Hydrophosphorylation of alkenes with dialkyl phosphites catalyzed by Mn(III) under air

Article abstract of DOI:10.1021/jo049657j

A facile method for the synthesis of organophosphonates from alkenes and dialkyl phosphites was developed by the use of Mn(II) under air. Thus, the reaction of 1-octene with diethyl phosphite in the presence of Mn(OAc) ₂ (5 mol %) under air at 90 °C led to diethyl octylphosphonate (78%) and diethyl (2-hexyl)decylphosphonate (6%). Internal alkenes such as cis-2-octene gave a regioisomeric mixture of the corresponding hydrophosphorylation products in 84% yields.

Full text of DOI:10.1021/jo049657j

TABLE 1. Hyd r op h osp h or yla tion of 1-Octen e (1a ) w ith
Dia lk yl P h osp h ite Ca ta lyzed by Mn (OAc)2 u n d er Air a
Hyd r op h osp h or yla tion of Alk en es w ith
Dia lk yl P h osp h ites Ca ta lyzed by Mn (III)
u n d er Air
yieldb (%)
Co(II)
Mn(II)
run
(mol %)
(mol %)
3a a
82
78 (61)
nd
79
nd
15
21
69
3a b (81)
3a c (73)
4a a
1
2
3
2
0
2
0
0
0
0
1
0
0
5
5
0
5
5
5
1
1
5
5
6
6
Osamu Tayama, Atsushi Nakano, Takahiro Iwahama,
Satoshi Sakaguchi, and Yasutaka Ishii*
nd
4c
5d
6c,d
7e
8f
6
Department of Applied Chemistry, Faculty of Engineering,
Kansai University, Suita, Osaka 564-8680, J apan
nd
3
2
5
ishii@ipcku.kansai-u.ac.jp
Received March 1, 2004
9g
10h
4a b (7)
4a c (6)
a
1a (3 mmol) was allowed to react with 2a (9 mmol) catalyzed
Abstr a ct: A facile method for the synthesis of organophos-
phonates from alkenes and dialkyl phosphites was developed
by the use of Mn(II) under air. Thus, the reaction of 1-octene
with diethyl phosphite in the presence of Mn(OAc)2 (5 mol
%) under air at 90 °C led to diethyl octylphosphonate (78%)
and diethyl (2-hexyl)decylphosphonate (6%). Internal al-
kenes such as cis-2-octene gave a regioisomeric mixture of
the corresponding hydrophosphorylation products in 84%
yields.
by Mn(OAc)2 (5 mol %) in the presence or absence of Co(OAc)2 (2
b
mol %) under air at 90 °C for 1 h. Based on 1a used. The number
in parentheses shows the isolated yield. c Mn(OAc)3 was used in
d
g
place of Mn(OAc)2. Under Ar. e 8 h. f 6 h. HP(O)(nBuO)2 (2b)
h
was used at 100 °C. HP(O)(MeO)2 (2c) was used at 110 °C.
by the action of Co(II) and oxygen oxidizes ketones to give
R-keto radicals which then add to alkenes leading to
alkylated ketones. Thus, these results prompted us to
investigate the generation of phosphorus radicals through
one-electron oxidation by Mn(III) ions, and we found that
Mn(OAc)2 efficiently catalyzes the addition of dialkyl
phosphites, HP(O)(OR)2, to alkenes through a radical
process under air. In this paper, we disclose the Mn-
catalyzed hydrophosphorylation of a variety of alkenes
with HP(O)(OR)2.
Organophosphonates are an important class of inter-
mediates in the synthesis of biologically active com-
pounds and are generally prepared by the Arbuzov
reaction.1 Recently, Tanaka et al. have reported Pd-
catalyzed hydrophosphorylation of alkynes via oxidative
addition of HP(O)(OR)2 leading to alkenyl- and alkyl-
phosphonates.2 In addition, the Pd-catalyzed hydrophos-
phorylation of alkenes with a five-membered cyclic
hydrogen phosphonate is successfully achieved by them.3
Montchamp et al. reported the Pd-catalyzed hydrophos-
phinylation of alkenes and alkynes with H2P(O)OR.4
Quite recently, Rh complexes are reported to catalyze the
regio- and stereoselective addition of diphenylphosphine
oxide to alkynes5 and the regioselective olefin hydrophos-
phorylation.6
To obtain the information on the hydrophosphorylation
of alkenes with phosphites, the reaction of 1-octene (1a )
with diethyl phosphite (2a ) was carried out under various
conditions (eq 1, Table 1).
On the other hand, the radical addition of HP(O)(OR)2
to alkenes is well-known.7 For example, peroxide (or
light)- or triethylborane-initiated radical addition of
hypophosphites to olefins is reported.8 In recent years,
we have developed a new catalytic radical addition of
ketones to alkenes by the Mn(II)/Co(II)/O2 redox sytem.9
In this reaction, Mn(III) generated in situ from Mn(II)
The reaction of 1a with 3 equiv of 2a in the presence
of Mn(OAc)2 (5 mol %) and Co(OAc)2 (2 mol %) under air
at 90 °C for 1 h gave diethyl octylphosphonate (3a a )
(82%) and diethyl (2-hexyl)decylphosphonate (4a a ) (6%)
(run 1). It was found that almost the same results were
obtained even in the absence of Co(OAc)2 from the
catalytic system (run 2).10 However, no reaction took
place by removing Mn(OAc)2 from the catalytic system
under these conditions (run 3). It is interesting that the
same results were obtained when Mn(OAc)3 was em-
ployed in place of Mn(OAc)2 (run 4). In the absence of
air, Mn(OAc)2 did not catalyze the hydrophophorylation
of 1a with 2a , although Mn(OAc)3 promoted slightly the
(1) (a) Organic Phosphorus Compounds; Kosolapoff, G. M., Maier,
L., Ed.; Wiley-Interscience: New York, 1972. (b) Corbridge, D. E. C.
Phosphorus: An Outline of Its Chemistry, Biochemistry and Uses, 5th
ed.; Elsevier: Amsterdam: 1995.
(2) Han, L.-B.; Tanaka, M. J . Am. Chem. Soc. 1996, 118, 1571.
(3) Han, L.-B.; Mirzaei, F.; Zhao, C.-Q.; Tanaka, M. J . Am. Chem.
Soc. 2000, 122, 5407.
(4) Deprele, S.; Montchamp, J .-L. J . Am. Chem. Soc. 2002, 124, 9386.
(5) Han, L.-B.; Zhao, C.-Q.; Tanaka, M. J . Org. Chem. 2000, 66, 5929.
(6) Reichwein, J . F.; Patel, M. C.; Pagenkopf, B. L. Org. Lett. 2001,
3, 4303.
(7) (a) Walling, C.; Peason, M. S. Top. Phosphorus Chem. 1966, 3,
1. (b) Bentrude, W. G. In The Chemistry of Organophosphorus
Compounds; Hartley, F. R., Ed.; Wiley: New York, 1990; Vol. 1,
Chapter 14. (c) Free Radicals; Kochi, J . K., Ed.; Wiley: New York, 1973;
Vol. 2, Chapter 22.
(9) Iwahama, T.; Sakaguchi, S.; Ishii, Y. Chem. Commun. 2000,
2317.
(8) (a) Stiles, A. R.; Vaughan, W. E.; Rust, F. F. J . Am. Chem. Soc.
1958, 80, 714. (b) Deprele, S.; Montchamp, J .-L. J . Org. Chem. 2001,
66, 6745.
(10) A typical reaction was carried out as follows: To a solution of
Mn(OAc)2 (0.15 mmol) and 2a (9 mmol) was added 1a (3 mmol). The
mixture was stirred at 90 °C for 1 h under air (1 atm).
10.1021/jo049657j CCC: $27.50 © 2004 American Chemical Society
Published on Web 07/03/2004
5494
J . Org. Chem. 2004, 69, 5494-5496

TABLE 2. Hyd r op h osp h or yla tion of Va r iou s Alk en es
w ith Dieth yl P h osp h ite (2a ) Ca ta lyzed by Mn (OAc)2
u n d er Air a
SCHEME 1
adducts, 3d a and 3ea , in 82% and 62% yields, respec-
tively (runs 3 and 4).
The reaction of â-pinene (1f) was found to proceed
through ring opening of its cyclobutane moiety affording
cleaved product 3fa (32%) (run 5), and the formation of
3fa can be rationally explained by Scheme 1. The
phosphonyl radical (A) formed added to 1f followed by
ring opening of the cyclobutane ring giving an alkyl
radical C, which subsequently abstract of hydrogen from
hydrogen donor like 2a afford the corresponding adduct
3fa .
When the alkyne instead of alkene was used as a
substrate, a similar coupling reaction was found to take
place. 1-Octyne (4) was allowed to react with 2a under
the influence of Mn(OAc)2 and air (1 atm) without solvent
to form a stereoisomeric mixture of adducts, cis- and
trans-5 whose ratio was approximately 2:1 (run 6).
It is interesting that the reaction of 1,5-cyclooctadiene
(6) with 2a in the presence of Mn(OAc)2 (5 mol %) under
air without solvent at 100 °C for 3 h produced cis-fused
product 7 in 72% yield (eq 2). In a previous paper, we
showed that the dimethyl malonate radical generated by
its one-electron oxidation of Mn(OAc)2/Co(OAc)2/O2 sys-
tem adds to 6 in a way similar to that described above to
give the corresponding cis-fused adduct.11
a
The reaction was run under the same conditions as Table 1,
run 2. The isolated yield. c 1d (2 mmol) and 2a (12 mmol) were
used. 1e (2 mmol) and 2a (14 mmol) were used.
b
d
hydrophophorylation (runs 5 and 6). These results show
that Mn(II) is oxidized to Mn(III) under these conditions,
and the resulting Mn(III) ion seems to catalyze the
hydrophophorylation of 1a with 2a . When the amount
of Mn(OAc)2 was reduced to 1 mol %, the yield of 3a a
decreased to 21% even for 8 h (run 7). However, the
addition of Co(OAc)2 to this catalytic solution led to 3a a
in 69% yield (run 8). Since the Co(II) ions under air are
well-known to generate Co(III)-oxygen complexes such
as Co(III)-OO•, it seems to be reasonable to assume Mn-
(II) is readily oxidized by the Co(III)-oxygen complexes
to Mn(III) which promotes smoothly the present hydro-
phophorylation. Dibutyl phosphite (2b) and dimethyl
phosphite (2c) added to 1a to form the corresponding
adducts, 3a b and 3a c, in good yields (runs 9 and 10).
To extend the present reaction to various alkenes, we
tried the reaction between alkenes and 2a in the presence
of Mn(OAc)2 (5 mol %) under air at 90-110 °C for 1-4 h
(Table 2).
In conclusion, we developed an efficient methodology
for the hydrophosphorylation of alkenes and alkynes with
dialkyl phosphites assisted by Mn salt under air (1 atm)
through radical process. Further application of this
catalytic system to many other key transformations are
now in progress.
cis-2-Octene (1b) was reacted with 2a at 110 °C under
these conditions to give a regioisomeric mixture of 2- and
3-hydrophophorylated products, 3ba and 3ba ′, in a ratio
of 49% to 35% (run 1). The reaction was achieved for
cyclic alkenes such as cyclooctene (1c), giving 3ca in good
yield (80%) (run 2). Ethyl allylmalonate (1d ) and allyl-
benzene (1e) reacted with 2a to give the corresponding
Exp er im en ta l Section
All starting materials were commercially available and used
without any purification. GLC analysis was performed with a
flame ionization detector using a 0.2 mm × 25 m capillary
(11) Hirase, K.; Iwahama, T.; Sakaguchi, S.; Ishii, Y. J . Org. Chem.
2002, 67, 970.
J . Org. Chem, Vol. 69, No. 16, 2004 5495

column (OV-1). 1H and 13C NMR were measured at 270 and 67.5
MHz, respectively, in CDCl3 with Me4Si as the internal standard.
A typical reaction procedure of the reaction of 1a with 2a is
as follows: To a solution of Mn(OAc)2 (0.15 mmol) and 2a (9
mmol) was added 1a (3 mmol). The mixture was stirred at 90
°C for 1 h under air (1 atm). The product was isolated by column
chromatography (230-400 mesh silica gel, n-hexane/ethyl ac-
etate ) 1:1). The conversions and yields of products were
estimated from the peak areas based on the internal standard
technique using GLC.
Ack n ow led gm en t. This work was partially sup-
ported by a Grant-in-Aid for Scientific Research (S) from
the Ministry of Education, Culture, Sports and Technol-
ogy (MEXT), J apan.
Su p p or tin g In for m a tion Ava ila ble: Characterization of
products. This material is available free of charge via the
Internet at http://pubs.acs.org.
J O049657J
5496 J . Org. Chem., Vol. 69, No. 16, 2004