Oxidative cleavage of alkenes catalyzed by a water/organic soluble manganese porphyrin complex

Article abstract of DOI:10.1016/j.tet.2006.12.029

Tetrakis(4-hydroxyphenyl)porphyrin [TPP-(OH)₄] was modified with poly(ethylene glycol) chain as four side arms, such that this compound is soluble in both organic and water solutions. Complexation of this porphyrin with manganese metal ions resulted in the formation of MnCl-TPP-(PEO₇₅₀)₄. This complex proved to be an excellent catalyst for the oxidative cleavage of C{double bond, long}C bonds, yielding the corresponding carbonyl compounds with sodium periodate as an oxidant. Mechanistic pathway for this cleavage is discussed.

Full text of DOI:10.1016/j.tet.2006.12.029

Tetrahedron 63 (2007) 1821–1825
Oxidative cleavage of alkenes catalyzed by a water/organic soluble
manganese porphyrin complex
*
Shiuh-Tzung Liu, K. Venugopal Reddy and Rung-Yi Lai
Department of Chemistry, National Taiwan University, Taipei 106, Taiwan
Received 11 August 2006; revised 12 December 2006; accepted 13 December 2006
Available online 8 January 2007
Abstract—Tetrakis(4-hydroxyphenyl)porphyrin [TPP–(OH)4] was modified with poly(ethylene glycol) chain as four side arms, such that this
compound is soluble in both organic and water solutions. Complexation of this porphyrin with manganese metal ions resulted in the formation
of MnCl–TPP–(PEO750)4. This complex proved to be an excellent catalyst for the oxidative cleavage of C]C bonds, yielding the correspond-
ing carbonyl compounds with sodium periodate as an oxidant. Mechanistic pathway for this cleavage is discussed.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
preparation of a water/organic soluble metal porphyrin com-
plex MnCl–TPP–(PEO750)4, and its high-catalytic activity
for the oxidative cleavage of alkenes, resulting in the corre-
sponding carbonyl compounds.
Metalloporphyrin species exist ubiquitously in nature and
have found a broad spectrum of applications. Amongst,
for example, the modeling of cytochrome P-450 for oxy-
genation of hydrocarbons has received much attention over
decades.1–24 As for the chemical reaction, great efforts
have been made to develop new metalloporphyrin-based cat-
alytic systems for the oxidation process, aiming at a higher
degree of chemo- and stereoselectivities as well as efficiency
under mild conditions.1–5 In this context, epoxidation and
hydroxylation of alkenes catalyzed by metal porphyrin com-
plexes have been a major focus.6–24
2. Results and discussion
PreparationofMnCl–TPP–(PEO750)4 isdepictedinScheme 1.
Incorporation of PEO side chain was achieved by direct
alkylation of [TPP–(OH)4] with CH3(OCH2CH2)16OTs in
88% yield. 1H NMR spectra of TPP–(PEO750)4 showed char-
acteristic shifts at 8.82 (8H) for the pyrrole methine protons
and a singlet at 2.79 ppm for the NH protons in the pyrrole
unit. In addition, the integration ratio of ethylene protons
for –OCH2CH2– versus pyrrole methine protons confirmed
the tetraalkylation on the porphyrin moiety. Treatment of
TPP–(PEO750)4 with MnCl2 under basic conditions afforded
the desired complex in 93% yield. Characterization of
this complex was performed via UV–vis and elemental
analysis. The characteristics UV–vis spectrum of MnCl–
TPP–(PEO750)4 in CH2Cl2 is similar to that of MnCl–TPP,
proving the formation of manganese complex.21,25 This com-
plex is soluble in water as well as in most organic solvents,
and its UV–vis spectrum in water is essentially identical to
that in dichloromethane.
Recently, porphyrin–Fe and porphyrin–Mn complexes and
their corresponding oxo species,15–17 heterogeneously sup-
ported manganese porphyrins18–20 and poly(ethylene glycol)
(PEO) side-chain manganese porphyrins21 have been widely
used as catalysts for either epoxidation or hydroxylation of
alkenes under ambient temperatures. However, to our knowl-
edge, there is no precedence concerning the use of manga-
nese porphyrin complexes in the catalytic cleavage of
C]C bonds.22,23 To obtain aldehydes from olefins that are
not fully substituted, two common methods are ozonization
of olefins followed by a reductive workup and oxidative
cleavage with osmium tetraoxide–sodium periodate, both of
which, however, required stringent reaction conditions.22,23
For the safety concern, chemists have been developing
alternative methods for the cleavage of C]C, especially on
the basis of catalytic approach.23 Herein we report the
To examine the catalytic activity, oxidation of alkenes with
oxidants over the prepared metal complex was investigated
(Table 1). The oxidation reaction of styrene, in the presence
of MnCl–TPP–(PEO750)4 as the catalyst, was first studied
under air or H2O2. In this reaction, however, trace of benz-
aldehyde was obtained as the product even with the addition
of imidazole, which acted as an axial ligand for the metal
Keywords: Oxidative cleavage; Porphyrin; Manganese; Olefin.
* Corresponding author. Tel.: +886 2 2366 0352; fax: +886 2 2363 6359;
e-mail: stliu@ntu.edu.tw
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.12.029

1822
S.-T. Liu et al. / Tetrahedron 63 (2007) 1821–1825
OH
O
PEO750OH
O
15
OR
NaOH
THF
TsCl
O
OTs
TPP–(PEO750 4
)
NH
N
N
O
OR
RO
15
HN
MnCl2
MnCl–TPP–(PEO750 4
)
OR
R = H, TPP–(OH)4
R = CH3, TPP–(OMe)4
Scheme 1. Preparation of the manganese porphyrin complex.
complex.26 Alternatively, using sodium periodate as the ox-
idant in CH2Cl2/H2O (1:1 v/v), a similar catalytic reaction at
room temperature revealed better conversion efficiency of
turning styrene into a mixture of benzaldehdye and phenyl-
acetaldehyde (see Table 1, entry 1). It is believed that the
production of phenylacetaldehyde is mainly via the epoxida-
tion of styrene, followed by the isomerization.11 Further-
more, as shown in entry 2, the selectivity of the reaction
improved significantly by using acetonitrile/water (2:1 v/v)
as solvent. For elevating temperatures (see entries 3 and
4), benzaldehyde became the exclusive product under simi-
lar conditions.
In view of the above results, the manganese catalytic system
with NaIO4 and imidazole in acetonitrile/water rendered the
best yield for oxidative cleavage of olefins and was followed
in the following studies. Subsequently, various alkenes were
tested under this catalytic system and the results are summa-
rized in Table 1. Except for simple 1-alkenes, olefinic
substrates underwent the oxidative cleavage to give the cor-
responding carbonyl compounds in excellent isolated yields.
For the phenyl-disubstituted alkene such as 1-diphenyl-
ethene, benzophenone (ketones) was observed to be the
major product (entry 6). Oxidative cleavage of cycloalkenes
proceeded smoothly at room temperature to give the
a
Table 1. Catalytic oxidation of various alkenes catalyzed by MnCl–TPP–(PEO750)4
b
Entry
Substrate
Cat.b
NaIO4
Imidazoleb
Tempc
Product
Yieldd (%)
1
2
3
4
5
6
7
8
9
Styrene (in CH2Cl2/water)
Styrene
Styrene
0.003
0.003
0.003
0.003
0.003
0.01
0.003
0.01
0.01
2.5
1.5
4.0
4.0
4.0
7.0
4.0
7.0
7.0
1.0
1.0
1.0
1.0
1.0
3.0
1.0
3.0
3.0
rt
rt
PhCHO, PhCH2CHO
PhCHO, styrene oxide
PhCHO
44, 30
51, 11
66
60
80
80
80
rt
Styrene
PhCHO
97
96
99
99
m-ClC6H4CH]CH2
1,1-Diphenylethene
1-Methylstyrene
trans-Stilbene
2-Vinylpyridine
m-ClC6H4CHO
Benzophenone
Acetophenone
80
80
PhCHO
87
70, 25
2-Vinylpyridineoxide,
2-Pyridinecarbaldehyde
1,6-Hexanedial
PhCHO
1,6-Hexanedial
1,5-Pentanedial
1,8-Octanedial
PhCHO
—
6-Phenyl-6-oxohexanal
—
10
11
12
13
14
15
16
17
18
19
20
21
Cyclohexene
0.0013
0.0013
0.0013
0.0013
0.01
0.03
0.01
0.01
0.01
3.0
3.0
3.0
3.0
4.0
7.0
7.0
4.0
4.0
7.0
3.0
4.0
0.5
0.5
0.5
0.5
0.5
3.0
3.0
0.5
1.0
1.0
1.0
1.0
rt
rt
rt
rt
97
99
96
99
65
60
—
77
—
33
89
44
Styrene oxide
Cyclohexene oxide
Cyclopentene
Cyclooctene
Benzyl alcohol
Diphenylacetylene
1-Phenylcyclohexene
Tartaric acid
rt
80
80
rt
rt
rt
Norbornylene
(ꢀ)-Limonene
a-Pinene
0.01
0.01
0.01
Cyclopentane-1,3-dicarbaldehyde
(+)-4-Methyl-3-(3-oxobutyl)-4-pentenal
(3-Acetyl-2,2-dimethylcyclobutyl)-
acetaldehyde
rt
rt
22e
Styrene
0.003
4.0
1.0
80
PhCHO
97
a
Reaction conditions: substrate (1 mmol) in CH3CN (2 ml)/H2O (1 ml) for 24 h.
In mmol.
b
c
d
e
Oil bath temperature in ꢁC.
Isolated yield, except entries 1 and 2 by NMR integration.
Under nitrogen atmosphere.

S.-T. Liu et al. / Tetrahedron 63 (2007) 1821–1825
1823
corresponding di-aldehyde in excellent yields (entries 10,
13, and 14). Interestingly, a mixture of 2-pyridine epoxide
(70%) and 2-pyridinecarbaldehdye (25%) was obtained from
2-vinylpyridine under similar reaction conditions. It was
also found that simple a-olefins or terminal alkenes such
as 1-octene, 1-hexene, carvone, b-pinene, and 2-methyl-
hexene did not undergo the oxygenation, as supported by
the starting material that is quantitatively recovered. In addi-
tion, the oxidation did not take place on alkyne or a,b-unsat-
urated carbonyl compounds, the results of which are in sharp
difference from the traditional methods. We thus tentatively
concluded that for the MnCl–TPP–(PEO750)4 catalytic reac-
tion, the internal double bond of limonene was cleaved to
yield the corresponding carbonyl functions, while the termi-
nal one remained intact (entry 20), demonstrating its remark-
able selectivity.
is not observed during this study, presumably its highly activ-
ity toward cleavage. As illustrated, styrene was completely
converted into benzaldehyde with the use of MnCl–TPP–
(PEO750)4 as the catalyst within 24 h, but the referenced cat-
alyst MnCl–TPP–(OMe)4 only reached up to 55% under the
similar reaction conditions. It appears that the activity of the
polyether attached catalyst is much better than the un-modi-
fied one, indicating the neediness of polyether linkage on this
catalyst for good activity.
To investigate the active oxidizing species in this catalysis,
we performed a reaction of MnCl–TPP–(PEO750)4 with
equal molar amount of methylimidazole and NaIO4 in water.
The UV–vis spectrum of the resulting solution showed the
initial formation of a periodate–Mn species (lmax¼476 nm),
and then the conversion into a high valent Mn–oxo species
(Soret lmax¼405 nm),26 but this species was slowly dimin-
ished. By the addition of styrene to this solution, the oxida-
tion product was formed. This observation suggests that the
oxidation process might involve either a periodate–Mn com-
plex or a Mn–oxo species.
Oxidation of styrene oxide and cyclohexene oxide with a
low loading of catalyst (0.13%) rendered benzaldehyde and
1,6-hexanedial as the desired products, respectively (entries
11 and 12) at room temperature. These results provided
a support to illustrate this oxygenation involving the epoxide
intermediate, which was subsequently hydrolyzed to yield
the 1,2-diol and then C–C cleavage (Scheme 2). In addition,
it was found that the cleavage of epoxide was much faster
than that of olefin, suggesting that the rate limiting step of
this oxidative cleavage is the formation of epoxide.
The re-use of catalyst is also possible for this catalytic
system. After the completion of the reaction, the organic
products were removed from the water layer. The aqueous
portion with the catalyst is ready for the further re-use. In
order to investigate the stability and duration of active cata-
lyst, the leaching of metal into the product mixture was
determined after three reaction cycles. From analysis, no
detectable leaching of manganese could be found, suggesting
that the catalytic species remains in aqueous solution. The re-
sults of the oxidation of styrene into benzaldehyde over the
catalyst with different reaction cycles are listed in Table 2.
It is noticed that the activity of catalyst slowly decreases
along with the repeated cycles, presumably due to the accu-
mulation of salt in aqueous phase. Under the similar condi-
O
HO
R
OH
IO4
[O]
O
-
R
R
R
r.d.s
R
R
R
Scheme 2. Pathway for oxidative cleavage.
Figure 1 shows the difference of MnCl–TPP–(PEO750)4 and
MnCl–TPP–(OMe)4 as catalysts for the oxidative cleavage
of styrene. It is noticed that the formation of styrene oxide
tions, the replacement of catalyst MnCl–TPP–(PEO750 4
)
with MnCl–TPP–(OMe)4 provided less than 60% of the
cleavage product, and the catalyst was mixed with organic
products, which was not easily separated, i.e. the re-use of
MnCl–TPP–(OMe)4 as a catalyst is not practical.
%
100
Table 2. Oxidation of styrene by the re-used catalysta
80
60
40
20
Run
1
2
3
4
Yieldb (%)
97
85
83
75
a
Reaction conditions: catalyst (0.003 mmol) and imidazole (1 mmol) in
CH3CN (2 ml)/H2O (1 ml) for 24 h. For each run, styrene (1 mmol),
NaIO4 (4 mmol), and CH3CN (2 ml) were added.
b
Yield of benzaldehyde was determined by NMR with an internal standard.
In summary, modification of the porphyrin moiety with four
poly(ethylene glycol) chains allows TPP–(PEO750)4 to be
soluble in both organic and water solutions. Using this
unique property, we have developed the manganese-based
catalytic oxidation methods for the cleavage of a wide range
of olefins to produce aldehydes. As this catalyst is easy to
handle and is much less toxic than OsO4, this cleavage
method is green-chemistry oriented and is expected to be
useful in a variety of organic syntheses. Works focusing on
detailed mechanistic pathway and the extension of this sys-
tem to other oxygenation reactions are currently in progress.
4
8
12
16
20
24 h
Figure 1. Plot of yields (benzaldehyde) versus time for the oxidative cleav-
age of styrene by MnCl–TPP–(PEO750)4 (-) and MnCl–TPP–(OMe)4 (C).
Reaction conditions: styrene (1 mmol), NaIO4 (4 mmol), and imidazol
(1 mmol) in CH3CN (2 ml)/H2O (1 ml) at 80 ꢁC.

1824
S.-T. Liu et al. / Tetrahedron 63 (2007) 1821–1825
3. Experimental
1:3) was employed to furnish the pure product (4.80 g,
88% yield). UV–vis (3, CH2Cl2): lmax 421 (3.6ꢃ105), 517
(2.3ꢃ104), 555 (1.6ꢃ104), 596 (9.2ꢃ103), 649 (1.0ꢃ104).
1H NMR (400 MHz, CDCl3) d 8.82 (s, 8H), 8.08 (d,
J¼8.8 Hz, 8H), 7.27 (d, J¼8.8 Hz, 8H), 4.41 (t, J¼5.2 Hz,
8H), 4.04 (t, J¼4.8 Hz, 8H), 3.87–3.61 (m, 232H), 3.54–
3.51 (m, 8H), 3.34 (s, 12H), ꢂ2.79 (s, 2H). Anal. Calcd
for C176H294N4O68: C, 59.48; H, 8.34; N, 1.58. Found: C,
59.00; H, 8.09; N, 2.02.
3.1. General
Nuclear magnetic resonance spectra were recorded in CDCl3
or acetone-d6 on either a Bruker AM-300 or AVANCE 400
spectrometer. Chemical shifts are given in parts per million
1
relative to Me4S for H NMR. Infrared spectra were mea-
sured on a Nicolet Magna-IR 550 spectrometer (Series-II)
as KBr pellets, unless otherwise noted. Chemicals and sol-
vents were of analytical grade and used as received unless
otherwise stated. TPP–(OMe)4 was prepared according to
the reported methods.27
3.1.4. Preparation of MnCl–TPP–(PEO750)4. The porphy-
rin (1 g, 0.28 mmol) was dissolved in 50 mL of refluxing
DMF for several minutes and MnCl2$4H2O (0.16 g,
0.84 mmol) was added to the solution. The solution was al-
lowed to reflux for 30 min. The reaction was monitored by
TLC. DMF was distilled off and the resulting syrupy oil
was chromatographed on silica gel with CH2Cl2–MeOH
(10:1) as an eluent to give the desired complex as green solid
(0.93 g, 93% yield). UV–vis (3, CH2Cl2): lmax 380
(8.7ꢃ104), 407 (8.2ꢃ104), 481 (1.7ꢃ104), 533 (1.2ꢃ104),
587 (1.7ꢃ104), 627 (2.5ꢃ104). Anal. Calcd for
C176H292ClMnN4O68$2H2O: C, 57.46; H, 8.11; N, 1.52.
Found: C, 57.86; H, 8.04; N, 1.76.
3.1.1. Preparation of 5,10,15,20-tetrakis(4-hydroxy-
phenyl)porphyrin [TPP–(OH)4]. The porphyrin TPP–
(OMe)4 (1 g, 1.3 mmol) was dissolved in 30 mL of dichloro-
methane with stirring. To this, borontribromide (8.1 g,
32.6 mmol) in dichloromethane (5 mL) was added slowly.
The resulting mixture was stirred for 12 h at room tempera-
ture and then was quenched with 5 mL of methanol and neu-
tralized with ammonia solution till the solution turned from
green to dark red color. The mixture was evaporated till dry-
ness, extracted with ethyl acetate and the organic layer was
washed several times with water. It was separated, dried over
anhydrous magnesium sulfate, filtered, and concentrated.
The residue was chromatographed on silica gel with ace-
tone/light petroleum (1:1) to yield pure compound [TPP–
(OH)4] (0.8 g, 87% yield).27 IR (neat) 3330.4, 1613.3,
3.2. Catalysis—general procedure
A mixture of MnCl–TPP–(PEO750)4, NaIO4, imidazole, and
the substrate was placed in a round bottomed flask. Solvents
were added to this mixture. The reaction was heated with
stirring at 80–100 ꢁC for a certain period of hours under
aerobic conditions. The progress of the reaction was moni-
1513.8, 1248.6, 1182.3, 804.4 cmꢂ1. H NMR (400 MHz,
1
acetone-d6) d 8.91 (s, 8H), 8.86 (s, 4H), 8.05 (d, J¼8.4 Hz,
1
8H), 7.29 (d, J¼6.5 Hz, 8H), ꢂ2.70 (s, 2H).
tored by H NMR spectrometer. For various substrates, the
reaction mixture was extracted with ether, which was then
filtered through a short column of silica gel. The filtrate
was evaporated under reduced pressure or distilled off
to give the desired product. Oxidative cleavage products
obtained in this work were characterized by spectral methods
particularly with 1H NMR and the data were consistent with
those reported.
3.1.2. Preparation of CH3(OCH2CH2)16OTs. Sodium
hydroxide (3.65 g, 91.3 mmol) and poly(ethylene glycol)
methylether CH3(OCH2CH2)16OH (45.70 g, 60.9 mmol)
were dissolved in a mixture of THF (140 mL) and water
(20 mL). A solution of p-toluenesulfonyl chloride (12.76 g,
67.0 mmol) in 20 mL of THF was added slowly to the above
solution at ice-cooled temperature. The solution was stirred
at 0 ꢁC for 3 h and then at room temperature for 12 h and
then poured into 50 mL of ice water. The mixture was
extracted several times with methylene chloride. The com-
bined organic layers were washed with dilute HCl followed
by brine and then dried over magnesium sulfate. After filtra-
tion, the solvent was removed under reduced pressure to give
the desired tosylate (41 g, 75% yield). 1H NMR (400 MHz,
CDCl3) d 7.77 (d, J¼7.6 Hz, 2H), 7.32 (d, J¼7.6 Hz, 2H),
4.14 (t, J¼4.8 Hz, 2H), 3.67 (t, J¼4.0 Hz, 2H), 3.65–3.56
(m, 60H), 3.54–3.51 (m, 2H), 3.35 (s, 3H), 2.43 (s, 3H).
These data are similar to those reported.28
3.2.1. p-Chlorobenzaldehdye.29 1H NMR (400 MHz,
CDCl3) d 9.96 (s, 1H), 7.80 (d, J¼8.0 Hz, 2H), 7.49 (d,
J¼8.1 Hz, 2H).
3.2.2. Benzophenone.30 1H NMR (400 MHz, CDCl3)
d 7.79–7.76 (m, 4H), 7.56 (t, J¼7.0 Hz, 2H), 7.45 (tt,
J¼7.0, 1.4 Hz, 4H).
3.2.3. Acetophenone.30 1H NMR (400 MHz, CDCl3) d 7.92
(d, J¼7.6 Hz, 2H), 7.50 (t, J¼7.6 Hz, 2H), 7.42 (dd, J¼7.6,
8.0 Hz, 2H), 2.55 (s, 3H).
3.1.3. Preparation of TPP–(PEO750)4. A mixture of
[TPP–(OH)4] (1 g, 1.47 mmol) and CH3(OCH2CH2)16OTs
(5.32 g, 5.89 mmol) [Ts¼p-CH3C6H4SO2–] was dissolved
in 50 mL of dimethylformamide. To this, potassium carbon-
ate (0.81 g, 5.9 mmol) was added and the solution was
stirred at 80 ꢁC for 16 h. After cooling to room temperature,
the solution was poured into water and extracted thrice with
methylene chloride. The combined organic layers were
washed with water and then with brine, dried over magne-
sium sulfate, filtered, and the solvent was removed at
reduced pressure. Chromatography (silica, ether/acetone,
3.2.4. 2-Vinylpyridineoxide.31 1H NMR (400 MHz,
CDCl3) d 8.52 (d, J¼4.8 Hz, 1H), 7.51–7.48 (m, 1H),
7.22–7.19 (m, 2H), 3.97 (t, J¼4.0 Hz, 1H), 3.14 (dd,
J¼10.3 Hz, 1H), 2.90 (dd, J¼8.2 Hz, 1H).
3.2.5. 2-Pyridinecarbaldehyde.31 1H NMR (400 MHz,
CDCl3) d 10.05 (s, 1H), 8.80 (d, J¼4.8 Hz, 1H), 7.90 (d,
J¼5.2 Hz, 1H), 7.82 (t, J¼3.6 Hz, 1H), 7.51–7.48 (m, 1H).
3.2.6. 1,6-Hexanedial.32 1H NMR (400 MHz, CDCl3) d 9.74
(t, J¼3.4 Hz, 2H), 2.45–2.43 (m, 4H), 1.64–1.61 (m, 4H).

S.-T. Liu et al. / Tetrahedron 63 (2007) 1821–1825
1825
3.2.7. 1,5-Pentanedial.32 1H NMR (400 MHz, CDCl3)
d 9.75 (t, J¼2.4 Hz, 2H), 2.50 (m, 4H), 1.96–1.91 (m, 2H).
3.2.8. 1,8-Octanedial.33 1H NMR (400 MHz, CDCl3) d 9.75
(t, J¼3.4 Hz, 2H), 2.41–2.38 (m, 4H), 1.59–1.55 (m, 4H),
1.34–1.30 (m, 4H).
10. Funyu, S.; Isobe, T.; Takagi, S.; Tryk, D. A.; Inoue, H. J. Am.
Chem. Soc. 2003, 125, 5734.
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16. Goto, Y.; Watanabe, Y.; Fukuzumi, S.; Dinnocenzo, J. P. J. Am.
Chem. Soc. 1980, 120, 10762.
3.2.9. 6-Phenyl-6-oxohexanal.34 1H NMR (400 MHz,
CDCl3) d 9.74 (t, J¼1.6 Hz, 1H), 7.93–7.91 (m, 2H), 7.52
(t, J¼7.6 Hz, 1H), 7.44–7.43 (m, 2H), 2.96 (t, J¼6.8 Hz,
2H), 2.48–2.45 (m, 2H), 1.75–1.70 (m, 4H).
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Synop. 1999, 168.
3.2.10. Cyclopentane-1,3-dicarbaldehyde.35 1H NMR
(400 MHz, CDCl3) d 9.63 (d, J¼2.0 Hz, 2H), 2.83–2.74
(m, 2H), 2.30–2.14 (m, 2H), 1.98–1.85 (m, 2H), 1.81–1.74
(m, 2H).
3.2.11. ( )-4-Methyl-3-(3-oxobutyl)-4-pentenal.36 1H
NMR (400 MHz, CDCl3) d 9.64 (t, J¼4.5 Hz, 1H), 4.82–
4.74 (m, 2H), 2.65–2.60 (m, 1H), 2.56–2.30 (m, 4H), 2.10
(s, 3H), 1.68–1.60 (m, 5H).
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€
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This work was partially supported by the National Science
Council, Taiwan, ROC for the financial support (NSC94-
2113-M002-035).
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