Synthesis of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) derivatives functionalised with two, four or eight hydroxyl groups

Article abstract of DOI:10.1039/b709823e

Short synthetic routes to a range of BEDT-TTF derivatives functionalised with two, four or eight hydroxyl groups are reported, of interest because of their potential for introducing hydrogen bonding between donor and anion into their radical cation salts. The cycloaddition of 1,3-dithiole-2,4,5-trithione with alkenes to construct 5,6-dihydro-1,3-dithiolo[4,5-b]1,4-dithiin-2-thiones is a key step, with homo- or hetero-coupling procedures and O-deprotection completing the syntheses. The first synthesis of a single diastereomer of tetrakis(hydroxymethyl)BEDT-TTF, the cis,trans product, was achieved by careful choice of O-protecting groups to facilitate separation of homo- and hetero-coupled products. Cyclisation of the trithione with enantiopure 1R,2R,5R,6R-bis(O,O-isopropylidene)hex-3-ene-1,2,5,6-tetrol (from d-mannitol) gave two separable diastereomeric thiones, which can be transformed to enantiomeric BEDT-TTF derivatives with four or eight hydroxyl groups. The Royal Society of Chemistry.

Full text of DOI:10.1039/b709823e

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Synthesis of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) derivatives
functionalised with two, four or eight hydroxyl groups
R. James Brown,a,b Andrew C. Brooks,a,b Jon-Paul Griffiths,a Betrand Vital,a Peter Dayb and John D. Wallis*a
Received 28th June 2007, Accepted 1st August 2007
First published as an Advance Article on the web 20th August 2007
DOI: 10.1039/b709823e
Short synthetic routes to a range of BEDT-TTF derivatives functionalised with two, four or eight
hydroxyl groups are reported, of interest because of their potential for introducing hydrogen bonding
between donor and anion into their radical cation salts. The cycloaddition of 1,3-dithiole-2,4,5-
trithione with alkenes to construct 5,6-dihydro-1,3-dithiolo[4,5-b]1,4-dithiin-2-thiones is a key step, with
homo- or hetero-coupling procedures and O-deprotection completing the syntheses. The first synthesis
of a single diastereomer of tetrakis(hydroxymethyl)BEDT-TTF, the cis,trans product, was achieved by
careful choice of O-protecting groups to facilitate separation of homo- and hetero-coupled products.
Cyclisation of the trithione with enantiopure 1R,2R,5R,6R-bis(O,O-isopropylidene)hex-3-ene-1,2,5,6-
tetrol (from D-mannitol) gave two separable diastereomeric thiones, which can be transformed to
enantiomeric BEDT-TTF derivatives with four or eight hydroxyl groups.
when each “end” of the ET molecule is substituted.7 A number of
interesting properties are emerging. Thus, a 2 : 1 superconducting
Introduction
Following on from the extensive studies on tetrathiafulvalene
(TTF),1 bis(ethylenedithio)tetrathiafulvalene, more commonly
known as BEDT-TTF or ET 1, has played a prominent role
in the recent development of molecular conductors, supercon-
perchlorate salt of enantiopure dimethyl-ET 6 (Tc = 3.0 K,
5.0 kbar) was reported by Hilti, Zambounis et al., while a 2 : 1
hexafluorophosphate superconducting salt was obtained from the
meso-isomer of this donor (Tc = 4.3 K, 4.0 kbar) by Mori et al.12
ductors and bifunctional materials, and a wide range of its
Troitksy has used the hexadecyl-ET 4 to prepare conducting thin
films.16 New ET derivatives containing metal binding sites such
as 10 with potential for preparing bifunctional materials with
magnetic metal ions,17,18 and an enantiopure donor 11 derived
from (−)-b-pinene, have recently been prepared.11 Cross-coupling
reactions have been utilised to prepare substituted derivatives
of the ethylenedithio-TTF system 12.19 Furthermore, substituted
derivatives of selenium-containing donors, such as BETS20 13,
may soon become available following developments in synthetic
approaches,21 which will be of interest since some BETS radical
cation salts have electrical properties which can be modified by an
external magnetic field.20
Here we describe the synthesis of a range of ET donors
carrying between one and eight hydroxyl groups. Introduction
of hydroxyl groups on to a donor molecule brings not only
the possibility of hydrogen bonding in the radical cation salts
to anchor the anions in unique sites and orientations, but also
provides a point for attachment of further functionality. In the
TTF series mono-, di- and tetra-(hydroxymethyl) derivatives have
been reported,22–24 hydrogen bonding to anions in their radical
cation salts has been observed,24 and they have been utilised in
the construction of more complex systems.25 We and others have
reported synthetic routes to racemic hydroxymethyl-ET 14,18,26,27
the cheapest and most efficient using the acetyl protecting group,
and we have also synthesized the enantiopure form.28 A number
of semiconducting microcrystalline 2 : 1 radical cation salts of
racemic 14 have been prepared.26 Routes to the ET donor with cis-
oriented hydroxymethyl groups 15,27 a stereoisomeric mixture of
the tetrakis(hydroxymethyl)-ET 1629 and donors with expanded
outer rings substituted with hydroxyl or hydroxymethyl groups
radical cation salts have been prepared and their properties
investigated.2 Particular highlights are the salts (ET)2(Cu(NCS)2)
and (ET)2(N(CN)2)X (X = Cl or Br) which become supercon-
ducting at low temperatures,3 the paramagnetic superconducting
radical salt (ET)4[Fe(oxalate)3]·H2O·C6H5CN,4 a layered salt with
a mixed chromium(III)/manganese(II) oxalate network which has
independent electrical and ferromagnetic properties,5 and salts
−
with MHg(SCN)4 (M = K or Tl) which form a chiral surface
metal in a magnetic field.6 The superconducting salts are of great
interest to theoretical physicists since the salts are clean systems
whose electrical behaviour can be modelled, and provide test beds
for exploring new aspects of superconductivity. A range of substi-
tuted ET derivatives is now becoming available.7 The installation
of a substituent on one of the ethylene bridges forms a stereogenic
centre, and a number of racemic monosubstituted ET donors
have been prepared, for example with sidechains terminating in
amino8 or amido9 groups, e.g. 2 and 3, or a long hydrocarbon
chain,10 e.g. 4. The enantiopure ester 511 has also been reported.
Disubstituted and tetrasubstituted derivatives e.g. the enantiopure
dimethyl-ET12 6 and its meso-isomer,12 enantiopure tetramethyl-
ET13 8 and racemic dichloro-ET14 7 as well as materials with
additional ring systems such as 915 have been prepared. However,
care is necessary to avoid preparing mixtures of stereoisomers
aSchool of Biomedical and Natural Sciences, Nottingham Trent University,
Clifton Lane, Nottingham, NG11 8NS, UK. E-mail: john.wallis@ntu.ac.uk
bDavy-Faraday Research Laboratory, The Royal Institution of Great Britain,
21 Albemarle St., London, W1S 4BS, UK. E-mail: pday@ri.ac.uk
3172 | Org. Biomol. Chem., 2007, 5, 3172–3182
This journal is
The Royal Society of Chemistry 2007
©

View Article Online
17 and 1830,31 have been reported. Two radical cation salts of
bis(hydroxymethyl)-substituted materials have been described:
(15)2Cl and (17)2I3. In the former27 the chloride is hydrogen bonded
by hydroxyl groups from three donors, and lies between stacks of
donors, while in the latter32 the donors hydrogen bond with each
other while the triiodides lie in isolated pockets. Here we describe,
with experimental details, syntheses of racemic hydroxyethyl-ET
19 and trans-bis(hydroxymethyl)-ET 20, the first synthesis of
a single diastereoisomer of the tetrol tetrakis(hydroxymethyl)-
ET, the cis,trans isomer 21, and the syntheses of the enan-
tiopure tetrol 22 and octol 23, with the aim of making these
new interesting donors accessible to the materials chemistry
community.
Discussion
Preparation of hydroxyethyl-ET 19
The general approach in these syntheses is illustrated by the
synthesis of hydroxyethyl-ET, HEET, 19. The synthetic routes rely
on the cyclisation of the trithione 24 with the appropriate alkene,
a reaction first used by Neilands.33 Refluxing but-3-en-1-ol with
trithione 24 in toluene gave the thione 25 in 83% yield, followed
by protection of the hydroxyl group as an acetate to give 26,
which was necessary for a successful subsequent cross-coupling
reaction. Thione sulfur/oxygen exchange gave oxo compound
27, which was cross-coupled with the unsubstituted thione 28
This journal is
The Royal Society of Chemistry 2007
Org. Biomol. Chem., 2007, 5, 3172–3182 | 3173
©

View Article Online
Scheme 1
to give the protected donor 29 in 54% yield. Hydrolysis gave
Preparation of cis,trans-tetrakis(hydroxymethyl)-ET 21
HEET 19 in five steps with an overall yield of 14% (Scheme 1).
Both hydroxymethyl-ET 1418 and HEET 19 have been func-
tionalised either by ester formation or by tosylation and sub-
stitution. For example, HEET forms ester 32 with thiophene-
3-carbonyl chloride and ester 34 with the thiophene-containing
carboxylic acid 33 in the presence of DCC/DMAP, and its
tosylate 30 is substituted with thiophene-3-methylthiolate to give
sulfide 31.
Tetrakis(hydroxymethyl)-substituted ETs are very attractive
donors because of the hydrogen bonding potential at both “ends”
of the molecule. However, there are five possible stereoisomers
depending on whether the two groups at each end of the molecule
lie cis or trans, 41–45 (R = CH2OH) (Scheme 3), and two
of these stereoisomers (41 and 45) are racemic mixtures. It is
important to develop syntheses of individual stereoisomers, since
electrocrystallisation of a stereoisomeric mixture is a strategy
fraught with problems; identification of the product relies on X-ray
crystallography to determine which stereoisomer or stereoisomers
are present,35 assuming that all crystals have the same composition
of course. An outline of the stereochemical consequences of
various coupling strategies is given in Scheme 3. Homo-coupling
of a racemic trans-disubstituted oxo compound 39 will give a
racemic mixture of the tetrasubstituted ET 41 from self-coupling
of each enantiomer of 39, as well as a meso compound 42 arising
from coupling of the two opposite enantiomers. Homo-coupling
of a cis-disubstituted oxo compound 40 will give diastereomeric
products 43 and 44. In both cases, separation of the products is
likely to be extremely difficult. Homo-coupling of one enantiomer
of the trans oxo compound 39 would yield one enantiomer of the
all-trans isomer 41, but attempts to prepare the appropriate single
enantiomer of the trans oxo compound 42 (R = CH2OH) have so
far been unsuccessful. The fifth stereoisomer 45 is the product of
Preparation of trans-vic-bis(hydroxymethyl)-ET 20
The ET derivative with two vicinal trans-oriented hydroxymethyl
groups was prepared in a similar way. Cyclisation of trithione
24 with the trans-but-2-en-1,4-diol, which was prepared from
butyn-1,4-diol by reduction with lithium aluminium hydride,34
gave diol 35 in 41% yield. Protection of hydroxyl groups as
acetates, to give 36, was followed by the standard three steps of
(a) sulfur/oxygen exchange to give oxo compound 37, (b) cross-
coupling with unsubstituted thione 28 to give the protected donor
38 in 55% yield, and (c) deprotection to give the trans diol 20 in an
overall yield of 17% (Scheme 2). The different disposition of the
hydroxymethyl groups, compared to the cis isomer 15, is expected
to affect the structures of its radical cation salts with anions which
can act as hydrogen bond acceptors.
3174 | Org. Biomol. Chem., 2007, 5, 3172–3182
This journal is
The Royal Society of Chemistry 2007
©

View Article Online
Scheme 2
cross-coupling of the cis- and trans-disubstituted oxo compounds
39 and 40, but is accompanied by all other homo-coupled products.
However, we have now developed a strategy for isolation of
this last stereoisomer cis,trans-tetrakis(hydroxymethyl)-ET 21.
The overall synthetic plan is shown in Scheme 4. The key step
is the protection of the hydroxyl groups of the cis and trans
compounds for coupling with groups of quite different polarities.
Thus, hydroxyl groups of the cis-bis(hydroxymethyl)thione 46 were
protected with two BTDMS groups to give thione 47,27 which
was converted to its oxo compound 48. The hydroxyl groups of
the trans-bis(hydroxymethyl)thione 35 were protected as acetates
to give thione 36. Cross-coupling of cis- and trans-compounds
48 and 36 in triethyl phosphite gave three sets of materials: the
desired cross-coupled material 53 (2 × TBDMS, 2 × acetyl O-
protecting groups) and the two pairs of homo-coupled materials:
49 and 50 (4 × TBDMS O-protecting groups) and 51 and 52
(4 × acetyl O-protecting groups). The three groups of materials
were separated by chromatography. The cross-coupled product,
with two protecting groups of each type, runs between the two
sets of homo-coupled products which each carry four protecting
groups of the same type. Finally, the tetrol 21 was prepared by
hydrolysis of the protecting groups of 53 with aqueous 20% HCl
in THF. We believe this principle of using two protecting groups
of quite different polarities will find application in the synthesis of
further polysubstituted donors.
Preparation of enantiopure tetrol and octol donors 22 and 23
We have already reported the total diastereoselectivity of the
reactions of the trithione 24 with enantiopure alkenes (−)-a-
pinene, (−)-b-pinene and (+)-2-carene.11 Encouraged by this, we
extended the study to the structurally less complex enantiopure
alkene 54 (Scheme 5) which has two stereocentres adjacent to the
double bond and four protected hydroxyl groups and which is
readily prepared from D-mannitol.36 Trithione 24 reacted with this
alkene to give major (31%) and minor (5%) 1 : 1 addition products
which were assigned structures 55 and 56 respectively, based on
the X-ray crystal structure of the minor isomer 56 (Fig. 1). Thus,
the major product is formed by addition of trithione 24 to the Si
face of enantiopure alkene 54 as shown in Fig. 2, while the minor
adduct is formed by addition to the Re face. Molecular mechanics
studies indicated there was no strong conformational preference
Scheme 3
This journal is
The Royal Society of Chemistry 2007
Org. Biomol. Chem., 2007, 5, 3172–3182 | 3175
©

View Article Online
Scheme 4
Scheme 5
3176 | Org. Biomol. Chem., 2007, 5, 3172–3182
This journal is
The Royal Society of Chemistry 2007
©

View Article Online
Table 1 Cyclic voltammetry data for selected donorsa
Compound
E1
E2
1
0.51
0.49
0.50
0.52
0.52
0.55
0.55
0.94
0.90
0.88
0.86
0.85
0.93
0.89
19
20
21
22
58
59
a Measured relative to Ag/AgCl at
a
platinum electrode in
dichloromethane containing 0.1 M Bu4NPF6 as charge carrier and using
a 100 mV s−1 scan.
shows a boat conformation in the solid state, has corresponding
shifts at dC 50.2 and 129.9.38 These larger shifts may relate in part
to the poorer conjugation of the dithiin S atoms with the dithiole
ring when the former has the boat conformation.
Fig. 1 Molecular structure of minor diastereomer 56.
The major product 55 was converted to its oxo compound 57
with mercuric acetate and coupled to the unsubstituted thione 28
using triethyl phosphite to give the protected donor 58 in 35% yield
after chromatography. Finally, deprotection with 2 M HCl in THF
yielded the enantiopure tetrol 22 in 94% yield. Furthermore, self-
coupling of the oxo compound 57 in triethyl phosphite furnished
the donor bearing four ketal groups 59 in 60% yield, which
could be deprotected in a similar way to give the enantiopure
octol 23.
Fig. 2 Preferred conformation of alkene 54 with the Si face upwards.
The oxidation potentials of the new hydroxyl-substituted
donors, measured in dichloromethane, indicate that the overall
pattern of two reversible oxidations is retained (Table 1), though
the octol 23 was completely insoluble in this solvent, and
measurements in THF did not indicate a reversible system. We
are now investigating the electrocrystallisation of these materials.
Of particular interest will be to see how the interaction of the
hydroxyl groups with the anions control the solid-state structures
of the radical cation salts.
for rotation about the bonds between the alkene and each cyclic
ketal, with a small energy minimum for the conformation shown
in Fig. 2.
The X-ray structure of the minor product 56 shows that the
dithiin ring takes up a twisted boat conformation with both ring
sp3 carbon atoms strongly displaced to the same side of the plane
defined by the other atoms of the fused ring system but with C5
˚
displaced by more than C4 (C4: by 1.277(4), C5 by 1.486(5) A).
The torsions about the dithiin sp2 C–S bonds are −48.8(5) and
52.0(5)◦, and the twist in the boat structure is indicated by the
largest torsion in this ring about the C5–S5 bond: −66.3(4)◦,
much larger than that of 28.4(5)◦ for the C4–S4 bond. The trans
arrangement of the dioxolane rings means that one lies over the
organosulfur ring system and the other lies away from it. Each
dioxolane ring adopts an envelope conformation with the flap at
the carbon atom between the oxygen atoms. The best planes of
these rings lies at 40.3(2) and 50.7(2)◦ to the best plane through
the planar portion of the organosulfur system. There are distinct
differences in the chemical shifts of the carbon atoms in the dithiin
ring for the major and minor diastereoisomers 55 and 56. The
major isomer exhibits chemical shifts for the sp3 C atoms at dC
44.3 and for the sp2 C atoms at dC 118.9, similar to those of other
trans-disubstituted derivatives e.g. the dimethyl derivative 60 (dC
43.5 and 120.4) whose solid-state conformation lies between a half-
chair and an envelope.37 In contrast, for the minor diastereomer
the shifts of the corresponding carbon atoms are larger: dC 51.7
and 128.3. The trans diester 61, which like the minor isomer also
Conclusion
We have reported syntheses of a series of ET-derivatives carrying
one, two, four and eight hydroxyl groups, two of them in
enantiopure form. Molecules 22 and 23 are particularly attractive
donors, since, apart from the potential for having chiral hydrogen
bonding networks in their radical cation salts, these donors are
starting materials for preparing dendrimeric materials. These
single enantiomers will also provide important substrates for
investigating the influence of chirality on electrical and magnetic
properties. The second enantiomer of 23 will be available from the
other enantiomer of alkene 54, and the racemate is available by
mixing equal amounts of the two enantiomers, a rare case where
it is more work to prepare the racemate than the enantiomer.
Rikken has reported magnetochiral anisotropy in the conductivity
of carbon nanotubes,39 and our donors will provide a test bed for
investigating the effect of chirality on the electrical properties of
organosulfur donors. Furthermore, the diastereoselectivity of the
cycloaddition of thione 24 with alkene 54 is a very encouraging
result, suggesting that cycloadditions of trithione 24 with further
enantiopure alkenes will be a key step in designing and preparing
further enantiopure donors.
This journal is
The Royal Society of Chemistry 2007
Org. Biomol. Chem., 2007, 5, 3172–3182 | 3177
©

View Article Online
1247, 1049, 895, 767, 469; found C, 36.7, H, 3.3%, C9H10O3S4
requires C, 36.7, H, 3.4%.
Experimental
General
(2-Acetyloxyethyl)-ET, 29. A mixture of oxo compound 27
(2.83 g, 9.90 mmol) and unsubstituted thione 28 (4.43 g,
19.8 mmol) were heated in triethyl phosphite to 80 ◦C under
N2 for 5 h to give an orange solution. Triethyl phosphite was
removed by distillation in vacuo and the residue purified by flash
chromatography (5 : 1 cyclohexane–ethyl acetate) to yield 29 as a
NMR spectra were measured on a JEOL JNM-EX270 spec-
trometer at 270 MHz for 1H and at 67.8 MHz for 13C using
CDCl3 as solvent and tetramethylsilane (TMS) as standard unless
otherwise stated, and measured in ppm downfield from TMS with
coupling constants reported in Hz. IR spectra were recorded
on a PerkinElmer Spectrum RX 1 FT-IR spectrometer, and
are reported in cm−1. Optical rotation data were measured on
a PerkinElmer 241 polarimeter. Mass spectra were recorded at
the EPSRC Mass Spectrometry Centre. Chemical analysis data
were obtained from Mr T. Spencer, University of Nottingham.
An X-ray diffraction dataset was measured by the EPSRC
National Crystallography Service at Southampton University.
Flash chromatography was performed on 40–63 silica gel (Merck).
◦
red–orange solid (2.50 g, 54.5%); mp 109–110 C; dH: 4.23 (2H,
m, 2ꢀ-CH2), 3.64 (1H, m, 5-H), 3.34 (1H, dd, J = 13.1, 3.2, 6-Ha),
3.32 (4H, s, 5ꢀꢀ- & 6ꢀꢀ-H2), 3.32 (1H, dd, J = 13.1, 6.5, 6-Hb), 2.05
ꢀ
2
=
(5H, m, CH3 & 1 -CH2); dC: 170.7 (C O) 113.9 & 113.0 (sp -C),
61.2 (1ꢀ-CH2), 40.1 (5-C), 35.3 (6-C), 33.7 (1ꢀ-CH2), 30.2 (5ꢀꢀ- &
6ꢀꢀ-C), 20.9 (CH3); mmax(KBr): 2955, 2920, 1731, 1365, 1239, 1039,
905, 772, 668; found C, 35.8, H, 3.0%, C14H14O2S8 requires C, 35.7,
H, 3.0%.
5,6-Dihydro-5-(2ꢀ -hydroxyethyl)-1,3-dithiolo[4,5-b]-1,4-dithiin-
2-thione, 25. 3-Buten-1-ol (7.00 g, 104.4 mmol) and trithione 2440
(8.00 g, 40.8 mmol) were refluxed in toluene (400 ml) for 4 h. After
cooling to room temperature the reaction mixture was filtered, and
the solid washed with ethanol. Combined washings and filtrate
were evaporated and the residue purified by flash chromatography
(ethyl acetate) to furnish 25 as an orange oil (8.84 g, 83.0%), which
solidified on standing; mp 52–53 ◦C; dH: 3.88 (3H, m, 2ꢀ-CH2 and
(2ꢀ-Hydroxyethyl)-ET, 19. A solution of 29 (0.65 g, 1.40 mmol)
in THF (10 ml) and 20% HCl solution (5 ml) was stirred under
N2 for 48 h. The solution was neutralised by the addition of solid
NaHCO3. The organic layer was collected, dried (Na2SO4) and
purified by flash chromatography (2 : 1 cyclohexane–ethyl acetate)
to afford 19 (0.31 g, 51%) as a bright orange powdery solid; mp
141–142 ◦C; dH: 4.69 (1H, t, J = 5.1, OH), 3.81 (1H, m, 5-H), 3.55
(2H, m, 2ꢀ-CH2), 3.45 (1H, dd, J = 13.2, 3.0, 6-Ha), 3.38 (4H, s, 5ꢀꢀ-,
6ꢀꢀ-H2), 3.27 (1H, dd, J = 13.2, 6.5, 6-Hb), 1.84 (2H, m, 1ꢀ-CH2);
dC: 115.1, 115.0 & 114.4 (sp2-C), 59.8 (2ꢀ-CH2), 42.5 (5-C), 39.5
(6-C), 36.9 (1ꢀ-CH2), 31.2 (5ꢀꢀ- & 6ꢀꢀ-C); mmax (KBr): 3450, 2922,
1652, 1458, 1280, 1046, 767; found C: 33.7, H: 3.0%, C12H12OS8
requires C: 33.6, H: 2.8%.
5-H), 3.46 (1H, dd, J = 13.4, 2.8, 6-Ha), 3.22 (1H, dd, J = 13.4, 6.7,
ꢀ
=
6-Hb), 2.02 (2H, m, 1 -CH2), 1.52 (1H, s, OH); dC: 207.7 (C S),
121.9, 121.5 (3a- & 7a-C), 59.3 (2ꢀ-CH2), 39.8 (5-C), 37.1 (6-C),
34.9 (1ꢀ-CH2); mmax (thin film): 3386, 2924, 1483, 1412, 1293, 1057,
890; found C, 31.3, H, 2.9%, C7H8OS5 requires C, 31.3, H, 3.0%.
5,6-Dihydro-5-(2ꢀ-acetyloxyethyl)-1,3-dithiolo[4,5-b]-1,4-dithiin-
2-thione, 26. Acetic anhydride (4 ml, 36.3 mmol) was added to
a solution of 25 (8.84 g, 33.9 mmol) in pyridine (50 ml) at room
temperature and then stirred at 70 ◦C for 12 h. Water (300 ml)
was added and the mixture extracted with CH2Cl2 (3 × 100 ml).
The organic solution was washed consecutively with 0.5 M HCl
solution (3 × 100 ml) and H2O (100 ml), dried (Na2SO4) and
evaporated to yield 26 as a brown oil (8.86 g, 86.0%); dH: 4.25 (2H,
m, 2ꢀ-CH2), 3.73 (1H, m, 5-H), 3.43 (1H, dd, J = 13.3, 3.0, 6-Ha),
3.20 (1H, dd, J = 13.3, 6.8, 6-Hb), 2.14 (2H, m, 1ꢀ-CH2), 2.05
(2ꢀ-Tosyloxyethyl)-ET, 30. Hydroxyethyl-ET 19 (0.20 g,
0.47 mmol) and tosyl chloride (0.36 g, 1.88 mmol) were stirred
together in dry pyridine (2 ml) under nitrogen for 2 h. The resulting
solution was diluted with chloroform (25 ml), absorbed on silica
and purified by flash chromatography (2 : 1 cyclohexane–ethyl
acetate) to give 30 (0.17 g, 64%) as an orange solid, mp 90 ◦C;
dH: 7.78 (2H, d, J = 8.2, Ar-H2), 7.36 (2H, d, J = 8.2, Ar-H2),
4.18 (2H, t, J = 5.7, -CH2O), 3.63 (1H, m, 5-H), 3.33 (1H, dd,
J = 3.1, 13.3, 6-Ha), 3.27 (4H, s, 5ꢀꢀ-,6ꢀꢀ-H2), 2.99 (1H, dd, J =
5.7, 13.3, 6-Hb), 2.45 (Ar-CH3), 2.03 (2H, m, 1ꢀ-CH2); dC (DMSO-
d6): 145.1, 132.3, 130.0, 127.8 (Ar-C6), 113.7, 113.0, 112.1 (sp2-C),
67.0 (2ꢀ-C), 38.3 (5-C), 34.8 (6-C), 33.6 (1ꢀ-CH2), 30.1 (5ꢀꢀ- & 6ꢀꢀ-
C), 21.6 (CH3); mmax (KBr): 2922, 1596, 1410, 1349, 1286, 1187,
1172, 1094, 966, 905, 811, 769, 663, 553; m/z (CI): 583 ([M + 1]+,
10), 411 ([M − TsO]+, 100); HRMS (ES): found [M+] 582.8822,
C19H18O3S9 requires 582.8820.
=
(3H, s, CH3); dC: 207.7 (2-C), 170.7 (C O) 122.0, 121.7 (3a- &
7a-C), 60.8 (2ꢀ-CH2), 39.7 (5-C), 34.6 (6-C), 33.8 (1ꢀ-CH2), 20.9
(CH3); mmax (thin film): 2955, 1737, 1485, 1426, 1384, 1364, 1236,
1062, 890; found C, 34.8, H, 3.1%, C9H10O2S5 requires C, 34.8, H,
3.3%.
5,6-Dihydro-5-(2ꢀ-acetyloxyethyl)-1,3-dithiolo[4,5-b]-1,4-dithiin-
2-one, 27. To a solution of 26 (8.86 g, 29.2 mmol) in CHCl3
(100 ml) and glacial acetic acid (30 ml) was added mercuric acetate
(15.02 g, 47.1 mmol). After 2 h stirring at room temperature the
mixture was filtered. The filtrate was washed consecutively with
saturated NaHCO3 solution (3 × 100 ml) and water (100 ml),
dried (Na2SO4) and evaporat◦ed to afford 27 as a light brown solid
(5.65 g, 67.5%); mp 46–47 C; dH: 4.23 (2H, m, 2ꢀ-CH2), 3.74
(1H, m, 5-H), 3.45 (1H, dd, J = 13.3, 2.7, 6-Ha), 3.20 (1H, dd,
J = 13.3, 6.7, 6-Hb), 2.14 (2H, m, 1ꢀ-CH2), 2.03 (3H, s, CH3);
Thiophen-3-ylmethylthioethyl-ET, 31. To a solution of sodium
metal (0.03 g, 1.2 mmol) in dry methanol (5 ml) under nitrogen
and in the dark was added a solution of thiophene-3-methylthiol41
(0.12 g, 1 mmol) in dry THF (10 ml). After 10 min stirring, a
solution of tosylate 30 (0.30 g, 0.52 mmol) in dry THF (20 ml)
was added and the resulting mixture stirred for 20 h. The mixture
was partitioned between DCM and water and the organic layer
collected, dried over MgSO4 and purified by flash chromatography
(8 : 1 cyclohexane–ethyl acetate) to yield 31 (0.21 g, 71%) as an
orange solid; mp 159–162 ◦C; dH: 7.30 (dd, 1H, J = 3.0, 5.0, 4ꢀꢀ-H),
7.10 (dd, 1H, J = 1.2, 3.0, 5ꢀꢀ-H), 7.07 (dd, 1H, J = 1.2, 5.0, 2ꢀꢀ-H),
3.74 (s, 2H, SCH2Ar), 3.65 (m, 1H, 5-H), 3.28 (m, 5H, 6a-, 5ꢀ-,
=
dC: 188.3 (2-C), 170.7 (CH3C O), 112.4, 112.3 (3a- & 7a-C),
60.8 (2ꢀ-CH2), 41.2 (5-C), 35.8 (6-C), 33.8 (1ꢀ-CH2), 20.8 (CH3);
mmax (KBr): 2967, 1729, 1670, 1634, 1509, 1464, 1425, 1398, 1368,
3178 | Org. Biomol. Chem., 2007, 5, 3172–3182
This journal is
The Royal Society of Chemistry 2007
©

View Article Online
6ꢀ-H), 2.95 (dd, 1H, J = 6.4, 13.1, 6b-H), 2.58 (m, 2H, SCH2CH2),
1.94 (m, 2H, SCH2CH2); dC: 138.4 (3ꢀꢀ-C), 128.0 (2ꢀꢀ-C), 126.3 (5ꢀꢀ-
C), 122.4 (4ꢀꢀ-C), 113.0, 112.9, 111.7, 111.6 (sp2-C), 42.0 (5-C),
35.1 (SCH2Ar), 33.8 (6-C), 30.9 (SCH2CH2), 30.1 (5ꢀ-, 6ꢀ-C), 28.4
(SCH2CH2); mmax (KBr): 2916, 1408, 1284, 1233, 886, 773, 726, 678,
616; m/z (EI): 540 ([M]+, 20%), 236 (55%), 224 (100%); HRMS
(EI): found [M+] 539.8454, C17H16S10 requires 539.8454.
was added to a solution of 35 (1.05 g, 3.70 mmol) in pyridine
(15 ml) at 0 ◦C and the mixture stirred at room temperature
overnight. DCM (100 ml) and water (30 ml) were added. The
mixture was shaken and the organic layer collected. This was
washed sequentially with 1 M HCl (3 × 100 ml) and water (50 ml),
dried (MgSO4) and evaporated to yield 36 as a dark orange–brown
oil (1.28 g, 94.1%); dH: 4.32 (4H, m, 2 × CH2O), 3.74 (2H, m, 5,
=
6-H), 2.07 (6H, s, 2 × OCH3); dC: 206.5 (2-C), 170.7 (2 × C O)
Thiophene-3-carboxylic acid, HEET ester, 32. To a solution
of HEET 19 (0.16 g, 0.38 mmol) in dry THF (10 ml) was
added triethylamine (2 ml) and thiophene-3-carbonyl chloride
(0.11 g, 0.77 mmol), which had been prepared from the carboxylic
acid42 and thionyl chloride. This mixture was stirred for 12 h,
concentrated and purified by flash chromatography (10 : 1
cyclohexane–ethyl acetate) to yield 32 (0.13 g, 62%) as an orange
solid; mp 125–128 ◦C; dH: 8.11 (dd, 1H, J = 1.1, 3.1, 2ꢀꢀ-H), 7.51
(dd, 1H, J = 5.0, 1.1, 5ꢀꢀ-H), 7.32 (dd, 1H, J = 3.1, 5.0, 4ꢀꢀ-H), 4.46
(m, 2H, CH2O), 3.66 (m, 1H, 5-H), 3.40 (dd, 1H, J = 3.1 13.1,
6-Ha), 3.27 (s, 4H, 5ꢀ-, 6ꢀ-H2), 3.14 (dd, 1H, J = 6.4, 13.1, 6-Hb),
118.8 (3a-, 7a-C), 64.7 (2 × CH2O), 40.1 (5-, 6-C), 20.7 (2 × CH3);
mmax (thin film): 2923, 1743, 1381, 1363, 1222, 1064, 1034; m/z (AP):
369 ([M + H]+,100), 309 (5); HRMS (ES): found: 368.9419 (M +
H)+, C11H12O4S5 + H requires: 368.9417.
trans-5,6-Bis(acetyloxymethyl)-5,6-dihydro-1,3-dithiolo[4,5-b]-
1,4-dithiin-2-one, 37. To a solution of 36 (0.15 g, 0.41 mmol) in
CHCl3 (10 ml) and glacial acetic acid (3 ml) was added mercuric
acetate (0.19 g, 0.61 mmol). After 2 h stirring at room temperature
the mixture was filtered. The filtrate was washed consecutively
with saturated NaHCO3 solution (3 × 10 ml) and H2O (10 ml),
dried (Na2SO4) and evaporated to afford 37 as a light brown oil
(0.13 g, 90.6%); dH: 4.34 (4H, m, 2 × CH2O), 3.72 (2H, m, 5-, 6-H),
ꢀꢀ
ꢀꢀ
=
2.22 (m, 2H, 5-CH2); dC: 162.4 (C O), 133.1 (4 -C), 133.0 (3 -C),
127.8 (2ꢀꢀ-C), 126.2 (5ꢀꢀ-C), 113.8, 113.0, 112.9, 111.4 (sp2-C), 61.4
(CH2O), 40.3 (5-C), 35.3 (6-C), 33.9 (5-CH2), 30.1 (5ꢀ-, 6ꢀ-C); mmax
(KBr): 3000, 2909, 1703, 1518, 1414, 1266, 1189, 1109, 1008, 824,
771, 752, 700, 502; m/z (EI): 537.8 ([M]+, 100%); HRMS (EI):
found 537.8463 [M]+, C17H14O2S9 requires 537.8480.
=
2.04 (6H, s, 2 × CH3); dC: 187.2 (2-C), 169.7 (2 × C O) 109.6
(3a-, 7a-C), 64.5 (5-, 6-CH2O), 41.2 (5-, 6-C), 20.4 (2 × CH3); mmax
(thin film): 3025, 2943, 1744, 1692, 1644, 1507, 1440, 1381, 1364,
1222, 1035, 891, 755; m/z (AP): 352 ([M]+,80), 293 (100); HRMS
(ES): found: 369.9914 (M + NH4)+, C11H12O5S4 + NH4 requires:
369.9911.
Thiophen-3-ylmethoxyacetic acid, HEET ester, 34. To a solu-
tion of HEET 19 (0.20 g, 0.47 mmol), thiophen-3-ylmethoxyacetic
acid43 (0.08 g, 0.47 mmol) and 4-dimethylaminopyridine
(5 mg) in dry dichloromethane (10 ml) was added N,Nꢀ-
dicyclohexylcarbodiimide (0.13 g, 0.61 mmol). This was stirred
for 20 h at room temperature, after which the mixture was
concentrated and purified by chromatography (5 : 1 cyclohexane–
ethyl acetate) to yield 34 (0.15 g, 56%) as an oily orange solid;
dH: 7.25 (dd, 1H, J = 3.0, 5.0, 5ꢀꢀ-H), 7.20 (br s, 1H, 2ꢀꢀ-H), 7.03
(br d, 1H, J = 5.0, 4ꢀꢀ-H), 4.57 (s, 2H, OCH2Ar), 4.25 (m, 2H,
CH2CH2O), 4.03 (s, 2H, C(O)CH2O), 3.55 (m, 1H, 5-H) 3.29 (dd,
1H, J = 3.0, 13.1, 6-Ha), 3.21 (s, 4H, 5ꢀ-, 6ꢀ-H2), 3.00 (dd, 1H, J =
trans-vic-Bis(acetyloxymethyl)-ET, 38. A mixture of oxo com-
pound 37 (0.75 g, 2.13 mmol) and thione 28 (0.72 g, 3.20 mmol)
were heated in triethyl phosphite (10 ml) to 90 ◦C under N2
for 5 h to give an orange solution. Triethyl phosphite was
removed by distillation in vacuo and the residue purified by flash
chromatography (3 : 1 cyclohexane–ethyl acetate) to yield 38 as an
orange solid (0.62 g, 55.1%); mp 122–123 ◦C; dH: 4.27 (2H, dd, J =
11.2, 5.7, 2 × CHaO), 4.23 (2H, dd, J = 11.2, 8.0, 2 × CHbO), 3.65
(2H, m, 5-, 6-H), 3.24 (4H, s, 5ꢀ-, 6ꢀ-H2), 2.04 (6H, s, 2 × CH3);
2
=
dC: 170.2 (2 × C O) 113.7, 110.2 (sp -C), 64.7 (2 × CH2O), 40.6
6.2, 13.1, 6-Hb), 2.02 (d, 2H, J = 6.4, 5-CH2); dC: 170.0 (C O),
(5-, 6-C), 30.0 (5ꢀ-,6ꢀ-C), 20.7 (2 × CH3); mmax (KBr): 2931, 1740,
1381, 1362, 1230, 1033, 909, 772; m/z (AP): 529 ([M + H]+, 100),
357 (80); HRMS (ES): found: 528.8886 (M + H)+, C16H16O4S8 +
H requires: 528.8892.
=
137.9 (3ꢀꢀ-C), 127.3 (2ꢀꢀ-C), 126.2 (5ꢀꢀ-C), 123.7 (4ꢀꢀ-C), 113.7, 112.9,
112.5, 111.8 (sp2-C), 68.3 (OCH2Ar), 66.8 (C(O)CH2O), 61.5
(CH2CH2O), 39.8 (5-C), 35.1 (6-C), 33.5 (5-CH2), 30.0 (5ꢀ-, 6ꢀ-C);
mmax (KBr): 2916, 2853, 1747, 1659, 1456, 1415, 1275, 1192, 1155,
1119, 1010, 917, 885, 854, 766, 693; m/z (CI): 583 ([M]+, 10%), 244
(100%); HRMS (EI): found 581.81737 [M]+, C19H18O3S9 requires
581.8741.
trans-vic-Bis(hydroxymethyl)-ET, 20. A solution of donor 38
(0.20 g, 0.38 mmol) in THF (20 ml) and 20% HCl solution (10 ml)
was stirred under N2 overnight. The solution was neutralised by
the addition of solid NaHCO3. The organic layer was collected,
dried (Na2SO4) and evaporated to afford 20 (0.15 g, 89.2%) as a
bright orange powdery solid; mp 150 ◦C (dec.); dH (MeOH-d4):
3.65 (6H, m, 2 × CHCH2), 3.25 (4H, s, 5ꢀ-, 6ꢀ-H2); dC (MeOH-d4):
114.8, 112.6 (sp2-C), 65.0 (2 × CH2O), 45.9 (5, 6-C), 31.1 (5ꢀ-,
6ꢀ-C); mmax (KBr): 3401, 2919, 2861, 1451, 1417, 1298, 1167, 1026,
1005, 884, 773; m/z (AP): 445 ([M + H]+, 100), 357 (51); HRMS
(EI): found: 443.8605, C12H12O2S8 requires: 443.8603.
trans-5,6-Bis(hydroxymethyl)-5,6-dihydro-1,3-dithiolo[4,5-b]-
1,4-dithiin-2-thione, 35. A mixture of (E)-but-2-en-1,4-diol34
(1.50 g, 17.0 mmol) and trithione 24 (2.23 g, 11.3 mmol) in toluene
(220 ml) was refluxed for 5 h. The solvent was removed under
reduced pressure and the residue purified by flash chromatography
(1 : 1 cyclohexane–ethyl acetate) to give 35 as a brown powdery
solid (1.33 g, 41.2%); mp 110–112 ◦C; dH (MeOH-d4): 3.80 (6H, m,
5-, 6-H & 2 × CH2O); dC (MeOH-d4): 209.5 (2-C), 122.7 (3a-, 7a-
C), 64.9 (2 × CH2OH), 45.4 (5-, 6-C); mmax (KBr): 3260, 2931, 2872,
1485, 1459, 1070, 1041, 1019; found C, 29.6, H, 2.8%, C7H8O2S5
requires C, 29.6, H, 2.8%.
cis-5,6-Bis(hydroxymethyl)-5,6-dihydro-1,3-dithiolo[4,5-b]-1,4-
dithiin-2-thione, 4629,33
. A mixture of cis-but-2-en-1,4-diol
(1.70 ml, 20.4 mmol) and the trithione 24 (2.00 g, 10.2 mmol)
in toluene (200 ml) was refluxed for 5 h. The solvent was
removed under reduced pressure and the residue purified by flash
chromatography (1 : 1 cyclohexane–ethyl acetate) to give 5 as a
trans-5,6-Bis(acetyloxymethyl)-5,6-dihydro-1,3-dithiolo[4,5-b]-
1,4-dithiin-2-thione, 36. Acetic anhydride (0.70 ml, 7.40 mmol)
This journal is
The Royal Society of Chemistry 2007
Org. Biomol. Chem., 2007, 5, 3172–3182 | 3179
©

View Article Online
bright yellow powder (1.10 g, 38.0%); dH: 4.96 (2H, s, 2 × OH),
4.06 (4H, m, 5-, 6-H & 2 × CHaO), 3.91 (2H, m, 2 × CHbO); dC:
209.9 (2-C), 122.7 (3a-, 7a-C), 63.0 (2 × CH2OH), 45.4 (5-, 6-C);
mmax (KBr): 3218, 2938, 1494, 1459, 1069, 1041, 1017, 894.
solution (10 ml) was stirred under N2 for 60 h. The solution was
neutralised by the addition of solid NaHCO3. The organic layer
was collected, dried (Na2SO4) and evaporated to afford 21 (0.08 g,
73.3%) as an orange–brown solid; mp 154–155 ◦C; dH (MeOH-d4):
3.83 (2H, m, 5ꢀ-, 6ꢀ-H), 3.64 (10H, m, 5-, 6-H & 5-, 6-, 5ꢀ, 6ꢀ-CH2O);
dC (MeOH-d4): 113.1, 112.3, (sp2-C), 65.0 (5-, 6-CH2O), 63.0 (5ꢀ,
6ꢀ-CH2O) 45.9 (5-, 5ꢀ-, 6-, 6ꢀ-C); mmax (KBr): 3378, 2912, 2862,
1654, 1384, 1179, 1028; m/z (AP): 505 ([M + H]+, 22); HRMS
(EI): found: 503.8817, C14H16O4S8 requires: 503.8814.
cis-5,6-Bis(tert-butyldiphenylsilyloxymethyl)-5,6-dihydro-1,3-
dithiolo[4,5-b]-1,4-dithiin-2-thione, 47. To a solution of 46
(2.00 g, 7.04 mmol) in dry DMF (120 ml) was added sequen-
tially imidazole (9.59 g, 140.8 mmol) and tert-butyldiphenylsilyl
chloride (4.51 ml, 17.6 mmol). After stirring at room temperature
overnight, water (100 ml) and dichloromethane (200 ml) were
added, the dichloromethane layer separated, and the aqueous
layer extracted twice more with dichloromethane (2 × 40 ml).
The combined organic solution was washed sequentially with ice-
cold HCl (3 M, 3 × 50 ml) and water (50 ml) and dried over
MgSO4. The solvent was removed under reduced pressure and
the residue purified by flash chromatography (dichloromethane)
to afford 47 as an orange oil (2.67 g, 49.8%); dH: 7.75 (8H, m,
Ar-H8), 7.50 (12H, m, Ar-H12), 4.06 (6H, m, 2 × CH2O, 5-, 6-H),
1.15 (18H, s, 2 × C(CH3)2); dC: 207.8 (2-C), 135.4, 132.4, 129.9,
127.8 (Ar-C24), 121.4 (3a-, 7a-C), 63.5 (2 × CH2O), 47.9 (5, 6-C),
26.7 (2 × C(CH3)3), 19.0 (2 × C(CH3)3); mmax (thin film): 2933,
2922, 2856, 1720, 1470, 1427, 1273, 1113, 1067, 823, 739, 701, 614;
m/z (AP): 778 ([M + H2O]+, 38), 249 (100); HRMS (EI): found:
760.1473, C39H44O2S5 Si2 requires: 760.1483.
Reaction of trithione 24 with alkene 54. A mixture of the
diketal 5436 (0.50 g, 2.20 mmol) and the trithione 24 (0.86 g,
4.40 mmol) in toluene (25 ml) was refluxed for 8 h. The
solvent was removed under reduced pressure and the residue
purified by flash chromatography (5 : 1 cyclohexane–ethyl ac-
etate) to elute 5R,6R-5,6-bis((4ꢀR)-2ꢀ,2ꢀ-dimethyl-1,3-dioxolan-
4ꢀ-yl)-5,6-dihydro-1,3-dithiolo[4,5-b]1,4-dithiin-2-thione 55 as a
yellow solid (0.28 g, 30.0%), mp 164–165 ◦C; dH (400 MHz): 4.45
(2H, m, 2 × CHO), 4.18 (2H, dd, J = 9.1, 6.0, 2 × CHaHO),
4.03 (2H, dd, J = 9.1, 4.2, 2 × CHHbO), 3.71 (2H, d, J = 9.8, 5-,
6-H), 1.41 (6H, s, 2 × CH3), 1.33 (6H, s, 2 × CH3); dC (100 MHz):
206.5 (2-C), 118.9 (3a-, 7a-C), 110.6 (2 × 2ꢀ-C), 75.9 (2 × 4ꢀ-C),
67.8 (2 × 5ꢀ-C), 44.3 (5, 6-C), 27.1 (2 × CH3), 25.3 (2 × CH3);
mmax (KBr): 2988, 2935, 1488, 1458, 1377, 1368, 1235, 1148, 1066,
830; m/z (AP): 425 ([M + H]+, 31), 177 (100); HRMS (ES): found:
425.0038 [M + H]+, C15H20O4S5 + H requires: 425.0035; [a]D25
=
cis-5,6-Bis(tert-butyldiphenylsilyloxymethyl)-5,6-dihydro-1,3-
dithiolo[4,5-b]-1,4-dithiin-2-one, 48. To a solution of thione 47
(2.50 g, 3.28 mmol) in CHCl3 (60 ml) and glacial acetic acid
(20 ml) was added mercuric acetate (1.57 g, 4.92 mmol). After 2 h
stirring at room temperature the mixture was filtered. The filtrate
was washed consecutively with saturated NaHCO3 solution (3 ×
100 ml) and H2O (100 ml), dried (Na2SO4) and evaporated to
afford 48 as an orange oil (2.37 g, 97.0%); dH: 7.80 (8H, m, Ar-
H8), 7.49 (12H, m, Ar-H12), 4.10 (6H, m, 2 × CH2O, 5-, 6-H), 1.18
(18H, s, 2 × C(CH3)3); dC: 188.5 (2-C), 135.2, 132.3, 129.6, 127.5
(Ar-C24), 111.3 (3a-, 7a-C), 63.5 (2 × CH2O), 48.9 (5-, 6-C), 26.5
(2 × C(CH3)3), 18.9 (2 × C(CH3)3); mmax (thin film): 3075, 2955,
2932, 2856, 1682, 1627, 1471, 1427, 1112, 823, 738, 700; found C,
62.5, H, 5.8%, C39H44O3S4Si2 requires C, 62.9, H, 6.0%.
+489 (c = 0.12, DCM). Further elution with 1 : 1 cyclohexane–
ethyl acetate gave a second fraction containing 56 and starting
material 54 which was further purified by flash chromatography
(dichloromethane) to give a yellow oil, which on trituration with
ether gave 5S,6S-5,6-bis((4ꢀR)-2ꢀ,2ꢀ-dimethyl-1,3-dioxolan-4ꢀ-yl)-
5,6-dihydro-1,3-dithiolo[4,5-b]1,4-dithiin-2-thione 56 as a yellow
◦
solid (0.05 g, 5.4%); mp 96–98 C; dH: 4.42 (2H, m, 2 × CHO),
4.12 (2H, dd, J = 8.7, 6.4, 2 × CHaHO), 3.86 (2H, dd, J = 8.7,
5.8, 2 × CHHbO), 3.46 (2H, m, 5-, 6-H), 1.44 (6H, s, 2 × CH3),
1.33 (6H, s, 2 × CH3); dC: 208.8 (2-C), 128.3 (3a-, 7a-C), 110.3
(2 × 2ꢀ-C), 75.8 (2 × 4ꢀ-C), 66.9 (2 × 5ꢀ-C), 51.7 (5-,6-C), 26.4 (2 ×
CH3), 25.0 (2 × CH3); mmax (KBr): 2990, 2929, 2877, 1464, 1380,
1269, 1212, 1154, 1052, 1024, 966, 920, 853, 514; [a]2D5 = −143 (c =
0.36, DCM); m/z (EI): 424 (M+, 8), 101 (38), 84 (30), 76 (24), 72
(28), 49 (38), 43 (100); HRMS (ES): found 425.0041, C15H20O4S5 +
H+ requires: 425.0038.
cis-Bis(tert-butyldiphenylsilyloxymethyl)-trans-bis(acetyloxy-
methyl)-ET, 53. A mixture of oxo compound 47 (2.37 g,
3.19 mmol) and thione 36 (1.20 g, 3.26 mmol) were heated in
triethyl phosphite (30 ml) to 90 ◦C under N2 for 5 h to give an
orange solution. Triethyl phosphite was removed by distillation
in vacuo and the residue purified by flash chromatography (5 : 1
cyclohexane–ethyl acetate) to yield 53 as an orange oil (0.68 g,
20.0%) from the second orange band; dH: 7.70 (8H, m, Ar-H8),
7.40 (12H, m, Ar-H12), 4.33 (2H, m, 5ꢀ, 6ꢀ-H), 3.80 (10H, m, 5-,
6-H & 5-, 6-, 5ꢀ, 6ꢀ-CH2O), 2.10 (6H, s, 2 × COCH3), 1.01 (18H, s,
Crystal data for 56. C15H20O4S5, Mr = 424.61, orthorhom-
˚
bic, a = 9.3614(7), b = 10.3321(4), c = 20.0889(15) A, V =
3
−3
˚
1943.1(2) A , Z = 4, P212121, Dc = 1.45 g cm , l(MoKa) =
0.061 mm−1, T = 120(2) K, 2508 unique reflections, 2239 with
F > 4r(F), R = 0.061, wR = 0.098. The structure was solved and
refined using the SHELXS and SHELXL computer packages.44
CCDC reference number 230196. For crystallographic data in CIF
or other electronic format see DOI: 10.1039/b709823e
=
2 × C(CH3)2); dC: 170.2 (2 × C O), 135.5, 132.5, 129.8, 127.7 (Ar-
5R,6R-5,6-Bis((4ꢀR)-2ꢀ,2ꢀ -dimethyl-1,3-dioxolan-4ꢀ -yl)-5,6-di-
hydro-1,3-dithiolo[4,5-b]-1,4-dithiin-2-one, 57. To a solution of
55 (0.47 g, 1.10 mmol) in CHCl3 (20 ml) and glacial acetic acid
(6 ml) was added mercuric acetate (0.53 g, 1.65 mmol). After 2 h
stirring at room temperature the mixture was filtered. The filtrate
was washed consecutively with saturated NaHCO3 solution (3 ×
50 ml) and H2O (50 ml), dried (Na2SO4) and evaporated to afford
57 as an orange solid (0.38 g, 84.0%); mp 116–118 ◦C; dH: 4.51
(2H, m, 2 × 4ꢀ-H), 4.20 (2H, dd, J = 8.9, 6.1, 2 × 5ꢀ-Ha), 4.04 (2H,
C24), 113.7, 112.0, 110.4, 109.3 (sp2-C), 64.8 (5, 6-CH2O), 63.7 (5ꢀ,
6ꢀ-CH2O), 48.3 (5-, 6-C), 40.7 (5ꢀ-, 6ꢀ-C) 26.7 (2 × C(CH3)3), 20.7
(2 × COCH3), 19.0 (2 × C(CH3)3); mmax (thin film): 2955, 2922,
2856, 1749, 1721, 1462, 1428, 1380, 1273, 1224, 1114, 1073, 1034,
739, 701; m/z (AP): 1065 ([M]+, 2), 893 (3), 565 (15), 383 (100);
HRMS (EI): found: 1065.1469, C50H56O6S8Si2 requires: 1065.1459.
cis,trans-Tetrakis(hydroxymethyl)-ET, 21. A solution of 53
(0.23 g, 0.22 mmol) in a mixture of THF (20 ml) and 20% HCl
3180 | Org. Biomol. Chem., 2007, 5, 3172–3182
This journal is
The Royal Society of Chemistry 2007
©

View Article Online
dd, J = 9.2, 4.2, 2 × 5ꢀ-Hb), 3.71 (2H, d, J = 9.9, 5-, 6-H), 1.42
(6H, s, 2 × CH3), 1.34 (6H, s, 2 × CH3); dC: 188.9 (2-C), 110.6
(2 × 2ꢀ-C), 109.6 (3a-, 7a-C), 76.1 (2 × 4ꢀ-C), 68.0 (2 × 5ꢀ-C), 45.7
(5, 6-C), 27.1 (2 × CH3), 25.4 (2 × CH3); mmax (KBr): 2988, 2935,
1683, 1381, 1372, 1260, 1245, 1229, 1214, 1074, 822; [a]2D5 = +206
(c = 0.14, DCM); m/z (EI): 408 (100, M+), 393 (15, [M − 15]+);
HRMS (EI): found 408.0190, C15H20O5S4 requires 408.0188.
R,R,R,R-Tetrakis((2ꢀꢀR)-1ꢀꢀ,2ꢀꢀ-dihydroxyethyl)-ET, 23. Tetra-
ketal 33 (40 mg, 0.051 mmol) was stirred with a mixture of aq.
HCl (4 M, 1.5 ml) and THF (11 ml) under nitrogen for 24 h.
Evaporation and drying in vacuo gave the tetrol 23 (26 mg, 82%)
as a brown–buff powder, mp >330 ◦C (some contraction at 170–
172 ◦C). dH (400 MHz, DMSO-d6 + one drop D2O): 3.61 (16H, m,
4 × SCH-CH(OH)-CH2OH); dC (100 MHz, DMSO-d6): 110.5 &
109.8 (3a-, 3aꢀ-, 7a-, 7aꢀ-C & 2ꢀ,2ꢀ-C), 71.8 (4 × -CH(OH)), 63.3
(4 × -CH2OH), 42.7 (5-, 5-ꢀ, 6-, 6ꢀ-C); mmax (KBr): 3254 br, 2962,
1404, 1259, 1082, 1013, 869, 792, 700, 676, 661; [a]2D5 = +187.5 (c =
0.048 in DMF); m/z (ES+): 647 ([M + Na], 3), 279 (20), 171 (23),
47 (100); m/z (ES−) 659 ([M + CH3OH], 4), 623 ([M − H], 6),
475 (5), 311 (8), 228 (14), 227 (15), (226, 14), 179 (12), 127 (5), 69
(100); HRMS (ES+): found: 624.9315, C18H24O8S8 + H requires:
624.9310; found C: 34.5, H: 4.1%, C18H24O8S8 requires C: 34.6, H:
3.9%.
R,R-vic-Bis((4ꢀꢀR)-2ꢀꢀ,2ꢀꢀ-dimethyl-1ꢀꢀ,3ꢀꢀ-dioxolan-4ꢀꢀ-yl)-ET, 58.
A mixture of oxo compound 57 (0.10 g, 0.25 mmol) and the thione
28 (0.08 g, 0.37 mmol) was heated in triethyl phosphite (5 ml)
to 90 ◦C under N2 for 5 h to give an orange solution. Triethyl
phosphite was removed by distillation in vacuo and the residue
purified by flash chromatography (3 : 1 cyclohexane–ethyl acetate)
◦
to yield 58 as an orange solid (0.05 g, 34.9%); mp 88–90 C; dH:
4.37 (2H, m, 2 × 4ꢀꢀ-H), 4.13 (2H, dd, J = 9.1, 5.9, 2 × 5ꢀꢀ-Ha),
4.00 (2H, dd, J = 9.1, 4.4, 2 × 5ꢀꢀ-Hb), 3.67 (2H, dd, J = 8.9, 1.0,
5-, 6-H), 3.26 (4H, s, 5ꢀ, 6ꢀ-H2), 1.40 (6H, s, 2 × CH3), 1.32 (6H, s,
2 × CH3); dC: 113.9, 112.3, 110.4 (sp2-C), 109.9 (2 × 2ꢀꢀ-C), 76.5
(2 × 4ꢀꢀ-C), 68.0 (2 × 5ꢀꢀ-C), 44.9 (5, 6-C), 30.2 (5ꢀ, 6ꢀ-C), 27.1 (2 ×
CH3), 25.4 (2 × CH3); mmax (KBr): 2978, 2916, 1654, 1650, 1638,
1618, 1560, 1510, 1456, 1384, 1368, 1249, 1213, 1145, 1062, 1016,
922, 834, 766, 507; [a]2D5 = +51.2 (c = 0.13, DCM); m/z (EI): 584
(M+, 2), 356 (5), 132 (9), 101 (14), 88 (23) 43 (100); HRMS (ES):
found: 584.9507, C20H24O4S8 + H+ requires: 584.9513; found C:
41.0, H: 4.0%, C20H24O4S8 requires C: 41.1, H: 4.1%.
Acknowledgements
We thank the EPSRC, Nottingham Trent University and the Royal
Institution of Great Britain for studentships (RJB, ACB, JPG) and
support. We thank the EPSRC Mass Spectrometry Service and
the EPRSC National Crystallography Service for data, and the
EPSRC Chemical Database Service45 for access to the Cambridge
Crystallographic Database.46
References
R,R-vic-Bis((2ꢀꢀR)-1ꢀꢀ,2ꢀꢀ-dihydroxyethyl)-ET, 22. Diketal 58
(60 mg, 0.12 mmol) was stirred with a mixture of aq. HCl (4 M,
4 ml) and THF (8 ml) under nitrogen for 12 h. Evaporation and
drying in vacuo gave the tetrol 22 (49 mg, 94%) as a buff powder, mp
201–202 ◦C; dH (DMSO-d6): 3.82 (2H, br d, J = 9.5, 5-, 6-H), 3.67
(2H, d, J = 10.2, 2 × CHaHbO), 3.60 (6H, m, 2 × CHCHaHbOH),
3.34 (4H, s, 5ꢀ, 6ꢀ-H2); dC (DMSO-d6): 112.9, 110.5, 110.0, 109.9
(sp2-C), 71.8 (2 × -CH(OH)), 63.3 (2 × -CH2OH), 42.7 (5, 6-C),
29.5 (5ꢀ, 6ꢀ-C); mmax (KBr): 3293, 2920, 1425, 1329, 1296, 1259,
1 M. R. Bryce, J. Mater. Chem., 2000, 10, 589; M. R. Bryce, Adv. Mater.,
1999, 11, 11; M. R. Bryce, W. Devonport, L. M. Goldenberg and C.
Wang, Chem. Commun., 1998, 945; M. Herranz, L. Sanchez and N.
Martin, Phosphorus, Sulfur Silicon Relat. Elem., 2005, 180, 1133; J. L.
Segura and N. Martin, Angew. Chem., Int. Ed., 2001, 40, 1372.
2 J. Singleton, C. Mielke and J. Singleton, Contemp. Phys., 2002, 43, 63;
J. Singleton, C. Mielke and J. Singleton, Phys. World, 2002, 35; P. Day,
C. R. Chim., 2003, 6, 301.
3 J. M. Williams, A. J. Schultz, U. Geiser, K. D. Carlson, A. M. Kini,
H. M. Wang, W. K. Kwok, M. H. Whangbo and J. E. Shirber, Science,
1991, 252, 1501; M. H. Whangbo and C. C. Torardi, Acc. Chem.
Res., 1991, 24, 127; T. Ishiguo, K. Yamaji and G. Saito, Organic
Superconductors, Springer Verlag, Berlin, 1998.
1182, 1109, 1078, 1051, 1026, 958, 870, 818, 766, 626, 523; [a]D25
=
+69 (c = 0.035, THF); m/z (EI): 504 (M+, 1); HRMS (EI): found:
503.8818, C14H16O4S8 requires: 503.8809; found C: 33.3, H: 3.4%,
C14H16O4S8 requires C: 33.3, H: 3.2%.
4 M. Kurmoo, A. W. Graham, P. Day, S. J. Coles, M. B. Hursthouse,
J. L. Caulfield, J. Singleton, F. L. Pratt, W. Hayes, L. Ducassse and P.
Guionneau, J. Am. Chem. Soc., 1995, 117, 12209.
5 E. Coronado, J. R. Gala´n-Mascaros, C. J. Gomez-Garcia and V.
Laukhin, Nature, 2000, 408, 447; E. Coronado and P. Day, Chem. Rev.,
2004, 104, 5419; E. Coronado and J. R. Gala´n-Mascaros, J. Mater.
Chem., 2005, 15, 66.
6 J. Singleton, N. Harrison, M. M. Honold, H. Yaguchi, C. Mielke, D.
Rickel, I. Deckers, P. H. P. Reinders, F. Herlach, M. Kurmoo and P. Day,
Physica B (Amsterdam), 1998, 246, 6; H. Yaguchi, N. Harrison, M. M.
Honold, C. Mielke, J. Singleton, P. J. Gee, D. Rickel, I. Deckers, P. H. P.
Reinders, F. Herlach, M. Kurmoo and P. Day, Physica B (Amsterdam),
1998, 251, 75; M. M. Honold, N. Harrison, M. V. Katsovnik, H.
Yaguchi, J. Singleton, C. H. Mielke, N. D. Kushch, M. Kurmoo and P.
Day, Phys. Rev. B: Condens. Matter, 2000, 62, 7908.
7 J.-P. Griffiths and J. D. Wallis, J. Mater. Chem., 2005, 15, 347.
8 J.-P. Griffiths, A. A. Arnal, G. Appleby and J. D. Wallis, Tetrahedron
Lett., 2004, 45, 2813.
9 R. J. Brown, G. Cameresa, J.-P. Griffiths, P. Day and J. D. Wallis,
Tetrahedron Lett., 2004, 45, 5103.
R,R,R,R-Tetrakis((4ꢀꢀR)-2ꢀꢀ,2ꢀꢀ-dimethyl-1ꢀꢀ,3ꢀꢀ -dioxolane-4ꢀꢀ -yl)-
ET, 59. Oxo compound 57 (0.19 g, 0.46 mmol) was heated in
triethyl phosphite (3 ml) to 90 ◦C under N2 for 18 h to give an
orange solution. Triethyl phosphite was removed by distillation
in vacuo and the residue purified by flash chromatography (8 :
1 cyclohexane–ethyl acetate) to yield 59 as a pale orange solid
(0.11 g, 60.2%); mp 176–178 ◦C (dec.); dH: 4.38 (4H, m, 4 × 4ꢀꢀ-H),
4.18 (4H, dd, J = 9.0, 6.0, 4 × 5ꢀꢀ-Ha), 4.03 (4H, dd, J = 9.0, 4.3,
4 × 5ꢀꢀ-Hb), 3.70 (4H, dd, J = 11.8, 2.0, 5-,6-, 5ꢀ-,6ꢀ-H), 1.43 (12H, s,
4 × CH3), 1.35 (12H, s, 4 × CH3); dC: 111.0 & 109.9 (2-,2ꢀ-C & 3a-,
7a-, 3aꢀ-, 7aꢀ-C), 110.4 (4 × 2ꢀꢀ-C), 76.0 (4 × 4ꢀꢀ-C), 68.0 (4 × 5ꢀꢀ-C),
44.9 (5-, 6-, 5ꢀ-, 6ꢀ-C), 27.1 (4 × CH3), 25.4 (4 × CH3); mmax (KBr):
2986, 2933, 2880, 1458, 1382, 1371, 1248, 1215, 1150, 1065, 970,
923, 836, 774, 513; [a]2D5 = +65.3 (c = 0.15, DCM); m/z (APCI):
785 ([M + 1]+, 25), 727 (24), 569 (100), 73 (58); HRMS (EI): found:
784.0485, C30H40O8S8 requires: 784.0483; found C: 46.0, H: 5.1%,
C30H40O8S8 requires C: 45.9, H: 5.1%.
10 B. Y. Khodorkovskii, G. Pukitis, A. Y. Puplovskii, A. Edzina and O. Y.
Neilands, Khim. Geterotsikl. Soedin., 1990, 131.
11 J.-P. Griffiths, H. Nie, R. J. Brown, P. Day and J. D. Wallis, Org. Biomol.
Chem., 2005, 3, 2155.
12 J. S. Zambounis, C. W. Mayer, K. Hauenstein, B. Hilti, W. Hofherr, J.
Pfeiffer, M. Buerkle and G. Rihs, Adv. Mater., 1992, 4, 33; S. Kimura,
This journal is
The Royal Society of Chemistry 2007
Org. Biomol. Chem., 2007, 5, 3172–3182 | 3181
©

View Article Online
T. Maejima, H. Suzuki, R. Chiba, H. Mori, T. Kawamoto, T. Mori, H.
Moriyama, Y. Nishio and K. Kajita, Chem. Commun., 2004, 2454.
13 J. D. Dunitz, A. Karrer and J. D. Wallis, Helv. Chim. Acta, 1986, 69, 69;
A. Karrer, J. D. Wallis, J. D. Dunitz, B. Hilti, C. W. Mayer, M. Bu¨rkle
and J. Pfeiffer, Helv. Chim. Acta, 1987, 70, 942.
14 O. J. Dautel and M. Fourmigue´, J. Chem. Soc., Perkin Trans. 1, 2001,
3399.
8163; W. Devonport, M. R. Bryce, G. J. Marshallsay, A. J. Moore and
L. M. Goldenberg, J. Mater. Chem., 1998, 8, 1361.
26 N. Saygili, R. J. Brown, P. Day, R. Hoelzl, P. Kathirgamanathan, E. E. R.
Mageean, T. Ozturk, M. Pilkington, M. M. B. Qayyum, S. S. Turner,
L. Vorwerg and J. D. Wallis, Tetrahedron, 2001, 57, 5015.
27 H. Li, D. Zhang, B. Zhang, Y. X. Yao, W. Xu, D. Zhu and Z. Wang,
J. Mater. Chem., 2000, 10, 2063.
15 A. I. Kotov, C. Faulmann, P. Cassoux and E. B. Yagubskii, J. Org.
28 F. Leurquin, T. Ozturk, M. Pilkington and J. D. Wallis, J. Chem. Soc.,
Perkin Trans. 1, 1997, 3173.
Chem., 1994, 59, 2626.
16 V. I. Troitsky, T. S. Berzina, E. Dalcanale and M. P. Fontana, Thin Solid
Films, 2002, 405, 276.
17 J.-P. Griffiths, R. J. Brown, B. Vital, P. Day, C. J. Matthews and J. D.
Wallis, Tetrahedron Lett., 2003, 44, 3127.
18 Q. Wang, H. Nie, J. P. Griffiths, P. Day and J. D. Wallis, New J. Chem.,
2006, 1790.
29 H. Li, D. Zhang, W. Xu, L. Fan and D. Zhu, Synth. Met., 1999, 106,
111; K. Balodis, J. Kacens, J. Kraupsa, A. Edzina and O. Y. Neilands,
Latv. Kim. Z., 1991, 627.
30 T. Ozturk, N. Saygili, S. Oskara, M. Pilkington, C. R. Rice, D. A.
Tranter, F. Turksoy and J. D. Wallis, J. Chem. Soc., Perkin Trans. 1,
2001, 407.
19 K. Heuze, M. Fourmigue´ and P. Batail, J. Mater. Chem., 1999, 9, 2373;
C. Rethore, M. Fourmigue´ and N. Avarvari, Chem. Commun., 2004,
1384.
20 H. Kobayashi, B. Zhang, H. Tanaka, T. Otsuka, E. Fujiwara and A.
Kobayashi, Synth. Met., 2003, 137, 1157; B. Zhang, H. Tanaka, H.
Fujiwara, H. Kobayashi, E. Fujimwara and A. Kobayashi, J. Am.
Chem. Soc., 2002, 124, 9982; S. Uji, H. Shinagawa, T. Tereshima, T.
Yakabe, Y. Teral, M. Tokumoto, A. Kobayashi, H. Tanaka and H.
Kobayashi, Nature, 2001, 410, 908.
21 T. Otsubo and K. Takimiya, Bull. Chem. Soc. Jpn., 2004, 77, 43;
K. Takimiya, T. Jigami, M. Kawashima, M. Kodani, Y. Aso and T.
Otsubo, J. Org. Chem., 2002, 67, 4218; M. Kodani, K. Takimiya, Y.
Aso, T. Otsubo, T. Nakayashiki and Y. Misaki, Synthesis, 2001, 1614;
A. Chesney, M. R. Bryce, S. Yoshida and I. F. Perepichka, Chem. Eur. J.,
2000, 6, 1153.
31 G. A. Horley, T. Ozturk, F. Turksoy and J. D. Wallis, J. Chem. Soc.,
Perkin Trans. 1, 1998, 3225.
32 S.-X. Liu, A. Neels, H. Stoeckli-Evans, M. Pilkington, J. D. Wallis and
S. Decurtins, Polyhedron, 2004, 23, 1185.
33 O. Y. Neilands, Y. Y. Katsens and Y. N. Kreitsberga, Zh. Org. Khim.,
1989, 25, 658.
34 J. V. Schoss and F. C. Hartman, Bioinorg. Chem., 1980, 9, 217.
35 A. M. Kini, J. P. Parakka, U. Geiser, H.-H. Wang, F. Rivas, E. DiNino,
S. Thomas, J. D. Dudek and J. M. Williams, J. Mater. Chem., 1999, 9,
883.
36 F. W. Eastwood, K. J. Harrrington, J. S. Josan and J. L. Pupra,
Tetrahedron Lett., 1970, 21, 5223; R. S. Tipson and A. Cohen,
Carbohydr. Res., 1968, 7, 232.
37 J. D. Wallis and J. D. Dunitz, Acta Crystallogr., Sect. C: Cryst. Struct.
Commun., 1988, 44, 1037.
22 J. Garin, J. Orduna, S. Uriel, A. J. Moore, M. R. Bryce, S. Wegener,
D. S. Yufit and J. A. K. Howard, Synthesis, 1994, 489.
23 P. Hudhomme, S. Le Moustardier, C. Durand, N. Gallego-Planas, N.
Mercier, P. Blanchard, E. Levillain, M. Allain, A. Gorgues and A. Riou,
Chem. Eur. J., 2001, 7, 5070.
38 T. Ozturk, D. C. Povey and J. D. Wallis, Tetrahedron, 1994, 50,
11205.
39 G. L. J. A. Rikken, E. Raupach, V. Krstic and S. Roth, Mol. Phys., 2002,
100, 1155; V. Krstic, S. Roth, M. Burghard, K. Kern and G. L. J. A.
Rikken, J. Chem. Phys., 2002, 117, 11315; V. Krstic and G. L. J. A.
Rikken, Chem. Phys. Lett., 2002, 364, 51.
40 N. Svenstrup and J. Becher, Synthesis, 1995, 215.
41 P. Cagniant and D. Cagniant, Bull. Soc. Chim. Fr., 1967, 2597.
42 H. Wynberg and J. Metselaar, Synth. Commun., 1984, 14, 1.
43 Y. Tschuiya, T. Nomoto, M. Hayashi, Y. Iwasawa, H. Masaki, M.
Ohkubo, Y. Sakuma, Y. Nagata, T. Satoh and T. Kamei, Eur. Pat.
Appl., 1991, EP 448078A2.
44 G. M. Sheldrick, SHELXS-97 and SHELXL-97, Computer Programs
for the Solution and Refinement of Crystal Structures, University of
Go¨ttingen, Germany, 1997.
24 S. Perruchas, K. Boubekeur and P. Batail, Cryst. Growth Des., 2005,
5, 1585; S. Perruchas, K. Boubekeur and P. Molinie, Polyhedron, 2005,
24, 1555; A. Dolbecq, A. Guirauden, M. Formigue´, K. Boubekeur,
P. Batail, M. M. Rohmer, M. Benard, C. Coulon, M. Salle´ and P.
Blanchard, J. Chem. Soc., Dalton Trans., 1999, 1241; S. G. Liu, M.
Cariou and A. Gorgues, Tetrahedron Lett., 1998, 39, 8663; T. Inoue, H.
Yamochi, G. Saito and K. Matsumoto, Synth. Met., 1995, 70, 1139.
25 M. A. Herranz, N. Martin, S. Campidelli, M. Prato, G. Brehm and
D. M. Guldi, Angew. Chem., Int. Ed., 2006, 45, 4478; J. Lyskawa, M.
Salle´, H.-Y. Balandier, F. Le Derf, E. Levillain, M. Allain, P. Viel and
S. Palacin, Chem. Commun., 2006, 2233; A. Y. Ziganshina, Y. H. Ko,
W. S. Jeon and K. Kim, Chem. Commun., 2004, 806; D. Kreher, M.
Cariou, D. G. Liu, E. Levillain, J. Veciana, C. Rovira, A. Gorgues
and P. Hudhomme, J. Mater. Chem., 2002, 12, 2137; G. Cooke, M. A.
Florence, V. M. Rotello and J. F. Stoddart, Tetrahedron Lett., 2000, 41,
45 D. A. Fletcher, R. F. McMeeking and D. J. Parkin, ‘The United
Kingdom Chemical Database Service’, Chem. Inf. Comput. Sci., 1996,
36, 746.
46 F. H. Allen, ‘Cambridge Structural Database’, Acta Crystallogr., Sect.
B: Struct. Sci., 2002, 58, 380.
3182 | Org. Biomol. Chem., 2007, 5, 3172–3182
This journal is
The Royal Society of Chemistry 2007
©