Preparation of 2-phospholene derivatives from zirconacyclopentenes

Article abstract of DOI:10.1016/j.tetlet.2010.09.061

Zirconacyclopentenes, which are easily prepared from alkynes, alkenes, and zirconocene compounds, reacted with dichlorophenylphosphine to give 2-phospholene in high yields. The reaction was performed conveniently in one-pot from an alkyne, alkene, dichlor

Full text of DOI:10.1016/j.tetlet.2010.09.061

Tetrahedron Letters 51 (2010) 6136–6138
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Tetrahedron Letters
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Preparation of 2-phospholene derivatives from zirconacyclopentenes
Yiqing Zhou a, Xiaoyu Yan a, Chanjuan Xi a,b,
⇑
a Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084, China
b State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 July 2010
Revised 14 September 2010
Accepted 17 September 2010
Available online 9 October 2010
Zirconacyclopentenes, which are easily prepared from alkynes, alkenes, and zirconocene compounds,
reacted with dichlorophenylphosphine to give 2-phospholene in high yields. The reaction was performed
conveniently in one-pot from an alkyne, alkene, dichlorophosphine, and zirconocene compounds.
Ó 2010 Elsevier Ltd. All rights reserved.
This Letter is dedicated to the memory of
Professor Pascal Le Floch
Keywords:
Zirconacyclopentenes
Dichlorophosphine
Phospholene
Heterocycles
P-heterocycles are of current interest due to their rich chemis-
try and applications.1–3 For example, the phospholenes including
the 3-phospholenes and 2-phospholenes are extremely versatile
reactive intermediates in organic synthesis2 and excellent ligands
in organometallic chemistry.1,3 Consequently, there is a significant
interest in the development of new synthetic methodologies to ac-
cess phospholenes. Although a number of synthetic methods
affording phospholenes have been reported,4 the most attractive
one seems to be the direct transformation of metallcyclopentenes
to phospholenes. In this regard especially attractive are zirconacy-
clopentenes, which can be easily prepared by the reaction of an
alkyne with zirconocene ethylene complex Cp2Zr(CH2@CH2) or
zirconacyclopentane.5 Fagan, Nugent, and co-workers have
reported a single example for the preparation of 3-phospholene
from zirconacyclopenta-3-ene.6 In this Letter we would like to
report a convenient method for the preparation of 2-phospholene
derivatives from zirconacyclopenta-2-enes.
afford the desired product 2a (72% isolated yield) (Scheme 1).
Other zirconacyclopentenes lb and 1c showed a similar reactivity,
and 2b and 2c were isolated in 76% and 65% yield, respectively.
Since trivalent phosphines 2 were sensitive to oxygen, the prod-
ucts were isolated as phosphine sulfides 3 after treatment of the
reaction mixture with elemental sulfur. To extend the reaction,
we tried out various substituted monocyclic as well as bicyclic zir-
conacyclopentenes bearing alkyl, aryl, and TMS groups. The repre-
sentative results are summarized in Table 1. In all cases, the
corresponding products were formed in high yields. When unsym-
metrical alkynes were used, two regioisomers were observed (en-
tries 5–8). The ratio of the two isomers depended on the selectivity
of the formation of zirconacyclopentenes.5 The reaction of bicyclic
zirconacyclopentene 1i7 with PhPCl2 formed cyclopenta[c]phos-
pholene 3i (entry 9). To our delight, the crystal of 3i was suitable
for single crystal analysis, and its structure was fully characterized
by the X-ray diffraction analysis (Fig. 1).8 The zirconacycle com-
pound 1j prepared from benzyne and styrene with Zr(II)9 reacted
Typical procedure is as follows. To the THF solution of zircona-
cyclopentene la (1 mmol), prepared in situ from Cp2ZrEt2 (1 mmol)
and 3-hexyne (1 mmol),5c was added dichlorophenylphosphine
R
R
(1 mmol, 145 lL) at room temperature. After the reaction mixture
R
R
was stirred at room temperature for l h, the solvent was removed
under reduced pressure. The residue was extracted with diethyl
ether and filtered. The solvent was evaporated in vacuo and the
residue was purified by column chromatography on alumina to
ZrCp2
P
Ph
+
PhPCl2
THF, rt
1
2
2a: R = Et, 1h, 72%
n
2b
: R = Pr, 1h, 76%
2c: R = nBu, 3h, 65%
⇑
Corresponding author. Tel.: +86 10 62782695.
E-mail address: cjxi@tsinghua.edu.cn (C. Xi).
Scheme 1.
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.09.061

Y. Zhou et al. / Tetrahedron Letters 51 (2010) 6136–6138
6137
Table 1
Reaction of zirconacyclopentene with PhPCl2
Entry
1
Zirconacyclopentene
Phospholene
Yielda (%)
Et
Et
Et
S
Et
72
80
Cp2Zr
P
Ph
1a
3a
nPr
nPr
S
nPr
nPr
2
Cp2Zr
P
Ph
1b
3b
nBu
nBu
S
nBu
nBu
3
4
5
6
7
8
75
64
P
Cp2Zr
Ph
3c
1c
Ph
Ph
Ph
S
Ph
Cp2Zr
P
Ph
1d
3d
Figure 1. Single-crystal structure of 3i.
Ph
Ph
S
Me
Me
61b
62b
58c
52d
Cp2Zr
P
Ph
R
R
1e
3e
R
R
R
R
Mo(CO)6
50oC, 24h
Ph
Ph
Et
Ph
S
PhPCl2
THF, rt, 1h
P
Ph
P
ZrCp2
Et
Mo(CO)5
P
Cp2Zr
1
2
4
Ph
3f
1f
4a
: R = Et, 62%
TMS
TMS
S
: R = nPr, 54%
nBu
nBu
4b
P
Cp2Zr
Ph
Scheme 2.
1g
3g
Ph
Ph
S
Acknowledgments
P
Cp2Zr
Ph
1h
3h
This work was supported by the National Natural Science Foun-
dation of China(21032004, 20972085, and 20872076), and by Spe-
cialized Research Fund for the Doctoral Program of Higher
Education (200800030072).
Ph
Ph
S
9
P
61
Cp2Zr
Ph
1i
3i
3j
Supplementary data
S
10
62e
P
Cp2Zr
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2010.09.061.
Ph
1j
Ph
Ph
References and notes
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Isolated yields.
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A mixture of two regioisomers in a ratio of 8:1, the ratio of two isomers was
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