Structural variation of liquid crystalline trioxadecalins Volkmar Vill,” Hanns-Walter Tunger and Markus von Minden Institute of Organic Chemistry, University of Hamburg, 0-20146 Hamburg, Germany Synthesis and mesogenic properties of new liquid crystals bearing a chiral trioxadecalin system are described. Boron-containing three-ring systems with a lateral methoxy group show cholesteric, TGBA and smectic A phases. Molecules containing four or five rings show mostly smectic C* phases. The insertion of a triple bond leads to ferroelectric smectic C* phases, but compounds with a flexible spacer between the rings show only monotropic smectic A phases. Lateral fluorination of the aromatic rings leads, depending on the position of the fluorine, either to stabilised smectic phases with lower transition temperatures or to cholesteric phases with complete suppression of all smectic phases.New technical applications for chiral liquid crystals and the discovery of new chiral mesophases have increased the interest in easily accessible mesogens with chiral centres.’ Most of the investigated and commercially used liquid crystals possess one chiral centre in the flexible side chain. However, we base our syntheses on carbohydrates, which allows the introduction of a chiral ring system into the molecular core, so that the chirality is located in the part of the molecule that determines the general mesogenic properties. Compounds with a chiral trioxadecalin ring system are obtained in a short synthesis from tri-0-acetyl-D-gluca1.2 They show an interesting and sometimes unusual mesogenic behav- iour, e.g.cholesteric helix inversion^^.^ and re-entrant TGBA phases.’ In mixed systems, the re-entrant TGBA phase is stabilized,6 and for some compounds a sign inversion of the spontaneous polarization in induced smectic C* phases is obser~ed.~ Here we present detailed structural modifications of com- pounds having a trioxadecalin ring system to study the scope of their chiral and mesogenic properties. We lengthened the mesogenic group by increasing the number of rings and fitted rigid alkynyl and flexible alkyl spacers between the rings. In addition, the effect of terminal methoxy groups instead of longer alkyl chains is examined. Lateral fluorine atoms should modify the global molecular shape and introduce dipole-dipole interactions. We synthesized compounds with lateral fluoro substituents at the aromatic rings in the molecular core and studied the influence of the position of the fluorine on the mesogenic behaviour.Experimenta1 The synthesis of the adducts is shown in Scheme 1. A three- step synthesis starting from tri-0-acetyl-D-glucal 1 (or a five- step synthesis starting from cheap glucose) leads in an overall yield of 28% to the enantiomerically pure diol4 (with a fluoro substituent the yield decreases to 6%). The diol can easily be combined with different boronic acids and aldehyde dimethyl acetals giving a broad variety of products (Scheme 2)., The synthesis of the alkynyl aldehyde 13 which is used for the synthesis of compounds 7 is outlined in Scheme 3.899 General reaction conditions Conditions A.A flask with diol 4 (0.076 mmol), 4-alkoxybenzaldehyde dimethyl acetal ( 1.2 equiv., 0.092 mmol) and toluene-p-sulfonic acid (monohydrate) (5.0 mg) in N,N-dimethylformamide (5 ml) was fitted to a rotary evaporator. The mixture was allowed to react for 1 h at reduced pressure (29-33 mbar) in a 60 “C water-bath, the methanol formed, distilled off during the reaction. Then the solvent was evapor- ated in uucuo (10 mbar) at 75 “C water-bath temperature. The solid residue was washed with saturated aqueous sodium hydrogen carbonate, filtered, washed with water and cold ethanol and then recrystallized from ethanol.Conditions B. Diol 4 (0.076 mmol) and 4-alkoxyphenyl- boronic acid (1.2 equiv., 0.092 mmol) were dissolved in toluene (5 ml). The water produced in the reaction was coevaporated three times with toluene (5 ml). The remaining crystalline solid was recrystallized from ethanol. Conditions C. The unsaturated compound (0.025 mmol) was dissolved in ethyl acetate (15 ml) and ethanol (5 ml) and stirred after the addition of a catalytic amount of palladium on charcoal (10%) under a hydrogen atmosphere for 1 h. The catalyst was filtered off, the solvent evaporated and the residue recrystallized from ethanol. Conditions D. These conditions were similar to conditions A, but using diol 4 (0.126 mmol) and the dialdehyde tetramethyl acetal (0.9 equiv., 0.057 mmol).Materials Amberlyst IR 120 ion-exchange resin (protonated form), dichloromethane (99”/), N,N-dimethylformamide (%WOO), etha- nol, ethyl acetate (WYO), light petroleum (50-70 “C), mag- nesium sulfate (99”/), methanol, palladium (10% on charcoal), sodium carbonate (98%), sodium hydrogen carbonate (99”/0), sodium methoxide, stannic(1v) chloride, toluene (99”/), tolu- ene-p-sulphonic acid (98%, monohydrate) were used as received. In all cases dry solvents were used. Dichloromethane was refluxed over phosphorus pentoxide and stored over molecular sieves 4 A after distillation. N,N-Dimethylform-amide was filtered over silica gel and freshly distilled before use. Techniques Thin-layer chromatography (TLC) was performed on silica gel (Merck GF,,,), and detection was effected by spraying with a solution of ethanol-sulfuric acid (9: l), followed by heating, and UV-absorbance.Column chromatography was performed on silica gel 60 (230-400 mesh, Merck). Optical rotations were recorded using a Perkin-Elmer 241 polarimeter. The NMR spectra (‘H: 400 MHz, I3C: 100.6 MHz) were recorded on a Bruker AMX-400 spectrometer with tetramethylsilane (TMS) as an internal standard (m, =centred multiplet). An Olympus BH optical polarizing microscope equipped with a Mettler FP 82 hot stage and a Mettler FP 80 central processor was used J. Muter. Chem., 1996, 6(5), 739-745 739 phenyi alkyl ether SnCI4 * Acr%Oh AcO CHzCIz -0OC"H2"+1 1 2 H2 PdIC ethanol ethyl acetate separation of anomers 4 X=H F 3 Scheme 1 Synthetic route to chiral building block 4 conditions A X=H F OC"H2" + 1 OCfi2n + 1 6 H2 PdJC 7(conditions C) I 8\conditions AfI Scheme 2 Structural variation of the trioxadecalines triphenylp hosphine carbon tetrabromide H1 7C800cH0 dichloromethane * 11 12 1 butyII ith ium N N-dimethyl-formamide trimethyl orthoformate 12 HCI 14 13 Scheme 3 Synthetic route to propynal 13 740 J Muter Chem , 1996, 6(5),739-745 to identify thermal transitions and characterize anisotropic textures. For further verification of the textures a contact preparation with p-butyl-p’-methoxyazoxybenzene (K 16 N 76 I) was carried out.The NMR data of a homologous series of compounds differ only in the integral of the signal at 6 1.3 (number of protons, -CH2 -).Thus, the experimental and NMR data of only one member of every series are given below. The yields and optical rotations of all compounds are listed in Table 1. Synthesis of 1-(2’,3-dideoxy-~-~-eryythro-hexopyranosyl)-2-fluoro-4-hexyloxybenzene4(n=6,x =F) To a mixture of tri-O-acetyl-D-glucal (3.0 g, 11 mmol) and 3- fluorohexyloxybenzene (3.3 g, 16.9 mmol) in dry dichloro- methane (50 ml) were added 2 drops of stannic tetrachloride. After stirring the reaction mixture for 2 h at room temperature solid sodium carbonate (2.0 g) was added. The reaction mixture was stirred for a further 15 min and then filtered. The solvent was removed in uucuo. The product was dissolved in ethanol Table 1 Yields and optical rotations of the synthesised compounds yield opt.rotation (CHC1,) comp. conditions mg YO [a];’ c/g per 100ml 5a 5b 5c 5d A A A A 19 22 25 20 42 53 62 25 +24.1 +27.0 +22.3 +25.0 1.o 0.1 0.5 0.1 5e 5f ” 5g6a 6b A A A B B 23 28 35 29 16 59 50 66 56 30 +26.2 +20.1 +20.8 +28.5 +30.0 1.o 0.5 0.5 1.o 0.1 6c 6d B B 18 11 32 18 +21.0 +22.0 0.1 0.1 6e B 14 22 +26.0 0.1 6f 6h 6i 6k 61 6m“ 6n 60“ 6P 6q“6r 6g 6.j B B B B B B B B B B B B B 13 17 11 25 18 25 10 18 29 33 24 35 32 32 30 27 63 46 65 26 39 60 73 50 79 65 +26.0 +23.0 +20.0 + 18.4 + 19.0 + 18.2 +22.0 + 19.0 +19.4 + 17.6 +17.6 +20.0 + 15.8 0.1 0.1 0.1 0.5 0.1 1.o 0.1 0.1 0.5, 1.o 0.2 0.1 0.5 6s” 6t 6u“ 6v 6w” 6x 7a 7b 7c 7d 7e 8a 8b 9a 9b 9c 9d 1Oa 10b 1oc 1Od 1Oe 10f 1% B B B B B B A A A A A C C A A A A D D D D D D D 29 28 12 25 25 13 24 12 14 12 27 10 15 26 32 10 40 20 16 14 12 22 24 43 57 49 21 50 52 29 44 24 28 24 57 80 74 43 60 15 66 28 23 20 18 33 36 34 +21.4 +26.8 +22.0 +25.0 +24.0 +26.0 +24.0 +20.0 + 19.0 +23.0 +23.0 +20.0 +20.0 +24.3 +22.0 +24.0 +27.0 +23.2 +22.0 +27.6 +28.0 +25.5 +27.5 +18.3 0.5 0.5 0.1 0.2 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 1.o 1.o 0.1 0.5 0.5 0.5 0.5 0.1 1.o 1.o 1.o “Ref.5.(40ml) and ethyl acetate (120ml) and, after addition of palladium on charcoal (lo%, 10 mg), hydrogenated under a hydrogen atmosphere. After stirring for 4 h at room tempera- ture, the solution was filtered, the solvent evaporated and the residue purified uiu column chromatography (eluent: light petroleum (bp 50-70 “C)-ethyl acetate, 20: 1) to give 3 which was stirred at room temperature for 4 h with sodium methoxide ( 10.0 mg) in methanol (50 ml).The solution was neutralized with acidic ion exchange resin (Amberlite IR 120, H+-form), filtered and evaporated to give the title compound (0.22 g, 6%), syrup, [a];’+ 19.0 (c=0.5, CHC1,); d~(cDC1,) 4.67 (dd, 1 H, H-1’), 1.77 (mc, 4 H, H-2’,,, H-3’,,, P-CH,), 1.96 (mc, 1 H, H-2’eq), 2.17 (mc, 1 H, H-3’eq), 3.35-3.95 (m, 6 H, H-4, H-5’, H-6’,, H-6’b7 a-CH,), 6.56 (dd, 1H, H-3), 7.34 (dd, 1H, H- 5), 6.68 (dd, 1 H, H-6), 1.44 (mc, 2 H, 7-CH,), 1.27 (br s, 4 H, -CH2-)7 0.88 (t7 3 H7 CH3); 3Jl!,2!ax 11.0, 3Jlr,2!eq 2-09 3J5,6 8.6, 4J3,6 2.4, ,J3,F 12.2, 4J5,~8.6 HZ; GC(CDC1,) 83.2 (c-l’), 32.9, 33.9 (C-2’, C-3’), 74.5 (C-4), 68.3 (C-5’), 64.5 (C-6’), 160.4 (C-2), 101.9 (C-3), 110.4 (C-5), 127.6 (C-6), 68.8 (a-CH,), 31.5, 29.2, 26.0, 22.7 (-CH2-), 14.1 (CH,); 1J2,F165, 2J3,F19 Hz.Synthesis of (lS,3R,6R,SR)-S-(4‘-hexyloxyphenyl)-3-(4”-methoxyphenyl)-2,4,7-trioxabicyclo[4.4.01decane 5b Reaction conditions A using 4-methoxybenzaldehyde dimethyl acetal. d~(cDC1,) 3.65 (ddd, 1 H, H-I), 5.56 (s, 1 H, H-3), 4.29 (dd, 1 H, H-5,), 3.77 (dd, 1 H, H-5b), 3.58 (ddd, 1 H, H-6), 4.47 (dd, 1 H, H-8), 1.85 (mc, 2 H, H-9,,, H-loax), 2.02 (mc, 1 H, H-94, 2.20 (mc, 1 H, H-lOeq), 7.26 (d, 2 H, H-2’, H-6’), 7.43 (d, 2 H, H-2”, H-6”), 6.88 (d, 4 H, H-3’, H-5’, H-3”, H-5”), 3.80 (s, 3 H, OMe), 3.94 (t, 2 H, a-CH,), 1.76 (mc, 2 H, P-CH,), 1.43 (mc, 2 H, y-CH,), 1.32 (br s, 4 H, -CH,-)), 0.90 (t, 6 H, CH3); ,Jl,6 9-57 ,Jl,lOax l0.87 3J5a,5b 10.27 ,J5a,6 10.2, ,J5b,6 5.47 ,J8,9ax 10.2, ,Jg,geq 2.4, ’JAryl 8.5 HZ; Gc(CDCl3) 74.1 (C-I), 101.8 (C-3), 69.6 (C-5), 78.3 (C-6), 79.7 (C-8), 31.6 (C-9), 33.1 (C-lo), 137.0 (C-1’), 130.1 (C-1”), 127.5, 127.2 (C-2’, C-6’, C- 2”, C-6”), 113.7, 114.5 (C-3’, C-5’, C-3”, C-5”), 158.8 (C-4’), 160.0 (C-4”), 55.3 (OMe), 68.1 (a-CH,), 29.3, 29.2, 25.7, 22.6 (-CH2-), 14.0 (CH,).Synthesis of (lS,3R,6R,SR)-S-(2-fluoro-4-hexyloxyphenyl)-3-(4-dodecyloxyphenyl)-2,4,7-trioxabicyclo[4.4.01decane 5g Reaction conditions A using 4-dodecyloxybenzaldehyde dimethyl acetal. 6,(CDC13) 3.64 (ddd, 1 H, H-1), 5.54 (s, 1 H, H-3), 4.28 (dd, 1 H, H-5,), 3.75 (dd, 1 H, H-5b), 3.58 (ddd, 1 H, H-6), 4.76 (dd, 1 H, H-8), 1.85 (mc, 2 H, H-9,,, H-loax), 2.03 (mc, 1 H, H-9,,), 2.19 (mc, 1 H, H-loeq), 6.56 (dd, 1 H, H-3’), 6.67 (dd, 1 H, H-5‘), 7.31 (dd, 1 H, H-6’), 7.41 (d, 2 H, H-2”, H-6”), 6.87 (d, 2 H, H-3”, H-S’), 3.93 (mc, 4 H, a-CH,), 1.75 (q,4 H, p-CH,), 1.42 (mc, 4 H, y-CH,), 1.30 (br s, 24 H, -CH,-), 0.88 (t7 6 H7 CH3); ,J1,6 8.97 3J1,10ax 10.8, 3J5a,5b 10.2, ,J5a,6 10.2, 3J5b,6 5*4, 3J8,9ax 3J8,9eq 2-073JAryl,, 8.67 3J5r,6r 8-67 4J31,5t 2.5, 3J3,,F12.1, 4J6,,F 8.6 Hz; Gc(CDC13) 73.5 (C-1), 101.8 (C-3), 69.5 (C-5), 78.2 (C-6), 74.2 (C-8), 31.9 (C-9), 32.2 (C-lo), 160.4 (C- 2’), 101.9 (C-3’), 110.4 (C-5’), 127.6 (C-6), 130.0 (C-l”), 127.4 (C-2”, C-6”), 114.4 (C-3”, C-5”), 159.7 (C-4”), 68.1 (N-CH,), 31.9, 29.7, 29.6, 29.4, 29.3, 29.2, 26.0, 22.7 (-CH2-), 14.1 (CH3); ‘J2t.F 162, ,J3,,F 19 Hz.Synthesis of (lS,6R,SR)-S-(4‘-methoxyphenyl)-3-( 4-hexyloxyphenyl)-2,4,7-trioxa-3-borabicyclo[4.4.01decane 6b Reaction conditions B using 4-hexyloxyphenylboronic acid. GH(CDC13) 3.87 (ddd, 1 H, H-1), 4.24 (dd, 1 H, H-5,), 3.95 (dd, 1 H, H-5,), 3.62 (ddd, 1 H, H-6), 4.48 (dd, 1 H, H-8), 1.70-1.91 (m, 4 H, H-9,,, H-lo,,, P-CH,), 2.03 (mc, 1 H, H- geq), 2.37 (mc, 1 H, H-lOeq), 7.26 (d, 2 H, H-2’, H-6’), 7.75 (d, 2 H, H-2”, H-6”), 6.87 (d, 4 H, H-3’, H-5’, H-3”, H-5”), 3.82 (s, J. Muter. Chem., 1996, 6(5),739-745 741 3 H, OMe), 3 94 (t, 2 H, a-CH,), 145 (mc, 2 H, y-CH,), 1 27 Synthesis of (1&3R,6R,SR)-8-( 4‘-hexyloxyphenyl)-3-[ 2-( 4- (brs,4H, -CH,-),090(t,6H,CH3),3J1691,3J110axoctyloxyphenyl ethyl]-2,4,7-trioxabicyclo [4.4.01 decane 8a 109, 5b 10 2, ,J5a 6 10 2, ,J5b 6 54, 3J8 9ax 10 9, 9eq 2 0, ,JAryl 8 0 Hz, Gc(CDC1,) 71 6 (C-1), 64 9 (C-5), 76 0 (C-6), 79 8 (C- 8), 31 2 (C-9), 32 9 (C-lo), 133 4 (C-l’), 127 3 (C-2, C-6’), 114 5 (C-3’, C-5’), 158 5 (C-4), 135 8 (C-2”, C-6”), 113 2 (C-3”, C-5”), 162 5 (C-4”), 55 1 (OMe), 68 1 (a-CH,), 31 2, 29 2, 25 7, 22 6 (-CH2-), 14 0 (CH3) Synthesis of (lS,6R,SR)-8-( 4’-octyloxyphenyl)-3-( 3”-fluoro-4”- hexyloxyphenyl)-2,4,7-trioxa-3-borabicyclo[4.4.01 decane 6n Reaction conditions B using 3-fluoro-4-hexoxyphenylboronic acid d~(cDC13)3 87 (ddd, 1 H, H-1), 4 23 (dd, 1 H, H-5,), 3 94 (dd, 1 H, H-5b), 3 61 (ddd, 1 H, H-6), 4 48 (dd, 1 H, H-8), 1 70-1 91 (m, 6 H, H-9,,, H-lo,,, 8-CH,), 203 (mc, 1 H, H- geq), 2 36 (mc, 1 H, H-lOeq), 7 26 (d, 2 H, H-2’, H-67, 6 87 (d, 2 H, H-3’, H-5’), 748 (dd, 1 H, H-2”), 692 (dd, 1 H, H-5”), 7 50 (dd, 1 H, H-6”), 3 98 (mc, 4 H, a-CH,), 145 (mc, 4 H, y-CH,), 131 (br s, 12 H, -CH,-), 089 (t, 6 H, CH,), ,J16 9 1, ”l lOax lo 9, ,J5a 5b lo 2, ,J5a 6 lo 2, ,55b 6 5 4, 3J8 9ax 10 9, ,J8 9eq O, ,JAryl 8, ,J5,, 6~ 2, 4J2t1 611 17, 3J2,/ F 12 2, 4J51 F 8 2 Hz, Gc(CDCl3) 71 6 (C-l), 64 9 (C-5), 760 (C-6), 79 8 (C-8), 31 1 (C-9), 32 8 (C-lo), 133 3 (C-1’), 127 2 (C-2’, C-6’), 114 5 (C-3’, C-5’), 158 9 (C-4’), 135 7 (C-2”, C-6”), 113 8 (C-3”, C-5”), 160 5 (C-4”), 68 1, 69 2 (a-CH,), 31 8, 31 6, 29 4, 29 3, 29 2, 29 1, 26 0, 25 6, 22 7, 22 6 (-CH2-), 14 1, 14 0 (CH,), ‘J3,, F 169, 2J2,, F 16 Hz Synthesis of (lS,6R,SR)-&(2’-fluoro-4’-hexyloxyphenyl)-3-(4-octyloxyphenyl)-2,4,7-trioxa-3-borabicyclo[4.4.01 decane 6t Reaction conditions B using 4-octyloxyphenylboronic acid &(CDCl,) 3 88 (ddd, 1 H, H-1), 4 24 (dd, 1 H, H-5,), 3 94 (dd, 1 H, H-5,), 3 62 (ddd, 1 H, H-6), 478 (dd, 1 H, H-8), 171-1 87 (m, 6 H, H-9,,, H-lO,,, P-CH,), 205 (mc, 1 H, H- geq), 2 35 (mc, 1 H, H-loeq), 6 58 (dd, 1 H, H-3’), 6 68 (dd, 1 H, H-5’), 7 33 (dd, 1 H, H-6’), 7 73 (d, 2 H, H-2”, H-6”), 6 87 (d, 2 H, H-3”, H-5”), 3 95 (mc, 4 H, a-CH,), 144 (mc, 4 H, y-CH,), 1 39 (br s, 12 H, -CH, -), 0 90 (t, 6 H, CH,), ,J16 9 1, ,J1 10 9, ,J5a 5b 10 2, ,J5a 6 10 2, ,J5b 6 5 4, 3J8 9ax 10 9, 3J8 9eq 2 0, 4J31,JAryl,, 8 7, ,J5’ 6, 8 2, 5, 2 6, ,J3( F 12 2, 4J6tF 8 5 Hz, Gc(CDCI3) 71 5 (C-1), 64 8 (C-5), 76 1 (C-6), 73 6 (C-8), 31 1 (C-9), 32 0 (C-lo), 120 4 (C-1’), 160 8 (C-2’), 101 9 (C-3’), 110 6 (C-5’), 135 7 (C-2”, C-6”), 113 8 (C-3”, C-5”), 162 5 (C-4”), 68 1, 67 8 (a-CH,), 31 8, 31 5, 29 4, 29 3, 29 2, 29 1, 26 0, 25 6, 22 7, 22 6 (-CH2-), 14 1,14 0 (CH,), ‘J2, F 169,,J3/ F 25, 3J6, F 6 HZ Synthesis of (lS,3R,6R,SR)-8-( 4‘-hexyloxyphenyl)-3-( 4”- octyloxyphen ylethyny1)-2,4,7- trioxabicyclo [4.4.01 decane 7a Reaction conditions A using l-(4-octyloxyphenyl)prop-l-ynal dimethyl acetal The product was dissolved in dichloromethane, stirred with charcoal and filtered through a pad of silica gel before recrystallisation h~(CDc13)3 69 (ddd, 1 H, H-l), 5 51 (s, 1 H, H-3), 424 (dd, 1 H, H-5,), 3 69 (dd, 1 H, H-5b), 3 56 (ddd, 1 H, H-6), 4 45 (dd, 1 H, H-8), 185 (mc, 2 H, H-9,,, H-loax), 201 (mc, 1 H, H-9,,), 2 20 (mc, 1 H, H-loeq), 7 23 (d, 2 H, H-2’, H-6’), 6 86 (d, 2 H, H-3’, H-5’), 7 42 (d, 2 H, H-2”, H-6”), 6 81 (d, 2 H, H- 3”, H-5”), 3 94 (mc, 4 H, a-CH,), 175 (mc, 4 H, P-CH,), 143 (mc, 4 H, y-CH,), 126 (brs, 12 H, -CH,-), 089 (t, 6 H, CH3), 3J1 6 5, 3Jl 1Oax lo 8, 3J5a 5b lo 5, ,J5a 6 lo 0, ,J5b 6 4, ,J89ax 10 2, 3J89eq 2 4, ,JArYl8 5 Hz, Gc(CDCl,) 73 6 (C-1), 92 5 (C-3), 69 6 (C-5), 78 6 (C-6), 79 7 (C-8), 31 9 (C-9), 33 0 (C-lo), 133 0 (C-1’), 113 0 (C-l”), 127 2 (C-2’, C-6’), 133 6 (C-2”, C-6”), 114 4, 114 5 (C-3’, C-5’, C-3”, C-5”), 158 8 (C-4’), 159 9 (C-4’7, 82 0, 85 5 (alkynyl-C), 68 1 (a-CH,), 31 8, 29 7, 29 6, 29 4, 29 3, 29 2, 26 0, 22 7 (-CH2-), 14 1 (CH,) 742 J Muter Chem , 1996, 6(5), 739-745 Reaction conditions C using 7a GH(CDC1,) 3 41 (mc, 2 H, H-1, H-6), 4 59 (t, 1 H, H-3), 4 14 (dd, 1 H, H-5,), 3 54 (dd, 1 H, H-5b), 442 (dd, 1 H, H-8), 1 76 (mc, 4 H, H-gax, H-lOax, P-CH,), 199 (mc, 3 H, H-9,,, C3-CH2-), 2 12 (mc, 2 H, H-loeq), 270 (t, 2 H, Aryl-CH,-), 7 23 (d, 4 H, H-2’, H-6’), 6 85 (d, 4 H, H-3’, H-5’), 7 10 (d, 2 H, H-2”, H-6”), 6 82 (d, 2 H, H-3 ’, H-5”), 3 93 (t, 4 H, a-CH,), 120-1 70 (m, 40 H, -CH2-)), 088 (t, 6 H, CH3), 3Jl 6 9 5, ,Jl lOax lo 8, 3J3 CH, 1, 3JAryl CH,,CH, 8 1, ,J5a 5b 9 77 3J5a 6 9 7, ,Jsb 6 3 8, 9ax 100, 9eq 1 7, ’J~ryl 8 5 HZ, Gc(CDC1,) 74 5 (C-1), 102 0 (C-3), 69 5 (C-5), 78 0 (C-6), 79 5 (C-8), 31 9 (C-9), 33 1 (C-lo), 133 5 (C-1’), 131 0 (C-1”), 127 2 (C-2’, C-6’), 129 3 (C-2”, C-6”), 114 5 (C-3’, C-5’, C-3”, C-5”), 158 5 (C-4’, C-4”), 68 1 (a-CH,), 31 8, 37 0 (ethyl-C), 29 7, 29 6, 29 3, 29 2, 26 0, 22 7 (-CH, -), 14 1 (CH,) Synthesis of (lS,3R,6R,SR)-8-( 4‘-hexyloxyphenyl)-3-[ 4-(4”‘-dodecyloxybenzoyloxy)phenyl]-2,4,7-trioxabicyclo [4.4.01 decane 9c Reaction conditions A using 4-( 4-dodecyloxybenzoyl) benzal- dehyde dimethyl acetal h~(CDc13)3 65 (ddd, 1 H, H-l), 5 62 (s, 1 H, H-3), 4 32 (dd, 1 H, H-5,), 3 78 (dd, 1 H, H-5b), 3 55 (ddd, 1 H, H-6), 445 (dd, 1 H, H-8), 170-1 90 (m, 6 H, H-9,,, H-lo,,, P-CH,), 203 (mc, 1 H, H-9,,), 2 20 (mc, 1 H, H-lOeq), 7 29 (d, 2 H, H-2’, H- 6’), 6 85 (d, 2 H, H-3’, H-5’), 7 57 (d, 2 H, H-2”, H-6’), 7 21 (d, 2 H, H-3”, H-5”), 8 13 (d, 2 H, H-2”’, H-6’”), 696 (d, 2 H, H- 3”’, H-S”), 3 93, 4 03 (t, 4 H, a-CH,), 1 40 (mc, 4 H, y-CH,), 130 (br S, 20 H, -CH2-), 090 (t, 6 H, CH3), 3J16 9 5, 3J1loax 10 8, ,J5a 5b 10 2, 3Jsa 6 10 2, ,J5b 6 5 4, 3Js 9ax 10 2, 9eq 2 4, 3J~ryl 8 5 Hz, Gc(CDCl3) 74 1 (C-I), 101 2 (C-3), 68 2 (C-5), 78 3 (C-6), 79 7 (C-8), 31 9 (C-9y, 33 1 (C-lo), 133 5 (C-l’), 121 0 (C-1’), 127 4, 127 2 (C-2’, C-6’, C-2”, C-6”), 132 3 (C-2”, C-,”’), 114 3, 1144 (C-3’, C-5’, C-3”’, C-5”’), 121 6 (C-3”, C-5”), 158 5 (C-4’), 152 5 (C-4”), 164 5 (C-4”’), 68 1 (a-CH,), 31 6, 297, 296, 294, 293, 292, 260, 257, 227, 226 (-CH2-), 14 1, 140 (CH,) Synthesis of (lS,3R,6R,SR)-8-( 2’-fluoro-4‘-hexyloxyphenyl)-3-[4-(4”’-hexoxybenzoyloxy)phenyl]-2,4,7-trioxabicyclo[4.4.01 decane 9d Reaction conditions A using 4-( 4-dodecyloxybenzoyl) benzal- dehyde dimethyl acetal GH(CDC1,) 3 65 (ddd, 1 H, H-1), 5 62 (s, 1 H, H-3), 4 31 (dd, 1 H, H-5,), 3 79 (dd, 1 H, H-5,), 3 55 (ddd, 1 H, H-6), 4 78 (dd, 1 H, H-8), 171-1 95 (m, 6 H, H-9,,, H-lo,,, P-CH,), 205 (mc, 1 H, H-9,,), 2 21 (mc, 1 H, H-loeq), 6 58 (dd, 1 H, H-3’), 6 68 (dd, 1 H, H-5’), 7 33 (dd, 1 H, H-6’), 7 57 (d, 2 H, H-2”, H-6”), 7 21 (d, 2 H, H-3“, H-5”), 8 13 (d, 2 H, H-2”’, H-6’”), 6 96 (d, 2 H, H-3”’, H-5”’), 3 93, 4 03 (t, 4 H, a-CH,), 1 40 (mc, 4 H, y-CH,), 130 (brs, 8 H, -CH,-), 090 (t, 6 H, CH,), 3Jl 6 5, 3J1 lOax lo 8, 3J5a 5b lo 3, 3J5a 6 lo 3, 3J5b 6 4 3, 3J8 9ax 110, 9eq 2 1, ’JA,~ 8 5, ,J5! 6, 8 5, 4J31 5, 2 4, ,J31 F 12 1, 4J6, F 8 5 Hz, Gc(CDCI3) 73 6 (C-1), 101 9 (C-3), 68 3 (C-5), 78 3 (C- 6), 74 1 (C-8), 31 5 (C-9), 31 2 (C-lo), 135 2 (C-l’), 1604 (C- 2’), 101 9 (C-3’), 110 4 (C-5’), 127 6 (C-6’), 120 2 (C-1”), 127 4 (C-2”, C-6”), 121 6 (C-3”, C-5”), 151 6 (C-4”), 132 3 (C-2”’, C- 6”’)) 114 3 (C-,”’, C-5”’), 68 3 (a-CH,), 29 2, 29 0, 25 7, 22 6 (-CH2-), 14 0 (CH,), ‘J2, F 147, ,J3, F 25 HZ Synthesis of (l’S,3’R,6’R,SR)-1,4-bis[8’-(4”-hexyloxypheny1)-2’,4’,7’-trioxabicyclo[4.4.01 decan-3-yll benzene lob Reaction conditions D using terephthalaldehyde tetramethyl acetal d~(cDC13) 3 65 (ddd, 2 H, H-l’), 5 50 (s, 2 H, H-3’), 4 30 (dd, 2 H, H-5’,), 3 75 (dd, 2 H, H-5’b), 3 55 (ddd, 2 H, H-6’), 4.47 (dd, 2 H, H-8’), 1.85 (mc, 4 H, H-9’,,, H-lO’ax), 2.02 (mc, 2 H, H-9’eq), 2.20 (mc, 2 H, H-lO’eq), 7.25 (d, 4 H, H-2”, H-6”), 6.85 (d, 4 H, H-3”, H-5”), 7.52 (s, 4 H, H-Aryl), 3.94 (t, 4 H, a- CH,), 1.76 (mc, 4 H, P-CH,), 1.40 (mc, 4 H, y-CH2), 1.32 (br s, 8 H, -CH,-), 0.90 (t, 6 H, CH,); 3Jl,,6, 10.8,9.5, 3J1,,10,ax 3J5ar,5b, 10.2, 3J5a,,6, 10.2, 3J5b1,6t 5-49 3J8/,9/ax 10-2, 3J8,,9req 2-47 3JAryl8.5 Hz; GC(CDCl3) 74.1 (C-1’), 101.5 (C-3’), 69.5 (C-57, 78.3 (C-6’), 79.7 (C-S’), 31.9 (C-9’), 33.1 (C-lo), 133.5 (C-1”), 127.2 (C-2”, C-6”), 114.5 (C-3”, C-5”), 158.8 (C-4”), 138.5 (C-1, C-4), 126.1 (C-2, C-3, C-5, C-6), 68.1 (a-CH,), 29.7, 29.6, 29.4, 29.2, 26.0, 22.7 (-CH2-), 14.1 (CH,).Synthesis of (l’S,3’R,6‘R,8’R)-1,4-bis[8’-(2”-fluoro-4”-hexyloxy-phenyl)-2’,4’,7’-trioxabicyclo[4.4.01 decanyl] benzene 10h Reaction conditions D using terephthalaldehyde tetramethyl acetal. GH(CDCl3) 3.64 (ddd, 2 H, H-1’), 5.60 (s, 2 H, H-3’), 4.28 (dd, 2 H, H-5’,), 3.75 (dd, 2 H, H-5’b), 3.58 (ddd, 2 H, H-6’), 4.76 (dd, 2 H, H-8’), 1.87 (mc, 4 H, H-9’,,, H-lO’ax), 2.02 (mc, 2 H, H-9’eq), 2.20 (mc,2 H, H-lO’eq), 6.56 (dd, 2 H, H-3”), 6.67 (dd, 2 H, H-5”), 7.31 (dd, 2 H, H-6”), 7.53 (s, 4 H, H-Aryl), 3.94 (t, 4 H, a-CH,), 1.76 (mc, 4 H, P-CH,), 1.42 (mc, 4 H, y-CH,), 1.32 (br s, 8 H, -CH,-), 0.90 (t, 6 H, CH,); 3Jl,,6, 9.5, 3Jl!,10,ax 3J5a,,5br 3J5a,,6, 3J5bt,6r 5-49 3J8,,9,ax 10.27 3J8,,9teq 2.4, 3JAryl 8.5, 3J51,,611 8.6, 4J3u,5u 2-57 3J311,F 12.1, 4J6rr,~ 8.6 Hz; Gc(CDCl3) 74.1 (C-1’), 101.2 (C-3’), 69.5 (C-5’), 78.7 (C-6’), 79.7 (C-S’), 31.9 (C-9’), 32.2 (C-lo’), 120.5 (C-1”), 160.4 (C-2”), 102.1 (C-3”), 110.5 (C-5”), 127.6 (C-6”), 138.5 (C-1, C- 4), 126.1 (C-2, C-3, C-5, C-6), 68.1 (a-CH,), 29.7, 29.6, 26.0, 22.7 (-CH2-), 14.1 (CH3); ‘J2,,,F 162 Hz.Results and discussion All new compounds show liquid crystalline behaviour of less ordered mesophases such as cholesteric (Ch), smectic A (SA), smectic C* (S,*), blue (BP) and twist grain boundary (TGBA) phases. The mesogenic properties are shown in Table 2. The cholesteric phase exhibits in most cases a fan texture, and is miscible with the nematic compound p-butyl-p’-methoxy- azoxybenzene. The smectic A phase shows a fan texture or is homeotropic.The smectic C* phase is observable as a fan texture with strongly developed pitch lines or as a schlieren texture. The TGBA phase appears with its typical filament tex- ture from the homeotropic smectic A phase. The blue phase with a pitch in the UV is determined by the characteristic paramorphic cholesteric texture that develops continuously in the whole sample from the isotropic state via a blue phase. In a contact preparation with p-butyl-p’-methoxyazoxybenzene, the pitch of the blue phase changes to visible light, and it is observable by its platelet texture. The compounds 5a-5e show a cholesteric mesophase, the preferred mesophase for methoxy-substituted trioxadecalines like compounds 5 and 6. In compounds 6, a tetrahedral carbon atom is replaced by a planar boron atom and, hence, the binding angle of the left alkoxyphenyl unit is different from compounds 5.This structural change causes a broader choles- teric mesophase from 10“C for 5 to 60 “C for 6 and the forming of a blue phase with the pitch in the UV or, in contact preparation, in the visible light. When the methoxy group is placed alongside the boron atom, what is realized for 6f-61, the mesogenic behaviour differs from that for 6a-6e. The cholesteric phase still dominates, but for an alkyl chain length greater than eight a TGBA and smectic A phase are observed Table 2 Transition temperatures of non-fluorinated compounds comp. m n transition temperaturesrc 5a 1 1 K 195.0 Ch 206.0 I 5b 1 6 K 142.9 Ch 155.3 I 5c 1 8 K 134.7 Ch 151.7 I 5d 1 10 K 133.0 Ch 146.9 I 5e 1 12 K 130.6 Ch 140.5 I 6a 1 1 K 158.0 Ch 211.1 (BP) I 6b 6 1 K 92.5 Ch 176.5 (BP) I 6c 8 1 K 90.1 Ch 170.0 (BP) I 6d 6e 10 12 1 1 K 93.5 K 96.6 Ch 163.3 (BP) Ch 151.5 (BP) I I 6f 6g6h 6i 6j6k 61 1 1 1 1 1 1 1 6 8 9 10 11 12 14 K 100.9 K 95.0 K 92.3 K 94.7 K 90.5 K 93.2 K 92.8 (SA 90.0) SA 93.5 SA 101.3 SA 112.0 Ch 177.9 (BP) Ch 165.5 (BP) (TGBA 78.O)Ch 159.5 (BP) (TGBA 90.5)Ch 156.8 (BP) TGBA 94.3 Ch 152.5 (BP) TGBA 103.0 Ch 148.8 (BP) TGBA 113.5 Ch 141.2 (BP) I I I I I I I .7a 8 6 K 163.3 Sc* 165.0 SA 166.6 Ch 173.7 7b 8 8 K 158.6 Sc* 166.9 SA 168.0 I 7c 8 10 K 148.4 Sc* 167.2 I 7d 8 12 K 142.9 Sc* 165.5 I 7e 8 14 K 131.2 Sc* 157.2 I 8a 8b 8 8 6 14 K 124.5 K 120.3 (SA 120.5) (SA 120.3) 9a 6 6 K 126.3 Ch 282.0 I 9b 6 12 K 108.5 Sc* 175.0 SA 206.6 9c 12 6 K 109.6 Sc* 174.8 SA 210.0 I 10a 1 1 K 220.0 Ch 300.0 dec.10b 6 6 K 193.4 Sc* 233.0 Ch 275.0 dec. 1oc 8 8 K 179.3 Sc* 209.0 SA 254.5 Ch 260.0 dec. 1Od 1Oe 10 12 10 12 K 173.2 Sp 211.5 K 163.3 Sc* 234.5 SA 250.0 SA 245.0 dec. dec. 10f 14 14 K 156.5 Sc* 255.0 dec. J. Mater. Chem., 1996, 6(5), 739-745 743 (6h-61) On heating, the TGBA filament texture develops from the homeotropic smectic A phase For chain lengths greater than ten, the smectic A and TGBA phases are enantiotropic, for shorter chains monotropic An analogy may be drawn with compounds such as 11,lo here SA phases are exhibited if the short alkyl chain is attached to the benzoate core We reported earlier that compounds of the general structure 5, eg 5f (Scheme 4) and boron-containing compounds of the general structure 6, eg 6u (Scheme 4) with longer alkoxy chains on both sides show smectic A and monotropic ferroelec- tric phases2 The smectic C* phase is shown only by boron- containing systems with a planar centre in the trioxadecalin system The changed binding angle results in a different molecular shape and, in this case, favours the forming of a smectic C* phase This effect can as well be achieved for non- boron containing compounds by lengthening a wing group with a rigid spacer relative to the molecular core TGBA and smectic C* phases have been found by Goodby et a1 for the phenyl propiolates" So we tried to fit a triple bond as a rigid spacer into our systems creating a structural analogy to these compounds In the compounds 7a-e, the alkynyl group is fitted between the aromatic ring and the trioxadecalin ring which lengthens the lateral group relative to the molecular core All these materials show a smectic C* phase, which for chains longer than eight carbon atoms is the only existing mesophase Shorter chain lengths give a smectic A phase as well as a cholesteric phase The hydrogenation of the rigid alkynyl bridge to a flexible alkyl spacer shows that the linearity of the spacer is essential for the exhibition of the smectic C* phase The hydrogenation causes the complete suppression of the smectic C* phase, leaving only a monotropic smectic A phase for the compounds 8 Even the cholesteric phase of 7a is suppressed in 8a The mesogenic behaviour is similar to the mesogenic properties of the two-ring systems such as 5h (Scheme 4) These compounds only show a monotropic SA phase A comparison of 8a with 5h shows that the right side of the molecule and the molecular core are identical They differ in the left wing group, for 5h an alkyl chain, and for 8a an alkyl chain with a phenyl ring located in the chain The phenyl ring is flexibly relative to the rigid molecular core, so it behaves more like a part of a flexible chain than like a rigid structural unit Thus, it shows like the two-ring compounds a monotropic smectic A phase Another possibility for introducing a lengthened wing group is the introduction of a further aromatic ring which is accomplished for compounds 9 by using a 44 4-alkoxybenzoyl- oxy) benzaldehyde for synthesis The mesogenic behaviour strongly depends on the terminal chain lengths The four-ring systems show for longer alkyl chains a smectic C* schlieren texture and a smectic A phase, but the symmetrically hexyloxy- substituted compound 9a exhibits only a cholesteric mesophase A different class of molecules is synthesized by the dimeris- ation of 4 using terephthalaldehyde as a reagent The resulting structure contains two trioxadecalin units, and the molecule is still chiral, no meso form is obtained Compound 10a with terminal methoxy groups forms a cholesteric phase at high temperatures, but for longer alkyl chains a smectic C* phase is observed, accompanied by a smectic A phase Only 10f with the longest terminal chain lengths shows exclusively the smectic C* phase All compounds possess high melting and clearing temperatures, and they are liable to decompose at high temperatures Next we wanted to study the influence of the introduction and position of a lateral fluoro atom on the mesogenic behaviour The effect of lateral fluoro substitution on the aromatic rings is examined with two different systems The fluorine atom is either located next to the decalin ring system or next to the terminal side chain The general structure of the compounds synthesized is shown in Scheme2 The influence of the position of the fluoro atom is studied for compounds 6 with either X1or X2=F In the case of X1=F, the fluorine is positioned in the aromatic 2-position next to the trioxadecalin ring system, protruding into the molecular core In the case of X2=F, the fluorine is positioned in the aromatic 3-position next to the terminal alkoxy chain, directed to the area of the terminal chains The small change from 2-F to a 3-F substitution causes a large difference in the mesogenic behaviour In Table 3 the transition temperatures are compared with the temperatures of the non-fluorosubstituted compounds Looking at the 3-fluoro compounds with the fluorine next 10 the terminal chain one can see that all compounds show the same phase sequence as the non-fluoro-substituted compounds, but at lower tem- peratures The monotropic smectic C* phase shown by 6m-6r is stabilized and is easier to observe In contrast, the 2-fluorinated compounds 6t, 6v, 6x (in which the fluorine pro- 5h m = 7, n = 6 K 75 (SA59)I H2rn+ crno~ 0 ~ 0 C , H 2 ,+ 1la rn = 2, n = 12, K 93 N 87 I 1 1 b m = 12, n = 2, K 76 5 (SA76) N 91 I Scheme 4 Structures with related mesogenic effects 744 J Muter Chem , 1996, 6(5), 739-745 Table 3 Transition temperatures of fluorinated compounds, compared with the corresponding unfluorinated compounds comp.m n XI 5f " 12 6 H 5g 12 6 F 6m" 6 8 H 6n 6 8 H 60" 6 10 H 6P 6 10 H 6q"6r 6 6 12 12 H H 6s" 8 6 H 6t 8 6 F 6u" 12 6 H 6v 12 6 F 6w" 6 6 H 6x 6 6 F 9a 6 6 H 9b 6 6 F 10b 6 6 H 10h 6 6 F "Ref.2. trudes into the molecular core) show only a cholesteric meso- phase and all smectic phases are completely suppressed. This effect is observed for all compounds having the fluorine in 2- position, even in 6x with two fluorine atoms in both positions (X1=X2=F) the effect of the fluoro substituent in the 2-position is larger. The position of the lateral fluorine causes a steric disturbance of the molecular shape. In the 2-position it changes the form of the rotational cylinder of the central ring system. The shape of the molecular core does not allow the aggregation of the ring segments to form a smectic phase anymore.Protruding out from the ring segment, the fluorine changes the molecular structure as well, but now it is located near the terminal chains that do not need as much space as the central ring systems, so the protruding fluorine atom does not cause a disturbance that is as large as the disturbance caused in 2-position. It only lowers the transition temperatures, and diminishes the risk of recrystallisation while cooling down to the smectic C* phase,12 so observation of this monotropic fan textured phase with pitch lines is more easily achieved. This 'inside-outside-effect' of the lateral substitution can be confirmed using the database LiqCryst.I3 It is possible to compare all mesogenic compounds known in the present literature with a substitution pattern similar to that described above.The result of this comparison is that the observation of lowering of the transition temperatures in one case and suppression of smectic phases in the other case for the different fluoro substitution positions is a general effect of molecules with this substitution pattern and not a special effect of the compounds described.12 x2 transition temperatures/"C H K 138.0 SA 155.0 I H K 93.6 Ch 106.0 I H F H F H F K K K K K K 83.0 66.7 77.0 67.7 82.0 69.0 (Sc* 60.0) (Sp 52.4) (Sc* 57.0) (Sp 39.3) (Sp 44.0) (Sp 35.9) SA 182.0 SA 163.7 S, 177.0 SA 158.7 S, 155.3 SA 168.0 I I I I I I H K 88.0 (Sp 73.0) SA 179.0 I H K 71.5 Ch 132.5 I H H K K 89.0 71.6 (Sp 59.0) S, 165.0 Ch 118.6 I I H K 84.0 SA 180.0 T F K 65.3 Ch 118.0 I H K 126.3 Ch 282.0 I H K 97.0 Ch 250.0 I H K 193.4 Sc* 233.0 Ch 275.0 dec.F K 143.9 Ch 280.0 dec. We thank the Deutsche Forschungsgemeinschuft for financial support. References 1 J. W. Goodby, J. Muter. Chem., 1991, 1, 307. -7 V. Vill and H.-W. Tunger, Liebigs Ann., 1995, 1055. 3 V. Vill, H.-W. Tunger, H. Stegemeyer and K. Diekmann, Tetrahedron: Asymmetry, 1994, 12,2443. 4 V. Vill, H.-W. Tunger, K. Hensen, H. Stegemeyer and K. Diekmann, Liq. Cryst., in the press. 5 V. Vill and H.-W. Tunger, J. Chem. SOC., Chem. Commun., 1995, 1047. 6 V. Vill, H.-W. Tunger and D. Peters, Liq. Cryst., in the press. 7 H. Stegemeyer,A. Sprick, M. A. Osipov, V. Vill and H.-W. Tunger, Phys. Rev. E, 1995,51,5721. 8 E. J. Corey and P. L. Fuchs, Tetrahedron Lett., 1972,36,3769. 9 E. R. H. Jones, L. Skattebol and M. C. Whiting, J. Chem. SOC., 1958, 1054. 10 T. T. Blair, M. E. Neubert, M. Tsai and C.-C. Tsai, J. Phys. Chem. Ref. Data, 1991, 20, 189; J. Malthete, J. Billard, J. Canceill, J. Gabard and J. Jacques, J. Phys. (Paris), 1976,37, Suppl. C3, 1. 11 J. W. Goodby, I. Nishiyama, A. J. Slaney, C. J. Booth and K. J. Toyne, Liq. Cryst., 1993, 14, 37. 12 V. Vill, unpublished results. 13 V. Vill, LiqCryst-Liquid Crystal Database, Fujitsu Kyushu Systems (FQS) Ltd, Fukuoka, Japan, 1995, LCI Publisher, Hamburg 1995. Paper 5/05032D; Received 28th July 1995 J. Muter. Chem., 1996, 6(5),739-745 745