solution was cooled to 0 ³C and diethyl azodicarboxylate
the resulting mixture was allowed to warm to room
temperature and stirred for 1 h before being poured into 2%
HCl solution. This mixture was extracted with DCM
(3650 ml), washed with 2% HCl solution (2650 ml), water
(50 ml), and dried over MgSO4 before puri®cation by eluting
though a short silica column. Yield 3.5 g, 94%.
1H-NMR [ppm]: d 1.13 (Me, t, J~8 Hz, 3H), 2.11 (CH2, p,
J~6 Hz, 2H), 2.33 (CH2Me, q, J~8 Hz, 2H), 4.04
(CH2OC(O), t, J~6 Hz, 2H), 4.26 (CH2O, t, J~6 Hz, 2H),
5.12 (LCH2, dd, J~1, 11 Hz, 1H), 5.60 (LCH2, dd, J~1, 18 Hz,
1H), 6.65 (CHL, dd, J~11, 18 Hz, 1H), 6.84 (Ph, d, J~9 Hz,
2H), 7.33 (Ph, d, J~9 Hz, 2H).
(DEAD) (0.32 ml, 2 mmol) was added dropwise over 2 min.
The resulting mixture was allowed to warm to room
temperature and was stirred for 18 h. The mixture was then
taken up in DCM (45 ml), washed with NaHCO3 (3630 ml),
water (2630 ml), and the organic layer dried with MgSO4. The
solvent was removed in vacuo and the residue puri®ed by
column chromatography (silica gel, eluent DCM). The product
2 was recrystallised from ethanolÐyield 197 mg, 62%.
1H-NMR [ppm]: d 2.17 (CH2CH2OC(O), p, J~6 Hz, 4H),
2.44 (PhMe, s, 3H), 4.08 (CH2OC(O), t, J~6 Hz, 4H), 4.37
(OCH2, t, J~6 Hz, 4H), 5.83 (CHLCH2, dd, J~2, 10 Hz, 2H),
6.13 (CHLCH2, dd, J~10, 17 Hz, 2H), 6.42 (CHLCH2, dd,
J~2, 17 Hz, 2H), 6.87 (Ph, d, J~9 Hz, 2H), 6.88 (PhMe, d,
J~9 Hz, 2H), 6.93 (PhCHLCHPhMe, d, J~16 Hz, 1H), 6.97
(PhCHLCHPhMe, d, J~16 Hz, 1H), 7.06 (PhCHLCHPhMe,
d, J~16 Hz, 1H), 7.18 (PhCHLCHPhMe, d, J~16 Hz, 1H),
7.29 (PhMe, d, J~2 Hz, 1H), 7.33 (PhMe, dd, J~2, 8 Hz, 1H),
7.44 (Ph, d, J~9 Hz, 2H), 7.45 (Ph, d, J~9 Hz, 2H), 7.57
(PhMe, d, J~8 Hz, 1H).
Preparation of 2-methyl-1,4-bis[2-(4-
propionyloxypropyloxyphenyl)ethenyl]benzene (1)
4-(3-Propionyloxypropyloxy)styrene (3.48 g, 13.2 mmol), 2,5-
dibromotoluene (1.5 g, 6 mmol), triethylamine (1.82 g, 2.50 ml,
18 mmol), DMF (50 ml) and palladacycle catalyst14 (40 mg,
0.7 mol%) were placed in a 100 ml ¯ask and thoroughly
degassed with nitrogen. The mixture was then heated to 125 ³C
for 5 h, cooled, poured into 2% HCl solution and extracted
with DCM (3650 ml). The organic fractions were combined
and washed with 2% HCl solution (4650 ml), 2% NaOH
solution (50 ml), water (2650 ml), dried over MgSO4 and the
solvent removed under reduced pressure. The bright yellow
powder was redissolved in DCM and passed through a short
column of Celite, the solvent removed and the product 1
recrystallised from isopropanol. Yield 1.8 g, 54%.
13C-NMR [ppm]: same as 1 except resonances for C1, C2, and
C3 are absent and resonances for the acryloyl groups are
observed at d 128.4 (CH2LCHC(O)), 130.9 (CH2LCHC(O)),
and 166.2 (CH2LCHC(O)).
High-resolution mass spectrometry for C35H36O6: calculated
552.251189, found 552.253470.
Results and discussion
1H-NMR [ppm]: d 1.14 (CH2Me, t, J~8 Hz, 6H), 2.13
(CH2CH2OC(O), p, J~6 Hz, 4H), 2.34 (CH2Me, q, J~8 Hz,
The conjugated reactive mesogen, 2-methyl-1,4-bis-[2-(4-acry-
loyloxypropyloxyphenyl)ethenyl]benzene (2), was synthesized
4H), 2.42 (PhMe, s, 3H), 4.07 (CH2CH2OC(O), t, J~6 Hz,
4H), 4.28 (OCH2, t, J~6 Hz, 4H), 6.87 (Ph, d, J~9 Hz, 2H),
6.88 (Ph, d, J~9 Hz, 2H), 6.93 (PhCHLCHPhMe, d, J~16 Hz,
1H), 6.97 (PhCHLCHPhMe, d, J~16 Hz, 1H), 7.06
(PhCHLCHPhMe, d, J~16 Hz, 1H), 7.18 (PhCHLCHPhMe,
d, J~16 Hz, 1H), 7.29 (PhMe, d, J~2 Hz, 1H), 7.33 (PhMe,
dd, J~2, 8 Hz, 1H), 7.44 (Ph, d, J~9 Hz, 2H), 7.45 (Ph, d,
J~9 Hz, 2H), 7.57 (PhMe, d, J~8 Hz, 1H).
13C-NMR [ppm]: d 9.1 (C1), 20.1 (C16), 27.6 (C2), 28.7 (C5),
61.4 (C4), 64.4 (C6), 114.7 (C8), 124.1 (C20), 124.1 (C19), 125.3
(C14), 126.5 (C11), 127.7 (C9), 127.7 (C12), 127.8 (C23), 128.4
(C18), 129.0 (C21), 130.5 (C10), 130.7 (C22), 135.6 (C13), 135.8
(C17), 136.5 (C15), 158.4 (C7), 169.0 (C3).
as shown in Scheme 1. The key step in this procedure is the
Heck reaction of 2,5-dibromotoluene with two equivalents of
4-(3-propionyloxypropyloxy)styrene to give 1. Deprotection of
the propionyl groups and reaction with acrylic acid under
Mitsunobu conditions12 gave 2.
The thermal behaviour of 1 and 2 was studied by DSC and
polarised optical microscopy. The DSC trace of 1 shows a large
melting endotherm (DH~40 kJ mol21) at 116 ³C and two
smaller transitions at 158 ³C (DH~0.25 kJ mol21) and 208 ³C
(DH~1.85 kJ mol21). Compound 1 recrystallised on cooling
and subsequent heating/cooling cycles gave identical results to
this ®rst cycle. The propionyl groups of 1 do not undergo
thermally induced crosslinking, and hence 1 serves as a useful
model compound to study the phase behaviour of more
reactive 2. A birefringent ¯uid phase between 116 and 208 ³C
was observed in the polarisation microscope, when compound
1 was heated. At higher temperatures (above 158 ³C), the
texture could clearly be identi®ed as nematic. However, cooling
below the transition at 158 ³C, a thin ®lm of 1 sandwiched
between two glass slides had a tendency to align home-
otropically, and displayed bright ¯ashing when a shear force
was applied to the upper glass slide. When ®lled into a LC
testing cell, the LC aligned into a monodomain only when
heated above 158 ³C; however, the monodomain was retained
on subsequent cooling below 158 ³C. Also, electrooptical
switching13 with an applied voltage of 9 V could be observed
only in the higher temperature phase. These observations
suggest the existence of a smectic A phase below the nematic.
High-resolution mass spectrometry for C35H40O6: calculated
556.282489, found 556.282874.
Preparation of 2-methyl-1,4-bis[2-(4-
acryloyloxypropyloxyphenyl)ethenyl]benzene (2)
Deprotection was carried out by dissolution of 1 (0.9 g,
1.7 mmol) and KOH (0.38 g, 6.8 mmol) in 100 ml of absolute
ethanol, followed by heating at re¯ux for 1 h. After cooling the
reaction mixture was washed three times with water and once
with acetone. After drying the resulting 2-methyl-1,4-bis[2-(4-
hydroxypropyloxyphenyl)ethenyl]benzene (264 mg, 0.5 mmol)
was suspended without further puri®cation in DCM (5 ml)
under an inert atmosphere and triphenylphosphine (524 mg,
2 mmol) and acrylic acid (0.1 ml, 1.5 mmol) added. The
2986
J. Mater. Chem., 1999, 9, 2985±2989