Cholesteric helix inversion: investigations on the influence of the terminal group on the inversion of the helical pitch in trioxadecalins Volkmar Vill,a H. Markus von Mindena and Duncan W. Bruceb aInstitute of Organic Chemistry, University of Hamburg, Martin-L uther-King-Platz 6, D-20146 Hamburg, Germany bDepartment of Chemistry, University of Exeter, Stocker Road, Exeter, UK EX4 4QD Synthesis and mesogenic properties of new liquid crystals, bearing a chiral trioxadecalin system, are described.As cholesteric helix inversions in trioxadecalin systems bearing a terminal cyano or nitro group have previously been observed, the terminal group has been changed systematically to elucidate its influence on the occurrence of inversions of the helical pitch. Chirality has become one of the most important and complex topics in liquid crystal research, since molecular asymmetry imparts form chirality to the liquid crystalline phases.1 Most of the chiral liquid crystals investigated possess only one chiral centre in the flexible side chain.2 However, the use of carbohydrates enables us to introduce a chiral trioxadecalin ring system directly into the molecular core.3 In this way it is possible to locate the chirality in that part of the molecule which determines the general mesogenic properties, and many of our compounds show interesting and unusual behaviour.Previously, we reported trioxadecalins with terminal cyano or nitro groups showing a cholesteric helix inversion.4,5 One of Scheme 2 these nitro compounds has presented a nearly double inversion of the helical twist sense, for the first time as far as we are aware. The aim of this work was to examine the influence of the synthesis of compounds with the trioxadecalin system at a terminal group on the helix inversion.We synthesized a dierent position to that for compounds 13b–23b (Scheme 3), homologous series of compounds with terminal halogen and was obtained by a modified Ferrier reaction.6 The dimethyl pseudo halogen groups, as well as molecules with small non- acetals and the corresponding aldehydes were synthesized polar head groups.Also the eect of the position of the chiral using standard methods in the cases where these aldehydes trioxadecalin system in the molecule has been examined by were not commerically available.synthesizing compounds in which the position of the molecular core was changed. Experimental The diols 12a–c were synthesized according to the previously described procedure starting from commercially available tri- Techniques O-acetyl-D-glucal.3 The diols can easily be combined with aldehyde dimethyl acetals giving the trioxadecalin structure TLC was performed on silica gel (Merck GF254), and detection was eected by UV absorbance, and spraying with a solution (Scheme 1).The diol 27 (Scheme 2), the starting point for the 1 XNH 12a RNC6H13 13b XNH, RNC8H17 2 XNF b RNC8H17 14a XNF, RNC6H13 3 XNCl c RNC10H21 14b XNF, RNC8H17 4 XNBr 15b XNCl, RNC8H17 5 XNI 16a XNBr, RNC6H13 6 XNN3 16b XNBr, RNC8H17 7 XNNCS 16c XNBr, RNC10H21 8 XNMe 17a XNI, RNC6H13 9 XNPri 17b XNI, RNC8H17 10 XNMe3SiCOC 18b XNN3, RNC8H17 11 XNHCOC 19b XNNCS, RNC8H17 20b XNMe, RNC8H17 21b XNPri, RNC8H17 22b XNMe3SiCOC, RNC8H17 23b XNHCOC, RNC8H17 Scheme 1 J.Mater. Chem., 1997, 7(6), 893–899 89328 XNH17C8OC6H4 27 33 XNH17C8OC6H4 29 XNH17C8OC6H4CO2 34 XNH17C8OC6H4CO2 30 XNH13C6OC6H4CO2 35 XNH13C6OC6H4CO2 31 XNH17C8OC6H4OCO 36 XNH17C8OC6H4OCO 32 XNH13C6OC6H4OCO 37 XNH13C6OC6H4OCO Scheme 3 of ethanol–sulfuric acid (951), followed by heating.Column H-3, H-5), 6.87 (d, 2H, H-3¾, H-5¾), 5.58 (s, 1H, H-3), 4.48 (dd, 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.77 chromatography was performed on silica gel 60 (230–240 mesh, Merck). Optical rotations were recorded using a Perkin- (dd, 1H, H-5ax), 3.66 (ddd, 1H, H-1), 3.57 (ddd, 1H, H-6), 2.20 (mc, 1H, H-10eq), 2.03 (mc , 1H, H-9eq), 1.85 (mc, 2H, H-9ax, Elmer 241 polarimeter.The NMR spectra (1H: 400 MHz, 13C: 100.6 MHz) were recorded on a Bruker AMX-400 spectrometer H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2 ), 1.30 (mc, 4H, CH2), 0.89 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.9, 3J3¾,F;5¾,F 8.8, with SiMe4 as internal standard (mc=centred multiplet). J values in Hz.An Olympus BH optical polarizing microscope 4J2¾,F;6¾,F 5.7, 3J2¾,3¾;5¾,6¾ 8.7, 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, 3J1,10ax 10.6, 3J1,6 8.9, 3J1,10eq 4.8; equipped with a Mettler FP 82 hot stage and a Mettler FP 80 cental processor was used to identify thermal transitions and dC (CDCl3 ) 163.1 (C-4), 158.8 (C-4¾), 133.78 (C-1), 133.5 (C- 1¾), 128.1 (C-2, C-6), 127.2 (C-2¾, C-6¾), 115.2 (C-3, C-5), characterize anisotropic textures.For further verification of the textures, a contact preparation with N4 (4-butyl-4¾-meth- 114.5 (C-3¾, C-5¾), 101.1 (C-3), 79.7 (C-8), 78.3 (C-6), 74.0 (C- 1), 69.6 (C-5), 68.1 (a-CH2), 33.0 (C-10), 31.8 (C-9), 29.3, 29.2, oxyazoxybenzene, K 16 N 76 I) was carried out. Analysis by DSC was carried out on a Perkin-Elmer DSC7 instrument 26.0, 22.7 (CH2), 14.1 (CH3); 1J4¾,F 163.1, 2J3¾,F;5¾,F 21.6, 3J2¾,F;6¾,F 8.6, 4J1¾,F 3.3.using heating and cooling rates of 5 K min-1. General reaction conditions for the synthesis of the Synthesis of (1S,3R,6R,8R)-3-(4-fluorophenyl)-8-(4¾-octyltrioxadecalin structure oxyphenyl)-2,4,7-trioxabicyclo[4.4.0]decane (14b) A flask with 40 mg of the diol, the para-substituted benzal- General reaction conditions using 4-fluorobenzaldehyde dehyde dimethyl acetal (1.2 equiv.) and toluene-p-sulfonic acid dimethyl acetal were followed.Yield 40 mg (76%); colourless (monohydrate) (5 mg) in abs. N,N-dimethylformamide was crystals; mp 113.8 °C; [a]D20+23.6 (c 0.93, CHCl3); dH (CDCl3) fitted to a rotatory evaporator.The mixture was heated at 7.50 (dd, 2H, H-2, H-6), 7.26 (d, 2H, H-2¾, H¾6), 7.05 (dd, 2H, reduced pressure (29–33 hPa) in a water-bath of 60°C, in order H-3, H-5), 6.87 (d, 2H, H-3¾, H-5¾), 5.58 (s, 1H, H-3), 4.48 to remove the formed methanol, until TLC revealed complete (dd, 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.77 reaction. The solvent was removed in vacuo (10 hPa) at a (dd, 1H, H-5ax), 3.66 (ddd, 1H, H-1), 3.57 (ddd, 1H, H-6), 2.20 water-bath temperature of 75°C.The solid residue was washed (mc, 1H, H-10eq), 2.03 (mc , 1H, H-9eq), 1.85 (mc, 2H, H-9ax, with saturated aqueous sodium hydrogen carbonate, filtered, H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2), 1.30 (mc 8H, washed with water and cold ethanol and then recrystallized CH2), 0.89 (t, 3H, CH3 ); 3J2¾,3¾;5¾,6¾ 8.9, 3J3¾,F;5¾,F 8.8, from ethanol. 4J2¾,F;6¾,F 5.7, 3J2¾,3¾;5¾,6¾ 8.7, 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, 3J1,10ax 10.6, 3J1,6 8.9, 3J1,10eq 4.8; Synthesis of (1S,3R,6R,8R)-3-phenyl-8-(4¾-octyloxyphenyl )- dC (CDCl3 ) 163.1 (C-4), 158.8 (C-4¾), 133.78 (C-1), 133.5 (C- 2,4,7-trioxabicyclo[4.4.0]decane (13b) 1¾), 128.1 (C-2, C-6), 127.2 (C-2¾, C-6¾), 115.2 (C-3, C-5), 114.5 (C-3¾, C-5¾), 101.1 (C-3), 79.7 (C-8), 78.3 (C-6), 74.0 (C- General reaction conditions using benzaldehyde dimethyl 1), 69.6 (C-5), 68.1 (a-CH2 ), 33.0 (C-10), 31.8 (C-9), 29.4, 29.3, acetal were followed.Yield 16.0 mg (31%); colourless crystals; 29.2, 26.0, 22.7 (CH2), 14.1 (CH3); 1J4¾,F 163.1, 2J3¾,F;5¾,F 21.6, mp 105.8°C; [a]D20+23.8 (c 9.87, CHCl3); dH (CDCl3) (=3- 3J2¾,F;6¾,F 8.6, 4J1¾,F 3.3.phenyl ring; ¾=8-octyloxyphenyl ring) 7.51 (dd, 2H, H-2, H- 6), 7.36 (mc, 3H, H-3, H-4, H-5), 7.26 (d, 2H, H-2¾, H-6¾), 6.87 (d, 2H, H-3¾, H-5¾), 5.60 (s, 1H, H-3), 4.48 (dd, 1H, H-8), Synthesis of (1S,3R,6R,8R)-3-(4-chlorophenyl )-8-(4¾-octyloxyphenyl)- 2,4,7-trioxabicyclo[4.4.0]decane (15b) 4.32 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.79 (dd, 1H, H-5ax), 3.67 (ddd, 1H, H-1), 3.59 (ddd, 1H, H-6), 2.21 (mc , 1H, H- General reaction conditions using 4-chlorobenzaldehyde 10eq), 2.03 (mc, 1H, H-9eq), 1.86 (mc, 2H, H-9ax, H-10ax), 1.75 dimethyl acetal were followed. Yield 16.8 mg (31%); colourless (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2), 1.30 (mc, 8H, CH2), 0.89 crystals; mp 128.8 °C; [a]D20+25.4 (c 0.72, CHCl3); dH (CDCl3) (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 7.5 3J2¾,4¾;6¾,4¾ 1.5, 3J2¾,3¾;5¾,6¾ 8.2, 7.45 (d, 2H, H-2, H-6), 7.34 (d, 2H, H-3, H-5), 7.26 (d, 2H, 3J8,9ax 10.2, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, H-2¾, H-6¾), 6.87 (d, 2H, H-3¾, H-5¾), 5.57 (s, 1H, H-3), 4.47 (dd, 3J1,10ax 10.2, 3J1,6 8.9, 3J1,10eq 4.8; dc (CDCl3) 158.8 (C-4¾), 137.8 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2 ), 3.77 (dd, (C-1), 133.6 (C-1¾), 129.0 (C-3, C-5), 128.3 (C-4), 127.2 (C- 1H, H-5ax), 3.66 (ddd, 1H, H-1), 3.57 (ddd, 1H, H-6), 2.20 2¾, C-6¾), 126.2 (C-2, C-6), 114.5 (C-3¾, C-5¾), 101.8 (C-3), 79.7 (mc, 1H, H-10eq), 2.03 (mc , 1H, H-9eq), 1.85 (mc, 2H, H-9ax, (C-8), 78.4 (C-6), 74.1 (C-1), 69.6 (C-5), 68.1 (a-CH2), 33.1 (C- H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2 ), 1.30 (mc, 10), 31.8 (C-9), 29.4, 29.3, 26.1, 22.7 (CH2), 14.1 (CH3). 8H, CH2), 0.89 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.7, 3J2¾,3¾;5¾,6¾ 8.7, 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, Synthesis of (1S,3R,6R,8R)-3-(4-fluorophenyl )-8-(4¾-hexyl- 3J1,10ax 10.2, 3J1,6 8.9, 3J1,10eq 4.8; dc (CDCl3) 158.8 (C-4¾), 136.3 oxyphenyl )-2,4,7-trioxabicyclo[4.4.0]decane (14a) (C-1), 134.8 (C-4), 133.4 (C-1¾), 128.5 (C-3, C-5), 127.7 (C- 2, C-6), 127.2 (C-2¾, C-6¾), 114.5 (C-3¾, C-5¾), 100.9 (C-3), 79.7 General reaction conditions using 4-fluorobenzaldehyde dimethyl acetal were followed.Yield 41.6 mg (77%); colourless (C-8), 78.4 (C-6), 74.0 (C-1), 69.5 (C-5), 68.1 (a-CH2), 33.0 (C-10), 31.8 (C-9), 29.4, 29.3, 29.2, 26.0, 22.7 crystals; mp 119.3°C; [a]D20+23.3 (c 0.91, CHCl3); dH (CDCl3) 7.50 (dd, 2H, H-2, H-6), 7.26 (d, 2H, H-2¾, H¾6), 7.05 (dd, 2H, (CH2), 14.1 (CH3 ). 894 J. Mater. Chem., 1997, 7(6), 893–899Synthesis of (1S,3R,6R,8R)-3-(4-bromophenyl )-8-(4¾-hexyl- 10eq), 2.03 (mc, 1H, H-9eq), 1.85 (mc, 2H, H-9ax, H-10ax), 1.75 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2), 1.33 (mc, 4H, CH2), 0.90 oxyphenyl )-2,4,7-trioxabicyclo[4.4.0]decane (16a) (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.2, 3J2¾,3¾;5¾,6¾ 8.5, 3J8,9ax 10.9, 3J8,9eq General reaction conditions using 4-bromobenzaldehyde 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, 3J1,10ax 10.9, 3J1,6 8.9, dimethyl acetal were followed.Yield 42.1 mg (68%); colourless 3J1,10eq 4.4; dC (CDCl3) 158.8 (C-4¾), 137.4 (C-3, C-5), 133.4 crystals; mp 144.9°C; [a]D20+23.2 (c 0.92, CHCl3); dH (CDCl3) (C-1¾), 128.1 (C-2, C-6), 127.2 (C-2¾, C-6¾), 114.5 (C-3¾, C-5¾), 7.50 (d, 2H, H-3, H-5), 7.39 (d, 2H, H-2, H-6), 7.26 (d, 2H, 101.0 (C-3), 94.9 (C-4), 79.7 (C-8), 78.3 (C-6), 74.0 (C-1), 69.5 H-2¾, H-6¾), 6.87 (d, 2H, H-3¾, H-5¾), 5.55 (s, 1H, H-3), 4.47 (dd, (C-5), 68.1 (a-CH2), 33.0 (C-10), 31.8 (C-9), 29.2, 25.7, 22.6 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.77 (dd, (CH2), 14.1 (CH3). 1H, H-5ax), 3.65 (ddd, 1H, H-1), 3.57 (ddd, 1H, H-6), 2.21 (mc, 1H, H-10eq), 2.03 (mc, 1H, H-9eq), 1.85 (mc , 2H, H-9ax, Synthesis of (1S,3R,6R,8R)-3-(4-iodophenyl )-8-(4¾-octyl- H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2), 1.33 (mc, oxyphenyl)-2,4,7-trioxabicyclo[4.4.0]decane (17b) 4H, CH2), 0.90 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.2, 3J2¾,3¾;5¾,6¾ 8.5, 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, General reaction conditions using 4-iodobenzaldehyde 3J1,10ax 10.2, 3J1,6 8.9, 3J1,10eq 4.8; dc (CDCl3) 158.8 (C-4¾), 136.8 dimethyl acetal were followed. Yield 47.8 mg (73%); colourless (C-1), 133.5 (C-1¾), 131.4 (C-3, C-5), 128.0 (C-2, C-6), 127.2 crystals; mp 134.5 °C; [a]D20+20.6 (c 0.89, CHCl3); dH (CDCl3) (C-2¾, C-6¾), 123.1 (C-4), 114.5 (C-3¾, C-5¾), 101.0 (C-3), 79.7 7.71 (d, 2H, H-3, H-5), 7.25 (d, 4H, H-2, H-6, H-2¾, H-6¾), (C-8), 78.4 (C-6), 74.0 (C-1), 69.6 (C-5), 68.1 (a-CH2 ), 33.0 6.86 (d, 2H, H-3¾, H-5¾), 5.54 (s, 1H, H-3), 4.47 (dd, 1H, H-8), (C-10), 31.6 (C-9), 29.2, 25.7, 22.6 (CH2), 14.1 (CH3). 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.76 (dd, 1H, H-5ax), 3.65 (ddd, 1H, H-1), 3.56 (ddd, 1H, H-6), 2.20 (mc, 1H, H- Synthesis of (1S,3R,6R,8R)-3-(4-bromophenyl )-8-(4¾-octyl- 10eq), 2.03 (mc, 1H, H-9eq), 1.85 (mc, 2H, H-9ax, H-10ax), 1.75 oxyphenyl )-2,4,7-trioxabicyclo[4.4.0]decane (16b) (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2), 1.30 (mc, 8H, CH2), 0.89 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.2, 3J2¾,3¾;5¾,6¾ 8.5, 3J8,9ax 10.9, 3J8,9eq General reaction conditions using 4-bromobenzaldehyde 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, 3J1,10ax 10.9, 3J1,6 8.9, dimethyl acetal were followed.Yield 32.0 mg (54%); colourless 3J1,10eq 4.4; dC (CDCl3) 158.8 (C-4¾), 137.4 (C-3, C-5), 133.4 crystals; mp 132.5°C; [a]D20+23.9 (c 0.82, CHCl3); dH (CDCl3) (C-1¾), 128.1 (C-2, C-6), 127.2 (C-2¾, C-6¾), 114.5 (C-3¾, C-5¾), 7.50 (d, 2H, H-3, H-5), 7.39 (d, 2H, H-2, H-6), 7.26 (d, 2H, 101.0 (C-3), 94.9 (C-4), 79.7 (C-8), 78.3 (C-6), 74.0 (C-1), 69.5 H-2¾, H-6¾), 6.87 (d, 2H, H-3¾, H-5¾), 5.55 (s, 1H, H-3), 4.47 (dd, (C-5), 68.1 (a-CH2), 33.0 (C-10), 31.8 (C-9), 29.4, 29.3, 29.2, 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.77 (dd, 26.04, 22.7 (CH2), 14.1 (CH3 ). 1H, H-5ax), 3.65 (ddd, 1H, H-1), 3.57 (ddd, 1H, H-6), 2.21 (mc, 1H, H-10eq), 2.03 (mc, 1H, H-9eq), 1.85 (mc , 2H, H-9ax, H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2), 1.33 (mc, Synthesis of 1S,3R,6R,8R)-3-(4-azidophenyl )-8-(4¾-octyl- 8H, CH2), 0.89 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.2, 3J2¾,3¾;5¾,6¾ 8.5, oxyphenyl)-2,4,7-trioxabicyclo[4.4.0]decane (18b) 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, General reaction conditions using 4-azidobenzaldehyde 3J1,10ax 10.2, 3J1,6 8.9, 3J1,10eq 4.8; dC (CDCl3 ) 158.8 (C-4¾), 136.8 dimethyl acetal were followed.Yield 37.5 mg (68%); colourless (C-1), 133.5 (C-1¾), 131.4 (C-3, C-5), 128.0 (C-2, C-6), 127.2 crystals; mp 118.2 °C; [a]D20+20.1 (c 0.82, CHCl3); dH (CDCl3) (C-2¾, C-6¾), 123.1 (C-4), 114.5 (C-3¾, C-5¾), 101.0 (C-3), 79.7 7.50 (d, 2H, H-2, H-6), 7.02 (d, 2H, H-3, H-5), 7.25 (d, 2H, (C-8), 78.4 (C-6), 74.0 (C-1), 69.6 (C-5), 68.1 (a-CH2 ), 33.0 H-2¾, H-6¾), 6.87 (d, 2H, H-3¾, H-5¾), 5.57 (s, 1H, H-3), 4.47 (dd, (C-10), 31.6 (C-9), 29.4, 29.3, 29.2, 26.0, 22.7 (CH2), 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2 ), 3.77 (dd, 14.1 (CH3). 1H, H-5ax), 3.66 (ddd, 1H, H-1), 3.57 (ddd, 1H, H-6), 2.20 Synthesis of (1S,3R,6R,8R)-3-(4-bromophenyl )-8-(4¾-decyl- (mc, 1H, H-10eq), 2.03 (mc , 1H, H-9eq), 1.85 (mc, 2H, H-9ax, oxyphenyl )-2,4,7-trioxabicyclo[4.4.0]decane (16c ) H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2 ), 1.30 (mc, 8H, CH2), 0.88 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.5, 3J2¾,3¾;5¾,6¾ 8.5, General reaction conditions using 4-bromobenzaldehyde 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, dimethyl acetal were followed.Yield 40.0 mg (69%); colourless 3J1,10ax 10.2, 3J1,6 8.9, 3J1,10eq 4.8; dC (CDCl3) 158.8 (C-4¾), 133.4 crystals; mp 128.0°C; [a]D20+22.2 (c 0.89, CHCl3); dH (CDCl3) (C-1¾), 127.8, 118.9 (C-2, C-3, C-5, C-6), 127.2 (C-2¾, C-6¾), 7.50 (d, 2H, H-3, H-5), 7.39 (d, 2H, H-2, H-6), 7.26 (d, 2H, 114.5 (C-3¾, C-5¾), 101.2 (C-3), 79.7 (C-8), 78.4 (C-6), 74.0 (C- H-2¾, H-6¾), 6.87 (d, 2H, H-3¾, H-5¾), 5.55 (s, 1H, H-3), 4.47 (dd, 1), 69.6 (C-5), 68.1 (a-CH2 ), 33.1 (C-10), 31.8 (C-9), 29.4, 29.3, 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.77 (dd, 26.0, 22.7 (CH2), 14.1 (CH3). 1H, H-5ax), 3.65 (ddd, 1H, H-1), 3.57 (ddd, 1H, H-6), 2.21 (mc, 1H, H-10eq), 2.03 (mc, 1H, H-9eq), 1.85 (mc , 2H, H-9ax, Synthesis of (1S,3R,6R,8R)-3-(4-thiocyanatophenyl )-8-(4¾- H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2), 1.33 (mc, octyloxyphenyl )-2,4,7-trioxabicyclo[ 4.4.0]decane (19b) 12H, CH2), 0.89 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.2, 3J2¾,3¾;5¾,6¾ 8.5, 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, General reaction conditions using 4-thiocyanatobenzaldehyde 3J1,10ax 10.2, 3J1,6 8.9, 3J1,10eq 4.8; dC (CDCl3 ) 158.8 (C-4¾), 136.8 dimethyl acetal were followed.Yield 26.9 mg (47%); colourless (C-1), 133.5 (C-1¾), 131.4 (C-3, C-5), 128.0 (C-2, C-6), 127.2 crystals; mp 80.7 °C; [a]D20+21.6 (c 0.21, CHCl3); dH (CDCl3) (C-2¾, C-6¾), 123.1 (C-4), 114.5 (C-3¾, C-5¾), 101.0 (C-3), 79.7 7.60, 7.53 (d, 2H, H-2, H-3) and (d, 2H, H-5, H-6), 7.26 (d, (C-8), 78.4 (C-6), 74.0 (C-1), 69.6 (C-5), 68.1 (a-CH2), 33.0 (C- 2H, H-2¾, H-6¾), 6.87 (d, 2H, H-3¾, H-5¾), 5.60 (s, 1H, H-3), 4.48 10), 31.6 (C-9), 29.6, 29.5, 29.4, 29.3, 29.3, 29.2, 26.0 22.7, (CH2), (dd, 1H, H-8), 4.31 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.78 14.1 (CH3).(dd, 1H, H-5ax), 3.67 (ddd, 1H, H-1), 3.57 (ddd, 1H,, H-6), 2.21 (mc, 1H, H-10eq), 2.04 (mc , 1H, H-9eq), 1.85 (mc, 2H, H-9ax, Synthesis of (1S,3R,6R,8R)-3-(4-iodophenyl )-8-(4¾-hexyl- H-10ax), 1.75 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2 ), 1.30 (mc, oxyphenyl )-2,4,7-trioxabicyclo[4.4.0]decane (17a) 8H, CH2), 0.89 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.3, 3J2¾,3¾;5¾,6¾ 8.7, 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, General reaction conditions using 4-iodobenzaldehyde dimethyl acetal were followed.Yield 37.2 mg (55%); colourless 3J1,10ax 10.9, 3J1,6 8.9, 3J1,10eq 4.4; dC (CDCl3) 158.8 (C-4¾), 139.4, 131.0 (C-4, C-1), 133.3 (C-1¾), 129.7, 128.2 (C-2, C-3, crystals; mp 148.8°C; [a]D20+22.6 (c 0.92, CHCl3); dH (CDCl3) 7.71 (d, 2H, H-3, H-5), 7.25 (d, 4H, H-2, H-6, H-2¾, H-6¾), C-5, C-6), 125.0 (SCN), 127.2 (C-2¾, C-6¾), 114.5 (C-3¾, C-5¾), 100.4 (C-3), 79.7 (C-8), 78.4 (C-6), 73.9 (C-1), 69.6 (C-5), 68.1 6.86 (d, 2H, H-3¾, H-5¾), 5.54 (s, 1H, H-3), 4.47 (dd, 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.76 (dd, 1H, H-5ax), (a-CH2), 33.0 (C-10), 31.8 (C-9), 29.36, 29.25, 29.18, 26.04, 22.66 (CH2), 14.1 (CH3). 3.65 (ddd, 1H, H-1), 3.56 (ddd, 1H, H-6), 2.20 (mc , 1H, HJ. Mater. Chem., 1997, 7(6), 893–899 895Synthesis of (1S,3R,6R,8R)-3-(4-methylphenyl )-8-(4¾-octyl- H-6), 2.20 (mc, 1H, H-10eq), 2.03 (mc, 1H, H-9eq), 1.86 (mc, 2H, H-9ax, H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2 ), oxyphenyl )-2,4,7-trioxabicyclo[4.4.0]decane (20b) 1.30 (mc, 8H, CH2), 0.88 (t, 3H, CH3), 0.25 (s, 9H, SiMe3 ); General reaction conditions using 4-methylbenzaldehyde 3J2¾,3¾;5¾,6¾ 8.5, 3J2¾,3¾;5¾,6¾ 8.7, 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax dimethyl acetal were followed.Yield 31.8 mg (61%); colourless 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, 3J1,10ax 10.2, 3J1,6 8.9, 3J1,10eq 4.8; crystals; mp 118.0°C; [a]D20+24.2 (c 0.92, CHCl3); dH (CDCl3) dC (CDCl3) 158.8 (C-4¾), 137.8 (C-1), 133.5 (C-1¾), 131.9 (C- 7.39 (d, 2H, H-2, H-6), 7.26 (d, 2H, H-2¾, H-6¾), 7.17 (d, 2H, 3, C-5), 127.2 (C-2¾, C-6¾), 126.1 (C-2, C-6), 123.8 (C-4), H-3, H-5), 6.86 (d, 2H, H-3¾, H-5¾), 5.57 (s, 1H, H-3), 4.47 114.5 (C-3¾, C-5¾), 104.9, 94.6 (C-alkyne), 101.2 (C-3), 79.7 (C- (dd, 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2 ), 3.77 8), 78.4 (C-6), 74.0 (C-1), 69.6 (C-5), 68.1 (a-CH2), 33.1 (C-10), (dd, 1H, H-5ax), 3.65 (ddd, 1H, H-1), 3.57 (ddd, 1H, H-5eq), 31.8 (C-9), 29.4, 29.3, 29.2, 26.1, 22.7 (CH2), 14.1 2.34 (s, 3H, CH3 Aryl), 2.20 (mc, 1H, H-10eq), 2.02 (mc, 1H, (CH3), 0.032 (SiMe3).H-9eq), 1.85 (mc, 2H, H-9ax, H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, c-CH2 ), 1.30 (mc, 8H, CH2), 0.89 (t, 3H, CH3); Synthesis of 4-ethynylbenzaldehyde dimethyl acetal (11) 3J2¾,3¾;5¾,6¾ 8.2, 3J2¾,3¾;5¾,6¾ 8.5, 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax Bu4NF (1.0 M solution in THF, 3.22 ml) was added to a 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, 3J1,10ax 10.2, 3J1,6 8.9, 3J1,10eq 4.4; solution of 10 (0.4 g, 1.61 mmol) in 10 ml of abs.THF at room dC (CDCl3) 158.8 (C-4¾), 138.8 (C-4), 135.0 (C-1), 133.6 (Ctemp. under nitrogen. The reaction mixture was stirred at 1¾), 129.0 (C-3, C-5), 127.2 (C-2¾, C-6¾), 126.1 (C-2, C-6), room temp.over night, and then water (80 ml) was added. 114.5 (C-3¾, C-5¾), 101.9 (C-3), 79.7 (C-8), 78.3 (C-6), 74.1 (CThe mixture was extracted with diethyl ether (3×50 ml), the 1), 69.6 (C-5), 68.1 (a-CH2), 33.1 (C-10), 31.8 (C-9), 29.4, 29.3, combined organic extracts dried with sodium carbonate, and 29.3, 29.2, 25.1, 22.7 (CH2), 21.3 (CH3 Aryl), 14.1 (CH3).concentrated. The crude residue was purified by column chrom- Synthesis of (1S,3R,6R,8R)-3-(4-isopropylphenyl )-8-(4¾-octyl- atography [light petroleum (bp 60–70 °C)–ethyl acetate 551]. oxyphenyl )-2,4,7-trioxabicyclo[4.4.0]decane (21b) Yield 0.24 g (85%); dH (CDCl3 ) 7.50 (d, 2H, H-3¾, H-5¾), 7.41 (d, 2H, H-2¾, H-6¾), 5.38 (s, 1H, CH), 3.30 (s, 6H, OCH3), 3.08 General reaction conditions using 4-isopropylbenzaldehyde (s, 1H, H alkyne); 3JAryl 8.2.dimethyl acetal were followed. Yield 28.1 mg (51%); colourless crystals; mp 88.3°C; [a]D20+18.3 (c 1.19, CHCl3 ); dH (CDCl3) Synthesis of (1S,3R,6R,8R)-3-(4-ethynylphenyl )-8-(4¾-octyl- 7.43 (d, 2H, H-2 H-6), 7.26 (d, 2H, H-2¾, H-6¾), 7.23 (d, 2H, oxyphenyl)-2,4,7-trioxabicyclo[4.4.0]decane (23b) H-3, H-5), 6.86 (d, 2H, H-3¾, H-5¾), 5.58 (s, 1H, H-3), 4.47 General reaction conditions using 4-ethynylbenzaldehyde (dd, 1H, H-8), 4.30 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2), 3.77 dimethyl acetal were followed.Yield 29.5 mg (55%); colourless (dd, 1H, H-5ax), 3.66 (ddd, 1H, H-1), 3.58 (ddd, 1H, H-6), 2.90 crystals; mp 114.1 °C; [a]D20+23.9 (c 0.91, CHCl3); dH (CDCl3) (sep, 2H, CH Pri), 2.20 (mc, 1H, H-10eq ), 2.02 (mc, 1H, H-9eq), 7.50 (d, 2H, H-2, H-6), 7.47 (d, 2H, H-3, H-5), 7.26 (d, 2H, 1.85 (mc, 2H, H-9ax, H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, H-2¾, H-6¾), 6.87 (d, 2H, H-3¾, H-5¾), 5.59 (s, 1H, H-3), 4.48 (dd, c-CH2), 1.30 (mc , 8H, CH2 ), 1.22 (d, 6H, CH3 Pri), 0.89 (t, 3H, 1H, H-8), 4.31 (dd, 1H, H-5eq), 3.94 (t, 2H, a-CH2 ), 3.77 (dd, CH3); 3J2¾,3¾;5¾,6¾ 8.5, 3J2¾,3¾;5¾,6¾ 8.2, 3J8,9ax 10.9, 3J8,9eq 2.4, 1H, H-5ax), 3.66 (ddd, 1H, H-1), 3.57 (ddd, 1H, H-6), 3.07 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, 3J1,10ax 10.2, 3J1,6 8.9, (s, 1H, H alkyne), 2.20 (mc, 1H, H-10eq), 2.03 (mc, 1H, H-9eq), 3J1,10eq 4.4; dC (CDCl3) 158.8 (C-4¾), 149.8 (C-4), 135.3 (C-1), 1.86 (mc, 2H, H-9ax, H-10ax), 1.76 (q, 2H, b-CH2), 1.44 (q, 2H, 133.6 (C-1¾), 127.2 (C-2¾, C-6¾), 126.4 (C-3, C-5), 126.1 (C-2, c-CH2), 1.30 (mc, 8H, CH2), 0.88 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ c-6), 114.5 (C-3¾, C-5¾), 101.9 (C-3), 79.7 (C-8), 78.3 (C-6), 74.1 8.6, 3J2¾,3¾;5¾,6¾ 8.9, 3J8,9ax 10.9, 3J8,9eq 2.4, 2J5eq,5ax 10.2, 3J5eq,6 (C-1), 69.6 (C-5), 68.1 (a-CH2), 34.0 (CH Pri), 33.1 (C-10), 31.8 4.8, 3J5ax,6 10.2, 3J1,10ax 10.2, 3J1,6 8.9, 3J1,10eq 4.8; dC (CDCl3) (C-9), 29.4, 29.3, 29.3, 29.2, 26.1, 22.7 (CH2), 23.9 (CH3 Pri), 158.8 (C-4¾), 138.2 (C-1), 133.5 (C-1¾), 132.1 (C-3, C-5), 127.2 14.1 (CH3).(C-2¾, C-6¾), 126.2 (C-2, C-6), 122.7 (C-4), 114.5 (C-3¾, C-5¾), Synthesis of 4-(trimethylsilylethynyl )benzaldehyde dimethyl 101.1 (C-3), 83.4 (C alkyne), 79.7 (C-8), 78.4 (C-6), 77.5 (C acetal (10) alkyne), 74.0 (C-1), 69.6 (C-5), 68.1 (a-CH2), 33.0 (C-10), 31.8 (C-9), 29.4, 29.3, 29.2, 26.1, 22.7 (CH2), 14.1 (CH3).Trimethylsilylacetylene (0.6 ml, 4.31 mmol) was added to a solution of 4-iodobenzaldehyde dimethyl acetal 5 (1.0 g, Synthesis of 4-octyloxybiphenyl-4¾-carbaldehyde dimethyl acetal 4.31 mmol), tetrakis(triphenylphosphine)-palladium(O) (258 (12) mg, 0.22 mmol), CuI (172 mg, 0.86 mmol) and butylamine A solution of 4-octyloxyphenylboronic acid (2.75 g, 11 mmol) (0.65 ml, 6.46 mmol) in 53 ml abs.toluene at room temp. in 20 ml ethanol was added to a stirred mixture of 4-bromobenz- under nitrogen. The reaction mixture was stirred at room aldehyde (1.96 g, 8.5 mmol) and tetrakis(triphenylphosphine)- temp. for 28 h and then quenched with water (200 ml).The palladium(O) (0.326 g, 0.28 mmol) in 15 ml benzene and aqueous layer was extracted with diethyl ether (3×70 ml), the aqueous sodium carbonate (2 M, 15 ml) at room temp. under combined organic extracts were dried with sodium carbonate nitrogen. The stirred mixture was heated at the temperature and concentrated. The crude residue was purified by column of reflux for 23 h.Then water was added, the product was chromatography [light petroleum (bp 60–70 °C)–ethyl acetate extracted with light petroleum (bp 60–70°C), the combined 2051+1% triethylamine]. Yield 0.81 g (91%); dH (CDCl3) 7.47 organic extracts dried with sodium carbonate and the solvent (d, 2H, H-3¾, H-5¾), 7.37 (d, 2H, H-2¾, H-6¾), 5.38 (s, 1H, CH), removed in vacuo. The crude residue was purified by repeated 3.30 (s, 6H, OCH3), 0.25 (s, 9H, SiMe3); 3JAryl 8.2.recrystallization from methanol. Yield 2.43 g (80%); colourless Synthesis of (1S,3R,6R,8R)-3-[4-(trimethylsilyethynyl )- crystals; mp 49.4 °C; dH (CDCl3 ) 7.55 (d, 2H, H-2, H-6), 7.52 phenyl]-8-(4¾-octyloxyphenyl )-2,4,7-trioxabicyclo[4.4.0]- (d, 2H, H-3, H-5), 7.48 (d, 2H, H-2¾, H-6¾), 6.96 (d, 2H, H-3¾, decane (22b) H-5¾), 5.42 (s, 1H, CH), 3.99 (t, 2H, a-CH2), 3.36 (s, 6H, OCH3), 1.80 (q, 2H, b-CH2 ), 1.47 (q, 2H, c-CH2), 1.31 (mc, General reaction conditions using 4-(trimethylsilyethynyl)ben- 8H, -CH2), 0.89 (t, 3H, -CH3); 3JAryl 8.8, 3JAryl¾ 8.5.zaldehyde dimethyl acetal were followed. Yield 36.0 mg (58%); colourless crystals; mp 146.1°C; [a]D20+21.5 (c 0.88, CHCl3); Synthesis of (1S,3R,6R)-2-(4-octyloxybiphenyl )-2,4,7- dH (CDCl3) 7.47 (d, 2H, H-2, H-6), 7.44 (d, 2H, H-3, H-5), trioxabicyclo[4.4.0]decane (33) 7.26 (d, 2H, H-2¾, H-6¾), 6.87 (d, 2H, H-3¾, H-5¾), 5.57 (s, 1H, H-3), 4.47 (dd, 1H, H-8), 4.31 (dd, 1H, H-5eq), 3.94 (t, 2H, a- General reaction conditions using 4-octyloxybiphenyl-4¾-carbaldehyde diemthyl acetal were followed. The product was CH2), 3.77 (dd, 1H, H-5ax), 3.65 (ddd, 1H, H-1), 3.57 (ddd, 1H, 896 J.Mater. Chem., 1997, 7(6), 893–899purified by column chromatography [light petroleum (bp (CDCl3 ) 8.18 (d, 2H, H-3¾, H-5¾), 7.63 (d, 2H, H-2¾, H-6¾), 7.11 (d, 2H, H-2, H-6), 6.92 (d, 2H, H-3, H-5), 5.63 (s, 1H, H- 60–70°C)–ethyl acetate 1051].Yield 75.4 mg (49%); colourless crystals; mp 122.9°C; [a]D20-4.8 (c 1.01, CHCl3 ); dH (CDCl3) 3), 4.28 (dd, 1H, H-5eq ), 3.96 (m, 3H, a-CH2, H-8eq), 3.71 (dd, 1H, H-5ax), 3.59 (ddd, 1H, H-1), 3.51 (ddd, 1H, H-8ax), 3.36 7.53 (s, 4H, H-2¾, H-3¾, H-5¾, H-6¾), 7.49 (d, 2H, H-2, H-6), 6.95 (d, 2H, H-3, H-5), 5.60 (s, 1H, H-3), 4.26 (dd, 1H, H- (ddd, 1H, H-6), 2.15 (mc, 1H, H-10eq), 1.74–1.93 (m, 4H, H- 9ax, H-9eq, b-CH2), 1.69 (dddd, 1H, H-10ax), 1.46 (q, 2H, c- 5eq), 3.92–4.02 (m, 3H, a-CH2, H-8eq), 3.70 (dd, 1H, H-5ax), 3.58 (ddd, 1H, H-1), 3.51 (ddd, 1H, H-8ax), 3.36 (ddd, 1H, H- CH2), 1.31 (mc, 8H, CH2), 0.89 (t, 3H, CH3 ); 3J2¾,3¾;5¾,6¾ 8.9, 3J2¾,3¾;5¾,6¾ 8.5, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, 3J1,10ax 11.5, 6), 2.13 (mc, 1H, H-10eq), 1.74–1.92 (m, 4H, H-9ax, H-9eq, b- CH2), 1.68 (dddd, 1H, H-10ax), 1.47 (q, 2H, c-CH2), 1.35 (mc, 3J1,6 8.9, 3J1,10eq 4.8, 2J8ax,8eq 11.6, 3J8ax,9ax 11.6, 3J8ax,9eq 3.4, 2J10ax,10eq 11.6, 3J10ax,9ax 11.6, 3J10ax,9eq 4.4; dC (CDCl3) 165.3 8H, CH2), 0.89 (t, 3H, CH3); 3J2¾,3¾;5¾,6¾ 8.7, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J5ax,6 10.2, 3J1,10ax 11.5, 3J1,6 8.9, 3J1,10eq 4.4, 2J8ax,8eq (C=O), 156.9 (C-4), 144.2 (C-1), 142.8 (C-1¾), 130.2 (C-3¾, C- 5¾), 130.1 (C-4¾), 126.4 (C-2¾, C-6¾), 122.4 (C-2, C-6), 115.1 11.6, 3J8ax,9ax 11.6, 3J8ax,9eq 3.4, 2J10ax,10eq 11.6, 3J10ax,9ax 11.6, 3J10ax,9eq 4.4; dC (CDCl3) 158.9 (C-4), 141.6 (C-4¾), 136.1 (C- (C-3, C-5), 100.9 (C-3), 78.7 (C-1), 74.0 (C-6), 69.5 (C-5), 68.5 (C-8), 68.1 (a-CH2 ), 31.8 (CH2 ), 29.3 (C-9), 28.8 (C-10), 1¾), 133.2 C-1), 128.2 (C-2, 6), 126.7, 126.5 (C-2¾, C-3¾, C-5¾, C-6¾), 114.8 (C-3, C-5), 101.7 (C-3), 78.6 (C-1), 74.2 (C-6), 29.4, 29.3, 26.1, 25.6, 22.7 (CH2), 14.1 (CH3). 69.4 (C-5), 68.1 (C-8), 31.8 (CH2), 29.4, 29.3, 29.3 (C-9, CH2), 28.9 (C-10), 26.1, 25.6, 22.7 (CH2), 14.1 (CH3). Synthesis of (1S,3R,6R)-3-[4¾-(4-hexyloxyphenyloxycarbonyl) phenyl]-2,4,7-trioxabicyclo[4.4.0] decane (37) Synthesis of (1S,3R,6R)-3-[ 4¾-(4-octyloxybenzoyloxy)- General reaction conditions using 4-(4-hexyloxyphenyloxycar- phenyl]-2,4,7-trioxabicyclo[4.4.0]decane (34) bonyl)benzaldehayde dimethyl acetal were followed.Yield General reaction conditions using 4-(4-octyloxybenzoyloxy) 25.2 mg (15%); colourless crystals; mp 122.5°C; [a]D20-10.3 benzaldehyde dimethyl acetal were followed. Yield 136.0 mg (c 1.01, CHCl3); dH (CDCl3 ) 8.18 (d, 2H, H-3¾, H-5¾), 7.63 (d, (65%); colourless crystals; mp 126.9 °C; [a]D20-4.3 (c 1.08, 2H, H-2¾, H-6¾), 7.11 (d, 2H, H-2, H-6), 6.92 (d, 2H, H-3, HCHCl 3); dH (CDCl3) 8.12 (d, 2H, H-2, H-6), 7.54 (d, 2H, H- 5), 5.63 (s, 1H, H-3), 4.28 (dd, 1H, H-5eq), 3.96 (m, 3H, a- 2¾, H-6¾), 7.20 (d, 2H, H-3¾, H-5¾), 6.96 (d, 2H, H-3, H-5), 5.59 CH2, H-8eq), 3.71 (dd, 1H, H-5ax), 3.59 (ddd, 1H, H-1), 3.51 (s, 1H, H-3), 4.26 (dd, 1H, H-5eq), 4.04 (t, 2H, a-CH2 ), 3.95 (ddd, 1H, H-8ax), 3.36 (ddd, 1H, H-6), 2.15 (mc, 1H, H-10eq), (ddd, 1H, H-8eq), 3.70 (dd, 1H, H-5ax), 3.57 (ddd, 1H, H-1), 1.74–1.93 (m, 4H, H-9ax, H-9eq, b-CH2), 1.69 (dddd, 1H, H- 3.51 (ddd, 1H, H-8ax), 3.35 (ddd, 1H, H-6), 2.13 (mc, 1H, H- 10ax), 1.47 (q, 2H, c-CH2), 1.35 (mc, 4H, CH2), 0.91 (t, 3H, 10eq), 1.74–1.92 (m, 4H, H-9ax, H-9eq, b-CH2), 1.67 (dddd, 1H, CH3); 3J2¾,3¾;5¾,6¾ 8.9, 3J2¾,3¾;5¾,6¾ 8.5, 2J5eq,5ax 10.2, 3J5eq,6 4.8, H-10ax), 1.47 (q, 2H, c-CH2), 1.32 (mc, 8H, CH2), 0.89 (t, 3H, 3J5ax,6 10.2, 3J1,10ax 11.5, 3J1,6 8.9, 3J1,10eq 4.8, 2J8ax,8eq 11.6, CH3); 3J2¾,3¾;5¾,6¾ 8.9, 3J2¾,3¾;5¾,6¾ 8.7, 2J5eq,5ax 10.2, 3J5eq,6 4.8, 3J8ax,9ax 11.6, 3J8ax,9eq 3.4, 2J10ax,10eq 11.6, 3J10ax,9ax 11.6, 2J8ax,8eq 11.5, 3J8eq,9ax 4.8, 3J8eq,9eq 3.4, 2J10ax,10eq 11.6, 3J10ax,9ax 3J10ax,9eq 4.4 Hz; dC (CDCl3) 165.3 (C=O), 156.9 (C-4), 144.2 11.6, 3J10ax,9eq 4.2; dC (CDCl3) 164.7 (C-4), 163.6 (C=O), 151.5 (C-1), 142.8 (C-1¾), 130.2 (C-3¾, C-5¾), 130.1 (C-4¾), 126.4 (C- (C-4¾), 135.2 (C-1¾), 132.3 (C-2, C-6), 127.4 (C-2¾, C-6¾), 121.6, 2¾, C-6¾), 122.4 (C-2, C-6), 115.1 (C-3, C-5), 100.9 (C-3), 121.5 (C-3¾, C-5¾, C-1), 114.3 (C-3, C-5), 101.2 (C-3), 78.6 78.7 (C-1), 74.0 (C-6), 69.5 (C-5), 68.5 (C-8), 68.1 (a-CH2), 31.6 (C-1), 74.1 (C-6), 69.4 (C-5), 68.3, 68.1 (C-8, a-CH2), 29.1 (C- (CH2), 29.3 (C-9), 28.8 (C-10), 25.7, 25.6, 22.6 (CH2), 14.1 9), 28.8 (C-10), 31.8, 29.3, 29.2, 26.0, 25.6, 22.7 (CH2), 14.0 (CH3).(CH3 ). Results and Discussion Synthesis of (1S,3R,6R)-3-[ 4¾-(4-hexyloxybenzoyloxy]- phenyl )-2,4,7-trioxabicyclo[4.4.0]decane (35) We first synthesized a series of compounds with a halogen or pseudo halogen head group, while the length of the terminal General reaction conditions using 4-(4-hexyloxybenzoyloxy) alkoxy chain was kept constant (Table 1).In the case of the benzaldehyde dimethyl acetal were followed. Yield 73.9 mg fluorine compound 14b we could observe a change of the (49%); colourless crystals; mp 146.6 °C; [a]D20-4.8 (c 1.01 helical pitch with increasing temperature, but the clearing CHCl3); dH (CDCl3) 8.12 (d, 2H, H-2, H-6), 7.54 (d, 2H, H- point of 125.0°C is too low to observe the complete inversion. 2¾, H-6¾), 7.20 (d, 2H, H-3¾, H-5¾), 6.96 (d, 2H, H-3, H-5), 5.59 The same holds true for the iodo compound 17b and the (s, 1H, H-3), 4.26 (dd, 1H, H-5eq), 4.04 (t, 2H, a-CH2 ), 3.95 thiocyanato compound 19b, but in these cases, a strong (ddd, 1H, H-8eq), 3.70 (dd, 1H, H-5ax), 3.57 (ddd, 1H, H-1), concentration-dependent inversion of the helical pitch in con- 3.51 (ddd, 1H, H-8ax), 3.35 (ddd, 1H, H-6), 2.13 (mc, 1H, H- tact with N4 was observed [sequence of textures in the contact 10eq), 1.74–1.92 (m, 4H, H-9ax, H-9eq, b-CH2), 1.67 (dddd, 1H, area: cholesteric (Grandjean texture), nematic (schlieren tex- H-10ax), 1.48 (q, 2H, c-CH2), 1.35 (mc, 4H, CH2), 0.92 (t, 3H, ture), cholesteric (fan texture), nematic (schlieren texture). Since CH3); 3J2¾,3¾;5¾,6¾ 8.9, 3J2¾,3¾;5¾,6¾ 8.7, 2J5eq,5ax 10.2, 3J5eq,6 4.8, the unwinding of the helix was mainly a function of the 2J8ax,8eq 11.5, 3J8eq,9ax 4.8, 3J8eq,9eq 1.7, 3J5ax,6 10.2, 3J1,10ax 11.5, concentration and a smectic A phase could not be observed, 3J1,6 8.9, 3J1,10eq 4.8, 3J8ax,9ax 11.6, 3J8ax,9eq 3.4, 2J10ax,10eq 11.6, an unwinding of the helix as a pretransitional eect of a 3J10ax,9ax 11.6, 3J10ax,9eq 4.2; dC (CDCl3) 164.7 (C-4), 163.6 transition to a smectic A phase can be excluded as reason for (C=O), 151.5 (C-4¾), 135.2 (C-1¾), 132.3 (C-2, C-6), 127.4 (C- this inversion eect.].In addition compound 19b shows a 2¾, C-6¾), 121.6, 121.5 (C-3¾, C-5¾, C-1), 114.3 (C-3, C-5), crystal–crystal interconversion to a crystalline phase resem- 101.2 (C-3), 78.6 (C-1), 74.1 (C-6), 69.4 (C-5), 68.3, 68.1 (C-8, bling a soft crystal.a-CH2), 29.1 (C-9), 28.8 (C-10), 31.6, 25.7, 25.6, 22.6 (CH2), The compounds with chloro 15b, bromo 16b and azido 18b 14.0 (CH3). terminal groups exhibited a helix inversion in the pure form, with inversion temperatures lying close togther at ca. 130 °C. Synthesis of (1S,3R,6R)-3-[ 4¾-(4-octyloxyphenyloxy- To elucidate the influence of volume eects, we synthesized carbonyl )phenyl]-2,4,7-trioxabicyclo[4.4.0]decane (36) 20b and 21b with a terminal methyl and isopropyl group.Neither compound 20b nor 21b showed an inversion of the General reaction conditions using 4-(4-octyloxyphenyloxycarbonyl) benzaldehyde dimethyl acetal were followed. The prod- helical pitch, and while the methyl compound still displayed a cholesteric phase besides a monotropic smectic A phase, we uct was purified by column chromatography [light petroleum (bp 60–70°C)–ethyl acetate 551].Yield 75.5 mg (62%); colour- could only observe a smectic A phase in the case of a broad terminal isopropyl group. less crystals; mp 106.7 °C; [a]D20-10.9 (c=1.04, CHCl3); dH J. Mater. Chem., 1997, 7(6), 893–899 897Table 1 Data for compounds 13b–23b recryst.a no.X /°C Cr/°C SA/°C Ch/°C Ti/°C C 13b H 105.8 — 61.4 14b F 48.0 113.8 — 125.0 >130.0 b 15b Cl 89.0 128.8 — 143.0 127.0 16b Br 132.5 — 140.1 132.0 Tm2 119.0°C 17b I 91.0 134.5 — 132.2 c 18b N3 83.0 118.2 — 145.2 123.0 19b NCS 80.7 — 97.0 c,d 20b Me 118.0 95.9 136.1 — 21b Pri 20.0 88.3 121.1 — — Tm2 85.0°C Tm3 79.0°C 22b Me3SiCOC 106.0 146.1 157.2 — — 23b HCOC 62.0 114.1 — 153.1 96.5 Tm2 104.0°C aAbbreviations: recryst.=recrystallization; Cr=crystallization; Ch=cholesteric; SA=smectic A; Ti=inversion temperature; Tmx=melting points of additional crystalline modifications.bThe inversion temperature is an extrapolated value. cConcentration-dependent helix inversion in contact with N4. dCr2 65.0 Cr1 80.7 Ch 97.0 decomp., Cr1=soft crystals.Table 2 Data for compounds 14a,b, 16a–c and 17a,b recryst. no. X OR /°C Cr/°C Ch/°C Ti/°C C 16a Br OC6H13 144.9 151.7 110.0 16b Br OC8H17 132.5 140.1 132.0 Tm2 119.0°C 16c Br OC10H21 70.0 128.0 136.5 >137.0 a 14a F OC6H13 119.3 135.2 124.0 14b F OC8H17 48.0 113.8 125.0 >130.0 a 17a I OC6H13 99.0 148.8 137.5 b 17b I OC8H17 91.0 134.5 132.2 b aThe inversion temperature is an extrapolated value.bConcentration-dependent helix inversion in contact with N4. Examining the synthesized trioxadecalin molecules discussed compounds, the following series is obtained: H<SCN<F< I<Me<Br<Cl<N3<NO2<OMe<ethynyl<CN. so far, it seemed that a polar terminal group might be necessary for the occurrence of a helix inversion.To verify this idea, we To examine the eect of the length of the alkoxy chains we synthesized the bromo compounds 16a and 16c with a hexyloxy synthesized 23b with an ethynyl head group, which we expected not to exhibit an inversion, in contrast to the same compound and a dexyloxy chain instead of the octyloxy chain of 16b. The shortening of the alkoxy chain by two CH2 groups led to a with a terminal cyano group.Contrary to our assumption, compound 23b exhibited a pitch inversion at a temperature of decrease of the inversion temperature by 22.0°C and to an increase of the clearing temperature by 11.6 °C (Table 2). In 96.5 °C, indicating that the reasons for the occurrence of the cholesteric helix inversions have to be more complex than our the case of 16c, with the extended chain, only a change of the helical pitch with increasing temperature could still be simple supposition.Moreover, we observed a second crystal modification of observed, since 16c cleared at 136.5 °C before reaching the inversion point. compound 23b. The frequently observed polymorphism of crystal forms of the compounds synthesized in this work Since the shortening of the alkoxy chain led to a distinct decrease of the inversion temperature, it seemed to be interes- reflects the dierent stacking possibilities and may be the polymorphism of orientation possibilities.Unfortunately, we ting to synthesize the compounds analogous to 14b and 17b, but with a hexyloxy instead of an octyloxy chain, since in the could not obtain crystals suitable for X-ray diraction to elucidate the stacking possibilities.Compound 22b with a trimethylsilylethynyl head group Table 3 Data for compound 33 showed, as well as compound 21b, only a smectic A phase indicating that this phase might be stabilized by a broad terminal group. A broad terminal group changes the molecular shape towards a cylinder; if the width of the terminal group is comparable to the width of the core, and favours therefore smectic phases.no. Cr/°C Ch/°C C If the terminal groups are arranged in order of increasing clearing temperature of the cholesteric phase and in consider- 33 122.9 96.0 N at TC, Tm2 100.6°C ation of the already described nitro, cyano and methoxy 898 J. Mater. Chem., 1997, 7(6), 893–899Table 4 Data for compounds 34–37 recryst.no. m Y /°C Cr/°C Ch/°C C 34 8 C(O)-O 126.9 90.1 a 35 6 C(O)-O 146.6 96.6 a 36 8 O-C(O) 72.0 106.7 87.5 a, Tm2 99.8°C, Tm3 91.7°C 37 6 O-C(O) 57.0 122.5 90.9 a, Tm2 ?, Tm3? aConcentration dependent helix inversion in contact with N4. case of the latter only a change of the helical pitch could be 15b and 16a,b exhibited an inversion whereas the methyl observed because of the low clearing temperatures.The short- compound 20b did not. ening of the alkoxy chain, in case of 14b, indeed led to a The polarity of the terminal group can be excluded as the sucient drop of the inversion temperature, so that the pitch cyano compound as well as compound 23b with its ethynyl inversion was observed, while 17b still showed only an inver- head group show an inversion of the helical pitch at a sion in contact with N4. comparable temperature.With the results obtained so far, it seems that the chiral The chiral trioxadecalin structure does not need to be trioxadecalin structure in the centre of the molecule is respon- located directly in the centre of the molecule, since compounds sible for the occurrence of the cholesteric helix inversion, but 33–37 with a terminal decalin system also display helix at the same time an unsymmetrical substitution pattern is inversions in contact with N4.necessary: that is X must not be an alkoxy or alkyl chain and The concentration dependence of the helical pitch is stronger further X must not have a broad structure, since otherwise a in most cases than the temperature dependence [the cholesteric smectic A phase will be stabilized, preventing the observation phase in the contact preparation (fan texture) shows selective of the helix inversion.reflection and has a short helical pitch. The absolute change In all the compounds discussed so far which show cholesteric of the helical pitch going from the area in the contact prep- helix inversion, the trioxadecalin structure was located in the aration with a cholesteric phase to the area with a nematic centre of the molecule.The molecules 33–37 were synthesized phase is large, while the helical pitch is great and hence the to elucidate whether this is a necessary requirement. absolute change quite low in the case of the compounds with Compound 33 exhibited a monotropic cholesteric phase e.g. a terminal nitro group5 which show a helix inversion in (fan texture at low temperatures) with a strong temperature- the pure form on heating].dependent helical pitch being just nematic (schlieren texture) Orientation eects of the molecular axis being defined by at the clearing temperature of 96.0 °C (Table 3). the chiral molecular core7 seem to be the reason for these The introduction of a carboxy linkage between the two inversion eects. Because of the dierent flexibility of the phenyl rings in 33 eects, almost independently from the molecular core and the wing groups the direction of the mean orientation of the linkage, a small decrease in the clearing molecular axis changes slightly with temperature, leading to a temperature (Table 4). All these compounds display cholesteric change of the eective chirality, which is a function of the phases with a fan texture without visible changes of the texture mean molecular axis. with temperature. However, all of them show a concentration dependent helix inversion in contact with N4. It is noteworthy that some of our dimethyl acetals used for We thank the DAAD/ARC for financial support and the the synthesis of the decalin system also showed mesogenic ‘Studieustiftung des deutschen Volkes’ for a grant for properties. The separation of the biphenyl system through a H. M. v. M. carboxy linkage eected in this case a decrease of the clearing point of the monotropic smectic A phase by 20°C. References 1 J. W. Goodby, J.Mater. Chem., 1991, 1, 307. 2 A. J. Slaney, I. NIshiyama, P. Styring and J. W. Goodby, J. Mater. Chem., 1992, 2, 805. 3 V. Vill, H.-W. Tunger and H. M. von Minden, J. Mater. Chem., 1996, 6, 739. 4 V. Vill, H.-W. Tunger, H. Stegemeyer and K. Diekmann, T etrahedron: Asymmetry, 1994, 5, 2443. 5 V. Vill and H.-W. Tunger, L iq. Cryst., 1996, 20, 449. 6 Z. Benko and B. Fraser-Reid, J. Org. Chem., 1988, 82, 2066. 7 H.-G. Kuball, H. Bru�ning, T. Mu�ller, O. Tu� rk and A. Scho�nhofer, J. Mater. Chem., 1995, 5, 2167. Conclusions The space filling of the terminal groups is not the reason for the helix inversion since chloro and bromo compounds Paper 7/00234C; Received 10th January, 1997 J. Mater. Chem., 1997, 7(6), 893&ndash