Novel chiral, sulfur-containing heteroarotinoids with liquid crystal properties

Article abstract of DOI:10.1080/10426500307852

Synthetic methods were developed to prepare ethyl (E)-4-[2-(3,4-dihydro-2-n-octyl-1-oxy-2H-1-benzothio-pyran-6-yl)-1- propenyl]-benzoate (1) and ethyl ( E)-4-[2-(3,4-dihydro-2-n-octyl-2H-1-benzothiopyran-6-yl)-1-propenyl]benzoate (10). These are the first examples of heteroarotinoids which possess properties of liquid crystals. The properties were evaluated using differential scanning calorimetry and by use of polarizing micrography. Both displayed textures which are typical of a smectic or cholesteric phase.

Full text of DOI:10.1080/10426500307852

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Phosphorus, Sulfur, and Silicon and the Related
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Novel Chiral, Sulfur-Containing Heteroarotinoids with
Liquid Crystal Properties
G. Mahika Weerasekare a , K. Darrell Berlin a , Haribabu Sunkara a & Warren T. Ford a
a Oklahoma State University, Stillwater, Oklahoma, USA
Published online: 27 Oct 2010.
To cite this article: G. Mahika Weerasekare , K. Darrell Berlin , Haribabu Sunkara & Warren T. Ford (2003): Novel Chiral,
Sulfur-Containing Heteroarotinoids with Liquid Crystal Properties, Phosphorus, Sulfur, and Silicon and the Related Elements,
178:5, 993-1006
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Phosphorus, Sulfur and Silicon, 2003, Vol. 178:993–1006
C
Copyright 2003 Taylor & Francis
1042-6507/03 $12.00 + .00
DOI: 10.1080/10426500390208839
NOVEL CHIRAL, SULFUR-CONTAINING
HETEROAROTINOIDS WITH LIQUID
CRYSTAL PROPERTIES
G. Mahika Weerasekare, K. Darrell Berlin, Haribabu Sunkara,
and Warren T. Ford
Oklahoma State University, Stillwater, Oklahoma, USA
(Received August 29, 2002; accepted October 15, 2002)
Synthetic methods were developed to prepare ethyl (E)-4-[2-(3,
4-dihydro-2-n-octyl-1-oxy-2H-1-benzothio-pyran-6-yl)-1-propenyl]-
benzoate (1) and ethyl ( E)-4-[2-(3,4-dihydro-2-n-octyl-2H-1-
benzothiopyran-6-yl)-1-propenyl]benzoate (10). These are the first
examples of heteroarotinoids which possess properties of liquid
crystals. The properties were evaluated using differential scanning
calorimetry and by use of polarizing micrography. Both displayed
textures which are typical of a smectic or cholesteric phase.
Keywords: Chiral liquid crystals; DSC data; ethyl (E)-4-[2-(3,4-
dihydro-2-n-octyl-1-oxy-2H-1-benzothiopyran-6-yl)-1-propenyl]benzo-
ate; ethyl (E)-4-[2-(3,4-dihydro-2-n-octyl-2H-1-benzothiopyran-6-yl)-
1-propenyl]benzoate; NMR data
In working to develop a methodology to obtain heteroarotinoids for
chemotherapeutic applications,1 it occurred to us that properly de-
signed members of this heterocyclic family might well exhibit liquid
crystal (LC) properties. Calimitic liquid crystalline compounds have a
rigid core and flexible ends that enable the molecules to order in one
or two dimensions at temperatures above the freezing point. The het-
eroarotinoids have rigid stilbene units in the center and can be substi-
tuted with flexible ends. Moreover, chiral units can be incorporated into
heteroarotinoid structures. Some of the most useful applications of liq-
uid crystals, such as cholesteric thermochromic devices, fast-switching
Grateful acknowledgment is given to the College of Arts and Sciences for support of
salary (KDB). Thanks are given for a Johnson Fellowship (GMW) for summer support.
Address correspondence to K. D. Berlin, Department of Chemistry, Oklahoma State
University, Stillwater, OK 74078 USA. E-mail: kdberlin@bmb-fs1.biochem.okstate.edu
993

994
G. M. Weerasekare et al.
ferroelectric light valves, and active matrix ferroelectric LC displays,
are due to chirality.2 The synthesis of ferroelectric liquid crystals (FLCs)
has been of interest since the discovery of bistable, fast-switching, elec-
trooptic light valves.2 Lengths of terminal chains are important param-
eters in LC formation.3 The net polarization of a molecule is markedly
affected by the strength of the lateral dipoles associated with an op-
tically active center.3,4 Many FLCs contain a chiral center at the ter-
minus of a molecule, but this is somewhat undesirable since at such
a position the chiral center is free to rotate independent of the highly
polarizable central core with the delocalized electrons. Thus, the con-
tribution of the core to the dipole associated with the chiral center is
reduced. Restriction of rotation of the chiral center with respect to the
rest of the compound could increase the strength of the spontaneous
polarization.2
RESULTS AND DISCUSSION
We have constructed a sulfur-containing heteroarotinoid systems 1
and have investigated its LC properties using differential scanning
calorimetry (DSC) and optical microscopy with polarized light, the lat-
ter being utilized to characterize mesophases.3 Sulfoxide 1, as well
as the precursor sulfide, exhibited the focal conic structure typical
of a smetic or cholesteric meso-phase. The synthesis of 1 is outlined
(Scheme 1), being initiated from 2. A modified Sharpless oxidation of
the sulfur atom in 2 led to 3 (82%) as a light yellow oil. Alkylation of the
ring holding the sulfoxide group, via deprotonation of the alpha position
with LDA, proved difficult but led to the new sulfoxide 4 (40%). Deoxy-
genation of the sulfur atom proceeded smoothly with NaI in TFAA to
give 5 (95%) as an oil. Acetylation of the aryl ring with acetic anhydride
in CS2:H3CNO2 produced ketone 6 in high yield (quantitative, after
chromatography). Reduction of the carbonyl group in 6 with LiAlH4 as
a suspension in dry ether gave alcohol 7 as an oil which was used at
once to prepare the phosphonium salt 8 (quantitative) as illustrated.

Heteroarotinoids with Liquid Crystal Properties
995
SCHEME 1
Potassium carbonate in the presence of 18-C-6 generated the cor-
responding anion from 8 which was then treated with ethyl 4-
formylbenzoate (9) in H2CCl2 to yield 10 (79%). Oxidation of 10 with a
modified Sharpless approach gave chiral sulfoxide 1 in moderate yield
after repeated recrystallization.
The absolute configurations at S-1 and C-2 have not been determined
since all attempts have proven futile to obtain adequate crystals of 1 (or
of 10) for an x-ray diffraction study. The stereochemistry of 1 depends
on the formation of the -sulfinyl carbanion from 10 via kinetic acidity
or thermodynamic acidity.5 Using THF and 20 C suggests that the
former parameter can be neglected.5 The alpha carbanion should have
sufficient time to form the most stable configuration prior to reaction
with the electrophile.5,6 In view of the large size of the complex in the
modified Sharpless oxidation, attack from the least hindered side is ex-
pected to occur.7 The argument is supported by the increased ee% in
the -alkylation of sulfoxides as the alkyl group enlarged.8 Although
1
the H NMR signal for H-8 was used with Eu(dpm)3 to estimate the
cis:trans ratio of isomers in 4,9 the complex nature of the 1H NMR sig-
nals for 1 prevented such an analysis, particularly in the region of aryl
protons. However, the narrow melting range of 1 (and of the precursor

996
G. M. Weerasekare et al.
TABLE I Phase Transition Temperatures and Enthalpies (cal/g) for 1 and
10 From DSC
Transition Temperatures and Transition Enthalpies for 1
Heating:
Cooling:
333.7 (0.05) → 346.5 (1.09) → 374.9 (0.84) → 384.5 (2.02) → 390.3 (0.13)
366 ( 3.34) → 337 ( 0.34) → 328 ( 0.72)
Transition Temperatures and Transition Enthalpies for 10
Heating:
Cooling:
338.8 (0.22) → 356.7 (10.83)
341.5 ( 0.54)
10) implies the presence of only one compound which we tentatively
label as the trans isomer, as illustrated, or its enantiomeric form.
LC phase transitions were observed for 1 by a polarizing microscopy
and by DSC (Table I). Slightly different heating curves (Figure 1) were
noted for the first and second heating of 1. In contrast, the cooling curves
essentially remained unchanged. No mesophase was detected during
the first heating of 1, but the phase observed on cooling of 1 (Figure 1)
did exhibit a focal conic or spherulitic texture of a mesophase or crystal
(Figure 2).10 This is not unusual. The small ( 0.5 cal/g) exotherm at
341.5 K on cooling and the large (10.8 cal/g) exotherm on heating of 1
suggest that the transition on cooling to 341.5 K forms a metastable
phase which undergoes a transition to a more stable LC or crystalline
phase while at <310 K between cooling and heating experiments. Since
FIGURE 1 DSC thermogram of 1 after cycling.

Heteroarotinoids with Liquid Crystal Properties
997
FIGURE 2 Polarizing micrograph of 1 at 339 K, cooled from the isotropic liquid
at 2 C/min.
crystalline 1 contains some nonstoichiometric amount of water, the loss
of such may account for part of the transition.
A similar examination of 10 (Table I), the precursor of 1, revealed
fewer phase transitions (Figure 3). Although the first and second

998
G. M. Weerasekare et al.
FIGURE 3 DSC thermogram of 10 after cycling.
heating curves varied slightly, the cooling curves for 10 were essentially
identical (Figure 3). Under a polarizing microscope, 10, upon cooling, ex-
hibited a focal conic texture (Figure 4), typical of a smectic or cholesteric
phase.11,12
In summary, we have obtained two heteroarotinoids with LC proper-
ties. The field is virtually unexplored, but the work herein may provide
a background for future development.
EXPERIMENTAL
General Methods
All reactions were performed under N2 with magnetic stirring unless
otherwise specified. IR spectra were recorded on a Perkin-Elmer 681
spectrophotometer as films or from KBr pellets. NMR spectral data
were obtained on solutions (DCCl3) using a Varian XL-300 spectrom-
1
eter with H and 13C data being taken at 299.99 MHz and 75.4 MHz,
1
respectively, and on a Varian XL-400 NMR BB spectrometer with H
and 13C data being taken at 399.99 MHz and 100.5 MHz respectively.
References were to TMS in values or ppm respectively. Mass spec-
tral data were recorded on a VG analytical instrument, model ZAB-
2SE. Melting points were determined on a Fischer-Johns melting point

Heteroarotinoids with Liquid Crystal Properties
999
FIGURE 4 Polarizing micrograph of 10 at 337 K, cooled from the isotropic
liquid at 2 C/min.
apparatus and a Thomas-Hoover melting point apparatus and were un-
corrected. Optical rotations were measured on a Perkin-Elmer 241 po-
larimeter. A standard check was made with a glucose solution which had
= 2.582 [l = 10 dm, c = 4.92 g/100 mL, H2O] and [ ] = +52.5 [lit.13

1000
G. M. Weerasekare et al.
[ ] = +52.5 ]. Differential Scanning Calorimetry (DSC) measurements
were performed with a Perkin-Elmer DSC-2 instrument equipped with
a TADs 3600 data station. The phase transitions and mesomorphic tex-
tures were observed with a Nikon OPTIPHOT-POL microscope with
crossed polarizer and equipped with a Instec hot stage (Boulder, CO). RT
= room temperature. Reagent grade solvents were used without further
purification. Chromatography was performed using the Chromatotron
(Harrison Research, model 7924) with silica gel (pF 254 containing gyp-
sum, EM Science) plates (2 mm and 4 mm thick). All elemental analyses
were performed by Galbraith Laboratories, Knoxville, TN 37921.
Ethyl ( E)-4-[2-(3,4-Dihydro-2-n-octyl-1-oxy-2H-1-
benzothiopyran-6-yl)-1-propenyl]benzoate (1)
Water (41 L) was introduced in a single portion to a stirred mixture
of Ti(O-i-Pr)4 (3.7 mL, 2.2 mmol) and (+)-diethyl L-tartrate (0.46 g,
4.5 mmol) in H2CCl2 (50 mL) (N2). The mixture was stirred to a ho-
mogeneous solution. To this was added sulfide 10 (1.02 g, 2.2 mmol)
(dropwise-addition funnel). To the cooled ( 20 C, dry ice-CCl4) mix-
ture was introduced dropwise a solution of TBHP (0.19 g, 2.2 mmol) in
H2CCl2 (0.7 mL). Stirring was continued at 20 C (4 h), and 4 mL of wa-
ter was then added dropwise (10 min). Stirring was continued at 20 C
(1 h) and then at RT (1 h). A white gel was filtered off (filter aid used), and
the filtrate was dried (Na2SO4) and evaporated to give sulfoxide 1 (light
yellow solid). Recrystallized (ethanol) product was a white 1 (0.2 g, 30%);
m.p. 122–124 C. 1H NMR (DCCl3, 300 MHz) 0.9 [t, 3JHCCH = 7.3 Hz,
3 H, (CH2)7CH3], 1.15 1.1–2.0 [m, 18 H, (CH2)7CH3, OCH2CH3 and
H(3)], 2.2–2.3 [s, 3 H, H(10)], 2.4–2.6 [m, 1 H, H(3)], 2.7–3.2, [m, 3 H,
H(2) and H(4)], 4.3 [q, 3JHCCH = 7.4 Hz, 2 H, H(19)], 6.8 [s, 1 H, H(11)],
7.25–8.05 [m, 7 H, Ar-H]. 13C NMR (DCCl3, 75 MHz) ppm aliphatic-
C: 16.85, 17.11, 20.33, 25.40, 28.57, 28.65, 29.36, 30.50, 31.95, 32.05,
32.17, 34.57, 62.19, 63.75; ArC and vinylic C: 127.12, 128.12, 129.59,
131.61, 131.75, 1131.79, 132.30, 139.30, 140.32, 140.71, 144.83, 150.27;
168.80 [C(18)]. [ ] = +29.9 (acetone). Anal. Calcd for C29H38O3S: C,
74.64; H, 8.21; S, 6.86. Anal. Calcd for C29H38O3S.0.5 H2O: C; 73.22; H,
8.24. Found: C, 73.09; H, 8.14.
3,4-Dihydro-2H-1-benzothiopyran (2)
In a standard setup chemicals were added in the following order of
thiochroman-4-one14 (3.0 g, 18 mmol), toluene (75 ml), water (120 mL),
conc HCl (60 mL), and the Clemmenson-Martin15 amalgam (50 g, pre-
pared by shaking for 5 min a mixture of mossy Zn [50 g, 765 g atom],
mercuric chloride [5 g, 18 mmol], conc HCl [2.5 mL], and water [75 mL.])
The heterogeneous mixture was boiled and stirred for 72 h, adding

Heteroarotinoids with Liquid Crystal Properties
1001
20-mL portions of conc HCl at intervals of about 6 h to maintain a total
volume of 500 mL. The mixture was allowed to cool to RT (1 h) and
was filtered. The aqueous layer was extracted (toluene, 2
50 mL).
Combined organic layers were separated and washed with saturated
NaHCO3 (2 50 mL), water (2 50 mL), and saturated NaCl (50 mL).
Then the solution was dried (MgSO4). Evaporation of the solvent gave
2 as a yellow oil (2.7 g, 98%) which was used directly to prepare sul-
foxide 3. IR (neat) 3020 (Ar-H), 2940 (alkyl-H) cm 1; 1H NMR (DCCl3,
3
3
400 MHz) 2.1 [quintet, JHCCH = 6.1 Hz, 2 H, H(3)], 2.8 [t, JHCCH
=
3
6.2 Hz, 2 H, H(4)], 3.0 [t, JHCCH = 6.0 Hz, 2 H, H(2)], 7.05–7.2 [m,
4 H, ArH]; 13C NMR (DCCl3, 100 MHz) ppm 22.75 [C(3)], 27.46 [C(4)],
29.56 [C(2)]; ArC: 123.79, 126.28, 126.45, 129.87, 132.77, 133.73. Only
two properties have been reported for 2:9 b.p. 81.5–82.5 C/1.2 mm; 1H
NMR (DCCl3) 1.90, 2.92, and 6.90.
3,4-Dihydro-2H-1-benzothiopyran-1-oxide (3)
A solution of Ti(O-i-Pr)4 (43 mL, 40.6 g, 143 mmol) and (+)-diethyl
L-tartrate (49 mL, 58.9 g, 286 mmol) was dissolved in H2CCl2 (250 mL).
Water (2.6 mL) was introduced, and the resulting mixture was stirred
(20 min) to a homogeneous solution. To this solution was added in a
single portion sulfide 2 (21.45 g, 143 mmol). The mixture was cooled
to 20 C (dry ice, CCl4), and a 3.1 M solution of TBHP (180 mmol)
in H2CCl2 (51 mL) was introduced dropwise (5 min). Stirring was con-
tinued for 4 h at 20 C, and 25 mL of water was then added dropwise
(10 min). Stirring was continued at 20 C for another hour and then for
1 h at RT. A white gel formed and was filtered off (filter aid used), and
the filtrate was dried (Na2SO4) and evaporated. The resulting mixture
was separated on silica gel (ethyl acetate:hexane, 85:15, 100% MeOH).
The fraction from methanol was evaporated to yield thiochroman-S-
oxide 3 (19 g, 82%) as a yellow oil. 1H NMR (DCCl3, 300 MHz) 2.0–2.2
[m, 1 H, H(3)], 2.4–2.7 [m, 1 H, H(3)], 2.8–3.3 [m, 4 H, H(2) and H(4)],
7.2–7.9 [m, 4 H, ArH]; 13C NMR (DCCl3, 75 MHz) ppm 14.12 [C(3)],
28.43 [C(4)], 46.37 [C(2)]; ArC: 127.42, 130.51, 130.81, 131.65, 136.01,
138.04. The optical rotation of 3 was taken in cells (l cm 10 cm) on
a Perkin-Elmer 241 polarimeter. At 26 C [ ]D
=
114.15 (acetone).
Our procedure was much easier to employ than that reported.9 The
only recorded properties9 of 3 are: b.p. 117–120 C/0.04 mm, H NMR
1
1.09–3.50 and 7.20–7.90 as well as a specific rotation [ ]D
=
21.8
(acetone) at 25 C.16
3,4-Dihydro-2-n-octyl-2H-1-benzothiopyran-1-oxide (4)
To a cooled ( 78 C, dry ice-acetone) solution of diisopropylamine
(4.8 mL, 34 mmol) in THF (50 mL) was added dropwise n-butyllithium

1002
G. M. Weerasekare et al.
(22 mL, 1.6 M in hexanes) over a period of 1 h. The resulting solu-
tion was stirred at RT for 1 h. After the solution was again cooled
to 78 C, sulfoxide 3 (5.72 g, 30 mmol) in THF (50 mL) was added
(15 min). The solution was then allowed to warm to 30 C (1 h) and
again cooled to 78 C. Then n-octyl bromide (5.4 mL, 34 mmol) was
added via syringe in a single portion. Stirring was continued for an-
other 12 h after which time 5% hydrochloric acid (50 mL) was added,
and the solution was extracted with HCCl3 (3
50 mL). Combined
extracts were washed with water (1 50 mL), NaHCO3 (2 50 mL),
water (50 mL), and brine (50 mL). When dried (Na2SO4), the solution
was concentrated to give a brown oil which was separated on a silica
gel column (hexane:HCCl3:ethyl acetate = 4:1:1). The second fraction
gave the alkylated product 3 (R = n-octyl, 3.2 g, 40%) as a light yel-
1
3
low oil. H NMR (DCCl3, 300 MHz) 0.9 [t, JHCCH = 0.7 Hz, 3 H,
CH3], 1.2–1.4 [bs, 12 H, (CH2)6CH3], 1.4–1.7 [m, 2 H, CH2(CH2)6], 1.85
[m, 1 H, H(3)], 2.45 [m, 1 H, H(3)], 2.8–3.1 [m, 3 H, H(2) and H(4)],
7.1–7.8 [m, 4 H, ArH]; 13C NMR (DCCl3, 75 MHz) ppm 14.06 [C(3)];
aliphatic-C: 20.75, 22.54, 26.32, 26.53, 28.31, 29.08, 29.25, 29.40, 31.71;
57.99 [C(2)]; ArC: 127.2, 129.18, 129.46, 130.67, 135.47, 140.0. The only
recorded9 property of 3 is: 1H NMR (DCCl3) 0.88, 1.1–3.10, and 7.24–
8.10.
3,4-Dihydro-2-n-octyl-2H-1-benzothiopyran (5)
To a stirred mixture of the sulfoxide 4 (1.7 g, 6 mmol) and NaI (2.2 g,
15 mmol) in acetone at 0 C (ice-water bath) was slowly added trifluo-
roacetic anhydride (2.5 ml, 18 mmol) in acetone. The reaction mixture
was stirred (1 h) at 0 C. Acetone was evaporated, water (50 mL) was
added, and the mixture was extracted with ether (3 25 mL). The ether
extracts were washed with water (50 mL), saturated Na2S2O3 (3 50
mL), water (50 mL) and saturated NaCl (50 mL). After drying (MgSO4),
the solvent was evaporated. The red oil obtained was passed through a
short silica gel column with hexane as eluent. Hexane was evaporated
to give sulfide 5 (1.5 g, 95%) as a light yellow oil which was used di-
rectly to make 6. 1H NMR (DCCl3, 300 MHz) 0.88 [t, 3JHCCH = 0.7 Hz,
3 H, CH3], 1.2–1.5 [bs, 12 H, (CH2)6CH3], 1.6–1.8 [m, 3 H, CH2(CH2)6
and H(3)], 2.2–2.3 [m, 1 H, H(3)], 2.75–2.9 [m, 2 H, H(4)], 3.25–3.57
[m, 1 H, H(2)], 6.9–7.1 [m, 4 H, ArH]; 13C NMR (DCCl3, 75 MHz)
ppm 13.67 [CH3]; aliphatic-C: 22.22, 22.37, 25.40, 26.70, 28.88, 29.13,
29.27, 31.43, 33.92, 37.21; ArC: 123.14, 123,31, 125.89, 125.92, 126.05,
1
129.44. Only the proton NMR spectrum has been recorded9 for 5: H
NMR (DCCl3) 1.03, 1.43, 1.8–2.62, 2.80–3.10, 3.15–3.57, and 6.97–
7.3.

Heteroarotinoids with Liquid Crystal Properties
1003
6-Acetyl-2-n-octylthiochroman (6)
Acetic anhydride (0.5 mL, 6 mmol) was added to a stirred suspen-
sion of AlCl3 (1.4 g, 9 mmol) in nitromethane [50 mL, 0 C (ice-water
bath]. To the above stirred mixture was added (5 min) a solution of 2-
octylthiochroman 5 (1.5 g, 6 mmol) in CS2:nitromethane (1:5, 25 mL).
The solution was stirred at 0 C for 1 h and then allowed to warm to RT
while stirring was continued for 48 h. The solution was then cooled to
0 C (ice-water bath) and finally quenched with water (50 mL, 15 min).
The aqueous layer was extracted with HCCl3 (4 50 mL). Combined
organic extracts were washed with saturated NaHCO3 (3 50 mL), wa-
ter (2 50 mL) and saturated NaCl (1 50 mL). After drying (Na2SO4),
the solution was evaporated to a red oil which was separated on a silica
gel column (hexane:ether = 20:80) to give ketone 6 (quantitative) as
an orange oil. IR (neat) 1680 (C O) cm 1; 1H NMR (DCCl3, 300 MHz)
3
0.9 [t, JHCCH = 0.7 Hz, 3 H, CH3], 1.35–1.45 [m 14 H, (CH2)7CH3],
2.0 [m, 1 H, H(3)], 2.3 [m, 1 H, H(3)], 2.7 [s, 3 H, CH3C(O)], 2.9–3.3
[m, 3 H, H(2) and H(4)], 7.2–7.7 [m, 3 H, ArH]; 13C NMR (DCCl3,
75 MHz) ppm 14.07 [CH3]; aliphatic-C: 22.62, 22.90, 25.11, 27.99, 29.37,
29.42, 29.51, 29.62, 31.82, 34.19, 37.67; ArC: 126.29, 126.34, 129.56,
132.67, 137.75, 139.89; 197.42 [C(O)]. The ketone 6 was used at once to
make 7.
2-n-Octylthiochroman-6-ethanol (7)
A solution of ketone 6 (1.5 g, 6 mmol) in dry ether (15 mL) was added
(10 min) to a stirred suspension of LiAlH4 (0.38 g, 9 mmol) in dry ether
(10 mL). This mixture was heated at reflux for 6 h. It was then cooled
to 0 C (ice-water bath), and ethyl acetate (25 mL) was slowly added
( 0.5 h) followed by 5% HCl (10 mL, 10 min). The mixture was stirred
for 5 min. The aqueous layer was extracted with ether (3
25 mL).
Combined organic layers were washed with saturated NaHCO3 (2 25
mL), water (25 mL), and saturated NaCl (25 mL). After drying (MgSO4),
the solvent was evaporated to give an orange oil which was separated
on a silica gel column (hexane:ether = 1:1) to give alcohol 7 (1.2 g, 80%)
as a yellow oil and which was used immediately to make 8. IR (neat)
3350 (O H) cm 1; 1H NMR (DCCl3, 300 MHz) 0.9 [t, 3JHCCH = 0.7 Hz,
3 H, CH3], 1.1–1.6 [m 17 H, (CH2)7CH3 and CH3C(OH)], 1.75–1.95 [m,
2 H, OH and H(3)], 2.0–2.2 [m, 1 H, H(3)], 2.8 [m, 2 H, H(4)], 3.1–
3.15 [m, 1 H, H(2)], 4.65–4.8 [m, 1 H, CH3CH(OH ], 6.9–7.1 [m, 3 H,
ArH]; 13C NMR (DCCl3, 75 MHz) ppm 14.07 [CH3]; aliphatic-C: 22.62,
22.70, 25.68, 25.70, 27.11, 29.27, 29.55, 29.64, 31.83, 34.34, 37.75; 70.05
[CH3C(OH)]; ArC: 123.540, 123.62, 126.50, 126.92, 126.98, 139.08,
141.01.

1004
G. M. Weerasekare et al.
1-[(2-n-Octylthiochroman-6-yl)ethyl]-
triphenylphosphonium Bromide (8)
A solution of alcohol 7 (4.4 g, 14 mmol) and triphenylphosphonium
hydrobromide (5.0 g, 14 mmol) in H2CCl2 (50 mL) was stirred at RT
(24 h). The solvent was then evaporated, and the oil obtained was trit-
urated (RT) with dry ether (50 mL) to obtain 8 as a white solid (9.0 g,
3
98%); m.p. 67–68 C. 1H NMR (DCCl3, 400 MHz) 0.9 [t, JHCCH
=
6.6 Hz, 3 H, CH3], 1.1–1.6 [m 14 H, (CH2)7CH3], 1.7–1.95 [m, 4 H,
CH3CH and H(3)], 2.0–2.2 [m, 1 H, H(3)], 2.5–2.7 [m, 1 H, H(4)], 2.8
[m, 1 H, H(4)], 3.0–3.1 [m, 1 H, H(2)], 6.55 [m, 1 H, CH3CH], 6.9–7.1
[m, 3 H, ArH], 7.3–7.7 [m, 15 H]; 13C NMR (DCCl3, 100 MHz) ppm
14.15 [CH3]; aliphatic-C: 16.89, 17.29, 22.68, 26.74, 26.95, 29.36, 29.44,
29.50, 29.74, 31.9, 34.12; 37.55 [CH3C(H)]; ArC: 117.42, 117.52, 118.24,
118.33, 126.88, 128.55, 128.67, 129.26, 129.36, 130.04, 130.08, 130.12,
130.16, 130.21, 130.24, 132.11, 132.21, 133.82, 133.97, 134.64, 134.67,
134.73, 134.76, 134.82. Salt 8 was used directly to prepare 10.
Ethyl 4-Formylbenzoate (9)
A solution of ethyl p-toluate (5.8 g, 35 mmol) in freshly distilled acetic
anhydride (50 mL) and glacial acetic acid (50 mL) was cooled to 0 C (ice-
salt water bath). To the stirred solution was added conc H2SO4 (2.5 mL).
To this solution was added (1 h) slowly CrO3(10.6 g, 100 mmol). Care
was taken to maintain the temperature below 5 C during the addition.
When the addition was complete, a dark green reaction mixture re-
mained which was stirred (2 h) at 0 C. Decomposition was effected by
slowly pouring the mixture onto crushed ice (250 g) and then adding
(very slowly) 250 mL of cold water. A green-colored solution formed,
and this was extracted with ether (4
50 mL). Combined ether ex-
tracts were washed with water (2 50 mL), 5% Na2CO3 (4 50 mL),
and brine (50 mL). When dried (Na2SO4), the solution was evaporated
to obtain the diacetate (4.7 g, 48%) as a yellow oil. To the diacetate was
added water (30 mL), 95% ethanol (30 mL), and conc H2SO4 (2 mL).
The resulting solution was boiled for 6 h. After allowing to cool to RT
(30 min), the solution was treated with water (20 mL), and the aqueous
phase was extracted with HCCl3 (3 50 mL). The combined extracts
were washed with water (1 50 mL), 10% NaHCO3 (2 50 mL), water
(1 50 mL), and saturated NaCl (50 mL). When dried (Na2SO4), the
solution was evaporated to give 9 (2.3 g, 44%) as a colorless oil which
appeared to be reactive and was thus used immediately in the Wit-
1
tig reaction. Properties of 9 are: IR (neat) 1740 (C O) cm 1; H NMR
(DCCl3, 100 MHz) 1.4 (t, J = 7.5 Hz, 3 H, CH3), 4.4 (q, J = 7.5 Hz, 2
H, CH2), 7.9–8.2 (m, 4 H, Ar-H), 10.1 (s, 1 H, CHO). 13C NMR (DCCl3,
75 MHz) ppm 14.15 [CH3], 61.48 [CH2]; ArC: 129.36, 130.02, 135.33,

Heteroarotinoids with Liquid Crystal Properties
1005
138.97, 166.91 [C(O)OEt], 191 .57 [C(O)H]. The b.p. (143 C/13 mm) of
9 has been reported.17
Ethyl (E)-4-[2-(3,4-Dihydro-2-n-octyl-2H-1-
benzothiopyran-6-yl)-1-propenyl]benzoate (10)
To a boiling mixture of phosphonium salt 8 (2.0 g, 3 mmol), K2CO3
(0.4 g, 3 mmol) and 18-C-6 (30 mg), in H2CCl2 (15 mL) was added ethyl
4-formylbenzoate (9, 0.5 g, 3 mmol) in H2CCl2 (10 mL) in a single por-
tion. The mixture was boiled for 12 h and was then concentrated to
yield an orange oil which was treated with hexane (150 mL). A suspen-
sion formed and was filtered. The filtrate was washed with saturated
NaCl (50 mL), dried (Na2SO4), and concentrated to give a yellow oil
which was separated on a silica gel column (hexane:ethylacetate = 1:1)
to give the sulfide 10 (1.1 g, 79%) as a white solid; m.p. 72–73 C. IR
1
1
(neat) 1750 cm (C O); H NMR (DCCl3, 400 MHz) 0.95 [t, J = 7.5
Hz, 3 H, (CH2)7CH3], 1.1–1.7 [m, 17 H, (CH2)7CH3 and OCH2CH3],
2.8–2.95 [m, 1 H, H(3)], 2.15–2.3 [m, 4 H, H(3) and H(10)], 2.8–2.9 [m,
2 H, H(4)], 3.1–3.2 [m, 1 H, H(2)], 4.3 [q, J = 7.5 Hz, 2 H, OCH2CH3],
6.8 [s, 1 H, H(11)], 7.0–8.1 [m, 7 H, ArH]; 13C NMR (DCCl3, 100 MHz)
ppm 14.05 [(CH2)3CH3]; aliphatic-C: 14.31, 17.46, 22.61, 25.55, 27.08,
29.26, 29.54, 29.63, 31.87, 36.83, 37.83, 42.31; 60.79 [C(19)]; ArC and
vinylic C: 124.03, 125.63, 126.34, 127.39, 128.93, 129.36, 132.08, 148.01,
149.10, 149.32, 143.8; 168.82 [C(18)]. Mass spectral (EI) data: Calcd
for C29H38O2S m/z (M+.): 450.2593; Found: 450.2595. Anal. Calcd for
C29H38O2S: C, 77.29; H, 8.51; Found: C, 77.61; H, 8.31.
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