N-bromosuccinimide-dimercaptoethane cobromination of alkenes: Synthesis of β,β′-dibromodithioethers

Article abstract of DOI:10.1016/S0040-4039(03)01221-8

Alkenes react in diethyl ether with N-bromosuccinimide (NBS) and dimercaptoethane to afford the corresponding β,β′-dibromodithioethers. Bromine and dimercaptoethane are added to the aliphatic terminal olefins in an anti-Markovnikov fashion.

Full text of DOI:10.1016/S0040-4039(03)01221-8

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 5263–5265
N-Bromosuccinimide-dimercaptoethane cobromination of alkenes:
synthesis of b,b%-dibromodithioethers
Moufida Romdhani Younes,a Mohamed Moncef Chaabounib,* and Ahmed Bakloutia
aLaboratoire de Chimie Structurale Organique, Faculte´ des Sciences de Tunis, 1060 Tunis, Tunisia
bEcole Supe´rieure des Industries Alimentaires, 58 Avenue Alain Savary, 1003 Tunis, Tunisia
Received 1 April 2003; revised 5 May 2003; accepted 16 May 2003
Abstract—Alkenes react in diethyl ether with N-bromosuccinimide (NBS) and dimercaptoethane to afford the corresponding
b,b%-dibromodithioethers. Bromine and dimercaptoethane are added to the aliphatic terminal olefins in an anti-Markovnikov
fashion. © 2003 Elsevier Science Ltd. All rights reserved.
The cohalogenation of alkenes with halogens and
nucleophilic solvents like water, dimethylsulfoxide,
dimethylformamide, carboxylic acids, alcohols, nitriles
and ethers is well documented,1 but little work has been
carried out on the formation of a CꢀS bond with
sulfur-containing nucleophiles. The two reactions
reported in the literature are related to the incorpora-
tion of the thiocyanate or the sulfone functionality by
cohalogenation of an olefin in the presence of
thiocyanate2–5 or by using sodium benzenesulfinate,6
but to our knowledge, the use of thiols has not been
described previously. In this paper, we report the prepa-
ration of b,b%-dibromodithioethers resulting from elec-
trophilic bromination by N-bromosuccinimide (NBS)
followed by dimercaptoethane addition to two mole
equivalents of olefins (Scheme 1).
anti-Markovnikov regioselectivity, probably because
nucleophilic attack of dimercaptoethane onto bromo-
nium cyclic ion takes place with steric factors con-
trolling the regioselectivity. This regioselectivity was not
observed in the case of styrene 1d, which gave a mixture
of Markovnikov and anti-Markovnikov products.7 In
resonance terms the bromonium ion formed from sty-
rene is in equilibrium with a carbocation form which is
stabilized by conjugation.
In all cases, variable amounts (16–33%) of the corre-
sponding dibromo compounds were found, except in
the case of alkene 1c. However, the separation of the
undesired side products from the corresponding
dithioethers was remarkably easy by evaporation at
reduced pressure (1.5 Torr) at 50°C and then by con-
ventional column chromatography on silica gel. After a
literature search, we have found that the formation of
dihalo derivatives is observed in the halofluorination
reaction of a variety of alkenes and a mechanism for
this side reaction was postulated.8
As shown in Table 1, this electrophilic cobromination
reaction allows the preparation of b,b%-dibromo-
dithioethers in good yields. With aliphatic terminal
alkenes 1a–c the addition proceeds with a marked
Scheme 1.
Keywords: alkenes; dimercaptoethane; cohalogenation; thioethers.
* Corresponding author. Fax: 216 71 885 008; e-mail: chaabouni.medmoncef@iresa.agrinet.tn
0040-4039/03/$ - see front matter © 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4039(03)01221-8

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M. Romdhani Younes et al. / Tetrahedron Letters 44 (2003) 5263–5265
Table 1. Cobromination of alkenes with NBS and dimercaptoethane
A typical procedure used in the synthesis of b,b%-dibromo-
dithioethers is as follows: Dimercaptoethane (27
mmol) was added dropwise over 30 min to a stirred
solution of alkene 1 (50 mmol) and N-bromosuccin-
imide (8.89 g, 50 mmol) in diethyl ether (50 mL) at
0°C under nitrogen. After addition, the reaction mix-
ture was stirred at rt for 30 min. The mixture obtained
was filtered, washed with water, dried over MgSO4 and
concentrated. After evaporation of the dibromo
product at 50°C/1.5 Torr, the residue was purified by
column chromatography on silica gel, eluting with
light petroleum. All products were fully characterized
1
by H and 13C NMR spectroscopy and HRMS meth-
ods.9

M. Romdhani Younes et al. / Tetrahedron Letters 44 (2003) 5263–5265
5265
Scheme 2.
Scheme 3.
Some applications of b,b%-dibromodithioethers in
organic synthesis are summarized in Schemes 2 and 3.
Dithiol 4a10 (Scheme 2) was synthesized from dibromo-
dithioether 2a by reaction of two mole equivalents of
dimercaptoethane in absolute ethanol in the presence of
sodium metal.
7. Compound 2d, HRMS: mol. mass calcd 458.94516 (for
C18H21S2Br2), found 458.94515 (M+H)+.
8. Camps, F.; Chamorro, E.; Gasol, V.; Guerrero, A. J.
Org. Chem. 1989, 54, 4294–4298.
9. Spectral data: compound 2a: 1H NMR (300 MHz,
CDCl3): l=0.93 (t, J=6.9 Hz, 6H), 1.39–1.49 (m, 8H),
2.77 (s, 4H), 3.02 (m, 4H), 3.68 (m, 2H). 13C NMR (75
MHz, CDCl3): l=13.78, 18.80, 33.84, 38.24, 40.09, 69.39.
When Cs2CO3 was used as the base in DMF,11,12 the
dibromide 2b reacted with dimercaptoethane to afford
the thiacrown ether 5b13 (Scheme 3).
1
Compound 2b: H NMR (300 MHz, CDCl3): l=0.92 (t,
J=6.9 Hz, 6H), 1.30–1.60 (m, 8H), 1.79 (m, 2H), 2.03 (m,
2H), 2.79 (s, 4H), 3.05 (m, 4H), 4.09 (m, 2H). 13C NMR
(75 MHz, CDCl3): l=13.83, 21.93, 29.33, 33.08, 36.73,
40.90, 55.09. Compound 2c: 1H NMR (300 MHz,
CDCl3): l=1.08 (s, 18H), 2.83–3.15 (m, 8H), 3.97 (m,
2H). 13C NMR (75 MHz, CDCl3): l=27.33, 33.09, 36.38,
37.73, 69.91. HRMS: mol. mass calcd 419.00776 (for
C14H29S2Br2), found 419.00765 (M+H)+. Compound 2e:
1H NMR (300 MHz, CDCl3): l=1.43–1.90 (m, 12H),
2.27–2.39 (m, 4H), 2.83 (s, 4H), 3.02 (m, 2H), 4.29 (m,
2H). 13C NMR (75 MHz, CDCl3): l=23.02, 30.29, 32.29,
33.48, 38.42, 50.34, 56.79.
In conclusion, this paper describes a simple route to
b,b%-dibromodithioethers. We have shown that the
addition of bromine and sulfur to terminal olefins takes
place regioselectively in an anti-Markovnikov manner.
The reaction products may prove to be useful, except in
the case of styrene, in synthesis and particularly for
thiacrown ethers as realized from the conversion of 2b
into 5b.
10. Spectral data: compound 4a: 1H NMR (300 MHz,
CDCl3): l=0.93 (t, J=6.9 Hz, 6H), 1.39–1.56 (m, 8H),
1.76 (br, 2H), 2.76 (m, 8H), 2.88 (m, 8H), 3.01 (m, 2H).
13C NMR (75 MHz, CDCl3): l=13.84, 19.82, 30.25,
32.34, 35.78, 37.49, 38.54, 46.04. MS (CI-NH3) m/z 435
(M+17)+, 419 (M+1)+, 418 (M+).
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