Deoxygenation of sulfoxides, selenoxides, telluroxides, sulfones, selenones and tellurones with Mg-MeOH

Article abstract of DOI:10.1016/j.tet.2006.11.027

The deoxygenation of a variety of sulfoxides, selenoxides, telluroxides, sulfones, selenones and tellurones has been reported with Mg-MeOH at room temperature in nearly quantitative yields. The deoxygenation is proposed to proceed by SET from Mg to the substrate.

Full text of DOI:10.1016/j.tet.2006.11.027

Tetrahedron 63 (2007) 966–969
Deoxygenation of sulfoxides, selenoxides, telluroxides, sulfones,
selenones and tellurones with Mg–MeOH
*
Jitender M. Khurana, Vandana Sharma and Silvi A. Chacko
Department of Chemistry, University of Delhi, Delhi-110007, India
Received 29 July 2006; revised 31 October 2006; accepted 9 November 2006
Available online 28 November 2006
Abstract—The deoxygenation of a variety of sulfoxides, selenoxides, telluroxides, sulfones, selenones and tellurones has been reported with
Mg–MeOH at room temperature in nearly quantitative yields. The deoxygenation is proposed to proceed by SET from Mg to the substrate.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
varying the molar ratios of substrate to magnesium to opti-
mize the molar ratios for quantitative conversions. The reac-
tions were induced by the addition of 1–2 crystals of iodine.
The induction times and hence the times for completion of
reactions were longer in the absence of iodine but did not
affect the products. No deoxygenations were observed with
magnesium in tetrahydrofuran or ethanol using diphenyl
sulfoxide as a model substrate. These results are summarized
in Tables 1 and 2.
Recently Mg–MeOH has evoked considerable interest as an
inexpensive and efficient reagent for a variety of organic
transformations.1 The dissolving metal reducing system gen-
erated by this reagent combination provides a convenient
electron transfer/protic source for the reduction of C–C
double bonds and triple bonds attached to esters, nitriles,
amides and other carbonyls,1 reduction of azides,2 reductive
coupling of nitroarenes,3 dehalogenation of bromides and
iodides,4 reduction of aromatic carbonyl compounds,5 de-
sulfonylation reactions of sulfones,6 deoxygenation of
N-oxides,7 and reductive cleavages and cyclizations.1 Inview
of its diverse role as a reducing reagent, we decided to
investigate the deoxygenation of sulfoxides, selenoxides,
telluroxides, sulfones, selenones and tellurones. Though
deoxygenation of sulfoxides8 is well known, deoxygenation
of selenoxides8a,9 and telluroxides9c has received only scant
attention. Sulfones are reported to undergo desulfonylation,6
while deoxygenation of selenones and tellurones is not
known.
O
Mg
(1)
(2)
R
X
R'
R'
R
R
X
R'
R'
MeOH, rt
O
X
Mg
R
X
MeOH, rt
O
X = S, Se, Te ; R', R = alkyl, aryl, benzyl
The progress of the reactions was monitored by thin layer
chromatography and the products were obtained by a
simple work-up procedure. Dialkyl and phenyl alkyl sulfox-
ides and sulfones were resistant to deoxygenation probably
because the a-hydrogens are more acidic and can be readily
abstracted by the magnesium methoxide formed in the reac-
tion, rather than undergoing electron transfer from magne-
sium. However, benzyl phenyl sulfoxide and sulfone did
undergo deoxygenation under these conditions. Phenyl sul-
fone, which has been reported to undergo desulfonylation,6
also underwent deoxygenation under our reaction condi-
tions. It is also worth noting that all classes of selenoxides
and selenones (diaryl, aryl alkyl and dialkyl) were deoxy-
genated successfully. Telluroxides and tellurones required
higher molar ratios of magnesium and longer reaction times
for complete deoxygenation compared to the sulfur and
2. Results and discussion
This is the first report on the deoxygenation of a variety of
sulfoxides, selenoxides, telluroxides, sulfones, selenones
and tellurones, to give the corresponding organo chalcogen-
ides using Mg–MeOH at ambient temperature. The reactions
have been performed with different sulfoxides, selenoxides,
telluroxides, sulfones, selenones and tellurones, and the
deoxygenated products were obtained in high yields (Eqs.
1 and 2). Reactions of all substrates were carried out by
* Corresponding author. Tel.: +91 11 27667725x1384; fax: +91 11
27666605; e-mail: jmkhurana@chemistry.du.ac.in
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.11.027

J. M. Khurana et al. / Tetrahedron 63 (2007) 966–969
Table 1. Reactions of sulfoxides, selenoxides and telluroxides with Mg–MeOH
967
Entry
Substrate
O
S:Mg
Time (h)
Yields (%)a
R–X–R0
Obsd mp (lit. mp) (ꢀC)
R
X R'
1
2
Diphenyl sulfoxide
1:10
1:10
1:20
1:20
1:20
1:20
1:20
1:20
1:20
1:20
1:20
1:20
1:20
1:20
1:20
1:25
1:25
1:25
1:30
1:30
1.5
2
3
3
3
3
3
24
2
3
3.5
3.5
3
3
3
3
5
5
24
4
7817
7517
8217
8017
8017
8117
8217
—
46 (44)
Benzyl phenyl sulfoxide
m-Chlorophenyl phenyl sulfoxide
p-Bromophenyl phenyl sulfoxide
Phenyl m-tolyl sulfoxide
Phenyl p-tolyl sulfoxide
p-Anisyl phenyl sulfoxide
n-Propyl phenyl sulfoxide
Diphenyl selenoxide
Di-p-tolyl selenoxide
Di-p-anisyl selenoxide
Di-p-bromophenyl selenoxide
n-Propyl p-tolyl selenoxide
n-Propyl phenyl selenoxide
Di-n-butyl selenoxide
3
4
—
—
5
6
—
—
7
8
—
—
b
—
9
8018
8218
8218
8218
7018
7118
7018
8719
8219
8219
7519
7319
—
68–69 (69)
54–55 (55–56)
112 (114–115)
—
—
—
90–91 (93–94)
55 (54–55)
64–65 (67)
—
10
11
12
13
14
15
16
17
18
19
20
Di-p-chlorophenyl telluroxide
Di-p-anisyl telluroxide
Di-p-tolyl telluroxide
Di-n-butyl telluroxide
Methyl phenyl telluroxide
—
a
Isolated yields.
No reaction.
b
selenium analogues, probably due to their higher metallic
character. No desulfurized, deselenized or detellurized
products were obtained in these reactions. The deoxygen-
ation of sulfones, selenones and tellurones proceeds via
the corresponding sulfoxides, selenoxides and telluroxides
as confirmed by monitoring the progress of the reaction
with lower ratios of magnesium. In all cases, the halogen
group attached to the aryl unit was unaffected. Mg reacts
very quickly with MeOH and, therefore, an excess of Mg
is required for completion of reactions.
Reduction of these substrates with magnesium methoxide
formed in situ, in a similar fashion to a Meerwein–Ponn-
dorff–Verley reduction, has been ruled out since diphenyl
sulfoxide and diphenyl sulfone did not undergo any reaction
with preformed magnesium methoxide in methanol. We pro-
pose that the deoxygenations are proceeding via SET from
magnesium to the LUMO of R2XO2 (X¼S, Se, Te) to give
a radical anion, which accepts another electron followed
by loss of magnesium oxide to give R2X¼O, which undergo
subsequent rapid deoxygenation to give the corresponding
Table 2. Reactions of sulfones, selenones and tellurones with Mg–MeOH
Entry
S:Mg
Time (h)
Yields (%)a
R–X–R0
Obsd mp (lit. mp) (ꢀC)
Substrate
O
R
X
R'
O
1
2
3
4
5
6
7
8
Diphenyl sulfone
1:20
1:20
1:20
1:20
1:20
1:20
1:20
1:20
1:20
1:20
1:20
1:20
1:20
1:25
1:25
1:25
1:25
1:35
1:35
1:35
1:35
1:35
1:35
1.5
3
3
2.5
3
3
8217
8217
8317
7517
8017
8017
8317
—
—
—
—
—
—
46 (44)
—
—
95–96 (95–96)
112 (114–115)
68–69 (69)
54–55 (55–56)
—
—
—
—
Phenyl p-tolyl sulfone
p-Anisyl phenyl sulfone
p-Bromophenyl phenyl sulfone
Phenyl-m-tolyl sulfone
m-Chlorophenyl phenyl sulfone
Benzyl phenyl sulfone
n-Propyl phenyl sulfone
Diphenyl selenone
3
b
24
1.5
3.5
4
3.5
4
4
4
4
4
5
5
5
5
5
5
—
9
7818
8618
9018
8718
8218
8218
8218
8218
6518
8519
8819
8819
8819
5819
7819
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Di-p-chlorophenyl selenone
Di-p-bromophenyl selenone
Di-p-tolyl selenone
Di-p-anisyl selenone
n-Propyl-p-tolyl selenone
n-Propyl phenyl selenone
n-Butyl phenyl selenone
Di-n-butyl selenone
Di-p-chlorophenyl tellurone
Di-p-bromophenyl tellurone
Di-p-anisyl tellurone
Di-p-tolyl tellurone
Di-n-butyl tellurone
Methyl phenyl tellurone
90–91 (93–94)
119 (120–121)
55 (54–55)
64–65 (67)
—
—
a
Isolated yields.
No reaction.
b

968
J. M. Khurana et al. / Tetrahedron 63 (2007) 966–969
chalcogenides (Scheme 1). The deoxygenation of sulfoxides
via free radical processes has already been reported.8f–h The
deoxygenation of diphenyl sulfoxide and diphenyl sulfone
was completely inhibited when the reaction was carried
out by bubbling oxygen into the reaction mixture or in
presence of p-dinitrobenzene, as expected.
the reaction was quenched with the minimum volume of satd
ammonium chloride solution and extracted with ether
(3ꢁ10 mL). The combined extract was washed with satd
sodium thiosulfate, dried over anhyd sodium sulfate and
concentrated on a Buchi rotavapour to give a crude, which
was purified by column chromatography on a silica gel
(100–200 mesh) column (1ꢁ10 cm) using petroleum ether
as eluent to give a pale yellow liquid, which was identified
as diphenyl sulfide (0.072 g, 78%). IR (neat) 3059.52,
1580.26, 1475.90, 1439.71, 1080.74, 1024.14, 738.30,
689.96 cmꢂ1; 1H NMR (60 MHz, CDCl3) d 7.0 (s, 10H).
O-Mg+
R X R
O
X
O
X
O
Mg(Mg+)
Mg(Mg+)
Mg
Mg
'
'
.
'
R
R +
MgO
R
R
R
O
O-Mg+
O
X
3.2.2. n-Propyl p-tolyl selenoxide. Reaction of n-propyl
p-tolyl selenoxide (0.1 g, 0.4652 mmol) was carried out
by the above procedure with magnesium (0.1959 g,
8.164 mmol). The product n-propyl p-tolyl selenide was
obtained as golden yellow oil (0.061 g, 70%). IR (neat)
'
.
'
'
MgO
R
X
R +
R
X
R
R
X = S, Se, Te
Scheme 1.
3018.26, 2919.43, 1486.97, 1013.91, 800.37, 480.80 cmꢂ1
;
1H NMR (60 MHz, CDCl3) d 6.9 (d, J¼9 Hz, 2H), 7.2 (d,
J¼9 Hz, 2H), 3.5 (d, J¼6 Hz, 2H), 2.4 (s, 3H), 1.6 (m, 2H),
1.0 (t, J¼6 Hz, 3H).
We conclude that magnesium–methanol provides a conve-
nient, mild and inexpensive method for the deoxygenation
of sulfoxides, selenoxides, telluroxides, sulfones, selenones
and tellurones to the corresponding chalcogenides at ambi-
ent temperature. It is an inexpensive and environmentally
benign reagent compared to other reagents known for these
deoxygenations, such as SmI2, WCl6, Lawesson’s reagent
and NaBH4–I2. None of these can deoxygenate all the
mono- and dioxides of chalcogenides.
3.2.3. Di-n-butyl telluroxide. Reaction of di-n-butyl tellur-
oxide (0.1 g, 0.3891 mmol) was carried out by the above
procedure with magnesium (0.2801 g, 11.673 mmol). The
product di-n-butyl telluride was obtained as golden yellow
oil (0.071 g, 75%). IR (neat) 2957.84, 2925.26, 1461.96,
1377.41, 1246.47, 1159.47, 886.32, 724.70 cmꢂ1
;
1H
NMR (60 MHz, CDCl3) d 2.6 (t, J¼6 Hz, 4H), 1.3–1.9 (m,
8H), 1.0 (t, J¼6 Hz, 6H).
3. Experimental
3.1. General
3.2.4. Phenyl p-tolyl sulfone. Reaction of phenyl p-tolyl
sulfone (0.1 g, 0.431 mmol) was carried out by the above
procedure with magnesium (0.2068 g, 8.62 mmol). The
product phenyl p-tolyl sulfide was obtained as pale yellow
oil (0.071 g, 82%). IR (neat) 3040.38, 2924.82, 1585.83,
Melting points were determined on a Tropical Labequip ap-
paratus and are uncorrected. IR spectra were recorded on
Perkin Elmer FTIR Spectrum-2000. H NMR spectra were
1
1485.35, 1066.38, 938.46, 883.39, 809.15, 483.76 cmꢂ1
;
recorded on FT-NMR model R-600 Hitachi (60 MHz) with
TMS as the internal standard. Methanol (Speckpure), resu-
blimed iodine (E. Merck) and magnesium turnings (S.D.
Fine) were used in all the reactions. Methanol was dried by
the published procedure.10 Magnesium turnings werewashed
with 1% hydrochloric acid, water and acetone and finally
dried. The starting sulfoxides,11 sulfones,12 tellurones13 and
selenones13 were prepared by the reported procedures. Syn-
thesis of selenoxides involved two-step preparations: (1) bro-
mine addition to selenides to give selenide dibromides14 and
(2) alkaline hydrolysis of selenide dibromides to give selen-
oxides.15 Telluroxides were prepared by a similar route to
that reported previously.16
1H NMR (60 MHz, CDCl3) d 7.0 (s, 4H), 7.1 (s, 5H), 2.2
(s, 3H).
3.2.5. Di-n-butyl selenone. Reaction of di-n-butyl selenone
(0.1 g, 0.4386 mmol) was carried out by the above procedure
with magnesium (0.2631 g, 10.965 mmol). The product di-
n-butyl selenide was obtained as colourless liquid (0.056 g,
65%). IR (neat) 2958.49, 2928.18, 1463.87, 1378.37,
1257.79, 1194.74, 902.29, 737.91 cmꢂ1
;
1H NMR
(60 MHz, CDCl3) d 2.5 (t, J¼6 Hz, 4H), 1.3–1.9 (m, 8H),
1.0 (t, J¼6 Hz, 6H).
3.2.6. Di-p-anisyl tellurone. Reaction of di-p-anisyl tellur-
one (0.1 g, 0.2681 mmol) was carried out by the above
procedure with magnesium (0.2252 g, 9.383 mmol). The
product di-p-anisyl telluride was obtained as creamish solid
(0.081 g, 88%), mp 55 ꢀC (lit.19 54–55 ꢀC). IR (KBr)
3001.08, 2936.94, 2835.60, 1586.09, 1487.95, 1283.66,
3.2. General procedures for deoxygenations
3.2.1. Diphenyl sulfoxide. In a typical procedure, a 50 mL
round-bottomed flask, fitted with a reflux condenser and
a CaCl2 guard tube, was mounted over a magnetic stirrer.
A mixture of diphenyl sulfoxide (0.1 g, 0.495 mmol), mag-
nesium turnings (0.118 g, 4.95 mmol) and dry methanol
(10 mL) was added. One or two crystals of iodine were
added while stirring the contents magnetically at room tem-
perature. A vigorous reaction ensued after w15 min. The
progress of the reaction was monitored by TLC using petro-
leum ether–ethyl acetate (85:15) as eluent. The starting ma-
terial disappeared completely after 1.5 h. After completion,
1245.46, 1176.57, 1029.93, 822.08, 587.36, 516.52 cmꢂ1
;
1H NMR (60 MHz, CDCl3) d 7.2 (d, J¼9 Hz, 4H), 8.0 (d,
J¼9 Hz, 4H), 3.9 (s, 6H).
Acknowledgements
V.S. is grateful to CSIR, New Delhi, India for the award of
Junior and Senior research fellowships.

J. M. Khurana et al. / Tetrahedron 63 (2007) 966–969
969
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