Ruthenium-catalyzed oxidation of allyl alcohols with intermolecular hydrogen transfer: Synthesis of α,β-unsaturated carbonyl compounds

Article abstract of DOI:10.1021/jo500042h

Ruthenium-catalyzed oxidation of multisubstituted allyl alcohols in the presence of benzaldehyde gives enals or enones in good yields. Unlike the commonly reported ruthenium-catalyzed isomerization reaction of allyl alcohols to give saturated ketones, an intermolecular rather than intramolecular hydrogen transfer is involved in this transformation. This reaction offers an efficient, mild, and high-yielding method for the preparation of substituted α,β-unsaturated compounds.

Full text of DOI:10.1021/jo500042h

Article
pubs.acs.org/joc
Ruthenium-Catalyzed Oxidation of Allyl Alcohols with Intermolecular
Hydrogen Transfer: Synthesis of α,β-Unsaturated Carbonyl
Compounds
Kai Ren,† Bei Hu,† Mengmeng Zhao,† Yahui Tu,† Xiaomin Xie,† and Zhaoguo Zhang*,†,‡
†School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240,
P. R. China
‡State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, 345 Lingling Road, Shanghai 200032,
P. R. China
S
* Supporting Information
ABSTRACT: Ruthenium-catalyzed oxidation of multisubstituted allyl alcohols in the presence of benzaldehyde gives enals or
enones in good yields. Unlike the commonly reported ruthenium-catalyzed isomerization reaction of allyl alcohols to give
saturated ketones, an intermolecular rather than intramolecular hydrogen transfer is involved in this transformation. This reaction
offers an efficient, mild, and high-yielding method for the preparation of substituted α,β-unsaturated compounds.
resulting in a mixture of unsaturated carbonyls and saturated
alcohols.
INTRODUCTION
■
The catalytic redox isomerization is an efficient, useful method
for the isomerization of allyl alcohols into the corresponding
saturated carbonyl compounds, which represents an atom-
economic and elegant shortcut to valuable carbonyl compounds
(Scheme 1).1 In the last few decades, various transition metal
Oxidation of allyl alcohols to the corresponding α,β-
unsaturated carbonyl compounds is one of the most common
and important reactions in organic chemistry, and numerous
useful reagents have been developed.9 However, many of these
methods required stoichiometric quantities of oxidants, which
are toxic or hazardous even after the reaction has been
completed.10 From both an environmental and an economical
point of view, transition metal-catalyzed transfer hydrogenation
has attracted considerable interest because of inexpensive
oxidants and mild reaction conditions which tolerate most
organic functional groups.11 Although a variety of transition
metal complexes of Ru,12 Fe,13 and Ir14 have been reported as
catalysts for secondary alcohols oxidation, among them, there are
only a few examples of the oxidation of primary allyl alcohols
Scheme 1. Metal-Catalyzed Reactions of Substituted Primary
Allyl Alcohols
reported.12a−c,13 For example, Backvall reported the oxidation of
̈
hept-1-en-3-ol using the Cp*Ru(II) dimer complex as the
catalyst in the presence of actone as the hydrogen acceptor.
However, with a simple triphenylphosphine complex of
ruthenium, [RuCl2(PPh3)3],12b it did not work with the same
type of substrate. Herein, we report our preliminary results on
the oxidation of allyl alcohols possessing three substituents at the
double bond to give enones or enals via sole intermolecular
hydrogen transfer in the presence of an aldehyde (Scheme 1).
complexes of Rh,2 Ru,3 Ir,4 Ni,5 and Fe6 have been explored as
catalysts for this reaction and an intramolecular hydrogen
transfer process have been regarded as a working mecha-
nism.2a,3a,7 However, the substrate often has a limitation, and the
catalytic activity tends to decrease as the degree of substitution
of the olefinic bond increases. For instance, allyl alcohols
with two substituents at the double bond of primary allyl
alcohols required a highly active catalyst to realize such a
transformation,7,8 and the enone intermediate may decoordinate,
Received: January 8, 2014
Published: February 17, 2014
© 2014 American Chemical Society
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a
Table 1. Screening of the Hydrogen Abstractors for the Oxidation of Geraniol
b
yield (%)
b
entry
1
hydrogen abstractor
conv. (%)
1b
1c
1d
no
92
46
34
0
52
1
20
44
32
0
20
1
c
2
but-3-en-2-one
hex-1-en-3-one
benzoquinone
1-octene
c
3
d
1
1
4
0
0
5
6
7
8
80
80
35
75
26
28
1
27
26
34
73
27
26
0
n-butyl vinyl ether
allyl alcohol
3-phenylpropanal
2
0
a
All reactions were carried out with a geraniol (1a, 2.0 mmol) at a concentration of 0.5 M at 90 °C for 12 h. Substrate: hydrogen abstractor:
b
c
d
[RuCl2(PPh3)3]:base = 100:300:2:4. Determined by GC analysis. Reaction time: 24 h. Reaction time: 48 h.
formed α,β-unsaturated aldehyde, generating a 1,4-hydride
RESULTS AND DISCUSSION
■
addition intermediate C, which is in equivilibrium to Ru-enolate
D. Finally, ligand exchange with the allyl alcohol liberates an enol,
which tautomerizes to the saturated aldehyde and regenerates
the ruthenium species A (left cycle, Scheme 2).
During the investigation of the isomerization of allyl alcohols to
give saturated carbonyl compounds via intramolecular hydrogen
transfer, geraniol (1a) was chosen as the substrate. When
[RuCl2(PPh3)3] (2 mol %) was used as a catalyst in the presence
of Cs2CO3 (4 mol %) after 12 h in DCE at 90 °C, the reaction
resulted in 92% conversion of the starting material to give 52% of
citronellal (1b) as a major product, together with citronellol (1d)
and citral (1c) at a ratio of 1:1 (Table 1, entry 1). These results
eloquently proved that intramolecular hydrogen transfer
occurred simultaneously with an intermolecular hydrogen
transfer. Compound 1d is either the intermolecular hydrogen
transfer product of 1b or the direct reduced product of 1a via
twice the intermolecular hydrogen transfer.
Compound 1c was formed by decoordination of the formed
unsaturated aldehyde from intermediate B, probably because
of the coordination ability of the unsaturated aldehyde to Ru
decreased with the increase of the steric hindrance of the
substituted CC bond. One approach to verify the hypothesis
is by performing the isomerization of allyl alcohol 1a in the
presence of a less hindered unsaturated ketone or aldehyde.
If this is true, the added less-hindered unsaturated ketone or
aldehyde will compete to react with the [Ru−H] species to form
the corresponding saturated ketone or aldehyde. As a result,
when 3 equiv of but-3-en-2-one were added, dehydrogenated
product 1c together with the saturated ketone butan-2-one, at a
ratio of 1:1, was detected by gas chromatography (GC) as the
products after prolonging the reaction time to 24 h (Table 1,
entry 2). A similar result was obtained when hex-1-en-3-one
(3 equiv) was added to the reaction (Table 1, entry 3), albeit with
a slightly lower conversion. It was obvious that the addition of
an unsaturated ketone, a stronger ligand, decreased the catalytic
activity of Ru complexes. This can be ascribed to the competing
coordination between allyl alcohol and the added unsaturated
ketone. As a result, when benzoquinone (3 equiv), which has
an even stronger coordination ability with the metal, was added
under the same reaction conditions, even after 48 h, the starting
material remained essentially intact (Table 1, entry 4).
The mechanism for the redox-isomerization of allyl alcohol to
aldehyde had been established as an intramolecular process through
competing and labeling experiments (Scheme 2).15,7,3b,d,2g,h
Scheme 2. Proposed Catalytic Cycle for the Formation of 1b,
1c, and 1d
If 1d is the direct reduction product of 1a, addition of a simple
alkene into the reaction will probably suppress the formation of
1d because of the competitive reduction between 1a and the
added alkene. The fact was that when 1-octene or n-butyl vinyl
ether was added to the reaction, although the conversion became
lower under the same reaction conditions, the formation of 1d
was not suppressed, nor were any reduction products of the
alkenes were detected, suggesting that simple alkenes did not
serve as the hydrogen abstractors (Table 1, entries 5 and 6).
With the addition of 3 equiv of allyl alcohol to the reaction, the
formation of 1b and 1d was greatly suppressed and 1c became
the overwhelming product together with an equal molar amount
First, the Ru−Cl species forms a new Ru−OR species A by
ligand exchange with the allyl alcohol, subsequently, β-hydrogen
elimination yields an α,β-unsaturated aldehyde, which is
coordinated to the [Ru−H] species. The [Ru−H] species
immediately transfers hydrogen to the C−C double bond of the
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a
Table 2. Optimization of the Aldehyde and Solvents for the Synthesis of α,β-Unsaturated Aldehyde
b
yield (%)
b
entry
solvent
DCE
aldehyde
conv. (%)
1b
1c
1d
c
1
(HCHO)n
CH3CHO
C3H7CHO
PhCHO
PhCHO
PhCHO
PhCHO
PhCHO
PhCHO
PhCHO
acetone
90
41
56
89
69
90
88
64
9
23
3
49
33
50
86
67
73
75
58
8
18
5
c
2
DCE
c
3
DCE
4
2
4
DCE
3
0
d
5
e
DCE
2
0
6
DCE
5
12
4
7
PhMe
1,4-Dioxane
EtOH
CH3CN
DCE
9
8
6
0
9
1
0
10
11
12
13
54
5
1
53
2
0
2
1
Acetone
Acetone
DCE
no
7
0
5
2
PhCHO
vinyl acetate
crotonitrile
styrene
11
48
30
78
1
8
2
c
14
1
46
28
26
1
c
15
c
DCE
1
1
16
DCE
27
25
a
All reactions were carried out with a geraniol (1a, 2.0 mmol) at a concentration of 0.5 M at 90 °C, substrate:aldehyde:[RuCl2(PPh3)3]:base =
b
c
d
e
100:300:2:4. Determined by GC analysis. Reaction time: 12 h. 6 equiv of benzaldehyde per mole of substrate was used. 1.5 equiv of
benzaldehyde per mole of substrate was used.
of 1-propanol, which was produced as detected by GC (Table 1,
entry 7). Furthermore, before the consumption of 1a, the excess
of allyl alcohol was transformed to propionaldehyde through
redox isomerization, indicating that the aldehyde can serve as a
hydrogen abstractor. This was verified by the fact that when
3-phenylpropanal (3 equiv was added), a molar ratio of 1:1
between 1c and 3-phenylpropan-1-ol was obtained and 1d was
not detected by GC (Table 1, entry 8).
These results are inconsistent with the observation by Backvall.12b
̈
It was probably because of the competing coordination between
allyl alcohol and acetone when acetone was used as the solvent. To
verify the hypothesis, we conducted the reaction in acetone in the
presence of 3 equivlents of benzaldehyde. Not to our surprise, the
reaction became very slow, and very low conversion of substrate
was observed (Table 2, entry 13). Meanwhile, other commonly
used hydrogen acceptors were tested. Styrene did not serve as the
hydrogenabstractors; vinylacetate and crotonitrile were inferior to
aldehyde (Table 2, entries 14−16). Apparently, an intermolecular
hydrogen transfer reaction in the presence of an aldehyde became
easier than intramolecular redox isomerization for allyl alcohols
under the catalysis of a Ru catalyst in a nonpolar solvent, and this
provided an entry to unsaturated compounds.
To make the reaction more efficient, different bases were also
examined for the model reaction, and the results were sum-
marized in Table 3. Sodium carbonate and potassium carbonate
gave even better results than cesium carbonate; stronger base
like t-BuOK and KOH, and weaker base like K3PO4, gave poor
results. Sodium carboxylates gave better results than other bases.
Among all of the sodium carboxylates (RCO2Na, R = CH3, t-Bu,
and Ph) tested, sodium acetate gave the best results, which led to
a 98% conversion of 1a into 1b (2%) and 1c (96%) in only 4 h
(Table 3, entry 6). Besides [RuCl2(PPh3)3], other catalysts such
as [RuCl2(p-cymene)]2, [RuCl2(benzene)]2, and [RuCl2(COD)]n
were also investigated. No products were detected at all, and the
starting material 1a was recovered. Meanwhile, the influence of
catalyst loading and reaction temperature were also investigated.
When only 1 mol % of catalyst was used, the desired product
(95%) was determined by GC and significant decrease of yield
was observed with 0.5 mol % of catalyst (Table 3, entries 11 and
12) and a low reaction temperature (50 °C) also led to significant
drop of yield to 65% in 10 h.
On the basis of our studies, the formation of α,β-unsaturated
aldehyde (1c) and saturated alcohol (1d) is shown in Scheme 2
(right cycle). Competing coordination of 1b with ruthenium
species B liberates α,β-unsaturated aldehyde (1c) to generate a
new ruthenium species E, which is then transformed to species F
by insertion of CO into Ru−H. Finally, ligand exchange with
1a liberates 1d and regenerates the ruthenium species A.
Other readily available aldehydes were chosen as hydrogen
abstractors to test the efficiency. Formaldehyde was not a good
hydrogen abstractor; acetaldehyde and butyraldehyde were
better than formaldehyde but were inferior to 3-phenylpropanal.
Benzaldehyde proved to be the most effective hydrogen ab-
stractor, and 3 equiv of benzaldehyde was enough for the reaction
(Table 2, entries 1−6). Toluene was also a usable solvent, but
when the reaction was carried out in a polar solvent, the reaction
rate was decreased possibly due to the competitive coordination
between the substrate and solvent. Alcohols are not good sol-
vents for this transformation. It can undergo β-hydride elimina-
tion and produce other catalytic species (Table 2, entries 7−10).
This reaction is by nature a transfer hydrogenation reaction. As
is well-known, acetone is commonly used as a hydride acceptor
in transfer hydrogenation reactions; however, when acetone
(3 equiv) was added to the reaction, a poor yield of the enone
(1c) was obtained, and the same poor yield was obtained when
we used acetone as the solvent (Table 2, entries 11 and 12).
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a
Table 3. Optimization of the Bases for the Synthesis of α,β-Unsaturated Aldehyde
b
yield (%)
b
entry
base
K2CO3
conv. (%)
1b
1c
1d
1
2
2
3
4
5
6
7
8
9
95
98
89
81
98
95
98
78
55
72
97
80
67
3
9
92
87
79
73
74
93
96
74
50
70
95
77
65
0
2
1
1
6
0
0
2
2
0
0
0
0
Na2CO3
KOH
8
t-BuOK
6
K3PO4
18
2
CH3CO2K
CH3CO2Na
CH3CO2Li
t-BuCO2Na
PhCO2Na
CH3CO2Na
CH3CO2Na
CH3CO2Na
2
2
3
2
c
11
2
d
12
3
e
13
3
a
All reactions were carried out with a geraniol (1a, 2.0 mmol) at a concentration of 0.5 M at 90 °C, substrate:aldehyde:[Ru]:base = 100:300:2:4.
Determined by GC analysis. 1 mol % of [RuCl2(PPh3)3] was used. 0.5 mol % of [RuCl2(PPh3)3] was used. Temperature was 50 °C.
b
c
d
e
a
Table 4. Synthesis of α,β-Unsaturated Carbonyl Compounds
b
yield (%)
b
entry
substrate
conv. (%)
b
c
1
2
3
4
5
6
1a
97
99
99
97
99
99
85
99
99
95
90
90
2
3
2
3
3
1
2
2
3
2
10
95(93)
96(94)
97(94)
94(91)
96(93)
98(96)
83(80)
97(94)
96(93)
93(90)
80(78)
0
2a
3a
4a
5a
6a
c
7
7a
8
8a
9
9a
10
10a
11a
12a
d
11
12
90(88)
a
All reactions were carried out with an allyl alcohol (2.0 mmol) at a concentration of 0.5 M at 90 °C, substrate:aldehyde:[Ru]:NaOAc = 100:300:1:2.
b
c
d
Determined by GC analysis. In parentheses, isolated yield of the pure product. Reaction time: 12 h. Reaction time: 24 h.
With the optimized reaction conditions in hand, the scope of
alkyl substituents at the CC bond did not impose much effect
the substrates for this transformation was investigated. As shown
in Table 4, trisubstituted primary (E)-allyl alcohols were
evaluated first. Not only aliphatic allyl alcohols, such as 1a and
2a, were converted to the corresponding enals in excellent yields
but also aromatic substrates were transformed to aryl enals under
the same reaction conditions. For aromatic allyl alcohols, the
on the reactivity and yields (Table 4, entries 3 and 4), but the
substituents at the aromatic ring had an obvious effect on the
intermolecular hydrogen transfer reaction (Table 4, entries
5−8). For example, for substrate 7a with an electron-withdrawing
(CF3) group at the para position of the aromatic ring, the
corresponding enone was obtained in only 83% yield after 12 h
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(Table 4, entry 7). The low activity of 7a was attributed to the
decreased coordination ability of the oxygen atom with metal
species. Furthermore, trisubstituted primary (Z)-allyl alcohols,
such as 9a and 10a, were also workable substrates under the same
reaction conditions (Table 4, entries 9 and 10). To our delight,
disubstituted secondary allyl alcohol (11a) could be transformed
to the corresponding enone in excellent yield (Table 4, entry 11).
However, when monosubstituted secondary allyl alcohol
(1-phenylprop-2-en-1-ol, 12a) was tried, the corresponding enones
could not be obtained at all; nevertheless, the starting material
was transformed to propiophenone by redox-isomerization
(Table 4, entry 12). When homoallyl alcohol 1-phenybut-3-en-
1-ol was used as substrate, no desired product could be obtained
probably because of homoallyl alcohol coordination inferior to
benzaldehyde. This implies that the CC double bond must
bind to ruthenium to promote the reaction. To check whether
the coordination of the CC double bond is really necessary,
hydrogenated product citronellol (1d) was tried and, even after
12 h, the starting material remained essentially intact.
EXPERIMENTAL SECTION
■
General Information. All reactions were carried out under an
atmosphere of nitrogen using standard Schlenk techniques or in a
nitrogen-filled glovebox, unless otherwise noted. Commercially
available reagents were used throughout without further purification,
other than those detailed below. Anhydrous EtOH was freshly distilled
from Mg. Anhydrous CH2ClCH2Cl was freshly distilled from calcium
hydride. Anhydrous PhMe and 1,4-dioxane were freshly distilled from
sodium. Anhydrous CH3CN was freshly distilled from anhydrous
1
calcium sulfate. H NMR and 13C NMR spectra were recorded on a
400 MHz spectrometer. The chemical shifts for 1H NMR were recorded
in ppm downfield from tetramethylsilane (TMS) with the solvent
resonance as the internal standard. The chemical shifts for 13C NMR
were recorded in ppm downfield using the central peak of deutero-
chloroform (77.00 ppm) as the internal standard. Coupling constants
(J) are reported in Hz and refer to apparent peak multiplications. Flash
column chromatography was performed on silica gel (300−400 mesh).
Flash column chromatography was performed on silica gel (300−
400 mesh).
Procedures for Synthesis of Substrates (2a−9a).21 Triethyl
phosphonoacetate (26.9 g, 120 mmol) was added dropwise under
nitrogen over a period of 5 min to a stirred suspension of NaH (60% on
mineral oil; 4.8 g, 120 mmol) in dry THF (120 mL), and the resulting
mixture was stirred for another 0.5 h at 0 °C. A solution of ketone
(110 mmol) in dry THF (30 mL) was slowly added to the resulting
mixture, and the reaction mixture was heated to reflux overnight. After
cooling to room temperature, the reaction was quenched with a
saturated aqueous solution of NH4Cl and extracted with EtOAc (3 ×
50 mL). The combined organic layer was washed with brine and dried
over Na2SO4. After concentration under vacuum, the residue was
purified by flash chromatography on silica gel (EtOAc:pentane = 1:40)
to afford (E)-oate and (Z)-oate as colorless oil.
On the basis of the results discussed above, we suggested
a mechanism as depicted in Scheme 3. First, the Cl− of
Scheme 3. Proposed Catalytic Cycle for Intermolecular
Hydrogen Transfer of Allyl Alcohols in the Presence of
Benzaldehyde
DIBAL-H (40 mL, 1.5 M in toluene) was added to a solution of ester
(60 mmol) in THF (100 mL) at −78 °C over a period of 1 h. The
reaction mixture was stirred at −78 °C for 1 h and the solution was
allowed to reach 0 °C. The solution was quenched with a saturated
aqueous solution of NH4Cl at 0 °C and stirred at room temperature until
a white precipitate was formed. The precipitate was filtered through a
pad of Celite and washed with Et2O. The resulting solution was washed
with brine and dried over Na2SO4. After concentration under vacuum,
the residue was purified by flash chromatography on silica gel
(EtOAc:pentane = 1:5) as colorless oil.
(E)-3,4,4-Trimethylpent-2-en-1-ol (2a):21 Colorless oil: 8.4 g, 60%
yield. 1H NMR (400 MHz, CDCl3): δ 5.46−5.40 (m, 1H), 4.16 (d, J =
6.4 Hz, 2H), 1.64 (s, 3H), 1.03 (s, 9H). 13C NMR (101 MHz, CDCl3): δ
146.3, 120.5, 59.6, 35.9, 28.7, 12.7.
(E)-3-Phenylbut-2-en-1-ol (3a):17 Colorless oil: 8.2 g, 50% yield. 1H
NMR (400 MHz, CDCl3): δ 7.43−7.40 (m, 2H), 7.36−7.30 (m, 2H),
7.29−7.25 (m, 1H), 5.98 (dt, J = 6.4, 1.2 Hz, 1H), 4.37 (d, J = 6.8 Hz,
2H), 2.08 (s, 3H), 1.87 (br, 1H). 13C NMR (101 MHz, CDCl3): δ 142.7,
137.7, 128.2, 127.2, 126.4, 125.7, 59.8, 16.0.
[RuCl2(PPh3)3] was replaced by OAc− to form Ru(OAc)2-
(PPh3)3 in the presence of NaOAc16 and then by ligand exchange
to give the ruthenium alkoxide species; subsequent β-hydrogen
elimination yields α,β-unsaturated aldehyde and a [Ru−H] spe-
cies, which is still coordinated with the resulted α,β-unsaturated
aldehyde. In the presence of a large excess amount of benzal-
dehyde (relative to the Ru−H species formed), the coordinated
α,β-unsaturated aldehyde is replaced by benzaldehyde, which is
reduced to the benzyl alcohol. Finally, ligand exchange with allyl
alcohol generates the Ru-allyl alkoxide catalytic species.
(E)-4-Methyl-3-phenylpent-2-en-1-ol (4a):21 Colorless oil: 9.2 g,
48% yield. 1H NMR (400 MHz, CDCl3): δ 7.32−7.25 (m, 3H), 7.21−
7.16 (m, 2H), 5.49 (t, J = 6.8 Hz, 1H), 4.36 (d, J = 6.8 Hz, 2H), 3.08−
2.98 (m, 1H), 1.81 (br, 1H), 1.07 (s, 3H), 1.05 (s, 3H). 13C NMR
(101 MHz, CDCl3): δ 149.4, 142.1, 128.2, 127.5, 127.3, 126.4, 58.6,
29.6, 21.9.
(E)-3-(p-Tolyl)but-2-en-1-ol (5a):22 Colorless oil: 9.3 g, 52% yield.
1H NMR (400 MHz, CDCl3): δ 7.35 (d, J = 8.0 Hz, 2H), 7.16 (d, J =
8.0 Hz, 2H), 6.00 (dt, J = 6.4, 1.2 Hz, 1H), 4.37 (d, J = 6.8 Hz, 2H), 2.84
(br, 1H), 2.39 (s, 3H), 2.08 (d, J = 0.8 Hz, 3H). 13C NMR (101 MHz,
CDCl3): δ 139.8, 137.1, 136.7, 128.8, 125.6, 125.4, 59.6, 20.9, 15.7.
(E)-3-(4-Methoxyphenyl)but-2-en-1-ol (6a):22 Colorless oil: 11.8 g,
60% yield. 1H NMR (400 MHz, CDCl3): δ 7.38−7.33 (m, 2H), 6.89−
6.84 (m, 2H), 5.94−5.90 (m, 1H), 4.35 (d, J = 6.8 Hz, 2H), 3.81 (s, 3H),
2.07−2.06 (m, 3H), 1.58 (br, 1H). 13C NMR (101 MHz, CDCl3): δ
158.9, 137.3, 135.2, 126.8, 124.8, 113.5, 59.9, 55.2.
CONCLUSION
■
In summary, we have developed a new synthetic method of enals
and enones through intermolecular rather than intramolecular
hydrogen transfer of allyl alcohols in the presence of an aldehyde.
Various substrates could be subjected under the optimized
reaction conditions and smoothly transformed into the corre-
sponding enals or enones in high yields.
(E)-3-[4-(Trifluoromethyl)phenyl]but-2-en-1-ol (7a):23 Colorless
oil: 13.5 g, 57% yield. 1H NMR (400 MHz, CDCl3): δ 7.56 (d, J = 8.2 Hz,
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2H), 7.48 (d, J = 8.2 Hz, 2H), 6.02 (dt, J = 6.4, 1.2 Hz, 1H), 4.38 (d,
J = 6.4 Hz, 2H), 2.08 (s, 3H), 1.72 (s, 1H). 13C NMR (101 MHz,
CDCl3): δ 146.5, 136.4, 129.2 (q, J = 30.0 Hz), 126.2, 125.8, 125.1 (d,
J = 3.4 Hz), 123.1, 59.9, 16.0.
substrate (2 mmol) were dissolved in DCE (4 mL), and then a benzal-
dehyde (6 mmol) was added into the solution at room temperature. The
solution was stirred at 90 °C under nitrogen and monitored by gas
chromatography. After completion of the reaction, the solvent was
evaporated and the residue was dissolved with EtOAc (5 mL) and water
(2 mL). The layers were separated, and the aqueous layer was washed
with EtOAc (2 × 2 mL). The combined organic extracts were washed
with brine (5 mL) and then dried over Na2SO4. After the solvent was
evaporated, the crude product was purified by column chromatography
over silica gel.
(E)-3-(o-Tolyl)but-2-en-1-ol (8a):23 Colorless oil: 7.1 g, 40% yield;
1H NMR (400 MHz, CDCl3): δ 7.20−7.08 (m, 4H), 5.55 (m, 1H), 4.35
(d, J = 6.4 Hz, 2H), 2.30 (s, 3H), 1.99−1.97 (m, 3H). 13C NMR
(101 MHz, CDCl3): δ 144.5, 139.1, 134.4, 123.0, 128.0, 127.9, 126.7,
125.5, 59.3, 19.6, 18.1.
(Z)-4-Methyl-3-phenylpent-2-en-1-ol (9a):21 Colorless oil: 3.9 g,
21% yield. 1H NMR (400 MHz, CDCl3): δ 7.36−7.23 (m, 3H), 7.10−
7.05 (m, 2H), 5.63 (dt, J = 6.8, 1.2 Hz, 1H), 3.95 (d, J = 6.8 Hz, 2H), 2.60
(m, 1H), 1.57 (s, 1H), 1.03 (d, J = 6.8 Hz, 6H). 13C NMR (101 MHz,
CDCl3): δ 150.8, 140.4, 128.7, 128.2, 127.0, 123.5, 60.5, 35.9, 21.8.
Preparation of 1-Phenylpro-2-en-1-ol (12a):18 To the solution
of benzaldehyde (1.1 g, 10 mmol) in anhydrous THF (40 mL) was
added vinylmagnesium chloride (7 mL, 1.6 M in THF) slowly at
−10 °C. After 2 h, the reaction was quenched with saturated aqueous
NH4Cl (40 mL), followed by the addition of 60 mL of ether. The
organic phase was washed with brine, dried with anhydrous sodium
sulfate, and removed under reduced pressure. The crude product was
Citral (1c):24 The crude material was purified by column
chromatography on silica gel (eluting with petroleum ether/ethyl
acetate = 10:1) to give the compound as oil (282.7 mg, 93%). 1H NMR
(400 MHz, CDCl3): δ 9.98 (d, J = 8.2 Hz, 1H), 5.88−5.86 (m, 1H),
5.07−5.03 (m, 1H), 2.23−2.12 (m, 7H), 1.67−1.60 (m, 6H). 13C NMR
(101 MHz, CDCl3): δ 191.3, 163.9, 132.9, 127.4, 122.5, 40.6, 25.7, 25.6,
17.7, 17.6.
(E)-3,4,4-Trimethylpent-2-enal (2c):25 The crude material was puri-
fied by column chromatography on silica gel (eluting with petroleum
ether/ethyl acetate = 10:1) to give the compound as oil (237.1 mg,
94%). 1H NMR (400 MHz, CDCl3): δ 10.03 (d, J = 8.0 Hz, 1H), 5.95−
5.92 (m, 1H), 2.16 (s, 3H), 1.11 (s, 9H). 13C NMR (101 MHz, CDCl3):
δ 192.6, 171.2, 124.5, 37.8, 28.3, 13.7.
1
purified by silica-gel column chromatography (1.3 g, 93% yield). H
NMR (400 MHz, CDCl3): δ 7.38−7.26 (m, 5H), 6.05 (ddd, J = 17.2,
10.0, 6.0 Hz, 1H), 5.38−5.31 (m, 1H), 5.23−5.16 (m, 2H), 2.05 (br,
1H). 13C NMR (101 MHz, CDCl3): δ 142.6, 140.2, 128.5, 127.7, 126.3,
115.1, 75.3.
(E)-3-Phenylbut-2-enal (3c):26 The crude material was purified by
column chromatography on silica gel (eluting with petroleum ether/
ethyl acetate = 10:1) to give the compound as oil (274.6 mg, 94%). 1H
NMR (400 MHz, CDCl3): δ 10.18 (d, J = 7.6 Hz, 1H), 7.56−7.53
(m, 2H), 7.43−7.39 (m, 3H), 6.40 (dq, J = 8.0, 1.2 Hz, 1H), 2.58 (d, J =
1.6 Hz, 3H). 13C NMR (101 MHz, CDCl3): δ 190.8, 157.2, 140.1, 129.7,
128.4, 126.8, 125.9, 15.9.
Preparation of 1-Phenylbut-3-en-1-ol.19 To a 50 mL three-
necked flask was equipped with a magnetic stirrer, a pressure equalizing
dropping funnel, and reflux condenser mounted with a nitrogen source.
To the flask were added magnesium (0.3 g, 10 mmol), a small amount
of iodine, and 5 mL of ether. To this was added a small amount
allyl chloride. The reaction mixture was stirred until the purple iodine
color disappeared at room temperature. To this was added 10 mL of
a solution of allyl chloride (0.8 g, 10 mmol) slowly at −10 °C. After
30 min, a solution of benzaldehyde (1.1 g, 10 mmol) in 20 mL of ether
was added dropwise at such a rate to maintain the internal temperature
below −10 °C. After 2 h, the reaction was quenched with saturated
aqueous NH4Cl (40 mL), followed by the addition of 60 mL ether. The
organic phase was washed with brine, dried with anhydrous sodium
sulfate, and removed under reduced pressure. The crude product was
purified by silica-gel column chromatography. 1-Phenylbut-3-en-1-ol
was obtained as a colorless oil (1.3 g, 87% yield). 1H NMR (400 MHz,
CDCl3): δ 7.39−7.30 (m, 5H), 5.84−5.79 (m, 1H), 5.17−5.12 (m, 2H),
4.68 (t, J = 8.0 Hz, 1H), 2.89 (br, 1H), 2.50 (t, J = 8.0 Hz, 2H). 13C NMR
(101 MHz, CDCl3): δ 143.8, 134.4, 128.2, 127.3, 125.7, 117.9, 73.2, 43.5.
Preparation of (E)-1-phenylbut-3-en-2-ol (11a).20 To a solution
of benzaldehyde (5.3 g, 50 mmol) in acetone (125 mL) was added
triethylamine (0.5 g, 5 mmol). The reaction mixture was stirred at 45 °C
in a 250 mL three-necked flask. After 24 h, the reaction mixture was
cooled to room temperature, and a saturated NaHCO3 solution (50 mL)
and ethyl acetate (50 mL) were added. After phase separation, the
aqueous phase was extracted three times with EtOAc and the organic
layer was dried over Na2SO4 and concentrated in vacuum to give (E)-4-
phenylbut-3-en-2-one (6.1 g, 84% yield). Next, to a solution of (E)-4-
phenylbut-3-en-2-one (4.4 g, 30 mmol) and CeCl3·7H2O (11.2 g,
30 mmol) in 20 mL of MeOH was added NaBH4 (1.7 g, 45 mmol) over
a 10 min period. The reaction mixture was stirred for 1 h at room
temperature and then quenched with saturated aqueous NH4Cl
(10 mL) and extracted with ether (3 × 10 mL). The combined organic
extracts were washed with brine, dried over Na2SO4, and removed under
reduced pressure. The crude product was purified by silica-gel column
(E)-4-Methyl-3-phenylpent-2-enal (4c):27 The crude material was
purified by column chromatography on silica gel (eluting with
petroleum ether/ethyl acetate = 10:1) to give the compound as oil
(318.9 mg, 91%). 1H NMR (400 MHz, CDCl3): δ 10.26 (d, J = 8.0 Hz,
1H), 7.40−7.18 (m, 5H), 5.91 (d, J = 8.0 Hz, 1H), 3.78−3.71 (m, 1H),
1.24 (d, J = 7.2 Hz, 6H). 13C NMR (101 MHz, CDCl3): δ 190.5, 169.8,
139.9, 128.9, 128.2, 127.9, 127.1, 30.2, 22.3.
(E)-3-(p-Tolyl)but-2-enal (5c):28 The crude material was purified by
column chromatography on silica gel (eluting with petroleum ether/
ethyl acetate = 10:1) to give the compound as oil (297.8 mg, 93%). 1H
NMR (400 MHz, CDCl3): δ 10.16 (d, J = 8.0 Hz, 1H), 7.47−7.43
(m, 2H), 7.23−7.19 (m, 2H), 6.39 (dq, J = 8.4, 2.0 Hz, 1H), 2.54 (d, J =
1.2 Hz, 3H), 2.37 (s, 3H). 13C NMR (101 MHz, CDCl3): δ 190.9, 157.2,
140.2, 137.1, 129.1, 128.9, 126.1, 125.9, 21.0, 15.8.
(E)-3-(4-Methoxyphenyl)but-2-enal (6c):22 The crude material was
purified by column chromatography on silica gel (eluting with petro-
leum ether/ethyl acetate = 6:1) to give the compound as oil (338.1 mg,
96%). 1H NMR (400 MHz, CDCl3): δ 10.14 (d, J = 8.0 Hz, 1H), 7.56−
7.49 (m, 2H), 6.94−6.90 (m, 2H), 6.42−6.35 (m, 1H), 3.84 (s, 3H),
2.53 (s, 3H). 13C NMR (101 MHz, CDCl3): δ 191.1, 161.1, 156.9, 132.1,
127.6, 125.2, 113.9, 55.2, 15.8.
(E)-3-[4-(Trifluoromethyl)phenyl]but-2-enal (7c):29 The crude ma-
terial was purified by column chromatography on silica gel (eluting with
petroleum ether/ethyl acetate = 10:1) to give the compound as oil
(342.5 mg, 80%). 1H NMR (400 MHz, CDCl3): δ 10.19 (d, J = 7.6 Hz,
1H), 7.68−7.62 (m, 4H), 6.40−6.37 (m, 1H), 2.58 (d, J = 1.2 Hz, 3H).
13C NMR (101 MHz, CDCl3): δ 191.0, 155.9, 144.1, 131.5 (d, J =
32.2 Hz), 128.4, 126.5, 125.6 (d, J = 3.0 Hz), 118.2, 16.3.
(E)-3-(o-Tolyl)but-2-enal (8c):30 The crude material was purified by
column chromatography on silica gel (eluting with petroleum ether/
ethyl acetate = 10:1) to give the compound as oil (301.2 mg, 94%). 1H
NMR (400 MHz, CDCl3): δ 10.17 (d, J = 8.0 Hz, 1H), 7.27−7.13
(m, 4H), 7.10 (m, 1H), 6.00−5.93 (m, 1H), 2.47 (d, J = 1.2 Hz, 3H),
2.31 (s, 3H). 13C NMR (101 MHz, CDCl3): δ 190.9, 160.9, 142.4, 133.4,
130.5, 129.9, 128.1, 126.5, 125.7, 19.6, 19.1.
1
chromatography (4.0 g, 90% yield). H NMR (400 MHz, CDCl3): δ
7.32−7.12 (m, 5H), 6.47 (d, J = 16 Hz, 1H), 6.17 (dd, J = 16.0, 6.4 Hz,
1H), 4.43−4.36 (m, 1H), 1.74 (br, 1H), 1.28 (d, J = 6.4 Hz, 3H). 13C
NMR (101 MHz, CDCl3): δ 136.5, 133.5, 129.0, 128.4, 127.4, 126.3,
68.5, 23.2.
A Typical Procedure for the Oxidation of Allyl Alcohols with
Intermolecular Hydrogen Transfer: Synthesis of α,β-Unsatu-
rated Carbonyl Compounds. In a dried Schlenk tube, [RuCl2-
(PPh3)3] (19.2 mg, 0.02 mmol), CH3CO2Na (3.5 mg, 0.04 mmol), and
(Z)-4-Methyl-3-phenylpent-2-enal (9c):27 The crude material was
purified by column chromatography on silica gel (eluting with petro-
leum ether/ethyl acetate = 10:1) to give the compound as oil (323.8 mg,
93%). 1H NMR (400 MHz, CDCl3): δ 9.36 (d, J = 8.0 Hz, 1H), 7.40−
7.36 (m, 3H), 7.23−7.19 (m, 2H), 6.07 (dd, J = 8.0, 1.2 Hz, 1H),
2175
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Article
2.81−2.74 (m, 1H), 1.11 (s, 3H), 1.10 (s, 3H). 13C NMR (101 MHz,
CDCl3): δ 193.6, 171.8, 137.5, 128.2, 127.8, 125.9, 36.4, 20.7.
(Z)-3,7-Dimethylocta-2,6-dienal (10c):31 The crude material was
purified by column chromatography on silica gel (eluting with petro-
leum ether/ethyl acetate = 10:1) to give the compound as oil (273.8 mg,
90%). 1H NMR (400 MHz, CDCl3): δ 9.87 (d, J = 8.2 Hz, 1H), 5.89−
5.81 (m, 1H), 5.10−5.06 (m, 1H), 2.59−2.53 (m, 2H), 2.21 (q, J =
7.2 Hz, 3H), 1.96 (t, J = 1.2 Hz, 3H), 1.66 (s, 3H), 1.59−1.55 (m, 3H).
13C NMR (101 MHz, CDCl3): δ 190.6, 163.7, 133.4, 128.4, 122.1, 32.4,
26.8, 25.4, 24.9, 17.5.
Carreaux, F.; Bruneau, C. New J. Chem. 2008, 32, 929. (h) van Rijn, J. A.;
Lutz, M.; von Chrzanowski, L. S.; Spek, A. L.; Bouwman, E.; Drent, E.
Adv. Synth. Catal. 2009, 351, 1637. (i) Azua, A.; Sanz, S.; Peris, E.
Organometallics 2010, 29, 3661. (j) Batuecas, M.; Esteruelas, M. A.;
García-Yebra, C.; Onate, E. Organometallics 2010, 29, 2166. (k) Díaz-
̃
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Alvarez, A. E.; Crochet, P.; Cadierno, V. Catal. Commun. 2011, 13, 91.
́
(l) García-Alvarez, J.; Gimeno, J.; Suarez, F. J. Organometallics 2011, 30,
2893. (m) Sahli, Z.; Sundararaju, B.; Achard, M.; Bruneau, C. Org. Lett.
2011, 13, 3964. (n) Crochet, P.; Díez, J.; Fernan
́
́
dez-Zumel, M. A.;
Gimeno, J. Adv. Synth. Catal. 2006, 348, 93.
(E)-4-Phenylbut-3-en-2-one (11c):32 The crude material was puri-
fied by column chromatography on silica gel (eluting with petroleum
ether/ethyl acetate = 10:1) to give the compound as oil (227.9 mg,
78%). 1H NMR (400 MHz, CDCl3): δ 7.58−7.51 (m, 3H), 7.43−7.37
(m, 3H), 6.72 (d, J = 16.4 Hz, 1H), 2.38 (s, 3H). 13C NMR (101 MHz,
CDCl3): δ 198.1, 143.2, 134.1, 130.3, 128.7, 128.0, 126.9, 27.3.
Propiophenone (12b):33 The crude material was purified by column
chromatography on silica gel (eluting with petroleum ether/ethyl
acetate = 20:1) to give the compound as oil (235.9 mg, 88%). 1H NMR
(400 MHz, CDCl3): δ 7.95−7.93 (m, 2H), 7.54−7.50 (m, 1H), 7.45−
7.41 (m, 2H), 2.98 (q, J = 8.0 Hz, 2H), 1.20 (t, J = 8.0 Hz, 3H). 13C NMR
(101 MHz, CDCl3): δ 200.7, 136.8, 132.8, 128.4, 127.8, 31.7, 8.1.
(4) For recent examples with Ir catalyst, see: (a) Mantilli, L.; Mazet, C.
Tetrahedron Lett. 2009, 50, 4141. (b) Mantilli, L.; Mazet, C. Chimia
2009, 63, 35.
(5) For recent examples with Ni catalyst, see: (a) Bricout, H.; Monflier,
E.; Carpentier, J.-F.; Mortreux, A. Eur. J. Inorg. Chem. 1998, 1998, 1739.
(b) Cuperly, D.; Petrignet, J.; Crevisy, C.; Gree, R. Chem.−Eur. J. 2006,
́
́
12, 3261.
(6) For recent examples with Fe catalyst, see: (a) Cherkaoui, H.;
Soufiaoui, M.; Gree, R. Tetrahedron 2001, 57, 2379. (b) Crevisy, C.;
Wietrich, M.; Le Boulaire, V.; Uma, R.; Gree, R. Tetrahedron Lett. 2001,
42, 395. (c) Branchadell, V.; Crevisy, C.; Gree, R. Chem.−Eur. J. 2003, 9,
2062.
́
́
́
́
́
(7) Bizet, V.; Pannecoucke, X.; Renaud, J.-L.; Cahard, D. Angew. Chem.,
Int. Ed. 2012, 51, 6467.
ASSOCIATED CONTENT
■
(8) (a) Tanaka, K.; Qiao, S.; Tobisu, M.; Lo, M. M. C.; Fu, G. C. J. Am.
S
* Supporting Information
1H and 13C NMR spectra. This material is available free of charge
via the Internet at http://pubs.acs.org.
Chem. Soc. 2000, 122, 9870. (b) Boeda, F.; Mosset, P.; Crev
Tetrahedron Lett. 2006, 47, 5021. (c) Mantilli, L.; Gerard, D.; Torche, S.;
Besnard, C.; Mazet, C. Angew. Chem., Int. Ed. 2009, 48, 5143.
(d) Mantilli, L.; Gerard, D.; Torche, S.; Besnard, C.; Mazet, C. Pure
Appl. Chem. 2010, 82, 1461. (e) Mantilli, L.; Gerard, D.; Torche, S.;
́
isy, C.
́
́
AUTHOR INFORMATION
■
́
Corresponding Author
*E-mail: zhaoguo@sjtu.edu.cn. Fax: (+86) 21-5474-8925.
Besnard, C.; Mazet, C. Chem.−Eur. J. 2010, 16, 12736. (f) Mantilli, L.;
Mazet, C. Chem. Commun. 2010, 46, 445. (g) Li, J. Q.; Peters, B.;
Andersson, P. G. Chem.−Eur. J. 2011, 17, 11143. (h) Wu, R.;
Beauchamps, M. G.; Laquidara, J. M.; Sowa, J. R., Jr. Angew. Chem.,
Int. Ed. 2012, 51, 2106. (i) Arai, N.; Sato, K.; Azuma, K.; Ohkuma, T.
Angew. Chem., Int. Ed. 2013, 52, 7500. (j) Ren, K.; Zhang, L.; Hu, B.;
Zhao, M.; Tu, Y.; Xie, X.; Zhang, T. Y.; Zhang, Z. ChemCatChem 2013,
5, 1317. (k) Tanaka, K.; Fu, G. C. J. Org. Chem. 2001, 66, 8177.
(l) Quintard, A.; Alexakis, A.; Mazet, C. Angew. Chem., Int. Ed. 2011, 50,
2354.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the National Natural Science Foundation of China for
the financial support.
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