Synthetic strategies to chiral organosulfur donors related to bis(ethylenedithio)tetrathiafulvalene

Article abstract of DOI:10.1039/b502437d

Syntheses of enantiopure organosulfur donors by three different strategies requiring only four-six steps are reported. The key step involves either double substitution of an enantiopure cyclic sulfate ester by a dithiolate, attachment of a chiral diol as

Full text of DOI:10.1039/b502437d

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A R T I C L E
Synthetic strategies to chiral organosulfur donors related to
bis(ethylenedithio)tetrathiafulvalene
Jon-Paul Griffiths,a Hui Nie,a R. James Brown,a,b Peter Dayb and John D. Wallis*a
a School of Biomedical and Natural Sciences, Nottingham Trent University, Clifton Lane,
Nottingham, UK NG11 8NS. E-mail: john.wallis@ntu.ac.uk; Fax: 0115-848-6636;
Tel: 0115-848-3149
b The Royal Institution of Great Britain, 21 Albemarle St., London, UK W1S 4BS
Received 21st February 2005, Accepted 5th April 2005
First published as an Advance Article on the web 28th April 2005
Syntheses of enantiopure organosulfur donors by three different strategies requiring only four–six steps are reported.
The key step involves either double substitution of an enantiopure cyclic sulfate ester by a dithiolate, attachment of a
chiral diol as a ketal, or completely diastereoselective cycloaddition of 1,3-dithiole-2,4,5-trithione to an enantiopure
alkene.
or all Kenantiomers, but in the latter the anion layers contain an
ordered array of both D and K enantiomers, which is sufficient
Introduction
to alter the packing arrangement of the ET molecules from bꢀꢀ to
pseudo-j via weak hydrogen bonding interactions. Interestingly,
the former is prepared from racemic Cr(C2O4)33−, but the latter
from enantiopure material which subsequently racemised.
We have reported the synthesis of two new enantiopure donors
from chiral pool materials, though the syntheses involve at least
ten steps. The hydroxymethyl–ET, R-HMET, 7 was prepared
from D-mannitol, the key step being double substitution of the
enantiopure cyclic sulfate ester 5 by dithiolate 4 to give the
thione 6 (Scheme 1).12 Similarly the 2-fluoro-1-hydroxyethyl–
ET 10 was prepared from the thione 9 which was an unexpected
product of the reaction of dithiolate 4 and the enantiopure cyclic
sulfate ester 8.13 We and others have prepared the enantiopure
donors 11–13, which contain one or more outer eight-membered
rings each with a pair of chirally disposed hydroxyl groups, from
dimethyl L-tartrate,14–15 and Fourmigue´ and Avarvari have pre-
pared the enantiopure ligand 1416 containing the ethylenedithio–
TTF molecular skeleton.
We were interested to expand the range of chiral organosulfur
donors available, to provide further systems for use in investi-
gations of the effects of chirality on electro-magnetic properties.
Here we report syntheses of three such donors 15–17 as single
enantiomers by three different strategies whose key steps are
(a) double substitutions of dithiolate 4 on an enantiopure cyclic
sulfate ester, (b) attachment of a chiral grouping to an achiral
donor and (c) diastereoselective cycloaddition to 1,3-dithiole-
2,4,5-trithione. Each strategy has potential for extension to the
preparation of a wide range of donors, and further results
of the diastereoselective cycloaddition strategy are reported.
Rajca has reported syntheses of alternative chiral building
blocks such as dodecaphenylenes and helical annelated oligoth-
iophenes for preparing conducting materials, wave guides and
molecular glasses.17,18 There have also been significant advances
in preparing chiral conducting polymers19,20 and nanotubes.21
Chiral metals may find applications as novel electrode ma-
terials for chiral electrochemical analysis, while chiral donors
have potential applications in enantioselective chromatographic
media. The first chiral single-molecule magnets have been
reported recently.22
Recently Rikken observed electrical magneto-chiral anisotropy
in individual (chiral) carbon nanotubes, that is the resistance
for current passing through a nanotube in a coaxial magnetic
field depends on the current and magnetic field and the sense of
chirality of the object.1 This is the first experimental indication
of the role of chirality in conduction, this particular effect being
predicted in theoretical studies.2 Recent studies on the radical
cation salts of achiral donor 1 known as BEDT–TTF or ET, with
MHg(SCN)4 (M = K or Tl) as the counterion suggest that in a
magnetic field a chiral surface metal forms, since the electrons
can only move in one direction under these conditions.3,4 Thus,
incorporation of chirality into a ET salt may provide new mate-
rials suitable for further investigations. Well before these results
were known, Dunitz had opened the discussion on whether
chirality might have an effect on electrical conduction, and
prepared the first chiral organic donor, S,S,S,S-tetramethyl–ET
2,5 and characterized several of its radical cation salts though
they adopted pseudo-centrosymmetric crystal structures.6 Hilti
and Zambounis have reported that the j-phase perchlorate salt
of the enantiopure dimethyl–ET 3 becomes superconducting
at 2 K7 and Sugawara and Kawada have reported the only
comparison to date of the crystal packing arrangements of a
−
racemic and enantiopure ET derived salt, for the 2 : 1 PF6
salt of 3.8 In both modifications each stack contains only one
enantiomer, and these molecules lie head over tail, but with a
lateral twist of ca. 30◦ in alternate directions along the stack.
Ordered PF6− ions sit in centrosymmetric pockets in the racemic
salt, but in the enantiopure salt the different symmetries of
−
the PF6 anion and the chiral pocket lead to the anion being
orientationally disordered between two positions. In contrast,
Schlueter and collaborators have included chirality in the anion
by making a ET salt with racemic SF5CHFCF2SO3−, however
the anions were orientationally disordered due to the similar
sizes of the H and F atoms at the stereogenic centre.9
A
number of ET salts with racemic tris-oxalato-metallate anions
are known.10,11 Of particular note is Day’s report of two
polymorphs of the racemic salt ET4[(H3O)Cr(C2O4)3]·C6H5CN,
one superconducting and one semiconducting.11 In the former,
the ET layer lies between two anion layers containing either all D
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 5 5 – 2 1 6 6
2 1 5 5
©

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Scheme 1
15 in 47% yield after chromatographic separation from the
homocoupled materials ET 1 and the two inseparable difunc-
tionalised ETs 25 and 26 (Scheme 2). Thesynthesis oftheracemic
donor 15 has been effected in just four steps, preparing the
thione 22 from dithiolate 4 and methyl 3,4-dibromobutanoate.24
We avoided direct attachment of the ester group to the ET
framework, since the stereogenic centre would be vulnerable to
epimerisation in some conditions due to the activating effects of
the carbonyl and sulfur atom on the acidity of the hydrogen atom
at the stereogenic centre. Furthermore, coupling of the diester
functionalised thione compound 27 failed,25 though hetero-
coupling of the corresponding oxo compound 28 and homo-
coupling of oxo compound 29 have been reported.26
Results and discussion
Synthesis of donors 15–17
Since a carboxyl functionality provides opportunities for at-
tachment of further molecular species, as well as functional
group interconversions, we identified donor 15 as an important
target. Starting from dimethyl L-malate, we have prepared this
molecule in six steps, with an overall yield of 10%, requiring
four straightforward chromatographic separations. Dimethyl L-
malate 18 is reduced regioselectively to the diol 19,23 and then
converted into its cyclic sulfate ester 21 in two steps via the
cyclic sulfite ester 20. A double substitution reaction by the
dithiolate 4 gives the bicyclic thione 22 in 35% yield. The thione
22 was converted to the corresponding oxo compound 23 (86%)
using mercuric acetate. Cross coupling with a two fold excess of
unsubstituted thione 24 in triethyl phosphite gave the donor
The attachment of an enantiopure fragment to a side chain is
another approach for introducing chirality, but to avoid produc-
tion of diastereoisomers, this would have to involve a reaction
2 1 5 6
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 5 5 – 2 1 6 6

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Scheme 2 a) BH3SMe2, cat. NaBH4; b) SOCl2, py; c) NaIO4, cat. RuO2; d) 4, MeOH, 0 ◦C, 24 h, then THF 65 ◦C; e) Hg(OAc)2, CHCl3, AcOH; f)
(EtO)3P.
with an enantiopure ET (e.g. by ester exchange on donor 15 with
an enantiopure alcohol)! However, the achiral donor 30, which
has 2-oxopropylene-1,3-dithio bridges instead of ethylenedithio
bridges, is an ideal molecular skeleton since the keto groups can
be converted to ketals with an enantiopure diol, for example,
to give our second target 16. This type of molecule is of
particular interest, since it offers the possibility of building stacks
which must have a continual twist if the chirally disubstituted
dioxolane rings on successive donors are to avoid one another.
It is known that increasing the size of the outer ring of ET
does not alter the oxidation potential too much.27 Enantiopure
diols are available from Sharpless’s asymmetric dihydroxylation
(AD) methodology. In this case we installed the ketal early in
the synthesis by reaction of S,S-1,2-diphenylethane-1,2-diol28,29
with the ketone 31,30 available fromthe zinccomplexof dithiolate
4 and 1,3-dichloroacetone, to give the ketal 32 in 80% yield. The
exchange of thione sulfur for oxygen to give oxo compound
33 was carried out in 95% yield using mercuric acetate in
chloroform and a small amount of acetic acid but for just fifteen
minutes to avoid hydrolysis of the ketal. Finally the donor 16
was obtained in 37% yield by homo-coupling of oxo compound
33 in triethyl phosphite, corresponding to an overall yield of 28%
from the enantiopure diol (Scheme 3).
Although these strategies have considerable scope for prepar-
ing further enantiopure donors, we wanted access to more
complex ET donors. The double substitution of a cyclic sulfate
ester from chiral pool materials has limited potential for the
preparation of such materials, since the cyclisation reaction
is much less effective when there are two larger substituents
on the cyclic sulfate ester. Thus, the double substitution of
the cyclic sulfate esters 34 and 35 gave 5% and 0% yields of
the thione product.31,32 Neilands introduced the cycloaddition
of the highly insoluble trithione 36 with either electron rich
or electron poor alkenes to prepare the thione precursors
Scheme 3 a) CHCl3, cat. TsOH, mol. sieves, reflux; b) Hg (OAc)2, CHCl3, AcOH, 15 min; c) (EtO)3P.
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 5 5 – 2 1 6 6
2 1 5 7

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Scheme 4
for donor synthesis,33 and the reaction has been widely used
en route to preparing many monosubstituted ET derivatives34
e.g. with aminomethyl,35 or hexadecyl36 sidechains, as well as
disubstituted ET derivatives37 and donors with fused carbocyclic
and heterocyclic rings.38 Toluene is often the solvent of choice
and, with long reaction times, leads to the optimum yields in
general. However, the reactions of trithione 36 with enantiopure
alkenes have not been investigated. Thus, we examined the
reaction with several chiral, sterically hindered, alkenes.
in 46% yield, and 48 in 42% yield. Both products are expected to
be mixtures of two diastereoisomers (a and b). However, the less
substituted donor 17, as a single diastereoisomer, was obtained
by cross coupling the oxo compound 44 with the unsubstituted
thione 24 in triethyl phosphite. Indeed this chiral donor 17 was
isolated in a very respectable yield of 42% after separation from
homocoupled donors and ethylated material by chromatography
and washing in methanol. Although donor 17 has a somewhat
bulky spiro substituent, which might be envisaged to disfavour pi
stacking of the organosulfur residues, it should be noted that the
donor DOET 49 which contains a dioxane ring at more or less
right angles to the organosulfur plane, still can form stacks and
Reaction of trithione 36 with monoterpenes (−)-a-pinene 37,
(−)-b-pinene 39 and (+)-2-carene 41 in refluxing toluene gave the
corresponding thiones 38, 40 and 42, as single diastereoisomers
in excellent yields of 80–90%, and with no sign of the second
its 4 : 1 salt with Hg2Cl6 is metallic down to 4 K!40 The size of
2−
1
diastereoisomer on chromatographic separation or in the H
the substituent leads to the molecules lying head to tail in stacks,
with the dioxane rings lying outside the stack. The 2 : 1 AsF6− salt
of the structurally related donor DODHT 50 also shows head to
tail stacks, though with shorter S · · · S contacts between stacks
than within them. Nevertheless, under pressure this material
becomes a metal-like conductor which shows superconductivity
below 3.3 K.41 Furthermore, donor DO–MET 51 forms a 2 :
and 13C NMR spectra of the main products (Scheme 4). The
molecular structures of these three thiones were measured by
single crystal X-ray crystallography.† In each case, the results
show that the trithione 36 has attacked exclusively from the less
hindered side of the alkene. Details of these interesting structures
are discussed later.
−
Thiones 38, 40 and 42 reacted with mercuric acetate in chlo-
roform and acetic acid to furnish the corresponding oxo com-
pounds 43–45 in high yields of 92–95%. Each oxo compound
was heated in triethyl phosphite to form the corresponding
homocoupled BEDT–TTF derivatives (Scheme 5). The most
strained oxo compound 43, however, gave a high yield (87%) of
tetra(ethylthio)–TTF 46, the product of Arbusov reactions. This
is probably due to the adduct undergoing a retro-cycloaddition
in the reaction conditions, as has been observed elsewhere.39 The
other two oxo compounds did yield the desired BEDT–TTF
derivatives. After chromatography they still contained ethylated
material, suggestive of competing Arbusov reactions, but these
products were removed by washing with methanol, to furnish 47
1 salt with AsF6 which is metallic down to 2 K in which the
donors pack head to head with a shift on the long molecular axis
so that the axial dioxolanes lie outside the stack.42 Our initial
attempts to cross couple the oxo compound 45, derived from 2-
carene, and the unsubstituted thione 24 were unsuccessful, due
to difficulties in separating the cross coupled donor from the
products of Arbusov reactions.
Cyclic voltammetry measurements on the enantiopure donors
15–17 and the homocoupled donors 47 and 48 showed two
reversible oxidation potentials (Table 1). The ET derivative 15
shows oxidation peaks typical of a ET system and identical
to those for its racemate,24 while those ET derivatives derived
from b-pinene and 2-carene consistently show lower oxidation
potentials (by ca. 0.06 V). We note that in the donor 52
lower oxidation potentials were also observed. We speculated
tentatively that this may be due to oxidation of associated ET
moieties. The donor 16 with outer seven-membered rings shows
† CCDC reference numbers 230195, 264422 and 264423. See http://
www.rsc.org/suppdata/ob/b5/b502437d/ for crystallographic data in
CIF or other electronic format.
2 1 5 8
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 5 5 – 2 1 6 6

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Scheme 5
mations, the 5-(2-pyridyl) substituted derivative45 prefers the half
chair conformation, and the trans 5,6-dimethyl derivative46 an
intermediate conformation. However, in 27 and 53 which have
two trans carbonyl groups,25,47 the conformations are close to
a boat with both sp3 carbon atoms strongly displaced to the
same side of the organosulfur ring system, though in 27 there is
also a substantial additional twist (ca. 40◦, cf. 11◦ in 53) about
the ring C,C bond. A notable feature of the six-membered ring
system in all cases is the large bond angles at the sp3 carbon
atoms, (111–118◦) which is a consequence of the smaller bond
angles at sulfur. Without the constraints of a six-membered ring,
the bis(alkylthio)dithioles 54 show a range of conformations in
the solid state, with both in-plane and strongly out of plane
orientations for alkyl groups.48
Table 1 Cyclic voltammetry of enantiopure donors, measured in
dichloromethane using 0.1 M tetrabutylammonium hexafluorophos-
phate as the charge carrier
1/2
1/2
Compound
E1
E2
15
0.50
0.56
0.44
0.44
0.43
0.91
0.94
0.85
0.86
0.86
16
17
47a/b
48a/b
an increase of ca. 0.06 V in its first oxidation potential compared
to ET systems, due to the change in the conjugation of the outer
sulfurs with the TTF system.
The molecular structures of the cycloaddition adducts will
be discussed in order of increasing strained structures. The
results are shown with selected geometric data in Figs. 1–5. The
structure of the carene adduct 42 shows that the trithione has
attacked the carene ring system on the face opposite to the
dimethylated cyclopropane ring (Fig. 1). The cyclohexane and
dithiin rings are fused along the C4–C5 bond. The cyclohexane
adopts an envelope conformation with C4 at the flap displaced
Molecular structures of thiones 38, 40, 42
Before describing the structures of the cycloaddition products,
it is useful to outline some details of the molecular geometry
of simpler substituted dithiolodithiin-thiones. X-Ray crystal
structure data for the unsubstituted thione 24 and its substituted
derivatives indicate that a range of conformations are possible
for the six-membered ring. Thus, the unsubstituted thione 2443
and its trans 5,6-diphenyl derivative39,44 show envelope confor-
˚
by 0.712(7) A from the plane defined by the other five ring carbon
atoms in the opposite direction to the fused cyclopropane ring.
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 5 5 – 2 1 6 6
2 1 5 9

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˚
A). The dithiin ring system adopts an approximate half chair
conformation in which the two sp2 C atoms and the two S
˚
atoms lie in a plane and C4 and C5 deviate by 0.407(4) A and
˚
˚
−0.489(3) A (0.560 (4) and −0.328(3) A) respectively from this
plane. The position of the larger displacement is different in
the two molecules. The spiro centre results in the best planes of
the carbocyclic skeleton and the dithiin ring being in a roughly
perpendicular orientation to one another. The structure has little
conformational freedom apart from the flexing of the dithiin
ring. The spiro centre results in a reduction in the normally wid◦e
bond angle at the sp3 carbon in the dithiin ring to 107.4(2)
(107.9(2)◦) at C5, compared to 115.3(3)◦ (114.4(2)◦) at C4. The
˚
˚
C–S bond to the spiro centre C5–S5 1.858(3) A (1.858(3) A)
is particularly long, especially when compared to the C4–S4
˚
bond which involves a methylene carbon 1.808(3) A (1.816(4)
A). Sulfur atom S5 is attached to a quaternary carbon and
˚
Fig. 1 Molecular structure of carene adduct 42. Selected molecu-
lar geometry: C2–C3 1.350(2), C2–S4 1.7470(17), C3–S5 1.7375(18),
C4–S4 1.8393(18), C4–C5 1.541(2), C4–C10 1.538(2), C5–S5 1.8183(18),
C5–C6 1.514(2), C6–C7 1.524(2), C7–C8 1.511(3), C8–C9 1.513(3),
C9–C10 1.535(3), C2–S4–C4 100.46(8), C3–S5–C5 100.78(8), S4–C4–C5
111.37(12), S4–C4–C10 105.64(12), C5–C4–C10 107.08(15), S5–C5–C4
113.40(12), S5–C5–C6 112.06(12), C4–C5–C6 113.59(14), C6–C7–C11
120.61(15), C6–C7–C12 117.58(16), C5–C6–C8 118.03(14), C8–C7–C11
119.87(16), C8–C7–C12 116.23(16), C6–C8–C9 120.60(15), C8–C9–C10
115.34(15), C4–C10–C9 114.73(15)o.
experiences additional steric pressure from the methylene bridge
(S5–H9b 2.72(4) A (2.62(3) A)).
˚
˚
The dithiin ring adopts an approximate half chair conformation
with the two sp2 C atoms and the two S atoms in plane, and C4
and C5 deviating from the plane defined by the five coplanar
˚
˚
sulfur atoms by 0.526(5) A and 0.323(9) A respectively. Thus the
cyclohexane ring lies nearly perpendicular to the organosulfur
system, reminiscent of the structure of the donor with a fused
1,4-dioxane ring, DOET, 49.49 The methyl group at the ring
fusion, C13, lies in a pseudo-equatorial position with respect to
the cyclohexane ring, and lies well away from the other atoms.
In contrast, methyl group C11 from the cyclopropyl group lies
over the cyclohexane ring, and there is some steric strain with
the two pseudo-axial hydrogen atoms from C5 and C10. This
is manifested in the methyl group being pushed away so that
the C11–C7 bond makes angles of 119.87(16)o and 120.61(15)o
with the cyclopropyl bonds C7–C8 and C7–C6 respectively,
while the bond to the other geminal methyl group C12–C7
makes smaller angles with these two bonds (116.23(16)o and
117.58(16)o). There are no substantial extensions of the two sp3
C–S bond lengths at the fusion of the rings: C4–S4 1.8393(18)
Fig. 2 Molecular structure of b-pinene adduct 40, molecule 1. Se-
lected geometry for molecules 1 (and 2): C2–C3 1.353(4) (1.349(4)),
C2–S4 1.739(3) (1.747(3)), C3–S5 1.755(3) (1.744(3)), C4–S4 1.808(3)
(1.816(4)), C5–S5 1.858(3) (1.858(3)), C4–C5 1.536(4) (1.535(5)),
C5–C6 1.555(5) (1.554(5)), C5–C10 1.535(5) (1.533(5)), C6–C7 1.554(5)
(1.552(5)), C7–C8 1.518(5) (1.528(6)), C8–C9 1.545(5) (1.538(5)),
C8–C11 1.552(5) (1.547(5)), C9–C10 1.547(5) (1.557(5)), C10–C11
1.576(4) (1.571(4)), C2–S4–C4 99.85(16) (99.07(16)), C3–S5–C5
101.70(15) (102.71(15)), S4–C4–C5 115.3(3) (114.4(2)), S5–C5–C4
107.4(2) (107.9(2)), S5–C5–C6 111.0(2) (110.3(2)), S5–C5–C10 102.1(2)
(103.2(2)), C4–C5–C6 113.3(3) (113.5(3)), C4–C5–C10 110.9(3)
(109.6(3)), C6–C5–C10 111.5(3) (111.7(3)), C5–C6–C7 115.7(3)
(115.6(3)), C6–C7–C8 113.3(3), (113.3(3)), C7–C8–C9 108.1(3)
(108.7(3)), C7–C8–C11 112.2(3) (110.9(3)), C9–C8–C11 88.0(3)
(88.1(3)), C8–C9–C10 86.5(2) (86.6(3)), C5–10–C9 108.6(3) (108.2(3)),
C5–C10–C11 113.4(3) (113.3(3)), C9–C10–C11 87.1(2) (86.6(2)),
C8–C11–C10 85.3(2) (85.9(2)), C8–C11–C12 117.7(3) (119.0(3)),
C8–C11–C13 111.8(3) (112.2(3)), C10–C11–C12 122.8(3) (122.0(3)),
C10–C11–C13 110.5(3) (109.9(3)), C12–C11–C13 107.3(3) (106.8(3))o.
˚
˚
˚
A and C5–S5 1.8183(18) A, cf. 1.811–1.825 A in unsubstituted
thione 24 and its trans dimethyl and diphenyl analogues, taking
into consideration that C4 is a quaternary centre. In adducts 38
and 40, these bond lengths are significantly longer.
The crystals of the b-pinene adduct 40 contain two unique
molecules per asymmetric unit. The molecules have similar
geometries, except in the particular half chair conformations
adopted by the dithiin rings. Data for molecule 1 are discussed,
with data for molecule 2 in parentheses. The molecular structure
shows that the trithione has attacked the double bond from the
less hindered side which contains the unsubstituted methylene
bridge to form an adduct with a spiro junction between the
carbocyclic system and the dithiin ring (Figs. 2 and 3). Five
carbon atoms of the bicyclo[3.1.1]heptane ring system adopt
an almost perfect planar arrangement, while the other two
carbons of the skeleton, C9 and C11, are displaced from this
Fig. 3 View of 40, molecule 2, showing atoms involved in main steric
interactions.
˚
˚
˚
plane by −1.073(3) A (−1.064(4) A) and 1.076(3) A (1.080(4)
2 1 6 0
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 5 5 – 2 1 6 6

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There is a steric interaction between the C4 methylene group
of the dithiin ring, and the methyl group C12, which are in
pseudo-axial positions relative to the carbocyclic system, (C4–
˚
˚
C12, 3.260(5) A (3.276(5) A)). The main distortion is displace-
ment of the methyl group C12 away from C4 and towards its
geminal partner C13, so that the C11–C12 bond makes angles
in the range 117.7(3)–122.8(3)o with cyclobutyl bonds C10–C11
and C8–C11, compared to the corresponding angles involving
the other geminal methyl group C13 (109.9(3)–112.2(3)o). C4
is not strongly displaced away from C12 primarily due to its
confinement in a ring. The steric pressures between C4 and C12
and between S5 and H9b are also reduced by an asymmetric
distortion of the cyclobutane ring of the alicyclic skeleton, thus
the two bonds nearer to the spiro centre are longer than those on
˚
the opposite side of the ring. More notably C10–C11 (1.576(4) A
˚
˚
(1.571(4) A)) is more than 0.02 A longer than C8–C11 (1.552(5)
˚
˚
˚
˚
A (1.547(5) A)) while C9–C10 (1.547(5) A (1.557(5) A)) is slightly
longer than C8–C9 (1.545(5) A (1.538(5) A)).
Fig. 5 View of 38 showing atoms involved in main steric interactions.
˚
˚
The structure of the a-pinene adduct 38 is the most remarkable
(Fig. 4). Cycloaddition has occurred on the face of the alkene
adjacent to the unsubstituted methylene bridge, and opposite
to the dimethylated bridge. However, the fusion of the dithiin
ring with the bicyclo[3.1.1]heptane ring system and interactions
between substituents leads to a very strained structure. The
dithiin ring is forced into a boat conformation, which is achieved
by flexing about the S4 · · · S5 vector. Thus, the torsion angle
about the C4–C5 bond is only 25.6(3)◦, and both C4 and C5 are
displaced in the same direction from the [S4, C2, C3, S5] plane
sulfur atom S5, and the close contact between methyl groups
C11 and C12, the former located at the fusion of the two ring
systems and the latter on the dimethylated bridge (Fig. 5). The
consequences for sulfur atom S5 of steric pressure from C10, are
˚
the remarkable elongation of the C5–S5 bond to 1.880(3) A, the
closing of the angle at C5 with the bridgehead methyl group C11
◦
˚
to 101.1(1) and the short 1,5 interaction S5–H10a of 2.92 A.
The interacting methyl groups are splayed apart, but the C–C
˚
separation between the two methyl carbons is only 3.321(5) A. At
the dimethyl bridge at C7, methyl group C12 is pushed towards
methyl group C13 so that the bond angles C7–C12 makes with
cyclobutyl bonds C7–C6 and C7–C8 are widened to 123.4(2)◦
and 118.5(3)◦ while those made by C13–C7 with these bonds are
reduced to 109.2(3)◦ and 112.7(2)◦.
˚
˚
by 1.415(3) A and 1.217(3) A respectively. The bicyclohexane
system is also strained by the ring fusion, and atoms C4, C5, C6,
C8 and C9 form only an approximate plane (average deviation
o
˚
of atoms from plane: 0.054 A) which lies at 74.42(11) to the
plane of the five sulfur atoms.
The organosulfur ring system lies anti to the bridgehead
methyl group C11, and there are additional close contacts be-
tween the heterocyclic system and the bicyclohexane system, no-
˚
tably a 1,5 interaction C2–H9a 2.79 A and a 1,6 interaction C3–
˚
H10a 2.69 A. The outward splaying of the bridgehead methyl
group is sufficient to disfavour the syn conformation. There
are further close intramolecular contacts from the dimethylated
bridge to methine hydrogen atom H4 and to the methylene
˚
˚
bridge: H12a–H4 (2.06 A) and H13b–H10b (2.08 A). Steric
pressure from methyl group C11 and the heterocyclic system
lead to an asymmetric distortion of the cyclobutane ring, with
bonds C6–C7 and C6–C10 being very long for C,C single bonds
˚
(1.582(4) and 1.561(4) A) and longer than the other two bonds to
the bridging carbons: C8–C7 and C8–C12 (1.556(4) and 1.538(4)
˚
A). The exceptionally long C6–C7 bond is involved in relieving
the steric pressure between the methyl groups C11 and C12.
Since both sp3 C–S bonds at the ring junction are elongated
˚
by the steric strain, (1.880(3) and 1.833(3) A), it is not surprising
that the oxo compound prepared from this adduct is prone
to a retro Diels Alder reaction. Longer C–S bonds are not
common and occur only if there is exceptional strain, as
50
˚
in bis(triphenyl)sulfide 55 (C–S: 1.891 and 1.916 A) and
51
˚
the tetrathiaprotoadamantane 56 (C–S: 1.914 and 1.844 A)
Fig. 4 Molecular structure of a-pinene adduct 38. Selected molecular
geometry: C2–C3 1.349(4), C2–S4 1.740(3), C3–S5 1.734(3), C4–S4
1.833(3), C4–C5 1.552(4), C4–C9 1.551(4), C5–S5 1.880(3), C5–C6
1.530(4), C5–C11 1.531(4), C6–C7 1.582(4), C6–C10 1.561(4), C7–C8
1.556(4), C7–C12 1.527(4), C7–C13 1.537(4), C8–C9 1.528(4), C8–C10
1.538(4), C2–S4–C4 98.72(13), C3–S5–C5 104.41(13), S4–C4–C5
115.8(2), S4–C4–C9 111.6(2), C5–C4–C9 115.3(2), S5–C5–C4 114.2(2),
S5–C5–C6 107.56(19), S5–C5–C11 101.1(2), C4–C5–C6 110.9(2),
C4–C5–C11 110.9(2), C6–C5–C11 111.9(2), C5–C6–C7 113.2(2),
C5–C6–C10 110.1(2), C7–C6–C10 86.4(2), C6–C7–C8 85.1(2),
C6–C7–C12 123.4(2), C6–C7–C13 109.2(3), C8–C7–C12 118.5(3),
C8–C7–C13 112.7(2), C12–C7–C13 106.8(3), C7–C8–C9 112.4(2),
C7–C8–C10 88.1(2), C9–C8–C10 107.4(2), C4–C9–C8 113.1(2),
C6–C10–C8 86.4(2)o.
or where the carbon is attached to one or more additional
heteroatoms, especially nitrogen, as in thiazolidine 57 or the
2-(dimethylamino)thiazolidinone derivative 58.52,53
Among the analogous dithiolodithiines, only the diketone 53
˚
shows such long bonds (1.864 and 1.879 A). The considerable
strain experienced at C5 in the a-pinene adduct 38 at the ring
fusion is shown by the 13C NMR shifts of C5 and C4 at d 71.4
and 51.2. In comparison for the b-pinene adduct, the equivalent
carbons show shifts of d 55.4 and 41.1, the former from the
quaternary spiro centre and the latter from the methylene group,
while in the 2-carene adduct the equivalent methine carbons have
shifts of d 48.0 and 45.4. Further evidence of the strain in the
thione 38 are the unexpectedly high 13C NMR shifts for the sp2
carbons at the fusion of the dithiole and dithiin rings d 133.0 and
140.7 compared to d 124.5 and 119.9 in adduct 40, d 122.9 and
There are two main sources of strain in the structure: the
close approach of the unsubstituted methylene bridge at C10 to
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 5 5 – 2 1 6 6
2 1 6 1

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117.4 in adduct 42 and ca. d 122 in 24 and simple substituted
materials. This relates partly to the boat conformation of the
dithiin ring, since compounds 27 and 53, which take the boat
conformation in the solid state, show higher sp2 C resonances of
d 129.9 and 128.3, while the envelope conformation allows more
electron donation from one dithiin S atom into the double bond.
For the dithiin sp2 C atoms in the bis(alkylthio)1,3-dithioles 54
(e.g. R = Et, n-octyl) the corresponding carbons have a chemical
shift of ca. 136 ppm.54
5.18 (1H, m, 4ꢀ-H), 4.32 (1H, t, J = 8.9 Hz, 5ꢀ-Ha), 4.07 (1H, dd,
J = 8.9, 5.6 Hz, 5ꢀ-Hb), 3.60 (3H, s, OCH3), 2.72 (1H, dd, J =
16.5, 6.3 Hz, 2-CHa), 2.54 (1H, dd, J = 16.5, 7.3 Hz, 2-CHb);
1H NMR (minor isomer): 5.18 (1H, m, 4ꢀ-H), 4.72 (1H, dd, J =
8.9, 6.2 Hz, 5ꢀ-Ha), 4.60 (1H, dd, J = 8.9, 6.4 Hz, 5ꢀ-Hb), 3.60
(3H, s, OCH3), 2.99 (1H, dd, J = 16.8, 6.4 Hz, 2-CHa), 2.79
(1H, dd, J = 16.8, 7.2 Hz, 2-CHb); 13C NMR (major isomer):
ꢀ
ꢀ
=
169.4 (C O), 76.5 (4 -C), 71.0 (5 -C), 52.1 (OCH3), 37.2 (2-C);
13
ꢀ
ꢀ
=
C NMR (minor isomer): 169.7 (C O), 76.0 (4 -C), 70.7 (5 -C),
51.7 (OCH3), 38.7 (2-C); mmax/cm−1 (thin film): 2955, 2860,
1734, 1281, 1212, 1123, 1070, 954, 743; HRMS (ES): found
198.0432 (M + H)+, C5H8O5S requires 198.0431 (M + H)+;
293[a]D = −7.92 (c = 1.06, CHCl3).
Conclusion
Three short synthetic strategies for preparing enantiopure
organosulfur donors are reported. All three donors have po-
tential for developing access to a wider range of materials, either
by reaction with the carbonyl group of 15, or use of alternative
enantiopure diols in the syntheses of donors analogous to 16.
Of particular significance is the total diastereoselectivity of the
cycloaddition of trithione 36 to selected enantiopure alkenes,
which we now intend to extend to other less structurally complex
alkenes.
Methyl S-(2ꢀ,2ꢀ-dioxo-1,3,2-dioxathiolan-4ꢀ-yl)ethanoate 21.
To a solution of cyclic sulfite ester 20 (0.50 g, 2.77 mmol) in
DCM (10 ml) at 0 ◦C were added a solution of NaIO4 (1.10 g,
5.11 mmol) in water (10 ml) and ruthenium dioxide (2–3 mg).
The mixture was stirred to ensure full mixing of the phases until
an apple-green colouration appeared. After 10 min, the organic
layer was separated and stirred with several drops of 2-propanol
for 15 min. After addition of anhydrous MgSO4, the mixture
was stirred for a further 10 min, filtered through Celite and
evaporated to furnish cyclic sulfate ester 21 as an orange oil
(0.56 g, 93.7%); 1H NMR: 5.26 (1H, m, 4ꢀ-H), 4.85 (1H, dd, J =
9.2, 6.2 Hz, 5ꢀ-Ha), 4.45 (1H, dd, J = 9.2, 7.2 Hz, 5ꢀ-Hb), 3.70
Experimental
General
NMR spectra were measured on a JEOL JNM-EX270 spec-
(3H, s, OCH3), 3.03 (1H, dd, J = 17.1, 6.4 Hz, 2-CHa), 2.84
1
trometer at 270 MHz for H and at 67.8 MHz for 13C using
13
=
(1H, dd, J = 17.1, 7.4 Hz, 2-CHb); C NMR: 168.4 (C O),
77.9 (4ꢀ-C), 72.5 (5ꢀ-C), 52.3 (OCH3), 36.5 (2-C); mmax/cm−1 (thin
film): 2912, 1719, 1402, 1378, 1243, 1189, 1051; 293[a]D = −18.89
(c = 0.27, MeOH).
CDCl3 as solvent and tetramethylsilane (TMS) as standard, and
measured in ppm downfield from TMS, unless otherwise stated.
IR spectra were recorded on a PerkinElmer Spectrum RX 1
FT-IR spectrometer. Optical rotation data were measured on a
PerkinElmer 21 polarimeter. Mass spectra were recorded at the
EPSRC Mass Spectrometry Centre. Chemical analysis data were
obtained from Mr T. Spencer, University of Nottingham. Flash
chromatography was performed on 40–63 silica gel (Merck).
Cyclic voltammetry was performed with a lAutolab Type II
apparatus.
Methyl R-(5ꢀ,6ꢀ-dihydro-2ꢀ -thioxo-1,3-dithiolo[4,5-b]-1, 4-
dithiin-5ꢀ-yl) ethanoate 22. 4,5-Bis(benzoylthio)-1,3-dithiole-2-
thione (1.16 g, 2.86 mmol) was added to a solution prepared
from sodium metal (0.14 g, 6.29 mmol) and dry methanol
(40 ml) under nitrogen and the mixture stirred for 1 h at
room temperature. A solution of cyclic sulfate ester 21 (0.56 g,
2.86 mmol) in dry methanol (5 ml) was added to the reaction
mixture at 0 ◦C and stirring continued overnight at room
temperature. The solvent was removed in vacuo and replaced
with dry THF (40 ml), and the mixture refluxed for 5 h under
nitrogen. The solvent was evaporated and the residue partitioned
between DCM (100 ml) and water (50 ml). The organic phase
was collected, washed with water (50 ml), dried (MgSO4)
and evaporated to yield a brown oil. Kugelrohr distillation
removed methyl benzoate, and the residue was purified by flash
chromatography (SiO2, 2 : 1 chloroform–cyclohexane) to furnish
Dimethyl S-3,4-dihydroxybutanoate 1923. Dimethyl L-malate
18 (3.07 g, 21.6 mmol) was reduced with BH3·SMe2 and 5 mol%
of NaBH4 in THF as in the literature to give diol 19 after flash
chromatography as a pale yellow oil (1.96 g, 77.2%); 1H NMR:
3.89 (1H, m, 3-H), 3.48 (3H, s, OCH3), 3.40 (1H, dd, J = 11.4,
3.7 Hz, 4-Ha), 3.28 (1H, dd, J = 11.4, 6.4 Hz, 4-Hb), 2.29 (2H, d,
J = 6.5 Hz, 2-H2); 13C NMR: 172.2 (C O), 68.3 (3-C), 65.2 (4-
=
C), 51.3 (OCH3), 37.5 (2-C); mmax/cm−1 (thin film): 3389, 2955,
1732, 1439, 1287, 1171, 1042; 293[a]D = −24.91 (c = 1.06, CHCl3).
1
thione 22 as a yellow oil (0.30 g, 35.5%); H NMR: 4.12 (1H,
Methyl (2ꢀ -oxo-1,3,2-dioxathiolan-4ꢀ -yl)ethanoate 20.
Thionyl chloride (0.50 ml, 6.90 mmol) was added dropwise to
a solution of diol 19 (0.84 g, 6.27 mmol) and pyridine (1.09 g,
13.8 mmol) in THF (25 ml) at 0 ◦C. The mixture was allowed to
warm to room temperature and left to stir overnight. Pyridinium
hydrochloride was filtered off and washed with THF (20 ml).
The combined washings and filtrate were evaporated under
reduced pressure and the residue partitioned between DCM
(50 ml) and water (20 ml). The organic phase was collected and
washed consecutively with water (20 ml) and 0.5 M HCl (2 ×
20 ml), dried (Na2SO4), evaporated and the crude oil purified
by flash chromatography (SiO2, 1 : 1 EtOAc–cyclohexane) to
afford cyclic sulfite ester 20 as a light yellow oil (1.11 g, 98.3%)
as a mixture of two diastereoisomers; 1H NMR (major isomer):
m, 5ꢀ-H), 3.75 (3H, s, OCH3), 3.45 (1H, dd, J = 13.5, 2.9 Hz,
6ꢀ-Ha), 3.26 (1H, dd, J = 13.5, 5.7 Hz, 6ꢀ-Hb), 2.92 (2H, d, J =
13
=
=
7.2 Hz, 2-H2); C NMR: 207.8 (C S), 170.5 (C O), 122.5,
121.3 (3ꢀa-, 7ꢀa-C), 52.3 (OCH3), 39.3 (2-C), 38.2 (5ꢀ-C), 34.0
(6ꢀ-C); mmax/cm−1 (thin film): 1732, 1486, 1437, 1408, 1361, 1296,
1242, 1220, 1173, 1061, 1032, 979, 891, 756; m/z: (APCI) 297
([M + H]+, 100), 197 ([C3S5 + H]+, 45), 121 (5); HRMS (EI):
found M+ 295.9117, C8H8O2S5 requires 295.9122; 293[a]D = +183
(c = 0.15, CHCl3).
Methyl R-(5ꢀ,6ꢀ-dihydro-2ꢀ-oxo-1,3-dithiolo[4,5-b]-1, 4-dithiin-
5ꢀ-yl) ethanoate 23. To a solution of thione 22 (0.21 g,
0.71 mmol) in CHCl3 (10 ml) and glacial acetic acid (3 ml) was
added mercuric acetate (0.34 g, 1.06 mmol). After 2 h stirring
2 1 6 2
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 5 5 – 2 1 6 6

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◦
20
at room temperature, the mixture was filtered, and the solution
was washed consecutively with saturated NaHCO3 solution (3 ×
20 ml) and H2O (20 ml), dried (Na2SO4) and evaporated to afford
oxo compound 23 as a brown oil (0.17 g, 85.6%); 1H NMR: 4.09
(1H, m, 5ꢀ-H), 3.75 (3H, s, OCH3), 3.45 (1H, dd, J = 13.4, 3.0 Hz,
6-Ha), 3.20 (1H, dd, J = 13.4, 5.8 Hz, 6-Hb), 2.89 (2H, d, J =
450.0327, C20H17O3S4 + NH4 requires 450.0321; [a]D = − 68.1
(c = 0.88 in DCM).
Bis(4ꢀS,5ꢀS-4ꢀ,5ꢀ-diphenyl-1ꢀ,3ꢀ-dioxolane-spiro[2ꢀ.2]propan-1,3-
dithio)TTF 16. The oxo compound 33 (0.39 g, 0.89 mmol)
was heated in triethyl phosphite (10 ml) at 90 ◦C under nitrogen
for 5 h. The triethyl phosphite was removed by kugelrohr
distillation. Chromatography of the residue eluting with DCM
gave the donor 16 (0.14 g, 37%); mp 149–153 ◦C (from
6.9 Hz, 2-H2); 13C NMR: 188.6 (S2C O), 170.5 (C O), 113.3,
112.1 (3aꢀ-, 7aꢀ-C), 52.2 (OCH3), 40.0 (2-C), 39.3 (5ꢀ-C), 35.2
(6ꢀ-C); mmax/cm−1 (thin film): 2955, 1733, 1677, 1625, 1505, 1436,
1410, 1363, 1298, 1222, 1171, 1013, 984, 892, 764; m/z (EI): 280
(M+, 74), 252 (32), 221 (24), 152 (44), 149 (53), 120 (100); HRMS
(EI): found M+ 279.9355, C8H8O3S4 requires 279.9351; 293[a]D =
+104 (c = 0.204, CHCl3).
=
=
1
chloroform); H NMR: 7.25 (12H, m, Ar-H12), 7.14 (8H, m,
Ar-H8), 4.76 (4H, s, 2 × 4ꢀ-, 5ꢀ-H), 3.02 (4H, br d, J = 14.5 Hz,
2 × 5-, 7-Ha), 2.92 (4H, br d, J = 14.5 Hz, 2 × 5-, 7-Hb); 13C
NMR: 135.1, 128.7, 128.6, 126.6 (Ar-C24), 112.0 (2 × 3a-, 8a-C)
and 106.2 (2 × 2-C), 86.0 (2 × 4ꢀ-, 5ꢀ-C), 41.1 (2 × 5-, 7-C); tmax
(KBr): 1604, 1496, 1453, 1390, 1283, 1260, 1238, 1211, 1187,
1100, 1012, 902, 764, 753, 731, 698, 647, 532; m/z (APCI): 833
([M + H]+, 100), 449 (30), 417 (17), 361 (19); found C, 57.7;
Methyl R-ET-ethanoate 15. A mixture of oxo compound 23
(0.12 g, 0.46 mmol) and the unsubstituted thione 24 (0.10 g,
0.64 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 (SiO2, 1 : 1 cyclohexane–DCM) to yield
H, 3.9% C40H32O4S8 requires C, 57.6; H, 3.9%; [a]D = − 99.3◦
20
(c = 0.6 in DCM).
(4aR,5R,7S,8aS)-4a,5,6,7,8,8a-Hexahydro-5,7-methano-4a,6,
1
the donor 15 as an orange oil (0.10 g, 47.2%); H NMR: 4.03
6-trimethyl-1,3-dithiolo[4,5-b][1,4]benzodithiin-2-thione 38.
A
(1H, m, 5-H), 3.71 (3H, s, OCH3), 3.31 (1H, dd, J = 13.3, 3.1 Hz,
suspension of trithione 36 (1.00 g, 5.1 mmol) in a solution of
(−)-a-pinene 37 (0.35 g, 2.5 mmol) and toluene (75 ml) was
heated to reflux for 13 h. The reaction mixture was filtered
hot and the filtrate was collected, evaporated and purified by
chromatography on silica eluting with cyclohexane to yield
thione 38 as a yellow brown solid (0.71 g, 83%); mp 139–140 ◦C;
1H NMR: 3.69 (1H, dd, J = 7.7, 9.5 Hz, 8a-H), 2.39 (1H,
ddd, J = 3.6, 9.5, 14.1 Hz, 8-Ha), 2.24 (1H, ddd, J = 2.2, 6.1,
10.9 Hz, 10-Ha), 2.15 (1H, t, J = 5.8 Hz, 5-H), 1.88 (1H, m,
7-H), 1.66 (1H, ddd, J = 2.3, 7.7, 14.1 Hz, 8-Hb), 1.48 (3H, s,
6-(CH3)a), 1.23 (3H, s, 6-(CH3)b), 1.23 (1H, m, 10-Hb), 1.00
(3H, s, 4a-CH3); 13C NMR: 210.7 (2-C), 140.4 (3a-C), 133.3
(9a-C), 70.9 (4a-C), 56.0 (5-C), 51.1 (8a-C), 42.4 (6-C), 39.5
(7-C), 36.4 (8-C), 29.8 (10-C), 29.4 (6-(CH3)a), 27.7 (6-(CH3)b),
23.5 (4a-CH3); mmax/cm−1 (KBr): 2910, 1465, 1443, 1385, 1373,
1268, 1225, 1057, 1043, 1021, 918, 898, 792, 574, 512; m/z (ES):
333 [M + H]+ (100%); found C, 46.9; H, 5.0% C13H16S5 requires
6-Ha), 3.28 (4H, s, 5ꢀ, 6ꢀ-CH2), 3.13 (1H, dd, J = 13.3, 5.4 Hz,
6-Hb), 2.84 (2H, d, J = 7.2 Hz, CH2C O); 13C NMR: 170.7
=
2
=
(C O), 113.8, 113.5, 112.7, 112.0, 111.3 (sp -C), 52.1 (OCH3),
39.4 (5-C(CO)), 38.6 (5-C), 34.7 (6-C), 30.1 (5ꢀ, 6ꢀ-C); mmax/cm−1
(KBr): 1733, 1434, 1408, 1359, 1290, 1220, 1170, 1006, 979, 917,
888, 773; HRMS (EI): found M+ 455.8602, C13H12O2S8 requires
455.8603. Found: C, 34.0; H, 2.6%; C13H12O2S8 requires C, 34.1;
H, 2.6%; 293[a]D = +12.5 (c = 0.16, CHCl3).
S,S-1,2-Diphenylethane-1,2-diol. The diol was prepared fol-
lowing the literature procedure29 using AD-mix-a, and isolated
in 70% with [a] −91.5◦ (c = 1.0 in ethanol), corresponding to an
optically pure product.28
(4ꢀS,5ꢀS) 4ꢀ,5ꢀ-Diphenyl-1ꢀ,3ꢀ-dioxolane-spiro[2ꢀ.6]-5,6-dihydro-
7H-1,3-dithiolo[4,5-b]1,4-dithiepin-2-thione 32. Ketone 3126
(0.63 g, 2.50 mmol) and S,S-1,2-diphenylethane-1,2-diol (0.64 g,
3.00 mmol) and a few crystals of tosic acid were refluxed
together in chloroform (100 ml) under a Soxhlet extractor which
contained molecular sieves, for 24 h. The reaction mixture was
washed with saturated sodium hydrogen carbonate solution
(2 × 30 ml) and water (2 × 30 ml) and dried (Na2SO4).
Chromatography, eluting with chloroform, gave ◦the thione 32
(0.85 g, 75.9%) as a pale yellow solid; mp 162–163 C; 1H NMR:
7.30 (6H, m, Ar-H6), 7.17 (4H, m, Ar-H4), 4.84 (2H, s, 4ꢀ-, 5ꢀ-H),
◦
20
C, 47.0; H, 4.9%; [a]D = +26.3 (c = 0.3, DCM).
(4aR,5R,7S,8aS)-4a,5,6,7,8,8a-Hexahydro-5,7-methano-4a,6,
6-trimethyl-1,3-dithiolo[4,5-b][1,4]benzodithiin-2-one 43. To a
solution of thione 38 (0.17 g, 0.51 mmol) in chloroform (10 ml)
were added mercuric acetate (0.24 g, 0.75 mmol) and glacial
acetic acid (1.5 ml). A white precipitate formed immediately.
After stirring for 2 h, the mixture was filtered and the solid
residue washed with chloroform. The combined filtrates were
collected and neutralised with aqueous sodium carbonate. The
organic layer was collected and washed with water, brine and
dried (MgSO4). Concentration in vacuo yielded oxo compound
43 as a pale yellow oil (0.15 g, 94%); 1H NMR: 3.72 (1H,
dd, J = 7.4, 9.4 Hz, 8a-H), 2.42 (1H, m, 8-Ha), 2.31 (1H, m,
10-Ha), 2.13 (1H, t, J = 5.9 Hz, 5-H), 1.94 (1H, m, 7-H), 1.74
(1H, ddd, J = 2.3, 7.4, 14.0 Hz, 8-Hb), 1.52 (3H, s, 6-(CH3)a),
1.28 (3H, s, 6-(CH3)b), 1.28 (1H, t, J = 5.3 Hz, 10-Hb), 1.05
(3H, s, 4a-CH3); 13C NMR: 190.0 (2-C), 131.1 (3a-C), 124.2
(9a-C), 71.7 (4a-C), 55.9 (5-C), 51.5 (8a-C), 42.3 (6-C), 39.5
(7-C), 36.4 (8-C), 29.8 (10-C), 29.3 (6-(CH3)a), 27.7 (6-(CH3)b),
23.6 (4a-CH3); mmax/cm−1 (thin film): 2922, 2870, 1674, 1621,
1472, 1449, 1387, 1375, 1270, 1126, 1013, 921, 880,◦792, 752;
3.25 (2H, br d, J = 14.5 Hz, 5-, 7-Ha), 3.07 (2H, br d, J = 14.5 Hz,
13
=
5-, 7-Hb); C NMR: 210.2 (C S), 138.6 br (3a-, 8a-C), 134.9,
128.9, 128.7, 126.6 (Ar-C12), 108.7 (6-C), 86.2 (4ꢀ-, 5ꢀ-C), 41.2
(5-, 7-C); tmax (KBr): 1496, 1260, 1110, 1090, 1052, 1032, 767,
746, 730, 700, 538; m/z (APCI): 449 ([M + H]+, 100), 417 (10),
282 (28); HRMS (ES): found [M + H]+ 448.9822, C20H16O2S5 +
◦
20
H requires 448.9827; [a]D = −56.2 (c = 0.21 in DCM).
(4ꢀS,5ꢀS) 4ꢀ,5ꢀ-Diphenyl-1ꢀ,3ꢀ-dioxolane-spiro[2ꢀ.6]-5,6-dihydro-
7H-1,3-dithiolo[4,5-b]1,4-dithiepin-2-one 33. Mercuric acetate
(0.74 g, 2.32 mmol) was added to a solution of thione 32 (0.69 g,
1.55 mmol) in chloroform (30 ml) and acetic acid (10 ml) and
stirred for 15 min. The mixture was filtered, and the solution
washed with saturated sodium hydrogen carbonate solution
(2 × 20 ml) and water (2 × 20 ml) and dried over anhydrous
magnesium sulfate. Evaporation gave the oxo compound 33 as a
cream solid (0.49 g, 73.6%); mp 98–99 ◦C; 1H NMR: 7.27 (6H,
m, Ar-H6), 7.15 (4H, m, Ar-H4), 4.81 (2H, s, 4ꢀ-, 5ꢀ-H), 3.20
20
m/z (ES): found [M + H]+ 317 (100%); [a]D = +35.2 (c = 0.3,
DCM).
(1ꢀR,5S,5ꢀS)-Spiro[6ꢀ,6ꢀ -dimethyl-bicyclo[3.1.1]heptane]-2ꢀ,5-
[5,6-dihydro-[1,3]dithiolo[4,5-b][1,4]dithiine-2-thione] 40. A sus-
pension of trithione 36 (7.00 g, 40 mmol) in a mixture of
(−)-b-pinene (2.70 g, 20 mmol) and toluene (500 ml) was
refluxed for 24 h. The reaction mixture was filtered hot and
the solid residue was washed with chloroform. The combined
filtrates were evaporated and the residue purified by column
chromatography on silica eluting with cyclohexane to yield
(2H, br d, J = 14.5 Hz, 5-, 7-Ha), 3.02 (2H, br d, J = 14.5 Hz,
13
=
5b-, 7-Hb); C NMR: 188.8 (C O), 134.9, 128.9, 128.6, 126.6
(Ar-C12), 128.3 (3a-, 8a-C), 108.2 (6-C), 86.2 (4ꢀ-, 5ꢀ-C), 41.3
(5-, 7-C); tmax (KBr): 1670, 1617, 1496, 1455, 1390, 1262, 1239,
1102, 1011, 751, 730, 699, 532; m/z (APCI): 433 ([M + H]+, 100),
239 (14), 238 (15), 237 (17); HRMS (ES): found [M + NH4]+
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 5 5 – 2 1 6 6
2 1 6 3

View Article Online
◦
1
thione 40 as a yellow solid (5.31 g, 80%); mp 99–100 C; H
NMR: 3.40 (1H, d, J = 13.6 Hz, 6-Ha), 3.29 (1H, d, J = 13.6 Hz,
6-Hb), 2.41 (1H, m, 7ꢀ-Ha), 2.28 (1H, m, 1ꢀ-H), 2.16 (1H, m,
3ꢀ-Ha), 1.98–2.12 (4H, m, 3ꢀ-Hb, 5ꢀ-H, 4ꢀ-H2), 1.59 (1H, d, J =
10.6 Hz, 7ꢀ-Hb), 1.30 (3H, s, 6ꢀ-(CH3)a), 1.07 (3H, s, 6ꢀ-(CH3)b);
13C NMR: 208.1 (2-C), 124.5, 119.9 (3a-, 7a-C), 55.4 (5-C),
50.5 (1ꢀ-C), 41.1 (6-C), 40.3 (5ꢀ-C), 40.2 (6ꢀ-C), 30.5 (3ꢀ-C), 29.4
(7ꢀ-C), 27.8 (6ꢀ-(CH3)a), 25.3 (4ꢀ-C), 23.4 (6ꢀ-(CH3)b); mmax/cm−1
(KBr): 2909, 1484, 1461, 1404, 1060, 921, 887, 515, 465; m/z
(ES): found [M + H]+ 333 (100%); found C, 47.0; H, 4.8%;
(2 × 6-C), 40.5 (2 × 5ꢀ-C), 40.3 (2 × 6ꢀ-C), 30.5 (2 × 3ꢀ-C),
29.6 (2 × 7ꢀ-C), 28.0 (2 × 6ꢀ-(CH3)a), 25.4 (2 × 4ꢀ-C), 23.6 (2 ×
6ꢀ-(CH3)b); mmax/cm−1 (KBr): 2978, 2908, 2866, 1463, 1404, 1383,
1364, 1261, 1218, 1005, 919, 884, 771; m/z (EI): found [M]+ 600
(10%), 69 (100%); HRMS (EI): found [M]+ 600.0273, C26H32S8
◦
20
requires 600.0264; [a]D = −35.0 (c = 0.3, DCM).
(4aR,7R,8S,8aS)-4a,5,6,7,8,8a-Hexahydro-7,8-isopropano-4a-
methyl-1,3-dithiolo[4,5-b][1,4]benzodithiin-2-thione 42. A sus-
pension of trithione 36 (7.00 g, 40 mmol) in a mixture of
(+)-2-carene (2.50 g, 18 mmol) and toluene (300 ml) was
refluxed for 24 h. The reaction mixture was filtered hot and
the solid residue was washed with chloroform. The combined
filtrates were collected, evaporated and purified by column
chromatography on silica eluting with cyclohexane to yield
C13H16S5 requires C, 47.0; H, 4.9%; [a]D = −8.7◦ (c = 0.3,
20
DCM).
(1ꢀR,5S,5ꢀS)-Spiro[6ꢀ,6ꢀ -dimethyl-bicyclo[3.1.1]heptane]-2ꢀ,5-
[5,6-dihydro-[1,3]dithiolo[4,5-b][1,4]dithiine-2-one] 44. To
a
◦
1
solution of the thione 40 (1.15 g, 36 mmol) in chloroform
(20 ml) were added mercuric acetate (1.6 g, 5 mmol) and
glacial acetic acid (5 ml). A white solid precipitated almost
immediately. The reaction mixture was stirred for 2 h, filtered
and the solid residue washed with chloroform. The combined
filtrates were collected and neutralised with aqueous sodium
carbonate, the organic layer collected and washed with water
and dried (MgSO4). Concentration in vacuo yielded 44 as a pale
thione 42 as a yellow solid (5.52 g, 90%); mp 125–126 C; H
NMR: 2.53 (1H, d, J = 5.0 Hz, 8a-H), 1.97 (1H, m, 6-Ha), 1.84
(1H, m, 6-Hb), 1.58 (1H, m, 5-Ha), 1.44 (3H, s, 10-(CH3)a), 1.40
(1H, m, 5-Hb), 1.02 (3H, s, 10-(CH3)b), 0.97 (3H, s, 4a-CH3),
0.89 (1H, dd, J = 9.1, 5.0 Hz, 8-H), 0.77 (1H, m, 7-H); 13C
NMR: 208.2 (2-C), 122.9, 117.4 (3a-, 9a-C), 47.9 (4a-C),
45.3 (8a-C), 31.0 (10-(CH3)a), 28.3 (10-(CH3)b), 36.2 (6-C),
28.9 (8-C), 19.8 (7-C), 18.6 (10-C), 15.6 (5-C), 15.4 (4a-CH3);
mmax/cm−1 (KBr): 2917, 2858 1484, 1450, 1376, 1262, 1062, 908,
844, 803, 737, 703; m/z (ES): found [M + H]+ 333 (100%);
found C, 47.0; ◦H, 4.8%; C13H16S5 requires C, 47.0; H, 4.9%;
1
oil (1.15 g, 95%); H NMR: 3.42 (1H, d, J = 13.6 Hz, 6-Ha),
3.34 (1H, d, J = 13.6 Hz, 6-Hb), 2.41 (1H, m, 7ꢀ-Ha), 2.32 (1H,
m, 1ꢀ-H), 1.97–2.25 (5H, m, 3ꢀ-,4ꢀ-H2, 5ꢀ-H), 1.59 (1H, d, J =
10.6 Hz, 7ꢀ-Hb), 1.30 (3H, s, 6ꢀ-(CH3)a), 1.06 (3H, s, 6ꢀ-(CH3)b);
13C NMR: 180.2 (2-C), 114.2, 110.2 (3a, 7a-C), 56.8 (5-C), 50.8
(1ꢀ-C), 42.6 (6-C), 40.4 (5ꢀ-C), 40.3 (6ꢀ-C), 30.7 (3ꢀ-C), 29.4
(7ꢀ-C), 27.9 (6ꢀ-(CH3)a), 25.3 (4ꢀ-C), 23.5 (6ꢀ-(CH3)b); mmax/cm−1
(KBr): 2916, 1680, 1638, 1503, 1461, 1384, 1369, 1213, 917,
20
[a]D = +421.0 (c = 0.3, DCM).
(4aR,7R,8S,8aS)-4a,5,6,7,8,8a-Hexahydro-7,8-isopropano-4a-
methyl-1,3-dithiolo[4,5-b][1,4]benzodithiin-2-one 45. To
a
solution of the thione 42 (0.58 g, 1.8 mmol) in chloroform
(20 ml) was added mercuric acetate (0.84 g, 2.6 mmol) and
glacial acetic acid (3 ml). A white solid precipitated almost
immediately. The reaction mixture was stirred for 2 h, filtered
and the solid residue washed with chloroform. The combined
filtrates were collected and neutralised with aqueous sodium
carbonate. The organic layer was collected, washed with
water and dried (MgSO4). Concentration in vacuo yielded oxo
compound 45 as a thick pale yellow oil (0.51 g, 92%); 1H NMR:
2.53 (1H, d, J = 5.2 Hz, 8a-H), 1.99 (1H, m, 6-Ha), 1.83 (1H,
dd, J = 8.9, 15.1 Hz, 6-Hb), 1.59 (1H, dd, J = 7.9, 14.8 Hz,
5-Ha), 1.50 (3H, s, 10-(CH3)a), 1.31 (1H, m, 5-Hb), 1.04 (3H, s,
10-(CH3)b), 0.98 (3H, s, 4a-CH3), 0.96 (1H, m, 8-H), 0.82 (1H,
m, 7-H); 13C NMR: 189.0 (2-C), 112.3, 107.1 (3a-, 9a-C), 49.1
(4a-C), 46.2 (8a-C), 30.9 (10-(CH3)a), 28.3 (10-(CH3)b), 36.3
(6-C), 28.9 (8-C), 19.8 (7-C), 18.4 (10-C), 15.7 (5-CH3), 15.4
(4a-CH3); mmax (KBr): 2921, 2862, 1681, 1640, 1504, 1453, 1377,
1126, 906, 731, 649 cm−1; m/z (ES): found [M + H]+ 317 (100%);
HRMS (ES): found [M + NH4]+ 334.0418, C13H16OS4 + NH4
891, 756; m/z (ES): found [M + H]+ 317 (100%); HRMS (EI):
found M+ 316.0072, C13H16OS4 requires 316.0078; [a]D
−36.0◦ (c = 0.3, DCM).
=
20
(1ꢀꢀR,5S,5ꢀꢀS)-Spiro[6ꢀꢀ,6ꢀꢀ -dimethyl-bicyclo[3.1.1]heptane]-2ꢀꢀ,
5-ET 17. A mixture of oxo compound 44 (0.20 g, 0.63 mmol),
unsubstituted thione 24 (0.30 g, 1.3 mmol) and freshly distilled
triethyl phosphite (10 ml) was heated to 90 ◦C for 12 h. The
reaction mixture was concentrated and purified by column
chromatography on silica eluting with cyclohexane to yield an
orange solid. The dried solid was finely divided and stirred with
dry methanol (10 ml) for 24 h. The orange solid was collected
and washed with further methanol and dried to yield donor 17
◦
1
(0.12 g, 42%); mp 172–174 C (dec.); H NMR: 3.31 (1H, d,
J = 13.4 Hz, 6-Ha), 3.28 (4H, s, 5ꢀꢀ-, 6ꢀꢀ-H2), 3.19 (1H, d, J =
13.4 Hz, 6-Hb), 2.39 (1H, m, 7ꢀ-Ha), 2.24 (1H, t, J = 5.4 Hz,
1ꢀ-H), 1.95–2.14 (5H, m, 3ꢀ-, 4ꢀ-H2, 5ꢀ-H), 1.61 (1H, d, J =
10.6 Hz, 7ꢀ-Hb), 1.29 (3H, s, 6ꢀ-(CH3)a), 1.05 (3H, s, 6ꢀ-(CH3)b);
13C NMR: 114.7, 113.9, 113.8, 112.6, 110.2 (sp2-C), 55.6 (5-C),
50.7 (1ꢀ-C), 41.7 (6-C), 40.5 (5ꢀ-C), 40.3 (6ꢀ-C), 30.4 (3ꢀ-C),
30.2 (5ꢀꢀ-, 6ꢀꢀ-C), 29.6 (7ꢀ-C), 27.9 (6ꢀ-(CH3)a), 25.4 (4ꢀ-C), 23.6
(6ꢀ-(CH3)b); mmax/cm−1 (KBr): 2924, 1508, 1458, 1401, 1382,
1363, 1261, 1230, 1188, 1003, 907, 878, 772; found C, 44.2; H,
◦
20
requires 334.0422; [a]D = −143.0 (c = 0.45, DCM).
Homocoupling of 45, preparation of mixture of donors 48a and
48b. A mixture of oxo compound 45 (0.20 g, 0.63 mmol) and
freshly distilled triethyl phosphite (5 ml) was heated to 90 ◦C
for 5 h. The reaction mixture was concentrated and purified by
column chromatography on silica gel eluting with cyclohexane
to yield an orange solid. This dried solid was finely divided before
being stirred with dry methanol (10 ml) for 24 h. The mixture
was filtered and the orange solid washed with further methanol
and dried to yield 48a/48b (0.08 g, 42%); mp >200 ◦C; 1H NMR:
2.49 (1H, d, J = 5.0 Hz, 8a-H), 2.00 (1H, m, 6-Ha), 1.83 (1H,
m, 6-Hb), 1.58 (1H, m, 5-Ha), 1.43 (3H, s, 10-(CH3)a), 1.36 (1H,
m, 5-Hb), 1.04 (3H, s, 10-(CH3)b), 0.99 (3H, s, 4a-CH3), 0.90
(1H, dd, J = 5.0, 9.0 Hz, 8-H), 0.79 (1H, m, 7-H); 13C NMR:
112.8, 111.0, 107.3 (sp2-C), 47.9 (2 × 4a-C), 45.6 (2 × 8a-C),
31.0 (2 × 10-(CH3)a), 28.4 (2 × 10-(CH3)b), 36.1 (2 × 6-C), 29.0
(2 × 8-C), 19.9 (2 × 7-C), 18.3 (2 × 10-C), 15.9 (2 × 5-C), 15.6
(2 × 4a-CH3); mmax/cm−1 (KBr): 2919, 2856, 1450, 1376, 1251,
1105, 1080, 1054, 1012, 910, 886, 773; m/z (EI): found [M]+ 600
(50%), 463 (50%), 77 (100%); HRMS (EI): found [M]+ 600.0270,
4.4%; C18H16S8 requires C, 43.9; H, 4.1%; [a]D = −35.7◦ (c =
20
0.3, DCM).
Homocoupling of 44, preparation of mixture of donors 47a and
47b. A mixture of oxo compound 44 (0.22 g, 0.68 mmol) and
freshly distilled triethyl phosphite (5 ml) was heated to 90 ◦C
for 5 h. The reaction mixture was concentrated and purified by
column chromatography on silica eluting with cyclohexane to
yield an orange solid. This solid was dried, then finely divided
before being stirred with dry methanol (10 ml) for 24 h. The
mixture was filtered and the orange solid washed w◦ith methanol
and dried to yield 47a/47b (0.10 g, 46%); mp 150 C (dec.); 1H
NMR: 3.30 (2H, d, J = 13.3 Hz, 2 × 6-Ha), 3.18 (2H, d, J =
13.3 Hz, 2 × 6-Hb), 2.38 (2H, m, 2 × 7ꢀ-Ha), 1.96–2.23 (12H, m,
2 × 3ꢀ-, 4ꢀ-H2, 1ꢀ-,5ꢀ-H), 1.58 (2H, d, J = 10.9 Hz, 2 × 3ꢀ-H), 1.26
(6H, s, 2 × 6ꢀ-(CH3)a), 1.03 (6H, s, 2 × 6ꢀ-(CH3)b); 13C NMR:
113.8, 112.6, 110.2 (sp2-C), 55.6 (2 × 5-C), 50.7 (2 × 1ꢀ-C), 41.8
◦
20
C26H32S8 requires 600.0264; [a]D = −68.5 (c = 0.26, DCM).
2 1 6 4
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 5 5 – 2 1 6 6

View Article Online
X-Ray crystallography of 38, 40 and 42†
Parakka, Y. S. Thomas, J. M. Williams, P. G. Nixon, R. W. Winter,
G. L. Gard, H.-J. Koo and M.-H. Whangbo, Chem. Mater., 2000,
12, 343.
The structures were solved by direct methods and refined on
F2 using SHELX-97.55 All H atoms were found from differ-
ence Fourier maps. Non-H atoms were assigned anisotropic
displacement parameters. Graphics and geometry calculations
were made using PLATON,56 ORTEP-357 and POVRAY.58
10 E. Coronado, J. R. Galen-Mascaros, C. J. Gomez-Garcia and C.
Laukhin, Nature, 2000, 408, 447.
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Hursthouse, Chem. Commun., 1999, 513; L. Martin, S. S. Turner,
P. Day, P. Guionneau, J. A. K. Howard, K. M. A. Malik, M. B.
Hursthouse, M. Uriuchi and K. Yakushi, Inorg. Chem., 2001, 40,
1363.
Crystal data for 38. C13H16S5, M = 332.6, monoclinic, a =
o
˚
7.2322(2), b = 9.3635(2), c = 11.3961(5) A, b = 106.405(1) ,
12 F. Leurquin, T. Ozturk, M. Pilkington and J. D. Wallis, J. Chem. Soc.,
3
˚
V = 740.31(3) A , P21, Z = 2, T = 120(2) K, l(Mo–Ka) =
Perkin Trans. 1, 1997, 3173.
0.762 mm−1, Dc = 1.49 g cm−3, 3383 unique reflections (Rint
0.081). The refinement converged for 3231 observed reflections
with I > 2r(I) to give R1 = 0.039 and wR2 = 0.091, goodness-
of-fit = 1.062 and Flack parameter = −0.08(9). Crystals were
grown from THF.
13 T. Ozturk, C. R. Rice and J. D. Wallis, J. Mater. Chem., 1995, 5, 1553.
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3725.
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A. Rajca, H. Wang, V. Pawitranon, T. J. Brett and J. J. Stezowski,
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Rajca, Angew. Chem., Int. Ed., 2000, 39, 4481.
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Zhang, T. R. Lee and L. Pu, Macromolecules, 1996, 29, 1082.
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2002, 18, 259.
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Amabilino, J. Tejada, B. E. Williamson and J. Veciana, J. Mater.
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48, 4067.
24 R. J. Brown, G. Cameresa, J.-P. Griffiths, P. Day and J. D. Wallis,
Tetrahedron Lett., 2004, 45, 5103.
Crystal data for 40. C13H16S5, M = 332.6, monoclinic, a =
o
˚
6.3217(2), b = 13.4551(4), c = 17.5120(5) A, b = 93.0600(16) ,
3
˚
V = 1487.43(8) A , P21, Z = 4, T = 120(2) K, l(Mo–Ka) =
0.758 mm−1, Dc = 1.49 g cm−3, 6771 unique reflections (Rint
0.0612). The refinement converged for 5327 observed reflections
with I > 2r(I) to give R1 = 0.041 and wR2 = 0.069, goodness-of-
fit = 0.925 and Flack parameter = 0.03(6). Crystals were grown
from cyclohexane–DCM.
Crystal data for 42. C13H16S5, M = 332.6, orthorhombic, a =
3
˚
˚
7.6090(1), b = 9.7890(2), c = 20.1711(5) A, V = 1502.43(1) A ,
P212121, Z = 4, T = 120(2) K, l(Mo–Ka) = 0.751 mm−1, Dc =
1.47 g cm−3, 3415 unique reflections (Rint 0.053). The refinement
converged for 3208 observed reflections with I > 2r(I) to give
R1 = 0.025 and wR2 = 0.059, goodness-of-fit = 1.044 and Flack
parameter = −0.03(6). Crystals were grown from cyclohexane–
DCM.
25 T. Ozturk, D. C. Povey and J. D. Wallis, Tetrahedron, 1994, 50, 11205.
26 W.-C. Wu and Y.-J. Shen, Youji Huaxue, 1999, 19, 587; G. C.
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Acknowledgements
We thank the EPSRC and Nottingham Trent University for two
studentships (RJB and JPG), and the Chinese Government for
a Visiting Scientist bursary (NH). We are grateful to the EPSRC
Mass Spectrometry Service and X-ray Crystallography Centre
for data. We thank Dr John Bickerton of Warwick University
for some mass spectral data.
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