Synthesis of new chiral smectic mesogenes with 4-(2-Phenylethyl)biphenyl and 4-[2-(3-Fluorophenyl)ethyl]biphenyl Molecular Cores

Article abstract of DOI:10.1055/s-0029-1219833

Two methods of synthesis of chosen 1-[4-(1-methyl-heptyloxycarbonyl)phenyl] -2-[4′-(2,2,3,3,4,4,4-heptafluorobutoxyalkoxy)biphenyl-4-yl]ethanes and 1-[3-fluoro-4-(1-methylheptyloxycarbonyl)phenyl]-2-[4′-(2,2,3,3,4,4, 4-heptafluorobutoxyalkoxy)bi-phenyl-4-yl]ethanes have been proposed, checked and compared. The compounds were prepared by Sonogashira coupling of 4-benzyloxy-4′-ethynylbiphenyl with appropriate 4-halobenzoate esters followed by parallel hydrogenation of ethynylene bridge and debenzylation of hydroxyl group. The 1-[4-(1-methylheptyloxycarbonyl)phenyl]-2-[4′- hydroxybiphenyl-4-yl]ethane and 1-[3-fluoro-4-(methoxycarbonyl)phenyl]-2- [4′-hydroxybiphenyl-4-yl]ethane thus obtained has been transformed into final products by Mitsunobu reaction with ω-(2,2,3,3,4,4,4- heptafluorobutoxy)alkan-1-ols, followed by the replacing of an ester terminal chain in the case of second method.

Full text of DOI:10.1055/s-0029-1219833

1394
LETTER
Synthesis of New Chiral Smectic Mesogenes with 4-(2-Phenylethyl)biphenyl
and 4-[2-(3-Fluorophenyl)ethyl]biphenyl Molecular Cores
Novel Chiral
S
r
mectic
M
z
esogenesemysław Kula,* Anna Spadło, Magdalena Żurowska, Roman Dąbrowski
Institute of Chemistry, Department of New Technologies and Chemistry, Military University of Technology,
Kaliskiego 2, 00-908 Warsaw, Poland
Fax +48(22)6839582; E-mail: pkula@wat.edu.pl
Received 19 January 2010
acetylenes followed by the hydrogenation of etynylene
Abstract: Two methods of synthesis of chosen 1-[4-(1-methyl-
heptyloxycarbonyl)phenyl]-2-[4¢-(2,2,3,3,4,4,4-heptafluorobutoxy-
alkoxy)biphenyl-4-yl]ethanes and 1-[3-fluoro-4-(1-methylheptyloxy-
carbonyl)phenyl]-2-[4¢-(2,2,3,3,4,4,4-heptafluorobutoxyalkoxy)bi-
bridge have been utilized, see Scheme 1 and Scheme 2.
The main starting compound, 4-benzyloxy-4¢-ethynylbi-
phenyl (2) has been prepared from 4-benzyloxy-4-bromo-
phenyl-4-yl]ethanes have been proposed, checked and compared. biphenyl by the Sonogashira coupling with 2-methyl-3-
The compounds were prepared by Sonogashira coupling of 4-benzyl-
butyn-2-ol followed by the elimination with sodium hy-
dride in toluene.5 The experimental procedure is described
oxy-4¢-ethynylbiphenyl with appropriate 4-halobenzoate esters fol-
lowed by parallel hydrogenation of ethynylene bridge and
in the literature.6 The (S)-1-[4-(1-methylheptyloxycarbo-
debenzylation of hydroxyl group. The 1-[4-(1-methylheptyloxycar-
nyl)phenyl]-2-[4¢-benzyloxybiphenyl-4-yl]ethyne (4) has
bonyl)phenyl]-2-[4¢-hydroxybiphenyl-4-yl]ethane and 1-[3-fluoro-
been prepared by Sonogashira coupling between (S)-oc-
tan-2-yl 4-iodobenzoate and compound 3. Then simulta-
neous reduction of triple bond and debenzylation,
followed by the Mitsunobu etherification with corre-
sponding w-(2,2,3,3,4,4,4-heptafluorobutoxy)alkyl chain
(16.n) resulted in final compounds, 1-[(S)-4-(1-methyl-
heptyloxycarbonyl)phenyl]-2-[4¢-(2,2,3,3,4,4,4-heptafluoro-
butoxyalkoxy)biphenyl-4-yl]ethanes (6.n).7 The second
series of compounds 12.n differ from the first series by the
fluorine atom in the proximal position to the chiral termi-
nal chain so the same synthetic approach could be easily
utilized (Scheme 1) but the more general method has been
4-(methoxycarbonyl)phenyl]-2-[4¢-hydroxybiphenyl-4-yl]ethane
thus obtained has been transformed into final products by Mitsunobu
reaction with w-(2,2,3,3,4,4,4-heptafluorobutoxy)alkan-1-ols, fol-
lowed by the replacing of an ester terminal chain in the case of sec-
ond method.
Key words: coupling, Mitsunobu reaction, alkynes, biaryls, self-
assembly
Great attention has been recently focused on searching
new ferroelectric and antiferroelectric liquid crystals hav-
ing high molecular tilt angle in smectic layers, long heli-
coidal structure, and reduced number of ester linking
groups.1 Such materials ensures very promising elec-
trooptical properties leading to a new generation of
orthoconic antiferroelectric liquid-crystal displays
(OAFLCD).2 Recently many new classes of highly tilted
ferroelectric and antiferroelectric materials from the
group of biphenyl benzoates, phenyl biphenylates, and
terphenyl derivatives with partially fluorinated terminal
chains have been synthesized and some utilitarian mix-
tures have been formulated and their properties deter-
mined.3 However, all of them suffer from the problem of
the too short helicoidal structure which has serious influ-
ence on the alignment quality of the liquid crystal in the
display cell. The synthesis of presented two series of com-
pounds is based on the idea of lower rigidity of 4-(phenyl-
ethyl)biphenyl molecular core in comparison with
analogous terphenyl one.4 Lower rigidity can have influ-
ence on the length of the helicoidal structure which is cre-
ated in synclinic and anticlinic liquid-crystal phase.
BnO
Br
+
OH
1. Sonogashira
coupling
2. NaH, toluene
1
O
O
H
H
BnO
+
I
C6H13
2
3
Sonogashira
coupling
O
O
BnO
C6H13
4
H2, Pd/C
THF
O
H
C6H13
HO
O
5
Mitsunobu
reaction
C3F7CH2OCnH2nOH
For the preparation of 4-(2-phenylethyl)biphenyls and 4-
[2-(3-fluorophenyl)ethyl]biphenyls, Sonogashira cou-
pling between corresponding aryl halides and terminal
O
H
C6H13
C3F7CH2OCnH2n
O
O
6.n where n = 2; 3; 4; 6
SYNLETT 2010, No. 9, pp 1394–1396
Advanced online publication: 15.04.2010
DOI: 10.1055/s-0029-1219833; Art ID: G00810ST
© Georg Thieme Verlag Stuttgart · New York
x
x.
x
x.
2
0
1
0
Scheme
1
Preparation of 1-[(S)-4-(1-methylheptyloxycarbo-
nyl)phenyl]-2-[4¢-(2,2,3,3,4,4,4-heptafluorobutoxyalkoxy)biphenyl-
4-yl]ethanes by the method I

LETTER
Novel Chiral Smectic Mesogenes
1395
chosen, allowing easy introduction of different chiral ter- Temperatures and enthalpies of phase transitions for com-
minal chain as well as the perfluorinated one, see pounds 6.n and 12.n were determined by polarizing ther-
Scheme 2.
momicroscopy and DSC technique are described in
Table 1. Electrooptical measurements and miscibility
study were performed to confirm the type of the smectic
phases.
The second method has a serious advantage over the first
approach due to much easier purification of compound 8
than 4. Compound 8 has been crystallized from THF with
good yield. Spectroscopic data for compound 12.4 pre-
pared according to method II (Scheme 2) is given in the
literature.8
Acknowledgment
The financial support from the Military University of Technology
grant PBW 982 is kindly acknowledged.
The preparation of w-(2,2,3,3,4,4,4-heptafluorobutoxy)
alkan-1-ols has been performed as depicted in Scheme 3.
Compounds 13.n have been prepared as described in the
references,9 the rest of the synthesis of 17.n has been de-
scribed in the literature.10 The synthesis of compounds 5,
6.n, 9, 10, 11, 12.n were performed similarly to the report-
ed method.4
References and Notes
(1) Kula, P.; Dąbrowski, R.; Tykarska, M. Phase Transitions
2007, 80, 771.
(2) Lagerwall, S. T.; Dahlgren, A.; Jägemalm, P.; Rudquist, P.;
Dhavé, K.; Pauwels, H.; Dąbrowski, R.; Drzewiński, W.
Adv. Funct. Mater. 2001, 11, 87.
(3) Dąbrowski, R.; Gąsowska, J.; Otón, J.; Piecek, W.;
Przedmojski, J.; Tykarska, M. Displays 2004, 25, 9.
(4) Kula, P.; Dąbrowski, R.; Kenig, K.; Chyczewska, D.
Ferroelectrics 2006, 343, 19.
(5) Havens, S. J.; Hergenrother, P. M. J. Org. Chem. 1985, 50,
1763.
F
O
BnO
+
Br
OMe
2
7
Sonogashira
coupling
F
(6) Synthesis of 4-Benzyloxy-4¢-ethynylbiphenyl (3)
4-Benzyloxy-4-bromobiphenyl (128.8 g, 0.38 mol), Et3N
(57.6 g, 0.57 mol), DBU (29 g, 0.19 mol), PdCl2 (PPh3)2 (2 g,
2.85 mmol), CuI (1 g, 5.27 mmol), and THF (400 mL) have
been added in a 1 L nitrogen-filled flask. The mixture were
heated(boiling) for 5 min, and 2-methyl-3-butyn-2-ol (38.3
g, 0.456 mol) has been dropped in slowly. After 4 h of
stirring the GC-MS analysis was performed. To complete the
reaction, 25% of the initial amount of 2-methyl-3-butyn-2-ol
and 0.5g of PdCl2 (PPh3)2 were added and stirred for
additional 8 h. Then the reaction mixture was poured onto
H2O and the solid was filtered off, dried and washed using
CH2Cl2 (0.5 L). The obtained 4-[4¢-(benzyloxy)biphenyl-4-
yl]-2-methylbut-3-yn-2-ol (112 g, 0.33 mol), NaH (1.1 g, 46
mmol) and dry toluene (1 L) have been placed in a flask
equipped with column and distillation head to distill off the
emerging acetone. When the distillate temperature reached
the bp of toluene, the reaction mixture was cooled down and
poured onto the H2O. The organic layer was separated and
poured through active carbon pad and dried over anhyd
MgSO4. The toluene solution was concentrated and the final
product crystallized in freezer. 4-Benzyloxy-4¢-ethynyl-
biphenyl (3) was obtained in 57% yield (61.5 g, 0.217 mol).
MS (EI 70eV): m/z = 284 [M+], 193, 165, 139, 91, 65. IR
(neat): 3282, 3061, 3036, 2861, 2359, 2340, 1600, 1488,
1454, 1380, 1284, 1246, 1026, 1008, 812, 738, 619. 1H NMR
(200 MHz, CDCl3): d = 7.53 (m, 2 H, ArH), 7.51 (m, 5 H,
ArH), 7.43 (m, 2 H, ArH), 7.39 (m, 2 H, ArH), 7.03 (m, 2 H,
ArH), 5.10 (s, CH2), 3.11 (s, 1 H C≡CH). 13C NMR (50
MHz, CDCl3): d = 158.89 (1 C), 141.31 (1 C), 137.04 (1 C),
133.15 (1 C), 132.74 (2 CH), 128.84 (2 CH), 128.32 (2 CH),
128.25 (2 CH), 127.69 (1 CH), 126.70 (2 CH), 120.49 (1 C),
O
BnO
OMe
8
H2, Pd/C
THF
F
O
HO
OMe
9
Mitsunobu
reaction
C3F7CH2OCnH2nOH
F
O
C3F7CH2OCnH2n
O
OMe
10.n
KOH
ethane-1,2-diol
F
O
C3F7CH2OCnH2n
O
OH
11.n
1. (COCl)2, toluene
2. (S)-2-octanol, py
F
O
H
C6H13
C3F7CH2OCnH2n
O
O
12.n
where n = 4> 6
Scheme 2 Preparation of 1-[(S)-3-fluoro-4-(1-methylheptyloxycar-
bonyl)phenyl]-2-[4¢-(2,2,3,3,4,4,4-heptafluorobutoxyalkoxy)biphe-
nyl-4-yl]ethanes by the method II
CH2Cl2, py
SO2Cl
CH2OCnH2nOSO2
CH2OCnH2nOH
+
13.n
14.n
H2, Pd/C
C3F7CH2OH, NaH
THF, DMF
CH2OCnH2nOCH2C3F7
C3F7CH2OCnH2nOH
EtOH
15.n
16.n
Scheme 3 Preparation of w-(2,2,3,3,4,4,4-heptafluorobutoxy)alkan-1-ols
Synlett 2010, No. 9, 1394–1396 © Thieme Stuttgart · New York

1396
P. Kula et al.
LETTER
Table 1 Comparison of Temperatures and Enthalpies of Phase Transitions for Compounds 6.n and 12.n
Compd
6.2
Cr
+
Temp (°C)
[J/mol]
SmCa*
Temp (°C)
[J/mol]
SmC*
Temp (°C)
[J/mol]
SmA
(+)
(+)
–
Temp (°C)
[J/mol]
iso
+
110.9
59500
(+)
(+)
+
(95)b
–
–
+
+
+
–
–
–
6.3
+
102.0
48000
(93)b
+
6.6
+
47.2
27000
84.7
85
99.2
11150
+
12.4
12.6
+
67.6
27300
+
79.3
68
83.0
+
84.1
9800
+
a
+
40.8
24700
+
72.0
50
86.0
1600
+
88.0
7400
+
a Value of the SmC*–SmA transition enthalpy has been added to the enthalpy of SmA-Iso transition because it was impossible to separate.
b Extrapolated value from miscibility study diagram (polarizing thermomicroscope measurement); the presence of monotropic phase transitions
are in brackets.
115.44 (2 CH), 83.87 (1 C), 77.87 (1 CH), 70.28 (1 CH2). Mp
156.7–157.2 °C (dec.).
(7) 1-[(S)-4-(1-Methylheptyloxycarbonyl)phenyl]-2-[4¢-
(2,2,3,3,4,4,4-heptafluorobutoxyhexyloxy)biphenyl-4-
yl]ethane (6.6)
CH2), 29.19 (2 CH2), 25.82 (1 CH2), 25.60 (1 CH2), 25.43 (1
CH2), 22.61 (1 CH2), 20.11 (CH3), 14.08 (CH3).
(8) 1-[(S)-3-Fluoro-4-(1-methylheptyloxycarbonyl)phenyl]-
2-[4¢-(2,2,3,3,4,4,4-heptafluorobutoxybutoxy)biphenyl-
4-yl]ethane (12.4)
MS (EI 70eV): 712 [M+], 465, 183, 55. MS (ESI+, MeOH–
H2O): 735 [M + Na+], 615. IR (neat): 2934, 2856, 1710,
1608, 1499, 1354, 1222, 1103, 810, 736 cm–1. 13C NMR (50
MHz, CDCl3): d = 166.29 (1 COO), 158.55 (1 CO), 146.94
(1 CEt), 139.63 (1 CEt), 138.69 (1 C), 133.38 (1 C), 129.67
(2 CH), 128.83 (2 CH), 128.75 (1 CCOO), 128.48 (2 CH),
127.95 (2 CH), 126.67 (2 CH), 114.74 (2 CH), 73.13 (1
COOC), 71.59 (1 CH2O), 67.88 (1 CH2O), 37.87 (1 CH2Ar),
37.12 (1 CH2Ar), 36.11 (1 CH2), 31.77 (1 CH2), 29.41 (1
MS (EI, 70eV): m/z = 702 [M+], 465, 183, 55. MS (ESI+,
MeOH–H2O): m/z = 725 [M + Na+], 605. IR (neat): 2950,
2859, 1699, 1622, 1499, 1354, 1219, 1117, 971, 817, 734.
(9) Drzewiński, W.; Dąbrowski, R.; Czupryński, K. Pol. J.
Chem. 2002, 76, 273.
(10) Żurowska, M.; Dąbrowski, R.; Dziaduszek, J.; Czupryński,
K.; Skrzypek, K.; Filipowicz, M. Mol. Cryst. Liq. Cryst.
2008, 495, 145.
Synlett 2010, No. 9, 1394–1396 © Thieme Stuttgart · New York

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