Synthesis of diorganyl selenides mediated by zinc in ionic liquid

Article abstract of DOI:10.1021/jo100454m

Figure presented A new approach for the synthesis of diorganyl selenides is described. By using economically attractive zinc dust in BMIM-BF₄, a series of diorganyl selenides were efficiently achieved in excellent yields, under neutral reaction conditions. Compared to the usual organic solvents, BMIM-BF₄ exhibited higher performance with the advantage to be reused up to five successive runs.

Full text of DOI:10.1021/jo100454m

pubs.acs.org/joc
Diorganyl selenides are versatile tools in organic chemistry,
and have found wide application as radical precursors, in
Synthesis of Diorganyl Selenides Mediated by Zinc in
Ionic Liquid
4
elimination reactions, and as selenium-stabilized carbanions.
Chiral diorganyl selenides are also used as efficient ligands in
asymmetric reactions.
†
Senthil Narayanaperumal, Eduardo E. Alberto,
†
5
†
Kashif Gul, Oscar E. D. Rodrigues,* and
,†
,
‡
These compounds are generally prepared by reductive
cleavage of Se-Se bonds, employing common reducing
agents such as NaBH , LiAlH , and other expensive metal
sources such as La, In, Yb, Sm, etc. Most of the procedures
require handling of unstable reagents, strongly acidic or
basic conditions, or two-step procedures. Thus, there is still
considerable interest in the development of highly efficient
Antonio L. Braga*
†
Departamento de Quı´mica, Universidade Federal de Santa
4
4
‡
6,7
Maria, 97105-900, Santa Maria, Brazil, and Departamento
de Quı´mica, Universidade Federal de Santa Catarina, 88040-
9
00, Florian oꢀ polis, Brazil
8
albraga@qmc.ufsc.br; rodriguesoed@smail.ufsm.br
Received March 12, 2010
methods for this transformation.
Ionic liquids are versatile and novel reaction media, for
organic transformations, and have also found application as
flexible “platforms” to establish highly effective and easily
separable systems. Room temperature ionic liquids, espe-
cially those based on the 1,3-dialkylimidazolium cation, have
attracted considerable attention due to their negligible vapor
9
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L u€ dtke, D. S.; Vargas, F. Curr. Org. Chem. 2006, 10, 1921–1938.
A new approach for the synthesis of diorganyl selenides is
described. By using economically attractive zinc dust in
BMIM-BF , a series of diorganyl selenides were effi-
4
(
e) Freudendahl, D. M.; Shahzad, S. A.; Wirth, T. Eur. J. Org. Chem.
2009, 1649–1664.
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ciently achieved in excellent yields, under neutral reaction
conditions. Compared to the usual organic solvents,
BMIM-BF exhibited higher performance with the ad-
(
(
4
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Kataoka, T. J. Org. Chem. 1994, 59, 1011–1019. (d) Andreadou, I.; Menge,
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´
1
organic synthesis and catalysis. The biological and medici-
4
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(
1
(
(
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(X = Cl or Br) species prepared from PhSeX and Zn, which act as
nucleophiles toward a series of electrophiles. However, we reasoned that
for our purposes use of diselenides and elemental zinc would be more
attractive since we would be able to prepare in situ a wide range of selenium
species that act exactly in the same way as those mentioned above. (a) Santi,
C.; Santoro, S.; Testaferri, L.; Tiecco, M. Synlett 2008, 1471–1474. (b) Santi,
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4229. (e) Cassol, C. C.; Umpierre, A. P.; Machado, G.; Wolke, S. I.; Dupont.,
J. J. Am. Chem. Soc. 2005, 127 (10), 3298–3299.
5
2
883. (f) Perin, G.; Lenard ~a o, E. J.; Jacob, R. G.; Panatieri., R. B. Chem. Rev.
009, 109, 1277–1301. (g) Freudendahl, D. M.; Santoro, S.; Shahzad, S. A.; Santi,
C.; Wirth, T. Angew. Chem., Int. Ed. 2009, 48, 8409–8411.
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(
255–6286. (b) Sarma, B. K.; Mugesh, G. Org. Biomol. Chem. 2008, 6, 965–
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6
9
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4
1
3
886 J. Org. Chem. 2010, 75, 3886–3889
Published on Web 05/03/2010
DOI: 10.1021/jo100454m
r 2010 American Chemical Society

Narayanaperumal et al.
JOCNote
TABLE 1. Reaction Optimization
a
b
entry
ionic liquid
Bpy-BF
BMMIM-BF
BMIM-NTf
BMIM-PF
X
time (min)
yield (%)
1
2
3
4
5
6
7
4
Cl
Cl
Cl
Cl
Cl
Br
I
40
40
40
35
30
25
20
25
25
55
65
29
86
93
95
98
96
92
4
2
6
FIGURE 1. Room temperature ionic liquids.
BMIM-BF
BMIM-BF
BMIM-BF
BMIM-BF
BMIM-BF
4
4
4
4
4
pressure, nonflammability, reasonable thermal stability, ease
1
0
of handling, and potential for recycling. Ionic liquids were
used as solvent in many organic transformations and have
shown enhanced reaction rates when compared with conven-
tional organic solvents. Thus, development of ionic liquid
c
8
9
Br
Br
d
a
10e b
Prepared according literature procedure.
isolated products. 1.2 equiv of zinc dust. 1.0 equiv of zinc dust.
Yields refer to pure
c
d
1
1
mediated organic transformation is gaining prominence.
In connection with our insights about the synthesis of
diorganyl selenides and their application in biological and
hydrogen bond acidity (related to the cationic portion),
and hydrogen bond basicity (related to the anionic portion)
would account for the complex solvent interactions exhibited
by ILs. In previous reports hydrogen bonds have been
evoked as a pivotal interaction in the formation of a given
product in reactions performed in ILs. Our experimental
results (Table 1) suggest that perhaps the scale of hydrogen
bond acidity of the tested ILs may be a distinguished
property for the formation of products. If one assumes that
this characteristic would facilitate the reaction through the
coordination of the acid hydrogen attached to C-2 in the
imidazolium ring with the leaving group (chloride) in an SN2
like reaction, the formation of products would be in the same
range of yield for BMIM-BF , BMIM-PF , and BMIM-N-
Tf) due to the similarity of their hydrogen bound donor
2
HBD) parameters. With the exception of BMIM-N(Tf)2,
9% yield (entry 3), BMIM-BF and BMIM-PF furnished
the desired product in 93% and 86% yields, respectively
entries 5 and 4). Moreover, if the extent of hydrogen bond
interactions really accounts for an effective formation of
1
2,13
asymmetric transformations,
we describe herein a sim-
1
4
ple, efficient, and versatile approach to the preparation of
diorganyl selenides. Employing zinc dust and ionic liquid, to
promote the direct coupling of diselenides and organic
halides, the respective selenides were achieved in good to
excellent yields in a short time at room temperature. To
optimize the protocol, we performed the reaction of benzyl
chloride with PhSeSePh and 1.6 equiv of zinc dust with
respect to diselenide, in five different ionic liquids (Figure 1).
The formation of the product could be easily observed by the
change of the reaction color from yellow to gray.
1
5
4
6
The results for BMIM-BF were found to be better than
4
(
(
those for the other ionic liquids (Table 1, entries 1-5).
Similar protocols have appeared in the literature for reduc-
tion of PhSeSePh with zinc followed by reaction with benzyl
chloride with use of other organic solvents. In a mixture of
1
6
2
4
6
(
MeCN/H O at 65 °C the desired product was obtained in
2
7
h
6
4% yield after 3 h, in CH Cl at rt, 57% of the yield was
2 2
7
j
products, reactions carried in Bpy-BF and BMMIM-BF4
4
obtained after 5 h. Although the improved capability of
ionic liquid to accelerate many organic reactions compared
to other organic solvents has been extensively reported, the
origin of its behavior is still an intriguing subject of study.
Properties such as strong dipolar and dispersion forces,
which have a much lower (HBD) value compared to the
above-mentioned ionic liquids would result in the formation
of products in lower yields. Actually, these ILs exhibited
poorer activity compared to BMIM-BF and BMIM-PF6
4
(entries 1 and 2). A reasonable explanation to the lower yield
observed for BMIM-N(Tf) is the influence of the anion
2
(
10) (a) Welton, T. Chem. Rev. 1999, 99, 2071–2084. (b) Dupont, J.;
Souza, R. F.; Suarez, P. A. Z. Chem. Rev. 2002, 102, 3667–3692. (c) Song,
C. E. Chem. Commun. 2004, 1033–1043. (d) Dupont, J.; Spencer, J. Angew.
Chem., Int. Ed. 2004, 43 (40), 5296–5297. (e) Cassol, C. C.; Ebeling, G.;
Ferrera, B.; Dupont., J. Adv. Synth. Catal. 2006, 348, 243–248.
N(Tf) . We speculate that it would interfere in the formation
2
17
and/or in the reactivity of zinc selenolate, PhSeZnSePh. On
the basis of these results, we investigated the influence of
halide in the substrate. When benzyl iodide was used a higher
(11) Selected examples: (a) Ellis, B.; Keim, W.; Wasserscheid, P. Chem.
Commun. 1999, 337–338. (b) For a review of metal-catalyzed reactions in ILs
see: Wasserscheid, P.; Keim, W. Angew. Chem., Int. Ed. 2000, 39, 3772–3789.
(
c) Wasserscheid, P.; Welton, T. Ionic Liquids in Synthesis; Wiley-VCH:
(14) Martins, M. A. P.; Frizzo, C. P.; Moreira, D. N.; Zanatta, N.;
Bonacorso, H. G. Chem. Rev. 2008, 108, 2015–2050.
Weinheim, Germany, 2002. (d) Wu, W. Z.; Han, B. X.; Gao, H. X.; Liu, Z. M.;
Jiang, T.; Huang, J. Angew. Chem., Int. Ed. 2004, 43, 2415–2417. (e) Singh, D.;
Alberto, E. E.; Rodrigues, O. E. D.; Braga, A. L. Green Chem. 2009, 11, 1521–
(15) Selected examples: (a) Fischer, T.; Sethi, A.; Welton, T.; Woolf, J.
Tetrahedron Lett. 1999, 40, 793–796. (b) Chakraborti, A. K.; Roy, S. R.
J. Am. Chem. Soc. 2009, 131, 6902–6903. (c) Baciocchi, E.; Chiappe, C.;
Giacco, T. D.; Fasciani, C.; Lanzalunga, O.; Lapi, A.; Melai, B. Org. Lett.
2009, 11, 1413–1416.
(16) (a) Anderson, J. L.; Ding, J.; Welton, T.; Armstrong, D. W. J. Am.
Chem. Soc. 2002, 124, 14247–14254. (b) Tokuda, H.; Tsuzuki, S.; Susan,
M. A. B. H.; Hayamizu, K.; Watanabe, M. J. Phys. Chem. B 2006, 110,
19593–19600. (c) Lungwitz, R.; Friedrich, M.; Linertc, W.; Spange, S. New
J. Chem. 2008, 32, 1493–1499.
1
524. (f) Narayanaperumal, S.; Alberto, E. E.; Andrade, F. M.; Lenard ~a o, E. J.;
Taube, P. S.; Braga, A. L. Org. Biomol. Chem. 2009, 7, 4647–4650.
12) Selected examples: (a) Braga, A. L.; Alberto, E. E.; Soares, L. C.;
Rocha, J. B. T.; Sudati, J. H.; Ross, D. H. Org. Biomol. Chem. 2009, 7, 43–45.
b) Alberto, E. E.; Soares, L. C.; Sudati, J. H.; Borges, A. C. A.; Rocha,
J. B. T.; Braga, A. L. Eur. J. Org. Chem. 2009, 4211–4214.
13) For selected examples see: (a) Braga, A. L.; Silva, S. J. N.; L u€ dtke,
(
(
(
D. S.; Drekener, R. L.; Silveira, C. C.; Rocha, J. B. T.; Wessjohann, L. A.
Tetrahedron Lett. 2002, 43, 7329–7331. (b) Braga, A. L.; Sehnem, J. A.;
Vargas, F.; Braga, R. C. J. Org. Chem. 2005, 70, 9021–9024. (c) Braga, A. L.;
Schneider, P. H.; Paix ~a o, M. W.; Deobald, A. M.; Peppe, C.; Bottega, D. P.
J. Org. Chem. 2006, 71, 4305–4307.
(17) A previous report using task-specific ILs has shown that this anion is
present in the coordination sphere of zinc salts: Nockemann, P.; Thijs, B.;
Hecke, K. V.; Meervelt, L. V.; Binnemans, K. Cryst. Growth Des. 2008, 8,
1353–1363.
J. Org. Chem. Vol. 75, No. 11, 2010 3887

Narayanaperumal et al.
JOCNote
TABLE 2. Synthesis of Diorganyl Selenides
yields, for both allyl chloride and iodide (entries 7 and 8).
Substituted benzylic halides and diaryl diselenides were also
applied to this protocol in order to check the steric and
electronic effects in the course of the reaction. When 4-methyl-
benzyl bromide was applied, the product was achieved in 98%
yield, while 2-methylbenzyl bromide gave the selenide in 79%
yield (entries 9 and 10). In the diselenide moiety, a lower yield
was observed by using 2-methoxy diphenyl diselenide as a
selenium source compared with 4-methoxy diphenyl disele-
nide (entries 14 and 15). These observations can be explained
by the steric dependence in this coupling reaction, driving
better yields to the less sterically hindered para-substituted
aryl halides and diselenides.
Electronic effects had no significant influence on the
reaction course and the coupling of diaryl diselenides, with
electron-donating or electron-withdrawing groups attached
to the aromatic ring, afforded the products with a similar
level of efficiency (entries 12-14). We also employed other
diselenide sources in this reaction, e.g. benzylic and alkylic.
For instance, dibenzyl diselenide and diethyl diselenide were
reacted with benzyl chloride, allowing the preparation of the
desired products in good yields (entries 11 and 16).
An important feature of our methodology is the tolerance
of different functional groups, such as protected aminoester,
ester, and nitrile, giving the corresponding products in good
yields (entries 17, 18, and 19). Exploiting the versatility of our
current methodology, the synthesis of the biologically im-
2
,3,18
portant selenocysteine
from the corresponding bromo amino ester derivative in
1% yield, employing our standard reaction conditions
entry 19). This result demonstrates the potential wide-
derivative was accomplished
19
6
(
ranging utility of this methodology by the preparation of
various chiral organoselenium compounds.
Furthermore, our approach allows the preparation of the
desired products in really smooth reaction conditions in a
shorter time. Althoughin the other related procedures with Zn
7
h-k,8
the products were successfully obtained,
these protocols
require severe reaction conditions such as long reaction time
under higher temperature. It is noteworthy to highlight that,
when the solvent for the synthesis of diorganyl selenides was
changed from conventional organic solvents to ionic liquid
(BMIM-BF ) excellent conversion rates and yields were ob-
tained under room temperature with very short reaction times
and mild conditions with BMIM-BF as a reusable solvent.
4
4
a
b
Yields refer to pure isolated products. Bromo ester (1 equiv), Zn
0.6 equiv), PhSe) (0.6 equiv), BMIM-BF (1 mL).
(
2
4
yield was obtained as compared with that of benzyl bromide
and chloride, which can be explained by the leaving group
ability of the halogens (entries 5-7). However, the difference
was not significant and all the halogens afforded the desired
product in excellent yields. The amount of zinc required to
promote the completion of the reaction was also evaluated.
Reactions with 1.2 and 1.0 equiv of zinc showed similar results,
leading to the product in excellent yields (entries 8 and 9).
After optimization, the coupling of different substrates
and diselenides was applied to check the versatility of the
protocol. A diverse range of alkyl halides were reacted with
diphenyl diselenide under standard reaction conditions to
provide the corresponding alkyl phenyl selenides in excellent
yields. The results are summarized in Table 2 (entries 1-6)
and indicate that the chain length has a positive effect on the
reaction course, affording improved yields in longer chains
After completion of the reaction, the desired products can
be conveniently obtained by extraction with diethyl ether
(3 Â 15 mL). After the workup of the first run, the remaining
ionic liquid (BMIM-BF ) was diluted in ethanol, filtered
4
through a Celite pad to remove inorganic materials, followed
by concentration to remove the organic solvents. Then, it
was subjected to the vacuum for 1 h to eliminate the moisture
and trace organic solvents. For the following runs, the
recovered ionic liquid was used after addition of 1 equiv of
Zn (33 mg, 0.5 mmol), diphenyl diselenide (156 mg, 0.5
mmol), and benzyl chloride (127 mg, 1 mmol) for each run
(Figure 2). The yields were almost constant for the first three
runs, followed by a slight decrease for the following two runs.
(18) (a) Roy, J.; Gordon, W.; Schwartz, I. L.; Walter, R. J. Org. Chem.
970, 35, 510–513. (b) Phadnis, P. P.; Mugesh, G. Org. Biomol. Chem. 2005,
, 2476–2481.
1
3
(entries 2, 4, and 6). Reactive allylic halides allowed the
corresponding allyl phenylselenide in near quantitative
(19) Stocking, E. M.; Schwarz, J. N.; Senn, H.; Salzmann, M.; Silks, L. A.
J. Chem. Soc., Perkin Trans. 1 1997, 2443–2447.
3
888 J. Org. Chem. Vol. 75, No. 11, 2010

Narayanaperumal et al.
JOCNote
BMIM-BF (0.5 mL) at room temperature under nitrogen. The
4
mixture was allowed to stir for 2-3 min. Then benzyl bromide
(
171 mg, 1 mmol) was slowly added. The reaction mixture was
stirred for another 25 min (monitored by TLC and assisted by
visual observation). The mixture was then extracted with ether
(
3 Â 15 mL), and the combined ether extract was washed with
brine, dried (MgSO ), and evaporated to leave the crude pro-
duct. Purification by column chromatography over silica gel
hexane/ethyl acetate 98:2) furnished the pure benzyl phenyl
selenide as a yellow oil (231 mg, 92%).
4
(
6
f
1
Benzyl phenyl selenide: 92% yield; H NMR (CDCl3,
00 MHz) δ 7.50-7.42 (m, 2H), 7.28-7.14 (m, 8H), 4.10 (s,
4
2
1
1
H); C (CDCl
3
3
, 100 MHz) δ 138.6, 133.5, 130.4, 128.9, 128.8,
28.4, 127.3, 126.8, 32.2.
Ethyl phenyl selenide: 80% yield; H NMR (CDCl3,
00 MHz) δ 7.50-7.45 (m, 2H), 7.27-7.20 (m, 3H), 2.91 (q,
6
h
1
4
J = 7.6 Hz, 2H), 1.43 (t, J = 7.2 Hz, 3H); C (CDCl
1
3
3
, 100 MHz)
4
FIGURE 2. Reuse of BMIM-BF .
δ 132.6, 130.3, 129.0, 126.7, 21.3, 15.5.
Representative Experimental Procedure To Reuse BMIM-
BF . After the workup of the first run, BMIM-BF is diluted
In conclusion, the present method has the following note-
worthy features: (1) good to excellent yields were obtained in a
short time; (2) ease of handling and better safety aspects as
compared with metal hydrides; (3) neutral reaction conditions;
4
4
in ethanol, filtered through a Celite pad, and then subjected
to the vacuum for 1 h. For the following run the recovered
ionic liquid was used after addition of 1 equiv of Zn (33 mg, 0.5
mmol), diphenyl diselenide (156 mg, 0.5 mmol), and benzyl
chloride (127 mg, 1 mmol) followed by the procedure described
above.
(4) from an industrial point of view, the use of commercially
available and inexpensive Zn is an interesting option to processes
which use La, Yb, Sm, or In salts to promote the reduction of
selenium-selenium bound; and (5) the solvent/ionic liquid is
reused in up to five successive runs without loss of its efficiency
and when compared to usual organic solvents, BMIM-BF4
exhibited higher performance. Continued investigations into the
utility of this novel methodology are underway in our laboratory
aiming at the synthesis of seleno aminoacids and derivatives.
Acknowledgment. Senthil and Kashif are recepients of
TWAS-CNPq doctoral fellowships, while E.E.A. is a CNPq
Ph.D. fellowship holder, and cordially acknowledge their
financial support. We are also obliged to CNPq (INCT-
Cat ꢀa lise, INCT_NANOBIOSIMES)
Experimental Section
Supporting Information Available: Synthetic procedures
and compound characterization data. This material is available
free of charge via the Internet at http://pubs.acs.org.
Typical Procedure. Commercially available Zn dust (33 mg,
.5 mmol) and PhSeSePh (156 mg, 0.5 mmol) were added to
0
J. Org. Chem. Vol. 75, No. 11, 2010 3889