Synthesis of 1-alkylselenocyclobutene via intermediate allenyl selenoketene

Article abstract of DOI:10.1016/j.tetlet.2005.01.019

Reactions of 2-alkynyl arylethynyl selenide 1 with alkyl iodides 3 in the presence of lithium aluminium hydride via allenyl selenoketene 2 afforded cyclobutene 4. Allenyl group of the intermediate allenyl selenoketene 2 was monitored by React IR.

Full text of DOI:10.1016/j.tetlet.2005.01.019

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 1479–1481
Synthesis of 1-alkylselenocyclobutene via intermediate allenyl
selenoketene
a,
Mamoru Koketsu, Masanori Kanoh, Yusuke Yamamura and Hideharu Ishihara
b
b
b,
*
*
a
Division of Instrumental Analysis, Life Science Research Center, Gifu University, Gifu 501-1193, Japan
b
Department of Chemistry, Faculty of Engineering, Gifu University, Gifu 501-1193, Japan
Received 22 September 2004; revised 27 December 2004; accepted 7 January 2005
Abstract—Reactions of 2-alkynyl arylethynyl selenide 1 with alkyl iodides 3 in the presence of lithium aluminium hydride via allenyl
selenoketene 2 afforded cyclobutene 4. Allenyl group of the intermediate allenyl selenoketene 2 was monitored by React IR.
Ó 2005 Elsevier Ltd. All rights reserved.
1
. Introduction
Se
R1
R2
R1
R2
Se
The selenoketene has been extensively investigated be-
cause of the interesting properties and reactivities using
reflux, THF
1
1
2
theoretical calculations. The selenoketene is found to
2
be more reactive than ketene in prototype reactions
such as ketene-ynol rearrangement, electrophilic and
Se-
R1
R1
SeR
LiAlH4
RI (3)
3
nucleophilic addition and [2+2] cycloaddition. Re-
R2
R2
cently, we have reported allenyl selenoketene formation
via a [3+3] sigmatropic rearrangement by trapping with
primary amines and its cyclization, however, we could
4
Scheme 1.
4
not trap the intermediate, allenyl selenoketene. Herein,
we investigated interesting reactivities of allenyl seleno-
ketene and an evident for the allenyl selenoketene by
using React IR.
aluminium hydride. The reaction gave 1-alkylseleno-3-
alkyl-2-aryl-4-methylidenecyclobutenes 4 (Scheme 1).
In a typical procedure, the selenide 1 was refluxed under
argon atmosphere. To the mixture in the presence of
lithium aluminium hydride, methyl iodide 1a was added
and stirred for 1 h. After standard workup 3-ethyl-4-
methylidene-1-methylseleno-2-phenylcyclobutene 4a was
2
. Results and discussion
Selenide 1 was obtained by a method previously re-
4
ported. In brief, 2-pentynyl chloride was added to
THF solution of the lithium alkyneselenoate, generated
in situ from phenylacetylene, n-BuLi and elementary
selenium, and the mixture was stirred at room tempera-
ture for 1.5 h. Subsequent silica gel flash column chro-
matography afforded 2-alkynyl arylethynyl selenide 1.
5
isolated in a 70% yield as yellow oil. At first, we could
not conclude whether the correct structure of the prod-
uct is 1-alkylselenocyclobutene type 4 or 2,5-dihydrose-
lenophene. The structure of 4 was determined by the
1
13
77
studies of IR, H, C, Se NMR, COSY, HMBC,
2
77
1
HMQC, MS and elemental analysis. J( Se– H) value
J = 108 Hz) was observed at the singlet methyl signal
of 4a. Spin system of CH –CH –CH– was observed in
We investigated reactions of 2-alkynyl arylethynyl sele-
nide 1 with alkyl iodides 3 in the presence of lithium
(
3
2
the spectra of COSY and HMBC of 4a. In the mass
spectrum (EI) of every 4, the stable fragment ion
Keywords: Allenyl selenoketene; Cyclobutene; React IR.
*
+
Corresponding authors. Fax: +81 58 293 2619; e-mail: koketsu@
cc.gifu-u.ac.jp
peaks of the corresponding alkyl (M ÀR) and alkylse-
+
leno (M ÀSe–R) groups were observed together with
0
040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.01.019

1480
M. Koketsu et al. / Tetrahedron Letters 46 (2005) 1479–1481
R1 Se
C H
Se
6
5
5
R
C H
R2
2
Reflux
4
5
molecular peak. The possibility of the formation of 2,5-
dihydroselenophene was ruled out by these observa-
tions. A ring closure of selenoketene 2 was reported to
occur under the thermal reaction conditions in the ab-
sence of nucleophiles to afford 2-methylidene-3-cyclobu-
0
5
10
15
20
25
30
35
Period (min)
Figure 1. React IR analysis: generation of allenyl group by refluxing of
-pentynyl phenylethynyl selenide 1. Arrow indicates a refluxing start
of the reaction mixture.
6
2
tene-1-selone 5. The present reaction by the addition of
alkyl iodides 3 in the presence of lithium aluminium
hydride gave 4 not 5. Several 1-alkylseleno-3-alkyl-2-
aryl-4-methylidenecyclobutenes 4 were obtained from
the reaction of selenide 1 with the corresponding alkyl
iodides 3 in moderate yields (Table 1).
of 2-alkylcyclobutenes 4, unfortunately it was failed.
In the case of 2-alkylcyclobutenes, though the product
4
was apparently confirmed to be formed in the reac-
The yields using haloalkanes bearing longer carbon
chains tended to decrease. Though we tried synthesis
tion mixture from the result of TLC monitoring, 4
could not be isolated for the decomposition on the pro-
cess of purification by a silica gel column chromatogra-
phy. The purification process gave several identifiable
products, desired corresponding 4 yielded in very low
yield.
Table 1. Synthesis of 1-alkylseleno-3-alkyl-2-aryl-4-methylidenecyclo-
butenes 4
a
Entry RI (3)
Product (4)
Yield (%)
To confirm a generation of allenyl selenoketene interme-
diate 2 by heating of selenide 1, React IR analysis of the
reaction mixture was conducted. A reaction was
C H
Se
Se
6
5
7
1
2
3
4
5
6
7
8
CH
3
I
70 (4a)
conducted on the selenide 1 in anhydrous THF under
argon atmosphere using flask fitted with the React IR
probe, monitoring typical absorbance for the allenyl
group. After 5 min when it started to reflux, the absor-
bance of the allenyl group increased drastically. The
generation of allenyl group was reached on a plateau
level in 10 min (Fig. 1). The generation of allenyl sele-
noketene intermediate 2 was confirmed by refluxing of
selenide 1 with a certainty. The allenyl selenoketene
intermediate 2 leads to 1-alkylselenocyclobutenes 4, by
the reactions with the corresponding alkyl iodides.
Alkylselenocyclobutene and alkylthiocyclobutene were
important molecules as a precursor for the preparation
C H
2
5
5
C H
6
C
C
C
2
2
2
H
H
H
5
5
5
I
I
I
74 (4b)
34 (4c)
29 (4d)
65 (4e)
47 (4f)
45 (4g)
45 (4h)
C H
2
5
4-CH C H
Se
3
6
4
C H
2
5
C H
6
Se
5
8
C H
of cyclobutenone. This paper provides not only charac-
terization of 1-alkylselenocyclobutenes 4 but also the
preparation method of 4.
5
11
5
C H
6
Se
Se
3 7
n-C H I
C H
2
5
5
Acknowledgements
C H
6
We thank Professor Robert J. Linhardt for the critical
reading of our manuscript.
3 2
(CH ) CHI
C H
2
5
5
C H
6
Se
Se
Supplementary data
n-C
4
H
9
I
C H
A supplementary data section is provided, which
includes experimental details and spectral data of
compound 4. The supplementary data is avai-
lable online with the paper in ScienceDirect. Supple-
mentary data associated with this article can be found,
in the online version, at doi:10.1016/j.tetlet.2005.
01.019.
2
5
5
C H
6
(CH
3
)
2
2 2
CH(CH ) I
C H
2
5
a
Isolated yield.

M. Koketsu et al. / Tetrahedron Letters 46 (2005) 1479–1481
1481
References and notes
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C H16Se: C, 63.88; H, 6.13. Found: C, 63.84; H, 5.98. 1-
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), 1.86–1.94 (1H, m, 1H of CH
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3
), 1.64–1.72 (1H, m, 1H
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3
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2
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(
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C
3
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3
77
6.2, 123.3, 126.8, 129.0, 131.0, 138.4, 152.3, 155.8; Se
9
+
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Anal. Calcd for C16
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methylidenecyclobutene 4. A solution of 2-pentynyl phenyl-
ethynyl selenide 1 (0.25 g, 1.0 mmol) in 10 mL anhydrous
THF under argon atmosphere was refluxed for 5 min. To
the reaction mixture, lithium aluminium hydride (0.04 g,
6
7
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atmosphere using flask fitted with the React IR probe.
After 5 min, the reaction mixture was refluxed. By scanning
4
5
the IR spectrum once for every 30 s from 650 to
4
À1
000 cm
during the reaction, the reaction monitoring
À1
was carried out. Typical absorbance, 1955 cm , of allenyl
group was plotted in Figure 1.
8
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1
.0 mmol) and methyl iodide 3a (0.13 mL, 2.0 mmol) was
added and refluxed for 1 h. The mixture was extracted with
diethyl ether and washed with saturated NaCl aqueous
solution. The organic layer was dried over sodium sulfate
and evaporated. The residue was purified by flash chroma-
tography on silica gel with n-hexane to give 4a (yield 70%).