Synthesis and photoreactivity of aryl substituted 4,5-dithienyl[1,3]dithiol-2-ones

Article abstract of DOI:10.1016/j.tet.2009.03.015

UV irradiation of hitherto unknown 4,5-bis-benzo[b]thiophen-3-yl-[1,3]dithiol-2-one gave 3-(3-benzo[b]thienyl)-thieno[3,4-c]benzo[e][1,2]dithiine by loss of carbon monoxide and rearrangement, whereas 4,5-bis-(2-bromo-phenyl)-[1,3]dithiol-2-one gave a poly

Full text of DOI:10.1016/j.tet.2009.03.015

Tetrahedron 65 (2009) 3858–3862
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and photoreactivity of aryl substituted 4,5-dithienyl[1,3]dithiol-2-ones
Anton Blencowe c, Angela Maria Celli a, Donato Donati a, Wayne C. Hayes c, Claire Martin b,
,
a
,
b
Patrick J. Murphy b , Fabio Ponticelli , Jessica K. Melville-Richards
*
*
a Department of Chemistry, University of Siena, 53100 Siena, Italy
b School of Chemistry, Bangor University, Gwynedd LL57 2UW, UK
c School of Chemistry, The University of Reading, Whiteknights, Reading RG6 6AD, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
UV irradiation of hitherto unknown 4,5-bis-benzo[b]thiophen-3-yl-[1,3]dithiol-2-one gave 3-(3-ben-
zo[b]thienyl)-thieno[3,4-c]benzo[e][1,2]dithiine by loss of carbon monoxide and rearrangement, whereas
4,5-bis-(2-bromo-phenyl)-[1,3]dithiol-2-one gave a polymeric material containing S–S bridges. The
structures of both photoproducts were demonstrated on the basis of chemical behaviour and/or X-ray
diffraction.
Received 23 September 2008
Received in revised form 17 February 2009
Accepted 6 March 2009
Available online 11 March 2009
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
process using other aromatic moieties. We thus report our studies
on the photochemical behaviour of the benzo-fused system 6
We recently reported the photoreactivity of 4,5-dithiophen-2-
and/or 3-yl[1,3]dithiol-2-ones 1a–c, showing that after the com-
mon reaction pathway of photochemical loss of carbon monoxide,
two different reaction pathways were observed, which depended
on the nature of the R1 and R2 substituent. Where thiophen-3-yl
substituents were present (1a and 1b), the formation of thieno[3,4-
c]dithiines 2a,b was observed, whereas with thiophen-2-yl sub-
stituents a loss of sulfur occurred followed by dimerisation to give
the 1,4-dithiine 3c (Scheme 1).1
(Scheme 2) and of the bromoaryl derivative 11 (Scheme 4).
2. Results and discussion
Compound 6 was prepared from the benzothiophen-3-carbox-
aldehyde 4, which was dimerised in a benzoin condensation to give
5. This in turn was converted into the target molecule via a three-
step cyclisation process.1 Irradiation of compound 6 gave the
dithiine 7, whose formation can be easily explained on the basis of
the previously reported behaviour of thiophen-3-yl derivatives 1a
and b. The structure of compound 7 was supported by X-ray2 dif-
fraction analysis (Fig. 1). As expected, dithiine 7 gave the dimethyl
dithioester 8 in quantitative yield by reduction with sodium boro-
hydride followed by methylation with methyl iodide.
S
S
hv
2a,b
R1
R2
S
R2
S
S
In analogy with our previous findings,1 the mechanism of the
reaction proceeds via loss of carbon monoxide from 6 to give a 1,2-
dithioketone. This converts into an intermediate diradical, which
then undergoes cyclisation, ring fragmentation and a further cyc-
lisation to give 7 (Scheme 3).
We next prepared the dithiol-2-one 11 (Scheme 4) with bromi-
nated aromatic substituents, which we hoped might intercept the S
centered radical and undergo displacement of the bromine atom and
lead to a benzothiophene structure. The required substrate was pre-
pared from 2-bromobenzaldehyde 9, which was dimerised in a ben-
zoin condensation to give 10, which in turn was converted in a three
stage process into the required dithiol-2-one 11 in good overall yield.
With this material in hand, a solution of 11 was irradiated and on
work-up, an amorphous material was obtained in 82% yield.
On analysis by 1H NMR spectroscopy this material displayed
only a very broad signal at 6.8 ppm and in its 13C NMR spectrum
O
hv
R1
R2
S
R1
R2
1a-c
a) R1 = R2 = thiophen-3-yl
S
b) R1 = thiophen-3-yl, R2 = thiophen-2-yl
c) R1 = R2 = thiophen-2-yl
3c
Scheme 1.
In order to gain further insight into the role of the substituents
on the photoreactivity of dithiol-2-ones and in an attempt to in-
crease the scope of the reaction we wished to investigate the
* Corresponding authors.
E-mail addresses: paddy@bangor.ac.uk (P.J. Murphy), ponticelli@unisi.it
(F. Ponticelli).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.03.015

A. Blencowe et al. / Tetrahedron 65 (2009) 3858–3862
3859
O
S
S
O
O
OH
(a)
(b)-(d)
S
S
S
S
S
4
5
6
S
S
S
S
S
S
(f),(g)
(e)
S
S
7
8
Scheme 2. Reagents and conditions: (a) 3-benzyl-5-(2-hydroxyethyl)-4-methyl-1,3-thiazolium chloride (cat.), NEt3, EtOH,
acetone. (d) HBr/AcOH, 34% from 5. (e) hv, 4.5 h, 63%. (f) NaBH4, EtOH. (g) MeI, Na2CO3, rt, 87% (2 steps).
D, 2.5 h, 48%. (b) PPh3, CCl4/CH2Cl2. (c) KS(CS)OEt,
S1a
O
O
OH
Br
Br
Br
(b)-(d)
S
S
(a)
S2a
CHO
Br
Br
S3a
9
10
11
S4a
Me
Br
S
Me
Br
S
S
Me
Br
Br
S
S
(f),(g)
(h),(i)
Figure 1. X-ray crystal structure of compound 7.2
2
S
Br
14
13
n
12
a series of broad signals centered at 123.0, 126.9, 129.5, 132.0, 136.0
and 136.9 ppm were observed, which were characteristic of
a polymeric material. This was confirmed by ES-MS analysis as the
spectrum displayed in the range 2000–4000 m/z several typical
signal clusters with a regular distance of 298/300/302 uma, sug-
gesting the formation of the disordered polymeric substance 12.
GPC analysis of this material (Fig. 2) confirmed this hypothesis in-
dicating for the polymer a MW distribution in the range 1000–
10,000, with a maximum around 2600 uma.
The presence of a disulfide bridge between the monomeric units
was supported by the reduction of 12 with sodium borohydride,
followed by methylation with methyl iodide to give the cis-di-
methyl ether 13. Compound 13 was also prepared from the
dithioester 143 by treatment with LDA and methyl iodide4 (Scheme
4). X-ray diffraction of a crystal of 13,5 obtained by slow evaporation
of a chloroform/cyclohexane solution, enabled the assignment of
a cis-configuration to this alkene (Fig. 3).
Scheme 4. Reagents and conditions: (a) 3-benzyl-5-(2-hydroxyethyl)-4-methyl-1,3-
thiazolium chloride (cat.), NEt3, EtOH, , 8 h, 59%. (b) PPh3, CCl4/CH2Cl2. (c) KS(CS)OEt,
, 4 h, 82%. (f) NaBH4, EtOH. (g) MeI, Na2CO3,
D
acetone. (d) HBr/AcOH, 43% from 10. (e) h
n
rt, 71% (2 steps). (h) LDA, dimethoxyethane, ꢀ78 ꢁC. (i) rt, MeI, quantitative yield.
one, however several reaction pathways are possible, depending on
the substitution pattern of the intermediates. Some polymeric
materials have been previously6 observed during irradiation of
dithiolones, but the physical (spectroscopic) and chemical charac-
terisation of the S–S polymer 12 is, to the best of our knowledge,
unprecedented.
4. Experimental
4.1. General
Melting points were determined on a Kofler hot stage. 1H and
13C NMR spectra were recorded in CDCl3 solutions unless stated
otherwise, on a Bruker AC 200, AC 250 or AC 500 spectrometer.
3. Conclusion
In conclusion, our observations confirm that loss of carbon
monoxide is a general photochemical process for [1,3]dithiol-2-
Chemical shifts (
to tetramethylsilane (TMS). All reagents were of reagents grade and
d) are reported in parts per million (ppm) relative
O
S
S
S
S
S
S
hv
hv
-C=O
S
S
S
S
S
S
6
cyclisation
S
S
S
S
S
S
S
cyclisation
fragmentation
S
S
S
S
S
7
Scheme 3.

3860
30
A. Blencowe et al. / Tetrahedron 65 (2009) 3858–3862
7.87 (1H, d, J 7.9 Hz, CH), 8.01 (1H, d, J 8.2 Hz, CH), 8.20 (1H, s, CH),
8.87 (1H, d, J 8.2 Hz, CH). dC 193.2, 140.9, 139.4, 139.1, 137.2, 136.7,
134.8, 131.1, 126.6, 126.3, 125.9, 125.5, 125.0, 124.8, 123.0, 122.3,
122.2, 71.7. nmax (film)/cmꢀ1 3425 (O–H), 3096 (C–H), 1664 (C]O).
HRMS (ESI) [MþNaþ]: [C18H12O2S2Na]þ requires 347.0176; found
347.0165. Anal. Calcd for C19H12O2S2: C, 66.64; H, 3.73. Found: C,
66.85; H, 3.33.
25
20
15
10
5
4.1.2. 4,5-Bis-benzo[b]thiophen-3-yl-[1,3]dithiol-2-one 6
0
1,2-Bis-benzo[b]thiophen-3-yl-2-hydroxy-ethanone 5 (2.39 g,
7.35 mmol) was dissolved in dichloromethane (8 mL) and carbon
tetrachloride (15 mL) was added (ensuring that precipitation of
5 did not occur, if this does happen then further addition
of dichloromethane is required). Triphenylphosphine (3.91 g,
14.9 mmol) was then added and the resulting solution was stirred
in the dark for 16 h. The reaction was then diluted with ether
(100 mL), then petrol (50 mL), which precipitates the triphenyl-
phosphine oxide by-products and the supernatant liquid, was
passed through a silica pad on a sinter funnel. The remaining yellow
precipitate in the flask was redissolved in dichloromethane (10–
20 mL) and precipitated again by the sequential addition of diethyl
ether (100 mL) and petroleum ether (50 mL) and once again the
supernatant layer was filtered through the silica pad. This process
was repeated twice more and the combined filtrates were evapo-
rated onto silica (6 g). This was loaded onto a column (20 g) and was
eluted using 50% dichloromethane/petrol. The combined fractions
containing a spot at Rf¼0.36 (50% dichloromethane/petrol) were
evaporated to give crude 1,2-Bis-benzo[b]thiophen-3-yl-2-chloro-
ethanone (1.69 g, 4.93 mmol, 67%), which was of sufficient purity to
be used in the next step. Partial data dH 6.65 (1H, s, CHCl).
0
5
00
0
1
0000
15000
Mol.Wt.
GPC analysis of thioplymer: Eluent DMF (100°C) -polystyrene calibration
Mn = 2042, Mw = 2577, PDI = 1.2620
Mn = 295, Mw = 323, PDI = 1.0949
Figure 2.
were used without purification. GC–MS analysis was carried out on
a Varian Saturn (electron impact) instrument equipped with a gas
chromatographic apparatus HP 5890. ESI-MS spectra were recor-
ded with a LCQ-DECA Thermo Finnigan instrument. TLC was per-
formed on precoated 4ꢂ6.7 silica gel 60 F254 plates silica gel on
aluminium (Aldrich) with detection by UV light. Column chroma-
tography was carried out on silica gel (E. Merck, 0.063–0.2 mm). IR
spectra were run in chloroform solution on a Bruker Tensor 27
machine, UV spectra were obtained using a Perkin–Elmer Lambda
900 spectrophotometer and molar extinction coefficient are given
stated in molꢀ1 cmꢀ1. CHN analysis was obtained using a CHNS-O
EA1108 elemental analyser from Carlo Erba instruments.
The crude chloride (1.69 g, 4.9 mmol) was dissolved in acetone
(50 mL) and a solution of potassium ethyl xanthate (2.81 g,
17.6 mmol) in acetone (50–100 mL) was then added. The reaction
mixture was stirred for 60 min and then diluted with diethyl ether
(250 mL) and the resultant suspension filtered through a silica pad,
which was washed with further diethyl ether (3ꢂ100 mL); these
filtrates on evaporation gave crude dithiocarbonic acid S-(1,2-bis-
benzo[b]thiophen-3-yl-2-oxo-ethyl) ester O-ethyl ester (1.94 g, ca.
92%) as a brown gum. Partial data dH 7.00 (1H, s, CHS(CS)OEt).
Crude S-(1,2-bis-benzo[b]thiophen-3-yl-2-oxo-ethyl) ester O-
ethyl ester (1.94 g, 4.5 mmol) was dissolved in the minimum
amount of dichloromethane (ca. 10 mL) and hydrobromic acid so-
lution (45% in acetic acid, 20 mL) was added. The mixturewas stirred
vigorously for 3 h whereupon dichloromethane (100 mL) and water
(300 mL) were added. The organic phase was separated and the
aqueous phase extracted with dichloromethane (2ꢂ50 mL) and the
combined organic fractions were washed with water (2ꢂ500 mL)
and saturated sodium bicarbonate until neutral. After drying
(MgSO4) and evaporation, the crude product was purified bycolumn
chromatography in dichloromethane/petrol (gradient elution 30%
to 70%) to give 6 (0.95 g, 34%) as a pale yellow crystalline solid.
Rf¼0.23 (in 30% dichloromethane/petrol), mp 178 ꢁC. dH 7.29–
7.37 (6H, m, 6ꢂCH), 7.77 (2H, d, J 7.6 Hz, CH), 7.80 (2H, d, J 7.9 Hz,
CH). dC 122.5, 122.8, 124.8, 124.8, 125.0, 126.7, 128.4, 137.1, 139.6,
4.1.1. 1,2-Bis-benzo[b]thiophen-3-yl-2-hydroxy-ethanone 5
Thianaphthene-3-carboxaldehyde 4 (5.00 g, 30.9 mmol) was
dissolved in absolute ethanol (9.4 mL) and triethylamine (1.4 mL,
10 mmol) and 3-benzyl-5-(2-hydroxyethyl)-4-methyl-1,3-thiazo-
lium chloride (0.17 g, 0.62 mmol) was added. The reaction was
heated to reflux for 2.5 h, then cooled and evaporated onto silica
(15 g). This was loaded onto a column of silica (30 g preflushed with
30% dichloromethane/petrol). Initial elution with 30% dichloro-
methane/petrol removes a yellow impurity and the product is then
obtained by gradient elution from 30% dichloromethane/petrol to
100% dichloromethane. This gave on evaporation the required
compound (3.66 g), which eluted in 50%–100% dichloromethane/
petrol. Recrystallisation from chloroform/petrol gave white crystals
of 5 (2.39 g, 48%).
Rf¼0.25 (in 80% dichloromethane/petrol), mp 130 ꢁC. dH 4.64–
4.66 (1H, d, J 5.7 Hz, CHOH), 6.25–6.26 (1H, d, J 5.7 Hz, CHOH), 7.37–
7.47 (4H, m, 4ꢂCH), 7.57 (1H, m, CH), 7.83–7.84 (1H, d, J 7.9 Hz, CH),
190.7. IR: nmax/cmꢀ1 3094 (CH), 1659 (C]O). UV: lmax 295 nm (log
3
4.61, c 1.6ꢂ10ꢀ5). HRMS (ESI) [MþNaþ]: [C19H10OS4Na]þ requires
404.9512; found 404.9518. Anal. Calcd for C19H10OS4: C, 59.65; H,
2.63. Found: C, 59.41; H, 2.52.
4.1.3. 3-(3-Benzo[b]thienyl)-thieno[3,4-c]benzo[e][1,2]dithiine 7
A solution of 1,3-dithiol-2-one 6 (0.050 g, 0.13 mmol) in benzene
(20 mL) was irradiated in an air-cooled Pyrex tube for 4.5 h with
a Rayonet irradiation system Mod. MLU 18 (Applied Photophysic
Ltd.) equipped with 12 lamps model 1024, emitting at 350 nm. After
removal of solvent the residue was purified by column chromato-
graphy with cyclohexane to give 0.020 g (63% based on recovered 6)
Figure 3. X-ray crystal structure of compound 13.5

A. Blencowe et al. / Tetrahedron 65 (2009) 3858–3862
3861
of dithiine 7 and starting material (0.015 g). Compound 7 was fur-
ther purified by crystallisation from benzene to give yellow crystals.
Rf¼0.60 (in 25% diethyl ether/petrol), mp 128–130 ꢁC. dH (C6D6)
6.85 (1H, td, J 8.0,1.9 Hz, CH), 7.00 (1H, td, J 8.0,1.9 Hz, CH), 7.02 (1H,
s, CH), 7.05 (1H, s, CH), 7.06–7.19 (2H, m, 2ꢂCH), 7.27 (1H, dd, J 8.0,
1.9 Hz, CH), 7.35 (1H, dd, J 8.0, 1.9 Hz, CH), 7.52 (1H, dd, J 8.1, 1.8 Hz,
CH), 7.94 (1H, dd, J 8.1,1.8 Hz, CH). dC 121.6,122.9,123.2,124.7, 124.9,
127.4, 127.6, 127.7, 128.1, 128.6, 129.0, 130.2, 132.1, 133.0, 135.0, 137.7,
to be used immediately in the next step. Partial data dH 6.76 (1H,
s, CH), 7.20–7.70 (8H, m, 8ꢂCH). nmax/cmꢀ1 3063 (CH), 1721
(C]O).
The chloride (2.0 g) was dissolved in dry acetone (10 mL) and
potassium ethyl xanthate (1.20 g, 8.0 mmol) was added. After stir-
ring for 1 h, diethyl ether (100 mL) was added and the resultant
solution was filtered through a silica pad (with ether rinsing) to
remove precipitated salts. Evaporation of the filtrate gave crude
dithiocarbonic acid S-[1,2-bis-(2-bromo-phenyl)-2-oxo-ethyl] ester
O-ethyl ester (2.2 g), which was used in the next step without
further purification. Partial data dH 6.95 (1H, s, CH), 7.10–7.80 (8H,
m, 8ꢂCH). nmax/cmꢀ1 3060, 2979 (CH), 1710 (C]O).
139.4, 140.1. IR: nmax/cmꢀ1 3078 (CH), 1504. UV lmax 292 nm (log
3
4.19, c 6.8ꢂ10ꢀ5). MS (EI) m/z (%): 354 (100), 322 (18), 290 (22), 177
(16). HRMS (EI) [Mþ]: [C18H10S4]þ requires 353.9665; found
353.9671. Anal. Calcd for C18H10S4: C, 60.98; H, 2.84. Found: C, 61.13;
H, 2.75.
The xanthate ester (2.2 g) was dissolved in dichloromethane
(10 mL) and a solution of hydrobromic acid (45% in acetic acid,
20 mL) was added. The mixture was stirred vigorously for 2.5 h,
whereupon dichloromethane (50 mL) and water (200 mL) were
added. The organic phase was separated and the aqueous phase
extracted with dichloromethane (3ꢂ25 mL). The combined organic
fractions were washed with water (2ꢂ500 mL), then saturated
sodium bicarbonate solution until neutral then dried (MgSO4)
and evaporated. Purification by column chromatography in
dichloromethane/petrol (gradient elution 20–30%) gave 11 (0.99 g,
2.31 mmol, 43% from 10) as white crystals.
4.1.4. 3-(3-(Methylthio)-4-(2-(methylthio)phenyl)thiophen-2-yl)-
benzo[b]thiophene 8
A stirred solution of dithiine 7 (0.010 g, 0.03 mmol) in ethanol
(2 mL) was treated under nitrogen with sodium borohydride
(0.004 g, 0.1 mmol) and a solution of sodium carbonate (0.003 g) in
the minimum amount of water. After 30 min, methyl iodide
(0.025 mL) was added and after 2 h the solvents were evaporated in
vacuo and the oily residue was purified by column chromatography
eluting with light petroleum/ether 3:1 (v/v) to give 8 (0.010 g, 87%)
as a white solid.
Rf¼0.66 (in 25% ethyl ether/petrol), mp 105–107 ꢁC (cyclohex-
ane). dH (C6D6) 1.67 (3H, s, Me), 2.00 (3H, s, Me), 7.02–7.25 (6H, m,
6ꢂCH), 7.37 (1H, d, J 7.8 Hz, CH), 7.41 (1H, s, CH), 7.57 (1H, d, J 8.0 Hz,
CH), 8.09 (1H, d, J 8.0 Hz, CH). dC 15.9, 18.8, 122.7, 123.5, 123.8, 124.4,
124.4, 124.7, 124.7, 127.0, 128.6, 129.5, 130.6, 131.6, 135.5, 136.9,
138.4, 139.0, 139.8, 143.6. IR: nmax/cmꢀ1 3055 (CH), 2964, 2920
(CH3),1435 (Ar). MS (EI) m/z (%) 384 (95), 338 (100), 323 (82). HRMS
(EI) [Mþ]: [C20H16S4]þ requires 384.0135; found 384.0131. Anal.
Calcd for C20H16S4: C, 62.46; H, 4.19. Found: C, 62.39; H, 4.02.
Rf¼0.25 (30% dichloromethane in petrol), mp 147–148 ꢁC. dH 7.15
(4H, m, 4ꢂCH), 7.38 (2H, m, 2ꢂCH), 7.52 (2H, m, 2ꢂCH). dC 124.0,
127.4, 130.1, 130.8, 131.8, 131.9, 132.9, 190.5. IR nmax/cmꢀ1 3059, 2358
(CH), 1698 (C]O), 1634 (C]C). UV: lmax 266 nm (log
3 3.72, c
79
5.4ꢂ10ꢀ5). HRMS (CI) [MþNH4þ]: found 443.8721; C15
H Br2NOS2
12
requires 443.8722. Anal. Calcd for C15H8Br2OS2: C, 42.08; H, 1.88.
Found: C, 42.42; H, 1.82.
4.1.7. (Z)-1,2-Bis(2-bromo-phenyl)-1,2-bis(methylthio)ethene 13
A solution of compound 11 (0.05 g, 0.12 mmol) in anhydrous
benzene (15 mL) was irradiated in a Pyrex vial with an external
lamp (Hg, medium pressure, 400 W) for 4 h. Solvent was removed
in vacuo and the residue was treated with acetonitrile (5 mL) to
give the dithiopolymer 12 as an amorphous yellow solid (0.038 g,
81.5%). UV: lmax broad band 400–200 nm, shoulder at 315 nm, for
NMR spectroscopy, MS data and GPC analysis see main text. A so-
lution of sodium carbonate (0.012 g) in water (2 mL) was added to
a stirred suspension of 12 (0.032 g) in ethanol (5 mL) followed by
the addition of sodium borohydride (0.014 g). After 2 h, methyl
iodide (0.1 mL) was added and stirring was continued for further
2 h. The pH of the solution was adjusted to 4 with HCl (1 M) and the
solution evaporated in vacuo. The solid residue was treated with
chloroform (20 mL), which was washed with water (20 mL), dried
(Na2SO4) and evaporated to give a residue, which was purified by
column chromatography (10% ether in petrol) to give 13 (0.030 g,
71%) as white crystals.
Rf¼0.77, mp 127–129 ꢁC (cyclohexane). dH 1.95 (6H, s, 2ꢂSMe),
6.90–7.49 (8H, m, 8ꢂCH). dC 15.2, 124.0, 127.0, 127.7, 129.1, 130.7,
132.3, 138.5. IR nmax/cmꢀ1 3056 (CH), 2927, 2851 (CH3), 1640 (C]C),
1562 (Ar). HRMS (EI) [Mþ]: [C16H14Br2S2]þ requires 427.8904; found
427.8909. MS (EI) m/z (%) 428/430/432 (25/50/25), 349/351 (96/
100), 302/304 (12/12), 255 (54),176 (21). Anal. Calcd for C16H14Br2S2:
C, 44.67; H, 3.28, Br, 37.15. Found: C, 44.83; H, 3.16; Br, 37.02.
An identical product (identical mp and NMR spectra) was
obtained from methyl-2-bromobenzodithioate 143 according to
a previously reported method.4
4.1.5. 1,2-Bis-(2-bromo-phenyl)-2-hydroxy-ethanone 10
2-Bromobenzaldehyde 9 (20.64 g, 111.6 mmol) was dissolved in
absolute ethanol (33.8 mL) and triethylamine (4.65 mL, 33.4 mmol),
and 3-benzyl-5-(2-hydroxyethyl)-4-methyl-1,3-thiazolium chlo-
ride (6.00 g, 22.5 mmol) were added. The reaction was heated to
reflux for 8 h, then cooled, diluted with water (400 mL) and
extracted with dichloromethane (3ꢂ100 mL). The combined or-
ganic fractions were washed with sodium bicarbonate (saturated,
3ꢂ50 mL), dried (MgSO4) and evaporated in vacuo to give a yellow
solid, which was purified by chromatography (0–100% dichloro-
methane in petrol gradient 20% steps) to give 10 (12.2 g, 27.7 mmol,
59%) as a white solid.
Rf¼0.3 (CH2Cl2), mp 76–78 ꢁC. dH 4.60 (1H, d, J 3.7 Hz, OH), 6.36
(1H, d, J 3.7 Hz, CH), 7.09–7.57 (m, 8H, 8ꢂCH). dC 77.1, 119.5, 124.0,
126.8, 127.8, 128.8, 129.2, 130.1, 132.1, 133.0, 133.4, 136.0, 137.2,
201.2. IR: nmax/cmꢀ1 3459 (OH), 2965 (CH), 1705 (C]O). HRMS (CI)
79
[MþNH4]: C14
H Br2NO2 requires 385.9386; found 385.9386.
14
4.1.6. 4,5-Bis-(2-bromo-phenyl)-[1,3]dithiol-2-one 11
Benzoin 10 (1.89 g, 5.34 mmol) was dissolved in dichloro-
methane (15 mL) and tetrachloromethane (20 mL) and triphe-
nylphosphine (2.8 g, 10.68 mmol) was added. The reaction
mixture was stirred in the dark for 16 h, then diluted with diethyl
ether (100 mL), which caused the precipitation of the phosphine
oxide by-products. The supernatant liquid was decanted with
filtration through a silica pad, and the precipitate left in the flask
was redissolved in dichloromethane (20 mL) and precipitated
again by the sequential addition of diethyl ether (100 mL) and
petroleum ether (50 mL). The supernatant layer was decanted
and filtered as before and this process was repeated twice more.
The combined filtrates were evaporated in vacuo to give 1,2-bis-
(2-bromo-phenyl)-2-chloro-ethanone (2.00 g) of sufficient purity
Acknowledgements
Permission to use the mass spectrometers and the X-ray dif-
fractometer in the ‘Centro di Analisi e Determinazioni strutturali’ of
the University of Siena is gratefully acknowledged as is the support
of the EPSRC mass spectrometry service at Swansea.

3862
A. Blencowe et al. / Tetrahedron 65 (2009) 3858–3862
5. Crystal data for 13: C16H14Br2S2, MW¼430.21, monoclinic, a¼9.584(3), b¼13.
References and notes
611(2), c¼13.157(2) Å,
b
¼98.20(5)ꢁ, V¼1715.7(11) Å3 (by least-squares re-
finement of 35 randomly selected and automatically centered reflections), space
1. Roberts-Bleming, S. J.; Davies, G. L.; Kalaji, M.; Murphy, P. J.; Celli, A. M.; Donati,
D.; Ponticelli, F. J. Org. Chem. 2003, 68, 7115–7118.
group P21/n, Z¼4, F(000)¼848, Dc¼1.666 g cmꢀ3
, m (Mo Ka
) 4.956 mmꢀ1. The
data were collected on a Siemens P4 four-circle diffractometer with graphite
2. Crystal data for 7: C18H10S4, MW¼354.54, monoclinic, a¼8.0004(3), b¼14.
monochromated Mo
ꢀ1ꢃkꢃ16, ꢀ15ꢃlꢃ15,
K
a
radiation
(
l
¼0.71069 Å) in the range ꢀ1ꢃhꢃ11,
0430(5), c¼27.2128(14) Å,
b
¼92.302(4)ꢁ, V¼3054.9(2) Å3 (by least-squares re-
u
scan mode for 2.15ꢃ
q
ꢃ25.0ꢁ scan range, scan width 1.1ꢁ,
finement of 14,619 reflections), space group P21/n, Z¼8, F(000)¼1456, Dc¼1.
constant scan speed 3.0ꢁ minꢀ1. Three standard reflections measured every 97
reflections showed no variations. 3868 total reflections (Rint¼0.09) were col-
lected at 22 ꢁC. Psi-scan absorption correction was applied. The structure was
solved by direct methods implemented in SHELX-97.6 The refinement was car-
ried out by full-matrix anisotropic least-squares on F2 for all reflections for all
non-H atoms by using SHELX-97.7 The hydrogen atoms were geometrically lo-
cated and included in the structure-factor calculations. Final refinement of 203
542 g cmꢀ3
, m (Mo Ka
) 0.613 mmꢀ1. The data were collected on a Xcalibur-3 Ox-
ford diffraction with graphite monochromated Mo K
a
q
radiation (
l
¼0.71069 Å) in
the range ꢀ10ꢃhꢃ10, ꢀ17ꢃkꢃ17, ꢀ32ꢃlꢃ32, 4.11ꢃ
ꢃ28.34ꢁ scan range. 8795
total reflections (Rint¼0.09) were collected with CCD detector at 22 ꢁC. Multi-scan
absorption correction was applied. The structure was solved by direct methods
implemented in SHELX-97.7 Refinement was carried out by full-matrix aniso-
tropic least-squares on F2 for all reflections for all non-H atoms by using
SHELX-97.6 Hydrogen atoms were geometrically located and included in the
structure-factor calculations. Final refinement of 409 parameters gave R1¼0.049
parameters gave R1¼0.072 and wR2¼0.164 using 2991 reflections with I>2
s(I).
Weighting scheme was w¼1/[
s
2(Fo)2þ0.08P2þ2.771P], where P¼(Fo2þ2F2c)/3.
Minimum and maximum heights in last map were ꢀ0.374 and 0.404 e Åꢀ3, re-
spectively. Atomic scattering factors, including f0 and f00 were taken from Ref. 6.
List of the fractional coordinates, bond lengths and angles, thermal parameters
have been deposited at the Crystallography Data Centre, UK as supplementary
material. Deposit number CCDC 695916.
and wR2¼0.106 using 4453 reflections with I>2
s(I). Weighting scheme was
w¼1/[
s
2(Fo2)þ0.000P2þ8.4049P], where P¼(Fo2þ2F2c)/3. Minimum and maximum
heights in last map were ꢀ0.273 and 0.269 e Åꢀ3, respectively. Atomic scattering
factors, including f0 and f00 were taken from Ref. 6. List of the fractional coordinates,
bond lengths and angles, thermal parameters have been deposited at the Crystal-
lography DataCentre, UKassupplementarymaterial. DepositnumberCCDC695917.
3. Guiu, E.; Claver, C.; Benet-Bucholz, J.; Castillo`n, S. Tetrahedron: Asymmetry 2004,
15, 3365–3373.
6. (a) Kusters, W.; de Mayo, P. J. Am. Chem. Soc. 1974, 96, 3502–3511; (b) Hartke, K.;
Kissel, T.; Quante, J.; Matusch, R. Chem. Ber. 1980, 113, 1898–1906.
7. Sheldrick, G. SHELX-97. Relat. 97-2, Program for X-ray Data Diffraction; Gottingen
University: Gottingen, 1997.
4. Hartke, K.; Bien, N.; Weller, F. Z. Naturforsch. 1996, 51b, 1173–1182.