Gold-catalyzed approach to multisubstituted fulvenes via cycloisomerization of furan/ynes

Article abstract of DOI:10.1021/jo2004023

A new approach to functionalized fulvenes with an enone or enal moiety has been developed through gold-catalyzed intramolecular cycloisomerization of furan/ynes with a two-carbon tether in between the furan and the triple bond. The reaction proceeds with complete regioselectivity via a 6-endo-cyclization and high stereoselectivity. Moreover, the E- or Z-stereochemistry of the double bond in fulvene products can be easily controlled by performing the reaction in different solvents.

Full text of DOI:10.1021/jo2004023

ARTICLE
pubs.acs.org/joc
Gold-Catalyzed Approach to Multisubstituted Fulvenes via
Cycloisomerization of Furan/Ynes
Yifeng Chen and Yuanhong Liu*
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
345 Lingling Lu, Shanghai 200032, People’s Republic of China
S Supporting Information
b
ABSTRACT: A new approach to functionalized fulvenes with
an enone or enal moiety has been developed through gold-
catalyzed intramolecular cycloisomerization of furan/ynes with
a two-carbon tether in between the furan and the triple bond.
The reaction proceeds with complete regioselectivity via a
6-endo-cyclization and high stereoselectivity. Moreover, the
E- or Z-stereochemistry of the double bond in fulvene products
can be easily controlled by performing the reaction in different
solvents.
’ INTRODUCTION
take place to generate fulvene derivatives via the π-complex
between the gold catalyst and the alkyne (Scheme 1, eq 2). In this
paper, we report our success in gold-catalyzed cycloisomerization
reactions of enynyl furans 2 to functionalized fulvenes with
controllable E- or Z-stereoselectivity. It is noted that there is
no report for the ring-opening cyclization of furan/ynes with a
two-carbon tether in between the furan and the alkyne moiety.15
Fulvenes, which exhibit intriguing cross-conjugated molecular
structures, have attracted much attention in theoretical studies,1
as precursors of cyclopentadienyl ligands for metallocene synthesis,2
and in natural product synthesis.3 They can also undergo a diverse
array of cycloaddition reactions such as [4 þ 2],4a,b [6 þ 2],4cꢀe
and [6 þ 3]4f cyclizations for the construction of fused ring
systems.4 In general, fulvenes are prepared by the condensation
reactions of cyclopentadienes with ketones or aldehydes in the
presence of an alkali metal base5,6 or through pyrrolidine-
promoted reactions.7 However, strongly alkaline conditions limit
the substrate scope of these methodologies. Fulvenes could also
be prepared by transition-metal-catalyzed reactions, such as Pd-
catalyzed cross-coupling reactions of alkynes with vinyl halides,8
Pd-catalyzed cyclotrimerization of alkynes,9 or Ti-catalyzed
cyclotrimerization of tert-butylacetylene.10 However, these reac-
tions were restricted to internal alkynes or special substituted
terminal alkynes. Recently, a silver-catalyzed Nazarov-type cycli-
zation of R-hydroxyallenes to benzofulvenes has been reported.11
Despite progress in this area, the development of synthetic routes
that allow the facile assembly of functionalized fulvenes under
mild reaction conditions still remains an important objective.
Recently, we have developed a new domino approach for the
synthesis of substituted benzenes bearing enone or enal func-
tionalities with excellent Z-stereoselectivity through gold(I)-
catalyzed reactions of (Z)-2-en-4-yn-1-ols with furans (Scheme 1,
eq 1).12a The gold catalyst was found to be quite efficient in
catalyzing both the FriedelꢀCrafts and furan/alkyne12ꢀ14 cycli-
zation reactions with a highly regioselective manner of 7-endo-dig
cyclization. We envisioned that the readily available enynols of
2-ylidene-buta-3-yn-1-ols 1 might also undergo the Friedelꢀ
Crafts reactions with furans to deliver the furanyl group in a close
proximity to the alkyne moiety. We hypothesize that a new type
of 6-endo-dig cyclization of the thus formed enynyl furans 2 might
’ RESULTS AND DISCUSSION
Initially, we focused on the development of a straightforward
synthesis directly from enynols 1 and furan derivatives that
combines the FriedelꢀCrafts and furan/alkyne cyclization reac-
tions in a one-pot procedure. However, although much effort has
been made, no satisfactory results were obtained. For example,
reactions of enynol 1a (R1 = R2 = R3 = Ph) with 2 equiv of
2-methylfuran in the presence of 5 mol % gold catalysts such as
PPh3AuCl/AgOTf, PPh3AuCl/AgBF4, or PPh3AuNTf2 in CH2Cl2
gave a complicated mixture. We then decided to first synthesize the
furanylated substrates 2 by Lewis-acid-catalyzed allylic substitu-
tion reactions. Optimization studies indicated that in the pre-
sence of 20 mol % of BF3 Et2O the FriedelꢀCrafts reactions
3
could be completed within 3ꢀ40 min, and good to high yields
were achieved in most cases (Table 1). 2-Methylfuran, 2,3-
disubstituted furan, 2-phenylfuran, and furan are all suitable for
substitution reactions. The (Z)-configuration of the enyne
double bond in 2 was determined by the 2D NOESY spectrum
of compound 2h. However, when enynol bearing two different
substituents (R1 and R2) at both ends of the allylic moiety was
employed, two regioisomers of 2l were formed, which could not
be separated by column chromatography (Table 1, entry 12).
The failure of the regioselective substitution reactions of
Received: March 4, 2011
Published: May 23, 2011
r
2011 American Chemical Society
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|

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ARTICLE
Scheme 1
Table 1. Lewis-Acid-Catalyzed Substitution of Enynols 1 with
Furans
entry R1
R2
R3
R4 R5 product yield (%)a
1
2
3
4
5
6
7
8
9
Ph Ph
Ph
Ph
Ph
Ph
Me
Ph
H
H
2a
2b
2c
2d
2e
2f
95
94
88
42
74
56
94
Ph Ph
Ph Ph
Ph Ph
Ph Ph
Ph Ph
Ph Ph
Ph Ph
Ph Ph
Me Me
H
H
H
H
H
H
H
H
H
H
unsymmetrically substituted enynol 1 with furans was the
limitations of the substrate synthesis.
p-MeC6H4
Me
3,4,5-(OMe)3C6H2 Me
With furan-ynes 2 in hand, we were interested in exploring the
feasibility of 2 in gold-catalyzed cycloisomerization reactions.
We first tried the cyclization reaction of 2a with PPh3AuTf2
(5 mol %) as the catalyst in CH2Cl2. It was found that fulvene 3a
with an enone moiety was formed in 52% yield as a single geo-
metric isomer (Table 2, entry 1). Unlike the previously reported
benzene formation,12a in this case, the E-isomer of the enone
moiety instead of the Z-isomer was obtained. Cyclization of 2a
with PPh3AuOTf as the catalyst in CH2Cl2 at 50 °C led to 72%
yield of 3a as an E-isomer exclusively within 30 min (entry 3).
The reaction could also be performed in DCE or toluene to
produce the desired 3a in 58% and 68% yields, respectively
(entries 4 and 5). PPh3AuBF4 and PPh3AuSbF6 could also be
used as the catalysts, furnishing 3a in 52ꢀ59% yield, whereas
p-ClC6H4
p-NO2C6H4
H
Me
Me
Me
Me
Me
Me
2g
2h
2i
b
ꢀ
ꢀ
c
10 Ph Ph
11 Ph Ph
cyclohexenyl
cyclopropyl
2j
55
2k
2l
89
97d
12 Ph p-CIC6H4 Ph
a Isolated yields. b Prepared by Sonogashira coupling of 1-iodo-4-nitro-
benzene with 2i. c Not calculated. d Two regioisomers were obtained in a
ratio of 1.3:1.
both at C-2 and C-3 on the furan ring was subjected to this
gold-catalyzed reaction, the expected cyclization occurred
smoothly to generate E- or Z-enals 3d and 4d in high yields
of 80% and 83%, respectively (entry 4). The substituent effects
of the aryl groups on the alkyne terminus (R3) were also
examined. It was found that the functionalities of Me, MeO, Cl,
and NO2 were well tolerated. The electronic properties of
these aryl substituents had an influence on the reaction process
for the formation of the E-isomer 3, and enynes with an
electron-withdrawing group usually afforded higher yields of
fulvenes 3 than that of the substrates with an electron-donating
group (entries 5ꢀ8). Notably, when terminal alkyne 2i was
employed, the desired furans 3i and 4i were still obtained in
moderate yield via an endo-cyclization (entry 9). The result is in
sharp contrast with the analogous gold-catalyzed cycloisome-
rization of furan/ynes bearing a terminal alkyne moiety re-
ported previously, which proceeded with exo-type cyclization
exclusively.13aꢀg Perhaps in our case, less strained intermedi-
ates were generated upon endo-cyclization during the reaction.
Cyclohexenyl or cyclopropyl tethered alkynes also underwent
the cyclization reactions readily in THF to give the correspond-
ing fulvenes 4j and 4k in 62ꢀ79% yields (entries 10 and 11).
However, when the reactions were performed in CH2Cl2,
either complicated results or low yield (3k) of the desired
product was observed.
gold(III) of NaAuCl4 2H2O afforded a low yield of 3a (entries
3
6ꢀ8). Interestingly, switching the solvent to coordinating sol-
vents such as 1,4-dioxane or THF provided the (Z)-isomer 4a in
high yields of 89ꢀ97% with high stereoselectivity (entries 9 and
10). It is probably due to the coordination of the electrophilic
gold cation species by the solvent molecule, which would
decrease the Lewis acidity of the gold catalyst to prevent the
sequential ZꢀE isomerization reactions.16 The Z/E ratio chan-
ged only slightly in THF when elevating the reaction temperature
to 50 °C (entry 11). As a control, the reaction was run in the
absence of a gold catalyst (entry 12). As expected, AgOTf alone
did not promote any transformation. The above results indicated
that by choosing the appropriate solvents it is possible to obtain
either the E- or Z-isomer of the desired fulvenes.
After establishing the optimized conditions for both of the
double bond isomers 3 and 4 (Table 2, entry 3 for E-isomer 3,
entry 10 for Z-isomer 4), we proceeded to examine the scope of
this novel approach for the synthesis of fulvene derivatives. The
results are shown in Table 3. In all cases, the E/Z isomers 3 and
4 were obtained with high levels of stereoselectivity regardless
of the substitution patterns of enynes 2. Generally, Z-isomer 4
was obtained in better yields than that of the E-isomer 3. The
structure of 3b was unambiguously determined by X-ray
crystallographic analysis.17 The substituent effects (R4, R5)
on the furan moiety were first investigated. 2-Phenyl and 2,3-
dimethyl substituents were all compatible under the cyclization
conditions, yielding multisubstituted fulvenes in good yields
(Table 3, entries 2 and 3). In the reaction of R4-phenyl-
substituted 2b in THF, Luche reduction was performed to
allow for product purification after the cyclization was com-
pleted (entry 2, for product 5b). When enyne 2c unsubstituted
The apparent ring opening of furans to enone-type products
led us to propose the mechanism depicted in Scheme 2.12a,13g
Initial coordination of the gold catalyst to the triple bond affords
intermediate 6. This is followed by intramolecular furan/yne
cyclization in a highly regioselective 6-endo-dig manner to form a
cyclopropyl gold carbenoid 8.18 Rearrangement of 8 followed by
deprotonation and deauration leads to fulvene 4 with a Z-enone
moiety. It should be noted that the endo-type cyclization in
furan/yne cycloisomerization is quite rare.12,13h The E-isomer 3
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ARTICLE
Table 2. Optimization Studies for the Formation of Fulvenes
entry
catalyst (5 mol %)
solvent
temp (°C)
time (h)
yield (%)a of 3a and/or 4a
1
PPh3AuNTf2
PPh3AuOTf
PPh3AuOTf
PPh3AuOTf
PPh3AuOTf
PPh3AuBF4
PPh3AuSbF6
CH2Cl2
CH2Cl2
CH2Cl2
DCE
rt
2
52 (3a)
65 (95:5)b
72 (3a)
58 (3a)
68 (3a)
59 (3a)
52 (3a)
37 (3a)d
89 (3:97)b
97 (4a)
95 (5:95)b
NRe
2
3c
rt
2
50
50
50
rt
0.5
2
4
5
toluene
CH2Cl2
CH2Cl2
CH2Cl2
1,4-dioxane
THF
2
6
4
7
rt
4
8
NaAuCl4 2H2O
rt
6
3
9
PPh3AuOTf
PPh3AuOTf
PPh3AuOTf
AgOTf
rt
4
10
11
12
13
rt
4
THF
50
rt
4
CH2Cl2
2
f
PtCl2
DCE
80
5
-
a Isolated yield. b The ratio of 3a:4a is shown in parentheses. c In a sealed tube. d 40% of starting material was recovered. e NR = no reaction. f Most of 2a remained.
Table 3. Synthesis of Fulvenes through Gold(I)-Catalyzed
Cyclization of Furan/Ynes
Scheme 2
yield (%)a yield (%)a
entry substrate
R3
R4 R5
of 3
of 4
’ CONCLUSION
1
2
2a
2b
2c
2d
2e
2f
Ph
Ph
Ph
Ph
Me
Ph
H
H
3a 72 4a
3b 59 5bb
97
In summary, we have developed an efficient gold-catalyzed
intramolecular furan/yne cyclization reaction to form functiona-
lized fulvenes with an enone or enal moiety under mild reac-
tion conditions. Notably, the reactions reported here represent
the first examples of gold-catalyzed ring-opening cyclizations of
furan/ynes with a shortest tether in between furan and the
alkyne moiety. The stereochemistry of the enone double bond
can be easily controlled by simply changing the solvents. A
variety of furan/yne substrates turned out to be applicable to this
catalytic system.
58
3
Me Me 3c 65 4c
77c
83e,f
97
4
H
H
H
H
H
H
H
H
H
3d 80d 4d
3e 51 4e
3f 55 4f
3g 70 4g
3h 82 4h
3i 45 4i
5
p-MeC6H4
Me
6
3,4,5-(OMe)3C6H2 Me
82
7
2g
2h
2i
p-CIC6H4
p-NO2C6H4
H
Me
Me
Me
Me
Me
93e
87e,f
48f
79
8
9
10
2j
cyclohexenyl
-
4j
11
2k
cyclopropyl
3k 30 4k
62
a Isolated yield. b After Luche reduction. 5b is (Z)-3-((E)-3-benzylidene-
2,5-diphenylcyclopenta-1,4-dienyl)-1-phenylprop-2-en-1-ol. c Z:E = 20:
1. d E:Z = 25:1. e Z:E = 50: 1. f The reaction was performed at 50 °C.
’ EXPERIMENTAL SECTION
General Methods. All reactions were carried out under argon. DCE
and DCM were distilled from P2O5. THF and Toluene were distilled from
sodium and benzophenone. Unless noted, all commercial reagents were
used without further purification. Ph3PAuCl19 and Ph3PAuNTf220 were
might be formed by gold-assisted isomerization of 4 through the
formation of zwitterionic intermediates.16
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ARTICLE
prepared according to the published method. AgOTf was used as a
0.05 M solution in THF.
(E)-2-Benzylidene-4-cyclohexenylbut-3-ynal (s-1f). Column chro-
matography on silica gel (eluent: petroleum ether/ethyl acetate = 25:1)
afforded the title product in 93% yield (8 mmol scale, 1.76 g) as a yellow
oil. 1H NMR (300 MHz, CDCl3, Me4Si) δ1.62ꢀ1.73 (m, 4H), 2.17ꢀ2.19
(m, 2H), 2.27ꢀ2.30 (m, 2H), 6.33ꢀ6.36 (m, 1H), 7.43ꢀ7.46 (m, 4H),
8.09 (dd, J = 5.7, 3.6 Hz, 2H), 9.57 (s, 1H); 13C NMR (75.5 MHz, CDCl3,
Me4Si) δ 21.2, 22.0, 25.7, 28.6, 80.6, 103.1, 120.3, 122.9, 128.5, 130.4,
131.2, 134.1, 137.2, 150.2, 191.1. HRMS (EI) calcd for C17H16O:
236.1201, found 236.1203.
(E)-2-Benzylidene-1-phenyl-4-p-tolylbut-3-yn-1-ol (1b). Column
chromatography on silica gel (eluent: petroleum ether/ethyl acetate =
10:1) afforded the title product in 85% yield (3.6 mmol scale, 996.2 mg)
as a brown oil. 1H NMR (300 MHz, CDCl3, Me4Si) δ 2.31 (s, 3H), 2.70
(d, J = 3.9 Hz, 1H), 5.41 (d, J = 4.8 Hz, 1H), 6.94 (s, 1H), 7.08 (d, J = 8.1
Hz, 2H), 7.24ꢀ7.37 (m, 8H), 7.51 (d, J = 7.2 Hz, 2H), 7.89 (d, J = 7.5
Hz, 2H); 13C NMR (75.5 MHz, CDCl3, Me4Si) δ 21.5, 77.7, 86.3, 98.4,
119.9, 124.5, 126.5, 127.8, 128.20, 128.24, 128.3, 128.8, 129.1, 131.3,
133.7, 135.9, 138.7, 141.9. HRMS (EI) calcd for C24H20O: 324.1514,
found 324.1510.
1H NMR spectra were recorded at 300 or 400 MHz, and 13C NMR
spectra were recorded at 75.4 or 100.6 MHz, in CDCl3 (containing 0.03%
TMS). 1H NMR spectra were recorded with tetramethylsilane (δ = 0.00
ppm) as internal reference; 13C NMR spectra were recorded with
CDCl3 (δ = 77.00 ppm) as internal reference.
General Procedure for the Synthesis of Enynols 1. Typical
Procedure for the Synthesis of (E)-2-Benzylidene-1,4-diphenylbut-
3-yn-1-ol (1a). To a solution of Z-R-bromocinnamaldehyde (2.11 g,
10 mmol) in triethylamine (10 mL) and THF (10 mL) were added
phenylacetylene (1.22 g, 1.32 mL, 12 mmol), Pd(PPh3)4 (0.12 g,
0.10 mmol), and CuI (0.095 g, 0.50 mmol) at room temperature, and
then the mixture was stirred overnight. After the starting material was
consumed, the solvent was removed in vacuo, and the residue was purified
by chromatography on silica gel (petroleum:ethyl acetate = 20:1 to 10:1)
to afford compound (E)-2-benzylidene-4-phenylbut-3-ynal (s-1a)
(2.31 g, 99%) as yellow oil. The spectroscopic data are in agreement
with that previously reported.21
(E)-2-Benzylidene-1-phenyl-4-(3,4,5-trimethoxyphenyl)but-3-yn-1-
ol (1c). Column chromatography on silica gel (eluent: petroleum ether/
ethyl acetate = 3:1) afforded the title product in 69% yield (2.9 mmol
scale, 805.4 mg) as a brown oil. 1H NMR (300 MHz, CDCl3, Me4Si)
δ 2.45 (d, J = 5.7 Hz, 1H), 3.83 (s, 6H), 3.85 (s, 3H), 5.48 (d, J = 5.1 Hz,
1H), 6.58 (s, 2H), 7.00 (s, 1H), 7.32ꢀ7.39 (m, 6H), 7.54 (d, J = 7.2 Hz,
2H), 7.90 (d, J = 7.8 Hz, 2H); 13C NMR (75 MHz, CDCl3, Me4Si) δ
56.0, 60.9, 77.6, 86.2, 98.1, 108.6, 117.9, 124.3, 126.6, 127.7, 128.15,
128.20, 128.4, 128.8, 134.0, 135.9, 138.9, 141.9, 152.9. HRMS (EI) calcd
for C26H24O4: 400.1675, found 400.1672.
(E)-2-Benzylidene-4-(4-chlorophenyl)-1-phenylbut-3-yn-1-ol (1d).
Column chromatography on silica gel (eluent: petroleum ether/ethyl
acetate = 10:1) afforded the title product in 59% yield (3.7 mmol scale,
753.7 mg) as a brown oil. 1H NMR (300 MHz, CDCl3, Me4Si) δ 3.27
(d, J = 0.6 Hz, 1H), 5.34 (s, 1H), 6.94 (s, 1H), 7.14ꢀ7.31 (m, 10H), 7.44
(d, J = 7.5 Hz, 2H), 7.81 (d, J = 7.5 Hz, 2H); 13C NMR (75.5 MHz,
CDCl3, Me4Si) δ 77.5, 88.0, 96.6, 121.3, 124.0, 126.4, 127.7, 128.1,
128.4, 128.5, 128.8, 132.5, 134.27, 134.29, 135.7, 141.6. HRMS (EI)
calcd for C23H17ClO: 344.0968, found 344.0962.
(E)-2-Benzylidene-1-phenyl-4-(trimethylsilyl)but-3-yn-1-ol (1e).
Column chromatography on silica gel (eluent: petroleum ether/ethyl
acetate = 3:1) afforded the title product in 84% yield (3.1 mmol scale,
798.7 mg) as a brown oil. 1H NMR (400 MHz, CDCl3, Me4Si) δ 0.34 (s,
9H), 2.72 (d, J = 5.2 Hz, 1H), 5.49 (d, J = 4.8 Hz, 1H), 7.05 (s, 1H),
7.43ꢀ7.52 (m, 6H), 7.61ꢀ7.63 (m, 2H), 8.03ꢀ8.05 (m, 2H); 13C NMR
(100.6 MHz, CDCl3, Me4Si) δ ꢀ0.4, 77.4, 102.3, 105.0, 124.3, 126.6,
127.8, 128.06, 128.2, 128.6, 128.9, 134.8, 135.6, 141.7. HRMS (EI) calcd
for C20H22OSi: 306.1440, found 306.1438.
To a solution of bromobenzene (3.96 g, 2.7 mL, 25.2 mmol) in THF
(50 mL) was added n-BuLi (10.0 mL, 25.2 mmol, 2.5 M solution in
hexanes) at ꢀ78 °C. After stirring at the same temperature for 1 h, s-1a
(4.88 g, 21.0 mmol in 50 mL of THF) was added. The resulting solution
was warmed to room temperature and stirred for 8 h. Then the mixture
was quenched with saturated ammonium chloride solution. The reaction
mixture was extracted with ether and dried over anhydrous Na2SO4. The
solvent was evaporated, and the residue was purified by chromatography
on silica gel (petroleum ether/ethyl acetate = 10:1) to afford compound
1a (6.49 g, 99%) as brown oil. 1H NMR (400 MHz, CDCl3, Me4Si) δ
3.11 (s, 1H), 5.36 (s, 1H), 6.95 (s, 1H), 7.19ꢀ7.33 (m, 11H), 7.47 (d, J =
7.2 Hz, 2H), 7.86 (d, J = 7.2 Hz, 2H); 13C NMR (100 MHz, CDCl3,
Me4Si) δ 77.6, 87.1, 97.9, 122.9, 124.3, 126.5, 127.6, 128.10, 128.12,
128.2, 128.26, 128.32, 128.8, 131.3, 133.8, 135.8, 141.8. HRMS (EI)
calcd for C23H18O: 310.1358, found 310.1357.
(E)-2-Benzylidene-4-p-tolylbut-3-ynal (s-1b). Column chromatog-
raphy on silica gel (eluent: petroleum ether/ethyl acetate = 10:1)
afforded the title product in 77% yield (5 mmol scale, 944 mg) as a
brown oil. 1H NMR (300 MHz, CDCl3, Me4Si) δ 2.36 (s, 3H), 7.17 (d,
J = 7.8 Hz, 2H), 7.45ꢀ7.49 (m, 6H), 8.12ꢀ8.14 (m, 2H), 9.61 (s, 1H);
13C NMR (75.5 MHz, CDCl3, Me4Si) δ 21.5, 82.6, 101.2, 119.4, 122.7,
128.7, 129.2, 130.6, 131.5, 131.7, 134.1, 139.3, 150.9, 191.0. HRMS (EI)
calcd for C18H14O: 246.1045, found 246.1050.
(E)-2-Benzylidene-4-(3,4,5-trimethoxyphenyl)but-3-ynal (s-1c).
Column chromatography on silica gel (eluent: petroleum ether/ethyl
acetate = 10:1 to 5:1) afforded the title product in 87% yield (8 mmol
scale, 2.25 g) as a yellow solid. 1H NMR (300 MHz, CDCl3, Me4Si)
δ 3.88 (s, 9H), 6.82 (s, 2H), 7.48ꢀ7.54 (m, 4H), 8.12ꢀ8.14 (m, 2H),
9.64 (s, 1H); 13C NMR (75.5 MHz, CDCl3, Me4Si) δ 56.1, 60.9, 82.2,
100.9, 108.9, 117.4, 122.6, 128.7, 130.6, 131.6, 134.1, 139.4, 151.5,
153.1, 191.0. HRMS (EI) calcd for C20H18O4: 322.1205, found
322.1206.
(E)-2-Benzylidene-4-cyclohexenyl-1-phenylbut-3-yn-1-ol (1f). Col-
umn chromatography on silica gel (eluent: petroleum ether/ethyl
acetate = 20:1 to 10:1) afforded the title product in 33% yield (7.2
1
mmol scale, 806.8 mg) as a brown oil. H NMR (300 MHz, CDCl3,
Me4Si) δ 1.55ꢀ1.61 (m, 4H), 2.09ꢀ2.11 (m, 4H), 2.63 (s, 1H), 5.33
(s, 1H), 6.08 (s, 1H), 6.85 (s, 1H), 7.24ꢀ7.35 (m, 6H), 7.46 (d, J =
7.5 Hz, 2H), 7.84 (d, J = 7.5 Hz, 2H); 13C NMR (75.5 MHz, CDCl3,
Me4Si) δ 21.3, 22.1, 25.7, 28.6, 77.7, 84.2, 100.5, 120.7, 124.7, 126.4,
127.6, 128.06, 128.11, 128.13, 128.7, 132.8, 135.9, 136.0, 142.0. HRMS
(EI) calcd for C23H22O: 314.1671, found 314.1674.
(E)-2-Benzylidene-4-(4-chlorophenyl)but-3-ynal (s-1d). Column
chromatography on silica gel (eluent: petroleum ether/ethyl acetate =
10:1) afforded the title product in 90% (3 mmol scale, 717 mg) yield as a
yellow solid. 1H NMR (300 MHz, CDCl3, Me4Si) δ 7.33 (d, J =
9.0 Hz, 2H), 7.46ꢀ7.52 (m, 6H), 8.08ꢀ8.11 (m, 2H), 9.61 (s, 1H); 13C
NMR (75.5 MHz, CDCl3, Me4Si) δ 84.0, 99.6, 120.9, 122.3, 128.75,
128.76, 130.6, 131.7, 132.9, 133.9, 135.1, 151.8, 190.8. HRMS (EI) calcd
for C17H11ClO: 266.0498, found 266.0500.
(E)-2-Benzylidene-4-(trimethylsilyl)but-3-ynal (s-1e). Column chro-
matography on silica gel (eluent: petroleum ether/ethyl acetate = 15:1)
afforded the title product in 69% yield (5 mmol scale, 783 mg) as a
yellow oil. The spectroscopic data are in agreement with that previously
reported.22
(E)-2-Benzylidene-1-(4-chlorophenyl)-4-phenylbut-3-yn-1-ol (1g).
Column chromatography on silica gel (eluent: petroleum ether/ethyl
acetate = 7:1) afforded the title product in 77% yield (3 mmol scale,
1
792.5 mg) as yellow oil. H NMR (400 MHz, CDCl3, Me4Si) δ 2.79
(bs, 1H), 5.38 (s, 1H), 6.94 (s, 1H), 7.26ꢀ7.37 (m, 10H), 7.42ꢀ7.44 (m,
2H), 7.87ꢀ7.89 (m, 2H); 13C NMR (75.5 MHz, CDCl3, Me4Si) δ 77.2,
86.6, 98.3, 122.7, 123.9, 127.9, 128.3, 128.36, 128.37, 128.61, 128.63,
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ARTICLE
128.9, 131.4, 133.5, 134.4, 135.6, 140.3. HRMS (EI) calcd for
C23H17ClO: 344.0968, found 344.0969.
129.0, 131.3, 135.5, 136.4, 138.4, 140.3, 151.4, 153.2. HRMS (EI) calcd
for C29H24O: 388.1827, found 388.1833.
(Z)-2-(2-Benzylidene-1-phenyl-4-(3,4,5-trimethoxyphenyl)but-3-ynyl)-
5-methylfuran (2f). Column chromatography on silica gel (eluent:
petroleum ether/ethyl acetate = 5:1) afforded the title product in 56%
Typical Procedure for the Synthesis of (Z)-2-(2-Benzyli-
dene-1,4-diphenylbut-3-ynyl)-5-methylfuran (2a). To a solu-
tion of (E)-2-benzylidene-1,4-diphenylbut-3-yn-1-ol 1a (62 mg, 0.2
mmol) in DCM (2 mL) were added 2-methylfuran (19.7 mg, 22 μL,
1
yield (1 mmol scale, 260.8 mg) as a yellow oil. H NMR 400 MHz,
CDCl3, Me4Si) δ 2.25 (s, 3H), 3.77 (s, 6H), 3.82 (s, 3H), 5.09 (s, 1H),
5.91 (d, J = 0.8 Hz, 1H), 6.08 (d, J = 3.2 Hz, 1H), 6.52 (s, 2H), 6.63 (s,
1H), 7.23ꢀ7.25 (m, 2H), 7.32 (t, J = 7.6 Hz, 4H), 7.40 (d, J = 7.2 Hz,
2H), 7.86 (d, J = 7.6 Hz, 2H); 13C NMR (100.6 MHz, CDCl3, Me4Si)
δ 13.5, 53.2, 55.9, 60.7, 88.4, 97.1, 106.0, 108.4, 109.0, 118.2, 122.5,
126.8, 128.0, 128.1, 128.6, 128.7, 135.7, 136.2, 140.2, 151.3, 152.9, 153.0.
HRMS (EI) calcd for C31H28O4: 464.1988, found 464.1991.
(Z)-2-(2-Benzylidene-4-(4-chlorophenyl)-1-phenylbut-3-ynyl)-5-
methylfuran (2g). Column chromatography on silica gel (eluent:
petroleum ether/ethyl acetate = 100:1) afforded the title product in
94% yield (1 mmol scale, 384.3 mg) as a yellow oil. 1H NMR 400 MHz,
CDCl3, Me4Si) δ 2.22 (s, 3H), 5.07 (s, 1H), 5.89ꢀ5.90 (m, 1H), 6.07 (d,
J = 3.2 Hz, 1H), 6.64 (s, 1H), 7.18ꢀ7.23 (m, 6H), 7.27ꢀ7.32 (m, 4H),
7.37ꢀ7.39 (m, 2H), 7.82ꢀ7.84 (m, 2H); 13C NMR (100.6 MHz,
CDCl3, Me4Si) δ 13.6, 53.4, 90.3, 95.7, 106.1, 109.2, 121.7, 122.4,
127.0, 128.1, 128.2, 128.3, 128.6, 128.7, 132.5, 134.2, 136.2, 136.4, 140.1,
151.4, 153.0. HRMS (EI) calcd for C28H21ClO: 408.1281, found
408.1280.
Synthesis of (Z)-2-(2-Benzylidene-4-(4-nitrophenyl)-1-phenylbut-3-
ynyl)-5-methylfuran (2h). To a solution of (Z)-2-(2-benzylidene-1-
phenylbut-3-ynyl)-5-methylfuran 2i (see below, 0.33 g, 1.1 mmol) in
triethylamine (5 mL) were added 1-iodo-4-nitrobenzene (0.25 g, 1.0
mmol), PdCl2(PPh3)2 (14 mg, 0.02 mmol), and CuI (9.5 mg, 0.05
mmol) at room temperature, and then the mixture was heated at 50 °C
for 5 h. After the starting material was consumed, the solvent was
removed in vacuo, and a saturated NH4Cl solution was added. The
reaction mixture was extracted with ether and dried over anhydrous
Na2SO4. The solvent was evaporated, and the residue was purified by
chromatography on silica gel (petroleum:dichloromethane = 10:1) to
afford the title compound (278.9 mg, 66%) as a yellow solid. Mp
86ꢀ87 °C. 1H NMR (400 MHz, CDCl3, Me4Si) δ 2.26 (s, 3H), 5.10
(s, 1H), 5.93(s, 1H), 6.07 (d, J = 1.6 Hz, 1H), 6.74 (s, 1H), 7.26ꢀ7.40
(m, 10 H), 7.81 (d, J = 8.0 Hz, 2H), 8.08 (d, J = 9.2 Hz, 2H); 13C NMR
(100.6 MHz, CDCl3, Me4Si) δ 13.5, 53.0, 94.5, 94.6, 106.1, 109.3, 121.9,
123.4, 127.1, 128.2, 128.3, 128.60, 128.64, 128.8, 129.6, 131.8, 135.8,
138.0, 139.8, 146.7, 151.6, 152.7. HRMS (EI) calcd for C28H21NO3:
419.1521, found 419.1528.
0.24 mmol) and BF3 Et2O (5.0 μL, 0.04 mmol). The resulting solution
3
was stirred at room temperature until the reaction was complete as
monitored by thin-layer chromatography. The solvent was evaporated in
vacuo, and the residue was purified by flash column chromatography on
silica gel (eluent: petroleum ether/ethyl acetate = 100:1) to afford the
1
title product 2a (70.7 mg, 95%) as a yellow oil. H NMR (400 MHz,
CDCl3, Me4Si) δ 2.25 (s, 3H), 5.07 (s, 1H), 5.91 (d, J = 2.0 Hz, 1H),
6.08 (d, J = 2.8 Hz, 1H), 6.63 (s, 1H), 7.23ꢀ7.26 (m, 5H), 7.31ꢀ7.34
(m, 6H), 7.40 (d, J = 7.6 Hz, 1H), 7.88 (d, J = 7.6 Hz, 1H); 13C NMR
(100.6 MHz, CDCl3, Me4Si) δ 13.6, 53.5, 89.3, 97.0, 106.1, 109.1, 122.7,
123.4, 127.0, 128.1, 128.25, 128.27, 128.8, 131.4, 135.9, 136.3, 140.2,
151.4, 153.1. HRMS (EI) calcd for C28H22O: 374.1671, found
374.1673.
(Z)-2-(2-Benzylidene-1,4-diphenylbut-3-ynyl)-5-phenylfuran (2b).
Column chromatography on silica gel (eluent: petroleum ether/ethyl
acetate = 100:1) afforded the title product in 94% yield (2 mmol scale,
821.1 mg) as a yellow oil. 1H NMR (300 MHz, CDCl3, Me4Si) δ 5.18
(s, 1H), 6.29 (d, J = 3.3 Hz, 1H), 6.57 (d, J = 3.3 Hz, 1H), 6.68 (s, 1H),
7.11ꢀ7.31 (m, 14H), 7.43 (d, J = 7.8 Hz, 2H), 7.60 (d, J = 8.1 Hz, 2H),
7.88 (d, J = 7.5 Hz, 2H); 13C NMR (75.5 MHz, CDCl3, Me4Si) δ 53.6,
89.2, 97.2, 105.7, 110.7, 122.4, 123.1, 123.5, 127.0, 127.1, 128.1, 128.19,
128.22, 128.27, 128.31, 128.5, 128.7, 130.8, 131.3, 136.1, 136.2, 139.9,
153.3, 154.6. HRMS (EI) calcd for C33H24O: 436.1827, found
436.1833.
(Z)-5-(2-Benzylidene-1,4-diphenylbut-3-ynyl)-2,3-dimethylfuran
(2c). It was synthesized from (Z)-2-benzylidene-1,4-diphenylbut-3-yn-
1-ol 1a (0.62 g, 2 mmol), DCM (20 mL), 2,3-dimethylfuran (0.25 mL, 2.4
mmol), and BF3 Et2O (50 μL, 0.4 mmol) according to the procedure
3
described for 2a. Column chromatography on silica gel (eluent: petroleum
ether/ethyl acetate = 100:1) afforded the title product (0.68 g, 88%) as a
1
yellow oil. H NMR (400 MHz, CDCl3, Me4Si) δ 1.87 (s, 3H), 2.14
(s, 3H), 5.04 (s, 1H), 5.98 (s, 1H), 6.64 (s, 1H), 7.18ꢀ7.22 (m, 5H),
7.27ꢀ7.31 (m, 6H), 7.39ꢀ7.41 (m, 2H), 7.86ꢀ7.88 (m, 2H); 13C NMR
(100.6 MHz, CDCl3, Me4Si) δ 9.9, 11.3, 53.5, 89.4, 97.0, 111.7, 114.3,
122.8, 123.3, 126.9, 128.06, 128.08, 128.18, 128.20, 128.22, 128.7, 128.8,
131.3, 135.9, 136.3, 140.3, 146.6, 151.9. HRMS (EI) calcd for C29H24O:
388.1827, found 388.1826.
Synthesis of (Z)-2-(2-Benzylidene-1-phenylbut-3-ynyl)-5-methylfuran
(2i). To a solution of (E)-2-benzylidene-1-phenyl-4-(trimethylsilyl)but-
3-yn-1-ol (0.45 g, 1.47 mmol) in methanol (20 mL) was added K2CO3
(0.24 g, 1.76 mmol) at room temperature. After the starting material was
consumed, the solvent was removed in vacuo. The mixture was extracted
with ether and dried over anhydrous Na2SO4. The crude product was
used in the next step without purification. To a solution of the above
crude product in DCM (15 mL) were added 2-methylfuran (0.15 g, 158
(Z)-2-(2-Benzylidene-1,4-diphenylbut-3-ynyl)furan (2d). It was
synthesized from (Z)-2-benzylidene-1,4-diphenylbut-3-yn-1-ol 1a (0.31 g,
1 mmol in 10 mL of DCM), furan (0.37 mL, 5.0 mmol), and BF3 Et2O
3
(25 μL, 0.2 mmol) according to the procedure described for 2a. Column
chromatography on silica gel (eluent: petroleum ether/ethyl acetate =
100:1) afforded the title product (151.3 mg, 42%) as a yellow oil. 1H NMR
(400 MHz, CDCl3, Me4Si) δ 5.12 (s, 1H), 6.23 (d, J = 3.6 Hz, 1H), 6.40
(dd, J = 3.0, 1.6 Hz, 1H), 6.63 (s, 1H), 7.26ꢀ7.40 (m, 14H), 7.88 (d, J = 7.2
Hz, 2H); 13C NMR (100.6 MHz, CDCl3, Me4Si) δ 53.4, 89.1, 97.2, 108.3,
110.2, 122.4, 123.2, 127.1, 128.1, 128.17, 128.23, 128.27, 128.31, 128.72,
128.73, 131.3, 136.1, 136.2, 140.0, 141.8, 155.1. HRMS (EI) calcd for
C27H20O: 360.1514, found 360.1518.
μL, 1.76 mmol) and BF3 Et2O (37 μL, 0.29 mmol). The mixture was
3
stirred at room temperature, and the reaction was monitored by TLC.
After 30 min, the reaction completed. The solvent was evaporated in
vacuo, and the residue was purified by flash column chromatography on
silica gel (eluent: petroleum ether) to afford the title product (0.37 g,
84%) as a yellow oil. 1H NMR (400 MHz, CDCl3, Me4Si) δ 2.25 (s, 3H),
3.25 (s, 1H), 4.99 (s, 1H), 5.90 (d, J = 0.8 Hz, 1H), 6.00 (s, 1H), 6.59 (s,
1H), 7.24ꢀ7.33 (m, 8H), 7.81 (d, J = 7.6 Hz, 2H); 13C NMR (100.6
MHz, CDCl3, Me4Si) δ 13.6, 53.3, 82.9, 85.1, 106.1, 109.3, 121.6, 127.0,
128.1, 128.28, 128.31, 128.67, 128.70, 135.7, 137.6, 139.7, 151.5, 152.7.
HRMS (EI) calcd for C22H18O: 298.1358, found 298.1355.
(Z)-2-(2-Benzylidene-1-phenyl-4-p-tolylbut-3-ynyl)-5-methylfuran
(2e). Column chromatography on silica gel (eluent: petroleum ether/
ethyl acetate = 100:1) afforded the title product in 74% yield (2.9 mmol
1
scale, 834.6 mg) as a blue oil. H NMR (300 MHz, CDCl3, Me4Si)
δ 2.25 (s, 3H), 2.30 (s, 3H), 5.06 (s, 1H), 5.90 (d, J = 1.2 Hz, 1H), 6.08
(d, J = 2.7 Hz, 1H), 6.61 (s, 1H), 7.07 (d, J = 7.8 Hz, 2H), 7.24 (t, J = 7.5
Hz, 4H), 7.32 (t, J = 6.9 Hz, 4H), 7.40 (d, J = 7.5 Hz, 2H), 7.88 (d, J = 7.2
Hz, 2H); 13C NMR (75.5 MHz, CDCl3, Me4Si) δ 13.6, 21.5, 53.6, 88.7,
97.4, 106.1, 109.1, 120.3, 122.8, 126.9, 128.0, 128.1, 128.2, 128.7, 128.8,
(Z)-2-(2-Benzylidene-4-cyclohexenyl-1-phenylbut-3-ynyl)-5-methylfur-
an (2j). Column chromatography on silica gel (eluent: petroleum ether/
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ARTICLE
ethyl acetate = 10:1) afforded the title product in 55% yield (2.4 mmol
scale, 491.3 mg) as a yellow oil. H NMR 400 MHz, CDCl3, Me4Si)
flask was sealed and immersed in an oil bath at 50 °C and stirred at this
temperature until the reaction was complete as monitored by thin-layer
chromatography. The solvent was evaporated under the reduced
pressure, and the residue was purified by chromatography on silica gel
(petroleum ether/ethyl acetate = 10:1) to afford (E)-4-((E)-3-benzyli-
dene-2,5-diphenylcyclopenta-1,4-dienyl)but-3-en-2-one 3a (53.8 mg,
1
δ 1.47ꢀ1.56 (m, 4H), 1.99ꢀ2.07 (m, 4H), 2.20 (s, 3H), 4.97 (s, 1H),
5.86 (dd, J = 0.8, 2.8 Hz, 1H), 5.99ꢀ6.01 (m, 1H), 6.04 (d, J = 2.8 Hz,
1H), 6.52 (s, 1H), 7.13ꢀ7.28 (m, 6H), 7.33ꢀ7.35 (m, 2H), 7.81 (d,
J = 7.6 Hz, 2H); 13C NMR (100.6 MHz, CDCl3, Me4Si) δ 13.5, 21.3,
22.1, 25.6, 28.5, 53.6, 86.8, 99.3, 106.0, 108.9, 120.9, 123.0, 126.7, 127.7,
127.9, 128.1, 128.5, 128.6, 134.6, 135.2, 136.4, 140.3, 151.1, 153.2.
HRMS (EI) calcd for C28H26O: 378.1984, found 378.1987.
Synthesis of (Z)-2-(2-Benzylidene-4-cyclopropyl-1-phenylbut-3-ynyl)-
5-methylfuran (2k). To a solution of Z-R-bromocinnamaldehyde
(2.11 g, 10 mmol) in triethylamine (10 mL) and THF (10 mL) were
added ethynylcyclopropane (1.02 mL, 12 mmol), Pd(PPh3)4 (0.12 g,
0.10 mmol), and CuI (95 mg, 0.50 mmol) at room temperature, and
then the mixture was stirred for 20 h. After the starting material was con-
sumed, the solvent was removed in vacuo, and the residue was purified
by chromatography on silica gel (petroleum: ethyl acetate = 20:1 to
10:1) to afford (E)-2-benzylidene-4-cyclopropylbut-3-ynal (1.85 g,
94%) as yellow oil.
To a solution of the above ynal (1.84 g, 9.36 mmol) in THF
(10.0 mL) was added PhLi (5.2 mL, 10.3 mmol, 2.0 M in dibutylether)
at ꢀ78 °C. The resulting solution was warmed to room temperature and
stirred for 2 h. Then the mixture was quenched with saturated ammonium
chloride solution. The reaction mixture was extracted with ether and dried
over anhydrous Na2SO4. The solvent was evaporated, and the residue
was purified by chromatography on silica gel (petroleum ether/ethyl
acetate = 5:1) to afford (E)-2-benzylidene-4-cyclopropyl-1-phenylbut-3-
yn-1-ol (2.16 g, 84%) as brown oil.
1
72%) as a brown oil. H NMR (400 MHz, CDCl3, Me4Si) δ 2.07
(s, 3H), 5.89 (d, J = 16.0 Hz, 1H), 6.82 (s, 1H), 7.11 (s, 1H), 7.35ꢀ7.51
(m, 14H), 7.57ꢀ7.59 (m, 2H); 13C NMR (100.6 MHz, CDCl3, Me4Si)
δ 27.5, 120.6, 127.85, 127.88, 128.2, 128.3, 128.4, 128.8, 129.6, 129.7,
130.8, 131.0, 134.0, 135.0, 136.3, 136.5, 136.6, 140.6, 143.8, 144.9, 148.0,
198.5. HRMS (EI) calcd for C28H22O: 374.1671, found 374.1667.
Method B. To a solution of enyne 2a (74.9 mg, 0.2 mmol) in THF
(2 mL) were added PPh3AuCl (5.0 mg, 0.01 mmol) and AgOTf (0.2 mL,
0.01 mmol, used as a 0.05 M solution in THF). The resulting solution
was stirred at room temperature until the reaction was complete as
monitored by thin-layer chromatography. The solvent was evaporated
under the reduced pressure, and the residue was purified by chroma-
tography on silica gel (petroleum ether/ethyl acetate = 10:1) to afford
(Z)-4-((E)-3-benzylidene-2,5-diphenylcyclopenta-1,4-dienyl)but-3-en-
2-one 4a (72.4 mg, 97%) as a brown oil. 1H NMR (400 MHz, CDCl3,
Me4Si) δ 1.70 (s, 3H), 6.06 (d, J = 11.6 Hz, 1H), 6.72 (d, J = 12.4 Hz,
1H), 6.89 (s, 1H), 7.13 (s, 1H), 7.13ꢀ7.43 (m, 13H), 7.58 (d, J = 6.8 Hz,
2H); 13C NMR (100.6 MHz, CDCl3, Me4Si) δ 29.0, 118.3, 127.2, 127.3,
127.8, 128.0, 128.1, 128.6, 129.2, 130.6, 130.8, 131.5, 134.4, 134.6, 136.2,
136.7, 136.9, 138.9, 139.4, 143.6, 148.2, 199.2. HRMS (EI) calcd for
C28H22O: 374.1671, found 374.1670.
(E)-3-((E)-3-Benzylidene-2,5-diphenylcyclopenta-1,4-dienyl)-1-phenyl-
prop-2-en-1-one (3b). Method A. Column chromatography on silica gel
(eluent: petroleum ether/ethyl acetate = 20:1) afforded the title product
in 59% yield (0.3 mmol scale, 77.4 mg) as a brown solid. Mp 165ꢀ166 °C.
1H NMR (300 MHz, CDCl3, Me4Si) δ 6.77 (d, J = 15.9 Hz, 1H), 6.86 (s,
To a solution of the above enynol (274 mg, 1.0 mmol) in DCM
(10.0 mL) were added 2-methylfuran (108 μL, 98.5 mg, 1.2 mmol) and
BF3 Et2O (25.0 μL, 0.20 mmol). The mixture was kept at room tempera-
3
ture and the reaction was monitored by TLC. After 20 min, the reaction
completed. The solvent was evaporated in vacuo, and the residue was
purified by flash column chromatography on silica gel (eluent: petroleum
ether/ethyl acetate = 100:1) to afford the title product (301 mg, 89%) as
yellow oil. The combined yield for three steps was 70%. 1H NMR (300
MHz, CDCl3, Me4Si) δ 0.59ꢀ0.64 (m, 2H), 0.72ꢀ0.77 (m, 2H),
1.31ꢀ1.36 (m, 1H), 2.24 (s, 3H), 4.92 (s, 1H), 5.88 (d, J = 1.8 Hz,
1H), 5.99 (d, J = 3.0 Hz, 1H), 6.46 (s, 1H), 7.18ꢀ7.31 (m, 8H), 7.79 (d,
J = 7.8 Hz, 2H); 13C NMR (75.5 MHz, CDCl3, Me4Si) δ 0.7, 8.7, 13.6,
53.8, 75.3, 102.1, 106.0, 108.9, 123.2, 126.8, 127.7, 128.0, 128.2, 128.3,
128.7, 134.4, 136.5, 140.4, 151.3, 153.3. HRMS (EI) calcd for C25H22O:
338.1671, found 338.1672.
1H), 7.15 (s, 1H), 7.29ꢀ7.60 (m, 20H), 7.80 (d, J = 15.9 Hz, 1H); 13
C
NMR (75.5 MHz, CDCl3, Me4Si) δ 120.6, 124.4, 127.7, 127.8, 128.1,
128.24, 128.28, 128.33, 128.7, 128.8, 129.6, 130.8, 131.1, 132.4, 134.0,
135.8, 136.5, 137.0, 137.1, 138.2, 140.7, 143.9, 145.4, 148.1, 189.7.
HRMS (EI) calcd for C33H24O: 436.1827, found 436.1830.
(E)-4-((E)-3-Benzylidene-2,5-diphenylcyclopenta-1,4-dienyl)-3-meth-
ylbut-3-en-2-one (3c). Method A. Column chromatography on silica gel
(eluent: petroleum ether/ethyl acetate = 10:1) afforded the title product
in 65% yield (0.2 mmol scale, 50.3 mg) as a brown oil. 1H NMR (400
MHz, CDCl3, Me4Si) δ 1.26 (s, 3H), 2.28 (s, 3H), 6.93 (s, 1H), 7.21
(s, 1H), 7.28ꢀ7.46 (m, 14H), 7.60 (d, J = 7.2 Hz, 2H); 13C NMR (100.6
MHz, CDCl3, Me4Si) δ 13.8, 26.0, 118.1, 127.2, 127.5, 127.7, 128.3,
128.4, 128.7, 129.3, 130.3, 130.7, 135.1, 135.3, 136.2, 136.3, 136.7, 139.3,
139.4, 139.5, 143.7, 148.7, 199.8. HRMS (EI) calcd for C29H24O:
388.1827, found 388.1823.
(Z)-4-((E)-3-Benzylidene-2,5-diphenylcyclopenta-1,4-dienyl)-3-methyl-
but-3-en-2-one (4c). Method B. Column chromatography on silica gel
(eluent: petroleum ether/ethyl acetate = 10:1) afforded the title product
in 77% yield (Z:E = 20:1) (0.2 mmol scale, 59.8 mg) as a brown oil. 1H
NMR (300 MHz, CDCl3, Me4Si) δ 1.81 (s, 3H), 1.87 (s, 3H), 6.62
(s, 1H), 6.90 (s, 1H), 7.13 (s, 1H), 7.29ꢀ7.46 (m, 13H), 7.58 (d, J = 7.2
Hz, 2H); 13C NMR (75.5 MHz, CDCl3, Me4Si) δ 20.7, 28.3, 118.2,
127.0, 127.5, 128.0, 128.1, 128.2, 128.6, 129.1, 130.0, 130.6, 130.8, 134.6,
135.9, 136.8, 137.6, 138.2, 138.6, 140.3, 143.6, 148.3, 202.1. HRMS (EI)
calcd for C29H24O: 388.1827, found 388.1833.
(Z)-2-(2-Benzylidene-1-(4-chlorophenyl)-4-phenylbut-3-ynyl)-5-
methylfuran and (Z)-2-(2-(4-Chlorobenzylidene)-1,4-diphenylbut-3-
ynyl)-5-methylfuran (2l). It was synthesized from (E)-2-benzylidene-
1-(4-chlorophenyl)-4-phenylbut-3-yn-1-ol and 2-methylfuran according
to the procedure described for 2a. Column chromatography on silica gel
(eluent: petroleum ether/ethyl acetate = 100:1) afforded the product 2l
as a mixture of two regioisomers in 97% yield in the ratio of 1.3:1 (0.33
1
mmol scale, 131.2 mg) as a yellow oil. H NMR (400 MHz, CDCl3,
Me4Si) δ two isomers: 2.26 (s), 5.03 (s), 5.06 (s), 5.92 (s), 6.07 (t, J = 3.2
Hz), 6.57 (s), 6.62 (s), 7.28ꢀ7.40 (m), 7.80 (d, J = 8.4 Hz), 7.88 (d,
J = 7.2 Hz); 13C NMR (75.5 MHz, CDCl3, Me4Si) δ two isomers: 13.6,
13.7, 52.9, 53.5, 88.86, 88.89, 97.2, 97.7, 106.09, 106.13, 109.2, 109.3,
122.1, 123.05, 123.12, 123.4, 127.1, 128.17, 128.26, 128.31, 128.40,
128.44, 128.72, 128.74, 129.9, 130.1, 131.3, 132.7, 133.5, 134.4, 134.8,
136.06, 136.09, 138.8, 140.0, 151.5, 151.7, 152.5, 152.9. HRMS (EI)
calcd for C28H21ClO: 408.1281, found 408.1283.
Typical Procedure for Gold(I)-Catalyzed Cyclization of En-
ynyl Furans 2 to Fulvene Derivatives. Method A. To a solution of
(Z)-2-(2-benzylidene-1,4-diphenylbut-3-ynyl)-5-methylfuran (2a) (74.9 mg,
0.2 mmol) in DCM (2 mL) were added PPh3AuCl (5.0 mg, 0.01 mmol)
and AgOTf (0.2 mL, 0.01 mmol, used as a 0.05 M solution in THF). The
(E)-3-((E)-3-Benzylidene-2,5-diphenylcyclopenta-1,4-dienyl)acryl-
aldehyde (3d). Method A. Column chromatography on silica gel
(eluent: petroleum ether/ethyl acetate = 10:1) afforded the title product
in 80% yield (0.15 mmol scale, 43.4 mg) as a brown solid (E:Z = 25:1). Mp
163ꢀ165 °C. 1H NMR (300 MHz, CDCl3, Me4Si) δ 5.90 (dd, J = 16.05,
7.8 Hz, 1H), 6.83 (s, 1H), 7.13 (s, 1H), 7.34ꢀ7.59 (m, 16H), 9.34 (dd,
J = 8.1 Hz, 1H); 13C NMR (75.5 MHz, CDCl3, Me4Si) δ 120.7, 128.0,
5279
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128.1, 128.29, 128.31, 128.4, 128.8, 129.9, 130.6, 130.9, 133.6, 134.7,
136.2, 136.3, 141.7, 143.6, 145.8, 146.2, 147.9, 194.4. HRMS (EI) calcd
for C27H20O: 360.1514, found 360.1515.
127.9, 128.3, 128.4, 128.8, 129.57, 129.62, 129.8, 130.8, 130.9, 133.7,
134.6, 134.9, 136.1, 136.3, 141.1, 143.5, 145.0, 146.6, 198.3. HRMS (EI)
calcd for C28H21ClO: 408.1281, found 408.1266.
(Z)-3-((E)-3-Benzylidene-2,5-diphenylcyclopenta-1,4-dienyl)acryla-
ldehyde (4d). Method B. Column chromatography on silica gel (eluent:
petroleum ether/ethyl acetate = 10:1) afforded the title product in 83%
yield (0.2 mmol scale, 60.1 mg) as a brown oil (Z:E = 50:1). 1H NMR
(400 MHz, CDCl3, Me4Si) δ 5.88 (dd, J = 11.8, 8.0 Hz, 1H), 6.96
(s, 1H), 7.21 (s, 1H), 7.25 (d, J = 11.6 Hz, 1H), 7.30ꢀ7.45 (m, 13H),
7.60 (d, J = 6.8 Hz, 2H), 9.39 (d, J = 8.0 Hz, 1H); 13C NMR (100.6 MHz,
CDCl3, Me4Si) δ 118.5, 127.6, 127.9, 128.2, 128.4, 128.5, 128.8, 129.68.
129.73, 130.8, 131.0, 133.7, 134.8, 135.2, 136.4, 141.0, 141.9, 142.7,
143.4, 148.3, 191.7. HRMS (EI) calcd for C27H20O: 360.1514, found
360.1518.
(Z)-4-((E)-3-Benzylidene-5-(4-chlorophenyl)-2-phenylcyclopenta-
1,4-dienyl)but-3-en-2-one (4g). Method B. Column chromatography
on silica gel (eluent: petroleum ether/ethyl acetate = 10:1) afforded the
title product in 93% yield (Z:E = 50:1) (0.2 mmol scale, 75.7 mg) as
a brown solid. Mp 120ꢀ123 °C. 1H NMR (400 MHz, CDCl3, Me4Si)
δ 1.72 (s, 3H), 6.08 (d, J = 12.0 Hz, 1H), 6.68 (d, J = 12.0 Hz, 1H), 6.87
(s, 1H), 7.14 (s, 1H), 2.28ꢀ7.44 (m, 12H), 7.56ꢀ7.58 (m, 2H); 13C
NMR (100.6 MHz, CDCl3, Me4Si) δ 29.2, 118.6, 127.3, 128.1, 128.2,
128.7, 129.0, 129.3, 130.6, 130.8, 131.3, 133.1, 134.3, 134.5, 134.8, 136.55,
136.60, 139.4, 139.6, 143.4, 147.0, 198.8. HRMS (EI) calcd for C28H21ClO:
408.1281, found 408.1284.
(E)-4-((E)-3-Benzylidene-2-phenyl-5-p-tolylcyclopenta-1,4-dienyl)-
but-3-en-2-one (3e). Method A. Column chromatography on silica gel
(eluent: petroleum ether/ethyl acetate = 20:1) afforded the title product
in 51% yield (0.3 mmol scale, 59.1 mg) as a brown oil. 1H NMR (300
MHz, CDCl3, Me4Si) δ 2.08 (s, 3H), 2.39 (s, 3H), 5.94 (d, J = 16.5 Hz,
1H), 6.80 (s, 1H), 7.08 (s, 1H), 7.18ꢀ7.58 (m, 15H); 13C NMR (75.5
MHz, CDCl3, Me4Si) δ 21.3, 27.3, 120.1, 127.8, 128.21, 128.23, 128.7,
128.9, 129.5, 129.7, 130.7, 130.9, 133.5, 133.9, 135.0, 136.4, 136.5, 137.6,
140.2, 143.8, 144.8, 148.0, 198.6. HRMS (EI) calcd for C29H24O:
388.1827, found 388.1831.
(Z)-4-((E)-3-Benzylidene-2-phenyl-5-p-tolylcyclopenta-1,4-dienyl)-
but-3-en-2-one (4e). Method B. Column chromatography on silica gel
(eluent: petroleum ether/ethyl acetate = 10:1) afforded the title product
in 97% yield (0.2 mmol scale, 75.6 mg) as a brown oil. 1H NMR (300
MHz, CDCl3, Me4Si) δ 1.74 (s, 3H), 2.34 (s, 3H), 6.04 (d, J = 12.3 Hz,
1H), 6.74 (d, J = 12.3 Hz, 1H), 6.87 (s, 1H), 7.11ꢀ7.15 (m, 3H),
7.32ꢀ7.43 (m, 10H), 7.57 (d, J = 7.2 Hz, 2H); 13C NMR (75.5 MHz,
CDCl3, Me4Si) δ 21.2, 29.0, 117.6, 127.1, 127.7, 128.0, 128.6, 128.8,
129.1, 130.6, 130.8, 131.6, 133.1, 134.4, 134.8, 136.7, 136.8, 137.2, 138.6,
139.3, 143.6, 148.1, 199.3. HRMS (EI) calcd for C29H24O: 388.1827,
found 388.1832.
(E)-4-((E)-3-Benzylidene-5-(4-nitrophenyl)-2-phenylcyclopenta-
1,4-dienyl)but-3-en-2-one (3h). Method A. Column chromatography
on silica gel (eluent: petroleum ether/ethyl acetate = 7:1) afforded the
title product in 82% yield (0.1 mmol scale, 34.2 mg) as a brown solid. Mp
158ꢀ159 °C. 1HNMR(400MHz, CDCl3, Me4Si) δ2.11 (s,3H),5.82 (d,
J = 16.4 Hz, 1H), 6.94 (s, 1H), 7.23 (s, 1H), 7.36ꢀ7.52 (m, 9H),
7.59ꢀ7.61 (m, 4H), 8.25ꢀ8.27 (m, 2H); 13C NMR (100.6 MHz, CDCl3,
Me4Si) δ 27.4, 122.8, 123.5, 128.2, 128.4, 128.9, 129.1, 129.8, 130.2, 130.8,
130.9, 133.4, 134.1, 135.8, 136.0, 142.8, 143.2, 143.3, 145.37, 145.41,
147.1, 198.1. HRMS (EI) calcd for C28H21NO3: 419.1521, found
419.1517.
(Z)-4-((E)-3-Benzylidene-5-(4-nitrophenyl)-2-phenylcyclopenta-
1,4-dienyl)but-3-en-2-one (4h). Method B. Column chromatography
on silica gel (eluent: petroleum ether/ethyl acetate = 8:1) afforded the
title product in 87% yield (Z:E = 50:1) (0.2 mmol scale, 72.8 mg) as a
1
brown solid. Mp 138ꢀ139 °C. H NMR (300 MHz, CDCl3, Me4Si)
δ 1.71 (s, 3H), 6.16 (d, J = 12.0 Hz, 1H), 6.70 (d, J = 12.0 Hz, 1H), 6.99
(s, 1H), 7.23 (s, 1H), 7.32ꢀ7.45 (m, 8H), 7.56ꢀ7.60 (m, 4H), 8.17 (d,
J = 8.7 Hz, 2H); 13C NMR (75.5 MHz, CDCl3, Me4Si) δ 29.6, 120.7,
123.3, 127.5, 128.0, 128.1, 128.8, 129.7, 130.6, 130.7, 130.8, 133.9, 134.4,
136.3, 140.4, 141.0, 143.0, 143.3, 146.0, 146.4, 198.3. HRMS (EI) calcd
for C28H21NO3: 419.1521, found 419.1524.
(E)-4-((E)-3-Benzylidene-2-phenyl-5-(3,4,5-trimethoxyphenyl)cycl-
openta-1,4-dienyl)but-3-en-2-one (3f). Method A. Column chroma-
tography on silica gel (eluent: petroleum ether/ethyl acetate = 3:1)
afforded the title product in 55% yield (0.2 mmol scale, 51.2 mg) as a
(E)-4-((E)-3-Benzylidene-2-phenylcyclopenta-1,4-dienyl)but-3-en-2-
one (3i). Method A. Column chromatography on silica gel (eluent:
petroleum ether/ethyl acetate = 10:1) afforded the title product in 45%
yield (0.22 mmol scale, 29.7 mg) as a brown oil. 1H NMR (400 MHz,
CDCl3, Me4Si) δ 2.26 (s, 3H), 6.51 (d, J = 16.0 Hz, 1H), 6.90 (d, J = 5.6
Hz, 1H), 6.95 (dd, J = 5.6, 1.2 Hz, 1H), 7.16 (s, 1H), 7.31ꢀ7.34 (m, 2H),
7.39ꢀ7.51 (m, 7H), 7.55ꢀ7.57 (m, 2H); 13C NMR (100.6 MHz,
CDCl3, Me4Si) δ 27.3, 122.3, 127.7, 127.8, 128.3, 128.8, 129.7, 130.8,
130.90, 130.94, 133.6, 136.4, 136.5, 136.6, 140.7, 143.3, 145.3, 198.7.
HRMS (EI) calcd for C22H18O: 298.1358, found 298.1360.
1
brown oil. H NMR (300 MHz, CDCl3, Me4Si) δ 2.11 (s, 3H), 3.87
(s, 6H), 3.92 (s, 3H), 6.01 (d, J = 16.5 Hz, 1H), 6.66 (s, 2H), 6.84
(s, 1H), 7.12 (s, 1H), 7.36ꢀ7.54 (m, 9H), 7.59ꢀ7.64 (m, 2H); 13C
NMR (75.5 MHz, CDCl3, Me4Si) δ 27.6, 56.1, 60.9, 105.6, 120.1, 127.9,
128.3, 128.8, 129.4, 129.7, 130.7, 130.9, 132.0, 133.8, 134.7, 136.1, 136.3,
137.8, 140.8, 143.6, 144.9, 147.9, 152.9, 198.3. HRMS (EI) calcd for
C31H28O4: 464.1988, found 464.1992.
(Z)-4-((E)-3-Benzylidene-2-phenyl-5-(3,4,5-trimethoxyphenyl)cycl-
openta-1,4-dienyl)but-3-en-2-one (4f). Method B. Column chroma-
tography on silica gel (eluent: petroleum ether/ethyl acetate = 3:1)
afforded the title product in 82% yield (0.2 mmol scale, 76.1 mg) as a
(Z)-4-((E)-3-Benzylidene-2-phenylcyclopenta-1,4-dienyl)but-3-en-2-
one (4i). Method B. Column chromatography on silica gel (eluent:
petroleum ether/ethyl acetate = 10:1) afforded the title product in 48%
yield (0.10 mmol scale, 14.3 mg) as a brown oil. 1H NMR (400 MHz,
CDCl3, Me4Si) δ 2.31 (s, 3H), 6.10 (d, J = 12.4 Hz, 1H), 6.51 (d, J = 12.4
Hz, 1H), 6.80 (d, J = 4.8 Hz, 1H), 7.09 (s, 1H), 7.10 (d, J = 4.8 Hz, 1H),
7.29ꢀ7.45 (m, 8H), 7.55ꢀ7.57 (m, 2H); 13C NMR (100.6 MHz,
CDCl3, Me4Si) δ 31.4, 120.3, 126.2, 127.6, 128.0, 128.7, 129.4, 130.8,
131.4, 134.1, 134.3, 135.1, 136.6, 136.9, 139.8, 143.6, 144.8, 199.3.
HRMS (EI) calcd for C22H18O: 298.1358, found 298.1360.
(Z)-4-((E)-3-Benzylidene-5-cyclohexenyl-2-phenylcyclopenta-1,4-
dienyl)but-3-en-2-one (4j). Method B. Column chromatography on
silica gel (eluent: petroleum ether/ethyl acetate = 10:1) afforded the title
product in 79% yield (0.2 mmol scale, 59.3 mg) as a brown oil. 1H NMR
(300 MHz, CDCl3, Me4Si) δ 1.61ꢀ1.75 (m, 4H), 2.02 (s, 3H), 2.14 (bs,
2H), 2.37 (bs, 2H), 6.01 (s, 1H), 6.03 (d, J = 12.3 Hz, 1H), 6.70 (s, 1H),
6.82 (d, J = 12.3 Hz, 1H), 6.98 (s, 1H), 7.25ꢀ7.41 (m, 8H), 7.54 (d,
J = 8.4 Hz, 2H); 13C NMR (75.5 MHz, CDCl3, Me4Si) δ 21.9, 22.7, 25.8,
1
brown solid. Mp 149ꢀ150 °C. H NMR (300 MHz, CDCl3, Me4Si)
δ 1.77 (s, 3H), 3.86 (s, 9H), 6.10 (d, J = 12.3 Hz, 1H), 6.67 (s, 2H), 6.73
(d, J = 12.3 Hz, 1H), 6.87 (s, 1H), 7.13 (s, 1H), 7.32ꢀ7.46 (m, 8H), 7.60
(d, J = 7.2 Hz, 2H); 13C NMR (75 MHz, CDCl3, Me4Si) δ 29.2, 56.2,
60.9, 105.3, 117.8, 127.3, 128.1, 128.7, 129.3, 130.7, 130.9, 131.5, 131.9,
134.4, 134.7, 136.7, 136.8, 137.7, 139.1, 139.7, 143.5, 148.1, 152.9, 199.1.
HRMS (EI) calcd for C31H28O4: 464.1988, found 464.1990.
(E)-4-((E)-3-Benzylidene-5-(4-chlorophenyl)-2-phenylcyclopen-
ta-1,4-dienyl)but-3-en-2-one (3g). Method A. Column chromatogra-
phy on silica gel (eluent: petroleum ether/ethyl acetate = 10:1) afforded
the title product in 70% yield (0.2 mmol scale, 57.3 mg) as a brown oil.
1H NMR (400 MHz, CDCl3, Me4Si) δ 2.09 (s, 3H), 5.89 (d, J = 16.4 Hz,
1H), 6.81 (s, 1H), 7.13 (s, 1H), 7.33ꢀ7.49 (m, 13H), 7.55ꢀ7.57
(m, 2H); 13C NMR (100.6 MHz, CDCl3, Me4Si) δ 27.4, 120.9,
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ARTICLE
27.3, 29.4, 114.8, 127.0, 128.0, 128.4, 128.6, 128.9, 130.5, 130.8, 131.2,
132.4, 134.4, 136.3, 136.7, 136.9, 137.3, 139.3, 143.6, 149.0, 199.7.
HRMS (EI) calcd for C28H26O: 378.1984, found 378.1982.
of Science, and the Major State Basic Research Development
Program (Grant No. 2011CB808700) for financial support.
(E)-4-((E)-3-Benzylidene-5-cyclopropyl-2-phenylcyclopenta-1,4-
dienyl)but-3-en-2-one (3k). Method A. Column chromatography on
silica gel (eluent: petroleum ether/ethyl acetate = 10:1) afforded the title
product in 30% yield (0.2 mmol scale, 20.1 mg) as a brown oil. 1H NMR
(400 MHz, CDCl3, Me4Si) δ 0.75ꢀ0.79 (m, 2H), 0.97ꢀ1.02 (m, 2H),
1.86ꢀ1.89 (m, 1H), 2.23 (s, 3H), 6.44 (s, 1H), 6.91 (d, J = 16.8 Hz, 1H),
6.97 (s, 1H), 7.30ꢀ7.53 (m, 11H); 13C NMR (100.6 MHz, CDCl3,
Me4Si) δ 8.2, 11.7, 26.7, 116.0, 127.8, 128.2, 128.5, 128.7, 129.3, 130.7,
131.0, 134.0, 136.1, 136.6, 137.6, 138.9, 143.5, 145.4, 150.8, 199.3.
HRMS (EI) calcd for C25H22O: 338.1671, found 338.1667.
’ REFERENCES
(1) For a recent review on fulvene chemistry, see: Neuenschwander,
M. In Chemistry of Double-Bonded Functional Groups; Patai, S., Ed.;
Wiely: Chichester, 1989; Vol. 2, pp 1131ꢀ1286.
(2) For recent examples, see: (a) Suzuka, T.; Ogasawara, M.;
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(Z)-4-((E)-3-Benzylidene-5-cyclopropyl-2-phenylcyclopenta-1,4-
dienyl)but-3-en-2-one (4k). Method B. Column chromatography on
silica gel (eluent: petroleum ether/ethyl acetate = 10:1) afforded the title
product in 62% yield (0.2 mmol scale, 42.0 mg) as a brown oil. 1H NMR
(400 MHz, CDCl3, Me4Si) δ 0.71ꢀ0.73 (m, 2H), 0.92ꢀ0.95 (m, 2H),
1.49ꢀ1.52 (m, 1H), 2.15 (s, 3H), 6.17 (d, J = 12.4 Hz, 1H), 6.26 (s, 1H),
6.81 (d, J = 12.4 Hz, 1H), 6.98 (s, 1H), 7.29ꢀ7.42 (m, 8H), 7.51 (d, J =
7.6 Hz, 2H); 13C NMR (100.6 MHz, CDCl3, Me4Si) δ 9.7, 10.2, 29.7,
111.1, 127.1, 128.1, 128.6, 128.8, 130.5, 130.6, 132.4, 134.4, 135.7, 136.9,
137.9, 138.2, 143.5, 152.7, 200.2. HRMS (EI) calcd for C25H22O:
338.1671, found 338.1676.
Synthesis of (Z)-3-((E)-3-Benzylidene-2,5-diphenylcyclopenta-1,4-
dienyl)-1-phenylprop-2-en-1-ol (5b). To a solution of (Z)-2-(2-benzy-
lidene-1,4-diphenylbut-3-ynyl)-5-phenylfuran (2b) (87.3 mg, 0.2 mmol)
in THF (2 mL) were added PPh3AuCl (5.0 mg, 0.01 mmol) and AgOTf
(0.2 mL, 0.01 mmol, used as a 0.05 M solution in THF) at 50 °C. After
stirring for 10 min, the reaction was quenched by 2 drops of Et3N. The
solvent was evaporated under the reduced pressure, and the residue was
dissolved in methanol (2 mL). To the above mixture were added
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B. C.; Austin, L. R.; Davis, C. A.; Nystrom, J.; Vogberg, J. O. Tetrahedron
1994, 50, 61.
(4) (a) Harre, M.; Raddatz, P.; Walenta, R.; Winterfeldt, E. Angew.
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A. L.; Tomꢀas, M. J. Am. Chem. Soc. 2001, 123, 11113. For other examples
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CeCl3 7H2O (149.0 mg, 0.4 mmol) and NaBH4 (14.9 mg, 0.4 mmol)
3
at 0 °C. The resulting solution was kept at 0 °C and stirred for 2 h. Then
the mixture was quenched with water, extracted with ether, and dried
over anhydrous Na2SO4. The solvent was evaporated under the reduced
pressure, and the residue was purified by chromatography on silica gel
(petroleum ether/ethyl acetate = 20:1) to afford 5b (50.6 mg, 58%) as a
brown oil. 1H NMR (400 MHz, CDCl3, Me4Si) δ 0.54 (d, J = 2.0 Hz,
1H), 5.09 (d, J = 9.6 Hz, 1H), 5.60 (td, J = 10.0, 0.8 Hz, 1H), 6.33 (d, J =
8.4 Hz, 1H), 6.95 (s, 1H), 7.12ꢀ7.24 (m, 6H), 7.31ꢀ7.47 (m, 11H),
7.58 (dd, J = 18.4, 8.0 Hz, 4H); 13C NMR (75.5 MHz, CDCl3, Me4Si)
δ 70.9, 118.1, 124.4, 125.4, 127.0, 127.2, 127.8, 128.0, 128.2, 128.4,
128.7, 129.1, 130.6, 131.0, 135.2, 135.5, 136.2, 138.8, 137.0, 137.1, 138.4,
142.3, 143.8, 148.6. HRMS (EI) calcd for C33H26O: 438.1984, found
438.1992.
(12) (a) Chen, Y.; Lu, Y.; Li, G.; Liu, Y. Org. Lett. 2009, 11, 3838. For
related gold-catalyzed cascade FriedelꢀCrafts/furan-yne cyclization/
heteroenyne metathesis reaction, see:(b) Chen, Y.; Li, G.; Liu, Y. Adv.
Synth. Catal. 2011, 353, 392.
’ ASSOCIATED CONTENT
S
Supporting Information. X-ray crystallography of com-
b
(13) For gold-catalyzed cyclization of furan/ynes, for example, see:
(a) Hashmi, A. S. K.; Frost, T. M.; Bats, J. W. J. Am. Chem. Soc. 2000,
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pound 3b and spectroscopic characterization of all new com-
pounds. This material is available free of charge via the Internet at
http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Fax: (þ86) 021-64166128. E-mail: yhliu@mail.sioc.ac.cn
’ ACKNOWLEDGMENT
We thank the National Natural Science Foundation of China
(Grant Nos. 20872163, 20732008, 20821002), Chinese Academy
(14) For other metal-catalyzed furan/alkyne cyclization, see:
(a) Martin-Matute, B.; Cꢀardenas, D. J.; Echavarren, A. M. Angew. Chem.,
ꢀ
5281
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(17) See Supporting Information.
(18) For the electrophilic attack in the C3-position of the furan ring,
see refs 13e and 13f.
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