The Oxidation of 3-Aryl-1-propenes by Oxidative System of RuCl 3-NaIO4-Phase Transfer Catalyst

Article abstract of DOI:10.1081/SCC-120026319

Methyleugenol 1a was oxidized to give 3,4-dimethoxyphenylacetaldehyde by the oxidative system containing the RuCl₃-NaIO₄-phase transfer catalyst. The yield and spectroscopic properties were obtained from the stable acetaldoxim 3a. Furthermore, this oxidation system could be applied to other arylpropenes, thus, safrole, 4-methoxyallylbenzene, allylbenzene, and the corresponding arylacetaldehyde formed.

Full text of DOI:10.1081/SCC-120026319

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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 22, pp. 3947–3952, 2003
The Oxidation of 3-Aryl-1-propenes by
Oxidative System of RuCl3-NaIO4-Phase
Transfer Catalyst
2
2
Yoshifumi Yuasa,1, Shiroshi Shibuya, and Yoko Yuasa
*
1Technical Engineering Department,
Fine Chemical Division, Takasago International
Corporation, Hiratsuka, Kanagawa, Japan
2School of Pharmacy, Tokyo University of
Pharmacy and Life Science, Hachioji, Tokyo, Japan
ABSTRACT
Methyleugenol 1a was oxidized to give 3,4-dimethoxyphenylacet-
aldehyde by the oxidative system containing the RuCl3-NaIO4-
phase transfer catalyst. The yield and spectroscopic properties were
obtained from the stable acetaldoxim 3a. Furthermore, this
oxidation system could be applied to other arylpropenes, thus,
*Correspondence: Yoshifumi Yuasa, Technical Engineering Department, Fine
Chemical Division, Takasago International Corporation, 1-5-1 Nishiyawata,
Hiratsuka, Kanagawa, 254-0073, Japan; E-mail: yoshifumi_yuasa@takasago.
com.
3947
DOI: 10.1081/SCC-120026319
Copyright & 2003 by Marcel Dekker, Inc.
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3948
Yuasa, Shibuya, and Yuasa
safrole, 4-methoxyallylbenzene, allylbenzene, and the corresponding
arylacetaldehyde formed.
Key Words: Oxidation; Ruthenium chloride; Sodium periodade;
Phase transfer catalyst; Arylacetaldehyde.
Arylacetaldehyde is used for perfume compositions[1] or as a useful
intermediate of drugs, especially, 3,4-dimethoxyphenylacetaldehyde is an
important intermediate of verapamil, a cardiac drug.[2]
The synthetic methods for preparing the arylacetaldehydes by
oxidation from the corresponding allyl compounds using ozone,[3,4]
[5–9]
[10–12]
OsO4/NaIO4
or HCO2H-30%H2O2/Pb(OAc)4
have been
reported. In addition, a number of preparations for arylacetaldehyde
have been known, such as,
(a) Rearrangement of styrene oxides.[13]
(b) Decarboxylation of phenylglycidate.[14]
(c) Synthesis via enamine of a-oxophenylpropanoic acids.[15]
On the other hand, there are many synthetic methods using the
oxidative cleavage of alkenes with a catalytic amount of ruthenium
metal,[16] however few results have been reported on the oxidative cleav-
age of allyl compounds to produce the corresponding arylacetaldehydes.
Recently, we have reported the safe and facile oxidation of b-pinene
to produce nopinone using RuCl3-NaIO4-phase transfer catalyst
(PTC) system.[17] As an extension of this oxidation system, we
now report the synthesis of 3,4-dimethoxyphenylacetaldehyde 2a from
methyleugenol 1a.
We have found that the oxidation of methyleugenol 1a using 1 mol%
of RuCl3, 5 mol% of benzyltriethylammonium chloride (BTEAC), and
5 mol equiv. of NaIO4 in EtOAc/H2O for 2 h at room temperature gave
3,4-dimethoxy-phenylacetaldehyde 2a with 100% conversion and 95%
selectivity by GC. The other 5% by-product was found to be
3,4-dimethoxybenzaldehyde by GC-MS (Mþ ¼ 166). The oxidation con-
ditions, i.e., the oxidant, solvent, and amount of catalyst were nearly
fixed according to our previous report[17] (see experimental section). We
also applied this oxidative system to other 3-aryl-1-propenes such as
safrole 1b, 4-methoxyallylbenzene 1c, and allylbenzene 1d, and thus the
corresponding arylacetaldehydes 2b–d were obtained (Sch. 1). Since the
peroxidation and/or polymerization of 2, the yield could not be shown as
optimized values. Therefore, the yield and spectroscopic properties were

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Oxidation of 3-Aryl-1-propenes
3949
R1
R1
R2
CHO
NaIO4
cat. RuCl , BTEAC
R2
3
2a-d
1a-d
a: R =R =OMe
N OH
1
2
R1
R2
HONH2•HCl
pyridine
b: R =R = -OCH O-
1
2
2
c: R =H, R =OMe
1
2
3a-d
d: R =R =H
1
2
Scheme 1.
obtained after transformation to the arylacetaldoxims 3a–d which are
useful precursors of amines or nitriles (Table 1). This oxidation did not
proceed in the absence of RuCl3 as a catalyst. We also have investigated
the effect of PTC. All of the PTCs smoothly promoted the oxidation to
give good conversion and selectivity of 2a in comparison with the GC
analysis value obtained in the absence of PTC as shown in Table 2.
In conclusion, we performed the syntheses of arylacetaldehydes from
3-aryl-1-propenes using RuCl3-NaIO4-PTC system.
EXPERIMENTAL SECTION
All reagents and solvents were obtained from commercial sources
and used without further purification. Melting points: Yanagimoto
micromelting apparatus, uncorrected values. IR: Jasco IR-810.
1H NMR (recorded in CDCl3 with TMS as an internal standard):
Bruker AM-400 (400 MHz). MS: Hitachi M-80A mass spectrometer at
70 eV. GC: HP 5890 with an FID detector. Column: silicon OV-1
(df ¼ 0.15 mm, 0.25 mm ꢀ 25 m); carrier gas N2, 0.1 MPa; oven temper-
ature, 70–200ꢁC (programmed at 4ꢁC/min); injection temperature,
250ꢁC; detector temperature, 250ꢁC.
Typical Procedure: 3,4-Dimetoxyphenylacetaldehyde (2a)
and Aldoxim (3a)
To a solution of methyleugenol 1a (8.0 g, 45 mmol), RuCl3 (50 mg,
0.25 mmol), and benzyltriethylammonium chloride (0.5 g, 2.2 mmol) in
EtOAc (80 mL), NaIO4 (47.5 g, 225 mmol) in water (500 mL) was

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3950
Yuasa, Shibuya, and Yuasa

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Oxidation of 3-Aryl-1-propenes
Table 2. The effect of PTC in the oxidation of 1a.
Product 2a
3951
Runa
PTC
Convb (%)
Selectb (%)
1
2
3
4
5
6
7
No addition
n-Bu4NI
49
100
100
100
92
90
93
92
95
94
87
85
n-Bu4NClO4
BnEt3NCl
(n-Oct)3MeNCl
n-Bu4PBr
95
90
BnPh3PCl
aReaction conditions: 1, 45 mmol; RuCl3, 0.25 mmol; PTC, 2.2 mmol; NaIO4,
225 mmol; EtOAc/H2O, r.t., 2 h.
bConversion yield and selectivity of 2a were determined by GC.
added slowly for 1 h at room temperature. The resulting solution was
stirred for additional 1 h (conversion yield and selectivity of 2a were
100 and 95% by GC, respectively). EtOAc (250 mL) was added to the
reaction mixture. The organic layer was separated, washed with water,
dried with anhydrous MgSO4 and concentrated in vacuo to give an oil
(6.3 g, 74%). The purity was determined to be 95% by GC. To the crude
product, hydroxyamine hydrochloride (7.8 g, 112 mmol), pyridine (6 mL),
and EtOH (44 mL) were added and refluxed for 1 h. After removal of
solvent in vacuo, EtOAc (50 mL) and water (50 mL) were added, the
organic layer was washed with 5% HCl, brine, dried with anhydrous
MgSO4, and concentrated in vacuo to give 3a (5.7 g, 65% based on 1a,
1
anti:syn ¼ 1:1; by H NMR) as a solid.
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©2003 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
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Received in Japan April 22, 2003

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