Regioselective bromination of 1,4-dimethoxy-2,3-dimethylbenzene and conversion into sulfur-functionalised benzoquinones

Article abstract of DOI:10.1016/j.tetlet.2016.02.091

The NBS bromination of 1,4-dimethoxy-2,3-dimethylbenzene has been examined under a variety of conditions in both 1,1,1-trichloroethane and benzotrifluoride. Four different bromination products have been isolated including the previously unknown 1-bromo-4-

Full text of DOI:10.1016/j.tetlet.2016.02.091

Accepted Manuscript
Regioselective bromination of 1,4-dimethoxy-2,3-dimethylbenzene and con-
version into sulfur-functionalised benzoquinones
R. Alan Aitken, Siddharth J. Jethwa, Neville V. Richardson, Alexandra M.Z.
Slawin
PII:
S0040-4039(16)30200-3
DOI:
http://dx.doi.org/10.1016/j.tetlet.2016.02.091
TETL 47366
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
7 February 2016
24 February 2016
25 February 2016
Please cite this article as: Alan Aitken, R., Jethwa, S.J., Richardson, N.V., Slawin, A.M.Z., Regioselective
bromination of 1,4-dimethoxy-2,3-dimethylbenzene and conversion into sulfur-functionalised benzoquinones,
Tetrahedron Letters (2016), doi: http://dx.doi.org/10.1016/j.tetlet.2016.02.091
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Regioselective bromination of 1,4-dimethoxy-
2,3-dimethylbenzene and conversion into
sulfur-functionalised benzoquinones
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R. Alan Aitken*, Siddharth J. Jethwa, Neville V. Richardson, Alexandra M. Z. Slawin

1
Tetrahedron Letters
jo u r n a l h o m e p a g e : w w w . e ls e v ie r . c o m
Regioselective bromination of 1,4-dimethoxy-2,3-dimethylbenzene and conversion
into sulfur-functionalised benzoquinones
R. Alan Aitkena,* Siddharth J. Jethwa,a Neville V. Richardsona and Alexandra M. Z. Slawina
aEaStCHEM School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST, U. K.
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
The NBS bromination of 1,4-dimethoxy-2,3-dimethylbenzene has been examined under a
variety of conditions in both 1,1,1-trichloroethane and benzotrifluoride. Four different
bromination products have been isolated including the previously unknown 1-bromo-4-
bromomethyl-2,5-dimethoxy-3-methylbenzene whose single crystal X-ray structure is presented.
The synthetically useful 2,3-bis(bromomethyl)-1,4-dimethoxybenzene is readily prepared using
either solvent and it has been converted into new sulfur-containing quinone derivatives
Available online
Keywords:
Bromination
2014 Elsevier Ltd. All rights reserved.
Benzotrifluoride
Solvent effects
X-ray structures
In connection with our ongoing studies on electroactive
compounds adsorbed onto metal surfaces,1 we were interested in
constructing simple thiol-tethered benzoquinones 3 and chose as
Because of the two activating methoxy groups, compound 1 is
reactive towards electrophilic ring bromination as well as radical
bromination of the two methyl groups and previous studies have
reported the formation of various mono-, di- and tribrominated
derivatives. The earliest derivative, the mono ring-brominated
product 4 was reported in 1944 from reaction of 1 with bromine
in chloroform,4 and is also formed by the reaction with bromine
in acetic acid5 or hexafluoropropan-2-ol6 and with NBS in
dichloromethane.7 In the first attempt at radical bromination,2
reaction with NBS in the presence of benzoyl peroxide in boiling
carbon tetrachloride for 1 h gave a 60% yield of the mono
bromomethyl compound 5 accompanied by 9% of the dibromide
2. It was noted that the NBS had to be dry otherwise ring
bromination to give 4 would occur, and use of a sample of 1
slightly contaminated by the methoxyphenol resulting from
incomplete methylation in its synthesis gave 4 as the only
product in 60% yield. Most of the reported syntheses of 2 from 1
have used the conditions originally reported by Horner and
coworkers3 involving at least 2 equivalents of NBS and catalytic
benzoyl peroxide in boiling carbon tetrachloride to give the
product in 71–99% yield,8–13 although initiation by AIBN14 and
photochemically15 have also proved effective. The ring dibromo
compound 6 has been prepared by treatment of 1 with two or
more equivalents of bromine in chloroform,16–18 and this could
then be further brominated on the two methyl groups to afford 7
using NBS in CCl4.16,17 The first report of the tribromo compound
8 was in 2001 when it was formed in low yield by treatment of 1
with 2.5 equivalents of NBS with benzoyl peroxide in boiling
carbon tetrachloride for 24 h,19 and its preparation on a 200 g
scale was later reported using 4 equivalents of NBS in CCl4 with
visible light irradiation giving a 51% yield.20 Neither of the
possible unsymmetrical dibrominated derivatives 9 or 10 nor the
a
convenient starting material 2,3-bis(bromomethyl)-1,4-
dimethoxybenzene 2 (Scheme 1). Although this compound was
first obtained as early as 1959 as a minor byproduct in the
monobromination of 1,2 and some nine years later in good yield
by dibromination of 1,3 these and all subsequent preparations of 2
have been conducted using N-bromosuccinimide (NBS) in carbon
tetrachloride as solvent. Since this solvent is now essentially
unavailable due to restrictions on its use under the Montreal
Protocol, we were forced to examine alternative solvents and
describe herein a detailed study on the regioselective bromination
of 1 resulting in the identification of 1,1,1-trichloroethane and
benzotrifluoride as suitable alternative solvents for formation of 2
as well as the formation, full characterisation and single crystal
X-ray structure of a new dibromide isomeric with 2. In addition,
conversion of
2
into sulfur-functionalised benzoquinone
derivatives is described.
Scheme 1: Planned synthetic route
* Corresponding author. Tel. +44 (0)1334 463865; fax +44 (0)1334
463808. E-mail address: raa@st-and.ac.uk (R. A. Aitken)

2
Tetrahedron
remaining possible tribromo compound 11 have so far been
More convincing evidence for structure 9 was provided by the
reported.
observation of a weak HMBC coupling of the ring proton at δH
6.92 with the CH2Br signal at δC 25.7 but not the methyl signal at
δC 12.3. The matter was finally resolved by a single crystal X-ray
diffraction study which confirmed the structure to be 9 (Figure
1).22
Figure 1: X-ray structure of 9 (ORTEP diagram at 50% level)
In the crystal structure the molecular dimensions are in good
agreement with those determined for the tribromo compound 820
and there are weak intermolecular OCH2-H…O and OCH2-
H…BrCH2 interactions, similar to but less extensive than those
reported for 8.
Scheme 2: Possible brominated derivatives of 1
We began by conducting a trial experiment in carbon
tetrachloride using conditions similar to those reported by Horner
and coworkers3 and were able to confirm that the major product
was 2 (Table 1, entry 1). However NMR analysis of the crude
reaction product showed the presence of two additional
compounds which could be separated from 2 by column
chromatography: the tribromide 8 and a dibromide resulting from
one ring bromination and radical bromination of only one methyl
group which was thus either 9 or 10.21 In order to distinguish
between these alternatives an HMBC study was carried out.
Comparison of the 13C NMR spectra of 1, 4, 2 and 8 shows that
ring bromination results in differentiation of the two C–OMe
carbons with the one ortho to Br coming around 149 ppm while
the one meta to Br comes at 154 ppm. Based on this pattern, the
HMBC coupling of the CH2Br protons at δH 4.57 with δC 154.0
but not 149.3, and the methyl protons at δH 2.37 with δC 149.3 but
not 154.0 clearly favours structure 9 but this is not unambiguous
since it depends on the assignment of the two C–OMe carbons.
With each of the reaction products identified we
examined the effect of varying the reaction solvent in the hope of
identifying solvents which would allow the high yielding
preparation of 2 from 1 and NBS but not suffer from the
availability problems of CCl4. Dichloromethane was discounted
since it has been reported to give only the ring bromination
product 4,7 and this was also found to be the case for chloroform.
In previous work where there was a problem of selectivity
between ring and side-chain bromination in diethylthiazoles
using NBS, we found 1,1,2-trichlorotrifluoroethane ("Arklone")
to be a suitable substitute for CCl4,23,24 but surprisingly this was
not the case here. Compound 1 was recovered unreacted after
prolonged treatment with 2.1 equiv. of NBS and either benzoyl
peroxide or AIBN at reflux in this solvent. Two solvents were
found that gave more promising results: 1,1,1-trichloroethane or
methylchloroform (also a Montreal Protocol restricted solvent)
and a,a,a-trifluorotoluene or benzotrifluoride.25 The results
obtained using these are summarised in Table 1.
Table 1: Bromination of 1 under different conditions
Entry
Solvent
CCl4
MeCCl3 2.5
MeCCl3 4.4
MeCCl3 2.5
MeCCl3 2.5
PhCF3
PhCF3
PhCF3
PhCF3
PhCF3
PhCF3
Equiv Initiation
Temp
(°C)
77
75
75
75
75
60
60
Time Product
composition
Product
isolated
NBS
2.5
method
(h)
2.5
2.5
12
1
%
2
%
8
%
9
%
0
0
0
>80
4
1
2
3
4
5
6
7
8
(PhCOO)2 (0.1 eq)
(PhCOO)2 (0.1 eq)
(PhCOO)2 (0.1 eq)
visible irradiation
visible irradiation
(PhCOO)2 (0.1 eq)
(PhCOO)2 (0.1 eq)
(PhCOO)2 (0.1 eq)
70
70
18
18
>80
12
12
2
2
8
4
9
(31%)
(40%)
(32%)
(55%)
(23%)
3
>80
0
35
0
33
0
0
2.5
2.5
4.0
4.0
4.0
4.0
3
0
0
65
0
33
50
90
100
0
100
0
0
0
20
3
0
0
70
9
10
11
(PhCOO)2 (0.03 eq) 102
3
2.5
3
33
50
10
(PhCOO)2 (0.1 eq)
UV irradiation
102
85
2
(35%)

3
Simply substituting trichloroethane for CCl4 gave an identical
crude product composition and after chromatographic
purification led to a slightly improved yield of 2 (entry 2). By
varying the conditions with this solvent, conditions were found to
maximise the yield of each product and thus isolate each of 8, 9
and 4 (entries 3–5). Increasing the amount of NBS gave the
tribromide 8 while ring bromination was favoured by using
photochemical initiation rather than benzoyl peroxide with 4
formed after 1 h which reacted further to give 9 after 3 h. The
initial attempt using benzotrifluoride and conditions otherwise
similar to before gave only ring bromination (entry 6) and
prolonging the reaction time (entry 7) led to 4 being further
brominated to 8 and 9 but none of the desired dibromide 2 was
formed. Increasing the amount of NBS (entry 8) had no effect
and 4 was still the only product. Success was finally achieved by
increasing the reaction temperature to the boiling point of 102 °C,
and conducting the reaction under reflux (entries 9 and 10) gave a
substantial amount of 2 in a mixture with 8 from which it was
readily isolated by recrystallisation. Finally, photochemical
initiation was also tried in this solvent (entry 11) but this gave
mainly the tribromide 8.
or 14 gave the rather unstable quinones 12 and 15,21
respectively, which were converted into their Diels Alder adducts
13 and 1621 by reaction with cyclopentadiene. Conversion of 13
into 16 by reaction with KSCN was demonstrated but proceeded
in low yield and the route from 2 via 14 and 15 to 16 is clearly
preferable. It has been reported24 that treatment of carbocyclic
compounds bearing adjacent CH2SCN groups with sodium
borohydride results in reductive removal of cyanide and
oxidative cyclisation of the resulting dithiol to give the six-
membered ring 1,2-dithiin. This form is suitable for direct
adsorption onto the surface of a metal such as gold. Since this
reductive method is not compatible with the presence of a
quinone, it was carried out with the methoxy groups still in place
and 14 was converted into 1721 in good yield. Unfortunately
however attempted removal of the O-methyl groups from 17
using CAN as before instead resulted in S-oxidation to give the
dithiin monosulfoxide 18 in impure form.21
In conclusion, conditions have been developed to obtain four
different brominated products, including the previously unknown
dibromide 9, from reaction of compound
bromosuccinimide in solvents other than the problematic CCl4.
Benzotrifluoride is satisfactory sustainable and non-
1
with N-
Using benzotrifluoride, multigram quantities of
compound 2 were prepared and so we have been able to
investigate introducing sulfur functionality as well as unmasking
the latent quinone. In connection with our previously reported
method of directly constructing dihydrotetrathiafulvalenes by
1,3-dipolar cycloaddition to the strained double bond of
norbornenes,26 the formation of bicyclo[2.2.1] derivatives was
also of interest (Scheme 3).
a
environmentally damaging solvent for the production of the
symmetrical dibromide 2, and this product has been further
transformed into several sulfur-containing intermediates aimed
towards the synthesis of electroactive organic compounds
suitable for direct adsorbtion on metal surfaces.
Supplementary data
Supplementary data (Detailed experimental procedures and
1
copies of H and 13C NMR spectra for all new compounds)
associated with this article can be found, in the online version, at
http://………… These data include MOL files and InChiKeys of
the most important compounds described in this article..
References and notes
1.
Jethwa, S. J.; Grillo, F.; Früchtl, H. A.; Simpson, G. J.; Treanor,
M.-J.; Schaub, R.; Francis, S. M.; Richardson, N. V.; Aitken, R.
A. Chem. Commun. 2014, 50, 10140–10143.
McHale, D.; Mamalis, P.; Marcinkiewicz, S.; Green, J. J. Chem.
Soc. 1959, 3358–3362.
Horner, L.; Subramaniam, P. V.; Eiben, K. Liebigs Ann. Chem.
1968, 714, 91–111.
Smith, L. I.; Tess, R. W. H. J. Am. Chem. Soc. 1944, 66, 1523–
1525.
Trost, B. M.; Shen, H. C.; Dong, L.; Surivet, J.-P. Sylvain, C. J.
Am. Chem. Soc. 2004, 126, 11966–11983.
Eberson, L.; Hartshorn, M. P.; Radner, F.; Persson, O. J. Chem.
Soc., Perkin Trans. 2 1998, 59–70.
Wu, Z.; Harutyunyan, S. R.; Minnaard, A. J. Chem. Eur. J. 2014,
20, 14250–14255.
Ardecky, R. J.; Kerdesky, F. A. J.; Cava, M. P. J. Org. Chem.
1981, 46, 1483–1485.
2.
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6.
7.
8.
9.
Kotha, S.; Kuki, A. Chem. Lett. 1993, 299–302.
10. Eskildsen, J.; Christensen, T.; Reenberg, T.; Larsen, U.;
Christensen, J. B. Org. Prep. Proced. Int. 2000, 32, 398–400.
11. Utley, J. H. P.; Ramesh, S.; Salvatella, X.; Szumerits, S.;
Motevalli, M.; Nielsen, M. F. J. Chem. Soc., Perkin Trans. 2 2001,
153–163.
Scheme 3: Reagents and conditions (i) CAN, aq MeCN, rt;
(ii) cyclopentadiene, MeCN, rt; (iii) KSCN, EtOH, reflux; (iv)
NaBH4, EtOH/THF (1:20)
12. Mazzini, F.; Galli, F.; Salvadori, P. Eur. J. Org. Chem. 2006,
5588–5593.
13. Schneider, P.; Riedl, R.; Tigges, M.; Gitzinger, M.; Pieren, M.;
Levi, A.; Sephton, M.; Schellhorn, B.; Zueger, P.; Brand, M.;
Gygax, D.; Spies, P. PCT Int. Appl. WO 2014/118361 (2014).
14. Honek, J. F.; Mancini, M. L.; Belleau, B. Tetrahedron Lett. 1983,
24, 257–260.
Oxidative removal of the O-methyl groups to give the
quinone function was achieved by treatment with ceric
ammonium nitrate (CAN) in aqueous acetonitrile12 and this could
be done before or after introduction of sulfur in the form of a
thiocyano group.27 Thus the reaction of 2 with potassium
thiocyanate in ethanol gave 14,21 and CAN treatment of either 2
15. Jansen, R. J.; de Gelder, R.; Rowan, A. E.; Scheeren, H. W.;
Nolte, R. J. M. J. Org. Chem. 2001, 66, 2643–2653.

4
Tetrahedron
16. Mendez-Rojas, M. A.; Ejsmont, K.; Watson, W. H. J. Chem.
9, 11-H syn); δC 196.1 (C-3, C-6), 144.8 (C-4, C-5), 135.3 (C-9, C-
10), 111.5 (SCN), 50.3 (C1, C-8 or C-2, C-7), 49.3 (C-11), 48.4
(C1, C-8 or C-2, C-7) and 29.0 (CH2SCN); m/z (ES) 339 (M+Na,
100%). 17: yellow solid, mp 123–130 °C (Found 229.0359.
C10H13O2S2 (M+H) requires 229.0357); δH 6.71 (2 H, s, CH), 3.99
(4 H, s, CH2) and 3.78 (6 H, s, CH3); δC 151.1 (C-5, C-8), 123.5
(C-4a, C-8a), 107.6 (C-6, C-7), 55.8 (OCH3) and 28.5 (C-1, C-4);
m/z (CI) 229 (M+H, 85 %), 228 (M+, 54), 165 (85), 164 (100) and
151 (86). 18: brown liquid (Found, 267.0128. C10H12O3NaS2
(M+Na) requires 267.0126); δH 6.874 (1 H, s, CH), 6.869 (1 H, s,
CH), 4.57 (1 H, s), 4.53 (1 H, s), 4.21 (1 H, d, J = 14), 3.95 (1 H,
d, J = 14), 3.84 (3 H, s, CH3) and 3.83 (3 H, s, CH3); δC 152.5 (C-5
or C-8), 149.3 (C-8 or C-5), 129.3 (C-4a or C-8a), 125.5 (C-8a or
C-4a), 110.8 (C-6 or C-7), 110.0 (C-6 or C-7), 56.2 (-OCH3), 55.9
(-OCH3), 51.4 (C-1) and 25.0 (C-4); m/z (ES) 267 (M+Na, 100
%), 179 (15) and 142 (8).
Crystallogr. 2002, 32, 177–184.
17. Sandulache, A.; Silva, A. M. S.; Cavaleiro, J. A. S. Monatsh.
Chem. 2003, 134, 551–563.
18. Poloukhtine, A.; Popik, V. V. J. Org. Chem. 2006, 71, 7417–7421.
19. Rinke, K.; Grunert, R.; Bednarski, P. J. Pharmazie, 2001, 56, 763–
769.
20. Hammershøj, P.; Riis, E.; Christensen, J. B. Acta Crystallogr.,
Sect. E 2005, 61, o2997–o2998.
21. 9: colourless crystals, mp 83–84 °C (Found 324.9265.
C10H1379Br81BrO2 (M+H) requires 324.9262; found 322.9289.
C10H1379Br2O2 (M+H) requires 322.9282); δH 6.92 (1 H, s, CH),
4.57 (2 H, s, CH2), 3.85 (3 H, s, OCH3), 3.75 (3 H, s, OCH3) and
2.37 (3 H, s, CH3); δC 154.0 (C-5), 149.3 (C-2), 133.4 (C-3), 125.1
(C-4), 117.9 (C-1), 113.1 (C-6), 60.6 (5-OCH3), 56.2 (2-OCH3),
25.7 (CH2Br) and 12.3 (CH3); HMBC study shows correlation of
δH 6.92 with δC 25.7, correlation of δH 4.57 with δC 154.0, and δH
2.37 with δC 149.3; m/z 327 (81Br2-M+H, 5%), 326 (81Br2-M, 4),
325 (81Br79Br-M+H, 10), 324 (81Br79Br-M, 7), 323 (79Br2-M+H, 6),
322 (79Br2-M, 3), 245 (79Br-M–Br, 89) and 243 (81Br-M–Br, 100).
12: brown oil (Found 292.8811. C8H7O279Br2 (M+H) requires
292.8813); δH 6.86 (2 H, s, CH) and 4.38 (4 H, s, CH2); δC 184.2
(C-1, C-4), 141.0 (C-2, C-3), 136.4 (C-5, C-6) and 19.5 (CH2Br);
m/z (CI) 297/295/293 (M+, 10/20/9 %), 215/213 (72/78), 134 (35),
123 (100) and 105 (76). 13: yellow crystals, mp 68–71 °C (Found
358.9290. C13H13O279Br2 (M+H), requires 358.9292); δH 6.10 (2 H,
t, J = 2, 9,10-H), 4.32 and 4.23 (4 H, AB pattern, J = 10, CH2Br),
3.58 (2 H, m, 1,8-H), 3.34 (2 H, m, 2,7-H), 1.55 (1 H, half AB
pattern of t, J = 9, 1.8, 11-H syn) and 1.46 (1 H, half AB pattern of
m, J = 9, 11-H anti); δC 196.1 (C-3, C-6), 146.4 (C-4, C-5), 135.2
(C-9, C-10), 49.8 (C-1, C-8 or C-2, C-7), 49.1 (C-11), 48.5 (C-1,
C-8 or C-2, C-7) and 20.6 (CH2Br); m/z (CI) 363/361/359 (M+,
10/22/12 %), 297/295/293 (30/62/30), 281/279 (50/45), 135 (50)
and 66 (100). 14: grey solid, mp 100–102 °C (Found 303.0232.
C12H12N2O2NaS2 (M+Na) requires 303.0238); δH 6.91 (2 H, s,
CH), 4.36 (4 H, s, CH2) and 3.86 (6 H, s, CH3); δC 151.6 (C-1, C-
4), 123.1 (C-2, C-3), 112.3 (SCN), 111.8 (C-5, C-6), 56.0 (OCH3)
and 29.4 (CH2); m/z (ES) 303 (M+Na, 100 %) and 222 (8). 15:
brown solid, mp 65–67 °C; δH 6.98 (2 H, s, CH) and 4.15 (4 H, s,
CH2); δC 184.1 (C-1, C-4), 139.3 (C-2, C-3), 136.8 (C-5, C-6),
111.4 (SCN) and 28.1 (CH2). 16: brown oil (Found 339.0233.
C15H12N2O2NaS2 (M+Na) requires 339.0238); δH 6.16 (2 H, t, J =
1.8, 9,10-H), 3.99 (4 H, d, J = 1.5, CH2SCN), 3.63 (2 H, m, 1,8-
H), 3.41 (2 H, dd, J = 2.4, 1.5, 2,7-H), 1.60 (1 H, half AB pattern
of t, J = 9, 1.8, 11-H anti) and 1.51 (1 H, half AB pattern of m, J =
22. Crystal data for 9, C10H12Br2O2, Mr = 324.01, colourless prism,
orthorhombic, space group P212121, a = 4.2831(10), b = 15.175(4),
c = 17.227(4) Å, V = 1119.7(5) Å3, Z = 4, Dc 1.922 Mg m-3, T =
93(2) K, R1 = 0.0347 and wR2 = 0.0782 for 1751 reflections [I >
2s(I)] and 130 parameters. Data were recorded using a Rigaku
XtaLB P200, MoKa radiation (confocal optic, l 0.71075 Å) and
Saturn detector. The structure was solved by direct methods and
refined using full-matrix least-squares methods. Crystallographic
data (excluding structure factors) for the structure have been
deposited at the Cambridge Crystallographic Data Centre as
supplementary publication No. CCDC-1443548. Copies of the
data can be obtained free of charge on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336 033;
email: deposit@ccdc.cam.ac.uk.
23. Aitken, K. M.; Aitken, R A. Tetrahedron 2008, 64, 4384–4386.
24. Aitken, K. M.; Aitken, R. A.; MacGregor, C. I.; Traore, M. D. M.;
Slawin, A. M. Z. J. Chem. Crystallogr. 2015, 45, 461–465.
25. Benzotrifluoride has previously been reported as an effective
solvent for benzylic bromination using NBS, but the examples
described did not include any where there was the risk of
competing ring bromination. See: Suarez, D.; Laval, G.; Tu, S.-
M.; Jiang, D.; Robinson, C. L.; Scott, R.; Golding, B. T. Synthesis
2009, 41, 1807–1810.
26. Aitken, R. A.; Hill, L.; Lightfoot, P. Tetrahedron Lett. 1997, 38,
7927–7930.
27. Oda, M.; Zhang, Y.; Thanh, N. C.; Hayashi, S.; Zuo, S.; Kuroda,
S. Heterocycles 2006, 68, 1031–1041.

*Highlights
 Four different bromination products can be prepared without using CCl4
 Benzotrifluoride is a suitable CCl4 replacement for radical bromination
 The X-ray structure of a new dibromination product is presented
 The target dibromide is converted to sulfur-containing quinone derivatives