A convenient method for the preparation of α-vinylfurans by phosphine-initiated reactions of various substituted enynes bearing a carbonyl group with aldehydes

Article abstract of DOI:10.1016/j.tet.2003.12.034

α-Vinylfurans were obtained by phosphine-initiated cyclization of various enynes bearing a carbonyl group at the ene end in the presence of various aldehydes, in moderate to high yields. The reaction may consist of 1,6-addition of phosphine to the enynes, ring closure, and Wittig reaction between the ylid resulting from cyclization and an aldehyde. Thus, various aldehydes were able to be used in the reaction. The reaction was influenced greatly by the substituents at the acetylene position (R¹) and the α-position of the carbonyl group (R³).

Full text of DOI:10.1016/j.tet.2003.12.034

Tetrahedron 60 (2004) 1913–1920
A convenient method for the preparation of a-vinylfurans by
phosphine-initiated reactions of various substituted enynes
bearing a carbonyl group with aldehydes
*
Hirofumi Kuroda, Emi Hanaki, Hironori Izawa, Michiko Kano and Hiromi Itahashi
Department of Chemical and Biochemical Engineering, Toyama National College of Technology, 13 Hongo-machi, Toyama-shi,
Toyama 939-8630, Japan
Received 14 July 2003; accepted 9 December 2003
Abstract—a-Vinylfurans were obtained by phosphine-initiated cyclization of various enynes bearing a carbonyl group at the ene end in the
presence of various aldehydes, in moderate to high yields. The reaction may consist of 1,6-addition of phosphine to the enynes, ring closure,
and Wittig reaction between the ylid resulting from cyclization and an aldehyde. Thus, various aldehydes were able to be used in the reaction.
The reaction was influenced greatly by the substituents at the acetylene position (R1) and the a-position of the carbonyl group (R3).
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
polyenes.12 Trost et al. have reported phosphine-catalyzed
cyclization of v-hydroxylynoates to the corresponding
tetrahydrofuran or tetrahydropyran derivatives.13 Herein,
we wish to describe in detail the preparation of multi-
substituted enynes (1A–C) and phosphine-initiated furan
ring construction with a vinyl group at the a-position, by
reaction of the various enynes (1) in the presence of various
aldehydes (Scheme 1).
The development of cyclization reactions is of vital
importance in organic chemistry, so that the cyclic systems
found in naturally occurring products can be constructed. A
number of cyclic systems containing one oxygen atom are
present in nature (e.g., hydrofuran, furan, pyran ring). Furan
rings, one example of five-membered heterocycles, are
found in a lot of naturally occurring products.1 The furan
ring is not only present as key structural units in naturally
occurring products, but is also important in the pharma-
ceutical industry.2 Therefore, there has been interest in the
synthesis of polysubstituted furans, and a number of useful
synthetic methods for furans have been reported, by many
synthetic chemists.3 The Paal–Knorr method,4 the Feist–
Benary method,5 etc. are known as long-standing methods
for furan ring construction. Conjugated enynols are useful
and important key intermediates for direct furan ring
construction.6 In our previous communication,7 we
described a novel synthetic method for the preparation of
a-vinylfurans in high yields by a phosphine-initiated
reaction of the simple 2-penten-4-yn-1-one system with
benzaldehyde in dichloromethane. Kim et al. have reported
furan ring construction by reaction of alkynic acetal,
aldehyde and phosphine.8 Trialkylphosphines are mild,
useful reagents in various organic reactions,9 including the
addition of alcohols to acetylenes having electron-with-
drawing groups,10 isomerization of ynones, ynoates, and
ynamides to the corresponding (2E, 3E)-diene11 and
Scheme 1.
2. Results and discussions
2.1. Preparation of various enynes (1)
The synthesis of enynes (1Aa–1Ad; R2¼R3¼H) with
disubstituted olefinic moieties was carried out by the
reaction of ynals (3) with Wittig reagent (4) (Y. 69–82%)
(Eq. 1 in Scheme 2). The enynes (1Ba and 1Bb; R3¼H) with
Keywords: Cyclization; Vinyl furans; Enynes; Phosphine; Wittig reaction.
*
Corresponding author. Tel./fax: þ81-76-493-5464;
e-mail address: kuroda@toyama-nct.ac.jp
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2003.12.034

1914
H. Kuroda et al. / Tetrahedron 60 (2004) 1913–1920
Scheme 2.
trisubstituted olefinic moieties were prepared by the
procedure reported by Trost et al. from terminal alkynes
(5) and ynones (6), in 87 and 40% yields, respectively (Eq. 2
in Scheme 2).14 The enynes (1Ca and 1Cb; R2¼H) with
trisubstituted olefinic moieties were synthesized in two
steps by acidic aldol reaction of ynal (3) with silyl enol ether
(7), followed by dehydration of the aldol products in 69 and
64% yields (two steps), respectively (Eq. 3 in Scheme 2). As
mentioned above, the three types of enynes (1A–1C) were
prepared conveniently by modification of the known
methods.
observed between the olefinic proton of the vinyl group and
the proton at the allylic position in the experiment (Fig. 1).
Furthermore, the reaction was carried out in the presence of
stoichiometric amounts of triphenylphosphine or triethyl-
amine instead of tributylphosphine. Although the corre-
sponding furan (2Aa) was obtained in 73% yield after 6 h in
the presence of triphenylphosphine, in the case of
triethylamine the reaction did not proceed, and mostly
1Aa was recovered. Moreover, when the amount of
tributylphosphine was reduced to a 0.5 stoichiometric
equiv., the yield was reduced approximately by half.
These results may suggest the mechanism shown in
Scheme 3. The reaction may be initiated by 1,6-addition
of phosphine to 1, followed by cyclization to yield the ylid
(8) as an intermediate, and then Wittig reaction of 9 with an
aldehyde may take place to give the furan (2) which has a
double bond at the a-position. It is known that ylids
stabilized by an aromatic ring, such as 9, generally give an
E-isomer as the major product.15 Thus, the E-isomer might
be obtained as the major product in this reaction. The
reaction might not proceed in the presence of triethylamine
due to prevention of the generation of 9. Furthermore, the
reaction might be stoichiometric with regard to the amount
2.2. Phosphine-initiated cyclization of 1
The tributylphosphine-initiated (Bu3P; 1 equiv.) cyclization
of 1 in the presence of a stoichiometric amount of
benzaldehyde was tried by using 1Aa in CH2Cl2 for 6 h at
room temperature, to obtain a-vinylfuran (2Aa) in 83%
yield. 1Aa was almost entirely consumed within 1 h under
these conditions, as shown by GC analysis, and it was found
that the reaction proceeded very smoothly under the mild
conditions. From the NMR, IR, and MS spectra, the
compound obtained was determined to be 2Aa, containing
an a-vinyl furan skeleton. 2Aa contained a small amount of
geometrical isomer† (E:Z¼90:10) and an NOE experiment
was carried out to determine the geometry of the major
isomer in 2Aa. The geometry of the major product was
determined to be the E-isomer because no effect was
†
We were not able to separate the isomers because their physical properties
were almost identical, the products were slightly unstable at rt in air, and
the amount of minor isomer in the mixture was very small. We presumed
the minor product was a geometric isomer of the major product because
20Aa containing no double bonds was obtained as a single product in the
reaction of 1Aa with water in the presence of tributylphosphine and the
found value almost agreed with the calculated value in the elemental
analysis of the mixture of major and minor products, as described below.
Figure 1. DNOE experiment for 2Aa.

H. Kuroda et al. / Tetrahedron 60 (2004) 1913–1920
1915
Scheme 3.
of phosphine because the phosphine was converted to the
corresponding phosphine oxide as shown in the suggested
reaction mechanism. Therefore, the yield might decrease if
the amount of phosphine is reduced. To detect the formation
of the ylid (9), 1Aa in CH2Cl2 was treated with tributyl-
phosphine (1 equiv.) in the presence of water (5 equiv.)
without aldehyde. The furan (20Aa) containing no double
bonds at the a-position was then obtained as a single
product after hydrolysis16 of the ylid, in 58% yield. 20Aa
was not obtained when 1Aa was treated with tributyl-
phosphine without water and aldehyde. These results may
suggest formation of the ylid (9) in the reaction process.
6), the yield was not influenced by the type of substituent on
the double bond. In contrast to this result, the substituent R3
greatly affected the yield. In the case of R3¼alkyl group
(i.e., 1Ca), although 1Ca was almost entirely consumed, the
corresponding furan was not obtained, due to unknown side-
reactions (run 7). When the reaction was retried by using
triphenylphosphine, as a milder initiator than tributyl-
phosphine, 1Ca was almost exclusively recovered. This
result may be attributable to the stability of the enolate in the
suggested reaction mechanism. Thus, in the case of
R3¼alkyl group, the enolate might become unstable due
to the electron-donating effect of the alkyl substituent,
compared with the case of R3¼H. When 1Cb (R3¼phenyl
group) was used as substrate, the reaction proceeded
smoothly to give the corresponding furan in good yield
(run 8). The phenyl group might stabilize the enolate by the
resonance effect. These results suggest that the substituent
R3 may be important for control of the stability of the
enolate. Although all the substituents (R1–R4) in the enynes
(1) were effective for obtaining a-vinylfurans (2) as
mentioned above, the substituents were not so effective
for geometrical selectivity.‡ The a-vinylfurans (2) were
obtained regardless of the kind of substituents, with high
geometrical selectivity (runs 1, 2, 5, 6, and 8) (Table 1).
The reaction of various substituted enynes (1A–1C) was
carried out in CH2Cl2 at room temperature (Table 2). The
influence of substituents R1 and R4 was examined by using
1Aa–1Ad (runs 1–4). When R1¼alkyl groups (i.e., 1Aa
and 1Ab; runs 1 and 2), 2Aa and 2Ab were obtained in 83
and 56% yields, respectively. On the other hand, when
R1¼aromatic (i.e., 1Ac and 1Ad; runs 3 and 4), the reaction
gave a complex mixture containing only a small amount of
the corresponding furan. From these results, it was found
that the yields were markedly influenced by R1 rather than
by R4. In the cases of 1Ac and 1Ad, 8 stabilized by two
aromatic rings might be generated as the intermediate, based
on the mechanism described above. Generally, such an ylid
is too inert to react with aldehyde.17 Therefore, the
corresponding furans might not be obtained in the reactions
with 1Ac and 1Ad. Furthermore, the reaction was
investigated by using enynes (1B and 1C) with trisubstituted
olefinic moieties to examine the influence of R2 and R3 in
this reaction. In the case of enynes (1Ba and 1Bc; runs 5 and
Table 2. Synthesis of furans from 1Aa and various carbonyl compoundsa
Run
Carbonyl compounds
Yieldb/%
E:Zc
1
2
3
4
5
PhCHO
EtCHO
trans-PhCHvCHCHO
p-MeOC6H4CHO
p-MeC6H4COCH3
83
92
90
89
0
90:10
80:20
79:21
92:8
a
Table 1. Synthesis of furans from various enynes (1) and benzaldehydea
The reaction of 1 with various carbonyl compounds (1 equiv.) was carried
out at room temperature for 5 h in the presence of tributylphosphine
(1 equiv.).
Isolated yield (SiO2, ethyl acetate and hexane eluent).
Determined by 1H NMR spectroscopy (400 MHz).
Run
R1
R2
R3
R4
Yieldb/%
E:Zc
b
c
1
2
3
4
5
6
7
8
Bu
Bu
Ph
Ph
Bu
Bu
Bu
Bu
H
H
H
H
H
H
H
H
H
Et
Ph
Ph
Me
Ph
Me
Me
Me
Ph
Aa
Ab
Ac
Ad
Ba
Bb
Ca
Cb
83
56
0
90:10
.99 (E)
The reaction of 1Aa with various carbonyl compounds was
also examined on the basis of the suggested reaction
mechanism (Scheme 3). Although ketones were not
suitable, various aldehydes were able to be used in this
reaction. Furthermore, the aldehyde substituents (R5) had a
H
0
Bu
Ph
H
64
63
0
91:9
93:7
H
Ph
70
90:10
a
The reaction of 1 with benzaldehyde (1 equiv.) was carried out at room
temperature for 5 h in the presence of tributylphosphine (1 equiv.).
Isolated yield (SiO2, ethyl acetate and hexane eluent).
Determined by 1H NMR spectroscopy (400 MHz, CDCl3).
‡
Although attempts to separate the isomers were unsuccessful, we
presumed the major isomer of all obtained a-vinylfurans was the E-
form, from the suggested mechanism mentioned above.
b
c

1916
H. Kuroda et al. / Tetrahedron 60 (2004) 1913–1920
greater affect on the geometry of a-vinylfurans (2) than the
substituents (R1–R4) in the enynes (1).‡ (Table 2)
purified by vacuum distillation to give 2-heptynal (5.19 g,
47.2 mmol, 86%: colorless oil, bp14 58–60 8C); IR (neat)
2959, 3310, 2961, 2872, 2282, 2202, 1670, 1138 cm21; 1H
NMR (90 MHz, d, ppm) 0.93 (t, J¼6.4 Hz, 3H, CH3CH2–),
1.14–1.89 (m, 4H, –CH2–), 2.42 (t, J¼6.4 Hz, 2H,
CH2CuC–), 9.18 (s, 1H, –CHO).
3. Conclusion
In this paper we described a novel phosphine-initiated
cyclization of enynes bearing a carbonyl group at the ene
end, in the presence of aldehydes, to obtain a-vinylfurans.
Although the reaction was influenced by some substituents
in the enyne compounds, the furans were obtained easily
with high geometrical selectivity in moderate to high yields.
We believe this reaction could become an important and
convenient method for the synthesis of compounds contain-
ing a-vinylfuran skeletons, which are currently being
investigated in detail.
4.2.2. Phenyl-2-propynal (3b). Similarly, phenyl-2-
propynal (3b) (colorless oil, Rf¼0.45 on TLC; SiO2,
hexane/ethyl acetate¼4/1) was synthesized and then
purified by column chromatography on silica gel (hexane/
ethyl acetate¼20/1). Yield 97%; IR (neat) 3301, 2984,
2856, 2239, 2189, 1736, 1661, 1489 cm21 1H NMR
;
(90 MHz, d, ppm) 7.1–7.8 (5H, Ph–), 9.41 (s, 1H, –CHO).
Phosphoranes were prepared from corresponding a-halo-
ketones and triphenylphosphine in two steps by modifi-
cation of the method described in the literature.19
4. Experimental
4.2.3. Phenylcarbonylmethylenetriphenylphosphorane
A
(4a).
solution of a-bromoacetophenone (4.53 g,
4.1. Materials and instruments
22.8 mmol) in benzene (15 mL) was added dropwise to a
solution of triphenylphosphine (5.96 g, 22.8 mmol) in
benzene (15 mL) under nitrogen. The mixture was stirred
overnight and the resulting phosphonium salt was filtered.
The precipitate was washed with benzene and collected to
dry in vacuo. The dried phosphonium salt was suspended in
a mixture of water (250 mL) and methanol (250 mL), and
the mixture was stirred for 1 h. Aqueous sodium
hydroxide (2.00 M) was added to the mixture until a pH
between 7 and 8 was reached. The mixture was then
stirred vigorously for 1 h. The phosphorane precipitate was
filtered and washed water. After drying in vacuo, the
phosphorane was recrystallized from ethyl acetate and dried
under vacuum to obtain 7.39 g (19.1 mmol, yield 89%,
white crystal) of pure product; IR (neat) 3051, 2361, 1971,
1896, 1824, 1774, 1588, 1522 cm21. 1H NMR (90 MHz, d,
ppm) 4.44 (bd, J¼24.3 Hz, 1H, PvCH–), 7.22–8.14 (20H,
Ph).
Tetrahydrofuran (THF), diethyl ether and benzene were
dried over sodium benzophenone ketyl and distilled under
nitrogen. Dichloromethane, dimethylformamide (DMF) and
triethyl amine were dried over calcium hydride and then
purified by distillation. Tributylphosphine and all aldehydes
were purified by distillation. Triphenylphosphine was
purified by recrystallization from ethyl acetate and dried
in vacuo. Other commercially available chemicals were
used without purification.
Infrared (IR) spectra were obtained with a JASCO FT/IR
8000 infrared spectrometer. 1H and 13C NMR spectra were
recorded on JNM-FX90 or AL400 spectrometers, in CDCl3
(using tetramethylsilane as an internal standard). MS spectra
were measured with a JMS-AX500 mass spectrometer.
Elemental analysis was carried out by using Yanagimoto
MT-5.
4.2.4. Methylcarbonylmethylenetriphenylphosphorane
(4b). Similarly, methylcarbonylmethylenetriphenylphos-
phorane (4b) was obtained from triphenylphosphine and
bromoacetone in 69% yield as a white crystal; IR (neat)
3049, 2990, 2912, 1572, 1535, 1481, 1437 cm21; 1H NMR
(90 MHz, d, ppm) 2.09 (d, J¼1.9 Hz, 3H, CH3), 3.29–4.06
(br, 1H, PvCH–), 7.32–7.84 (15H, Ph).
4.2. Synthesis of enynes
Enynes (1A, R2¼R3¼H) with disubstituted olefinic
moieties were synthesized by Wittig reaction of the
corresponding ynals (3) with phosphoranes (4).
The ynals were prepared from terminal acetylenes and DMF
by modification of the method described in literature.18
4.2.5. trans-1-Phenyl-2-nonen-4-yn-1-one (1Aa). 2-Hep-
tynal (1.00 g, 9.09 mmol) was added slowly to a mixture of
4.2.1. 2-Heptynal (3a). n-Butyllithium (1.54 M in hexane,
39.6 mL, 61.0 mmol) was added dropwise to a solution of
1-hexyne (5.00 g, 61.0 mmol) in diethyl ether (40 mL) at
270 8C under nitrogen. After 30 min, dried DMF (6.68 g,
91.5 mmol) was added, and then the temperature of the
mixture was allowed to rise to room temperature, and
stirring was continued for 30 min. The mixture was poured
into ice water and acidified slightly with conc. hydrochloric
acid. The mixture was then neutralized with sodium
hydrogen carbonate until a pH between 6 and 7 was
reached. The organic layer was separated and the aqueous
layer was extracted four times with 25 mL of ethyl acetate.
The combined organic solution was dried over magnesium
sulfate. After evaporation of the solvents, the residue was
phenylcarbonylmethylenetriphenylphosphorane
(3.45 g,
9.09 mmol) in CH2Cl2 (56 mL). The mixture was stirred
at room temperature for 5 h and then concentrated by using
an evaporator. Hexane (100 mL) was added to the mixture,
and the triphenylphosphine oxide crystals were filtered. The
filtrate was concentrated by using an evaporator, and the
residue was purified by column chromatography on silica
gel (hexane/ethyl acetate¼100/1) to obtain the enyne (1Aa,
1.53 g, 7.20 mmol) in 79% yield (pale yellow oil, Rf¼0.63
on TLC: SiO2, hexane/ethyl acetate¼4/1); IR (neat) 2959,
2934, 2872, 2210, 1660, 1591, 1448, 1290 cm21; 1H NMR
(90 MHz, d, ppm) 0.93 (t, J¼6.6 Hz, 3H, CH3–), 1.24–1.57
(m, 4H, –CH2–), 2.42 (dt, J¼2.3, 6.8 Hz, 2H, –CH2Cu,

H. Kuroda et al. / Tetrahedron 60 (2004) 1913–1920
1917
6.68 (dt, J¼15.6, 2.3 Hz, 1H, uCCHv), 7.29 (d,
J¼15.6 Hz, 1H, vCHCO–), 7.44–7.58 (m, 3H, Ph),
7.89–8.00 (m, 2H, Ph).
was added dropwise to the mixture. The temperature of the
mixture was allowed to rise to 0 8C. After 30 min,
acetylchloride (3.85 g, 49.0 mmol) was added. The mixture
was stirred at 0 8C for 5 h and then poured into saturated
aqueous ammonium chloride. The mixture was extracted
four times with 25 mL of ethyl acetate and then dried over
magnesium sulfate. After evaporation of the solvents, the
residue was purified by column chromatography (SiO2,
hexane/ethyl acetate¼100/1) to give 4-phenyl-3-butyn-2-
one (4.70 g, 32.6 mmol, 67% yield, pale yellow oil, Rf¼0.48
on TLC; SiO2, hexane/ethyl acetate¼4/1); IR (neat) 2202,
Similarly, other 1A were synthesized from their correspond-
ing ynals and phosphoranes.
4.2.6. trans-3-Decen-5-yn-2-one (1Ab). Yield 82%, color-
less oil, Rf¼0.53 on TLC (SiO2, hexane/ethyl acetate¼4/1);
IR (neat) 2961, 2936, 2872, 2213, 1693, 1674, 1595,
1356 cm21; 1H NMR (90 MHz, d, ppm) 0.93 (t, J¼7.2 Hz,
3H, CH3–), 1.26–1.74 (m, 4H, –CH2–), 2.25 (s, 3H,
CH3CO), 2.24 (t, J¼7.2 Hz, 2H, uCCH2–), 6.36 (d,
J¼18.0 Hz, 1H, vCHCO–), 6.55 (dt, J¼18.0, 2.3 Hz,
1H, uCCHv).
1
1674, 1359, 1280, 1157, 978, 758, 690 cm21; H NMR
(90 MHz, d, ppm) 2.44 (s, 3H, CH3–), 7.25 (5H, Ph–).
4.2.11. (3E)-4-Butyl-3-decen-5-yn-2-one (1Ba). Tris (2,6-
dimethoxyphenyl)phosphine (0.092 g, 0.261 mmol) was
added to a suspension of palladium (II) acetate (0.035 g,
0.156 mmol) in benzene (9 mL). After 5 min, 6a (1.00 g,
8.06 mmol) was added, and the mixture was stirred for
10 min. 1-Hexyne (0.661 g, 8.06 mmol) was then added
slowly to the mixture, and the stirring was continued for
24 h. The mixture was subsequently concentrated in vacuo.
The residue was purified by column chromatography (SiO2,
hexane/ethyl acetate¼100/1) to obtain 1Ba (1.45 g,
7.03 mmol) (colorless oil, Rf¼0.63 on TLC; SiO2, hexane/
ethyl acetate¼4/1) in 87% yield; IR (neat) 2932, 2872,
2214, 1682, 1590, 1356, 1169 cm21; 1H NMR (90 MHz, d,
ppm) 0.94 (t, J¼7.6 Hz, 6H, CH3–) 1.36–1.58 (8H, –CH2–),
2.17 (s, 3H, CH3CO–), 2.36 (t, J¼6.4 Hz, –CH2CHv), 2.69
(t, J¼7.62 Hz, 2H, –CH2Cu), 6.34 (s, 1H, vCHCO–).
4.2.7. trans-1,5-Diphenyl-2-penten-4-yn-1-one (1Ac).
Yield 69%, pale yellow solid, mp 46 8C, Rf¼0.72 on TLC
(SiO2, hexane/ethyl acetate¼4/1); IR (neat) 3063, 2191,
1661, 1597, 1580, 1337, 1308, 1254, 1211 cm21; 1H NMR
(90 MHz, d, ppm) 7.01 (d, J¼16.2 Hz, 1H, –CHvCHCO–),
7.20–7.80 (9H, vCHCO–, Ph), 7.80–8.10 (m, 2H, Ph).
4.2.8. trans-6-Phenyl-3-hexen-5-yn-2-one (1Ad). Yield
75%, pale yellow solid, mp 104 8C, Rf¼0.38 on TLC
(SiO2, hexane/ethyl acetate¼4/1); IR (neat) 3038, 3015,
2195, 1657, 1590, 1489, 1445, 1363 cm21 1H NMR
;
(90 MHz, d, ppm) 2.24 (s, 3H, CH3CO–), 6.28 (d,
J¼16.1 Hz, 1H, uCCHv), 6.49 (d, J¼16.1 Hz, 1H,
vCHCO–), 7.20–7.56 (m, 5H, Ph).
Enynes (1B) with trisubstituted olefinic moieties were
prepared by the palladium-catalyzed cross coupling reaction
of ynones with terminal alkynes described in the literature.14
The ynones used in the cross coupling reaction were
prepared as follows:20
4.2.12. (3E)-4-phenyl-3-decen-5-yn-2-one (1Bb). Simi-
larly, (3E)-4-phenyl-3-decen-5-yn-2-one (1Bb) (pale
yellow oil, Rf¼0.63 on TLC; SiO2, hexane/ethyl
acetate¼4/1) was prepared by the palladium catalyzed
reaction (reaction time: 4 h) of 6b and 1-hexyne in 40%
yield; IR (neat) 2959, 2231, 1685, 1657, 1361, 1259, 763,
1
4.2.9. 3-Octyn-2-one (6a). n-Butyllithium (1.54 M in
hexane, 39.6 mL, 61.0 mmol) was added dropwise to a
solution of 1-hexyne (5.00 g, 61.0 mmol) in THF (60 mL) at
270 8C. After 30 min, acetic anhydride (12.4 g, 122 mmol)
was added to the mixture over 30 min and the mixture was
then stirred for an additional 20 min. The temperature was
then allowed to rise to 0 8C, and aqueous ammonium
chloride (3 M, 100 mL) was poured into the mixture,
followed by dropwise addition of concentrated aqueous
ammonia, over 30 min. The mixture was extracted four
times with 25 mL of ethyl acetate. The combined organic
solution was washed twice with 50 mL of saturated aqueous
ammonium chloride solution and then dried over mag-
nesium sulfate. After solvent evaporation, the residue was
purified by vacuum distillation to give 3-octyn-2-one
(4.60 g, 37.1 mmol, yield 68%: colorless oil, bp22 71–
77 8C); IR (neat) 3335, 2961, 2212, 1678, 1466, 1625, 1300,
1234 cm21; 1H NMR (90 MHz, d, ppm) 0.93 (t, J¼7.4 Hz,
3H, CH3CH2–), 1.14–1.89 (m, 4H, –CH2–), 2.32 (s, 3H,
CH3CO–), 2.36 (t, J¼7.4 Hz, 2H, –CH2CuC–).
692 cm21; H NMR (90 MHz, d, ppm) 0.96 (t, J¼6.6 Hz,
6H, CH3–) 1.36–1.66 (4H, –CH2–), 2.56 (s, 3H, CH3CO–),
2.58 (t, J¼6.6 Hz, 2H, –CH2Cu), 6.71 (s, 1H, vCHCO–),
7.34 (m, 5H, Ph–).
Enynes (1C) with trisubstituted olefinic moieties were
synthesized from 2-heptynal (3a) and silyl enol ethers (7)
in two steps. The silyl enol ethers were prepared as
follows, by modification of the method described in the
literature:21
4.2.13. 1-phenyl-1-trimethylsiloxy-1-butene (7a). Butyl-
lithium (1.54 M in hexane, 21.9 mL, 33.7 mmol) was added
slowly at 0 8C to a solution of diisopropylamine (3.40 g,
33.7 mmol) and THF (150 mL). After 10 min, 1-phenyl-1-
butanone (5.00 g, 33.7 mmol) was added slowly to the
solution at 278 8C. The mixture was stirred for a further
30 min, and then chlorotrimethylsilane (4.39 g, 40.5 mmol)
was added at the same temperature. The solution was
allowed to warm slowly from 278 8C to room temperature.
After 12 h, the solvent had almost evaporated completely,
and hexane was added. The resulting precipitate was
removed and the obtained filtrate was evaporated, and
purified by distillation to obtain 7a (colorless oil, bp7 75–
80 8C) (7.01 g, 31.9 mmol, 95% yield); IR (neat) 2963,
4.2.10. 4-Phenyl-3-butyn-2-one (6b). n-Butyllithium
(1.54 M in hexane, 31.8 mL, 49.0 mmol) was added
dropwise to a solution of ethynylbenzene (5.00 g,
49.0 mmol) in THF (28 mL), at 230 8C. After 30 min, a
solution of zinc chloride (6.69 g, 49 mmol) in THF (18 mL)
1649, 1446, 1342, 1251, 1074, 843 cm21 1H NMR
;

1918
H. Kuroda et al. / Tetrahedron 60 (2004) 1913–1920
(90 MHz, d, ppm) 0.13 (s, 9H, CH3Si–), 1.04 (t, J¼7.4 Hz,
3H, CH3–), 2.22 (q, J¼7.4 Hz, 2H, –CH2Cv), 5.23 (t,
J¼7.2 Hz, 1H, –CHv), 7.22–7.44 (m, 5H, Ph–).
(d, J¼6.3 Hz, 1H, –CH(OH)–), 7.00–8.00 (m, 10H, Ph–).
0.82 (t, J¼7.3 Hz, 3H, CH3–), 1.32–1.60 (m, –CH2–, 4H),
2.13 (t, J¼6.8 Hz, 2H, –CH2Cu), 3.15 (br, 1H, –OH), 4.80
(d, J¼7.8 Hz, 1H, –CHPh–), 5.06 (d, J¼7.8 Hz, 1H,
–CH(OH)–), 7.00–8.00 (m, 10H, Ph–). 1Cb (pale yellow
oil, Rf¼0.48 on TLC; SiO2, hexane/ethyl acetate¼4/1); IR
1H NMR (90 MHz, d, ppm) 0.88 (t, J¼7.7 Hz, 3H, CH3–),
1.11–1.69 (m, 4H, –CH2–), 2.34 (dt, J¼2.6, 7.7 Hz, 2H,
–CH2Cu), 6.30 (t, J¼2.6 Hz, 1H, –CHv), 7.11–8.09 (m,
10H, Ph–).
4.2.14. 1,2-Diphenyl-1-trimethylsiloxyethene (7b). Color-
less oil, bp7 125–140 8C) was prepared similarly in 48%
yield; IR (neat) 2959, 1630, 1448, 1350, 1253, 1066, 897,
846 cm21; 1H NMR (90 MHz, d, ppm) 0.13 (s, 9H, CH3Si–),
6.29 (s, 1H, –CHv), 7.15–7.88 (m, 10H, Ph–).
(neat) 2959, 2208, 1657, 1591, 1259, 1068, 731, 696 cm21
;
4.2.15. 2-Ethyl-1-phenyl-2-nonen-4-yn-1-one (1Ca). 1Ca
was synthesized via 2-ethyl-3-hydroxy-1-phenyl-4-nonyn-
1-one. 2-Ethyl-3-hydroxy-1-phenyl-4-nonyn-1-one (8a):
Trifluoroborone diethyl ether complex (1.97 g, 13.9 mmol)
was added dropwise at 278 8C to a solution of 3a (1.00 g,
9.09 mmol) and 7a (2.00 g, 9.09 mmol) in CH2Cl2 (25 mL).
After 1 h, the mixture was poured into cold water (100 mL),
and neutralized with sodium bicarbonate until a pH of 7 was
attained. After separation of the organic layer, the aqueous
phase was extracted four times with 25 mL of ethyl acetate.
The combined organic phase was dried over magnesium
sulfate. After solvent evaporation, the residue was purified
by column chromatography (SiO2, hexane/ethyl
acetate¼20/1) to give 8a (2.15 g, 8.33 mmol) (pale yellow
oil, Rf¼0.10 and 0.20 on TLC; SiO2, hexane/ethyl
acetate¼4/1) as a diastereo mixture (The diastereo ratio
was estimated from the 1H NMR spectrum as 1:1.5) in 92%
yield; IR (neat) 3443, 2963, 2229, 1676, 1448, 1205, 1028,
4.2.17. Phosphine-initiated cyclization of 1. 2-(1-Butyl-2-
phenylethenyl)-5-phenylfuran (2Aa). Tributylphosphine
(190 mg, 0.943 mmol) was added at room temperature to a
solution of 1Aa (200 mg, 0.943 mmol) and benzaldehyde
(100 mg, 0.943 mmol) in CH2Cl2 (1.9 mL). After stirring
for 5 h, the reaction mixture was concentrated under
vacuum. The residue was purified by column chromato-
graphy on silica gel (hexane/ethyl acetate¼200/1) to give
236 mg (83%) of 2Aa as a mixture of geometric isomers;
colorless oil, Rf¼0.63 on TLC (hexane/ethyl acetate¼4/1);
IR (neat) 3059, 2957, 1685, 1599, 1483, 1468, 1449, 1024,
1
785, 758, 692 cm21; H NMR (400 MHz, d, ppm) 0.95 (t,
J¼7.3 Hz, 3H, CH3–), 1.44 (m, 2H, CH3CH2–), 1.66 (m,
2H, –CH2CH2CH2–), 2.53 (t, J¼7.6 Hz, 2H, –CH2-furan;
minor isomer), 2.61 (t, J¼8.3 Hz, 2H, –CH2CH2CH2–),
6.23 (d J¼3.6 Hz, 1H, furan-H; minor isomer), 6.45 (d,
J¼3.4 Hz, 1H, furan-H), 6.56 (d J¼3.6 Hz, 1H, furan-H;
minor isomer), 6.68 (d, J¼3.4 Hz, 1H, furan-H) 7.19 (s, 1H,
–CHv), 7.20–7.75 (m, 10H, Ph),; 13C NMR (100 MHz, d,
ppm; major isomer) 13.9 (CH3), 23.0 (–CH2–), 28.2
(–CH2–), 32.0 (–CH2–), 107.0 (CH in furan ring), 108.6
(CH in furan ring), 123.7 (Ph), 124.2 (vCHPh), 126.6 (Ph),
127.3 (Ph), 128.3 (Ph), 128.7 (Ph), 128.8 (Ph), 130.8 (Ph),
131.6 (Ph), 137.5 (sCvCHPh), 153.0 (O–C in furan ring),
155.2 (O–C in furan ring). MS (EI, m/z) 302 (Mþ). Anal.
Calcd for C22H22O: C 87.38, H 7.33. Found: C 87.41, H
7.65.
1
704 cm21; H NMR (90 MHz, d, ppm) 0.78 (t, J¼7.0 Hz,
3H, CH3–), 0.91 (t, J¼7.0 Hz, 3H, CH3–), 1.17–1.80 (m,
–CH2–, 4H), 2.86 (br, 1H, –OH) (this peak may be
attributable to the minor diastereoisomer), 3.20 (br, 1H,
–OH), 3.68 (q, J¼6.6 Hz, 1H, –CH(Et)CO–), 4.64 (br, 1H,
–CH(OH)–), 7.00–8.00 (m, 5H, Ph–). Methanesulfonyl
chloride (0.177 g, 1.55 mmol) and then triethylamine
(0.157 g, 1.55 mmol) were added at 0 8C to a solution of
8a (diastereo mixture) (0.400 g 1.55 mmol) in CH2Cl2
(1.5 mL). This mixture was refluxed for 3 h and then poured
into saturated aqueous ammonium chloride (25 mL). After
separation of the organic layer, the aqueous phase was
extracted four times with 15 mL portions of ethyl acetate.
The combined organic phase was dried over magnesium
sulfate. After evaporation of the solvents, the residue was
purified by column chromatography (SiO2, hexane/ethyl
acetate¼20/1) to give 1Ca (0.280 g, 1.17 mmol) (pale
yellow oil, Rf¼0.58 on TLC; SiO2, hexane/ethyl acetate¼
4/1) as a single isomer in 75.2% yield; IR (neat) 2963, 2208,
Similarly, the cyclization was carried out by using various
enynes and aldehydes in the presence of tributylphosphine.
4.2.18. 2-(1-Butyl-2-phenylethenyl)-5-methylfuran
(2Ab). 2-(1-Butyl-2-phenylethenyl)-5-methylfuran (2Ab)
(pale yellow oil, Rf¼0.75 on TLC; SiO2, hexane/ethyl
acetate¼4/1) was obtained in 56% yield; IR (neat) 2957,
2930, 2870, 1701, 1653, 1599, 1456 cm21 1H NMR
;
1
1774, 1649, 1597, 1250, 1057, 880, 720 cm21; H NMR
(90 MHz, d, ppm) 0.96 (t, J¼7.9 Hz, 3H, CH3–), 1.12 (t,
J¼7.9 Hz, 3H, CH3–), 1.32–1.90 (m, –CH2–, 4H), 2.48
(t, J¼7.8 Hz, 2H, –CH2Cu), 3.76 (q, J¼7.9 Hz, 2H,
–CH2Cv), 6.10 (s, 1H, –CHv), 7.28–7.76 (m, 5H, Ph–).
(400 MHz, d, ppm) 0.93 (t, J¼7.4 Hz, 3H, CH3–), 1.41
(m, 2H, –CH2–), 1.63 (m, 2H, –CH2–), 2.34 (d, J¼0.8 Hz,
3H, CH3-furan), 2.53 (t, J¼8.2 Hz, 2H, –CH2Cv), 6.00
(dq, J¼3.2, 0.8 Hz, 1H, furan-H), 6.26 (d, J¼3.2 Hz, 1H,
furan-H) 7.01 (s, 1H, –CHv), 7.20–7.50 (m, 5H, Ph); 13C
NMR (100 MHz, d, ppm) 13.8 (CH3), 13.9 (CH3), 22.9
(–CH2–), 28.1 (–CH2–), 31.9 (–CH2–), 107.1 (CH in
furan ring), 107.2 (CH in furan ring), 122.4 (vCHPh),
126.0 (Ph), 127.9 (Ph), 128.4 (Ph), 131.4 (Ph), 137.4
(sCvCHPh), 150.5 (O–C in furan ring), 153.7 (O–C in
furan ring). MS (EI, m/z) 240 (Mþ). Anal. Calcd for
C17H20O: C 84.96, H 8.39. Found: C 84.60, H 8.52.
4.2.16. 1,2-Diphenyl-2-nonen-4-yn-1-one (1Cb). Simi-
larly, 1,2-diphenyl-2-nonen-4-yn-1-one (1Cb) was prepared
as a single isomer via 3-hydroxy-1,2-diphenyl-4-nonyn-1-
one (8b) in two steps. 8b (pale yellow oil, Rf¼0.33 on TLC;
SiO2, hexane/ethyl acetate¼4/1) was obtained as a mixture
of diastereoisomers (1:1.7) in 81% yield; IR (neat) 3458,
1
2959, 2231, 1678, 1450, 1205, 1047, 700 cm21; H NMR
(400 MHz, d, ppm) 0.81 (t, J¼7.3 Hz, 3H, CH3–), 1.32–
1.60 (m, –CH2–, 4H), 2.12 (t, J¼6.8 Hz, 2H, –CH2Cu),
2.80 (br, 1H, –OH), 4.80 (d, J¼6.3 Hz, 1H, –CHPh–), 5.12
4.2.19. 2-(1-Butyl-2-phenylethenyl)-3-butyl-5-methyl-
furan (2Ba). Pale yellow oil, Rf¼0.63 on TLC; SiO2,

H. Kuroda et al. / Tetrahedron 60 (2004) 1913–1920
1919
hexane/ethyl acetate¼4/1) was obtained as a mixture of
1685, 1599, 1483, 1024, 785, 758 cm21
;
1H NMR
geometric isomers in 64% yield; IR (neat) 2957, 2860, 1616,
(400 MHz, d, ppm) 0.91 (t, J¼7.0 Hz, 3H, CH3–), 1.37
(m, 4H, –CH2–), 1.69 (m, 2H, –CH2–), 2.67 (t, J¼7.6 Hz,
2H, –CH2-furan), 6.05 (d, J¼3.20 Hz, 1H, furan-H), 6.54
(d, J¼3.2 Hz, 1H, furan-H), 7.21 (m, 1H, –Ph), 7.34 (m, 2H,
Ph), 7.62 (m, 2H, Ph); 13C NMR (100 MHz, d, ppm) 14.2
(CH3), 22.6 (CH2), 27.9 (CH2), 28.3 (CH2), 31.5 (CH2),
105.5 (CH in furan ring), 106.7 (CH in furan ring), 123.2
(Ph), 126.5 (Ph), 128.4 (Ph), 131.1 (Ph), 151.9 (O–C in
furan ring), 156.2 (O–C in furan ring). MS (EI, m/z) 214
(Mþ). Anal. Calcd for C15H18O: C 84.07, H 8.47. Found: C
84.00, H 8.60.
1
1458, 1259, 750, 698 cm21; H NMR (400 MHz, d, ppm)
0.74 (t, J¼7.1 Hz, 3H, CH3–; minor isomer), 0.84 (t,
J¼7.2 Hz, 3H, CH3–), 0.92 (t, J¼7.6 Hz, 3H, CH3–),
1.20–1.60 (m, 8H, –CH2–), 1.80 (t, J¼7.6 Hz, 2H, –CH2-
furan; minor isomer), 2.28 (s, 3H, CH3-Furan), 2.51 (t,
J¼7.6 Hz, 2H, CH2-furan), 2.61 (t, J¼7.6 Hz, 2H,
–CH2Cv), 5.80 (s, 1H, furan-H; minor isomer), 5.92 (s,
1H, furan-H), 6.46 (s, 1H, –CHv; minor isomer), 6.62 (s,
1H, –CHv), 6.46 (s, 1H, –CHv; minor isomer), 7.20–
7.50 (m, 5H, Ph),; 13C NMR (100 MHz, d, ppm) 13.6 (CH3),
13.9 (CH3), 14.0 (CH2), 22.5 (CH2), 22.7 (CH2), 25.7 (CH2),
28.7 (CH2), 31.4 (CH2), 32.5 (CH2), 109.0 (CH in furan
ring), 122.8 (Bu–C in furan), 126.0 (Ph), 126.1 (PhCHv),
127.9 (Ph), 128.4 (Ph), 133.7 (Ph), 137.6 (sCvCHPh),
148.9 (O–C in furan ring), 149.4 (O–C in furan ring). MS
(EI, m/z) 296 (Mþ). Anal. Calcd for C21H28O: C 85.08, H
9.52. Found: C 85.03, H 9.71.
4.2.22. 2-(1-Butyl-2-ethylethenyl)-5-phenylfuran. Pale
yellow oil, Rf¼0.73 on TLC; SiO2, hexane/ethyl
acetate¼4/1) was obtained as a mixture of geometric
isomers in 92% yield; IR (neat) 2959, 2932, 1606, 1523,
1485, 1458, 1024, 783, 758, 688 cm21; 1H NMR (400 MHz,
d, ppm) 0.94 (t, J¼7.2 Hz, 3H, CH3–), 0.96 (t, J¼7.2 Hz,
3H; minor isomer), 1.09 (t, J¼7.6 Hz, 3H, CH3–), 1.12 (t,
J¼7.6 Hz, 2H, CH3–; minor isomer), 1.39 (m, 2H, –CH2–
), 1.49 (m, 2H, –CH2–), 1.74 (quint, J¼7.6 Hz, 2H,
CH3CH2CHv; minor isomer), 2.24 (quint, J¼7.6 Hz, 2H,
CH3CH2CHv), 2.38 (t, J¼7.2 Hz, 2H, –CH2CH2Cv),
2.50 (t, J¼7.2 Hz, 2H, –CH2CH2Cv; minor isomer), 5.45
(t, J¼7.2 Hz, 1H, –CHv; minor isomer), 6.15 (t, J¼7.6 Hz,
1H, –CHv), 6.26 (d, J¼3.2 Hz, 1H, furan-H), 6.34 (d,
J¼3.6 Hz, 1H, furan-H; minor isomer), 6.63 (d, J¼3.2 Hz,
1H, furan-H), 6.67 (d, J¼3.6 Hz, 1H, furan-H; minor
isomer), 7.10–7.80 (m, 5H, Ph); 13C NMR (100 MHz, d,
ppm; major isomer) 14.0 (CH3), 14.3 (CH3), 21.2 (CH2),
22.8 (CH2), 27.6 (CH2), 31.8 (CH2), 106.2 (CH in furan
ring), 106.4 (CH in furan ring), 123.2 (Ph), 126.6 (vCHPh),
127.5 (Ph), 128.3 (Ph), 128.9 (Ph), 130.7 (sCvCHPh),
151.8 (O–C in furan ring), 154.9 (O–C in furan ring). MS
(EI, m/z) 254 (Mþ). Anal. Calcd for C18H22O: C 84.99, H
8.72. Found: C 84.72, H 8.79.
4.2.20. 2-(1-Butyl-2-phenylethenyl)-5-methyl-3-phenyl-
furan (2Bb). Pale yellow oil, Rf¼0.68 on TLC; SiO2,
hexane/ethyl acetate¼4/1) was obtained as a mixture of
geometric isomers in 63% yield; IR (neat) 3026, 2926, 1740,
1
1601, 1444, 1126, 956, 763 cm21; H NMR (400 MHz, d,
ppm) 0.84 (t, J¼7.2 Hz, 3H, CH3–), 1.26 (m, 2H, –CH2–),
1.51 (m, 2H, –CH2–), 2.33 (d, J¼0.8 Hz, 3H, CH3-furan),
2.39 (d, J¼0.8 Hz, 3H, CH3-furan), 2.42 (t, J¼8.0 Hz, 2H,
–CH2Cv; minor isomer), 2.58 (t, J¼8.0 Hz, 2H, CH2Cv),
6.16 (q, J¼0.8 Hz, 1H, furan-H), 6.24 (q, J¼0.8 Hz, 1H,
furan-H, minor isomer), 6.58 (s, 1H, –CHv; minor isomer),
6.77 (s, 1H, –CHv), 7.20–7.50 (m, 10H, Ph); 13C NMR
(100 MHz, d, ppm; major isomer) 13.8 (CH3), 13.9 (CH3),
22.8 (CH2), 28.6 (CH2), 31.5 (CH2), 109.6 (CH in furan
ring), 123.3 (Ph–C in furan), 126.4 (vCHPh), 126.5 (Ph),
128.0 (Ph), 128.1 (Ph), 128.4 (Ph), 128.5 (Ph), 133.1 (Ph),
135.0 (Ph), 137.4 (sCvCHPh), 149.1 (O–C in furan ring),
150.2 (O–C in furan ring). MS (EI, m/z) 316 (Mþ). Anal.
Calcd for C23H24O: C 87.30, H 7.64. Found: C 86.86, H
7.87.
4.2.23. 2-(1-Butyl-4-phenyl-1,3-butadienyl)-5-phenyl-
furan. Pale yellow oil, Rf¼0.73 on TLC; SiO2, hexane/ethyl
acetate¼4/1) was obtained as a mixture of geometric
isomers in 90% yield; IR (neat) 3032, 2957, 2932, 1606,
4.2.21. 2-(1-Butyl-2-phenylethenyl)-4,5-diphenylfuran
(2Cb). Pale yellow oil, Rf¼0.60 on TLC; SiO2, hexane/
ethyl acetate¼4/1) was obtained as a mixture of geometric
isomers in 70% yield; IR (neat) 2959, 2870, 1703, 1599,
1532, 1506, 1250, 1176, 1035, 758, 690 cm21; H NMR
1
(400 MHz, d, ppm) 0.94 (t, J¼7.2 Hz, 3H, CH3–; minor
isomer), 0.97 (t, J¼7.6 Hz, 3H, CH3–), 1.44 (m, 2H,
–CH2–), 1.61 (m, 2H, –CH2–), 2.46 (t, J¼7.6 Hz, 2H,
–CH2CH2Cv; minor isomer), 2.60 (t, J¼7.2 Hz, 2H,
–CH2CH2Cv), 6.21 (d, J¼11.6 Hz, 1H, PhCHvCHCHv;
minor isomer), 6.44 (d, J¼3.6 Hz, 1H, furan-H), 6.49 (d,
J¼3.6 Hz, 1H, furan-H; minor isomer), 6.64 (d, J¼15.6 Hz,
1H, PhCHvCH–; minor isomer), 6.68 (d, J¼3.20 Hz, 1H,
furan-H), 6.72 (d, J¼3.6 Hz, 1H, furan-H; minor isomer),
6.73 (d, J¼15.2 Hz, 1H, PhCHvCH–), 6.95 (d, J¼11.6 Hz,
1H, PhCHvCHCHv), 7.16 (dd, J¼11.6, 15.6 Hz, 1H,
PhCHvCH–), 7.20–7.80 (m, 10H, Ph) 7.96 (dd, J¼11.6,
15.6 Hz, 1H, PhCHvCH–; minor isomer); 13C NMR
(100 MHz, d, ppm; major isomer) 13.9 (CH3). 22.8 (CH2),
28.0 (CH2), 32.3 (CH2), 107.0 (CH in furan ring), 108.5 (CH
in furan ring), 123.4 (Ph), 123.8 (PhCHvCH–CHv),
124.6 (PhCHvCH–), 126.0 (Ph), 127.0 (Ph), 127.0 (Ph),
128.3 (Ph), 130.4 (vCH–CHvC,), 130.7 (Ph), 132.6
(PhCHvCH–), 137.5 (Ph), 152.8 (O–C in furan ring),
154.7 (O–C in furan ring). MS (EI, m/z) 328 (Mþ). Anal.
1
1446, 1147, 763, 696 cm21; H NMR (400 MHz, d, ppm)
0.88 (t, J¼7.6 Hz, 3H, CH3–), 1.38 (m, 2H, –CH2–), 1.63
(m, 2H, –CH2–), 2.47 (t, J¼7.6 Hz, 2H, –CH2Cv; minor
isomer), 2.56 (t, J¼8.2 Hz, 2H, –CH2Cv), 6.24 (s, 1H,
furan-H; minor isomer), 6.47 (s, 1H, furan-H), 7.14 (s, 1H,
–CHv), 7.10–7.55 (m, 15H, Ph); 13C NMR (100 MHz, d,
ppm) 14.0 (CH3), 23.2 (CH2), 28.4 (CH2), 32.1 (CH2), 110.7
(CH in furan ring), 124.2 (Ph–C in furan), 124.5 (vCHPh),
126.0 (Ph), 126.5 (Ph), 127.1 (Ph), 127.3 (Ph), 128.2 (Ph),
128.3 (Ph), 128.5 (Ph), 128.6 (Ph), 128.7 (Ph), 130.9 (Ph),
131.2 (Ph), 134.2 (Ph), 137.3 (sCvCHPh), 147.3 (O–C in
furan ring), 154.1 (O–C in furan ring). MS (EI, m/z) 378
(Mþ). Anal. Calcd for C28H26O: C 88.85, H 6.92. Found: C
88.64, H 7.14.
4.2.21. 2-Pentyl-5-phenylfuran (20Aa). Colorless oil,
Rf¼0.63 on TLC; SiO2, hexane/ethyl acetate¼4/1) was
obtained in 58% yield; IR (neat) 2957, 2930, 2870, 1738,

1920
H. Kuroda et al. / Tetrahedron 60 (2004) 1913–1920
2. Nakanishi, K. Natural products chemistry; Kodan-sha: Tokyo,
1974.
Calcd for C24H24O: C 87.76, H 7.37. Found: C 87.34, H
7.53.
3. Hou, X. L.; Cheung, H. Y.; Hon, T. Y.; Kwan, P. L.; Lo, T. H.;
Tong, S. Y.; Wong, H. N. C. Tetrahedron 1998, 54, 1955.
4. Konfeld, E. C.; Jones, R. G. J. Org. Chem. 1954, 19, 1671.
5. Rinkes, I. J. Rec. Trav. Chim. 1931, 50, 1127.
6. (a) Seiller, B.; Bruneau, C.; Dixneuf, P. H. J. Chem. Soc.
Chem. Commun. 1994, 493. (b) Seiller, B.; Bruneau, C.;
Dixneuf, P. H. Tetrahedron 1995, 51, 13089. (c) Kucukbay,
H.; Cetinkaya, B.; Guesmi, S.; Dixneuf, P. H. Organometallics
1996, 51, 2423. (d) Marshall, J. A.; Bennet, C. E. J. Org.
Chem. 1994, 59, 6110.
4.2.24. 2-[1-Butyl-2-(p-methoxyphenyl)ethenyl]-5-phe-
nylfuran. Pale yellow oil, Rf¼0.70 on TLC; SiO2,
hexane/ethyl acetate¼4/1) was obtained as a mixture of
geometric isomers in 89% yield; IR (neat) 2957, 29.32,
1
1606, 1524, 1506, 1464, 1250, 1176, 758 cm21; H NMR
(400 MHz, d, ppm) 0.88 (t, J¼6.8 Hz, 3H, CH3–; minor
isomer), 0.96 (t, J¼7.2 Hz, 3H, CH3–), 1.45 (m, 2H,
–CH2–), 1.66 (m, 2H, –CH2–), 2.51 (t, J¼8.0 Hz, 2H,
–CH2CH2CHv; minor isomer), 2.60 (t, J¼8.0 Hz, 2H,
–CH2CH2CHv), 3.80 (s, 3H, CH3O–; minor isomer), 3.82
(s, 3H, CH3O–), 6.24 (d, J¼3.6 Hz, 1H, furan-H; minor
isomer), 6.42 (d, J¼3.6 Hz, 1H, furan-H), 6.57 (d,
J¼3.6 Hz, 1H, furan-H; minor isomer), 6.68 (d, J¼3.6 Hz,
1H, furan-H), 6.91 (m, 2H, MeOPh–; minor isomer), 6.92
(m, 2H, MeOPh–), 7.13 (s, 1H, –CHv), 7.20–7.80 (m, 7H,
Ph, MeOPh–); 13C NMR (100 MHz, d, ppm) 13.9 (CH3),
23.0 (CH2), 28.2 (CH2), 31.8 (CH2), 55.1 (CH3O), 106.7
(CH in furan ring), 107.7 (CH in furan ring), 113.1
(p-MeC6H4–), 123.3 (Ph), 123.5 (Ph), 126.8 (–CHv),
128.3 (Ph), 129.7 (p-MeOC6H4–), 129.8 (p-MeOC6H4–,
Ph), 130.5 (sCvCH–), 152.4 (O–C in furan ring), 155.1
(O–C in furan ring), 158.0 (p-MeC6H4–),. MS (EI, m/z) 332
(Mþ). Anal. Calcd for C23H24O2: C 83.10, H 7.28. Found: C
82.98, H 7.52.
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References and notes
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