Ruthenium-catalyzed isomerization of alkenol into alkanone in water under irradiation of microwaves

Article abstract of DOI:10.1246/cl.2005.664

Ruthenium catalyzed isomerization of alkenol into alkanone through a migration of C-C double bond was performed in water under irradiation of microwaves. When the reaction was performed in deuterium oxide instead of water, the trail of the migration was shown by H-D exchange reaction. Copyright

Full text of DOI:10.1246/cl.2005.664

664
Chemistry Letters Vol.34, No.5 (2005)
Ruthenium-catalyzed Isomerization of Alkenol into Alkanone
in Water under Irradiation of Microwaves
Kenichi Ishibashi, Masaaki Takahashi, Yutaka Yokota, Koichiro Oshima, and Seijiro MatsubaraÃ
Department of Material Chemistry, Graduate School of Engineering, Kyoto University,
Kyoudai-katsura, Nishikyo, Kyoto 615-8510
(Received March 3, 2005; CL-050286)
Table 1. Isomerization of alkenol into alkanonea
Ruthenium catalyzed isomerization of alkenol into alkanone
through a migration of C–C double bond was performed in water
under irradiation of microwaves. When the reaction was per-
formed in deuterium oxide instead of water, the trail of the mi-
gration was shown by H–D exchange reaction.
RuCl (PPh ) (5 mol%)
2
3 3
R
R"
OH
R
R"
n
n
H O, Microwaves
2
185 °C, 10 atm
R'
O
R'
1
2
Run
1
Substrates (1)
Yield of 2
96%
Ph
Isomerization of allylic alcohols into carbonyl compounds
via C–C double bond migration has been performed efficiently
using transition metal catalysts.1a,b In the reactions starting from
allylic alcohols, the reaction pathway may be considered to be
the result of formation of an enol via a 1,3-hydride shift. The cor-
responding reactions starting from homoallylic alcohols or !-al-
kenols which have more than three sp3 carbons between the al-
kene group carbon and the hydroxyl group substituted carbon
have not been performed efficiently, except for a few examples.2
In the case of ruthenium catalyzed reactions, allylic alcohols are
isomerized into carbonyl compounds efficiently, but homoallylic
alcohols cannot be converted into carbonyl compounds even at
high temperature.3 We have found that treatment of alkenes with
ruthenium catalyst in water under irradiation of microwaves
shows an effective alkene migration reaction. Here we wish to
report the novel ruthenium catalyzed isomeriation of !-alkene-
nols into carbonyl compounds in water.3c,d
A mixture of 14-pentadecen-5-ol (1a, 1.0 mmol), water (3.0
mL), and Ru catalyst (5 mol %) in a 10-mL sealed vial was heat-
ed by irradiation of microwaves (185 ꢀC, 10 atm).4 After irradi-
ation of microwaves for 60 min, the resulting mixture was ex-
tracted with ether. As shown in Scheme 1, tris(triphenylphosphi-
ne)ruthenium(II) dichloride (RuCl2(PPh3)3) showed good effi-
ciency as a catalyst for the isomerization of 1a into alkanone 2a.
Results using other substrates are summarized in Table 1.
The reaction mixture became acidic as ruthenium catalyst was
hydrolyzed to form hydrochloric acid. As shown in Runs 2
and 5, the reaction should be performed in 0.1 M NaOH to pre-
vent the decomposition of the acid sensitive substrate. The sub-
OH
2
3
4
5
6
b,c
77
OH
OH
Ph
87
d
OH
<5
80
b
OH
Ph
b,e
82
HO
93
aCondition: substrate (1.0 mmol) and RuCl2(PPh3)2 (5 mol %) in
H2O (3.0 mL) at 185 ꢀC/10 atm for 15–60 min. Reaction was
b
performed in 0.1 M NaOH (3.0 mL). c4-Nonanone was also
formed in 6% yield. dAn acid-catalyzed cyclization occurred
to give 2,2,6-trimethyltetrahydropyran quantitatively. 1,3-Di-
phenyl-1-propanone was also formed in 14% yield.
e
strate in Run 4 gave cyclic ether via acid catalyzed ether forma-
tion.5 In this case too, the isomerization reaction should be per-
formed in 0.1 M NaOH to obtain the saturated ketone.
In all reactions in Table 1, a small amount of unsaturated ke-
tones (<1% yield) accompanied the main process as byproducts.
As we reported previously, hydrogen-transfer type oxidation by
ruthenium catalyst may explain such formation of the ketone.6
From this point of view, the reactions in Table 1 may not be in-
tramolecular isomerizations of alkene, but may be intermolecu-
lar or intramolecular hydrogen-transfer-type oxidations between
alkene and alcohol. The reaction in deuterium oxide, however,
implies that the intramolecular alkene isomerization into enol
is more plausible. As shown in Eq 1, alkenol 3 was treated with
ruthenium catalyst in deuterium oxide under irradiation of mi-
crowaves. The hydrogen-atoms on the carbons between the al-
kene group and hydroxy group were exchanged with D-atoms.
These D-atoms can be regarded as a track of the migration of
the alkene.
OH
n-C H
O
Ru catalyst
n-C H
4
9
4
9
8
8
H O,
2
Microwaves (185 °C, 10 atm)
1a
2a
60 min
0 %
0 %
RuCl (5 mol%)
3
Ru (CO) (1.7 mol%)*
3
12
93 %
16 %
0 %
RuCl (PPh ) (5 mol%)
2
3 3
RuCl (PPh ) (1 mol%)
2
3 3
RuCl (5 mol%) + P(m-NaO S-C H ) (10 mol%)
3
3
6 4 3
RuCl (PPh )
2
3 3
80%D
69%D 14%D
(5 mol%)
69%D
Ph
*Warning: In the case of Ru (CO) catslyst, internal pressure
3
12
Ph
(1)
increased extraordinary during microwaves irradiation.
D O, Microwaves
2
72%D
80%D
~0%
OH
185 °C, 10 atm,
3
O
15 min
4 95%
Scheme 1. Isomerization of 14-pentadecen-5-ol (1a) with vari-
ous ruthenium catalysts.
Copyright Ó 2005 The Chemical Society of Japan

Chemistry Letters Vol.34, No.5 (2005)
665
82%D
52%D
75%D
75%D
35%D
16%D
RuCl (PPh ) + H O
Ru(OH) L
2 n
2
3 3
2
75%D
75%D
35%D
16%D
CH OH + Ru(OH) L
Ru(OCH )(OH)L + H O
3 n 2
3
2
n
Ru(OCH )(OH)L
RuH(OH)L + H C=O
n 2
3
n
11
RuCl2(PPh3)3 (5 mol%)
D2O, Microwaves,
CH3OH (10 mol%)
RuCl2(PPh3)3 (5 mol%)
D2O, Microwaves,
185 °C, 10 atm, 15 min
L Ru(OH)
n
5
6
H
185 °C, 10 atm, 15 min
3%D
60%D
+
RuH(OH)L
n
11
H
Figure 1. H–D-exchange reaction of cyclodedecene with
RuCl2(PPh3)3–D2O–microwaves (5) and RuCl2(PPh3)3–D2O–
methanol–microwaves (6).
+
RuH(OH)L
n
RuH L
2 n
12
11
Scheme 2. Plausible mechanism of the isomerization.
Isomerization of simple alkene was also observed. As shown
in Figure 1, a migration of alkene was demonstrated by H–D ex-
change reaction of cyclododecene.7,8 Treatment of cyclodode-
cene with RuCl2(PPh3)3 in D2O under irradiation of microwaves
for 15 min at 185 ꢀC/10 atm gave 5, while that in the presence of
catalytic amount of methanol gave the more deuterium enriched
6. It is clear that an addition of a catalytic amount of methanol
improved the efficiency of H–D exchange reaction dramatically.
The saturated hydrocarbon cyclododecane was not deuterated
under any condition in Figure 1, so the ratio of D-atom in the
product 5 and 6 showed the alkene migration frequency. In these
H–D exchange reactions, that is alkene migration reaction, an
active catalyst should be ruthenium hydride species, which is
formed effectively from methanol and RuCl2(PPh3)3.3a,b,6
In the reaction in Table 1, ruthenium hydride species will be
formed by an oxidative interaction of RuCl2(PPh3)3 with an al-
cohol function in the substrate. The addition of alcohol was nec-
essary in the isomerization reaction of the protected alkenol into
the corresponding ketone. This is consonant with the result in
Figure 1. As shown in Eq 2, a methyl ether of alkenol was con-
verted into alkanone 8 via enol ether hydrolysis in situ. Without
some addition of methanol, the ketone 8 was not obtained at all,
although isomerization of terminal alkene into an internal one
was observed in some extent.
standable, as H–D exchange ruthenium monohydride with deu-
terium oxide was shown by Whittlesey.10 Irradiation of micro-
waves accelerates both formation of 11 and the addition-elimina-
tion process in Scheme 2.
This work was supported financially by Kyoto University,
International Innovation Centre. The financial support provided
by Chugai Pharmaceutical Co., Ltd., and that from Takahashi
Industrial and Economical Research Foundation are also ac-
knowledged.
References and Notes
´
´
1
For reviews see: a) R. Uma, C. Crevisy, and R. Gree, Chem.
Rev., 27, 103 (2003). b) R. C. van der Drift, E. Bouwman, and
E. Drent, J. Organomet. Chem., 1, 650 (2002).
2
a) R. Damico and T. J. Logan, J. Org. Chem., 32, 2356 (1967).
b) N. Iranpoor, H. Imanieh, and E. J. Forbes, Synth. Commun.,
19, 2955 (1989). c) M. Kraus, Collect. Czech. Chem. Commun.,
´
37, 460 (1972). d) B. Ganchegui, S. Bouquillon, F. Henin, and J.
Muzart, J. Mol. Catal. A: Chem., 214, 65 (2004). e) K. Felfoldi
¨
´
and M. Bartok, J. Organomet. Chem., 297, C37 (1985).
3
a) B. M. Trost and R. J. Kulawiec, J. Am. Chem. Soc., 115, 2027
(1993). b) D. V. McGrath and R. H. Grubbs, Organometallics,
´
13, 224 (1994). c) R. Uma, M. K. Davies, C. Crevisy, and R.
Gree, Eur. J. Org. Chem., 2001, 3141. d) D. Wang, D. Chen,
´
J. X. Haberman, and C.-J. Li, Tetrahedron, 54, 5129 (1998).
RuCl (PPh ) (5 mol%)
´
e) V. Cadierno, S. E. Garcıa-Garrido, and J. Gimeno, Chem.
Commun., 2004, 232.
As microwave system, we used Discover system from CEM
corporation. B. L. Hayes, ‘‘Microwave Synthesis,’’ CEM
Publishing, Matthews (2002).
a) J. An, L. Bagnell, T. Cablewski, C. R. Strauss, and R. W.
Trainor, J. Org. Chem., 62, 2505 (1997). b) G. B. Jones and
B. J. Chapman, J. Org. Chem., 58, 5558 (1993).
Oxidation of alcohol by hydrogen transfer under microwave
irradiation: M. Takahashi, K. Oshima, and S. Matsubara,
Tetrahedron Lett., 44, 9201 (2003).
a) S. Matsubara, Y. Yokota, and K. Oshima, Chem. Lett., 33, 294
(2004). b) S. Matsubara, Y. Yokota, and K. Oshima, Org. Lett.,
6, 2071 (2004).
Deuteration under microwave, hydrothermal or supercritical
conditions: J. Yao and R. F. Evilia, J. Am. Chem. Soc., 116,
11229 (1994); T. Junk and W. J. Catallo, Tetrahedron Lett.,
37, 3445 (1996); K. Fodor-Csorba, G. Galli, S. Holly, and E.
2
3 3
Ph
Ph
H O, Microwaves
2
(2)
185 °C, 10 atm, 60 min
O
OCH
8
78%
3
7
CH OH (10 mol%)
3
4
5
6
7
8
As shown in Eq 3, one of two methyl ether groups in dime-
thoxy alkene 9 can be converted into the methoxyketone 10 se-
lectively via the isomerization reaction. Alkene migrated from
the end in good order.
RuCl (PPh ) (5 mol%)
Ph
Ph
2
3 3
(3)
H O, Microwaves
2
OCH
OCH
O
OCH
3
3
3
185 °C, 10 atm, 60 min
9
CH OH (10 mol%)
3
10 61%
In these isomerization reactions, water (or deuterium oxide)
was indispensable as a solvent. Treatment of alkenol 1a with
RuCl2(PPh3)3 in dioxane under irradiation of microwaves
(185 ꢀC, 10 atm, 60 min) did not give any saturated ketone, al-
though isomerization of a terminal alkene group into an internal
one occurred to some extent. As shown in Scheme 2, we assume
that the reactive catalyst is monohydride 11. Water and alcohol
are necessary to form 11. Without water, dihydride 12 may be
formed, and this will not be an efficient isomerization catalyst.9
The isomerization will proceed via hydrometallation and ꢀ-
elimination.1,3 It was demonstrated by Krische that a lifetime
of organometallic intermediate was extended in R–Mtl–X spe-
cies compare to R–Mtl–H one.9a The former will be formed
via hydrometallation of monohydride 11 to alkene, and the latter
will be formed via hydrometallation of dihydride 12 to alkene.
The H–D exchange reactions in Eq 1 and Figure 1 are under-
´
Gacs-Baitz, Tetrahedron Lett., 43, 3789 (2002); J. M. Barthez,
A. V. Filikov, L. B. Frederiksen, M.-L. Huguet, J. R. Jones,
and S.-Y. Lu, Can. J. Chem., 76, 726 (1998); N. H. Werstiuk
and T. Kadai, Can. J. Chem., 63, 530 (1985); N. H. Werstiuk
and T. Kadai, Can. J. Chem., 52, 2169 (1974).
The different reactivity of Mtl–H and H–Mtl–H: a) H.-Y. Jang
and M. J. Kriche, Eur. J. Org. Chem., 2004, 3953. b) E.
Mizushima, M. Yamaguchi, and T. Yamagishi, Chem. Lett.,
1997, 237.
9
10 R. F. R. Jazzar, P. H. Bhatia, M. F. Mahon, and M. K.
Whittlesey, Organometallics, 22, 670 (2003).
Published on the web (Advance View) April 2, 2005; DOI 10.1246/cl.2005.664