Hydroselenation of alkynes using NaBH4/BMIMBF4: easy access to vinyl selenides

Article abstract of DOI:10.1016/j.tetlet.2007.09.042

A general and easy method for the synthesis of several vinyl selenides using NaBH₄ and BMIMBF₄ as a recyclable solvent is described. This efficient and improved method furnishes the corresponding vinyl chalcogenides preferentially wi

Full text of DOI:10.1016/j.tetlet.2007.09.042

Tetrahedron Letters 48 (2007) 8011–8013
Hydroselenation of alkynes using NaBH4/BMIMBF4:
easy access to vinyl selenides
Eder J. Lenardao,* Luiz G. Dutra, Maiara T. Saraiva, Raquel G. Jacob and Gelson Perin
˜
ˆ
Instituto de Quı´mica e Geociencias, LASOL, Universidade Federal de Pelotas, UFPel, PO Box 354, 96010-900 Pelotas, RS, Brazil
Received 13 August 2007; revised 5 September 2007; accepted 6 September 2007
Available online 11 September 2007
Abstract—A general and easy method for the synthesis of several vinyl selenides using NaBH4 and BMIMBF4 as a recyclable sol-
vent is described. This efficient and improved method furnishes the corresponding vinyl chalcogenides preferentially with Z config-
uration. We also observed that when the same protocol was applied to phenyl acetylene, (E)-bis-phenylseleno styrene was obtained
in good yield and with high selectivity.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Vinyl selenides have been found to be a very useful tool
in organic synthesis, since they are very versatile inter-
mediates for the selective construction of isolated or
conjugated olefins.1 Besides, organoselenium com-
pounds have attracted an increasing interest because of
their useful biological activities.2 On this way, various
methods are mentioned for the preparation of vinyl sel-
enides and the most common protocols involve the addi-
tion of organo selenols, or the respective chalcogenolate
anions, to terminal or internal alkynes.1b,3 On the other
hand, ionic liquids (ILs) are receiving much attention in
organic synthesis, both as recyclable solvents and/or cat-
alysts.4 Because product isolation or catalyst recycling is
very easy in ILs and, in some cases, rate accelerations
and/or selectivity improvements are also observed, they
are regarded as environmentally friendly green solvents.
In despite of the high versatility of vinyl selenides and
the greener feature of ILs, the use of ionic liquids as sol-
vent for hydroselenation reaction of alkynes was not de-
scribed. As a continuation of our studies toward the
development of new and cleaner methods for the synthe-
sis of vinyl chalcogenides,5 we report herein the results
of the hydroselenation of alkynes using NaBH4/
BMIMBF4 (Scheme 1).6
conditions for the hydroselenation reaction. We exam-
ined the temperature, amount of IL, NaBH4 and the
use of N2 atmosphere. It was found that using 0.046 g
of NaBH4 and 0.5 mL of IL at room temperature and
under N2 atmosphere, the reaction proceeded slowly
and in 30% yield after stirring for 26 h. However, when
the mixture was heated at 60 ꢁC, the desired products 3a
and 4a were obtained in good yield (87%) after 6 h
(Table 1, entry 1). When the same protocol was per-
formed without N2, after 10 h, incomplete consumption
of 2 was observed and the products were isolated in 48%
yield. When the reaction was performed in the presence
of BMIMBF4 alone, without NaBH4, no reaction took
place in all conditions tested and the starting materials
were recovered. Besides, using a smaller amount of
NaBH4 (0.038 g), the desired products 3a and 4a were
obtained only in 52% yield.
Since the best conditions were established, the protocols
were extended to other alkynyl alcohols (Scheme 1). In
all the studied cases, a mixture of (Z)-3 and gem-4 was
obtained in good yields (entries 1–5) and, except for
homopropargyl alcohol (1e, entry 5), the anti-Mark-
ovnikov adduct 3 was obtained in higher amount than
the Markovnikov one 4. For the reaction of phenyl-
selenolate anions with sterically hindered alcohols, it
was observed that steric factors are important, because
both, the 3:4 ratio and the reaction time, increase with
the group R size (Table 1, compare entries 2–4 with 1
and 5). This regioselectivity is similar to that reported
for the methods which use organic solvents.1b,3 How-
ever, in a general way, using our IL based protocol,
Initially, we chose propargyl alcohol (1a; 2 mmol) and
diphenyl diselenide (2; 0.5 equiv) to establish the best
Keywords: Ionic liquids; Hydroselenation; Vinyl selenide.
*
Corresponding author. Tel./fax: +55 53 3275 7354; e-mail:
lenardao@ufpel.edu.br
0040-4039/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.09.042

8012
E. J. Lenarda˜o et al. / Tetrahedron Letters 48 (2007) 8011–8013
(C6H5Se)2 2, 60 o
NaBH4, BMIMBF4
C
(C6H5Se)2 2, 60 o
NaBH4, BMIMBF4
C
C6H5
SeC6H5
R
C6H5
SeC6H5
+
+
R
H
R
SeC6H5
(Z)-3a-f
C6H5Se
R = C6H5
SeC6H5
R = CH2OH, C(CH3)C2H5OH,
1a-g
(Z
)-3g
(E)-5
CH2CH2OH, C(CH3)2OH,
4a-f
OH
C5H11
,
Scheme 1.
Table 1. Hydroselenation of Alkynes using BMIMBF4 as recyclable solvent
Entry
Alkyne 1
Products 3 + 4
Time (h)
6
Yielda (%)
87
Ratiob (Z)-3:4
SeC6H5
OH
OH
+
1
C6H5Se
C6H5Se
72:28
1a
OH
3a
3b
4a
4b
SeC6H5
OH
+
2
3
10
9
62
90
91:9
OH
OH
1b
1c
OH
OH
SeC6H5
+
C6H5Se
C6H5Se
80:20
3c
4c
OH
SeC6H5
+
HO
4
10
81
>95:5
44:56
HO
4d
1d
OH
3d
SeC6H5
OH
OH
5
6
7
6
9
3
74
+
OH
C6H5Se
C5H11
4e
1e
1f
3e
3f
C6H5Se
C5H11
C5H11
+
Trace
85
—
SeC6H5
4f
C6H5Se
C6H5
C
H
5
6
c
+
C6H5
SeC6H5
1g
SeC6H5
3g
5
a Yields of pure products isolated by column chromatography (hexanes/AcOEt) and identified by mass spectrometry, 1H, 13C NMR.
b Determined by GC of the crude reaction mixture and confirmed after isolation of the individual isomers.
c Obtained as mixture of (Z)-3g and (E)-5 (3g:5 ratio = 26:74).
the reaction time was reduced from days to hours, with
gentle heating.6 In addition, after completion of the
reaction, the products are simply extracted with ether
and the ionic liquid is reused without significant loss
in yields. When the same protocol was applied to phenyl
acetylene (1g), (E)-1,2-bis-phenylseleno styrene (5) was
obtained in 63% yield after 3 h at 60 ꢁC. This result is
similar to that obtained under solvent-free conditions.5a
References and notes
1. For the preparation and synthetic utility of vinyl selenides,
see, for example: (a) Organoselenium Chemistry. A Practical
Approach; Back, T. G., Ed.; Oxford: New York, 2000; (b)
Comasseto, J. V.; Ling, L. W.; Petragnani, N.; Stefani, H.
A. Synthesis 1997, 373; (c) Paulmier, C. In Organic
Chemistry Series 4; Baldwin, J. E., Ed.; Selenium Reagents
and Intermediates in Organic Synthesis; Pergamon Press:
Oxford, 1986.
In conclusion, we have presented here a new methodol-
ogy for the addition of selenolate anions to alkynyl alco-
hols and phenyl acetylene, under mild conditions and
with non-aqueous work-up. This improved, simple, fast,
and clean protocol uses recyclable ionic liquid as a
solvent, as well as selectively affords mono- and bis-
organoselenium alkenes.
2. (a) Nogueira, C. W.; Zeni, G.; Rocha, J. B. T. Chem. Rev.
2004, 104, 6255; (b) Mugesh, G.; du Mont, W.-W.; Sies, H.
Chem. Rev. 2001, 101, 2125.
3. (a) Zeni, G.; Stracke, M. P.; Nogueira, C. W.; Braga, A. L.;
Menezes, P. H.; Stefani, H. A. Org. Lett. 2004, 6, 1135; (b)
Dabdoub, M. J.; Baroni, A. C. M.; Lenardao, E. J.;
˜
Gianeti, T. R.; Hurtado, G. R. Tetrahedron 2001, 57, 4271;
(c) Barros, O. S. D.; Lang, E. S.; de Oliveira, C. A. F.;
Peppe, C.; Zeni, G. Tetrahedron Lett. 2002, 43, 7921; (d)
Comasseto, J. V. J. Organomet. Chem. 1983, 253, 131; (e)
Dabdoub, M. J.; Cassol, T. M.; Batista, A. C. F. Tetra-
hedron Lett. 1996, 37, 9005.
Acknowledgments
This project is funded by CNPq, FAPERGS, and in part
by a grant from the ChemRAWN XIV International
Green Chemistry Grants Program. Professor C. C.
Silveira (UFSM/Brazil) is acknowledged for the 1H
and 13C NMR analysis.
4. See, for instance: (a) Jain, N.; Kumar, A.; Chauhan, S.;
Chauhan, S. M. S. Tetrahedron 2005, 61, 1015; (b) Dupont,
J.; Souza, R. F.; Suarez, P. A. Z. Chem. Rev. 2002, 102,
3667; (c) Dupont, J.; Consorti, C. S.; Spencer, J. J. Braz.
Chem. Soc. 2000, 11, 337; (d) Consorti, C. S.; Souza, R. F.;

E. J. Lenarda˜o et al. / Tetrahedron Letters 48 (2007) 8011–8013
8013
Dupont, J.; Suarez, P. A. Z. Quı´m. Nova 2001, 24, 830; (e)
Wasserscheid, P.; Welton, T. Ionic Liquids in Synthesis;
Wiley-VCH: New York, 2002; (f) Welton, T. Chem. Rev.
1999, 99, 2071; (g) Wassercheid, P.; Keim, W. Angew.
Chem., Int. Ed. 2000, 39, 3772; (h) Davis, J. H., Jr.; Fox, P.
A. Chem. Commun. 2003, 1209.
6. General procedure for the synthesis of vinyl selenides: To a
mixture of propargyl alcohol (1a; 0.112 g; 2 mmol) and
diphenyl diselenide (2; 0.157 g; 0.5 mmol) in BMIMBF4
(0.5 mL) under N2 atmosphere, NaBH4 (0.046 g) was
added at room temperature. Then, the temperature was
slowly raised to 60 ꢁC. The reaction progress was fol-
lowed by TLC and after 6 h (see Table 1) the reaction
mixture was extracted using ether (5 · 3 mL). The solvent
was evaporated under reduced pressure and the residue
was purified by column chromatography over silica gel
eluting with hexanes/ethyl acetate (90:10), yielding prod-
ucts 3a (0.136 g, 63%) and 4a (0.052 g, 24%). (Z)-3a:
1H NMR (200 MHz, CDCl3) d (ppm) 7.43–7.54 (m, 2H);
7.22–7.27 (m, 3H); 6.58 (dt, J = 9.4 and 1.4 Hz, 1H); 6.19
(dt, J = 9.4 and 6.0 Hz, 1H); 4.24 (dd, J = 6.0 and 1.0 Hz,
2H); 3.02 (broad s, 1H); 4a: 7.43–7.54 (m, 2H); 7.22–7.27
(m, 3H); 5.86 (s, 1H); 5.40 (s, 1H); 4.15 (s, 2H); 3.02
(broad s, 1H).3a,e
5. (a) Perin, G.; Jacob, R. G.; Dutra, L. G.; Azambuja, F.;
Santos, G. F. F.; Lenardao, E. J. Tetrahedron Lett. 2006,
˜
47, 935; (b) Perin, G.; Mendes, S. R.; Silva, M. S.;
Lenardao, E. J.; Jacob, R. G.; Santos, P. C. S. Synth.
˜
Commun. 2006, 36, 2587; (c) Perin, G.; Jacob, R. G.;
Botteselle, G. V.; Kublik, E. L.; Lenardao, E. J.; Cella, R.;
˜
Santos, P. C. S. J. Braz. Chem. Soc. 2005, 16, 857; (d) Perin,
G.; Jacob, R. G.; Azambuja, F.; Botteselle, G. V.; Siqueira,
G. M.; Freitag, R. A.; Lenardao, E. J. Tetrahedron Lett.
˜
2005, 46, 1679; (e) Lenardao, E. J.; Silva, M. S.; Mendes, S.
˜
R.; Azambuja, F.; Jacob, R. G.; Santos, P. C. S.; Perin, G.
J. Braz. Chem. Soc. 2007, 18, 943.