Highly regioselective simultaneous introduction of phosphino and seleno groups into unsaturated bonds by the novel combination of (Ph2P) 2 and (PhSe)2 upon photoirradiation

Full text of DOI:10.1021/jo8020067

SCHEME 1. Group 16 Heteroatom-Mixed Systems
Highly Regioselective Simultaneous Introduction
of Phosphino and Seleno Groups into
Unsaturated Bonds by the Novel Combination of
(Ph2P)2 and (PhSe)2 upon Photoirradiation
Shin-ichi Kawaguchi, Takamune Shirai, Takashi Ohe,
Akihiro Nomoto,* Motohiro Sonoda, and Akiya Ogawa*
Department of Applied Chemistry, Graduate School of
Engineering, Osaka Prefecture UniVersity, 1-1 Gakuen-cho,
Nakaku, Sakai, Osaka 599-8531, Japan
ogawa@chem.osakafu-u.ac.jp
ReceiVed September 22, 2008
mixed systems under photoirradiation conditions realize con-
venient synthesis of a wide variety of group 16 heteroatom
compounds, as indicated in Scheme 1.6 By using a (PhS)2-
(PhSe)2 mixed system, for example, a series of unsaturated
compounds such as alkynes, alkenes, allenes, and isocyanides
undergo regioselective thioselenation to give the corresponding
thioselenated products without formation of the dithiolated
adducts or diselenated adducts. The higher reactivity of phe-
A novel combination of tetraphenyldiphosphine and diphenyl
diselenide under photoirradiation conditions attains simul-
taneous introduction of diphenylphosphino and phenylseleno
groups into carbon-carbon unsaturated bonds such as ter-
minal alkynes or allenes, regioselectively.
nylthio radical compared with phenylseleno radical (kS/kSe
)
Highly selective introduction of different heteroatom-includ-
ing functional groups into unsaturated bonds provides a useful
tool to synthesize multifunctionalized heteroatom compounds
in one portion.1-5 We have revealed that group 16 heteroatom-
10-50)7 and the higher carbon radical capturing ability of
diphenyl diselenide compared with diphenyl disulfide (kSe/kS )
160)8 contribute to the excellent regioselectivity and product
selectivity. In the case of enynes, the photoinduced thioselena-
(1) For books concerning the recent advance of radical chemistry in organic
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Renaud, P., Sibi, M. P., Eds.; Wiley-VCH: Weinheim, 2001; Vols. 1 and 2. (b)
Stereochemistry of Radical Reactions; Curran, D. P., Porter, N. A., Giese, B.,
Eds.; VCH: Weinheim, 1996. (c) Giese, B.; Kopping, B.; Go¨bel, T.; Dickhaut,
J.; Thoma, G.; Kulicke, K. J.; Trach, F. Org. React. 1996, 48, 301. (d) Free
Radicals in Organic Chemistry; Fossey, J., Lefort, D., Sorba, J., Eds.; Wiley:
Chichester, 1995.
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2, Chapter 15. (b) Topics in Current Chemistry; Wirth, T., Ed.; Springer: Berlin,
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(3) For books concerning the chemistry of organophosphorous compounds,
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In Heteroatom Chemistry; Block, E., Ed.; VCH Publishers, Inc.: New York,
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Org. Chem. 1992, 57, 111. (d) Ogawa, A.; Sonoda, N. Phosphorus, Sulfur, Silicon
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N.; Hirao, T. J. Org. Chem. 1998, 63, 881. (f) Ogawa, A.; Obayashi, R.; Sonoda,
N.; Hirao, T. Tetrahedron Lett. 1998, 39, 1577. (g) Ogawa, A.; Obayashi, R.;
Doi, M.; Sonoda, N.; Hirao, T. J. Org. Chem. 1998, 63, 4277. (h) Ogawa, A.;
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64, 86. (i) Tsuchii, K.; Tsuboi, Y.; Kawaguchi, S.-i.; Takahashi, J.; Sonoda, N.;
Nomoto, A.; Ogawa, A. J. Org. Chem. 2007, 72, 423. (j) Mitamura, T.; Tsuboi,
Y.; Iwata, K.; Tsuchii, K.; Nomoto, A.; Sonoda, M.; Ogawa, A. Tetrahedron
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10.1021/jo8020067 CCC: $40.75
Published on Web 01/27/2009
2009 American Chemical Society
J. Org. Chem. 2009, 74, 1751–1754 1751

TABLE 1. Photoinduced Selenophosphination of Alkynes with
(Ph2P)2 and (PhSe)2
tion proceeds through the 5-exo cyclization, affording the
corresponding five-membered ring compounds bearing both thio
and seleno groups. On the other hand, the thioselenation of
vinylcyclopropanes takes place via the ring-opening of cyclo-
propane ring. Not only the thioselenation but also the thiotel-
luration and selenotelluration of alkynes can be attained by using
(PhS)2-(PhTe)2 mixed system and (PhSe)2-(PhTe)2 mixed
system, respectively.
Very recently, we have succeeded in application of this
methodology to a novel combination of group 16 heteroatom
compounds and others such as group 17 and group 15 hetero-
atom compounds: perfluoroalkylselenation by using a (PhSe)2-
RFI mixed system9 and thiophosphination by using a (PhS)2-
(Ph2P)2 mixed system10 take place successfully with excellent
regioselectivity (eqs 1 and 2).
In this paper, we report novel selenophosphination of car-
bon-carbon unsaturated compounds by the combination of
(PhSe)2 and (Ph2P)2 upon photoirradiation (eq 3).
a
1
1-Ethynyl-4-trifluorobenzene (1a, 0.5 mmol), tetraphenyl-
diphosphine (2, 0.5 mmol), and diphenyl diselenide (3, 0.5
mmol) in CDCl3 (0.6 mL, degassed) were placed in an NMR
(φ ) 4 mm, Pyrex) tube filled with nitrogen, and then the tube
was sealed. Irradiation through a filter with a xenon lamp (hν
> 350 nm) was conducted at room tempetature for 2 h. A novel
selenophosphination successfully took place with excellent
regioselectivity, affording the corresponding phosphine oxide
(5a) by air-oxidation during workup (eq 4).
Determined by H NMR.
this reaction, the corresponding regioisomer,11 the diphosphi-
nation product,12 and the diselenation product13 are not obtained
at all, and the selenophosphination product (5a) is obtained with
excellent selectivity.
Table 1 shows the representative results of the selenophos-
phination of several alkynes. When aromatic alkynes were
employed as the substrates, the desired selenophosphination
smoothly proceeded in good yield, regioselectively (entries
1-4). A conjugated alkyne such as 1-ethynylcyclohexene also
gave the corresponding selenophosphination product in good
yield (entry 5). In the case of the aliphatic alkyne such as
1-octyne, unfortunately, the desired selenophosphination did not
occur. In general, the addition to aromatic alkynes proceeds via
the formation of vinylic π-radical intermediate,14 whereas the
addition to aliphatic alkynes involves the formation of less stable
vinylic σ-radical intermediate.15 The difference of the stability
between these radical intermediates may contribute to the
difference of the reactivity between aromatic alkynes and
aliphatic ones.
X-ray crystallographic analysis of 5a clearly indicates the
regioselectivity of this selenophosphination: the seleno group
and phosphine oxide group are located selectively at the terminal
and the inner positions of the triple bond of 1a, respectively. In
Similarly, in an NMR tube, a mixture of cyclohexylallene (6a,
0.5 mmol), tetraphenyldiphosphine (2, 0.5 mmol), and diphenyl
diselenide (3, 0.5 mmol) was placed in CDCl3 (0.6 mL, degassed),
and then the tube was sealed. Upon irradiation with a xenon lamp
(9) (a) Tsuchii, K.; Ogawa, A. Tetrahedron Lett. 2003, 44, 8777. See also: (b)
Ogawa, A.; Imura, M.; Kamada, N.; Hirao, T. Tetrahedron Lett. 2001, 42, 2489.
(c) Tsuchii, K.; Imura, M.; Kamada, N.; Hirao, T.; Ogawa, A. J. Org. Chem.
2004, 69, 6658. (d) Nomoto, A.; Ogawa, A. In Handbook of Reagents for Organic
Synthesis:Fluorine-Containing Reagents; Paquette, L. A., Ed.; John Wiley &
Sons Ltd.: New York, 2007; p 289.
(10) Shirai, T.; Kawaguchi, S.-i.; Nomoto, A.; Ogawa, A. Tetrahedron Lett.
2008, 49, 4043.
(11) The palladium-catalyzed selenophosphorylation of terminal alkynes
provides (Z)-1-phosphoryl-2-seleno-1-alkenes: Han, L.-B.; Choi, N.; Tanaka, M.
J. Am. Chem. Soc. 1996, 118, 7000.
(12) For the photoinduced addition of tetraphenyldiphosphine to alkynes, see:
Kawaguchi, S.; Nagata, S.; Tsuchii, K.; Nomoto, A.; Ogawa, A. Tetrahedron
Lett. 2006, 47, 3919.
(13) For the photoinduced addition of diphenyl diselenide to alkynes, see:
(a) Back, T. G.; Krishna, M. V. J. Org. Chem. 1988, 53, 2533. (b) Ogawa, A.;
Yokoyama, H.; Yokoyama, K.; Masawaki, T.; Kambe, N.; Sonoda, N. J. Org.
Chem. 1991, 56, 5721.
(14) Singer, L. A.; Chen, J. Tetrahedron Lett. 1969, 10, 4849.
(15) Fessenden, R. W.; Schuler, R. H. J. Chem. Phys. 1963, 39, 2147.
1752 J. Org. Chem. Vol. 74, No. 4, 2009

TABLE 2. Photoinduced Selonophosphination of Allenes with
(Ph2P)2 and (PhSe)2
(500 W) though the filter (hν > 350 nm) at room temperature for
1 h, the desired selenophosphination of the allene took place
regioselectively at the terminal double bond, affording the adduct
(7a) in 83% yield (eq 5). A trace amount of diselenation product16
was obtained, but no formation of the regioisomers of the
selenophosphination product was detected. The selenophosphina-
tion product provided the corresponding phosphine oxide 8a by
air-oxidation during workup. The location of seleno group and
phosphino group of the selenophosphination product was deter-
mined by X-ray crystallographic analysis of 8a.
Similar conditions can be employed with several allenes
(6a-e) (Table 2). In the case of aliphatic allenes (entries 1-3),
selenophosphination proceeded smoothly, and Z isomers were
obtained preferentially. Aromatic allene also underwent the
regioselective selenophosphination (entry 4). The disubstituted
terminal allene such as vinylidenecyclohexane also provided
the corresponding selenophosphination product smoothly (entry
5). When the internal allene such as cyclonona-1,2-diene was
employed, the selenophosphination did not proceed (entry 6).
Isolation of the selenophosphination products was conducted
by preparative TLC. The reason for the lower isolated yields
of 8 is probably due to the relative instability of allylic
phosphine.
a
The selenophosphination of alkynes or allenes did not proceed
in the dark (eqs 6 and 7). Therefore, we assume the present
selenophosphination may proceed via a radical mechanism.
Diphenyl diselenide (3) has its absorption maximum (λmax) at
340 nm (ꢀ ) 103)17 and the absorption reaches to 450 nm,
1
Determined by H NMR.
SCHEME 2. A Plausible Pathway of Selenophosphination of
Alkynes or Allenes
whereas the absorption of tetraphenyldiphosphine (2) (λmax
)
260 nm, ꢀ ) 41.3) reaches to 330 nm.18 Therefore, irradiation
with the light of wavelength over 350 nm induces selective
homolysis of diselenide (3) generating phenylseleno radical
(PhSe•) at least in the initial stage. The seleno radical (PhSe•)
can also be formed by the photoinduced homolysis of Ph2PSePh
(9), which is gradually generated in situ under photoirradiation
conditions. In the case of alkynes, the PhSe• attacks the terminal
carbon of alkynes, generating vinyl radical intermediate, and
then trapping with Ph2PSePh19 leads to the selenophosphination
products 4. In the case of allenes, the PhSe• attacks the central
carbon of allenes,20 generating allylic radical intermediate. The
subsequent SH2 reaction of the allyl radical intermediate with
Ph2PSePh19 affords the adduct 7, regioselectively. (Scheme 2).
We have demonstrated the first simultaneous and regiose-
lective selenophosphination to carbon-carbon unsaturated bonds
(16) (a) Ogawa, A.; Yokoyama, K.; Yokoyama, H.; Sekiguchi, M.; Kambe,
N.; Sonoda, N. Tetrahedron Lett. 1990, 31, 5931. (b) Kamiya, I.; Nishinaka, E.;
Ogawa, A. Tetrahedron Lett. 2005, 46, 3649. (c) Kodama, S.; Nishinaka, E.;
Nomoto, A.; Sonoda, M.; Ogawa, A. Tetrahedron Lett. 2007, 48, 6312.
(17) Schmidt, U.; Mu¨ller, A.; Markau, K. Chem. Ber. 1964, 97, 405.
J. Org. Chem. Vol. 74, No. 4, 2009 1753

by using the (Ph2P)2-(PhSe)2 mixed system upon photoirra-
diation under the mild reaction condition. This (Ph2P)2-(PhSe)2
binary system is well-controlled by taking advantage of the
different reactivity between phosphino atom and seleno atom
in radical reactions. We are now investigating the other
combinations of heteroatom compounds in radical addition
reactions.
Acknowledgment. This work is supported by a Grant-in-
Aid for Scientific Research on Priority Areas (Area 444, No.
19020061) and Scientific Research (B, 19350095) from the
Ministry of Education, Culture, Sports, Science and Technology,
Japan.
Supporting Information Available: X-ray structure details
for compounds 5a and 5m (CIF). Spectral and analytical data,
ORTEP plots, Crystal Data and Structure Analysis Results for
(E)-5a and (Z)-9a, and copies of 1H NMR and 13C NMR spectra
of 5a-f and 8a-e. This material is available free of charge via
the Internet at http://pubs.acs.org.
Experimental Section
General Procedure for Photoinduced Selenophosphination
of Alkynes or Allenes. (Ph2P)2 (188 mg, 0.5 mmol), (PhSe)2 (156
mg, 0.5 mmol), and alkyne or allene (0.5 mmol) were placed in
CDCl3 (0.6 mL) in a sealed Pyrex glass NMR tube under nitrogen
atmosphere. The mixture was stirred for 30 s, and then the mixture
was irradiated with a xenon lamp (500 W) though the filter (hν >
350 nm) at room temperature for 1-2 h. The reaction mixture was
left under air overnight. Purification of the crude was performed
by preparative TLC.
JO8020067
(18) Troy, D.; Turpin, R.; Voigt, D. Bull. Soc. Chim. Fr. 1979, 241.
(19) Alternatively, the formed vinyl or allyl radical may abstract diphe-
nylphosphino group from (Ph2P)2. In this case, Ph2P• concomitantly reacts with
(PhSe)2 generataing Ph2PSePh and PhSe•.
(20) Masawaki, T.; Ogawa, A.; Kambe, N.; Ryu, I.; Sonoda, N. Chem. Lett.
1987, 12, 2408.
1754 J. Org. Chem. Vol. 74, No. 4, 2009