Highly efficient one-step conversion of selenol esters into symmetrical diselenides in the presence of elemental iodine in methanolic solution

Article abstract of DOI:10.1080/10426500902753379

A facile, efficient, and convenient procedure has been developed for the direct conversion of selenol esters into the corresponding diselenides in the presence of elemental iodine at room temperature.

Full text of DOI:10.1080/10426500902753379

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Phosphorus, Sulfur, and Silicon and the
Related Elements
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Highly Efficient One-Step Conversion
of Selenol Esters into Symmetrical
Diselenides in the Presence of Elemental
Iodine in Methanolic Solution
Barahman Movassagh a & Mona Moradi a
a Department of Chemistry, K. N. Toosi University of Technology,
Tehran, Iran
Available online: 28 Dec 2009
To cite this article: Barahman Movassagh & Mona Moradi (2009): Highly Efficient One-Step Conversion
of Selenol Esters into Symmetrical Diselenides in the Presence of Elemental Iodine in Methanolic
Solution, Phosphorus, Sulfur, and Silicon and the Related Elements, 185:1, 154-157
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Phosphorus, Sulfur, and Silicon, 185:154–157, 2010
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500902753379
HIGHLY EFFICIENT ONE-STEP CONVERSION
OF SELENOL ESTERS INTO SYMMETRICAL
DISELENIDES IN THE PRESENCE OF ELEMENTAL IODINE
IN METHANOLIC SOLUTION
Barahman Movassagh and Mona Moradi
Department of Chemistry, K. N. Toosi University of Technology, Tehran, Iran
A facile, efficient, and convenient procedure has been developed for the direct conversion of
selenol esters into the corresponding diselenides in the presence of elemental iodine at room
temperature.
Keywords Deprotection; diselenides; iodine; oxidation; selenol esters
INTRODUCTION
Organoselenium compounds have emerged as important reagents and intermediates
in organic synthesis,1 and they also have biological importance, because proteins containing
selenium are essential components of certain bacterial and mammalian enzyme syntheses.2
Since selenium chemistry is relatively underdeveloped, there are needs for novel synthetic
strategies in selenium functionality incorporation, protection, deprotection, and conversion.
The preparation of organic selenols and diselenides has been extensively studied
during the last few decades concerning synthetic application for the efficient selenyla-
tion of organic compounds.3 Among the selenium reagents, diphenyl diselenide is com-
monly employed for organoselenylation reactions because of its versatile reactivity (nu-
cleophilic as well as electrophilic) depending on the reaction conditions and thus allows
a myriad of transformations through α-selenocarbanions,4 α-selenocarbenium ions,5 and
α-selenocarbon-centered radicals.6
In the recent years, a number of researchers have employed selenoacetates as effi-
cient sources of acyl radicals.7 The numerous examples for the homolytic cleavage of the
acyl C Se bond to give the corresponding selenyl radicals are contrasted by the surpris-
ing paucity of examples of selenolate anions derived from selenoacyl compounds. Vinyl
selenoacetates have been cleaved by sodium/HMPA in DMF to give vinyl selenolates
that were oxidized with iodine to yield divinyl diselenides.8 Also, aryl selenoesters have
been deprotected with potassium carbonate in aqueous THF to give selenolates that add
Received 6 December 2008; accepted 15 January 2009.
Financial support from the K. N. Toosi University of Technology Research Council and the Iranian National
Science Foundation (INSF, Grant No. 86063/21) is gratefully acknowledged.
Address correspondence to Barahman Movassagh, Department of Chemistry, K. N. Toosi University of
Technology, P. O. Box 16315-1618, Tehran, Iran. E-mail: bmovass1178@yahoo.com
154

CONVERSION OF SELENOL ESTERS INTO SYMMETRICAL DISELENIDES
155
to phenylpropionitrile and give selenocinnamonitriles.9 Aqueous ammonia in THF10 and
n-butylamine in ethanol11 have also been used for acyl–selenium cleavage of selenoesters.
In one report, UV-irradiation of a selenoester afforded a mixture of products, from which
57% of the corresponding diselenide was isolated.12
Elemental iodine is a mild, cheap, nontoxic, and easily available oxidizing reagent.
In recent years, it has received considerable attention as an effective catalyst for various
organic transformations13 under mild and convenient conditions to afford the corresponding
products in excellent yields with high selectivity. However, there is no example of direct
iodine-induced cleavage of selenol esters to afford symmetrical diselenides.
RESULTS AND DISCUSSION
In the course of our investigations on the synthesis of selenol esters from dise-
lenides,14,15 we discovered a simple process for the facile cleavage of the acyl–selenium
bond and subsequent oxidation promoted by elemental iodine in dry methanol at room tem-
perature in an aerial atmosphere to afford diselenides in high to excellent yields (Scheme 1).
Scheme 1
In a model reaction, Se-phenyl butaneselenoate (1 mmol) was taken as a represen-
tative selenol ester. The effects of several solvents such as acetonitrile, ethanol, methanol,
trichloromethane, and ethyl acetate were examined in the presence of iodine (0.4 mmol)
at room temperature under ambient atmosphere, and the best result was obtained with dry
methanol. Under the same reaction conditions, other experiments were also carried out with
various amounts of iodine in dry methanol at room temperature (Table I); the best molar
ratio of selenolester:iodine was found to be 1:0.4.
A series of selenolesters was treated with anhydrous methanol in the presence of
nearly equimolar amounts of iodine (molar ratio of selenolesters:iodine = 1:0.4, as above).
The results are summarized in Table II. Diselenides prepared from aryl selenolesters
(Table II, entries 1–8) generally give higher yields than those produced from alkyl (benzyl)
Table I Deprotection-oxidation of Se-phenyl butaneselenoate with different molar ratios of iodinea
Entry
I2 (mmol)
Time (h)
Yield (%)b
1
2
3
4
5
0.1
0.2
0.3
0.4
0.5
10.5
10
9
4.5
4.5
63
65
92
99
95
aReaction conditions: Se-phenyl butaneselenoate (1 mmol), dry methanol (3 mL), room temperature.
bYields of isolated products.

156
B. MOVASSAGH AND M. MORADI
Table II Diselenides obtained by iodine-promoted cleavage of Se CO bonds
Reaction
Time (h)
Entry
R1
R2
Diselenide
Yield (%)a,b
1
2
3
4
5
6
7
8
9
10
11
12
13
Ph
Ph
Ph
Ph
Ph
CH3
2a
2a
2a
2a
2a
2b
2c
2c
2d
2d
2d
2d
2d
2
8316
8716
9916
9316
9116
9417
9817
9617
813a
843a
783a
853a
883a
CH3CH2
CH3CH2CH2
(CH3)3C
Ph
5.5
4.5
1
1
4-ClC6H4
4-CH3C6H4
4-CH3C6H4
PhCH2
PhCH2
PhCH2
Ph
5.5
4.5
6
3.5
5
3
4
3
CH3CH2CH2
CH3CH2
CH3
CH3CH2
CH3CH2CH2
(CH3)3C
Ph
PhCH2
PhCH2
aYields of isolated products.
bReferences for known compounds.
selenolesters (Table II, entries 9–13). It is predicted that iodine first facilitates the Se CO
bond cleavage and effects removal of the acyl group with formation of the corresponding
selenols, and in the next step, it catalyzes the oxidation of the selenols to the diselenides.
CONCLUSION
In summary, we have developed a new mild, convenient, and efficient protocol for the
deprotection–oxidation of selenolesters to the corresponding diselenides in the presence of
iodine at room temperature.
EXPERIMENTAL
Selenolesters were prepared according to the method reported earlier.14 Yields refer
to isolated products. Melting points were determined by a Bu¨chi B-540 apparatus. IR
1
spectra were run on an AAB FTLA 2000 instrument. The H NMR (300 MHz) and 13C
NMR (75MHz) spectra were recorded on a Bruker AQS-300 Avance NMR spectrometer.
The progress of the reaction was followed by TLC using silica-gel SILG/UV 254 plates.
Products were characterized by comparing their physical and spectral data with those of
the authentic samples.
Typical Procedure for the Preparation of Diphenyl Diselenide
A mixture of Se-phenyl butaneselenoate (0.227 g, 1 mmol), I2 (0.1 g, 0.4 mmol), and
anhydrous MeOH (3 mL) was stirred in a round-bottom flask open to air at room temperature
for 4.5 h. The progress of the reaction was monitored by TLC. After completion of the
reaction, MeOH was removed under reduced pressure, and the residue was diluted with
EtOAc (10 mL), washed with aqueous sodium thiosulfate (2 × 5 mL, 10%) and subsequently
with water (2 × 5 mL). The organic layer was dried over anhydrous Na2SO4, followed by
evaporation of the solvent to obtain the crude product, which was subjected to preparative

CONVERSION OF SELENOL ESTERS INTO SYMMETRICAL DISELENIDES
157
TLC (silica gel, eluent n-hexane:CH2Cl2 = 7:1) to afford 0.154 g (99%) of pure diphenyl
diselenide as orange crystals; mp 59–60◦C (lit.16 mp 58–61◦C).
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