101 I (m.p. 72℃) Δε=-6,25, Δn=0.0762；γ1
=433 mPa∙s。相：C 72 N 144 I (m.p. 72℃) Δε=-8,23, Δn=0.0832；γ1
=706 mPa∙s。相：C 48 N (4) I (m.p. 48℃) Δε=-8.25, Δn=0.0572；γ1
=71 mPa∙s 類似地製備其他說明性化合物：除非另有說明，否則基團R1/2
係直鏈的，即不具支鏈。個別化合物之結構自表1發現。 式Cn
H2n+1
之烷基係無支鏈烷基。 表1. 物理數據<img wi="93" he="75" file="IMG-2/Draw/02_image076.jpg" img-format="jpg"><img wi="93" he="76" file="IMG-2/Draw/02_image078.jpg" img-format="jpg"><img wi="94" he="72" file="IMG-2/Draw/02_image080.jpg" img-format="jpg"><img wi="116" he="64" file="IMG-2/Draw/02_image082.jpg" img-format="jpg"><img wi="93" he="80" file="IMG-2/Draw/02_image084.jpg" img-format="jpg"><img wi="115" he="57" file="IMG-2/Draw/02_image086.jpg" img-format="jpg"><img wi="93" he="75" file="IMG-2/Draw/02_image088.jpg" img-format="jpg"><img wi="116" he="62" file="IMG-2/Draw/02_image090.jpg" img-format="jpg"><img wi="94" he="74" file="IMG-2/Draw/02_image092.jpg" img-format="jpg"><img wi="116" he="57" file="IMG-2/Draw/02_image094.jpg" img-format="jpg"><img wi="107" he="85" file="IMG-2/Draw/02_image096.jpg" img-format="jpg"><img wi="115" he="56" file="IMG-2/Draw/02_image098.jpg" img-format="jpg"><img wi="107" he="88" file="IMG-2/Draw/02_image100.jpg" img-format="jpg"><img wi="168" he="68" file="IMG-2/Draw/02_image102.jpg" img-format="jpg"><img wi="170" he="72" file="IMG-2/Draw/02_image104.jpg" img-format="jpg"><img wi="168" he="71" file="IMG-2/Draw/02_image106.jpg" img-format="jpg"><img wi="167" he="68" file="IMG-2/Draw/02_image108.jpg" img-format="jpg"><img wi="170" he="69" file="IMG-2/Draw/02_image110.jpg" img-format="jpg"><img wi="168" he="70" file="IMG-2/Draw/02_image112.jpg" img-format="jpg"><img wi="132" he="94" file="IMG-2/Draw/02_image114.jpg" img-format="jpg"> Hereinafter, the present invention is explained in more detail and preferred embodiments are disclosed. The sum m + n of the parameters m and n of the formula I preferably has a value of 1, 2, or 3, more preferably 2. Therefore, m is preferably 0 or 1, particularly preferably 1, and n is preferably 1. R 1 preferably represents an alkoxy, alkyl or alkenyl group having 1 to 7 or 2 to 7 carbon atoms, respectively. R 2 preferably represents an unsubstituted alkyl, S-alkyl (alkylthio), S-alkenyl (alkenylthio) or alkoxy group having 1 to 15 carbon atoms or having 2 to 15 The alkenyl, alkenyloxy or alkynyl group of each C atom is monohalogenated or polyhalogenated as appropriate. R 2 in the general formula I is preferably an alkoxy group or an alkylthio group having 1 to 7 C atoms, more preferably 2 to 5 C atoms, and very particularly 2 C atoms. The total number of carbon atoms in R 1 and R 2 together is preferably 3, 4, 5, 6, 7, 8, 9 or 10, more preferably 4, 5, 6, 7, 8 or 9. If R 1 and R 2 in formula I each independently represent an alkyl group, these are linear or branched. Preferably, each of these groups is linear, and unless otherwise indicated, has 1, 2, 3, 4, 5, 6 or 7 C atoms and is therefore preferably methyl, ethyl, Propyl, butyl, pentyl, hexyl or heptyl. If R 1 and R 2 in formula I each independently represent an alkoxy group, these are straight or branched chains. Preferably, each of these groups is linear, and unless otherwise indicated, has 1, 2, 3, 4, 5, 6 or 7 C atoms and is therefore preferably methoxy, ethoxy Group, propoxy, butoxy, pentoxy, hexoxy or heptoxy. If R 2 in formula I in each case independently represents an alkylthio group (synonymous with S-alkyl), then this is straight or branched. Preferably, this group is straight chain and unless otherwise indicated, it has 1, 2, 3, 4, 5, 6 or 7 C atoms and is therefore preferably methylthio, ethylthio, propyl Thiol, butylthio, pentylthio, hexylthio, or heptylthio. In addition, R 1 and R 2 in formula I may each independently be an alkenyl group having 2 to 15 C atoms, which is linear or branched and has at least one CC double bond. It is preferably a straight chain and has 2 to 7 C atoms. Therefore, it is preferably vinyl, prop-1- or -2-enyl, but-1-, -2- or -3-enyl, pent-1-, -2-, -3- or -4 -Alkenyl, hex-1-, -2-, -3-, -4- or -5-enyl or hept-1-, -2-, -3-, -4-, -5- or -6 -Alkenyl. If the two C atoms of the CC double bond are substituted, the alkenyl group can be in the form of E and/or Z isomers (trans/cis). Generally speaking, the respective E isomers are preferred. Among the alkenyl groups, particularly preferred are prop-2-enyl, but-2- or -3-enyl, and pent-3- or -4-enyl. R 1 and R 2 in formula I can also independently be an alkynyl group having 2 to 15 C atoms, which is linear or branched and has at least one CC triple bond. The alkynyl group is preferably 1- or 2-propynyl or 1-, 2- or 3-propynyl. The group A 1 preferably independently represents a di-substituted cyclic group selected from the following formula and Especially . The group A 2 preferably independently represents a disubstituted cyclic group selected from the following formulae in each case and Groups of the formula . The group L preferably represents F, Cl, -CF 3 or an alkyl or alkoxy group having 1, 2 or 3 carbon atoms. Halogen in the context of the present invention means fluorine, chlorine, bromine or iodine, in particular fluorine or chlorine. In conjunction with the present invention, unless otherwise defined in this specification or elsewhere in the scope of the patent application, the term "alkyl" means having 1 to 15 (ie 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15) straight-chain or branched, saturated, aliphatic hydrocarbon groups with carbon atoms. The compound of formula I of the present invention is particularly preferably selected from sub-formulas IA, IB, IC and ID, Wherein R 1 , R 2 , A 1 and A 2 have the meanings as defined for formula I. Preferred compounds of formula IA, IB, IC and ID are compounds of the following formula: Wherein, "alkyl" and "alkyl*" each independently represent a linear alkyl group having 1-7 C atoms. "Alkyl" particularly preferably means an alkyl group having 2, 3, 4, 5 or 6, especially 3 or 5 C atoms. Alkyl* preferably represents an alkyl group having 1, 2, 3 or 4 C atoms. The particularly preferred compounds of formula I are selected from the following formulae: Wherein "alkyl" is as defined above for IA-1, IB-1, etc. Among them, particularly preferred ones are compounds of formula IB-1-1 and IB-2-1, especially in which the alkyl group represents n-propyl. If the group or substituent of the compound of the present invention or the compound of the present invention itself is in the form of an optically active or stereoisomeric group, substituent or compound due to, for example, an asymmetric center, these are also covered by the present invention middle. It goes without saying here that the compounds of general formula I of the present invention may exist in isomeric pure forms (for example, pure enantiomers, diastereomers, E or Z isomers, trans or cis isomers). , Or in the form of a mixture of multiple isomers in any desired ratio (e.g., racemate, E/Z isomer mixture, or cis/trans isomer mixture). The formula in the compound disclosed for the liquid crystal medium The 1,4-substituted cyclohexyl ring of or -Cyc- preferably has a trans configuration, that is, both substituents are in the equatorial position of the thermodynamically preferred chair configuration. This applies similarly to the preferred conformations of tetrahydropyran and dioxane rings. Mode The formula of 1,4-substituted 1-fluorocyclohexyl ring The ring is a 1,4-trans-configuration cyclohexane ring substituted with F in the axial position and in a thermodynamically better configuration. Compounds of general formula I can be used by methods known per se, as described in the literature (for example, standard works, such as Houben-Weyl, Methoden der organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart). It is prepared under known and suitable reaction conditions for these reactions. It can also use its own known variants, and no more details will be mentioned here. If desired, the starting material can also not be separated from the reaction mixture, but can be further converted into the compound of general formula I immediately to be formed in situ. In the examples, the synthesis of the compound of general formula I of the present invention is illustrated by way of example. The starting materials can be obtained by generally available literature procedures or commercially available. Particularly suitable synthetic routes for the compounds of the present invention are explained in the following schemes. The substituents R 1 , R 2 and the subscripts m and n in the following schemes have the meanings as indicated for formula I. The synthesis of the compound of formula I is advantageously carried out by epoxidizing cyclohexanone 5 using a sulfur dipolar nucleophile (Corey), using HF to open the ring of epoxide 6 , and then using a phenol compound (see Scheme 1 ) The alcohol 7 is esterified to obtain the title compound 8 (see formula I). Scheme 1. Illustrative synthesis of the compound of formula I. R corresponds to the group R 1 -[A 1 ] n -. The reactions shown should be considered illustrative. Part of the reaction is basically familiar to those who are familiar with this technique. Compounds containing different rings and substituents are prepared according to the outlined synthesis. The group R in Scheme 1 represents the general group in the general formula I -[A 1 ] n -R 1 . Those skilled in the art will be able to implement the corresponding variants of the shown synthesis and follow other suitable synthetic routes to obtain compounds of formula I. According to the synthesis described above, the present invention also covers one or more preparation processes of the compound of formula I in one embodiment. Therefore, the present invention covers a process for preparing the compound of formula I, which is characterized in that it comprises the following process steps: wherein the compound of formula (A) Where m, A 1 and R 1 are independently as defined in formula I and react with the compound of formula (B) Where independently A 2 , n and R 2 are as defined in formula I. The reaction of A and B is followed by other process steps as appropriate, which ultimately produces the compound of formula I. The reaction preferably directly produces the compound of formula I. One aspect of the present invention is also an intermediate compound of formula (A). There are preferred species of compounds similar to the preferred embodiments of the compounds of formula I disclosed in the context herein. The compound of formula (A) can be advantageously prepared by epoxide ring opening from the corresponding ethylene oxide using HF, which in turn is obtained directly from cyclohexanone. The intermediate compound of formula (A) can be directly converted into the final compound of formula I. Therefore, it represents a valuable intermediate. The process of the present invention allows the substituents and parameters A 1 , A 2 , m, n, R 1 and R 2 to be changed simply and independently. This is because the two rings A 1 and A 2 are only combined at the end of the polymerization The compound of formula I. The preparation process, the previous reaction step and the subsequent treatment of the reaction mixture can basically be carried out in a batch reaction or in a continuous reaction procedure. Continuous reaction procedures encompass, for example, reactions in continuous stirred tank reactors, stirred reactor cascades, loop or cross flow reactors, flow tubes, or microreactors. The reaction mixture is optionally separated by solid phase filtration, chromatography, immiscible phase separation (e.g. extraction), adsorption onto a solid support, removal of solvent and/or azeotropic mixture by distillation, selective distillation, sublimation, Crystallization, co-crystallization or by nanofiltration on the membrane can be processed as needed. As already mentioned, the compounds of the general formula I can be used in liquid crystal media. Therefore, the present invention also relates to a liquid crystal medium comprising at least two liquid crystal compounds and at least one compound of general formula I. The present invention also relates to a liquid crystal medium containing 2 to 40, preferably 4 to 30, components as other components in addition to one or more of the compounds of formula I of the present invention. Such media particularly preferably contain 7 to 25 components in addition to one or more compounds of the invention. These other components are preferably selected from nematic or nematic (monomorphic or isotropic) substances, in particular substances from the following categories: oxyazobenzene, benzylidene aniline, biphenyl, ditriphenylamine Benzene, 1,3-dioxane, 2,5-tetrahydropyran, phenyl benzoate or cyclohexyl benzoate, phenyl or cyclohexyl ester of cyclohexanecarboxylic acid, benzene of cyclohexyl benzoate Phenyl ester or cyclohexyl ester, phenyl ester or cyclohexyl ester of cyclohexylcyclohexanecarboxylic acid; cyclohexylphenyl ester of benzoic acid, cyclohexanecarboxylic acid or cyclohexylcyclohexanecarboxylic acid; phenylcyclohexane, cyclohexyl Hexylbiphenyl, phenylcyclohexylcyclohexane, cyclohexylcyclohexane, cyclohexylcyclohexylcyclohexene, 1,4-bicyclohexylbenzene, 4',4'-bicyclohexylbiphenyl, phenylpyrimidine or ring Hexylpyrimidine, phenylpyridine or cyclohexylpyridine, phenyldioxane or cyclohexyldioxane, phenyl-1,3-dithiol or cyclohexyl-1,3-dithiol, 1,2-di Phenylethane, 1,2-dicyclohexylethane, 1-phenyl-2-cyclohexylethane, 1-cyclohexyl-2-(4-phenylcyclohexyl)ethane, 1-cyclohexyl- 2-Biphenylethane, 1-phenyl-2-cyclohexylphenylethane, optionally halogenated stilbene, benzyl phenyl ether, diphenyl acetylene and substituted cinnamic acid. The 1,4-phenylene in these compounds may also be monofluorinated or polyfluorinated. The most important compounds suitable as other components of the medium of the present invention can be characterized by the formulas (II), (III), (IV), (V) and (VI): R'-LE-R'' (II) R'- L-COO-E-R'' (III) R'-L-OOC-E-R'' (IV) R'-L-CH 2 CH 2 -E-R'' (V) R'-L- CF 2 OE-R'' (VI) In formulas (II), (III), (IV), (V), and (VI), L and E may be the same or different, and each independently of each other represents free- Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-, -Thp-, -G-Phe- and -G-Cyc- and A divalent group formed as a mirror image, where Phe represents unsubstituted or fluorine-substituted 1,4-phenylene, and Cyc represents trans-1,4-cyclohexylene or 1,4-cyclohexene Pyr represents pyrimidine-2,5-diyl or pyridine-2,5-diyl, Dio represents 1,3-dioxane-2,5-diyl, Thp represents tetrahydropyran-2,5- Diyl, and G represents 2-(trans-1,4-cyclohexyl) ethyl, pyrimidine-2,5-diyl, pyridine-2,5-diyl, 1,3-dioxane-2, 5-diyl or tetrahydropyran-2,5-diyl. One of the groups L and E is preferably Cyc or Phe. E is preferably Cyc, Phe or Phe-Cyc. The medium of the present invention preferably contains one or more components selected from compounds of formula (II), (III), (IV), (V) and (VI), wherein L and E are selected from the group consisting of Cyc and Phe And at the same time one or more components selected from the compounds of formula (II), (III), (IV), (V) and (VI), wherein one of the groups L and E is selected from Cyc and Phe The group consisting of and the other group is selected from the group consisting of -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-; and one or more groups as appropriate A component selected from the compounds of formula (II), (III), (IV), (V) and (VI), wherein the groups L and E are selected from -Phe-Cyc-, -Cyc-Cyc-,- Group of G-Phe- and -G-Cyc-. In the smaller subgroups of compounds of formula (II), (III), (IV), (V) and (VI), R'and R" each independently represent an alkyl group having up to 8 C atoms, Alkenyl, alkoxy, alkoxyalkyl (oxaalkyl), alkenyloxy or alkanoyloxy. This smaller subgroup is hereinafter referred to as group A, and these compounds are represented by the sub-formula ( IIa), (IIIa), (IVa), (Va) and (VIa) mentioned. In most of these compounds, R'and R" are different from each other, and one of these groups is usually an alkyl group, Alkenyl, alkoxy, or alkoxyalkyl (oxaalkyl). In another smaller subgroup of compounds of formula (II), (III), (IV), (V) and (VI) (which is called group B), E represents . Among the compounds of group B mentioned by sub-formulas (IIb), (IIIb), (IVb), (Vb) and (VIb), R'and R" are as for the compounds of sub-formulas (IIa) to (VIa) It is defined and preferably is alkyl, alkenyl, alkoxy or alkoxyalkyl (oxaalkyl). Among formulas (II), (III), (IV), (V) and (VI) In the further smaller subgroups of compounds, R" represents -CN. This subgroup is hereinafter referred to as group C, and the compounds of this subgroup are correspondingly illustrated by the sub-formulas (IIc), (IIIc), (IVc), (Vc) and (VIc). In the compounds of sub-formulas (IIc), (IIIc), (IVc), (Vc) and (VIc), R'is as defined for the compounds of sub-formulas (IIa) to (VIa) and is preferably an alkyl group , Alkenyl, alkoxy or alkoxyalkyl (oxaalkyl). In addition to the preferred compounds of groups A, B and C, other compounds of formula (II), (III), (IV), (V) and (VI) with other variants of the suggested substituents are also common. All these substances can be obtained by methods known from the literature or in a similar manner. In addition to the compound of general formula I of the present invention, the medium of the present invention preferably contains one or more compounds from group A, B and/or C. The weight ratio of the compounds from these groups in the medium of the present invention is: Group A: 0% to 90%, preferably 20% to 90%, specifically 30% to 90%. Group B: 0% to 80%, preferably 10% to 80%, specifically 10% to 70%. Group C: 0% to 80%, preferably 5% to 80%, specifically 5% to 50%. The medium of the present invention preferably contains 1% to 40%, more preferably 5% to 30% of the compound of formula I of the present invention. These media preferably contain one, two, three, four or five compounds of formula I of the present invention. The medium of the present invention is prepared in a customary manner. Generally, it is preferable to dissolve the components with each other at a high temperature. With the aid of suitable additives, the liquid crystal phase of the present invention can be modified so that it can be used in all types of liquid crystal display elements disclosed so far. This type of additive is known to those skilled in the art and is described in detail in the literature (H. Kelker/R. Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980). For example, pleochroic dyes can be added to produce a colored guest-host system or substances can be added to improve the dielectric anisotropy, viscosity, and/or alignment of the nematic phase. Due to its negative Δε, the compound of formula I is particularly suitable for use in VA-TFT displays or passive VA displays. Therefore, the present invention also relates to an electro-optical display element containing the liquid crystal medium of the present invention. The display element is preferably a VA-TFT display element (VA: vertical alignment; TFT: thin film transistor). Other combinations and variations of the embodiments of the present invention according to the specification can be derived from technical solutions and combinations of two or more of these technical solutions. Hereinafter, the present invention is explained in more detail with reference to working examples, but it is not intended to be limited thereby. Those who are familiar with this technology will be able to find work details that are not given in the general description from these examples, summarize them according to general professional knowledge and apply them to specific problems. In addition to the usual and well-known abbreviations, the following abbreviations are used: mp: melting point; C: liquid crystal phase; N: nematic phase; Sm: smectic phase (specified in more detail where appropriate); I: isotropic phase. The numbers between these symbols indicate the transition temperature of the relevant substance. Unless otherwise indicated, temperature data is expressed in degrees Celsius (degrees Celsius). Physical, physicochemical or electro-optical parameters are measured by well-known methods, as described in the manual "Merck Liquid Crystals-Licristal®-Physical Properties of Liquid Crystals-Description of the Measurement Methods", 1998, Merck KGaA, Darmstadt. In this context, Δn represents optical anisotropy (589 nm, 20°C) and Δε represents dielectric anisotropy (1 kHz, 20°C). The dielectric anisotropy Δε is measured at 20°C and 1 kHz. The optical anisotropy ∆n is measured at 20°C and a wavelength of 589.3 nm. The Δε and Δn values, extrapolated clear point (cl.p.) and rotational viscosity (γ 1 ) of the compound of the present invention are determined by free 5% to 10% of the compound of the present invention and 90% to 95% of the commercially available liquid crystal mixture ZLI-2857 (for Δε, cl. p.) or ZLI-4792 (for Δn, γ 1 ) (mixture, Merck KGaA, Darmstadt) composed of liquid crystal mixtures can be obtained by linear extrapolation. Examples The starting materials can be obtained by generally available literature procedures or commercially available. Example 1: Step 1 Add a solution of potassium tert-butoxide (21.9 g, 195.6 mmol) in dimethyl sulfoxide (90 ml) dropwise to ketone 9 (29.0 g, 130.4 mmol) and trimethylsulfonium iodide at room temperature (43.0 g, 195.6 mmol) in a mixture of dimethylsulfoxide (210 ml). The resulting mixture was stirred for 36 h, then heptane (500 ml) was added, and the mixture was stirred for another 0.5 h. The heptane phase was separated, filtered with the aid of Celite®, washed with water, dried over Na 2 SO 4 and evaporated in vacuum. The residue (16.7 g) was purified by Puriflash (300 g SiO 2 , heptane/methyl tert-butyl ether 9:1) to obtain epoxide 10 (95.8% HPLC) as colorless crystals. Step 2 A solution of HF in pyridine (65%, 5.0 ml, 185.5 mmol) was added dropwise to Epoxide 10 (15.6 g, 61.8 mmol, HPLC: 93.7%) in dichloromethane (275 ml) at -5°C的solution. The resulting mixture was stirred at -5°C for 1 h and then filtered through a SiO 2 layer (1 l, washed with dichloromethane) to obtain alcohol 11 (HPLC: 31.9%) as a colorless oil. Step 3 Add diisopropyl azodicarboxylate (DIAD, 10.9 ml, 55.5 mmol) dropwise to alcohol 11 (10.2 g, 12.6 mmol, HPLC: 31.9%), phenol 12 (6.9 g, 47.8 mmol) and In a stirred solution of triphenylphosphine (12.5 g, 47.6 mmol) in tetrahydrofuran (THF, 161 ml). The resulting mixture was stirred at room temperature for 7 days and at 45°C for 1 day, then filtered with a layer of SiO 2 (100 g) and purified twice by flash chromatography (heptane/methyl tert-butyl ether). It was recrystallized twice from isopropanol to obtain the final compound 2 (1.2 g, 25%, HPLC: 99.7%) as colorless crystals. 1 H NMR: 0.81-1.87 (m, 24H), 2.03-2.15 (m, 2H), 2.25 (d, J = 2.1 Hz, 3H), 3.98 (d, J = 16.4 Hz, 2H), 6.68 (ddd, J = 8.7, 8.1, 1.9 Hz, 1H), 6.82 (ddd, J = 8.2, 8.2, 2.1 Hz, 1H); 19 F NMR: -140.6 (ddt, J = 19.3, 7.8, 1.8 Hz, 1F), − 159.0 (ddd, J = 19.4, 7.4, 2.4 Hz, 1F), -165.8 (qt, J = 24.3, 9.3 Hz, 1F); EI-MS: 382.3 Phase: C 91 N 118 I (mp 91℃), Δε = -6.73, Δn=0.0792; γ 1 =454 mPa∙s. The following compounds were prepared similarly to Example 1: Phase: C 72 SmB (61) N 101 I (mp 72℃) Δε=-6,25, Δn=0.0762; γ 1 =433 mPa∙s. Phase: C 72 N 144 I (mp 72℃) Δε=-8,23, Δn=0.0832; γ 1 =706 mPa∙s. Phase: C 48 N (4) I (mp 48°C) Δε=-8.25, Δn=0.0572; γ 1 =71 mPa∙s Prepare other illustrative compounds similarly: Unless otherwise specified, the group R 1/2 is linear, that is, it is not branched. The structures of individual compounds are found in Table 1. The alkyl group of the formula C n H 2n+1 is an unbranched alkyl group. Table 1. 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