Synthesis of Allyl Acetals and Their Catalytic Claisen-Cope Rearrangement

Article abstract of DOI:10.1246/bcsj.77.157

We have synthesized various types of acetals using 3-methyl-3-butenal and 2-alkenyl, furfuryl, benzyl, p-substituted benzyl, and 2-pentynyl alcohols. These acetals have given corresponding aldehydes after an acid catalytic reaction. Trifluoroacetic acid (CF3COOH) was the best catalyst. The best yield attained was 79% when 3-methyl-3-butenal di(trans-2-pentenyl) acetal was used as a substrate. We also demonstrated that this reaction proceeded via a Claisen-Cope rearrangement.

Full text of DOI:10.1246/bcsj.77.157

Ó 2004 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 77, 157–164 (2004)
157
Synthesis of Allyl Acetals and Their Catalytic Claisen–Cope
Rearrangement
1
2
ꢀ
Kazuhiro Nakabayashi, Masato Ooho, Teppei Niino, Tsugio Kitamura, and Teizo Yamaji
Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University,
Hakozaki, Fukuoka 812-8581
1
Fukui Research Institute, Ono Pharmaceutical Co., Ltd., Yamagishi Technoport,
Mikuni-cho, Fukui 913-8538
2
Department of Chemistry and Applied Chemistry, Faculty of Science and Engineering, Saga University,
Honjo-machi, Saga 840-8502
Received March 10, 2003; E-mail: tzyamaji@poppy.ocn.ne.jp
We have synthesized various types of acetals using 3-methyl-3-butenal and 2-alkenyl, furfuryl, benzyl, p-substituted
benzyl, and 2-pentynyl alcohols. These acetals have given corresponding aldehydes after an acid catalytic reaction. Tri-
fluoroacetic acid (CF3COOH) was the best catalyst. The best yield attained was 79% when 3-methyl-3-butenal di(trans-2-
pentenyl) acetal was used as a substrate. We also demonstrated that this reaction proceeded via a Claisen–Cope rearrange-
ment.
After 1970, the demand for synthetic organic products has
increased in accordance with the need for natural organic com-
pounds. The use of synthetic organic perfumes and fragrances
has also multiplied very much recently. With this movement,
many methods for the synthesis of organic perfumes and fra-
grances have been investigated.1
ried out by Ichikawa and Yamaji.7,8 This reaction is shown in
reaction (3).
This reaction can be called a Claisen–Cope rearrangement
reaction; it is very interesting to execute the two rearrange-
ments in one step. It would be useful to investigate this reaction
more in order to increase the conversion and selectivity, and to
solve the reaction mechanism to develop an industrial process
for perfumes and fragrances. We have synthesized various
kinds of acetals, and conducted further experiments to clarify
this reaction. Here, we report on the details of the results.
–6
For instance, citral has been synthesized from pinene via ge-
5
raniol, as shown by reaction (1) in Fig. 1. It has also been syn-
thesized from 6-methyl-5-hepten-2-one, as shown by reaction
5
(
2). The synthesis of terpene perfume aldehydes has been car-
pyrolysis
hydration
oxidation
(1)
CHO
OH
myrcene
HC CH
geraniol (E)
nerol (Z)
β
-pinene
citral
OH
O
CHO
(2)
6-methyl-5-hepten-2-one
citral
OEt
acid
+
CHO
(3)
OEt
OH
∆
citral
Fig. 1. Synthesis of citral.
Published on the web January 13, 2004; DOI 10.1246/bcsj.77.157

1
58 Bull. Chem. Soc. Jpn., 77, No. 1 (2004)
Synthesis and Rearrangement of Allyl Acetals
aÞ
Table 1. Effect of Catalysts in Synthesis of Citral
OEt
Cat.
+
CHO
OEt
OH
mesitylene
1
2a
3a
bÞ
bÞ
bÞ
E:Z
Entry
Cat.
pKa1
ꢁ3
ꢁ1:2
Time/h
Conv./%
Selectivity/%
Yield/%
1
2
H2SO4
0.5
0.5
100
100
100
22
85
83
100
14
59
0
1.7
3.7
9.3
2.7
13.6
33.9
5.9
4.5
2.2
—
1.7
3.7
9.3
0.6
48:52
57:43
58:42
63:37
53:47
60:40
32:68
58:42
55:45
—
CH3SO3H
cÞ
0
.25
3
CF3COOH
0.25
0.5
4
4
1
0.5
4
4
4
1
11.7
28.0
cÞ
4
5
6
7
p-TsOH
0.9
5.9
0.6
cÞ
(COOH)2
H3PO4
Isophthalic acid
1.27
2.15
3.6
1.3
0
2.2
cÞ
37
0
1
5.9
—
0
59:41
—
—
8
CH3COOH
4.8
0
0
0
.5
ꢁ
4
a) Reaction conditions: Glass tube (6 mm ꢂ 13 cm), a catalyst (7:9 ꢂ 10 mmol), 1 (0.63 mmol), 2a (1.27
ꢃ
ꢃ
mmol), 150 C. b) Determined by GC. c) 190 C.
OEt
OEt
OH
H+
O
2
H+
a
O
1
4a
Transetherification
H
O
O
–
H+
O
H
OH
Claisen
rearrangement
CHO
CHO
O
O
Cope
rearrangement
CHO
Isomerization
CHO
(Z)
(E)
Fig. 2. Possible mechanism.
methyl-2-butenyl alcohol (2a) in an acidic solution, giving cit-
ral, 3,7-dimethylocta-2,6-dienal (3a). Table 1 gives the results.
By changing pKa of the acids from ꢁ3 to 4.8, we could selected
CF3COOH as the best catalyst for this rearrangement reaction
(entry 3). Other catalysts showed poor catalytic properties. A
high conversion was attained by using acids with a low pKa (en-
Results and Discussion
Effect of Catalysts in the Synthesis of Citral. In order to
understand the formation of citral, we first examined of all of
the best acidic catalyst in a direct synthesis of citral. We carried
out a reaction of 3-methyl-3-butenal diethyl acetal (1) and 3-

K. Nakabayashi et al.
Bull. Chem. Soc. Jpn., 77, No. 1 (2004)
159
ꢃ
tries 1, 2, 4). On the contrary, those acids with a high pKa
showed a low conversion (entries 5, 7, 8). The E:Z ratio re-
mained almost constant 60% in the case of CF3COOH. Howev-
er, p-TsOH showed a unique ratio (entry 4). This is presently
under investigation. The low yield of an aldehyde by using
an acid catalyst with a low pKa may be caused by further reac-
tions of the aldehydes, as observed in the rather complex gas
chromatograph of the products.
ature, we investigated the rearrangement of 4a from 150 C to
ꢃ
210 C. The results are given in Table 2. It shows that citral was
ꢃ
prepared in 60% yield at 190 C (entry 3). However, by high-
ering or lowering the temperature, the reaction gave inferior re-
sults (entries 1, 2, 4). The E:Z ratio increased slightly with high-
ꢃ
ꢃ
er temperatures from 54% (150 C) to 63% (210 C). This
means that cis–trans isomerization occurred after the rear-
rangement reaction.
Possible Reaction Mechanism. We may be able to induce
a reaction mechanism in the following way, as shown in Fig. 2.
Acetal 1 undergoes a transetherification readily to give a new
acetal, 3-methyl-3-butenal bis(3-methyl-2-butenyl) acetal (4a).
Acetal 4a demonstrates a departure of 3-methy-2-butenyl alco-
hol by an acid catalyst. This process produces a particularly sta-
bilized carbocation, in which deprotonation affords an allyl di-
enyl ether. This allyl dienyl ether undergoes a Claisen rear-
rangement, and a Cope rearrangement then occurs to give the
intended aldehyde. If the allyl dienyl ether is formed, the reac-
tion proceeds mainly with heat. Because we could not isolate
the ally dienyl ether, we prepared acetal 4a and examined the
reaction conditions for successive rearrangements.
Effect of a Solvent without a Catalyst. In order to inves-
tigate the effect of solvents, we heated 4a without a catalyst.
The results are given in Table 3. Only aromatic solvents gave
the aldehyde practically (entries 1–3, 7, 8). It was observed that
the reaction without a solvent did not proceed effectively.
Effect of a Solvent with an Acidic Catalyst. An aromatic
solvent exhibited a good result. We proceeded the reaction in
various aromatic solvents. The results are given in Table 4.
The best result, 60% of citral 3a, was obtained from the corre-
sponding acetal 4a in mesitylene with an E ratio of 57% (entry
3). Toluene and mesitylene gave rather good results (entries 2,
3). When we extended the reaction time to 4 h, the yield and E
ratio did not change at all. This means that the produced alde-
hydes are stable in these aromatic solvents within this range of
time.
Effect of Temperature. In order to improve the yield of cit-
ral 3a, we examined the reaction conditions of the successive
rearrangement of acetal 4a. In order to find the effect of temper-
Effect of Various Lewis Acid Catalysts. We could not ob-
aÞ
Table 2. Effect of Temperature
Cat. CF COOH
O
3
CHO
mesitylene
O
3
a
4
a
ꢃ
bÞ
bÞ
bÞ
E:Z
Entry
Temp./ C
Conv./%
Selectivity/%
Yield/%
1
2
3
4
150
170
190
210
25
39
97
>99
14
50
62
44
4
19
60
44
54:46
55:45
57:43
63:37
ꢁ4
a) Reaction conditions: Glass tube (6 mm ꢂ 13 cm), CF3COOH (7:9 ꢂ 10 mmol), 4a
ꢃ
(
0.63 mmol), mesitylene (1 mL), 190 C, 2 h. b) Determined by GC.
aÞ
Table 3. Effect of Solvents without the Catalyst
aÞ
Table 4. Effect of Solvents with CF3COOH Catalyst
Solvent
O
CHO
O
Cat. CF COOH
3
O
3
a
4
a
CHO
solvent
O
bÞ
bÞ
E:Z
Entry
Solvent
Yield/%
3
a
4
a
1
2
3
4
5
6
7
8
9
mesitylene
benzene
benzonitrile
THF
DMF
8
13
8
—
—
6
16
17
5
53:47
56:44
61:39
—
bÞ
bÞ
Entry
Solvent
Yield/%
E:Z
1
2
3
4
5
6
hexane
toluene
mesitylene
benzene
chlorobenzene
anisole
21
48
60
50
41
33
57:43
61:39
57:43
61:39
61:39
61:39
—
CH3CN
56:44
53:47
53:47
61:39
methoxybenzene
chlorobenzene
none
a) Reaction conditions: Glass tube (6 mm ꢂ 13 cm), CF3COOH
ꢁ
4
ꢃ
a) Reaction conditions: Glass tube (6 mm ꢂ 13 cm), 4a (0.63
(7:9 ꢂ 10 mmol), 4a (0.63 mmol), a solvent (2 mL), 190 C, 2
ꢃ
mmol), solvent (1 mL), 190 C, 2 h. b) Determined by GC.
h. b) Determined by GC.

1
60 Bull. Chem. Soc. Jpn., 77, No. 1 (2004)
Synthesis and Rearrangement of Allyl Acetals
Table 5. Preparation and Reaction of 2-Alkenyl and Arylmethyl Acetals 4
OEt
OEt
R
1
O
CF COOH
3
R OH
Product
R
(NH ) SO , toluene
O
benzene or mesitylene
90 °C or 230 °C
2
4
2
4
3
4
1
a)
b)
Formation of 4
Formation of 3
Entry
1
Yield/%c)
72
Yield/%c) E : Zd)
R−OH
Temp./ºC
70
Time/h
24
Time/ h
2e)
Product
CHO
43
63 : 37
60 : 40
52 : 48
59 : 41
54 : 46
57 : 43
63 : 37
58 : 42
61 : 39
58 : 42
62 : 38
59 : 41
OH
2
a
3
a
2
3
4
5
6
7
8
9
2e,f)
2e,f)
5e)
3a
54g)
71g)
54
CHO
OH
70
70
24
24
52
39
Et
Z-2b
E-2b
3
b
3b
3b
3b
2e,f)
71g)
79
OH
5e)
OH
CHO
CHO
24
24
24
24
28
54
50
36
62
78
82
77
4h)
46
70
70
70
3
c
2
c
O
O
4h)
OH
OH
59
3
d
2
d
O
4h,i)
4h,j)
4h)
CHO
CHO
CHO
CHO
50
O
3
e
2
e
OH
1
1
1
0
1
2
CH O
3
90
90
6
3
f
CH O
2
f
3
OH
CH3
27
3
g
CH3
2
g
OH
90k)
4h)
F
44
F
3h
2
h
a) Reaction conditions: a flask (50 mL), (NH4)2SO4 (1.0 mmol), 1 (23 mmol), ROH (69 mmol), toluene (150 mmol). b)
Reaction conditions: a glass tube (6 mm ꢂ 13 cm), CF3COOH (7:9 ꢂ 10 mmol), 4 (0.63 mmol), benzene (1 mL). c)
ꢁ4
1
ꢃ
Isolated yield. d) Determined by H NMR. e) 190 C. f) Mesitylene (2 mL) was used as solvent. g) GC yield. h) 230
ꢃC. i) CF3COOH (3:15 ꢂ 10ꢁ3 mmol). j) CF3COOH (7:9 ꢂ 10ꢁ5 mmol). k) Mesitylene was used as solvent.

K. Nakabayashi et al.
Table 6. Preparation and Reaction of Other Acetals 4
Bull. Chem. Soc. Jpn., 77, No. 1 (2004)
161
R
O
CF3COOH
1
R−OH
2
Product
R
O
benzene
190 °C
(NH4)2SO4, toluene
5
4
7
0 °C
Entry
Formation of 4a)
Yield/%c)
Formation of 5b)
R−OH
Time/h
4
Product
Yield/%c)
E : Zd)
82 : 18
OH
1
2
3
4
5
77
18
48
78
50
Ph
O
23
14
Ph
2
2
i
5
a
5
100 : 0

OH
OH
O
j
5
b
e)
5

36

O
2
k
5c
O
O
OH
4
O
73 : 37

5
d
2
l
4f)
Et
CH OH
No reaction
2
2
m
a) Reaction conditions: a flask (50 mL), (NH4)2SO4 (1.0 mmol), 1 (23 mmol), ROH (69 mmol),
ꢃ
toluene (150 mmol), 70 C, 24 h. b) Reaction conditions: a glass tube (6 mm ꢂ 13 cm),
ꢁ
4
ꢃ
CF3COOH (7:9 ꢂ 10 mmol), 4 (0.63 mmol), benzene (1 mL), 190 C. c) Isolated yield. d) De-
1
1
ꢃ
termined by H NMR. e) Vinyl ether was observed by H NMR. f) 230 C.
tain any aldehyde products from 4a by using various Lewis acid
catalysts (TiCl4, Ti(OEt)4, Ti(Oi-Pr)4, FeCl3, and Et2AlCl),
even in a polar or nonpolar solvent (CH2Cl2 or benzene) at
low temperatures. After the reactions, substrate 4a decomposed
and did not give any products, or recover.
yields were obtained for cis- and trans-2-pentenyl acetals (en-
tries 3, 5). Furylmethyl acetal required a rather higher reaction
temperature (entries 8, 9) compared to that used for 2-alkenyl
acetals to obtain the same grade of yield. Arylmethyl acetals al-
so required the same range of temperature for the reaction
(Table 5, entries 7, 10–12). These may be caused by the diffi-
culty of a Claisen rearrangement via double bonding in the ring.
A Claisen rearrangement may be easier in the furfuryl ring than
in the benzene ring based on these results.
As we chose the reaction conditions for the rearrangement of
a to 3a, we furthermore examined the synthesis of various ace-
4
tals 4 and the rearrangement.
Synthesis of Acetals 4. More various acetals were prepared
by changing the substrate alcohols. The results are given in
Table 5. Mainly, five types of acetals were prepared. Allyl al-
cohols, alkyl alcohols, furfuryl alcohols, and benzyl alcohols
were reacted with 3-methyl-3-butenal diethyl acetal (1) at 70
Rearrangement of 3-Alkenyl and Alkyl Acetals 4. In con-
nection with the reaction mechanism, we used 3-alkenyl and al-
kyl alcohols for the acetal. The preparation and rearrangement
results are given in Table 6. However, aldehydes were not pro-
duced in these rearrangement reactions. Dienyl compounds
were obtained instead. These results suggest that dealcohol oc-
curs first to form the dienyl ether by the action of an acid cata-
lyst, followed by first a Claisen rearrangement and then a Cope
rearrangement. The dienyl ether formed without a proper dou-
ble bonding does not execute a Claisen rearrangement. The re-
action stops instantly. The substrate can not proceed eventually
to a Cope rearrangement. In these cases, no aldehydes were
formed. It is appropriate to call this reaction a Claisen–Cope re-
action. When the rearrangement of 2-pentynyl acetal (entry 5)
ꢃ
C for 24 h. para-Substituted benzyl alcohols did not give the
ꢃ
ꢃ
corresponding acetals at 70 C. They reacted at 90 C for a
longer time. From these data, we can state the followings.
The yield of acetals by 4-substituted benzyl alcohols was best,
8
2% (entry 11). Good yields of over 70% were also obtained in
the case of 4-methoxybenzyl, 4-fluorobenzyl, and 3-methyl-2-
butenyl alcohols (entries 10, 12, 16, and 1).
Rearrangement of 2-Alkenyl and Arylmethyl Acetals 4.
The conditions for the synthesis of terpene aldehydes have be-
come clear. Various 2-alkenyl acetals were allowed to rear-
range with CF3COOH as a catalyst in benzene or mesitylene
ꢃ
was performed at 230 C, no reaction occurred. The substrate
was recovered. The formation of dienyl ether was difficult at
this temperature.
ꢃ
at 190 C. The data for 2-alkenyl acetals are given in Table 5.
The data for arylmethyl acetals are also given in Table 5. 2-Pen-
tenyl alcohol gave the best yield of 79% (entry 6). Moderate

1
62 Bull. Chem. Soc. Jpn., 77, No. 1 (2004)
Synthesis and Rearrangement of Allyl Acetals
with ether (20 mL ꢂ 3). Then, the combined organic layer was
dried by anhydrous Na2SO4. After removal of Na2SO4, the mixture
was separated by distillation under reduced pressure or column
chromatography on silica gel with a mixed solvent.
Conclusion
We have synthesized various types of acetals using 3-meth-
yl-3-butenal and alkyl-2,3-olefinic, 2-furylmethyl, benzylic,
and para-substituted benzylic, and pentylic alcohols. These ace-
tals gave corresponding aldehydes after the acid catalytic reac-
tion. CF3COOH was the best catalyst. The best yield attained
was 79% when 3-methyl-3-butenal di(trans-2-pentenyl)acetal
was used as a substrate. We also have demonstrated that this re-
action proceeds via a Claisen–Cope rearrangement.
3
Yield (72%), colorless liquid, bp 94–96 C (120 Pa). H NMR
-Methyl-3-butenal Bis(3-methyl-2-butenyl) Acetal (4a):
ꢃ
1
(
(
(
5
300 MHz, CDCl3) ꢀ 1.72 (s, 3H, CH3), 1.70 (s, 3H, CH3), 1.78
s, 3H, CH3), 2.40 (d, 2H, J ¼ 6:0 Hz), 4.05 (m, 2H, CH2), 4.72
t, 1H, J ¼ 6:0 Hz), 4.79 (s, 1H, CH2=) 4.81 (s, 1H, CH2=),
1
3
.35 (m, 1H, CH). C NMR (75 MHz, CDCl3) ꢀ 17.9, 22.9,
2
6.7, 41.7, 61.5, 100.5, 112.7, 120.9, 136.7, 141.4.
3
52%), colorless liquid, bp 71–72 C (20 Pa). H NMR (300 MHz,
-Methyl-3-butenal Di[(Z)-2-pentenyl] Acetal (4b-Z): Yield
1
Experimental
ꢃ
(
General. GC analyses were performed on a Shimadzu GC-8A
system equipped with a 3.0 m ꢂ 3.2 mm i.d. glass column packed
with a [Unisole Thermon-3000 (5%)] on 80/100 Chromosorb for a
CDCl3) ꢀ 0.98 (t, J ¼ 7:5 Hz, 6H, CH3), 1.77 (s, 3H, CH3), 2.08 (d,
J ¼ 7:5 Hz, 4H, CH2), 2.39 (d, J ¼ 5:7 Hz, 2H, CH2), 4.11 (m, 4H,
OCH2), 4.73 (t, J ¼ 5:7 Hz, 1H, CH), 4.79 (s, 1H, CH2=), 4.82 (s,
ꢃ
13
certain injection/detector temperature (250 C), column tempera-
ꢃ
1H, CH2=), 5.54 (m, 4H, CH=CH). C NMR (75 MHz, CDCl3) ꢀ
ꢃ
ture (70–230 C, 4 C/min) and N2 pressure (70 kPa), and a Shi-
madzu GC-14B system equipped with a 60 m ꢂ 0.25 mm i.d. ca-
14.2, 20.8, 22.9, 41.7, 60.6, 100.6, 112.9, 125.1, 135.1, 141.3.
3-Methyl-3-butenal Di[(E)-2-pentenyl] Acetal (4b-E): Yield
TM
ꢃ
1
pillary column [SPB -OCTYL] for a certain injection/detector
ꢃ
(39%), colorless liquid, bp 85–86 C (67 Pa). H NMR (300 Hz,
CDCl3) ꢀ 1.00 (t, J ¼ 7:2 Hz, 6H, CH3), 1.76 (s, 1H, CH3), 2.38
(d, J ¼ 5:7 Hz, 2H, CH2), 4.01 (m, 4H, OCH2), 4.72 (t, J ¼ 5:7
Hz, 1H, CH), 4.78 (s, 1H, CH2=), 4.81 (s, 1H, CH2=), 5.65 (m,
4H, CH=CH). 13C NMR (75 MHz, CDCl3) ꢀ 13.2, 23.0, 25.2,
41.8, 66.1, 100.5, 112.8, 125.0, 136.1, 141.3.
ꢃ
ꢃ
temperature (250 C), column temperature (50–230 C, 4 C/
min), and He pressure (200 kPa).
1
H NMR spectra were recorded on a JEOL JNM-AL300 (300
MHz) spectrometer and 13C NMR spectra were recorded with a
JEOL JNM-AL300 (75 MHz) spectrometer. The chemical shifts
were expressed in parts per million downfield from tetramethylsi-
lane. The IR spectra were recorded on an FT-IR HORIBA 200
spectrophotometer. Elemental analyses were performed by the
Service Center of the Elementary Analysis of Organic Compounds,
Faculty of Science, Kyushu University. GC-MS analyses were per-
formed on a Shimadzu GCMS-QP5050A system equipped with an
electron ionization detector using a 60 m ꢂ 0.25 mm i.d. capillary
3-Methyl-3-butenal Dibenzyl Acetal (4c): Yield (50%), yel-
ꢃ
1
low oil, bp 115–117 C (27 Pa). H NMR (300 MHz, CDCl3) ꢀ
1.14 (t, J ¼ 7:5 Hz, 6H, CH3), 1.79 (s, 3H, CH3), 2.23 (q, 4H,
CH2), 2.41 (d, J ¼ 5:7 Hz, 2H, CH2), 4.24 (s, 4H, OCH2), 4.83
(s, 1H, CH2=), 4.90 (t, J ¼ 5:7 Hz, 1H, CH), 7.28–7.37 (m,
ArH, 10H). 13C NMR (75 MHz, CDCl3) ꢀ 23.0, 41.6, 67.1,
100.8, 113.2, 127.5, 127.7, 128.3, 138.1, 141.0.
TM
column [SPB -OCTYL] under the conditions of an injection tem-
3-Methyl-3-butenal Difurfuryl Acetal (4d): Yield (36%),
ꢃ
ꢃ
ꢃ
1
perature of 280 C, a detector temperature of 280 C, a column
yellow oil, bp 108–110 C (37 Pa). H NMR (300 Hz, CDCl3) ꢀ
1.77 (s, 3H, CH3), 2.34 (d, J ¼ 5:9 Hz, 2H, CH2), 3.43 (m, 2H,
CH2), 3.68 (m, 2H, CH2), 4.63 (t, J ¼ 5:9 Hz, 1H, CH), 4.79 (s,
1H, CH2=), 4.81 (s, 1H, CH2=), 6.17 (dd, J ¼ 1:9, 1.5 Hz, 2H,
ArH), 6.35 (dd, J ¼ 0:9, 1.9 Hz, 2H, ArH), 7.41 (dd, J ¼ 1:5,
ꢃ
ꢃ
temperature of 70–230 C, 4 C/min and He pressure of 200
kPa. HRMS analyses were performed on a JMS-HX110A-type
MS system.
Material. All reagents were obtained from commercial sources
and used as received. Benzene, benzonitrile, acetonitrile, anisole,
N,N-dimethylformamide (DMF), toluene, hexane, 3-methyl-2-but-
en-1-ol were distilled. Tetrahydrofuran (THF) was distilled from
sodium diphenylketyl. Chloroform and dichloromethane were dis-
tilled from P2O5.
13
0.9 Hz, 2H, ArH). C NMR (75 MHz, CDCl3) ꢀ 22.7, 41.4,
59.0, 100.2, 109.1, 110.2, 113.0, 140.8, 142.7, 151.6. IR (neat)
1147 (C–O), 2919 (C–H), 3122 cm 1 (C–H). Anal. Calcd for
C15H18O4: C, 68.68; H, 6.92%. Found: C 68.42; H 6.85%.
3-Methyl-3-butenal Bis(3-furylmethyl) Acetal (4e): Yield
ꢁ
-Methyl-3-butenal Diethyl Acetal (1).9 The synthesis of 3-
(62%), yellow oil, bp 102–103 C (37 Pa). 1H NMR (300 Hz,
CDCl3) ꢀ 1.75 (s, 3H, CH3), 2.44 (d, J ¼ 5:7 Hz, 2H, CH2),
4.49 (m, 4H, CH2), 4.80 (t, J ¼ 5:7 Hz, 1H, CH), 4.83 (m, 2H,
CH2), 6.40 (s, 2H, ArH), 7.40 (s, 1H, ArH). 13C NMR (75 MHz,
CDCl3) ꢀ 22.9, 41.6, 58.6, 100.3, 110.2, 113.2, 122.2, 140.5,
ꢃ
3
methyl-3-butenal diethyl acetal was based on the literature. Yield
9
ꢃ
3
1
(
44%), colorless liquid, bp 75–76 C (2:7 ꢂ 10 Pa). H NMR (300
Hz, CDCl3) ꢀ 1.20 (t, J ¼ 4:0 Hz, 3H, CH3), 1.77 (s, 3H, CH3),
2
3
(
.28 (d, J ¼ 5:85 Hz, 2H, CH2), 2.34 (d, J ¼ 5:7, 2H, CH2),
.43 (m, 2H, CH2), 3.68 (m, 2H, CH2), 4.81 (s, 1H, CH2=), 4.79
ꢁ
1
141.0, 143.3. IR (neat) 1106 (C–O), 2871 (C–H), 3122 cm
(C–H).
1
3
s, 1H, CH2=), 4.63 (t, J ¼ 5:9 Hz, 1H, CH). C NMR (75 Hz,
CDCl3) ꢀ 15.2, 23.0, 41.8, 60.9, 101.8, 112.7, 141.5. IR (neat):
3-Methyl-3-butenal Bis(4-methoxybenzyl) Acetal (4f): Yield
1
ꢁ1
1
050, 1133 (C–O), 1650 cm
Preparation of Various Acetals (4). 3-Methyl-3-butenal di-
.
(78%), colorless oil. H NMR (300 MHz, CDCl3) ꢀ 1.74 (s, 3H,
CH3), 2.47 (d, J ¼ 5:7 Hz, 2H, CH2CH), 3.80 (s, 3H, OCH3),
4.50 (d, J ¼ 11:4 Hz, 2H, OCH2), 4.60 (d, J ¼ 10:8 Hz, 2H,
OCH2), 4.80 (m, 1H, CH2=), 4.83 (m, 1H, CH2=), 4.85 (t, J ¼
ethyl acetal, alcohols (3 molar amounts), (NH4)2SO4 (0.044 mol.
amt.), and toluene were placed in a 50 mL flask. The flask was con-
nected to a packed fractionating column, and the solution was stir-
red at a stated temperature for a stated time. The mixture was then
stirred at a stated temperature for a stated time under reduced pres-
sure to remove ethanol. At last, it was distilled under reduced pres-
sure until an azeotropic mixture of toluene and ethanol was com-
pletely removed. The reaction mixture was washed with H2O (20
mL ꢂ 2) and saturated aqueous NaCl. A water layer was extracted
1
3
5:9 Hz, 1H, CH), 6.87 (m, 4H, ArH), 7.26 (m, 4H, ArH). C NMR
(75 MHz, CDCl3) ꢀ 23.1, 41.9, 55.0, 66.9, 71.5, 100.7, 113.1,
113.8, 129.3, 130.4, 141.3, 159.3.
3-Methyl-3-butenal Bis(4-methylbenzyl) Acetal (4g): Yield
(82%), yellow oil. 1H NMR (300 MHz, CDCl3) ꢀ 1.74 (s, 3H,
CH3), 2.31 (s, 3H, ArCH3), 2.48 (d, J ¼ 2:9 Hz, 2H, CH2), 4.51
(d, J ¼ 5:9 Hz, 2H, OCH2), 4.61 (d, J ¼ 5:9 Hz, 2H, OCH2),

K. Nakabayashi et al.
Bull. Chem. Soc. Jpn., 77, No. 1 (2004)
163
4
.82 (s, 1H, CH2=), 4.86 (s, 1H, CH2=), 4.86 (t, J ¼ 2:9 Hz, 1H,
catalyst in the solvent were placed in a glass tube (6 mm ꢂ 13 cm).
The sealed tube was stirred at the stated temperature for the stated
time. After the reaction, the sealed tube was cooled in an ice bath.
The mixture was analyzed by the GC-8A and GC-14B system. The
products in Tables 1–5 were analyzed by GC-8A system.
CH), 7.11 (d, J ¼ 3:9 Hz, 5H, ArH), 7.21 (d, J ¼ 3:9 Hz, 5H,
1
3
ArH). C NMR (75 MHz, CDCl3) ꢀ 20.1, 22.9, 41.6, 66.9,
00.6, 113.0, 127.8, 128.9, 135.1, 137.0, 141.0.
-Methyl-3-butenal Bis(4-fluorobenzyl) Acetal (4h): Yield
1
3
1
(
77%), yellow oil. H NMR (300 MHz, CDCl3) ꢀ 1.68 (s, 3H,
CH3), 2.41 (d, J ¼ 2:9 Hz, 2H, CH2CH), 4.44 (d, J ¼ 5:9 Hz,
H, OCH2), 4.55 (d, J ¼ 5:9 Hz, 2H, OCH2), 4.74 (s, 1H,
General Procedure for the Reaction of 3-Methyl-3-butenal
Bis(3-methyl-2-butenyl) Acetal in the Presence of Lewis Acid.
Method A: To a solution of 3-methyl-3-butenal bis(3-methyl-
2-butenyl) acetal in a solvent, a Lewis acid was slowly added.
The mixture was stirred for a stated time and at a stated tempera-
ture under an Ar atmosphere. The reaction mixture was quenched
2
CH2=), 4.78 (s, 1H, CH2=), 4.80 (t, J ¼ 5:9 Hz, 1H, CH), 7.16–
1
3
7.29 (m, 10H, ArH). C NMR (75 MHz, CDCl3) ꢀ 23.0, 31.6,
66.5, 100.9, 113.3, 115.1, 115.4, 129.4, 129.5, 133.8, 133.9,
140.9, 160.7, 163.9.
by the addition of 2 M (1 M = 1 mol dm 3) aq. NaOH and extract-
ed. The organic layer was washed with water and dried over anhy-
drous Na2SO4. The resultant residue was analyzed by GC.
Method B: To the solution of a Lewis acid in the solvent, 3-
methyl-3-butenal bis(3-methyl-2-butenyl) acetal was added slow-
ly. The mixture was stirred for a stated time and at a stated temper-
ature under an Ar atmosphere. The reaction mixture was quenched
by the addition of 2 M aq. NaOH and extracted. The organic layer
was washed with water and dried over anhydrous Na2SO4. The re-
sultant residue was analyzed by GC.
ꢁ
3-Methyl-3-butenal Diphenethyl Acetal (4i): Yield (77%),
1
colorless oil. H NMR (300 MHz, CDCl3) ꢀ 1.69 (s, 3H, CH3),
.32 (d, J ¼ 5:7 Hz, 2H, CH2CH), 2.82 (t, J ¼ 7:2 Hz, 4H,
2
CH2Ph), 3.61 (t, J ¼ 7:2 Hz, 2H, OCH2), 3.71 (m, J ¼ 7:2 Hz,
2
4
H, OCH2), 4.61 (t, J ¼ 5:7 Hz, 1H, CH), 4.75 (s, 1H, CH2=),
13
.79 (s, 1H, CH2=), 7.16–7.29 (m, 10H, ArH). C NMR (75
MHz, CDCl3) ꢀ 23.0, 36.4, 41.7, 66.3, 102.1, 112.8, 126.1,
28.2, 128.9, 139.0, 141.3, 141.4.
-Methyl-3-butenal Bis(3-methyl-3-butenyl) Acetal (4j):
1
3
ꢃ
1
Yield (18%), colorless liquid, bp 70–72 C (13.3 Pa). H NMR
General Procedure for the Reaction of Various Acetals (3a–
h). A solution of an acetal (0.63 mmol) and trifluoroacetic acid
(
(
300 MHz, CDCl3) ꢀ 1.75 (s, 6H, CH3), 1.76 (s, 3H, CH3), 2.29
t, J ¼ 6:6 Hz, 4H, CH2), 2.36 (d, J ¼ 5:7 Hz, 2H, CH2), 4.66 (t,
ꢁ
4
(7:9 ꢂ 10 mmol) in benzene or mesitylene (1 mL) was placed
in a glass tube (6 mm ꢂ 13 cm). The sealed tube was stirred at
J ¼ 5:7 Hz, 1H, CH), 4.73 (s, 1H, CH2=), 4.78 (s, 1H, CH2=),
1
3
ꢃ
4
.78 (s, 1H, CH2=), 4.81 (s, 1H, CH2=). C NMR (75 MHz,
CDCl3) ꢀ 22.7, 23.0, 37.8, 41.6, 63.7, 101.9, 111.4, 112.8, 141.4,
42.8.
-Methyl-3-butenal Dipentyl Acetal (4k): Yield (48%), col-
190 C for the stated time. After the reaction, the sealed tube
was cooled in an ice bath. The mixture was concentrated and sep-
arated by column chromatography on silica gel with a mixed sol-
vent.
1
3
ꢃ
1
orless liquid, bp 61–63 C (60 Pa). H NMR (300 MHz, CDCl3) ꢀ
.89 (t, J ¼ 7:2 Hz, 6H, CH3), 1.33 (m, 8H, CH2), 1.55 (m, 4H,
CH2), 1.77 (s, 3H, CH3), 2.34 (d, J ¼ 5:7 Hz, 2H, CH2), 3.42
Citral (3a): Yield (43%), yellow oil. (E)-3,7-dimethyl-2,6-oc-
1
0
tadienal: H NMR (300 MHz, CDCl3) ꢀ 1.59 (s, 3H, CH3), 1.68 (s,
3H, CH3), 2.17 (d, J ¼ 1:0 Hz, 3H, CH3), 2.21–2.24 (m, 4H, CH2),
5.04–5.13 (m, 1H, (CH3)2=CH), 5.87 (dd, J ¼ 8:0, 1.0 Hz, 1H,
CH), 9.99 (d, J ¼ 8:0 Hz, 1H, CHO). (Z)-3,7-Dimethyl-2,6-octa-
(
m, 2H, OCH2), 3.58 (m, 2H, OCH2), 4.60 (t, J ¼ 5:7 Hz, 1H,
13
CH), 4.77 (s, 1H, CH2=), 4.80 (s, 1H, CH2=). C NMR (75
1
MHz, CDCl3) ꢀ 14.0, 22.5, 23.1, 28.4, 29.5, 41.8, 65.6, 102.1,
dienal: H NMR (300 MHz, CDCl3) ꢀ 1.61 (s, 3H, CH3), 1.68 (s,
1
12.6, 141.6. Anal. Calcd for C15H30O2: C, 74.32; H, 12.47%.
Found C, 74.23; H, 12.43%.
-Methyl-3-butenal Bis(tetrahydrofurfuryl) Acetal (4l):
3H, CH3), 1.98 (d, J ¼ 1:2 Hz, 3H, CH3), 2.17–2.24 (m, 2H,
CH2), 2.58 (t, J ¼ 7:8 Hz, 2H, CH2), 5.04–5.13 (m, 1H,
(CH3)2=CH), 5.87 (dd, J ¼ 8:0, 1.0 Hz, 1H, CH), 9.89 (d, J ¼
8:0 Hz, 1H, CHO).
3
ꢃ
1
Yield (78%), yellow oil, bp 120–122 C (53 Pa). H NMR (300
Hz, CDCl3) ꢀ 1.63 (m, 2H, CH2) 1.77 (s, 3H, CH3) 1.90 (m, 5H,
CH2), 2.38 (m, 2H, CH2), 3.50 (m, 2H, OCH2), 3.75 (m, 4H,
OCH2), 4.07 (m, 2H, CH), 4.75 (m, 2H, CH2=). 13C NMR (75
MHz, CDCl3) ꢀ 22.9, 25.5, 25.6, 28.1, 28.2, 41.3, 41.4, 67.6,
(6E)-3-Methyl-2,6-nonadienal (3b): Yield (54 and 79%), col-
1
orless oil. (2E; 6E)-3-Methyl-2,6-nonadienal: H NMR (300 MHz,
CDCl3) ꢀ 0.95 (t, J ¼ 7:2 Hz, 3H, CH3), 1.99 (m, 2H, CH2), 2.16
(d, J ¼ 0:9 Hz, 3H, CH3), 2.19–2.30 (m, 4H, CH2), 5.30–5.55 (m,
2H, –CH=CH–), 5.88 (dd, J ¼ 8:1, 0.9 Hz, 1H, CH), 9.99 (d, J ¼
6
1
8.1, 68.2, 77.7, 77.8, 101.9, 102.1, 102.2, 112.8, 141.2. IR (neat)
130 (C–O), 2927 (C–H), 3078 cm (C–H). Anal. Calcd for
ꢁ1
1
8:1 Hz, 1H, CHO). (2Z,6E)-3-Methyl-2,6-nonadienal: H NMR
C15H24O4: C, 66.64; H, 9.69%. Found: C, 66.26; H, 9.63%.
-Methyl-3-butenal Di(2-pentynyl) Acetal (4m):
(
(300 MHz, CDCl3) ꢀ 0.95 (t, J ¼ 7:2 Hz, 3H, CH3), 1.97 (d, J ¼
0:9 Hz, 3H, CH3), 1.99 (m, 2H, CH2), 2.25 (m, 2H, CH2), 2.62 (t,
J ¼ 7:3 Hz, 2H, CH2), 5.31–5.55 (m, 2H, –CH=CH–), 5.88 (dd,
J ¼ 8:1, 0.9 Hz, 1H, CH), 9.91 (d, J ¼ 8:1 Hz, 1H, CHO).
3
Yield
50%), colorless oil, bp 95–96 C (47 Pa). H NMR (300 MHz,
CDCl3) ꢀ 1.76 (s, 3H, CH3), 2.23 (q, J ¼ 7:5 Hz, 4H, CH2),
.14 (d, J ¼ 5:7 Hz, 2H, CH2), 4.24 (s, 4H, CH2), 4.83 (s, 2H,
ꢃ
1
1
3
2
C NMR (75 MHz, CDCl3) ꢀ 13.6, 13.7, 17.5, 25.0, 25.4, 25.5,
1
3
CH2=), 4.97 (t, J ¼ 5:7 Hz, 1H, CH). C NMR (75 MHz, CDCl3)
30.0, 31.4, 32.6, 40.5, 126.7, 127.0, 127.4, 128.5, 133.4, 134.1,
163.6, 163.7, 190.9, 191.3. IR (neat) 970, 1673 cm (C=O).
ꢁ1
ꢀ
12.4, 13.7, 22.8, 41.6, 53.8, 75.1, 88.0, 99.6, 113.1, 140.8.
Effect of Catalysts on the Synthesis of Citral. 3-Methyl-3-bu-
HRMS (EI) Found: m=z 151.1129. Calcd for C10H16O [M ꢁ
þ
tenal diethyl acetal, 3-methyl-2-buten-1-ol, and a catalyst solution
in mesitylene (1 mL) were placed in a glass tube (6 mm ꢁ ꢂ 8 cm).
1] : 151.1123.
3-Methyl-5-phenyl-2-pentenal (3c): Yield (46%), yellow oil.
ꢃ
1
The sealed tube was stirred at 150–230 C for 0.5–4 h. After the
(E)-3-Methyl-5-phenyl-2-pentenal: H NMR (300 MHz, CDCl3) ꢀ
reaction, the sealed tube was cooled in an ice bath. The reaction
mixture was analyzed by GC using biphenyl as an internal stand-
ard. These results are listed in Table 1.
General Procedure for the Reaction of 3-Methyl-3-butenal
Bis(3-methyl-2-butenyl) Acetal. 3-Methyl-3-buenal bis(3-meth-
yl-2-butenyl) acetal (0.150 g, 0.63 mmol) and a solution of the acid
2.00 (s, 3H, CH3), 2.52 (m, 2H, CH2), 2.85 (m, 2H, CH2), 5.89 (d,
J ¼ 7:8 Hz, 1H, CH), 7.15–7.31 (m, 5H, ArH), 9.99 (d, J ¼ 7:8
1
Hz, 1H, CHO). (Z)-3-Methyl-5-phenyl-2-pentenal: H NMR (300
MHz, CDCl3) ꢀ 1.96 (s, 3H, CH3), 2.82 (m, 2H, CH2), 2.85 (m,
2H, CH2), 5.88 (d, J ¼ 7:8 Hz, 1H, CH), 7.15–7.31 (m, 5H,
1
3
ArH), 9.71 (d, J ¼ 7:8, 1.5 Hz, 1H, CHO). C NMR (75 MHz,

1
64 Bull. Chem. Soc. Jpn., 77, No. 1 (2004)
Synthesis and Rearrangement of Allyl Acetals
CDCl3) ꢀ 17.7, 25.0, 33.5, 34.6, 34.9, 42.1, 126.2, 126.5, 127.6,
6.98 (m, 2H, ArH), 7.13 (m, 2H, ArH), 9.99 (d, J ¼ 3:9 Hz, 1H,
1
1
1
28.2, 128.3, 128.5, 128.6, 128.8, 140.1, 140.5, 162.6, 162.8,
90.4, 191.1. IR (neat) 702, 746, 1670 (C=O), 3027 cm . HRMS
CHO). (Z)-5-(4-Fluorophenyl)-3-methyl-2-pentenal:
H NMR
ꢁ1
(300 MHz, CDCl3) ꢀ 2.00 (d, J ¼ 0:8 Hz, 3H, CH3), 2.80 (m,
2H, CH2), 2.84 (m, 2H, ArCH2), 5.88 (dd, J ¼ 8:3, 0.5 Hz, 1H,
CH), 6.98 (m, 2H, ArH), 7.13 (m, 2H, ArH), 9.71 (d, J ¼ 4:1
þ
(
1
EI) Found: m=z 173.0998. Calcd for C12H14O [M ꢁ 1] :
73.0966.
-(2-Furyl)-3-methyl-2-pentenal (3d): Yield (59%), yellow
1
3
5
Hz, 1H, CHO). C NMR (75 MHz, CDCl3) ꢀ 17.1, 25.1, 32.6,
34.1, 34.6, 42.2, 115.1, 115.2, 115.4, 115.5, 127.6, 128.8, 129.5,
129.6, 129.7, 129.8, 136.1, 136.1, 159.8, 162.4, 162.6, 163.0,
190.4, 191.2.
1
oil. (E)-5-(2-Furyl)-3-methyl-2-pentenal: H NMR (300 MHz,
CDCl3) ꢀ 2.18 (d, J ¼ 1:2 Hz, 3H, CH3) 2.80–2.95 (m, 4H,
CH2), 5.88 (m, 1H, CH), 6.01 (dd, J ¼ 3:3, 0.9 Hz, 1H, ArH),
6
1
.24 (dd, J ¼ 3:3, 1.8 Hz, 1H, ArH), 7.04 (dd, J ¼ 1:8, 0.9 Hz,
3-Methyl-1-phenethyloxy-1,3-butadiene (5a): Yield (23%).
1
H, ArH), 9.99 (d, J ¼ 7:2 Hz, 1H, CHO). (Z)-5-(2-Furyl)-3-meth-
yellow oil. (E)-3-Methyl-1-phenethyloxy-1,3-butadiene: H NMR
1
yl-2-pentenal: H NMR (300 MHz, CDCl3) ꢀ 1.97 (d, J ¼ 1:2 Hz,
(300 MHz, CDCl3) ꢀ 1.79 (s, 3H, CH3), 2.98 (t, J ¼ 7:2 Hz, 2H,
CH2), 3.96 (t, J ¼ 7:2 Hz, 2H, OCH2), 5.67 (d, J ¼ 12:9 Hz,
1H, vinyl H), 6.52 (d, J ¼ 12:9 Hz, 1H, vinyl H), 7.20–7.33 (m,
3
H, CH3) 2.56 (t, J ¼ 9:0 Hz, 2H, CH2), 2.86 (t, J ¼ 9:0 Hz, 2H,
CH2), 5.88 (m, 1H, CH), 6.01 (dd, J ¼ 3:3, 0.9 Hz, 1H, ArH), 6.24
dd, J ¼ 3:3, 1.8 Hz, 1H, ArH), 7.04 (dd, J ¼ 1:8, 0.9 Hz, 1H,
1
(
5H, ArH). (Z)-3-Methyl-1-phenethyloxy-1,3-butadiene: H NMR
1
3
ArH), 9.76 (d, J ¼ 8:4 Hz, 1H, CHO). C NMR (75 MHz, CDCl3)
(300 MHz, CDCl3) ꢀ 1.79 (s, 3H, CH3), 2.98 (t, J ¼ 7:2 Hz, 2H,
CH2), 3.96 (t, J ¼ 7:2 Hz, 2H, OCH2), 4.82 (d, J ¼ 7:2 Hz, 1H, vi-
nyl H), 5.93 (d, J ¼ 7:2 Hz, 1H, vinyl H), 7.20–7.33 (m, 5H, ArH).
ꢀ
1
1
7
17.5, 24.7, 25.7, 26.9, 31.2, 38.7, 105.5, 106.1, 110.2, 127.6,
29.1, 141.2, 141.4, 153.5, 154.0, 162.2, 190.5, 191.1. IR (neat)
670 cm 1 (C=O). Anal. Calcd for C10H12O2: C, 73.15; H,
ꢁ
3-Methyl-1-(3-methyl-3-butenyloxy)-1,3-butadiene
(5b):
.37%. Found: C, 72.18; H, 7.26%.
Yield (14%), colorless liquid. (E)-3-Methyl-1-(3-methyl-3-buten-
1
5
-(3-Furyl)-3-methyl-2-pentenal (3e): Yield (50%), yellow
1
yloxy)-1,3-butadiene: H NMR (300 MHz, CDCl3) ꢀ 1.77 (s, 3H,
oil. (E)-5-(3-Furyl)-3-methyl-2-pentenal: H NMR (300 MHz,
CDCl3) ꢀ 2.19 (d, J ¼ 1:2 Hz, 3H, CH3) 2.66 (t, J ¼ 7:5 Hz,
CH3), 1.81 (s, 3H, CH3), 2.38 (t, J ¼ 7:2 Hz, 2H, CH2), 3.86 (t,
J ¼ 6:6 Hz, 2H, OCH2), 4.68 (s, 1H, CH2=), 4.76 (s, 1H,
CH2=), 4.76 (s, 1H, CH2=), 4.82 (s, 1H, CH2=), 5.68 (d, J ¼
13:2 Hz, 1H, vinyl H), 6.54 (d, J ¼ 13:2 Hz, 1H, vinyl H).
2
6
1
H, CH2), 2.81 (t, J ¼ 7:5 Hz, 2H, CH2), 5.89 (m, 1H, CH),
.27 (s, 1H, ArH), 7.20–7.40 (m, 2H, ArH), 10.0 (d, J ¼ 7:8 Hz,
1
13
H, CHO). (Z)-5-(3-Furyl)-3-methyl-2-pentenal: H NMR (300
C NMR (75 MHz, CDCl3) ꢀ 22.6, 37.2, 67.9, 109.2, 111.5,
MHz, CDCl3) ꢀ 2.00 (d, J ¼ 1:5 Hz, 3H, CH3) 2.48 (t, J ¼ 7:4
Hz, 2H, CH2), 2.68 (t, J ¼ 7:1 Hz, 2H, CH2), 5.89 (m, 1H, CH),
112.0, 139.7, 142.0, 147.9.
3-Methyl-1-(tetrahydrofurfuryloxy)-1,3-butadiene
(5d):
Yield (36%), yellow oil. (E)-3-Methyl-1-(tetrahydrofurfuryloxy)-
6
1
3
1
.27 (s, 1H, ArH), 7.20–7.40 (m, 2H, ArH), 9.82 (d, J ¼ 8:1 Hz,
1
3
1
H, CHO). C NMR (75 MHz, CDCl3) ꢀ 17.5, 22.5, 23.9, 24.8,
3.1, 40.6, 110.6, 123.1, 123.4, 127.6, 128.8, 138.9, 139.1,
42.9, 143.1, 162.6, 190.4, 191.1.
1,3-butadiene: H NMR (300 MHz, CDCl3) ꢀ 1.81 (s, 3H, CH3)
1.85–2.05 (m, 4H, CH2), 3.70–3.94 (m, 4H, ArH), 4.06–4.18 (m,
1H, OCH), 4.73 (m, 2H, CH2), 5.68 (d, J ¼ 12:8 Hz, 1H,
5-(4-Methoxyphenyl)-3-methyl-2-pentenal (3f): Yield (6%),
yellow oil. (E)-5-(4-Methoxyphenyl)-3-methyl-2-pentenal:
CH=CH), 6.57 (d, J ¼ 12:8 Hz, 1H, CH=CH). (Z)-3-Methyl-1-
1
(tetrahydrofurfuryloxy)-1,3-butadiene:
H NMR (300 MHz,
1
H NMR (300 MHz, CDCl3) ꢀ 2.19 (d, J ¼ 0:6 Hz, 3H, CH3),
CDCl3) ꢀ 1.81 (s, 3H, CH3) 1.85–2.05 (m, 4H, CH2), 3.70–3.94
(m, 4H, ArH), 4.06–4.18 (m, 1H, OCH), 4.73 (m, 2H, CH2),
4.82 (d, J ¼ 7:1 Hz, 1H, CH=CH), 5.98 (d, J ¼ 7:1 Hz, 1H,
2
5
.49 (m, 2H, CH2), 2.81 (m, 2H, ArCH2), 3.79 (s, 3H, OCH3),
.88 (m, 1H, CH), 6.83 (m, 2H, ArH), 7.09 (m, 4H, ArH), 9.99
ꢁ1
(
d, J ¼ 4:1 Hz, 1H, CHO). (Z)-5-(4-Methylphenyl)-3-methyl-2-
CH=CH). IR (neat) 1128 (C–H), 2872 cm (C–H).
1
pentenal: H NMR (300 MHz, CDCl3) ꢀ 2.00 (d, J ¼ 0:6 Hz,
H, CH3), 2.78 (m, 2H, CH2), 2.81 (m, 2H, ArCH2), 3.79 (s, 3H,
3
References
OCH3), 5.88 (m, 1H, CH), 6.83 (m, 4H, ArH), 7.09 (m, 4H,
ArH), 9.72 (d, J ¼ 4:1 Hz, 1H, CHO). 13C NMR (75 MHz, CDCl3)
1
I. N. Nazarov and Z. A. Krasnaya, J. Gen. Chem. USSR, 28,
ꢀ
1
17.7, 25.1, 32.7, 34.1, 34.9, 42.5, 55.2, 113.9, 127.6, 128.8,
29.2, 129.3, 132.6, 158.0, 163.0, 163.1, 190.6, 191.3.
2477 (1958); Z. A. Krasnaya and V. F. Kucherov, J. Gen. Chem.
USSR, 30, 3875 (1960).
5-(4-Methylphenyl)-3-methyl-2-pentenal (3g): Yield (27%),
1
yellow oil. (E)-5-(4-Methylphenyl)-3-methyl-2-pentenal: H NMR
2
3
K. V. Leets, J. Gen. Chem. USSR, 28, 1868 (1958).
S. Suzuki, Y. Fujita, and T. Nishida, Tetrahedron Lett., 24,
(
300 MHz, CDCl3) ꢀ 2.19 (d, J ¼ 0:6 Hz, 3H, CH3), 2.32 (s, 3H,
5737 (1983).
ArCH3), 2.51 (m, 2H, CH2), 2.83 (m, 2H, ArCH2), 5.89 (dd,
J ¼ 8:3, 0.8 Hz, 1H, CH), 7.07 (m, 4H, ArH), 9.99 (d, J ¼ 4:1
Hz, 1H, CHO). (Z)-5-(4-Methylphenyl)-3-methyl-2-pentenal:
4 G. Indo, ‘‘Synthetic Fragrances,’’ The Chemical Daily, Co.,
Ltd (1996), pp. 232–235.
5 H. Matsuda, M. Okahara, and M. Nomura, ‘‘Organic Indus-
trial Chemistry,’’ Maruzen, Tokyo (1996), pp. 177–183.
6 C. Pierre and K. Emile, U. S. Patent 4463196 (1987); Chem.
Abstr., 87, 136056 (1977).
7 Y. Ichikawa, T. Yamaji, and M. Yamamoto, Japan Patent
59310 (1975); Chem. Abstr., 83, 59112e (1975).
1
H NMR (300 MHz, CDCl3) ꢀ 2.00 (d, J ¼ 0:6 Hz, 3H, CH3),
2
5
.32 (s, 3H, ArCH3), 2.78 (m, 2H, CH2), 2.83 (m, 2H, ArCH2),
.89 (dd, J ¼ 9:9, 0.6 Hz, 1H, CH), 7.07 (m, 4H, ArH), 9.72 (d,
1
3
J ¼ 4:1 Hz, 1H, CHO). C NMR (75 MHz, CDCl3) ꢀ 17.7,
2
1
1.0, 25.1, 33.1, 34.5, 34.7, 42.4, 127.6, 128.1, 128.2, 128.8,
29.2, 129.3, 135.8, 137.4, 163.1, 190.6, 191.3.
8
Vani et al. reported synthesis of citral from 3-methyl-2-
5
-(4-Fluorophenyl)-3-methyl-2-pentenal (3h): Yield (44%),
butenal, see: P. V. S. N. Vani, A. S. Chida, R. Srinivasan, M.
Chandraasekharam, and A. K. Singh, Synth. Commun., 31, 219
(2001).
1
yellow oil. (E)-5-(4-Fluorophenyl)-3-methyl-2-pentenal: H NMR
300 MHz, CDCl3) ꢀ 2.19 (d, J ¼ 0:6 Hz, 3H, CH3), 2.50 (m, 2H,
CH2), 2.84 (m, 2H, ArCH2), 5.88 (dd, J ¼ 8:3, 0.5 Hz, 1H, CH),
(
9
J. W. Cornforth and M. E. Firth, J. Chem. Soc., 1958, 1091.