Chiral tetraphenylethenes as novel dopants for calamitic and discotic liquid crystals

Article abstract of DOI:10.1002/poc.1506

Three series of novel chiral tetraphenylethenes have been prepared: citronellyl-derived ethers 1a, b, lactate-derived ethers 2d, g, h, i and lactate-derived esters 3a-c, e-h. Helical twisting powers (HTPs) were determined for those derivatives of 1-3, whi

Full text of DOI:10.1002/poc.1506

Research Article
Received: 23 September 2008,
Revised: 12 November 2008,
Accepted: 13 November 2008,
Published online in Wiley InterScience: 15 January 2009
(www.interscience.wiley.com) DOI 10.1002/poc.1506
Chiral tetraphenylethenes as novel dopants
for calamitic and discotic liquid crystals
Alina Schreivogela, Ute Dawinb, Angelika Baroa, Frank Giesselmannb
and Sabine Laschata
*
Three series of novel chiral tetraphenylethenes have been prepared: citronellyl-derived ethers 1a, b, lactate-derived
ethers 2d, g, h, i and lactate-derived esters 3a–c, e–h. Helical twisting powers (HTPs) were determined for those
derivatives of 1–3, which were sufficiently miscible with the nematic host 5CB 13 or the discotic nematic host hexayne
14. For binary solutions HTP values of 5.7–10.4 mmꢀ1 for 13/1, 12.8–16.5 mmꢀ1 for 13/2, 8.0–28.7 mmꢀ1 for 13/3 and
2.1–2.9 mmꢀ1 for hexayne 14/3 were determined, indicating a much stronger interaction between the C4-symmetrical
propeller-shaped tetraphenylethenes 1–3 with the calamitc host 5CB 13 than with the discotic C6-symmetrical
propeller-shaped host hexayne 14. Copyright ß 2009 John Wiley & Sons, Ltd.
Keywords: tetraphenylethenes; helical twisting power; chiral dopant; chiral nematic liquid crystals
directly correlated with the helical periodicity (pitch) p via d ¼
p/2. The efficiency of the dopant induced twisting depends on
the temperature, the dopant concentration and, above all, on the
dopant molecule itself. In order to compare the chiral induction of
different dopants independent of their concentration and the
temperature, the helical twisting power (HTP) has been
INTRODUCTION
Tetraarylethenes are an attractive class of compounds because of
their various interesting chemical and physical properties. For
example, Kochi and others have shown that they can undergo
reversible redox reactions[1–4] and X-ray crystal structure analyses
of their dianions and dications[1,5–10] revealed that the twisted
molecular structure of the tetraarylethene[11] is strongly affected
by redox reactions. Tang recently reported that tetrapheny-
lethenes tethered to ammonium salts are fluorescent ‘light-up’
bioprobes due to aggregation induced emission in the presence
of biopolymers such as DNA or proteins.[12] We have shown that
tetraarylethenes provide useful building blocks for discotic liquid
crystals[13–21] which can be converted to the corresponding liquid
crystalline phenanthrenes by oxidative photocyclization.[22–46]
For switching devices, molecules are particularly attractive, which
show significant spectral changes upon photo- and electro-
chemical transformations. A redox-driven chiroptical switch
based on optically active tetrakis(p-alkoxyphenyl)ethenes has
been reported by Mori and Inoue.[47]
In addition, enantiomerically pure tetraarylethenes should be
able to transfer their chirality to an achiral liquid crystalline host
phase, a unique phenomenon that is generally known for chiral
compounds added to e.g. nematic liquid crystalline phases.
Uniaxial nematic liquid crystalline phases are characterized by
long-range orientational order of the principal axes of the
so-called mesogens. The average common orientation of the
mesogens is represented by the director, which in optically
uniaxial mesophases coincides with the optic axis of the medium.
The presence of chiral molecules (dopants) in the phase results in
the formation of a chiral nematic phase where the dopant
induces a helical twisting of the director field.[48–58] This can be
[59]
´
introduced by Solladie
as
@ð1=pÞ
@x
HTP ¼ lim
(1)
x!0
where x is the molar fraction of the chiral dopant and the pitch is
measured at a certain relative temperature with respect to the
nematic–isotropic transition temperature (clearing point).
For rod-like dopants numerous studies have been conducted
towards structure–property relationships concerning the chiral
induction;[48–57,60–79] however, surprisingly, much less is known
about chiral discotic dopants in liquid crystals. In particular,
studies on the relationship between chiral molecular structure
and HTP in an achiral host phase are quite rare for discotic
compounds,[21] although early investigations by Destrade and
Malthete[80,81] on chiral alkyl carboxylates and p-alkoxy benzo-
ates of triphenylenes, truxenes and benzenes revealed a striking
dependence of mesomorphic properties and the chirality transfer
to achiral host phases on the molecular structure of the chiral
chain. Thus, we synthesized
a series of chiral tetrakis
*
Correspondence to: S. Laschat, Institut fu¨r Organische Chemie der Universita¨t
Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
E-mail: sabine.laschat@oc.uni-stuttgart.de
a
b
A. Schreivogel, A. Baro, S. Laschat
Institut fu¨r Organische Chemie der Universita¨t Stuttgart, Pfaffenwaldring 55,
70569 Stuttgart, Germany
visualized under the polarizing optical microscope by
a
characteristic fingerprint texture of equidistant bright and dark
stripes, which reveal different director orientations (see e.g.
Fig. 1). The distance d between two equally bright lines are
U. Dawin, F. Giesselmann
Institut fu¨r Physikalische Chemie der Universita¨t Stuttgart, Pfaffenwaldring
55, 70569 Stuttgart, Germany
J. Phys. Org. Chem. 2009, 22 484–494
Copyright ß 2009 John Wiley & Sons, Ltd.

CHIRAL TETRAPHENYLETHENES AS NOVEL DOPANTS
Figure 1. Fingerprint textures of solutions of 5CB 13 with various mole fractions x of 1a at TIN*, 10 K (magnification 200ꢂ). A: x ¼ 0.5 mol%.
B: x ¼ 1.0 mol%. C: x ¼ 1.5 mol%. The dark circles originate from air bubbles. D: x ¼ 5.0 mol%. Phase separation is found (formation of chiral nematic
droplets within an isotropic phase)
(p-alkoxyphenyl)ethenes and studied their chirality transfer in
doping experiments with achiral nematic host phases formed by
calamitic and discotic molecules, respectively. The results are
discussed below.
The chiral nematic solutions of the novel synthesized chiral
dopants and the nematic liquid crystalline hosts 13 and 14 were
prepared by weighing the components together into small glass
vials. To homogenize the solution CHCl3 was added (0.5–1 mL)
and stirred. A drop of this solution was placed on a cleaned
microscope slide and CHCl3 allowed to evaporate. Several such
drops were covered with a cover slip giving a liquid–crystal
thickness of about 30 mm. The overall error of the dopant
concentration is about ꢁ5%. An optical polarizing microscope
was used to determine the binary phase diagrams via the
observed textures. The pitch of the chiral nematic phase at a
certain temperature was measured directly from calibrated
texture images using the image processing program Analysis1
3.0. The overall error of the pitch is about ꢁ3%.
EXPERIMENTAL SECTION
General
1H NMR spectra were recorded on a Bruker ASC 250, ARX 300 and
ARX 500 with tetramethylsilane as internal standard. 13C
multiplicities were assigned by DEPT experiments. IR spectra
were recorded on a Bruker Vector 22 FT-IR spectrometer with ATR
technique. Mass spectrometry was performed on a Varian MAT
711 mass spectrometer with EI ionization (70 eV), a Finnigan MAT
95 with CI ionization using methane as reactand gas and a Bruker
micrOTOF_Q with electrospray ionization. UV/Vis spectra were
recorded on a PerkinElmer Lambda7 spectrometer. Elemental
analyses were performed on a Carlo Erba Strumentazione
Elemental Analyzer Modell 1106. Column chromatography was
performed using silica gel 60 (Fluka, mesh 40–63 mm) with
hexanes (b.p. 30–75 8C). Optical rotations were performed on a
PerkinElmer Polarimeter 241 at 589 nm (NaD). Differential
scanning calorimetry was performed using a Mettler Toledo
DSC822 and optical polarizing microscopy using an Olympus BX
50 polarizing microscope combined with a Linkam LTS 350 hot
stage. Reactions were performed using standard Schlenk type
conditions under inert athmosphere. Compounds 9a–d and
10a–c, e were prepared according to the literature.[82–90]
Tetrakis-{4-[(3(R)-3(,7(-dimethyloct-6(enyloxy]phenyl}ethene
(1a)
A mixture of 2.07 g (15.0 mmol) K2CO3 and 0.5 g (1.3 mmol)
tetrakis(4-hydroxyphenyl)ethene 7 in 20 mL DMF was treated
with 1.21 g (5.5 mmol) (3R)-citronellylbromide 5 and stirred at
80 8C for 48 h. Then the mixture was poured onto 30 g ice, filtered
via Celite and diluted with 30 mL CH2Cl2. The layers were
separated and the aqueous layer was extracted with 3 ꢂ 30 mL
CH2Cl2, the organic layers were dried over MgSO4, evaporated
and the residue was purified by flash chromatography (hexanes/
ethyl acetate 40: 1) to yield 0.49 g (43%) of a highly viscous,
green oil.
3
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 0.93 (d, J ¼ 6.6 Hz, 12H,
30-CH3), 1.15-1.45 (m, 8H, 40-H), 1.50-1.86 (m, 12H, 30-H, 20-H), 1.60
(d, 4J ¼ 0.8 Hz, 12H, CCH3), 1.68 (d, 4J ¼ 1.35 Hz, 12H, CCH3),
1.92–2.08 (m, 8H, 50-H), 3.83–3.98 (m, 8H, 10-H), 5.10 (‘‘t’’,
3J ¼ 7.1 Hz, 4H, 60-H), 6.62 (d, 3J ¼ 8.9 Hz, 8H, 6H, 2H), 6.91 (d,
3J ¼ 8.6 Hz, 8H, 5H, 3H). 13C-NMR (125 MHz, CDCl3): d (ppm) ¼ 17.7
(CCH3), 19.6 (CHCH3), 25.5 (C-50), 25.7 (CCH3), 29.5 (C-30), 36.2
Physicochemical properties of the chiral dopants in
nematic hosts
The nematic liquid crystal 5CB 13 was purchased from AlfaAesar
and used without further purification. Hexayne 14 was prepared
following literature procedures.[91–93]
(C-200), 37.2 (C-40), 66.1 (C-10), 113.5 (C-2, C-6), 124.7 (C-60), 131.3
—
(C-7 ), 132.5 (C-3, C-5), 138.3 (C C), 136.8, 157.3 (C-1, C-6). MS (EI):
—
J. Phys. Org. Chem. 2009, 22 484–494
Copyright ß 2009 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/poc

A. SCHREIVOGEL ET AL.
m/z (%) ¼ 949 (100) [M]þ, 878 (3), 810 (5), 717 (1), 672 (1), 396 (8),
303 (5), 211 (3), 185 (8), 109 (5), 95 (8), 83 (15), 69 (65). CHN:
C66H92O4 (949.43) calcd. C 83.49%, H 9.77%, found C 83.28%, H
9.81%. FT-IR (ATR): n ¼ 3033 (w), 2958 (s), 2912, 2870 (s), 2037 (w),
d (ppm) ¼ 14.1 [CH2(CH2)6CH3], 18.7 (C-3), 22.7, 26.0, 29.2, 29.4,
29.7, 31.8 [CH2(CH2)6CH3], 51.9 (COOCH3), 70.5 [CH2(CH2)6CH3],
74.9 (C-2), 174.0 (COOCH3). MS (EI): m/z (%) ¼ 216 (5) [M]þ, 173 (1),
157 (100), 113 (20), 105 (5), 88 (60), 71 (85), 57 (90), 45 (15), 43 (35).
HRMS (EI): m/z (%) calcd. for C12H24O3 216.1725, found 216.1703.
FT-IR (ATR): n ¼ 2925, 2855 (vs), 2559 (m), 2189 (m), 2004 (m), 1971
(m), 1720 (vs), 1458 (s), 1239 (s), 1126 (vs) cmꢀ1. [a]D20 ¼ –36.6
(c ¼ 1.0, CHCl3).
1605 (m), 1506, 1474, 1453 (vs), 1377 (s), 1238 (vs) cmꢀ1
.
[a]2D0 ¼ þ3.1 (c ¼ 3.5, CHCl3).
Tetrakis-{4-[(3(R)-3(,7(-dimethyloctyloxy]phenyl}ethene (1b)
Following the procedure described for 1a flash chromatography
(hexanes/ethyl acetate 200:1) yielded 0.87 g (70%) of a highly
viscous, green oil.
Methyl (2S)-2-decyloxypropionate (9g)
According to the general procedure flash chromatography
(hexanes/Et2O 100:1) yielded 2.35 g (20%) of a colourless oil.
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 0.88 [t, 3J ¼ 6.9 Hz, 3H,
CH2CH2(CH2)7CH3], 1.19–1.32 [m, 16H, CH2CH2(CH2)7CH3], 1.40 (d,
3J ¼ 6.8 Hz, 3H, 3-H), 1.56–1.64 [m, 2H, CH2CH2(CH2)7CH3], 3.35 [dt,
2J ¼ 8.9 Hz, 3J ¼ 6.9 Hz, 1H, CH2ACH2(CH2)7CH3], 3.54 [dt,
2J ¼ 8.9 Hz, 3J ¼ 6.7 Hz, 1H, CH2BCH2(CH2)7CH3], 3.75 (s, 3H,
OCH3), 3.96 (q, 3J ¼ 6.9 Hz, 1H, 2H). 13C-NMR (125 MHz, CDCl3):
d (ppm) ¼ 14.1 [CH2(CH2)8CH3], 18.7 (C-3), 22.9, 26.0, 29.3, 29.4,
29.6, 29.7, 31.9 [CH2(CH2)8CH3], 51.9 (COOCH3), 70.5
[CH2(CH2)8CH3], 74.9 (C-2), 174.0 (COOCH3). MS (ESI): m/z
(%) ¼ 267.19 [M þ Na]þ. HMRS (ESI): calcd. for C14H28NaO3
[M þ Na]þ 267.1936, found 267.1931. FT-IR (ATR): n ¼ 2923,
2854 (vs), 1755, 1738 (vs), 1457 (m), 1371 (w), 1271 (w), 1201
(s), 1127 (vs), 1073 (m) cmꢀ1. [a]D20 ¼ –40.4 (c ¼ 1.0, CHCl3).
3
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 0.87 (d, J ¼ 6.6 Hz, 24H,
CH3), 0.92 (d, 3J ¼ 6.5 Hz, 12H, 3-CH3), 1.06-1.39 (m, 24H),
1.45–1.88 (m, 16H), 3.64–4.01 (m, br, 8H, 10-H), 6.62 (d, 3J ¼ 8.6 Hz,
Hz, 8H, 2H, 6H), 6.91 (m, 8H, 3H, 5H). 13C-NMR (125 MHz, CDCl3): d
(ppm) ¼ 19.7 (CHCH3), 22.6, 22.7 (CHCH3CH3), 27.9, 29.9 (C-30,
C-70), 24.7, 36.3, 37.3, 39.2 (C-20, C-40, C-50, C-60), 66.1 (C-10), 113.5
—
(C-2, C-6), 132.5 (C-3, C-5), 138.3 (C C), 136.8, 157.3 (C-1, C-4). MS
—
(EI): m/z (%) ¼ 956.8 (60) [M]þ, 830.6 (100), 816 (5), 690 (5), 69 (5),
57 (10), 44 (10). CHN: C66H100O4 (957.50) calcd. C 82.79%, H
10.53%, found C 82.81%, H 10.43%. FT-IR (ATR): n ¼ 3035 (w), 2952
(s), 2924, 2868 (vs), 1884 (m), 1607, 1506, 1466, 1439 (vs), 1382,
1365 (s), 1237, 1172 (vs) cmꢀ1. [a]D20 ¼ þ4.3 (c ¼ 7.0, CHCl3).
General procedure for the preparation of methyl
(2S)-alkoxypropionates (9e–g)
General procedure for the (2S)-alkoxypropionic acids (10f, g)
To a solution of 14.4 mmol methyl (2S)-lactate 8 and 21.6 mmol
alkyl bromide in 20 mL Et2O was added 3.34 g (14.4 mmol) freshly
prepared silver oxide in ten portions over 1 h and the mixture was
heated at 40 8C for 18 h. After cooling to room temperature the
mixture was filtered and evaporated and the crude product was
purified by flash chromatography.
To a cooled solution of 11.5 mmol (2S)-alkoxypropionate 9 in
15 mL MeOH was slowly added LiOH 25.5 mmol in H2O at 0 8C
and then heated under reflux for 6 h. After cooling to room
temperature the mixture was washed with 10 mL CH2Cl2, the
aqueous layer was separated, the pH was adjusted to 1–2 with 3 N
HCl. After extraction with 3 ꢂ 20 mL CH2Cl2, drying over MgSO4
and evaporating the solvent, a colorless liquid was obtained.
Methyl (2S)-pentyloxypropionate (9e)
According to the general procedure flash chromatography
(hexanes/Et2O 40:1) yielded 1.8 g (26%) of a colourless oil.
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 0.90 (t, 3J ¼ 7.0 Hz, 3H,
(2S)-Octyloxypropionic acid (10f)
3
According to the general procedure 0.18 g (79%) of a colourless
liquid was obtained.
50-H), 1.30–1.37 (m, 4H, 30-H, 40-H), 1.40 (d, J ¼ 6.9 Hz, 3H, 3-H),
1.56–1.65 (m, 2H, 20-H), 3.36 (dt, 2J ¼ 8.8 Hz, 3J ¼ 6.9 Hz, 1H, 10-HA),
3.55 (dt, 2J ¼ 8.8 Hz, 3J ¼ 6.9 Hz, 1H, 10-HB), 3.75 (s, 3H, OCH3), 3.96
(q, 3J ¼ 6.9 Hz, 1H, 2-H). 13C-NMR (125 MHz, CDCl3): d (ppm) ¼ 14.0
(C-50), 18.7 (C-3), 22.5, 29.5 (C-30, C-40), 28.2 (C-20), 51.9 (COOCH3),
70.5 (C-10), 74.9 (C-2), 174.0 (COOCH3). MS (EI): m/z (%) ¼ 174 (5)
[M]þ, 144 (5), 131 (5), 115 (75), 97 (5), 88 (40), 84 (10), 71 (100), 59
(10), 55 (20), 45 (40), 43 (80), 41 (20), 39 (10), 28 (20). HRMS (EI): m/
z (%) calcd. for C9H18O3 174.1256, found 174.1239. FT-IR (ATR):
n ¼ 2955, 2932, 2860 (vs), 1753, 1737 (vs), 1448 (m), 1371 (w), 1270
(w), 1201 (s), 1152, 1125 (vs), 1048 (m) cmꢀ1. [a]D20 ¼ ꢀ40.0
(c ¼ 1.0, CHCl3).
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 0.88 [t, 3J ¼ 6.9 Hz, 3H,
CH2CH2(CH2)5CH3], 1.21–1.38 [m, 10H, CH2CH2(CH2)5CH3], 1.45 (d,
3J ¼ 6.9 Hz, 3H, 3-H), 1.56–1.66 [m, 2H, CH2CH2(CH2)5CH3], 3.50 [dt,
2J ¼ 9.1 Hz, 3J ¼ 6.7 Hz, 1H, CH2ACH2(CH2)5CH3], 3.56 [dt,
3
3
2J ¼ 9.1 Hz, J¼ 6.7 Hz, 1H, CH2BCH2(CH2)5CH3], 3.99 (q, J ¼ 6.9 Hz,
1H, 2H). 13C-NMR (125 MHz, CDCl3): d (ppm) ¼ 14.1 [CH2CH2
(CH2)5CH3], 17.9 (C-3), 22.6, 25.9,29.2, 29.3, 29.7 [CH2CH2(CH2)5CH3],
31.8 [CH2CH2(CH2)5CH3], 70.6 [CH2CH2(CH2)5CH3], 74.6 (C-2), 174.7
(C-1). MS (EI): m/z (%) ¼ 203.2 (5) [M þ H]þ, 185 (1), 157.2 (80), 127
(2), 113.1 (40), 91 (5), 74 (20), 71.1 (100), 69 (10), 57 (90), 45 (15), 43
(35). HMRS (ESI): calcd. for C11H22NaO3 [M þ Na]þ 225.1467, found
225.1461. FT-IR (ATR): n¼ 3101 (s), 2925, 2855 (vs), 2456 (m), 1738
(vs), 1399 (m), 1338 (w), 1121, 1099 (vs), 938 (m) cmꢀ1. [a]D20 ¼ ꢀ20.5
(c ¼ 1.0, CHCl3).
Methyl (2S)-octyloxypropionate (9f)
According to the general procedure flash chromatography
(hexanes/Et2O 100:1) yielded 37.0 mg (16%) of a colourless oil.
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 0.88 [t, 3J ¼ 7.0 Hz, 3H,
CH2CH2(CH2)5CH3], 1.19–1.38 [m, 10H, CH2CH2(CH2)5CH3], 1.40 (d,
3J ¼ 6.9 Hz, 3H, 3H), 1.57–1.63 [m, 2H, CH2CH2(CH2)5CH3], 3.35 [dt,
2J ¼ 9.0 Hz, 3J ¼ 6.8 Hz, 1H, CH2ACH2(CH2)5CH3], 3.54 [dt,
2J ¼ 9.0 Hz, 3J ¼ 6.8 Hz, 1H, CH2BCH2(CH2)5CH3], 3.75 (s, 3H,
OCH3), 3.96 (q, 3J ¼ 6.9 Hz, 1H, 2H). 13C-NMR (125 MHz, CDCl3):
(2S)-Decyloxypropionic acid (10g)
According to the general procedure 0.54 g (83%) of a colourless
liquid was obtained.
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 0.88 [t, 3J ¼ 7.0 Hz, 3H,
CH2CH2(CH2)7CH3], 1.18–1.38 [m, 16H, CH2CH2(CH2)7CH3], 1.45 (d,
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Copyright ß 2009 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2009, 22 484–494

CHIRAL TETRAPHENYLETHENES AS NOVEL DOPANTS
3J ¼ 7.0 Hz, 3H, 3-H), 1.56–1.66 [m, 2H, CH2CH2(CH2)7CH3], 3.49 [dt,
2J ¼ 8.9 Hz, 3J ¼ 6.7 Hz, 1H, CH2ACH2(CH2)7CH3], 3.56 [dt,
2J ¼ 8.9 Hz, 3J ¼ 6.7 Hz, 1H, CH2BCH2(CH2)7CH3], 3.99 (q,
3J ¼ 7.0 Hz, 1H, 2-H). 13C-NMR (125 MHz, CDCl3): d (ppm) ¼ 14.1
[CH2CH2(CH2)7CH3], 18.0 (C-3), 20.7, 25.9, 29.3, 29.4, 29.5, 29.7,
31.9 [CH2(CH2)8CH3], 70.6 [CH2CH2(CH2)7CH3], 74.5 (C-2), 176.8
(COOH). MS (ESI): m/z (%) ¼ 253.18 [M þ Na]þ. HMRS (ESI): calcd.
for C13H26NaO3 [M þ Na]þ 253.1780, found 253.1774. FT-IR (ATR):
n ¼ 3075 (s), 2922, 2854 (vs), 1722 (vs), 1458 (m), 1372 (w), 1198
(w), 1126 (vs), 1072 (m) cmꢀ1. [a]D20 ¼ –19.9 (c ¼ 1.0, CHCl3).
(2S)-1-Brom-2-decyloxypropane (12g)
To a solution of 1.01 g (4.6 mmol) (2S)-2-decyloxypropanol 11g in
40 mL CH2Cl2 were added 3.62 g (13.8 mmol) PPh3, 1.81 g
(6.9 mmol) CBr4 and 4.5 mL (3.3 g, 32.0 mmol) triethylamine at
0 8C and the mixture was stirred at room temperature for 18 h.
Then, 40 mL H2O was added, the layers separated and the
aqueous layer was extracted with 3 ꢂ 20 mL CH2Cl2, the organic
layers were dried over MgSO4, evaporated and the crude product
purified by flash chromatography (hexanes/ethyl acetate) to yield
0.89 g (67%) of a pale yellow oil.
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 0.88 [t, 3J ¼ 7.1 Hz, 3H,
CH2CH2(CH2)7CH3], 1.27 (d, 3J ¼ 6.2 Hz, 3H, 3H), 1.20-1.38 [m, 16H,
CH2CH2(CH2)7CH3], 1.52–1.62 [m, 2H, CH2CH2(CH2)7CH3], 3.33 (dd,
2J ¼ 10.4 Hz, 3J ¼ 5.9 Hz, 1H, 1-H2A), 3.41 (dd, 2J ¼ 10.4 Hz,
3J ¼ 4.9 Hz, 1H, 1-H2B), 3.47 [td, 3J ¼ 6.7 Hz, 4J ¼ 1.5 Hz, 2H,
General procedure for the preparation of
(2S)-2-alkoxypropan-1-ols (11d, g)
To a suspension of 40.6 mmol LiAlH4 in 50 mL Et2O was dropwise
added a solution of 12.3 mmol methyl (2S)-2-alkyloxypropionate
9 in 20 mL Et2O at 0 8C and the resulting mixture was heated
under reflux for 18 h. After cooling to 0 8C, 7 mL H2O, 10 mL NaOH
(10 wt%) and 25 mL H2O were added sequentially over 1 h, the
precipitate was removed by filtration and the aqueous layer was
extracted with 5 ꢂ 50 mL Et2O, the organic layers were dried over
MgSO4, evaporated and the residue was purified by flash
chromatography.
3
3
3
CH2CH2(CH2)7CH3], 3.60 (qdd, J ¼ 6.2 Hz, J ¼ 5.9 Hz, J ¼ 4.9 Hz,
1H, 1H). 13C-NMR (125 MHz, CDCl3):
d
(ppm) ¼ 14.1
(CH2(CH2)8CH3), 18.9 (C-3), 22.7, 26.1, 29.3, 29.4, 29.58, 29.61,
30.0, 31.9 (CH2(CH2)8CH3), 36.5 (C-1), 69.4 (CH2(CH2)8CH3), 74.8
(C-1). MS (EI): m/z (%) ¼ 279 (1) [Mþ], 263 (1), 185 (100), 168 (5),
153 (5), 141 (30), 121 (10), 112 (5), 99 (15), 85 (50), 71 (45), 57 (50),
43 (30). HMRS (ESI): calcd. for C13H27BrNaO [M þ Na]þ 301.1143,
found 301.1137. FT-IR (ATR): n ¼ 2923, 2853 (vs), 2359 (s), 2341 (s),
1457 (m), 1375 (m), 1325 (m), 1228 (w), 1195 (w), 1140 (s), 1096
(vs), 669 (s) cmꢀ1. [a]D20 ¼ þ5.8 (c ¼ 1.0, CHCl3).
(2S)-2-Butyloxypropan-1-ol (11d)
According to the general procedure flash chromatography
(hexanes/Et2O 1:1) yielded 1.25 g (80%) of a pale yellow oil.
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 0.93 (t, 3J ¼ 7.6 Hz, 3H,
CH2CH2CH2CH3), 1.11 (d, 3J ¼ 6.0 Hz, 3H, 3-H), 1.38 (qt, 3J ¼ 7.6 Hz,
General procedure for the preparation of
tetrakis{4-[(2S)-alkoxypropionate]-phenyl}ethenes (3a–c,
e–h)
3J ¼ 7.5 Hz,
2H,
CH2CH2CH2CH3),
1.57–1.62
(m,
2H,
2
3
CH2CH2CH2CH3), 2.11 (s, br, OH), 3.38 (dt, J ¼ 9.2 Hz, J ¼ 6.7 Hz,
2
3
Hz, 1H, CH2ACH2CH2CH3), 3.43 (dd, J ¼ 10.9 Hz, J ¼ 7.9 Hz, 1H,
1-HA), 3.52 (dqd, 3J ¼ 7.1 Hz, 3J ¼ 6.0 Hz, 3J ¼ 3.3 Hz, 1H, 2-H),
3.54–3.60 (m, 1H, 1-HB), 3.58 (dt, 2J ¼ 9.2 Hz, 3J ¼ 6.7 Hz, 1H,
CH2BCH2CH2CH3). 13C-NMR (125 MHz, CDCl3): d (ppm) ¼ 13.9
(CH2CH2CH2CH3), 15.9 (C-3), 19.4 (CH2CH2CH2CH3), 32.2
(CH2CH2CH2CH3), 66.4 (C-1), 69.6 (CH2CH2CH2CH3), 75.7 (C-2).
MS (EI): m/z (%) ¼ 132 (<1) [M]þ, 101 (80) [M–HOCH2]þ, 83 (5), 59
(15), 57 (95), 55 (10), 45 (100) [M–HOCH2—C4H9]þ, 41 (35), 39 (5).
HRMS (CI): m/z (%) calcd for C7H17O2 [M þ H]þ 133.1229, found
133.1214. FT-IR (ATR): n ¼ 3423 (vs), 2959, 2931, 2871 (vs), 2228,
2186 (w), 1713, 1667 (w), 1457 (m), 1376 (s), 1342 (w), 1231 (m),
1090 (vs), 986 (m) cmꢀ1. [a]D20 ¼ þ34.3 (c ¼ 1.0, CHCl3).
To a solution of 0.4 g (1.0 mmol) tetrakis(4-hydroxyphenyl)ethene
7 and 0.54 g (4.4 mmol) DMAP in 50 mL CH2Cl2 was dropwise
added at 0 8C
a solution of 0.79 g (4.4 mmol) methyl
(2S)-benzyloxypropionic acid 10 h and 1.69 g (8.8 mmol)
N-3-dimethylaminopropyl-N-ethylcarbodiimide (EDC) in 20 mL
CH2Cl2. After stirring at room temperature for 18 h, the mixture
was filtered via Celite, washed with 2 ꢂ 50 mL 1 N HCl, 50 mL H2O,
dried over MgSO4 and evaporated. The crude product was
purified by flash chromatography.
Tetrakis{4-[(2S)-methoxypropionate]phenyl}ethene (3a)
According to the general procedure flash chromatography
(hexanes/ethyl acetate 10:1) yielded 0.33 g (89%) of a colourless
solid.
(2S)-2-Decyloxypropan-1-ol (11g)
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 1.54 (d, J ¼ 6.9 Hz, 12H,
3
According to the general procedure flash chromatography
(hexanes/Et2O 3:1) yielded 1.25 g (99%) of a pale yellow oil.
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 0.88 [t, 3J ¼ 7.1 Hz, 3H,
CH2CH2(CH2)7CH3], 1.11 (d, 3J ¼ 6.2 Hz, 3H, 3H), 1.20–1.38 [m, 16H,
CH2CH2(CH2)7CH3], 1.52–1.61 [m, 2H, CH2CH2(CH2)7CH3], 2.09
(s, br, 1H, OH), 3.37 [dt, 2J ¼ 9.2 Hz, 3J ¼ 6.7 Hz, 1H,
3
30-H), 3.48 (s, 12H, OCH3), 4.07 (q, J ¼ 6.9 Hz, 4H, 20-H), 6.89 (d,
3J ¼ 8.9 Hz, 8H, 2H, 6H), 7.03 (d, 3J ¼ 8.9 Hz, 8H, 3H, 5H). 13C-NMR
(125 MHz, CDCl3): d (ppm) ¼ 18.4 (C-30), 57.9 (OCH3), 76.4 (C-20),
—
120.8 (C-2, C-6), 132.4 (C-3, C-5), 139.7 (C C), 140.7 (C-1), 149.1
—
(C-4), 171.4 (C-10). MS (EI): m/z (%) ¼ 740 (100) [M]þ, 654 (60), 568
(50), 482 (40), 410 (5), 396 (75), 379 (5), 303 (5), 273 (5), 185 (5), 59
(80). CHN: C42H44O12 calcd. C 68.10%, H 5.99%, found C 67.92%, H
6.01%. FT-IR (ATR): n ¼ 3040 (w), 2988, 2936, 2829 (m), 2323 (w),
1754 (vs), 1602 (m), 1502, 1445, 1354 (s), 1197, 1162, 1000 (vs)
cmꢀ1. [a]2D0 ¼ ꢀ92.0 (c ¼ 1.0, CHCl3).
2
CH2ACH2(CH2)7CH3], 3.41–3.46 (m, 1H, 2H), 3.57 [dt, J ¼ 9.2 Hz,
3J ¼ 6.7 Hz, 1H, CH2BCH2(CH2)7CH3], 3.48–3.60 (m, 2H, 1-H).
13C-NMR (125 MHz, CDCl3): d (ppm) ¼ 14.1 (CH2(CH2)8CH3), 15.9
(C-3), 22.7, 26.2, 29.4, 29.5, 29.6, 29.7, 30.1, 31.9 (CH2(CH2)8CH3),
66.4 (C-1), 68.9 (CH2(CH2)8CH3), 75.8 (C-2). MS (EI): m/z (%) ¼ 217
(2) [M þ H]þ, 185 (100), 168 (10), 141 (40), 112 (5), 99 (20), 97 (10),
85 (80), 83 (15), 71 (70), 69 (15), 57 (80), 55 (25), 45 (10), 43 (45).
HMRS (ESI): calcd. for C13H28NaO2 [M þ Na]þ 239.1987, found
239.1982. FT-IR (ATR): n ¼ 3392 (vs), 2922, 2853 (vs), 2359 (w),
Tetrakis{4-[(2S)-ethoxypropionate]phenyl}ethene (3b)
According to the general procedure flash chromatography
(hexanes/ethyl acetate 3:1) yielded 0.18 g (99%) of a highly
viscous, pale green oil.
1464 (m), 1375 (w), 1341 (w), 1094, 1046 (vs), 988 (m) cmꢀ1
[a]2D0 ¼ þ20.2 (c ¼ 1.0, CHCl3).
.
J. Phys. Org. Chem. 2009, 22 484–494
Copyright ß 2009 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/poc

A. SCHREIVOGEL ET AL.
3
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 1.27 (t, J ¼ 7.0 Hz, 12H,
2J ¼ 9.0 Hz, 3J ¼ 6.6 Hz, 4H, CH2ACH2CH2(CH2)4CH3], 3.66 [dt,
2J ¼ 9.0 Hz, 3J ¼ 6.6 Hz, 4H, CH2BCH2CH2(CH2)4CH3], 4.14 (q,
3J ¼ 6.9 Hz, 4H, 20-H), 6.88, 7.02 (d, 3J ¼ 8.7 Hz, 8H, 3J ¼ 8.7 Hz,
8H, 2H, 3H, 5H, 6H). 13C-NMR (125 MHz, CDCl3): d (ppm) ¼ 14.1
[CH2(CH2)6CH3], 18.7 (C-30), 22.7, 26.1, 29.2, 29.4, 29.8, 31.8
[CH2(CH2)6CH3], 70.7 [CH2(CH2)6CH3], 74.9 (C-20), 120.8 (C-3, C-5),
CH2CH3), 1.54 (d, J ¼ 6.8 Hz, 12H, 30-H), 3.54 (dq, 2J ¼ 8.9 Hz,
3
3J ¼ 7.0 Hz, 4H, CH2ACH3), 3.73 (dq, 2J ¼ 8.9 Hz, 3J ¼ 7.0 Hz, 4H,
CH2BCH3), 4.16 (q, 3J ¼ 6.8 Hz, 4H, 20-H), 6.89 (d, 3J ¼ 8.8 Hz, 8H, 2H,
6H), 7.03 (d, 3J ¼ 8.8 Hz, 8H, 3H, 5H). 13C-NMR (125 MHz, CDCl3): d
(ppm) ¼ 14.2 (CH2CH3), 18.7 (C-30), 65.9 (CH2CH3), 74.8 (C-20),
—
—
—
132.4 (C-2, C-6), 139.7 (C C), 140.7 (C-1), 149.2 (C-4), 171.8 (C
—
120.8 (C-2, C-6), 132.4 (C-3, C-5), 139.7 (C C), 140.7 (C-1), 149.1
—
—
(C-4), 171.8 (C-10). MS (EI): m/z (%) ¼ 796 (100) [M]þ, 696 (90), 596
(80), 496 (60), 452 (5), 424 (10), 396 (100), 379 (5), 273 (5), 185 (5),
73 (80), 45 (75). HMRS (ESI): calcd. for C46H52NaO12 [M þ Na]þ
819.3356, found 819.3344. FT-IR (ATR): n ¼ 3038 (w), 2979, 2935,
2875 (s), 2572 (m), 2364 (m), 2183 (m), 1980 (m), 1765 (vs), 1600
(m), 1503, 1445 (vs), 1406, 1372 (m), 1239 (m), 1198, 1163, 1110
(vs) cmꢀ1. [a]2D0 ¼ ꢀ65.8 (c ¼ 1.0, CHCl3).
O). MS (ESI): m/z ¼ 1155.7 [M þ Na]þ. HRMS (ESI): calcd. for
C70H100NaO12 [M þ Na]þ 1155.7112, found 1155.7096. FT-IR (ATR):
n ¼ 2923, 2854 (vs), 1720 (vs), 1458 (s), 1371 (m), 1239 (m), 1127,
1071 (vs) cmꢀ1. [a]D20 ¼ ꢀ68.8 (c ¼ 1.0, CHCl3).
Tetrakis{4-[(2S)-decyloxypropionate]phenyl}ethene (3g)
According to the general procedure flash chromatography
(hexanes/ethyl acetate 20:1) yielded 0.19 g (52%) of a highly
viscous, pale green oil.
Tetrakis{4-[(2S)-propyloxypropionate]phenyl}ethene (3c)
3
According to the general procedure flash chromatography
(hexanes/ethyl acetate 5:1) yielded 0.13 g (82%) of a highly
viscous, pale green oil.
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 0.87 [t, J ¼ 6.9 Hz, 12H,
CH2CH2CH2(CH2)6CH3], 1.19–1.32 [m, 48H, CH2CH2CH2(CH2)6CH3],
1.32–1.40 [m, 8H, CH2CH2CH2(CH2)6CH3], 1.53 (d, 3J ¼ 6.9 Hz, 12H,
30-H), 1.59–1.66 [m, 8H, CH2CH2CH2(CH2)6CH3], 3.44 [dt,
2J ¼ 8.8 Hz, 3J ¼ 6.8 Hz, 4H, CH2ACH2CH2(CH2)6CH3], 3.66 [dt,
2J ¼ 8.8 Hz, 3J ¼ 6.8 Hz, 4H, CH2BCH2CH2(CH2)6CH3], 4.14 (q,
3J ¼ 6.8 Hz, 4H, 20-H), 6.88, 7.02 (d, 3J ¼ 8.7 Hz, 8H, 3J ¼ 8.7 Hz,
8H, 2H, 3H, 5H, 6H). 13C-NMR (125 MHz, CDCl3): d (ppm) ¼ 14.1
[CH2(CH2)8CH3], 18.7 (C-30), 22.7, 26.1, 29.3, 29.5, 29.6, 29.8, 30.9
[CH2(CH2)8CH3], 70.7 [CH2(CH2)8CH3], 74.9 (C-20), 120.8 (C-3, C-5),
3
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 0.95 (t, J ¼ 7.0 Hz, 12H,
CH2CH2CH3), 1.54 (d, 3J ¼ 6.9 Hz, 12H, 30-H), 1.66 (qdd, 3J ¼ 7.4 Hz,
3J ¼ 6.7 Hz, 3J ¼ 6.7 Hz, 8H, CH2CH2CH3), 3.42 (dt, 2J ¼ 8.9 Hz,
3J ¼ 6.7 Hz, 4H, CH2ACH2CH3), 3.63 (dt, 2J ¼ 8.9 Hz, 3J ¼ 6.7 Hz, 4H,
CH2BCH2CH3), 4.15 (q, 3J ¼ 7.0 Hz, 4H, 2H),6.89 (d, 3J ¼ 8.8 Hz, 8H,
2H, 6H), 7.02 (d, 3J ¼ 8.8 Hz, 8H, 3H, 5H). 13C-NMR (125 MHz,
CDCl3):
d
(ppm) ¼ 10.5 (CH2CH2CH3), 18.7 (C-30), 22.9
(CH2CH2CH3), 72.2 (CH2CH2CH3), 74.9 (C-20), 120.8 (C-2, C-6),
—
132.4 (C-2, C-6), 139.7 (C C), 140.7 (C-1), 149.2 (C-4), 171.8 (C
—
—
—
132.4 (C-3, C-5), 139.7 (C C), 140.7 (C-1), 149.2 (C-4), 171.8 (C-1 ).
—
O). MS (ESI): m/z ¼ 1267.8 [M þ Na]þ. HRMS (ESI): calcd. for
C78H116NaO12 [M þ Na]þ 1267.8364, found 1267.8345. FT-IR (ATR):
n ¼ 2922, 2853 (vs), 1770 (vs), 1503, 1456 (s,), 1372 (m), 1237 (m),
1199, 1163, 1111, 1016 (vs) cmꢀ1. [a]D20 ¼ ꢀ62.0 (c ¼ 1.0, CHCl3).
0
—
MS (ESI): m/z (%) ¼ 875.4 [M þ Na]þ. HRMS (ESI): m/z (%) calcd. for
C50H60O12Na [M þ Na]þ 875.3982, found 875.3971. FT-IR (ATR):
n ¼ 2963, 2936, 2876 (m), 1768 (s), 1601, 1503, 1454 (s), 1372 (m),
1238 (m), 1198, 1163, 1111, 1015 (vs), 903 (s), 873 (s) cmꢀ1
.
[a]2D0 ¼ ꢀ71.6 (c ¼ 1.0, CHCl3).
Tetrakis{4-[(2S)-benzyloxypropionate]phenyl}ethene (3h)
According to the general procedure flash chromatography
(hexanes/ethyl acetate 4:1) yielded 0.85 g (82%) of a highly
viscous, pale green oil.
Tetrakis{4-[(2S)-pentyloxypropionate]phenyl}ethene (3e)
According to the general procedure flash chromatography
(hexanes/ethyl acetate 10:1) yielded 32.0 mg (7%) of a highly
viscous, pale green oil.
3
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 1.58 (d, J ¼ 6.8 Hz, 12H,
30-H), 4.26 (q, 3J ¼ 6.8 Hz, 4H, 20-H), 4.55 (d, 2J ¼ 11.6 Hz, 4H, CH2A),
3
2
3
1H-NMR (250 MHz, CDCl3): d (ppm) ¼ 0.90 (t, J ¼ 6.9 Hz, 12H,
4.78 (d, J ¼ 11.6 Hz, 4H, CH2B), 6.89 (d, J ¼ 8.8 Hz, 8H, 2H, 6H),
7.04 (d, 3J ¼ 8.8 Hz, 8H, 3H, 5H), 7.27-7.32 (m, 4H, 400-H), 7.33-7.42
(m, 16 H, 200-H, 300-H, 500-H, 600-H). 13C-NMR (125 MHz, CDCl3): d
(ppm) ¼ 18.7 (C-30), 72.3 (CH2), 74.0 (C-20), 120.8 (C-2, C-6), 128.0
200-H), 1.27–1.44 (m, 16H, 300-H, 400-H), 1.54 (d, 3J ¼ 7.0 Hz, 12H,
30-H), 1.55–1.74 (m, 8H, 200-H), 3.45 (dq, 2J ¼ 9.1 Hz, 3J ¼ 6.7 Hz, 4H,
3
100-HA), 3.66 (dq, 2J ¼ 9.1 Hz, J ¼ 6.7 Hz, 4H, 100-HB), 4.13 (q,
3
3J ¼ 7.0 Hz, 4H, 20-H), 6.88 (d, J ¼ 8.6 Hz, 8H, 2-H, 6-H), 7.03 (d,
(C-4 ), 128.1, 128.5 (C-200, C-300, C-500, C-600), 132.4 (C-3, C-5), 137.3
00
3J ¼ 8.6 Hz, 8H, 3H, 5H). 13C-NMR (125 MHz, CDCl3): d (ppm) ¼ 14.0
(C-1 ), 139.7 (C C), 140.8 (C-1), 149.1 (C-4), 171.5 (C-1 ). MS (EI):
—
00
0
—
(C-500), 18.7 (C-30), 22.5, 29.5 (C-300, C-400), 28.2 (C-200), 70.7 (C-100),
m/z (%) ¼ 1044 (15) [M]þ, 972 (15), 938 (40), 894 (10), 882 (80), 810
(20), 776 (40), 737 (10), 720 (50), 704 (10), 105 (20), 91 (100), 43
(20). CHN: C66H60O12 (1045.18 g molꢀ1) calcd. C 75.84%, H 5.79%,
found C 75.75%, H 5.94%. FT-IR (ATR): n ¼ 3320 (w), 3031 (w),
2984, 2936, 2870 (m), 2356 (w), 1763 (s), 1599, 1502, 1453 (s),
1197, 1162, 1105, 1014 (s) cmꢀ1. [a]D20 ¼ –95.8 (c ¼ 1.0, CHCl3).
0
—
74.9 (C-2 ), 120.8 (C-2, C-6), 132.4 (C-3, C-5), 139.7 (C C), 140.7
—
(C-1), 149.2 (C-4), 171.8 (C-10). HRMS (ESI): m/z (%) calcd. for
C58H76O12Na [M þ Na]þ 987.5234, found 987.5238. FT-IR (ATR):
n ¼ 2955, 2932, 2870 (vs), 2365, 2184 (m), 1757 (vs), 1613, 1501,
1445 (s), 1196, 1165, 1114, 1017 (vs), 734 (s) cmꢀ1. [a]D20 ¼ ꢀ60.3
(c ¼ 1.0, CHCl3).
General procedure for the preparation of
tetrakis{4-[(2S)-alkoxypropyl]phenyl}-ethenes (2d, g–i)
Tetrakis{4-[(2S)-octyloxypropionate]phenyl}ethene (3f)
According to the general procedure flash chromatography
(hexanes/ethyl acetate 20:1) yielded 48.0 mg (47%) of a highly
viscous, pale green oil.
To a suspension of 4.2 g (30.0 to a solution of 0.4 g (1.0 mmol)
tetrakis(4-hydroxyphenyl)ethene 7 and 0.54 g (4.4 mmol) DMAP
in 50 mL CH2Cl2 was dropwise added at 0 8C a solution of 0.79 g
(4.4 mmol) methyl (2S)-benzyloxypropionic acid 10 h und 1.69 g
(8.8 mmol) EDC in 20 mL CH2Cl2. After stirring at room
temperature for 18 h, the mixture was filtered via Celite, washed
with 2 ꢂ 50 mL 1 N HCl, 50 mL H2O, dried over MgSO4 and
3
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 0.87 [t, J ¼ 7.1 Hz, 12H,
CH2CH2CH2(CH2)4CH3], 1.19–1.33 [m, 32H, CH2CH2CH2(CH2)4CH3],
1.33-1.42 [m, 8H, CH2CH2CH2(CH2)4CH3], 1.54 (d, 3J ¼ 6.9 Hz, 12H,
30-H), 1.58–1.68 [m, 8H, CH2CH2CH2(CH2)4CH3], 3.45 [dt,
www.interscience.wiley.com/journal/poc
Copyright ß 2009 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2009, 22 484–494

CHIRAL TETRAPHENYLETHENES AS NOVEL DOPANTS
evaporated. (The crude product was purified by flash chroma-
tography.) Cs2CO3 and 0.91 g (2.3To a solution of 0.4 g (1.0 mmol)
tetrakis(4-hydroxyphenyl)ethene 7 and 0.54 g (4.4 mmol) DMAP
in 50 mL CH2Cl2 was dropwise added at 0 8C a solution of 0.79 g
(4.4 mmol) methyl (2S)-benzyloxypropionic acid 10 h und 1.69 g
(8.8 mmol) EDC in 20 mL CH2Cl2. After stirring at room
temperature for 18 h, the mixture was filtered via Celite, washed
with 2 ꢂ 50 mL 1 N HCl, 50 mL H2O, dried over MgSO4 and
evaporated. (The crude product was purified by flash chroma-
tography.) Tetrakis(4-hydroxyphenyl)ethene 7 in 40 mL DMF were
added 2.5 g (10.9To a solution of 0.4 g (1.0 mmol) tetra-
kis(4-hydroxyphenyl)ethene 7 and 0.54 g (4.4 mmol) DMAP in
50 mL CH2Cl2 was dropwise added at 0 8C a solution of 0.79 g
(4.4 mmol) methyl (2S)-benzyloxypropionic acid 10 h und 1.69 g
(8.8 mmol) EDC in 20 mL CH2Cl2. After stirring at room
temperature for 18 h, the mixture was filtered via Celite, washed
with 2 ꢂ 50 mL 1 N HCl, 50 mL H2O, dried over MgSO4 and
evaporated. The crude product was purified by flash chroma-
tography.) (2S)-Benzyloxypropylbromide 12c and the mixture
was heated at 80 8C for 72 h and then poured onto 50 g ice and
diluted with 150 mL CH2Cl2. The layers were separated, the
aequos layer was extracted with 150 mL CH2Cl2, the combined
organic layers were dried over MgSO4, evaporated and purified
by flash chromatography.
897.7 (30), 831.5 (2), 757.5 (5), 595.5 (5). HRMS (CI): calcd. for
C78H125O8 [M þ H]þ 1189.9374, found 1189.9369. FT-IR (ATR):
n ¼ 2955, 2924, 2853 (vs), 1949 (m), 1733 (m), 1613 (s), 1507, 1455,
1439 (vs), 1375 (m), 1259, 1239 (vs), 1123, 1101, 1037 (vs), 840, 801
(vs) cmꢀ1. [a]2D0 ¼ ꢀ28.1 (c ¼ 1.0, CHCl3).
Tetrakis{4-[(2S)-benzyloxypropyl]phenyl}ethene (2h)
According to the general procedure flash chromatography
(hexanes/ethyl acetate 10:1) yielded 0.82 g (36%) of a highly
viscous, pale green oil.
3
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 1.28 (d, J ¼ 6.2 Hz, 12H,
30-H), 3.76–3.82 (m, 4H, 20-H), 4.17 (dd, 2J ¼ 11.4 Hz, 3J ¼ 6.2 Hz, 4H,
3
10-HA), 4.22 (dd, 2J ¼ 11.4 Hz, J ¼ 4.3 Hz, 4H, 10-HB), 4.55 (d,
3J ¼ 11.9 Hz, 4H, CH2A), 4.61 (d, 3J ¼ 11.9 Hz, 4H, CH2B), 6.5–6.7 (m,
8H, 3H, 5H), 6.8–6.9 (m, 8H, 2H, 6H), 7.26–7.38 (m, 20H, 2H00, 3H00,
13
4H00, 5H00, 6H00). C-NMR (125 MHz, CDCl3): d (ppm) ¼ 17.8 (C-30),
72.5 (C-10), 73.2 (C-20), 126.9, 127.5, 127.7, 128.36, 128.6 (C-200,
C-300, C-400, C-500, C-600), 127.6, 128.44 (C-2, C-3, C-5, C-6), 138.3 (C-4),
00
—
138.7 (C-1), 140.9 (C C), 177.1 (C-1 ). MS (ESI): m/z ¼ 1011.5
—
[M þ Na]þ. HRMS (ESI): calcd. for C66H68NaO8 [M þ Na]þ
1011.4812, found 1011.4824. FT-IR (ATR): n ¼ 3063 (m), 2978,
2872 (m), 1958 (m), 1613 (s), 1453, 1376 (s), 1271, 1238 (vs), 1139,
1055 (vs), 735, 696 (vs) cmꢀ1. [a]D20 ¼ ꢀ32.4 (c ¼ 1.0, CHCl3).
Tetrakis{4-[(2S)-methoxymethoxypropyl]phenyl}ethene (2i)
Tetrakis{4-[(2S)-butyloxypropyl]phenyl}ethene (2d)
According to the general procedure flash chromatography
(hexanes/ethyl acetate 5:1) yielded 0.15 g (63%) of a highly
viscous, pale green oil.
According to the general procedure flash chromatography
(hexanes/ethyl acetate 20:1) yielded 0.29 g (72%) of a highly
viscous, pale green oil.
3
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 1.28 (d, J ¼ 6.4 Hz, 12H,
3
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 0.91 (t, J ¼ 7.3 Hz, 12H,
30-H), 3.39 (s, 12H, OMe), 3.84 (dd, 2J ¼ 9.8 Hz, 3J ¼ 4.5 Hz, 4H,
CH2CH2CH2CH3), 1.24 (d, 3J ¼ 6.1 Hz, 12H, 30-H), 1.33–1.42 (m, 8H,
CH2CH2CH2CH3), 1.52–1.59 (m, 8H, CH2CH2CH2CH3), 3.52 (dt,
2J ¼ 9.3 Hz, 3J ¼ 6.6 Hz, 4H, CH2ACH2CH2CH3), 3.55 (dt, 2J ¼ 9.3 Hz,
3J ¼ 6.6 Hz, 4H, CH2BCH2CH2CH3), 3.71–3.77 (m, 4H, 20-H), 3.78 (dd,
2J ¼ 9.3 Hz, 3J ¼ 5.0 Hz, 4H, 10-HA), 3.91 (dd, 2J ¼ 9.3 Hz, 3J ¼ 5.5 Hz,
4H, 10-HB), 6.63, 6.90 (d, 3J ¼ 9.0 Hz, 8H, 3J ¼ 8.9 Hz, 8H, 2H, 3H, 5H,
6H). 13C-NMR (125 MHz, CDCl3): d (ppm) ¼ 13.9 (CH2CH2CH2CH3),
17.5 (C-30), 19.3 (CH2CH2CH2CH3), 32.2 (CH2CH2CH2CH3C-2), 69.3
3
10-HA), 3.91 (dd, 2J ¼ 9.8 Hz, J ¼ 6.2 Hz, 4H, 10-HB), 4.06 (qdd,
3
3
2
3J ¼ 6.4 Hz, J ¼ 6.2 Hz, J ¼ 4.5 Hz, 4H, 20-H), 4.73 (d, J ¼ 6.8 Hz,
4H, OCH2O-HA), 4.75 (d, 2J ¼ 6.8 Hz, 4H, OCH2O-HB), 6.63 (d,
3J ¼ 8.9 Hz, 8H, 2H, 6H), 6.90 (d, 3J ¼ 8.9 Hz, 8H, 3H, 5H). 13C-NMR
(125 MHz, CDCl3): d (ppm) ¼ 17.5 (C-30), 55.3 (OCH3), 71.3 (C-20),
71.4 (C-10), 95.4 (OCH2O), 113.6, 132.5 (C-2, C-3, C-5, C-6), 136.9
þ
—
(C-1), 138.4 (C C), 156.9 (C-4). MS (ESI): m/z ¼ 804 [M] . HRMS
—
(ESI): calcd. for C46H60NaO12 [M þ Na]þ 827.3982, found 827.3957.
FT-IR (ATR): n ¼ 3032 (w), 2973 (s), 2930 (s), 2889 (s), 2537 (m),
2164 (m), 2009 (m), 1604 (vs), 1506 (vs), 1454 (vs), 1376 (m), 1238,
(CH2CH2CH2CH3), 71.4 (C-10), 73.8 (C-20), 113.7, 132.5 (C-2, C-3, C-5,
—
C-6), 136.9 (C-1), 138.4 (C C), 157.1 (C-4). MS (ESI): m/z ¼ 852.0
—
[M]þ. HRMS (ESI): calcd. for C54H80NO8 [M þ NH4]þ 870.5884,
found 870.5866. FT-IR (ATR): n ¼ 3035 (w), 2957, 2930, 2869 (vs),
1604 (vs), 1506, 1455 (vs), 1374 (m), 1286 (m), 1237, 1149, 1104,
1038 (vs), 827 (vs) cmꢀ1. [a]D20 ¼ ꢀ35.2 (c ¼ 1.0, CHCl3).
1143, 1103 (vs), 1027, 989 (vs), 915 (vs), 829 (vs) cmꢀ1
.
[a]2D0 ¼ ꢀ38.0 (c ¼ 1.0, CHCl3).
RESULTS AND DISCUSSION
Tetrakis{4-[(2S)-decyloxypropyl]phenyl}ethene (2g)
Synthesis
According to the general procedure flash chromatography
(hexanes/ethyl acetate 40:1) yielded 0.32 g (72%) of a highly
viscous, pale green oil.
The following three series of compounds were prepared:
citronellyl ethers 1a, b, lactate-derived ethers 2d, g–i and
lactates 3a–c, e–h (Scheme 1). These derivatives were chosen
because they are readily available building blocks. In the case of
lactates, a common precursor can be used for the synthesis of
both esters and ethers. Thus, the influence of different
parameters on the HTP could be studied very easily, i.e. dipole
moment of ester versus ether moiety as well as chain lengths.
Various chain lengths up to ten carbon atoms were chosen in
order to obtain good miscibility between the nematic host phase
and the dopant. Following the procedure by Chattopadhyay[94]
(R)-citronellol 4 was treated with bromine and PPh3 in the
presence of pyridine in CH2Cl2 at 0 8C for 24 h and the
3
1H-NMR (500 MHz, CDCl3): d (ppm) ¼ 0.81 [t, J ¼ 6.8 Hz, 12H,
3
CH2CH2(CH2)7CH3], 1.17 (d, J ¼ 6.2 Hz, 12H, 30-H), 1.14-1.31 [m,
56H, CH2CH2(CH2)7CH3], 1.44–1.55 [m, 8H, CH2CH2(CH2)7CH3],
3.46 [dt, 2J ¼ 6.8 Hz, 4J ¼ 2.2 Hz, 8H, CH2CH2(CH2)7CH3], 3.63–3.73
2
3
(m, 8H, 20-H, 10-HA), 3.48 (dd, J ¼ 9.2 Hz, J ¼ 5.4 Hz, 4H, 10-HB),
6.56, 6.83 (d, 3J ¼ 8.6 Hz, 8H, 3J ¼ 8.6 Hz, 8H, 2H, 3H, 5H, 6H).
13C-NMR (125 MHz, CDCl3): d (ppm) ¼ 13.1 [CH2(CH2)8CH3], 16.4
(C-30), 21.7, 25.1, 28.3, 28.56, 28.60, 28.68, 29.1, 30.89
[CH2(CH2)8CH3], 68.6 [CH2(CH2)8CH3], 70.3 (C-10), 72.7 (C-20),
—
112.6 (C-3, C-5), 126.5 (C-1), 128.7 (C C), 131.5 (C-2, C-6), 156.1
—
(C-4). MS (CI): m/z ¼ 1189.9 (100) [M þ H]þ, 1029.7 (30), 987.7 (5),
J. Phys. Org. Chem. 2009, 22 484–494
Copyright ß 2009 John Wiley & Sons, Ltd.
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A. SCHREIVOGEL ET AL.
for R2 = MOM
R1O
OR1
O
O
Ag2O, R2Br
OR2
R1
=
MOMCl
OH
1a
b
8
O
O
Et2O, 40 °C, 18 h
EtN(i-Pr)2, CH2Cl2
0 °C, 48 h
9a i
8
O
LiAlH4, Et2O
0 °C, 18 h
LiOH, MeOH
rt, 24 h
OR2
OR2
X
HO
R1O
O
OR1
O
11d,g i X = OH
12d,g i X = Br
7
10a c,e h
R2O
OR2
CBr4, PPh3, NEt3,
CH2Cl2, 0 °C, 24 h
2d
g
R
2 = C4H9
C10H21
7
Cs2CO3, DMF
90 °C, 72 h
DMAP, EDC
CH2Cl2, rt, 18 h
h
i
Bn
CH2OCH3
2d,g i
3a c,e h
O
O
O
O
Scheme 3.
R2O
R2O
OR2
OR2
The synthesis of lactate ethers 2 and lactates 3 commenced
with alkylation of methyl lactate 8 with alkyl bromides in the
presence of Ag2O in Et2O at 40 8C for 18 h according to the
procedure by Molteni[95] to give the corresponding ethers 9 in
10–99% yield (Scheme 3, Table 1). The yields of alkylation
products 9 were extremely sensitive to the quality of Ag2O. Thus,
Ag2O had to be freshly prepared. We observed decreased
conversions with increasing chain lengths which is probably due
to steric effects in this SN2 type reaction. It should be noted that
other conditions compromised the optical purity of the lactate
and were therefore not considered. Subsequent saponification
with LiOH in MeOH at room temperature produced the carboxylic
acids 10 in 69–99% yield, which were esterified with tetrakis(4-
hydroxyphenyl)ethene 7 in the presence of DMAP and EDC in
CH2Cl2 at room temperature to give the lactates 3 in 7–99% yield.
Treatment of methyl lactate 8 with methoxymethylchloride and
Hu¨nig’s base at room temperature for 48 h yielded the
O-MOM-protected lactate 9i in 71%.[96,97] After reduction of
methyl lactates 9 with LiAlH4 in Et2O at 0 8C, the alcohols 11 were
isolated in 80–99% yield. Bromination of 11 with bromine and
PPh3 in the presence of NEt3 in CH2Cl2 at 0 8C gave the bromides
12 in 42–98% yield. Upon final Williamson etherification with 7
under the usual conditions the lactate-derived ethers 2 were
obtained in 36–72%.
3a R2 = CH3
b
c
e
C2H5
C3H7
C5H11
O
O
O
O
C8H17
f
C10H21
g
O
O
R2O
OR2
h
Bn
Scheme 1.
corresponding bromide 5 was isolated in 80% yield (Scheme 2).
Subsequent catalytic hydrogenation under 1 atm of hydrogen in
the presence of Pd/C in MeOH at room temperature yielded the
saturated bromide 6. Tetrakis(4-hydroxytetraphenyl)ethene 7
was then submitted to Williamson etherification with bromides 5
and 6, respectively, in the presence of K2CO3 in DMF at 80 8C for
72 h to give the citronellyl ethers 1a, b in 43 and 70% yield,
respectively. Although, similar conversions of the four-fold
etherification were obtained in both cases, the yield of
compound 1a was compromised by tedious chromatographic
removal of partially alkylated byproducts.
Chiral properties of the dopants in nematic phases
Pd/C, H2, MeOH
rt, 3 h, 99%
X
Br
The chiral nematic liquid crystalline solutions were prepared by
adding the chiral dopant, i.e. the tetraphenylethene derivatives
1–3 in various concentrations to the commercially available
calamitic host liquid crystal 4-pentylcyanobiphenyl 5CB 13
(Scheme 4), which displays a nematic mesophase between
23 8C and 35 8C.[98] Alternatively, the discotic hexakis(4-
nonylphenylethynyl)benzene 14,[91–93] which displays a discotic
nematic mesophase ND between 67 and 83 8C, was used as host
material. It should be noted that pure compounds 1–3 are
non-mesogenic.
4
5
X = OH
X = Br
6
Br2, PPh3, Py, CH2Cl2
0 °C, 24 h, 80%
HO
OH
, K2CO3, DMF, 80 °C, 72 h
Citronellyl-derived tetraphenylethenes 1a, b were miscible up
to 5 mol% with 5CB 13 and thus characteristic fingerprint
textures could be obtained, as shown in Fig. 1 for different
solutions of 1a with 13.
For the binary solutions of 5CB 13 with the tetraphenylethenes
1–3 phase diagrams were determined. Depending on the molar
HO
OH
7
1a 43%
1b 70%
Scheme 2.
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Copyright ß 2009 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2009, 22 484–494

CHIRAL TETRAPHENYLETHENES AS NOVEL DOPANTS
0.1
0.08
0.06
0.04
0.02
0
NC
C5H11
13
5CB (Cr 23 N 35 I)
C9H19
C9H19
C9H19
0
0.005
0.01
X
0.015
0.02
Figure 3. Reciprocal pitch 1/p as a function of the molar fraction x for
binary solutions of 5CB 13/1a (~) and 5CB 13/1b (&)
40
35
30
C9H19
C9H19
I
25
C9H19
20
15
10
5
*
14
I + N
*
hexayne (Cr 67 ND 83 I)
N
Scheme 4.
0
0.4
0.8
1.2
1.6
x / mol%
fraction and the temperature an isotropic phase, a two-phase
region with coexisting isotropic and chiral nematic phase and a
chiral nematic phase were observed. The phase diagram for the
solution of 5CB 13 and citronellyl-derivative 1a is shown in Fig. 2.
Helical pitches were determined after cooling the solution
(cooling rate 1 K minꢀ1) from the isotropic phase to the specified
temperature and subsequent annealing for 1 h in order to obtain
stable textures. The reciprocal pitches were plotted versus the
molar fractions of the dopant and the HTP values were obtained
from the initial slopes at low dopant concentrations (Fig. 3).
A typical phase diagram for binary solutions of 5CB 13 and
lactate-derived tetraphenylene ester 3b is shown in Fig. 4. The
reciprocal pitches were plotted versus the molar fraction for
binary solutions of 5CB 13 and 3b, c, e–g (Fig. 5) and HTP values
were determined as described above.
Figure 4. Partial phase diagram of binary solutions of 5CB 13 and
*
*
dopant 3b. N denotes the chiral nematic phase, I þ N denotes the
two-phase region, I denotes the isotropic phase
In contrast, for most of the other tetraphenylethene derivatives
2, 3 phase separation occurred at dopant concentrations
higher than 3 mol% and therefore only solutions between 0.2
and 2.0 mol% were considered for the HTP measurements.
Figure 5. Reciprocal pitch 1/p as a function of the molar fraction x for
binary solutions of 5CB 13 and 3b (^), 3c (&), 3e (~), 3f (*), 3g (~)
0.21
0.18
0.15
0.12
0.09
0.06
0.03
0
40
35
30
25
20
15
10
5
I
I + N
N*
0
0.5
1
1.5
2
x / mol%
0
0.005
0.01
0.015
0.02
0.025
x
Figure 2. Partial phase diagram of binary solutions of 5CB 13 and
*
*
dopant 1a. N denotes the chiral nematic phase, I þ N denotes the
Figure 6. Reciprocal pitch 1/p as a function of the molar fraction x for
binary solutions of 5CB 13 and 2g (&), 2d (x), 2i (~)
two-phase region, I denotes the isotropic phase
J. Phys. Org. Chem. 2009, 22 484–494
Copyright ß 2009 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/poc

A. SCHREIVOGEL ET AL.
Figure 7. Fingerprint textures of solutions of hexayne 14 with 2 mol% 3b (A) and 5 mol% 3b (B) (magnification 200ꢂ)
90
80
70
I
60
I +N*
50
N*
40
30
20
Cr
0
2
4
6
8
10
x / mol%
Figure 8. Partial phase diagram of binary solutions of hexayne 14 and
Figure 9. Reciprocal pitch 1/p as a function of the molar fraction ꢂ for
binary solutions of hexayne 14 and 3b (^), 3c (~), 3e (&), 3f (*), 3g (~)
*
*
dopant 3b. N denotes the chiral nematic phase, I þ N denotes the
two-phase region, I denotes the isotropic phase, Cr denotes the crystalline
phase
Benzyloxy-substituted tetraphenylene ether 2h and ester 3h
were not suitable as dopants because they were completely
immiscible with 5CB 13 even at low concentrations. Also
methoxy-substituted tetraphenylene ester 3a could not be used,
because even very dilute solutions which were spin-coated onto
the glass slide immediately crystallized.
Next, reciprocal pitch versus molar fraction diagrams of binary
solutions of 5CB 13 and 2 were prepared (Fig. 6) and the HTP
values calculated.
Neither citronellyl-derived tetraphenylethene ethers 1a, b nor
lactate-derived ethers 2 did induce fingerprint textures in the
nematic discotic host 14. However, lactate-derived tetrapheny-
lethene esters 3 were suitable as dopants (Fig. 7) and HTP values
could be obtained by the above-described procedure. A typical
phase diagram for binary solution of hexayne 14 and 3b and the
reciprocal pitch versus molar fraction diagram of binary solutions
of 14 with 3b, c, e–g are shown in Figs 8 and 9, respectively.
The results concerning HTPs are summarized in Table 2. HTP
values are in the range between 2.1 and 28.7 mmꢀ1 and molar
HTP (MHTP) values in the range between 1.7 and
35.8 mmꢀ1 molꢀ1 kg were observed. Dihydrocitronellyl-derivative
1b displayed a higher HTP as compared to the corresponding
citronellyl-derivative 1a (entries 1, 2). It is known from the
literature,[54,99] that even small variations at the lateral side chains
can have a large influence on mesomorphic properties. In case of
compound 1a the less flexible olefinic moiety presumably
interfers with tight packing of the side chains within the chiral
nematic helix. Solutions of lactate-derived ethers 2d, g, i in host
5CB 13 showed HTPs around 14–15 mmꢀ1 irrespective of the
substituent R2 (entries 3–5). For solutions of lactate-derived esters
3 and 5CB 13 HTP values decrease with increase in side chain
Table 1. Yields of compounds 9–12, 2 and 3 according to
Scheme 3
R2¼
9 (%) 10 (%) 3 (%) 11 (%) 12 (%) 2 (%)
a
b
c
d
e
f
g
h
i
CH3
70
88
34
10
26
16
14
99
71
80
69
95
—
84
79
99
95
—
89
99
82
—
7a
47
52
82
—
C2H5
C3H7
C4H9
C5H11
C8H17
C10H21
Bn
80
62
72
99
92
80
67
98
42
72
36
63
MOM
a The poor yield is due to tedious chromatographic separation.
lengths from C2 to C5 (entries 6–8), whereas longer alkyl chains
again resulted in increased HTP values as compared to C5
derivative 3e (entries 8–10). This observation is in good
agreement with results by Tsukamoto, who studied chiral
4-alkyl-40-alkyloxyazobenzenes systematically and found
a
decrease of the HTP in the series methoxy—hexyloxy and a
slight increase for longer side chains.[100] Other authors reported
even–odd effects and an overall increase of the HTP values with
increasing chain lengths.[101,102] While the effect of the chain
lengths on the HTP values were much more pronounced in
solutions of 5CB 13 with 3, a completely different picture
emerged for solutions of hexayne 14 with 3. Overall, HTP values
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Copyright ß 2009 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2009, 22 484–494

CHIRAL TETRAPHENYLETHENES AS NOVEL DOPANTS
shaped dopant to a flat rod-shaped host seems to be more
efficient as compared to a propeller-shaped host. One might
expect that the difference in the twist elastic constants are the
reason for the different behaviour of hosts 5CB 13 and hexayne
14 with regard to the same dopant 3. However, as shown by
Glushchenko[106] and Kru¨erke,[107] the twist elastic constants of
13 and 14 are in the same range. Further works to understand
this disc to rod versus disc-to-disc interaction is currently in
progress.
Table 2. HTPs of chiral tetraphenylethenes 1–3 in nematic
host 13 or discotic host 14a
Entry Host Dopant HTP, mmꢀ1 MHTP, mmꢀ1 molꢀ1 kg
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
13
13
13
13
13
13
13
13
13
13
14
14
14
14
14
1a
1b
2d
2g
2i
3b
3c
3e
3f
3g
3b
3c
3e
3f
5.7
10.4
16.5
12.6
16.5
12.8
11.3
8.0
17.3
28.7
2.1
2.2
2.3
5.4
10.0
14.1
15.0
14.1
10.2
9.6
Acknowledgements
Generous financial support by the Deutsche Forschungsge-
meinschaft, the Fonds der Chemischen Industrie, the Ministerium
fu¨r Wissenschaft, Forschung und Kunst des Landes Baden-
Wu¨rttemberg and the Bundesministerium fu¨r Bildung und For-
schung is gratefully acknowledged.
7.7
19.6
35.8
1.7
1.9
2.2
2.9
2.5
3.3
3.1
3g
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*
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CONCLUSIONS
The HTP of novel chiral tetraphenylethenes with citronellyl ethers
(1a, b), with lactate-derived ethers (2d, g, i) and the
corresponding esters (3b, c, e–g) in solution with achiral hosts
5CB 13 and hexayne 14 was studied. In solutions of citronellyl
ethers 1 in nematic host 13 the side chain had a considerable
effect on the HTP value. HTPs of lactate-derived ethers 2 in 5CB 13
were larger than those for 1 in 13, but changed only slightly with
the substituent in contrast to solutions of lactate-derived esters 3
in 13, where a strong substituent effect was observed. In contrast,
HTP values of 3 in discotic host 14 were one order of magnitude
smaller than those in host 13 and did not show any pronounced
substituent effect. Thus, the chirality transfer from a propeller-
¨
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Copyright ß 2009 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/poc

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