Alkyl substituted [2.2]paracyclophane-1,9-dienes

Article abstract of DOI:10.1039/c6ob00885b

[2.2]Paracyclophane-1,9-dienes substituted with n-octyl chains have been synthesised from the corresponding dithia[3.3]paracyclophanes using a benzyne induced Stevens rearrangement. The use of 2-(trimethylsilyl)phenyl trifluoromethanesulfonate and tetra-n-butylammonium fluoride as the in situ benzyne source gave significantly improved yields over traditional sources of benzyne and enabled the preparation of n-octyl substituted [2.2]paracyclophane-1,9-dienes on a multi-gram scale.

Full text of DOI:10.1039/c6ob00885b

Organic &
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PAPER
Alkyl substituted [2.2]paracyclophane-1,9-dienes†
Benjamin J. Lidster, Dharam R. Kumar, Andrew M. Spring,‡ Chin-Yang Yu,§
Madeleine Helliwell, James Raftery and Michael L. Turner*
Cite this: Org. Biomol. Chem., 2016,
14, 6079
[2.2]Paracyclophane-1,9-dienes substituted with n-octyl chains have been synthesised from the corres-
ponding dithia[3.3]paracyclophanes using a benzyne induced Stevens rearrangement. The use of 2-(tri-
methylsilyl)phenyl trifluoromethanesulfonate and tetra-n-butylammonium fluoride as the in situ benzyne
source gave significantly improved yields over traditional sources of benzyne and enabled the preparation
of n-octyl substituted [2.2]paracyclophane-1,9-dienes on a multi-gram scale.
Received 25th April 2016,
Accepted 23rd May 2016
DOI: 10.1039/c6ob00885b
www.rsc.org/obc
mers over that of the parent unsubstituted PPV.23 By contrast
alkyl substituted PPVs show minimal change in the energy of
Introduction
[2.2]Paracyclophanes have received considerable attention due the band gap, in comparison to the parent PPV, whilst provid-
to their confined molecular motions and the close proximity ing the required solubility.24
of the two stacked phenylene groups.1–3 This restricted geo-
The introduction of alkyl groups on the phenylene groups
metry gives rise to unique electronic and optical properties, of 1 has not been reported. It is of interest as PPVs prepared by
characteristic NMR spectra and applications in asymmetric the ROMP of [2.2]paracyclophane-1,9-dienes show greater
catalysis for planar chiral derivatives.4–10 Linking of the pheny- control of the polymer structure, molecular weight and enable
lene groups by two cis-vinylene bonds in [2.2]paracyclophane- the preparation of block copolymers.14
1,9-diene (1) results in extensive steric repulsion, with an intra-
Synthetic routes towards [2.2]paracyclophane-1,9-dienes are
molecular distance of just 2.85 Å between the phenylene group extremely limited (Scheme 1).25–28 Boekelheide et al. reported
bridge head carbons.11 The high ring strain of this class of a route from dithia[3.3]paracyclophane (2) that uses a benzyne
molecules, calculated to be 176 kJ mol−1 for cyclophanediene induced Stevens rearrangement (BSR) to contract the dithia-
1, makes them interesting monomers in polymer science.2,12,13 cyclophane ring (3), followed by oxidation of the phenyl sulfides
Specifically, alkoxy-substituted [2.2]paracyclophane-1,9-dienes (4) and a thermal syn-elimination to obtain 1.25 Recently Pasini
have been used in ruthenium carbene initiated ring et al. described a synthesis of 1 from 2 that involved a Pum-
opening metathesis polymerisation (ROMP), forming soluble merer rearrangement to give 5, followed by ring contraction
poly(phenylenevinylene)s (PPVs).14–18 These conjugated poly- through photochemical sulfur extrusion to give 6 and a final
mers have been extensively studied for application in elec- thermal elimination of the acetate groups to produce 1.26 The
tronic and optoelectronic devices, and recently in fluorescence BSR route generally gives low yields of the desired paracyclo-
imaging.19–22 Traditionally alkoxy groups have been appended phanedienes, whereas the Pummerer rearrangement gives
to the polymer backbone to improve solubility, however, this improved yields but has been demonstrated only for synthesis of
results in a significant red-shift of the emission of these poly- the parent [2.2]paracyclophane-1,9-diene and not for the substi-
tuted derivatives that are required to form soluble PPVs. The
route of Boekelheide et al. utilises the diazotization of anthranilic
acid with isoamyl nitrite as the in situ source of benzyne. A more
Organic Materials Innovation Centre, School of Chemistry, The University of
convenient source of benzyne has been reported through the
reaction of 2-(trimethylsilyl)phenyl trifluoromethanesulfonate (7)
with tetra-n-butylammonium fluoride (TBAF).29,30 This system
offers a wider substrate scope, less toxic reagents, milder reaction
conditions and much greater yields.31,32
In our previous reports on the synthesis of tetraoctyloxy-
substituted [2.2]paracyclophane-1,9-dienes we have used the
method of Boekelheide et al., however, only low yields (<31%)
were obtained.33 Herein we report an improved process to
prepare substituted [2.2]paracyclophane-1,9-dienes using 7 and
TBAF·3H2O as the benzyne source and the use of this process to
Manchester, Oxford Road, Manchester, M13 9PL, UK.
E-mail: Michael.Turner@Manchester.ac.uk; Fax: +44(0) 161-275-4273
†Electronic supplementary information (ESI) available: Synthesis of 1,4-benzene-
dimethanethiol, 1,4-dioctylbenzene, compound 7, 1H and 13C NMR spectra and
HPLC chromatogram of 20/21 and synthesis of 13 and 18 from isoamyl nitrite
and anthranilic acid. Metrical parameters for the structure of 20. CCDC
1473670. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c6ob00885b
‡Current address: Institute for Materials Chemistry and Engineering, Kyushu
University, 6-1 Kasuga-koen Kasuga, Fukuoka 816-8580, Japan.
§Current address: Department of Materials Science and Engineering, National
Taiwan University of Science and Technology, 43, Section 4, Keelung Road,
Taipei, 10607, Taiwan.
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Scheme 1 Synthetic routes to [2.2]paracyclophane-1,9-dienes.25,26
prepare [2.2]paracyclophane-1,9-dienes with alkyl side chains,
an important precursor to alkyl substituted PPVs by ROMP.
Results and discussion
Synthesis of 2-(trimethylsilyl)phenyl
trifluoromethanesulfonate
Benzyne precursor 7 offers major advantages over traditional
sources of benzyne, but it is exceptionally expensive. Conse-
quently, a method to prepare compound 7 on a large scale was
developed and this was adapted from a procedure reported by
Brimble et al.34 The procedure involved the protection of the
hydroxy group of 2-chlorophenol with TMSCl, followed by a
retro-Brook rearrangement in the presence of molten
sodium.35 Reaction of 2-(trimethylsilyl)phenol with trifluoro-
methanesulfonic anhydride gave compound 7 in a good yield
(overall 78%). The procedure could be scaled to provide multi-
gram quantities (experimental procedure in ESI†).
Scheme 2 Synthesis of dithia[3.3]paracyclophanes; 12, 16 and 17,
R = n-octyl.
Synthesis of 4,7-dioctyl-[2.2]paracyclophane-1,9-diene
The initial step in the synthesis of 4,7-dioctyl-[2.2]paracyclo-
phane-1,9-diene (15) and the two isomeric cyclophanedienes;
4,7,12,15-tetraoctyl-[2.2]paracyclophane-1,9-diene (20) and
5,8,12,15-tetraoctyl-[2.2]paracyclophane-1,9-diene (21) is the
synthesis of 1,4-bis(bromomethyl)-2,5-bis(octyl)benzene (9).
Preparation of compound 9 required the incorporation of two
bromomethyl groups on the 2,5-positions of dioctylbenzene (8)
and this was achieved by adapting the procedure of Tanaka
et al. (Scheme 2).36 Compound 8 was heated at reflux in acetic
acid with HBr and paraformaldehyde, over 5 days to give 9 in a
single step (see ESI†).
5,8-Dioctyl-2,11-dithia[3.3]paracyclophane (12) was pre-
pared by the intramolecular cyclisation between an equimolar
amount of 1,4-benzenedimethanethiol (11) and 9 (Scheme 2).
A toluene solution of the two coupling components was added
dropwise to a large volume of ethanol containing KOH. A slow
addition is required to prevent oligomerisation. After column
chromatography dithiacyclophane 12 was obtained as a colour-
less viscous oil in a yield of 43%.
The BSR of dithiacyclophane 12 was performed by the slow
addition of TBAF·3H2O to a THF solution of 7 and 12
(Scheme 3). Isolation of the mixture of phenyl sulfides (13) was Scheme 3 Synthesis of [2.2]paracyclophane-1,9-diene 15, R = n-octyl.
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achieved using simple filtration through silica to remove separation of 16 and 17 was not conducted due to this
biphenylene (by-product from the dimerisation of benzyne). expected isomerisation.33
Compound 13 was obtained as a highly viscous yellow oil in a
The mixture of dithiacyclophanes 16 and 17 was subjected
yield of 67%. The analogous reaction with isoamyl nitrite and to the BSR with compound 7 and TBAF·3H2O (Scheme 4). After
anthranilic acid in 1,2-dichloroethane gave 13 in a yield of column chromatography the mixture of phenyl sulfides (18)
only 25% (ESI).
was isolated as a viscous yellow oil in a yield of 83%. The ana-
Oxidation of the phenyl sulfides to the corresponding logous reaction with isoamyl nitrite and anthranilic acid in
phenyl sulfoxides (14) was performed using aqueous H2O2 in 1,2-dichloroethane gave 18 in a yield of only 32% (ESI). Oxi-
acetic acid and toluene at room temperature. Compound 14 dation of the phenyl sulfides of 18 to give 19 was performed
was isolated as a highly viscous oil in a yield of 96% after with aqueous H2O2 in toluene and acetic acid in an excellent
work-up, with no further purification performed. The thermal yield (95%). Heating compound 19 at reflux in a mixture of
syn-elimination of the phenyl sulfoxide groups of compound xylenes with Cs2CO3 resulted in the thermal syn-elimination of
14 to obtain the corresponding cis-vinylene bonds of 15 was the phenyl sulfoxide groups and the formation of cyclophane-
performed by refluxing in a mixture of xylenes in the presence dienes 20 and 21. Purification by column chromatography
of Cs2CO3. The addition of Cs2CO3 gave slightly improved gave cyclophanedienes 20 and 21 as a colourless oil in a
yields, presumably due to reaction of the acidic by-products of combined yield of 45%. Integration of the phenylene group
1
the elimination reaction. Purification by column chromato- hydrogens in the H NMR spectrum gave the ratio of 20 : 21 to
graphy gave cyclophanediene 15 as a clear oil in a yield of 57%.
17 : 83. Preparative separation of the two isomers was not poss-
ible through column chromatography, HPLC or recrystallisa-
tion (see ESI†). However, a single crystal of 20 was obtained for
X-ray crystallography through multiple fractional crystallisa-
tions from hexane, at −10 °C.
Synthesis of 4,7,12,15-tetraoctyl-[2.2]paracyclophane-1,9-diene
and 5,8,12,15-tetraoctyl-[2.2]paracyclophane-1,9-diene
The synthesis of tetraoctyl-substituted [2.2]paracyclophane-1,9-
dienes; 20 and 21 required the conversion of compound 9 to
dithiol compound 10, to introduce n-octyl groups on to both
phenylene groups. This was achieved by the reaction of 9 with
Characterisation of intermediates 12, 13, 14 and 4,7-dioctyl-
[2.2]paracyclophane-1,9-diene (15)
thiourea followed by hydrolysis of the intermediate isothio- Dithia[3.3]paracyclophanes
and
[2.2]paracyclophane-1,9-
uronium salt and acidification. Dithiacyclophanes 16 and 17 were dienes, where at least one phenylene group is substituted, are
prepared by the same procedure as described for dithiacyclo- planar chiral as a consequence of restricted rotation of the
phane 12 by the slow addition of a toluene solution containing phenylene group through the dithiacyclophane ring. Substi-
an equimolar amount of 9 and 10, to a large volume of ethanol tution with n-octyl chains causes both the methylene hydro-
containing KOH (Scheme 2). Purification by column chromato- gens of the alkyl chain and of the thioether bonds to become
1
graphy gave a mixture of dithiacyclophanes 16 and 17 as a col- diastereotopic. The H NMR spectrum of dithiacyclophane 12
ourless solid in a combined yield of 40%. Integration of the (Fig. 1a) showed two hydrogen environments for the unsubsti-
1
ArCH2S groups in the H NMR spectrum gave a ratio of 16 : 17 tuted phenylene group, which were observed as AA′XX′ spin
of 6 : 94. In relation to the synthesis of tetraoctyloxy-substi- systems at 6.96 and 6.86 ppm. The hydrogens of the substi-
tuted [2.2]paracyclophane-1,9-dienes, performing the BSR on a tuted phenylene group appear as a singlet at 6.64 ppm. Due to
single dithiacyclophane resulted in the formation of both the planar chirality of these molecules the methylene hydro-
cyclophanediene isomers, after the final syn-elimination, as a gens of the thioether bridges are diastereotopic and four doub-
consequence of isomerisation in this reaction.33 Consequently, lets are observed, between 3.83–3.62 ppm, for the 8 hydrogens.
Scheme 4 Synthesis of [2.2]paracyclophane-1,9-dienes 20 and 21, R = n-octyl.
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which corresponded to the SvO stretch. Over oxidation to the
sulfone did not occur to any significant degree, as minimal
absorbances are observed between 1160–1120 cm−1, that are
characteristic for this group.37 MS measurements showed
major molecular ions at 681 and 556 Da (m/z) which corres-
ponded to the expected species and the fragmentation species
by loss of a phenyl sulfoxide group, respectively.
The 1H NMR spectrum of cyclophanediene 15 (Fig. 1b)
showed two hydrogen environments for the cis-vinylenes at
7.08 and 7.04 ppm. The two hydrogen environments of the
unsubstituted phenylene group appear as two AA′XX′ spin
systems at 6.71 and 6.42 ppm, and the hydrogens of the substi-
tuted phenylene group appear as a upfield singlet at 6.11 ppm.
As with dithiacyclophane 12 the hydrogens of the methylene
group of the n-octyl chain bonded to the phenylene group are
diastereotopic and appear as two sets of doublet of triplets at
2.55 and 2.23 ppm. The loss of the sulfoxide group was con-
firmed by FT-IR spectroscopy with no intense absorbance at
1041 cm−1. Further, an absorbance at 690 cm−1 was associated
with the out-of-plane stretch of the C–H bond of the cis-vinyl-
ene bond. High resolution MS (HR-MS) observed the mole-
cular ion corresponding to 15 at 429.3510 Da (m/z) (calc.
429.3516).
Characterisation of intermediates 16, 17, 18, 19 and 4,7,12,15-
tetraoctyl-[2.2]paracyclophane-1,9-diene (20) and 5,8,12,15-
tetraoctyl-[2.2]paracyclophane-1,9-diene (21)
Fig. 1 1H NMR spectra (CDCl3) of (a) dithia[3.3]paracyclophane 12 and
(b) [2.2]paracyclophane-1,9-diene 15.
The tetra-octyl substituted dithiacyclophane 17 is planar chiral
as previously described for the dithiacyclophane 12. However,
as dithiacyclophane 16 exhibits a plane of symmetry it is not
A large difference in chemical shift is observed between the chiral. The 1H NMR spectrum (Fig. 2a) of mixture of dithia-
two diastereotopic methylene hydrogens bonded to the substi- cyclophanes 16 and 17 shows two singlets at 6.76 and 6.78 ppm,
tuted phenylene group. This is a consequence of the close respectively, which correspond to the four equivalent hydro-
proximity of one of these hydrogens to the n-octyl chain. The gens of the phenylene groups of each isomer. The hydrogens
methylene hydrogens adjacent to the unsubstituted phenylene of methylene groups of the thioether bond are diastereotopic
group have a similar chemical shift and appear close to the and two doublets are observed at 4.07 and 3.57 ppm for 16
equivalent hydrogens in the unsubsistutued dithiacyclophane and at 3.82 and 3.63 ppm for 17. The chemical shift difference
2.26 The hydrogens of the methylene group of the n-octyl chain between the two diastereotopic hydrogens of 16 is 0.50 ppm,
adjacent to the phenylene group are also diastereotopic and whereas, for 17 a difference of just 0.19 ppm is observed. The
appear as doublet of doublet of doublets at 2.71 and 2.44 ppm. multiplets between 2.82–2.69 and 2.48–2.35 ppm are assigned
The 1H NMR spectrum of compound 13 exhibited a to the hydrogens of the methylene groups of the n-octyl chains
complex range of signals and complete characterisation was adjacent to the phenylene group in both 16 and 17. As
not possible. This is a consequence of the BSR not being regio- expected the product of the BSR, compound 18, exhibits a
selective and migration of the phenyl sulfide groups occurring complex 1H NMR spectrum and as with 13 complete character-
to either carbon of the thioether bond. Consequently each of isation was not possible. MS confirmed the BSR with the mole-
these carbon centres becomes a stereogenic centre and a large cular ion of the expected product observed at 874 Da (m/z).
number of regio and stereoisomers are possible. The success Additional mass ions were observed that correspond to the
of the BSR was confirmed by mass spectrometry (MS) with the fragmentation species by the loss of a phenyl group and a
molecular ion observed at 650 Da (m/z) and through the frag- phenyl sulfide group.
mentation species by loss of a phenyl group and a phenyl
After oxidation characterisation of the phenyl-sulfoxide
sulfide group. Characterisation of phenyl-sulfoxide compound compound 19 by NMR spectroscopy again proved difficult,
1
14 by H NMR spectroscopy again proved difficult due to the however, a higher chemical shift of the phenyl sulfoxide
large number of possible stereoisomers, and this was further groups was observed, in comparison to the phenyl sulfide
complicated as each sulfoxide group is also a stereocentre. group of 18. Oxidation was confirmed by FT-IR spectroscopy
FT-IR spectroscopy confirmed the oxidation of the sulfide by the absorbance of the SvO stretch at 1044 cm−1. Over oxi-
group through an intense absorbance observed at 1041 cm−1
,
dation to the sulfone again was not detected. MS showed the
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Fig. 2 1H NMR spectra (CDCl3) of (a) dithia[3.3]paracyclophanes 16 and 17, and (b) [2.2]paracyclophane-1,9-dienes 20 and 21, R = n-octyl.
presence of the oxidised product at 906 Da (m/z) corresponding
to the expected molecular species and the fragmentation
species by loss of a phenyl sulfoxide group at 780 Da (m/z).
1
The H NMR spectrum of the mixture of cyclophanedienes
20 and 21 (Fig. 2b) showed the four hydrogens of the phenyl-
ene groups of each isomer to appear as singlets at 6.10 and
6.34 ppm, respectively. The four equivalent cis-vinylene hydro-
gens are observed as singlets at 7.07 ppm for 20 and at
6.92 ppm for 21. The hydrogens of the methylene group of the
octyl chain bonded to the phenylene group are diastereotopic
and are observed in cyclophanediene 20 as two doublets of tri-
plets at 2.59 and 2.31 ppm. In cyclophanediene 21 the equi-
Fig. 3 Solid-state structure of 20 as ORTEP plot. Hydrogen atoms are
omitted for clarity.
valent hydrogens appear as two doublet of triplets at 2.52 and
2.15 ppm. HR-MS of the mixture of isomers 20 and 21
observed the molecular ion at 652.5925 Da (m/z) (calc.
652.5942).
phenylene group bonded to the vinylene bond is shorter at
2.80 Å.
The highly strained nature of the molecule is shown by the
large distortion in the phenylene groups as the carbon atoms
bonded to the vinylene bond lie between 0.17 and 0.21 Å out
Solid-state structure of 4,7,12,15-tetraoctyl-[2.2]paracyclo-
phane-1,9-diene
The solid-state structure of cyclophanediene 20 was deter- of the plane of the ring. The vinylene bond length is 1.34 Å,
mined by X-ray crystallography (Fig. 3). The intramolecular dis- which is in agreement with that of a standard cis-vinylene
tance between the two carbon atoms of the phenylene groups bond 1.32 Å).38 In comparison to the unsubstituted cyclo-
bonded to the n-octyl group is 3.21 Å, whilst the equivalent dis- phanediene 1, no significant differences in the intramolecular
tance between the two unsubstituted carbons is 3.13 Å. distances of the phenylene groups are present and a compar-
The intramolecular distance between the two carbons of the able vinylene bond length of 1.33 Å is observed.11
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Acros and used as received. Deoxygenated solvents were pre-
pared either by purging with argon or nitrogen. Column
Conclusion
[2.2]Paracyclophane-1,9-dienes substituted with two and four chromatography was performed using silica gel (60 Å,
n-octyl chains have been prepared from the corresponding 230–400 mesh). Petroleum ether refers to the fraction obtained
dithia[3.3]paracyclophanes. The use of benzyne precursor 7 at 40–60 °C.
and TBAF·3H2O as the in situ source of benzyne in the BSR
Synthesis of 1,4-bis(bromomethyl)-2,5-bis(octyl)benzene (9).
gave significantly improved yields over the traditional source Compound 8 (53.0 g, 175 mmol) and paraformaldehyde
of anthranilic acid and isoamyl nitrite. A yield of 67% was (21.0 g, 701 mmol) were dissolved in 33 wt% HBr(acetic
acid)
obtained for 13 and 83% for 18, in comparison to 25 and 32% (123 mL) and heated under reflux for 5 days. The reaction was
from the traditional reaction. The tetraoctyl substituted [2.2] cooled to RT and the suspension poured onto ice. The precipi-
paracyclophane-1,9-dienes were isolated as a mixture of the tate was isolated by filtration and washed with water. The dark
structural isomers 20 and 21 in ratio of 17 : 83. A single crystal brown residue was dissolved in chloroform (500 mL) and the
of 20 was obtained by fractional crystallisation and the highly organic layer washed with 2 M NaHCO3(aq) (3 × 250 mL). The
strained nature of this molecule was shown from the solid organic layer was dried over MgSO4, filtered and the solvent
state structure by the large distortion of the bridging atoms of removed in vacuo to reveal a dark brown solid. The residue was
the phenylene group from the plane of the ring. The ability to recrystallised from ethanol to reveal colourless crystals (33.8 g,
prepare these alkyl substituted cyclophanedienes on a multi- 40%). 1H NMR, (CDCl3, 400 MHz): δ 7.14 (2H, s, ArH), 4.49
gram scale offers great potential in polymer science where they (4H, s, ArCH2Br), 2.66 (4H, t, J = 7.9 Hz, ArCH2CH2), 1.69–1.58
can be subjected to ROMP to obtain PPVs with semiconduct- (4H, m, ArCH2CH2), 1.46–1.22 (20H, m, CH2(CH2)5CH3), 0.89
ing and fluorescent properties.
(6H, t, J = 6.9 Hz, CH2CH3). 13C NMR, (CDCl3, 126 MHz): δ
139.68, 135.88, 131.75, 31.86, 31.76, 31.31, 30.83, 29.71, 29.44,
29.24, 22.58, 14.11. MS (EI, M+): calc. for [C24H40Br2]+: m/z 488,
found m/z 488.
Experimental
Synthesis of 1,4-bis(thiolatomethyl)-2,5-bis(octyl)benzene
(10). Compound 9 (33.0 g, 67.6 mmol) and thiourea (12.3 g,
162 mmol) were dissolved in deoxygenated THF (700 mL) and
heated under reflux for 5 hours. The suspension was cooled to
RT and the solvent removed in vacuo to reveal a white solid.
Deoxygenated water (700 mL) and KOH (11.37 g, 203 mmol)
were added and heated under reflux for 5 hours. The reaction
was cooled to RT, neutralised with 50% H2SO4(aq) (v/v) and
extracted with DCM (3 × 300 mL). The organic layers were com-
bined, dried over MgSO4, filtered and the solvent removed
in vacuo to reveal a yellow solid. The product was dissolved in
CHCl3 and precipitated into MeOH. The precipitate was iso-
lated by filtration, washed with MeOH and dried under
Methods
Nuclear magnetic resonance (NMR) spectra were obtained on
Bruker spectrometers operating at either 300, 400 or 500 MHz,
for 1H nuclei and 75, 101 or 126 MHz for 13C nuclei. Chemical
shifts are reported in ppm relative to the indicated residual
solvent (1H NMR spectroscopy: CDCl3: δ = 7.26 ppm and 13C
NMR spectroscopy: CDCl3: δ = 77.00 ppm). All coupling con-
stants (J values) are reported in hertz (Hz) and the following
abbreviations are used to indicate multiplicity: s = singlet, d =
doublet, t = triplet, dt = doublet of triplets, ddd = doublet of
doublet of doublets, q = quartet, AA′XX′ = AA′XX′ spin system,
and m = multiplet. HR-APCI mass spectra were obtained using
a Thermo Scientific Exactive plus EMR. APCI-MS analysis was
performed on Agilent technologies 6120 quadrupole LC/MS.
HR-EI-MS were recorded on a Thermo Finningham MAT95XP.
GC-MS (EI/CI) were performed on an Agilent 5975C Triple Axis
GC-MS. Fourier transform-infrared spectroscopy (FT-IR) was
conducted using a Nicolet iS5 (Thermo Scientific) with an iD5
attenuated total reflection accessory. The abbreviations: w =
weak, m = medium, s = strong and vs = very strong are used to
denote relative absorbance intensities. Elemental compo-
sitions of carbon, hydrogen and sulfur atoms were measured
using a Flash 2000 Organic Elemental Analyser (Thermo Scien-
tific). Slow additions were performed using a Watsons-Marlow
205S peristaltic pump.
1
vacuum to reveal a fine white powder (16.1 g, 60%). H NMR,
(CDCl3, 500 MHz): δ 7.05 (2H, s, ArH), 3.71 (4H, d, J = 7.1 Hz,
ArCH2SH), 2.62 (4H, t, J = 7.9 Hz, ArCH2CH2), 1.67 (2H, t, J =
7.1 Hz CH2SH), 1.65–1.56 (4H, m, ArCH2CH2), 1.45–1.22 (20H,
m, CH2(CH2)5CH3), 0.89 (6H, t, J = 7.0 Hz, CH2CH3). 13C NMR,
(CDCl3, 126 MHz): δ 138.29, 137.64, 130.31, 32.13, 31.88,
31.32, 29.81, 29.49, 29.28, 25.95, 22.67, 14.11. MS (APCI, M−):
calc. for [C24H42S2 − 1H]−: m/z 394, found m/z 394; calc. for
[C24H42S2 − 1SH]−: m/z 361, found; m/z 361.
Synthesis of 5,8-dioctyl-2,11-dithia[3.3]paracyclophane (12).
Compound 11 (8.72 g, 51.2 mmol) and compound 9 (25.0 g,
51.2 mmol) were dissolved in deoxygenated toluene (1000 mL).
This solution was added dropwise to KOH (8.62 g, 154 mmol)
in deoxygenated ethanol (2500 mL), over 72 hours at RT. After
a further 2 hours the solvent was removed in vacuo and the
Materials
All reactions were carried out under an argon or nitrogen residue dissolved in diethyl ether (500 mL). Water (500 mL)
atmosphere using standard Schlenk techniques. Anhydrous was added and the solution neutralised with 6 M HCl(aq). The
THF was freshly distilled over sodium/benzophenone. All organic layer was further washed with water (2 × 500 mL),
other anhydrous solvents and reagents were purchased from dried over MgSO4, filtered and the solvent removed in vacuo to
Apollo Scientific, Sigma-Aldrich, Fisher Scientific, Alfa Aesar or reveal an orange oil. The residue was purified by column
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chromatography (DCM : petroleum ether, 10 : 90 (v/v)) yielding reaction was cooled to RT, filtered and the solvent removed
a colourless oil (10.9 g, 43%). 1H NMR, (CDCl3, 500 MHz): δ in vacuo to reveal
dark brown oil. The residue was
a
6.96 (2H, AA′XX′, Japp = 7.9, 1.7 Hz, ArH), 6.86 (2H, AA′XX′, Japp purified by column chromatography (n-hexane) to reveal a
= 7.9, 1.7 Hz, ArH), 6.64 (2H, s, ArH), 3.92 (2H, d, J = 14.7 Hz, colourless viscous oil (3.37 g, 57%), which was stored at
ArCH2S), 3.83 (2H, d, J = 15.2 Hz, ArCH2S), 3.77 (2H, d, J = 15.2 −25 °C. 1H NMR, (CDCl3, 500 MHz): δ 7.08 (2H, d, J = 10.5 Hz,
Hz, ArCH2S), 3.62 (2H, d, J = 14.7 Hz, ArCH2S), 2.71 (2H, ddd, ArCHvCH), 7.04 (2H, d, J = 10.5 Hz, ArCHvCH), 6.71 (2H, AA′
J = 14.7, 8.8, 6.0 Hz, ArCH2CH2), 2.42 (2H, ddd, J = 14.7, 8.8, XX′, Japp = 8.0, 1.5 Hz, ArH), 6.42 (2H, AA′XX′, Japp = 8.0, 1.5 Hz,
6.0 Hz, ArCH2CH2), 1.55–1.22 (24H, m, CH2(CH2)6CH3), 0.90 ArH), 6.11 (2H, s, ArH), 2.55 (2H, dt, J = 13.9, 7.8 Hz,
(6H, t, J = 6.7 Hz, CH2CH3). 13C NMR, (CDCl3, 101 MHz): ArCH2CH2), 2.23 (2H, dt, J = 13.9, 7.8 Hz, ArCH2CH2),
δ 137.64, 134.96, 132.94, 131.65, 129.28, 127.72, 37.72, 34.68, 1.45–1.35 (4H, m, ArCH2CH2), 1.35–1.19 (20H, m,
32.78, 31.86, 30.56, 29.78, 29.52, 29.27, 22.65, 14.10. MS (APCI, CH2(CH2)5CH3), 0.88 (6H, t, J = 7.0 Hz, CH2CH3). 13C NMR,
M+): calc. for [C32H48S2 + 1H]+: m/z 497, found m/z 497. HR-MS (CDCl3, 126 MHz): δ 139.49, 138.95, 136.74, 136.64, 135.00,
(EI, M+): calc. for [C32H48S2]+: m/z 496.3197 found; m/z 133.03, 130.92, 126.80, 34.22, 31.89, 30.60, 29.60, 29.49, 29.26,
496.3208. Elemental analysis: found: C, 77.23; H, 10.20; S, 22.67, 14.11. MS (APCI, M+): calc. for [C32H44 + 1H]+: m/z 429,
12.50%; calc. for C32H48S2: C, 77.36; H, 9.74; S, 12.91%. FT-IR found m/z 429. HR-MS (APCI, M+): calc. for [C32H44 + 1H]+: m/z
(thin film, cm−1) 2954m, 2922s, 2852m, 1510m, 1464m, 429.3516 found; m/z 429.3510. Elemental analysis: Found: C,
1422m, 907s, 731s.
89.31; H, 10.41, calc. for C32H44: C, 89.65; H, 10.35%. FT-IR
Benzyne induced stevens rearrangement of compound 12 (thin film, cm−1) 3000w, 2954w, 2922s, 2852m, 1585w, 1465m,
(13). Dithiacyclophane 12 (10.9 g, 21.9 mmol) and compound 1435w, 903m, 690s.
7 (15.7 g, 52.5 mmol) were dissolved in anhydrous THF
Synthesis of 5,8,14,17-tetraoctyl-2,11-dithia[3.3]paracyclo-
(450 mL) and stirred at RT. TBAF·3H2O (20.7 g, 65.6 mmol) phane (16) and 6,9,14,17-tetraoctyl-2,11-dithia[3.3]paracyclo-
was dissolved in anhydrous THF (100 mL) and added dropwise phane (17). Compound 9 (19.8 g, 40.5 mmol) and compound
to the former solution over 4 hours. The solution was stirred 10 (16.0 g, 40.5 mmol) were dissolved in deoxygenated toluene
for one hour and the solvent removed in vacuo revealing a (1000 mL). In a separate flask KOH (6.82 g, 122 mmol) was dis-
yellow oil. The residue was purified by column chromato- solved in degassed ethanol (2500 mL). The toluene solution
graphy (petroleum ether to DCM : petroleum ether, 20 : 80 was added dropwise to the ethanol solution over 90 hours fol-
(v/v)) yielding a pale yellow oil (9.58 g, 67%). MS (APCI, M+): lowed by stirring for an additional 2 hours. The solvent was
calc. for [C44H56S2 + 1H]+: m/z 650, found m/z 650; calc. for removed in vacuo to reveal a yellow residue which was dis-
[C44H56S2 − 1SPh]+: m/z 540, found; m/z 540; calc. for solved in DCM (500 mL). Water (500 mL) was added and the
[C44H56S2 − 1Ph]+: m/z 572, found; m/z 572. HR-MS (EI, M+): solution neutralised with 6 M HCl(aq). The organic layer was
calc. for [C44H56S2]+: m/z 648.3823 found; m/z 648.3825. separated and the aqueous layer further extracted with DCM
Elemental analysis: found: C, 81.79; H, 9.09; S, 9.81, calc. for (2 × 500 mL). The organic layers were combined, dried over
C44H56S2: C, 81.42; H, 8.70; S, 9.88%. FT-IR (thin film, cm−1
2953m, 2923s, 2853m, 1480m, 1466m, 1438m, 1215m, 755s, yellow solid. The product was purified by column chromato-
734s, 689s. graphy (DCM : petroleum ether, 10 : 90 (v/v)) to reveal a white
)
MgSO4, filtered and the solvent removed in vacuo to reveal a
Oxidation of phenyl sulfides of compound 13 (14). Com- solid (11.7 g, 40%). The solid consisted of a mixture of 16 and
1
pound 13 (9.58 g, 14.8 mmol) was dissolved in toluene 17 in ratio of 6 : 94. H NMR, (CDCl3, 500 MHz): δ 6.78 (3.75H,
(200 mL) and acetic acid (100 mL) and cooled to 0 °C. Then s, ArH (17)), 6.76 (0.25H, s, ArH (16)). 4.07 (0.25H, d, J = 15.1
30 wt% H2O2(aq) (3.68 mL, 32.5 mmol) was added dropwise Hz, ArCH2S(16)), 3.82 (3.75H, d, J = 14.9 Hz, ArCH2S(17)), 3.63
over 30 minutes then the solution was warmed to RT and (3.75H, d, J = 14.9 Hz, ArCH2S(17)), 3.57 (0.25H, d, J = 15.1 Hz,
stirred for 20 hours. The organic layer was washed with water ArCH2S(16)), 2.82–2.69 (4H, m, ArCH2CH2), 2.48–2.35 (4H, m,
(3 × 500 mL) followed by saturated NaHCO3(aq) (1 × 250 mL), ArCH2CH2), 1.51–1.19 (48H, m, CH2(CH2)6CH3), 0.92–0.82
dried over MgSO4 and filtered. The solvent was removed (12H, m, CH2CH3). 13C NMR, (CDCl3, 126 MHz): δ dithia[3.3]
in vacuo revealing a highly viscous oil (9.68 g, 96%), which was paracyclophane 17; 137.88, 132.72, 129.95, 34.70, 32.82, 31.89,
used without further purification. MS (APCI, M+): calc. for 30.36, 29.87, 29.57, 29.31, 22.68, 14.11. Signals for dithia[3.3]
[C44H56O2S2 + 1H]+: m/z 682, found m/z 682; calc. for paracyclophane 16 were not observed due to low abundance.
[C44H56O2S2 − 1S(O)Ph]+: m/z 556, found; m/z 556. HR-MS HR-MS (EI, M+): calc. for [C48H80S2]+: m/z 720.5696: found: m/z
(APCI, M+): calc. for [C44H57S2O2]+: m/z. 681.3794 found; m/z 720.5695. Elemental analysis: found: C, 80.05; H, 11.04; S,
681.3785. Elemental analysis: Found: C, 77.34; H, 8.59; S, 9.36, 8.77; calc. for C48H80S2: C, 79.93; H, 11.18; S, 8.89%. FT-IR
calc. for C44H56O2S2: C, 77.60; H, 8.29; S, 9.42%. FT-IR (thin (thin film, cm−1) 2949m, 2921s, 2846m, 1500w, 1466m, 1221w,
film, cm−1) 2952m, 2922s, 2852m, 1495w, 1477w, 1465m, 894m, 753w, 723m, 693w.
1442m, 1304w, 1083m, 1041s, 746s, 689s.
Benzyne induced stevens rearrangement of mixture of
Synthesis of 4,7-dioctyl-[2.2]paracyclophane-1,9-diene (15). isomers 16 and 17 (18). A mixture of dithiacyclophanes 16 and
Compound 14 (9.45 g, 13.9 mmol) and Cs2CO3 (18.08 g, 17 (11.6 g, 16.1 mmol) and 7 (11.5 g, 38.5 mmol) were dis-
55.5 mmol) were added to deoxygenated anhydrous mixture of solved in anhydrous THF (325 mL) and stirred at RT.
xylenes (300 mL) and heated under reflux for 4 hours. The TBAF·3H2O (15.2 g, 48.2 mmol) was dissolved in anhydrous
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THF (100 mL) and added dropwise to the former solution over
4 hours. The solution was stirred for one hour and the solvent
Acknowledgements
removed in vacuo revealing a yellow solid. The residue was pur- The authors acknowledge the support of the EPSRC for award
ified by column chromatography (DCM : petroleum ether, of studentships (BJL and AMS) and project (EP/F056397). The
10 : 90 (v/v)) yielding a pale yellow oil (11.6 g, 83%). MS (APCI, high commission of India Education Wing-London, Govern-
M+): calc. for [C60H88S2 + 1H]+: m/z 874, found m/z 874; calc. ment of India for studentship (DK) and project (11015/16/
for [C60H88S2 − 1SPh]+: m/z 764, found; m/z 764, calc. for 2012-SCD-V).
[C60H88S2 − 1Ph]+: m/z 796, found; m/z 796. HR-MS (APCI, M+):
calc. for [C60H88S2 + H]+: m/z 873.6406: found: m/z 873.6389.
Elemental analysis: found: C, 81.64; H, 10.19; S, 7.14, calc. for
References
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2953w, 2922s, 2852m, 1582w, 1478m, 1465m, 1438m, 1090w,
736s, 689s.
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