Addition of chalcogenolate anions to terminal alkynes using microwave and solvent-free conditions: Easy access to bis-organochalcogen alkenes

Article abstract of DOI:10.1016/j.tetlet.2005.11.158

We present here the reaction of diphenyl dichalcogenides (Se and Te) with propargyl alcohols using alumina supported sodium borohydride under solvent-free conditions. This efficient and improved method is general and furnishes the corresponding vinyl chal

Full text of DOI:10.1016/j.tetlet.2005.11.158

Tetrahedron
Letters
Tetrahedron Letters 47 (2006) 935–938
Addition of chalcogenolate anions to terminal alkynes
using microwave and solvent-free conditions: easy access to
bis-organochalcogen alkenes
Gelson Perin,a,* Raquel G. Jacob,b Luiz G. Dutra,a Francisco de Azambuja,a
Greice F. F. dos Santosa and Eder J. Lenardaoa,*
˜
a
ˆ
Instituto de Quı´mica e Geociencias, LASOL, Universidade Federal de Pelotas, UFPel, PO Box 354, 96010-900 Pelotas, RS, Brazil
bDepartamento de Quı´mica, Universidade Federal de Santa Maria, UFSM, 97105-900 Santa Maria, RS, Brazil
Received 15 November 2005; revised 25 November 2005; accepted 29 November 2005
Available online 20 December 2005
Abstract—We present here the reaction of diphenyl dichalcogenides (Se and Te) with propargyl alcohols using alumina supported
sodium borohydride under solvent-free conditions. This efficient and improved method is general and furnishes the corresponding
vinyl chalcogenide preferentially with a Z configuration. We also observed that when the same protocol was applied to phenyl acet-
ylene, the (E)-bis-organochalcogen alkenes were obtained in good yields and high selectivity. The use of MW irradiation facilitates
the procedure and accelerates the reaction.
Ó 2005 Elsevier Ltd. All rights reserved.
Vinyl chalcogenides have been found to be a very useful
tool in organic synthesis, since they are very versatile
intermediates for the selective construction of isolated
or conjugated olefins.1 Among the vinyl chalcogenides,
1,2-bis-organochalcogen alkenes are very utile synthons
in organic synthesis, because they can be used as precur-
sor to enediynes and other functionalized olefins. How-
ever, the number of methodologies for accessing 1,2-bis
chalcogenide alkenes is limited and the development of
protocols for rigorous regio- and stereochemical con-
trolled synthesis of these compounds remains yet a
challenge.
The authors observed that the presence of the acidic
hydrogen from hidroxyl group is essential for the selec-
tivity control of the addition. They also described that
with diorganoyl ditelluride the reaction failed com-
pletely and in a similar condition, terminal acetylenes
afforded the respective tris-organochalcogen alkenes.
Due to the increasing use of vinyl chalcogenides,1,2 the
development of new and efficient methods for the prepa-
ration of bis-organochalcogen alkenes with defined
regio- and stereochemistry is of general interest in organic
synthesis.
Looking for cleaner approaches to classical syntheses,
we have developed several protocols involving solid sup-
ported catalyst under solvent-free conditions6 and MW
irradiation.7 As a continuation of our studies toward
the development of new methods for the synthesis of
vinyl chalcogenides,6,7a we report herein the results of
the hydrochalcogenation of propargylic alcohols and
chalcogenolate anion in addition to phenyl acetylene
using Al2O3/NaBH4 without any solvent (Scheme 1).8,9
Vinyl chalcogenides have been prepared by the addition
of organo chalcogenols, or the respective chalcogenolate
anions, to acetylenes.1,2 Besides, it is known that di-
selenides3 and ditellurides4 add to terminal alkynes, in
the presence of UV irradiation3a–d,4 or a transition-metal
catalyst3e,f to afford the respective 1,2-bis(organylchalco-
genide) alkenes in moderate to good yields. Recently,
the in situ addition of chalcogenides to propargylic alco-
hols (alkynyl-lithium species) to afford bis-chalcogenide
alkenes (S and Se) in very good yields was described.5
Initially, we chose propargyl alcohol 1a (1.5 equiv) and
diphenyl diselenide (0.5 equiv) to establish the best con-
ditions for the hydrochalcogenation reaction. We exam-
ined the reaction time, the amount of Al2O3/NaBH4
(50%) and the use of microwave.9 It was found that
Keywords: Microwave irradiation; Solvent-free reaction; Bis(organo-
chalcogen)alkenes; Vinyl chalcogenides.
*
Corresponding authors. E-mail: gelson_perin@ufpel.edu.br
0040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.11.158

936
G. Perin et al. / Tetrahedron Letters 47 (2006) 935–938
1
1
YYR
1
1
1
R
1
R
YYR
R Y
YR
R
Method A, B or C
Method A, B or C
+
R
H
1
R
R Y
R = CH2OH, C(CH3)2OH,
C(CH3)C2H5OH
R = C6H5
1
R
YR
(E)-2a-d
1
1a-d
R Y = C6H5Se, C6H5Te,
p-CH3C6H4Se, p-CH3C6H4Te
3a-f
4a-f
1
R Y = C6H5Se, C6H5Te
Scheme 1. Method A: Al2O3/NaBH4 (50%), stirring, rt, 3–72 h; Method B: Al2O3/NaBH4 (50%), MW (548 W), 6–35 min; Method C: Al2O3/NaBH4
(50%), stirring, 60 °C (oil bath), 1.5–42 h.
using 0.050 g of Al2O3/NaBH4, at room temperature,
the reaction proceeded slowly and in 30% yield after stir-
ring for 72 h. However, by using 0.076 g of Al2O3/
NaBH4, the desired products 3a and 4a were obtained
in good yield (76%) after 46 h (Table 1, entry 1, Method
A). Aiming to reduce the reaction time, the mixture was
irradiated with MW (548 W). It was observed there was
complete consumption of the starting materials after
10 min and the products were obtained in comparable
yield and selectivity (Table 1, entry 2, Method B). When
the same protocol was performed at reduced MW power
(353 W) it was observed, after 10 min, there was incom-
plete consumption of diphenyl diselenide, and the pro-
duct was isolated in 51% yield.
all conditions tested and the starting materials were
recovered. By using only NaBH4, the desired products
3a and 4a were obtained only in 32% yield.
In order to check the possibility of intervention of spe-
cific (non-purely thermal) microwave effects, the reac-
tion with Al2O3/NaBH4 (50%) was also examined
using a pre-heated oil bath for the same final tempera-
ture (60 °C), as measured at the end of exposure during
the MW-assisted synthesis (Table 1, entry 3, Method C).
However, it was observed that 22 h was required for
complete consumption of diphenyl diselenide.
Since the best conditions were established, the protocols
were extended to other propargylic alcohols with diphen-
yl diselenide and also with diphenyl ditelluride (Scheme
1). In all the cases studied, a mixture of 3 and 4 was
When the reaction was performed in the presence of alu-
mina alone, without NaBH4, no reaction took place in
Table 1. Synthesis of vinyl chalcogenides 3 and 4 under solvent-free conditions
Entry
Alkyne 1
R1Y)2
Products 3 + 4
Methoda
A
Time
46 h
Yieldb (%)
76
Ratioc 3:4
SeC6H5
OH
1
C6H5Se)2
75:25
+
OH
1a
OH
C6H5Se
3a
4a
2
3
1a
1a
C6H5Se)2
C6H5Se)2
3a + 4a
3a + 4a
B
C
10 min
22 h
79
77
70:30
73:27
TeC6H5
OH
4
5
1a
1a
C6H5Te)2
C6H5Te)2
+
A
B
72 h
73
84
80:20
80:20
C6H5Te
OH
3b
4b
3b + 4b
6 min
SeC6H5
OH
+
C6H5Se
6
7
8
C6H5Se)2
C6H5Se)2
C6H5Te)2
A
B
B
48 h
68
71
85
93:07
90:10
90:10
3c
4c
1b
1b
OH
OH
3c + 4c
13 min
15 min
TeC6H5
+
C6H5Te
1b
1b
3d
3e
4d
OH
OH
OH
9
C6H5Te)2
C6H5Se)2
3d + 4d
C
A
27 h
48 h
91
65
91:09
81:19
SeC6H5
OH
+
C6H5Se
10
1c
OH
4e
4f
11
1c
C6H5Se)2
3e + 4e
C6H5Te
3f + 4f
B
14 min
82
84:16
TeC6H5
OH
+
12
13
1c
1c
C6H5Te)2
C6H5Te)2
B
C
13 min
42 h
63
68
91:09
88:12
3f
OH
a Method A: The experiments were performed at room temperature. Method B: The experiments were performed at 548 W. Method C: The reaction
mixture was heated at 60 °C using an oil bath.9
b Yields of pure products isolated by column chromatography (AcOEt/hexanes) and identified by mass spectrometry, 1H, 13C NMR.
c Determined by GC of the crude reaction mixture and confirmed after isolation of the individual isomers.

G. Perin et al. / Tetrahedron Letters 47 (2006) 935–938
937
obtained in good yields by using the optimized conditions
described above for the preparation of 3a and 4a (Table
1, entries 4–13).9 The anti-Markovnikov adduct 3 was
obtained in a higher amount than the Markovnikov
one 4 in all the tested examples. It was observed that ste-
ric factors are important, because the 3:4 ratio increases
with the group R size. This regioselectivity is similar to
that reported for the methods which use organic sol-
vents and inert atmosphere.1,2 It was observed that for
the reaction of phenyltellurolate anions with the steri-
cally hindered alcohols 1b and 1c the Method A was
not efficient, even after stirring for 72 h (yield < 35%).
However, when the reaction was performed under heat-
ing at 60 °C, the respective tellurides 3 and 4 were
obtained in good yields (Table 1, entries 9 and 13).
Probably, that happens because temperature P 60 °C
is necessary for the diphenyl ditelluride/acetylene mix-
ture to become homogeneous.3c
was irradiated with MW (548 W, Method B). It was
observed there was complete consumption of diphenyl
diselenide after 6 min and the product was obtained in
comparable yield and selectivity (Table 2, entry 2).
When the same reaction was performed using a pre-
heated oil bath (60 °C), 2a was obtained with similar
yield after 1.5 h (Table 2, entry 4, Method C). The reac-
tion was extended to other diaryl dichalcogenides, and
in all the tested cases the respective bis-arylchalcogenide
alkenes 2 were obtained in good yields and preferentially
with E configuration (Scheme 1, Table 2). Although the
energy transfer and distribution in a domestic micro-
wave oven is not controlled as in professional chemistry
one, we found that the microwave-assisted reactions are
more efficient, more convenient and cleaner.
A possible mechanism for explaining the formation of
the (E)-bis-organochalcogen alkenes 2a–d from phenyl
acetylene is depicted in Scheme 2 and involves the inter-
mediate 5. This mechanism is similar to that reported
recently to explain the synthesis of tris-phenylchalcogen
alkenes by hydrochalcogenation of acetylenes.5 A free-
radical chain addition mechanism could also be
involved. However, the fact that propargylic alcohols do
not afford the respective bis-chalcogen alkenes suggests
that the intermediates 6 and 7 are involved in the forma-
tion of 3 and 4, respectively.2e
When the same protocol (Method A) was applied to
phenyl acetylene 1d and diphenyl diselenide, 1,2-bis-phen-
ylseleno alkenes 2a were obtained in good yield (95%)
after 3 h at room temperature.10 This is a new and unex-
pected result that allows to obtain bis-organochalcogen
alkenes in an easy and clean way. The structure of 2a
was confirmed by the appearance of two different signals
in the olefinic region of the 1H NMR spectrum (7.08 and
7.60 ppm) indicating the formation of two isomers,
which were identified as being (E)-2a and (Z)-2a.3e The
reaction was stereoselective, giving predominantly the
(E)-stereoisomer in a E:Z ratio = 80:20 (Table 2, entry
1). Aiming to reduce the reaction time, the mixture
In conclusion, we have presented here a new methodol-
ogy for the addition of chalcogenolate anions to propar-
gylic alcohols and phenyl acetylene under solid
Table 2. Synthesis of bis-organochalcogen alkenes 2a–d starting from phenylacetylene (1d) under solvent-free conditions
Entry R1Y)2
Products 2
Methoda Time
Yieldb (%) Ratioc E:Z
dH vinyl (or CH3)
E
Z
C6H5
SeC6H5
1
C6H5Se)2
A
3 h
95
80:20
7.08
7.60
C6H5Se
2a
2
3
4
C6H5Se)2
C6H5Se)2
C6H5Se)2
2a
2a
2a
B
C
C
6 min
6 min
1.5 h
94
22
94
74:26
—
71:29
C6H5
TeC6H5
5
C6H5Te)2
A
48 h
20
—
7.36
8.37
C6H5Te
2b
6
7
C6H5Te)2
C6H5Te)2
2b
2b
B
C
25 min 72
83:17
82:18
18 h
75
C6H5
SeC6H4CH3-p
TeC6H4CH3-p
8
p-CH3C6H4Se)2
A
B
C
B
19 h
72
87:13
85:15
88:12
85:15
(2.26 and 2.30)
(2.31 and 2.32)
(2.22 and
2.33)
p-CH3C6H4Se 2c
9
p-CH3C6H4Se)2 2c
35 min 85
C6H5
10
11
p-CH3C6H4Te)2
24 h
80
(2.26 and
2.35)
p-CH3C6H4Te
2d
p-CH3C6H4Te)2 2d
30 min 75
a Method A: The experiments were performed at room temperature. Method B: The experiments were performed at 548 W. Method C: The reaction
mixture was heated at 60 °C using an oil bath.9
b Yields of pure products isolated by column chromatography (AcOEt/hexanes) and identified by mass spectrometry, 1H, 13C NMR.3,4
c Determined by GC of the crude reaction mixture and confirmed after isolation of the individual isomers.

938
G. Perin et al. / Tetrahedron Letters 47 (2006) 935–938
Tetrahedron 1993, 49, 1177; (c) Ogawa, A.; Tsuboi, Y.;
δ−
YC6H5
C6H5Y YC6H5
Obayashi, R.; Yokoyama, K.; Ryu, I.; Sonoda, N. J. Org.
Chem. 1994, 59, 1600.
5. Moro, A. V.; Nogueira, C. W.; Barbosa, N. B. V.;
Menezes, P. H.; Rocha, J. B. T.; Zeni, G. J. Org. Chem.
2005, 70, 5257.
H
C6H5Y
C6H5
δ+
C6H5Y
H
C6H5
H
YC6H5
2a-d
C6H5
δ−
NaYC6H5
YC6H5
5
6. Perin, G.; Jacob, R. G.; Botteselle, G. V.; Kublik, E. L.;
δ−
δ−
Lenardao, E. J.; Cella, R.; Santos, P. C. S. J. Braz. Chem.
˜
YC6H5
O
H
Soc. 2005, 16, 857.
δ+
H
7. (a) Perin, G.; Jacob, R. G.; Azambuja, F.; Botteselle, G.
H
δ+
H
V.; Siqueira, G. M.; Freitag, R. A.; Lenardao, E. J.
˜
Tetrahedron Lett. 2005, 46, 1679; (b) Jacob, R. G.; Perin,
δ−
O
6
δ−
OH
C6H5Y
7
G.; Loi, L. N.; Pinno, C. S.; Lenardao, E. J. Tetrahedron
˜
Lett. 2003, 44, 3605; (c) Jacob, R. G.; Perin, G.; Botteselle,
Scheme 2.
G. V.; Lenardao, E. J. Tetrahedron Lett. 2003, 44, 6809.
˜
8. The solid supported catalysts were prepared by the
following procedure: To a pestle mortar was added
alumina (0.038 g of Al2O3 90, 0.063–0.200 mm, Merck)
and NaBH4 (0.038 g). The mixture was stirred for 1 min
and immediately used in the reaction.11
supported catalyst. This improved, simple, fast and
clean protocol eliminates the use of inert atmosphere
and minimizes the organic solvent and energy demands,
as well as, affords selectively mono- and bis-organochal-
cogen alkenes. Besides these advantages, the reaction
time could be reduced from hours to a few minutes
(when MW was employed), under milder conditions
and with non-aqueous work-up.
9. General procedure for the synthesis of vinyl chalcogenides
3a–f and 4a–f. Method A: A mixture of propargyl alcohol
1a (0.084 g; 1.5 mmol) and diphenyl diselenide (0.157 g;
0.5 mmol) was added to aluminum oxide impregnated
8
with NaBH4 (0.076 g). The mixture was stirred at room
temperature. The reaction progress was followed by TLC,
and after 46 h (see Table 1) the product was filtered off the
aluminum oxide by washing with ethyl acetate (10 mL).
The solvent was evaporated under reduced pressure and
the residue was purified by column chromatography over
silica gel (SiO2) eluting with hexane/ethyl acetate (90:10),
yielding the product 3a (0.121 g, 57%) and 4a (0.040 g,
Acknowledgements
This project is funded by FAPERGS, CNPq and by a
grant from the ChemRAWN XIV International Green
Chemistry Grants Program.
1
19%). (Z)-3a: H 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). Method B: The aforemen-
tioned whole mixture was previously stirred for 1 min and
then irradiated with microwave (used a domestic Pana-
sonic model Piccolo NN-S42BK, operating at 2.45 MHz)
at 548 W12 for 6–15 min (Table 1) and the product
extracted and purified according to the described Method
A. Method C: The procedure described in Method A was
followed and the reaction mixture was stirred under
heating at 60 °C (oil bath) for 22 h (Table 1).
References and notes
1. For the preparation and synthetic utility of vinyl selenides,
tellurides and sulfides, see, for example: (a) Comasseto, J.
V.; Ling, L. W.; Petragnani, N.; Stefani, H. A. Synthesis
1997, 373; (b) Petragnani, N.; Stefani, H. A. Tetrahedron
2005, 61, 1613; (c) Comasseto, J. V.; Barrientos-Astigar-
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Chem. Soc. Rev. 1982, 11, 493.
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10. General procedure for the synthesis of bis-chalcogen
alkenes 2a–d. Method A: A mixture of phenyl acetylene
1d (0.153 g; 1.5 mmol) and diphenyl diselenide (0.314 g;
1.0 mmol) was added to aluminum oxide impregnated
with NaBH4 (0.076 g).8 The mixture was stirred at room
temperature. The reaction progress was followed by TLC,
and after 3 h (see Table 2) the product was filtered off the
aluminum oxide by washing with ethyl acetate (10 mL).
The solvent was evaporated under reduced pressure and
the residue was purified by column chromatography over
silica gel (SiO2) eluting with hexane/ethyl acetate (98:2),
yielding the product 2a (0.395 g, 95%, E:Z = 80:20). 1H
NMR (200 MHz, CDCl3) d (ppm) (E + Z) 7.36–7.48 (m,
6H); 7.10–7.29 (m, 9H); 7.60 (s, 1H, Z isomer); 7.08 (s, 1H,
E isomer).3e
Lenardao, E. J.; Gianeti, T. R.; Hurtado, G. R. Tetra-
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12. The oven powers were determined as described by
Kingston, H. M. In Introduction to Microwave Sample
Preparation—Theory and Practice; Jassie, L. B., Ed.;
American Chemical Society: Washington, DC, 1988.