Synthesis of (E)-1,2-diphosphanylethene derivatives from alkynes by radical addition of tetraorganodiphosphane generated in situ

Article abstract of DOI:10.1002/anie.200462603

(Chemical Equation Presented) E-asy radical addition: A tetraorganodiphosphane, generated in situ from a diorganophosphane and a chlorodiorganophosphane in the presence of triethylamine, adds to terminal alkynes by a radical process (see scheme) to afford

Full text of DOI:10.1002/anie.200462603

Communications
Diphosphanylethenes
A mixture of 1-dodecyne (1a), diphenylphosphane,[7]
chlorodiphenylphosphane, triethylamine, and 1,1’-azobis(cy-
clohexanecarbonitrile) (V-40)[8] was heated in boiling ben-
zene for 10 h (Scheme 1). The product was isolated as a 91:9
mixture of E and Z isomers of phosphane sulfide 3a in 84%
yield. These two stereoisomers were separable from each
other by thorough chromatographic purification on silica gel.
Synthesis of (E)-1,2-Diphosphanylethene
Derivatives from Alkynes by Radical Addition of
Tetraorganodiphosphane Generated In Situ**
Akinori Sato, Hideki Yorimitsu, and Koichiro Oshima*
Organophosphorus compounds serve as reagents, ligands for
transition metals, biologically active substances, and building
blocks of nanoarchitectures, and thus play vital roles in
organic chemistry. Among them, (E)-1,2-bis(diphenylphos-
phanyl)ethene has recently attracted increasing attention in
the field of self-assembly.[1] Construction of hierarchical
structures for use as new functional materials[2] calls for
derivatives of (E)-1,2-bis(diphenylphosphanyl)ethene that
have functional groups to induce further assembly. However,
there are a limited number of methods for the synthesis of
such peculiar diphosphanylethene skeletons; these syntheses
are always carried out under harsh and/or strongly basic
conditions.[3] Highly efficient and mild reactions affording
(E)-1,2-bis(diphenylphosphanyl)ethene derivatives are there-
fore required.
Scheme 1.
The presence of an excess of chlorodiphenylphosphane is
essential for the success of the reaction: the use of a smaller
amount (1.0 mmol) of chlorodiphenylphosphane gave (1-
dodecenyl)diphenylphosphane sulfide (4, 9%, E/Z = 18:82)
along with 3a (78%, E/Z = 90:10). Complete conversion of
diphenylphosphane to tetraphenyldiphosphane is important
to avoid contamination by monoadduct 4.
Tetraphenyldiphosphane is commercially available. How-
ever, the reaction of 1a (0.75 mmol) with the purchased
tetraphenyldiphosphane[9] (1.5 mmol) yielded both 3a (60%,
E/Z = 88:12) and 4 (27%, E/Z = 37:63). It is worth noting that
addition of chlorodiphenylphosphane to the reaction mixture
suppressed the generation of 4, and generated 3a (87%, E/Z
= 89:11) selectively.
A variety of terminal alkynes undergo this radical
diphosphanylation reaction (Table 1). Aryl-substituted ace-
tylenes react with tetraphenyldiphosphane prepared in situ to
yield 1-aryl-1,2-bis(diphenylthiophosphanyl)ethenes in excel-
lent yield with high stereoselectivity (entries 1–5). The E
configuration of the major isomer of 3c was determined by X-
ray crystallographic analysis (see the Supporting informa-
tion). Purification of 2b under argon allowed us to isolate this
compound in 78% yield (E/Z = 92:8). Ester (entries 3 and 7),
iodo (entry 4), keto (entry 5), and thioester (entry 8) moieties
remained unchanged under the reaction conditions; these
groups are not tolerated in the conventional incorporation of
a diphenylphosphanyl group which requires the use of a
highly nucleophilic and basic metal diphenylphosphide.[3]
Gratifyingly, an carbon(sp3)–halogen bond was also stable
during the reaction, although 1j is prone to form the
corresponding Wittig salt (entry 9). Tetracyclohexyldiphos-
phane, prepared in situ from dicyclohexylphosphane[7] and
chlorodicyclohexylphosphane, added to 1b in a similar
fashion to afford (E)-3b’ in excellent yield after careful
separation from contaminants such as (Z)-3b’ (Scheme 2).
The reactions with tert-butylacetylene failed to yield the
desired product, and internal alkynes such as diphenylacety-
Here we report a general, facile, and reliable synthesis of
(E)-diphosphanylethene derivatives starting from an alkyne
and a tetraorganodiphosphane. Radical addition of a tetra-
À
organodiphosphane across a C C triple bond seems to be a
straightforward strategy for the synthesis of 1,2-diphospha-
nylethenes.[4,5] However, tetraorganodiphosphanes are so
sensitive to oxygen that their preparation, purification, and
handling are quite difficult and must be carried out under a
strictly inert atmosphere.[6] The inherent instability of diphos-
phanes in the presence of oxygen poses a serious problem in
their synthetic use. The present diphosphanylation reaction
employs a tetraorganodiphosphane that is cleanly generated
in situ prior to the reaction. The high efficiency of this method
will allow the 1,2-diphosphanylethenes synthesized to be
applicable in organic materials science.
[*] A. Sato, Dr. H. Yorimitsu, Prof. Dr. K. Oshima
Department of Material Chemistry
Graduate School of Engineering
Kyoto University
Kyoto-daigaku Katsura, Nishikyo-ku, Kyoto 615-8510 (Japan)
Fax: (+81)75-383-2438
E-mail: oshima@orgrxn.mbox.media.kyoto-u.ac.jp
[**] This work was supported by Grants-in-Aid for Scientific Research,
Young Scientists, and COE Research from the Ministry of Education,
Culture, Sports, Science, and Technology, Japan. We thank Prof.
Masaki Shimizu (Department of Material Chemistry, Kyoto Univer-
sity) and Dr. Yasuyuki Ura (Department of Energy and Hydrocarbon
Chemistry, Kyoto University) for generous help with the X-ray
crystallographic analysis and for teaching us how to purify air-
sensitive compounds, respectively. We also acknowledge Mr.
Hiroshi Hata and Prof. Naoki Aratani and Prof. Hiroshi Shinokubo
(Department of Science, Kyoto University) for measuring UV/Vis
and fluorescence spectra. Chlorodicyclohexylphosphane was a gift
from Hokko Chemical Industry Co., Ltd.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
1694
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/anie.200462603
Angew. Chem. Int. Ed. 2005, 44, 1694 –1696

Angewandte
Chemie
addition of a phosphorus-centered radical[10] followed by 5-
Table 1: Radical diphosphanylation of terminal alkynes.
exo-dig radical cyclization. Isomerization of 6 to 7 reduces the
steric hindrance in the cyclization, and subsequent radical SH2
substitution[11] affords the doubly phosphinated diene.[12]
The high efficiency of this reaction might offer a reliable
method for the synthesis of organic compounds for use in
single-molecule devices, self-assembled monolayers (Table 1,
entry 8), or optically intriguing organic materials. Scheme 4
illustrates the synthesis of a new fluorescent compound 10
which exhibits a couple of intense absorption bands in the UV
region (lmax = 302, 320 nm; e = 2.0 ꢀ 104 mÀ1 cmÀ1 for both)
and blue fluorescence (lmax = 469 nm) upon irradiation at 302
or 320 nm.
Entry
3
R
Yield [%][a]
E/Z[a]
1
2
3
4
5
6
7
8
9
3b
3c
3d
3e
3 f
3g
3h
3i
Ph
87 (96)[b]
89
95
83
96
78
86
80
86
93:7
94:6
94:6
94:6
95:5
90:10
90:10
90:10
91:9
p-MeOC6H4
p-MeOC(O)C6H4
p-IC6H4
p-AcC6H4
PhCH2OCH2CH2CH2
EtOC(O)(CH2)6
AcS(CH2)9
3j
Cl(CH2)9
31
=
[a] Determined by P NMR spectroscopy with (MeO)3P O as internal
standard. [b] Performed on a 5.0-mmol scale.
Scheme 4.
In summary, we have developed a highly efficient and
concise diphosphanylation reaction for terminal alkynes. The
radical addition of a tetraorganodiphosphane to an alkyne
affords 1,2-diphosphanylethenes in good yield with high E
selectivity. The required tetraorganodiphosphane was readily
prepared by mixing a diorganophosphane and a chlorodior-
ganophosphane in situ in the presence of triethylamine, which
allowed us to avoid the troublesome isolation of tetraorga-
nodiphosphane. The mild reaction conditions offer excellent
functional-group compatibility and hence provide a powerful
tool for the synthesis of important compounds by introducing
two phosphorus atoms in one shot.
Scheme 2.
lene and 6-dodecyne also remained intact. Under the same
reaction conditions 4-pentyn-1-ol or 3-butyn-2-one gave
complex mixtures containing small amounts of the desired
products.
Received: November 14, 2004
Published online: February 2, 2005
The reaction clearly proceeds via a radical pathway, as
demonstrated in Scheme 3. The formation of 5 necessitates
Keywords: alkenes · alkynes · diphosphanylethenes ·
radical reactions · synthetic methods
.
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Communications
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À
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[12] Along with 5, the crude mixture contained several byproducts,
which could not be exactly identified. 2,3-Bis(diphenylthiophos-
phanyl)-2-propenyl propargyl ether seemed to be the main by-
product.
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ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
Angew. Chem. Int. Ed. 2005, 44, 1694 –1696