Palladium-catalyzed tandem dimerization and cyclization of acetylenic ketones: A convenient method for 3,3′-bifurans using PdCl2(PPh3)2

Article abstract of DOI:10.1021/jo010188k

Alkynones undergo tandem dimerization and cyclization in the presence of PdCl₂(PPh₃)₂ and triethylamine in tetrahydrofuran at room temperature to give 3,3′-bifurans predominantly. Other palladium catalysts while under similar conditions, by rearrangement, lead to 2,5-disubstituted furans. This distinguished property of PdCl₂(PPh₃)₂ has been attributed to the involvement of hydridopalladium halide. This method provides a simpler route to a variety of furans and a regioselective synthesis of polysubstituted 3,3′-bifurans using easily accessible acetylenic ketones.

Full text of DOI:10.1021/jo010188k

6014
J . Org. Chem. 2001, 66, 6014-6020
P a lla d iu m -Ca ta lyzed Ta n d em Dim er iza tion a n d Cycliza tion of
Acetylen ic Keton es: A Con ven ien t Meth od for 3,3′-Bifu r a n s Usin g
P d Cl2(P P h 3)2
Arumugasamy J eevanandam, Kesavaram Narkunan, and Yong-Chien Ling*
Department of Chemistry, National Tsing Hua University, Hsinchu, 30043, Taiwan
ycling@mx.nthu.edu.tw
Received February 20, 2001
Alkynones undergo tandem dimerization and cyclization in the presence of PdCl2(PPh3)2 and
triethylamine in tetrahydrofuran at room temperature to give 3,3′-bifurans predominantly. Other
palladium catalysts while under similar conditions, by rearrangement, lead to 2,5-disubstituted
furans. This distinguished property of PdCl2(PPh3)2 has been attributed to the involvement of
hydridopalladium halide. This method provides a simpler route to a variety of furans and a
regioselective synthesis of polysubstituted 3,3′-bifurans using easily accessible acetylenic ketones.
In tr od u ction
A novel palladium-catalyzed rearrangement of acetyl-
enic ketones into furans has been reported.16 The reac-
tions were carried out in toluene at reflux and were not
applicable to the preparation of simple alkylated furans.
In addition, the yields of furan derivatives were low. It
has been explained17 that the same ketones are trans-
formed into dienones by palladium catalysts. Treatment
of the alkynones under carbonylation conditions has
resulted in the formation of mixture of furans and
dienones.18 Wong et al. have described5 very interesting
furan chemistry starting from 3,4-bis(trimethylsilyl)-
furan. The latter has been prepared at 300 °C by a Diels-
Alder reaction between phenyloxazole and bis(trimeth-
ylsilyl)acetylene. They have performed two successive
sequences of reaction on 3,4-bis(trimethylsilyl)furan such
as ipso substitution to boroxine using BCl3 and Suzuki
coupling to obtain aryl- and heteroaryl-substituted furans.
One interesting extension of this sequence was the
preparation of bifurans, and it has been achieved by
treating boroxine with 2,3-bis(bromomethyl)quinoxaline
in the presence of palladium catalyst at 120 °C. The
necessity of using 3,4-bis(trimethylsilyl)furan as a start-
ing material to generate boroxine and its further conver-
sion to bifuran limits the potential of this method from
a more general pool of substrates. Moreover, synthesis
The furan moiety is frequently found in natural
products and in important pharmaceuticals as well as
flavoring, aroma, and fragrance compounds. It is often
used as a building block in organic synthesis and has
always been the driving force for numerous synthetic
efforts toward furans.1-3 Furans can be, in principle,
synthesized by either cyclization of acyclic precursors or
derivatization of furan rings.4,5 Introduction of the sub-
stituents at the 2- or 5-position of furan is relatively easy,
while similar operations at the 3- or 4-position is rather
difficult. Thus, much attention has been paid to the
synthesis of polysubstituted furans from acyclic precurs-
ors.6-15
(1) Danheiser, R. L.; Stoner, E. J .; Koyama, H.; Yamashita, D. S.;
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Contemp. Org. Synth. 1995, 2, 1.
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B. A. Chem. Soc. Rev. 1999, 28, 209-216.
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1947, 1586-1590. (b) J acobs, T. L.; Dankner, D.; Danker, A. R. J . Am.
Chem. Soc. 1958, 80, 864-866. (C) Landor, S. R.; Pepper, E. S. J . Chem.
Soc. C 1966, 2283-2285. (d) Buchi, G.; Wuest, H. J . Org. Chem. 1969,
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10.1021/jo010188k CCC: $20.00 © 2001 American Chemical Society
Published on Web 08/04/2001

Tandem Dimerization/Cyclization of Acetylenic Ketones
J . Org. Chem., Vol. 66, No. 18, 2001 6015
Sch em e 1
alkynone 2g with PdCl2(PPh3)2, and they make no
difference in yielding bifurans (Table 2, entry 26 and
Table 5). It has been reported9b that palladacycles19
convert iodoenones more efficiently to furans than Pd-
(OAc)2. In our present study Pd(OAc)2 was found to work
better with alkynones than the palladacycle. It could
convert various alkynones to furans (Table 2, entries
1-6) in good yields. The palladacycle transformed
alkynones (2a , 2b, 2g) selectively into furans (Table 2,
entries 18, 19, 20), but it yielded a mixture of furans and
bifurans (Table 2, entries 16 and 17) from alkynones 2c
and 2d . The yields of furans from alkynone (2g) and
iodoenone 5 were compared on treatment with Pd(OAc)2
(Table 2, entry 6) as well as with the palladacycle (Table
2, entry 20) under identical conditions. The yield of furans
obtained from alkynone (Table 2, entry 6, 20) were almost
the same as from iodoenone (Table 5). Thus, for the
synthesis of furans, the palladacycle and iodoenone could
be replaced by their starting materials Pd(OAc)2 and
acetylenic ketones. The results of the reaction between
alkynones and Pd(OAc)2 (Table 2, entries 1-6) were close
to that of alkynones and Pd(PPh3)4 (Table 2, entries
8-15). While extending the same reaction by using 5 mol
% Pd(acac)2 or Pd2(dba)3 under identical condition, we
obtained mixture of furans and bifurans in lower yields.
Alkynones (R1 ) alkyl) failed to give either of the furan
compounds under similar reaction conditions. This could
be attributed to the less lability of methylene protons
adjacent to the triple bond than to the protons in the
corresponding alkynones with R1 ) aryl. To the best of
our knowledge, only the two methods discussed in the
introduction involving boroxine and iodoenone are avail-
able in the literature for the synthesis of 3,3′-bifurans.
The third one discussed here is based on simple starting
materials, a single step, and mild reaction conditions.
Moreover, fine tuning the catalyst could improve selectiv-
ity of either furans or bifurans from the same acetylenic
ketones.
of substituted 3,3′-bifurans involved five to six steps. (Z)-
3-Iodo-3-alken-1-ones, acyclic precursors prepared from
alkynones, have been converted into furans9b and
bifurans9a using trans-di(µ-acetato)-bis[o-(di-o-tolylphos-
phino)benzyl]dipalladium(II)19 (palladacycle) and Pd-
(PPh3)4 or PdCl2(PPh3)2, respectively. It was initially
conceived to prepare polyaryl furans and bifurans for
electroluminescence studies. The preparation20 of io-
doenones by the reported procedure for this purpose from
appropriate alkynone (2g) resulted in poor yield. In
addition, the purity deterioration of iodo compounds and
its light sensitivity deter its general application. Neither
(Z)- nor (E)-3-iodo-2-alken-1-ones were reported9a to
undergo cyclization to furans. During the synthesis of 2,5-
disubstituted furans by the reported procedure,16 we
found that in addition to the desired furans, bifurans
were formed in trace amounts as detected by MALDI-
TOF-MS (Matrix Assisted Laser Desorption Ionization
Time-of-Flight Mass Spectrometry) experiments.21 How-
ever, further studies revealed that alkynones themselves
could be efficiently converted into alkyl and aryl as well
as heteroaryl-substituted furans and bifurans in the
presence of palladium catalysts and tertiary amine.
Indeed, we could achieve the synthesis of desired com-
pounds in good yields in a single step at room tempera-
ture from alkynones.
Thus the use of easily accessible acetylenic ketones and
Pd(PPh3)4 or Pd(OAc)2 catalysts appears to be a simple
and more efficient method for the formation of furans,
while acetylenic ketones and PdCl2(PPh3)2 catalyst leads
to the regioselective formation of 3,3′-bifurans.
Resu lts a n d Discu ssion
In our effort21 toward the synthesis of furans and 3,3′-
bifurans, we focused our attention to the use of various
palladium catalysts and bases in order to study selective
formation of mono- and bifurans, the regiochemistry of
bifurans, and the mechanism of the reaction. Our studies
disclosed (Scheme 1, Table 1) that furans and/or bifurans
were formed in various proportions depending on the
palladium catalyst that was used in the presence of
triethylamine (Table 2). The product distribution in the
presence of various amine bases is given in Table 3.
We observed that from alkynones, furans were formed21
exclusively or predominately in the presence of Pd(PPh3)4
(Table 2, entries 8-13 and 15). The same alkynones
afforded bifurans21 regioselectively in the presence of
PdCl2(PPh3)2 (Table 2, entries 21-27). Bifurans forma-
tions have been described9a in the reaction between (Z)-
3-iodo-3-alken-1-ones and Pd(PPh3)4 or PdCl2(PPh3)2. We
studied the reaction of iodoenone 5 and its corresponding
Our studies of the base (amines) effects on the reactiv-
ity of alkynones revealed that tertiary amines are the
bases of choice for the reaction. The yields and consis-
tency were very much higher compared to that of second-
ary (Table 3, entries 4 and 12) or primary amines. The
reaction of alkynones (Table 1, 2f and 2g) was also
studied with morpholine in the presence of Pd(PPh3)4 and
PdCl2(PPh3)2. The formation of furans and bifurans were
only in trace amounts. Control experiments (Table 3,
entry 11) verified the absence of any detectable amount
of desired products in the presence of tertiary amine
alone. The transformations of alkynones to furans could
only be effected along with palladium. N,N-Diisopropyl-
ethylamine and triethylamine provided the same reaction
pattern (Table 3, entries 2, 3, 9, 10) when they were used
as a base in the reaction medium.
1H NMR, NOE, and HMBC data unambiguously
determined the formation of bifuran as a single regio-
isomer. The structural assignment has also been cor-
roborated by X-ray analysis of crystalline derivative 4f.
X-ray analysis data and the ORTEP diagram of the
bifuran compound 4f (Table 2, entry 25) are given in
Table 4.
(19) Herrmann, W. A.; Brossmer, C.; Ofele, K.; Reisinger, C. P.;
Priermeier, T.; Beller, M.; Fisher, H. Angew Chem., Int. Ed. Engl. 1995,
34, 1844.
(20) Luo, F. T.; Kumar, K. A.; Hsieh, L. C.; Wang, R. T. Tetrahedron
Lett. 1994, 35, 2553.
(21) J eevanandam, A.; Narkunan, K.; Cartwright, C.; Ling, Y. C.
Tetrahedron Lett. 1999, 40, 4841-4844

6016 J . Org. Chem., Vol. 66, No. 18, 2001
Ta ble 1. Su bstitu en ts of Com p ou n d s 1-4
J eevanandam et al.
Ta ble 2. Syn th esis of F u r a n s a n d 3,3′-Bifu r a n s
isol yield:
Ta ble 3. In flu en ce of th e Ba ses on th e Rea r r a n gem en t
of Keton e (2b) in th e P r esen ce of P d (P P h 3)4 or
P d Cl2(P P h 3)2
furans (%)
isol yield (%)
time
(h) furan 3,3′-bifuran
entry
catalysts
R1
R2
3
4
entry
base
n-Bu3N
i-Pr2Net
Et3N
morpholine
1-methylpyrrole Pd(PPh3)4
PhCH(CH3)NH2 Pd(PPh3)4
pyridine
n-Bu3N
i-Pr2Net
Et3N
Et3N
morpholine
catalyst
1
2
3
4
5
6
7
8
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Ph
Ph
-Ph
n-C5H11
40
54
07
06
09
05
1
2
3
4
5
6
7
8
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
12
10
12
24
52
67
70
12
03a
Ph
04a
2-thiophene 57
07
(3-MeO)Ph 2-thiophene 51
tracea
tracea
tracea
tracea
38
Ph
Ph
Ph
Ph
Ph
Ph
Ph
n-C8H17
(4-Me)Ph
(4-Me)Ph
Ph
2-thiophene 70
n-C5H11
n-C8H17
44 tracea
24 tracea
53
14
04a
26b
24 tracea
24
PdC2(PPh3)2 12
PdC2(PPh3)2 10
PdC2(PPh3)2 12
55 tracea
Pd(PPh3)4
04
06
04
06
-
9
07
07
9
52
53
-
05
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
41
52 tracea
10
11
12
-
24
(3-MeO)Ph 2-thiophene 49
05
02a
34c
03a
11
09
04
08
02a
48
56
53
71
42
50
46
11
09
08
08
09
06
PdC2(PPh3)2 24
06
Ph
Ph
Ph
(4-Me)Ph
(4-Me)Ph
(3-MeO)Ph
n-C5H11
n-C8H17
Ph
52
13
53
31
29
52
a
Detected by GC analysis.
palladacycled Ph
halide can be formed in the reaction between Et3NHX
and Pd(0) species generated in situ from triethylamine
and PdCl2(PPh3)2. The hydridopalladium halide can be
generated from Pd(PPh3)4 as given in the eq 1 in the
presence of Et3NHI. Addition of this halide to alkynone
may give vinyl palladium intermediate B via base-
catalyzed isomerization18 of A. The intermediate B can
be generated from iodoenone 5 (eq 2) directly by both Pd-
(PPh3)4 and PdCl2(PPh3)2 and lead to bifuran. It may be
difficult to rationalize the formation of this intermediate
when Pd(PPh3)4 alone was treated with alkynone.
palladacycle
palladacycle
palladacycle
palladacycle
PdC2(PPh3)2
PdC2(PPh3)2
PdC2(PPh3)2
PdC2(PPh3)2
PdC2(PPh3)2
PdC2(PPh3)2
PdC2(PPh3)2
Pd(acac)2
Ph
Ph
Ph
Ph
Ph
Ph
Ph
2-thiophene 54
(4-Me)Ph
n-C5H11
Ph
51
05
08
2-thiophene 06
(3-MeO)Ph 2-thiophene 05
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
n-C8H17
(4-Me)Ph
(3-MeO)Ph
Ph
2-thiophene 42
n-C5H11
08
07
06
30
Pd(acac)2
Pd(acac)2
Pd2(dba)3
Pd2(dba)3
28
26
Ph
2-thiophene 28
n-C5H11 24
Pd2(dba)3
a
Detected by GC analysis. b Used 1 equiv of Et3NHI and 4 equiv
of PPh3. c Used 1 equiv of Et3NHI. trans-Di(µ-acetato)-bis[o-(di-
d
o-tolylphosphino)benzyl]dipalladium(II).19
P ossible Mech an ism s. The formation of simple furans
could be justified through allene formation and subse-
quent cyclization. A plausible mechanism for the forma-
tion of bifurans is discussed below.
Synthesis of iodoenone (5) was not pursued since the
yield was poor. Nevertheless, the reaction with Pd(PPh3)4
and PdCl2(PPh3)2 was studied and compared with the
results of corresponding alkynones. Pd(PPh3)4 as well as
PdCl2(PPh3)2 reacted with iodoenone 5 to afford bifurans
(Table 5) as a major product.
PdCl2(PPh3)2 in the reaction with corresponding alkyn-
one (2g) also afforded bifuran (Table 2, entry 26), but Pd-
(PPh3)4 failed to form the bifuran and yielded only furan
(Table 2, entry 13) as a major product. However, Pd-
(PPh3)4 in the presence of 1 equiv of Et3NHI with
alkynone (2g) gave bifuran in 34% yield (Table 2, entry
14). On the basis of these differences, it may be reason-
able to consider the catalytic reaction that involves
hydridopalladium halide. In the case of PdCl2(PPh3)2, this
Pd(OAc)2, palladacycle, and Pd2(dba)3 with the same
iodoenone (5) could yield only furan as a major product.
Pd(OAc)2 with alkynone (2g) even in the presence of Et3-
NHI afforded again furan as a major one, and no
improvement in the yield of bifuran was observed. Pd-
(OAc)2 in the reaction with 2g in the presence of 1 equiv
of Et3NHI and 4 equiv of PPh3 improved the yield of
bifuran to 26% (Table 2, entry 7). All these observations
further support the probability for the involvement of
HPdX (eq 3). Moreover, the failure of the catalysts Pd-
(OAc)2, palladacycle, and Pd2(dba)3 on treatment with
iodoenone and the inability of Pd(OAc)2 and Et3NHI in
the absence of PPh3 to afford bifuran may support the
statement that the presence of PPh3 ligand favors the

Tandem Dimerization/Cyclization of Acetylenic Ketones
J . Org. Chem., Vol. 66, No. 18, 2001 6017
Ta ble 4. X-r a y An a lysis Da ta a n d ORTEP Dia gr a m for Com p ou n d 4f
Ta ble 5. F u r a n s fr om Iod oen on e (5)
The reverse regiosiomer D of A may not have potential
to contribute to the formation of furan. It could lead to
unsymmetrical (Scheme 2) bifuran 7 on carbopalladation
to native 2. Complete absence of other isomers of bifuran
in the crude reaction mixture supports the involvement
of intermediate A. On the basis of these observations and
on the similar role of Pd(PPh3)4 and PdCl2(PPh3)2 with
iodoenoene 5 and their difference with alkynone 2, it may
be more appropriate to consider the involvement of HPdX
rather than PdH.
If intermediate A is chosen, it might also be added to
either alkynones or allenones to afford bifurans in the
same way as explained for B except the sequence isomer-
ization and carbopalladation should be reversed. Alkyn-
ones 2 could also undergo carbopalladation with inter-
mediate B and lead to symmetrical bifurans as given in
Scheme 3 through the intermediate C. All these possible
carbopalladations while involving A/B could only result
in the formation of a single symmetrical regioisomer 4.
This could explain the reason for alkynone 2g yielding
bifuran as efficiently as that obtained from iodoenone 5,
though the latter could undergo direct palladation to
intermediate B.
One could speculate that Pd(II) is initially reduced to
Pd(0) by the organic substrate,24 and then the analogous
Pd(0)/Pd(II)-cycles could be formulated. Pd(0) generated
is stabilized by ligands and further favors formation of
simple furan under unfavorable conditions, absence of
Et3NHX, for the formation of HPdX.
transformation of alkynones to bifurans. The plausible
mechanism is depicted in the Scheme 2.
According to the Scheme 2, the complex A is generated
by the addition of HPdX to alkynone. It subsequently
undergoes base-catalyzed isomerization to afford complex
B. Carbopalladation of allenes are known to favor C-C
bond formation at the central carbon of the allene.22
Accordingly, carbopalladation of allenyl ketone 6 gener-
ated in situ with native B followed by isomerization lead
to C. Ring closure of C results in the formation of bifuran
with regeneration of the key catalytic species. In the case
of hydropalladation of allene, instead of carbopalladation,
the hydrogen should end up at the central carbon of the
allene,23 which was not observed. Bifurans were formed
as a single regioisomer (symmetrical). We have chosen
A as the sole intermediate in the hydropalladation of 2.
Mechanistic possibilities for the formation of bifuran
in small amounts from catalysts other than PdCl2(PPh3)2,
based on existing mechanisms that involve steps and
(22) (a) Shimizu, I.; Tsuji, J . Chem. Lett. 1984, 233-236. (b) Larock,
R. C.; Varaprath, S.; Lau, H. H.; Fellows, C. A. J . Am. Chem. Soc.
1984, 106, 5274-5284. (c) Larock, R. C.; Berrios-Pena, N. G.; Fried,
C. A. J . Org. Chem. 1991, 56, 2615-2617. (d) Davies, I. W.; Scopes, D.
I. C.; Gallagher, T. Synlett 1993, 85-87
(23) (a) Trost, B. M.; Gerusz, V. J . J . Am. Chem. Soc. 1995, 117,
5156-5157. (b) Yamamoto, Y.; Al-Masum, M.; Fujiwara, N. J . Chem.
Commun. 1996, 381-382
(24) Still, J . K.; Groh, B. L. J . Am. Chem. Soc. 1987, 109, 813-817.

6018 J . Org. Chem., Vol. 66, No. 18, 2001
J eevanandam et al.
Sch em e 2
Sch em e 3
species E. Reaction of this species with unreacted alle-
none 6 results in the formation of bifuran.
In conclusion, a palladium-based method has the
advantage of being truly catalytic. It offers the prospect
of controlling the nature of the products, shown in Table
2, depending largely upon the nature of the palladium
catalyst. This procedure describes an interesting ap-
proach, tandem dimerization and cyclization, to bifurans.
The reaction proceeds under mild conditions and is highly
regioselective. Among the various catalysts, palladium
chloride bis(triphenylphosphine) was found to be an ideal
candidate for the transformation of alkynones to 3,3′-
bifurans. This unique property can be attributed to the
involvement of the hydridopalladium halide species.
Sch em e 4
Exp er im en ta l Section
Gen er a l Meth od s. Melting points were determined in open
capillary tube using a Thomas-Hoover apparatus and were
1
uncorrected. H NMR and 13C NMR spectra were recorded on
a Brucker AC 300 or Brucker AM 400 or Brucker Avance 600
spectrometer. Chemical shifts were recorded relative to CDCl3
or DMSO-d6. IR spectra were recorded by using Perkin-Elmer
2000 FT-IR spectrometer. High-resolution mass spectra were
obtained on a J EOL J MS-HX110 spectrometer. Pd(OAc)2, Pd2-
25
(dba)3, and Pd(acac)2 are commercial products. Pd(PPh3)4
,
intermediates known from other palladium-catalyzed
reactions, are given in Scheme 4. Scheme 4 shows that
the interaction of Pd(II) with intermediate allenone 6,
generated from alkynone, leads to furanyl palladium
PdCl2(PPh3)2,26 and palladacycle19 were prepared by known
procedures.
(25) Coulson, D. R. Inorg. Synth. 1972, 13, 121-124.

Tandem Dimerization/Cyclization of Acetylenic Ketones
J . Org. Chem., Vol. 66, No. 18, 2001 6019
Gen er a l P r oced u r e for th e Syn th esis of Acetylen ic
Alcoh ols27 (1a -g). A solution of 3-aryl-1-propyne28 (5 mmol)
in THF (8 mL) was treated with 1.6 M n-BuLi in hexane (5.2
mmol, -78 °C) followed 30 min later by a solution of corre-
sponding aldehyde (5 mmol) in THF (2 mL). The reaction
mixture was warmed to 25 °C, treated with aqueous NH4Cl,
extracted with ethyl acetate, washed with brine, dried over
Na2SO4, filtered, and evaporated. Chromatography of silica gel
(96/4 hexane/ethyl acetate) afforded 1,4-disubstituted-2-butyn-
1-ol (1a -g) in 58-71% yield.
Gen er a l P r oced u r e for Acetylen ic Keton e (2a -g). A
mixture of acetylenic alcohol (500 mg) and activated manga-
nese dioxide (1.5 g, commercial sample) in chloroform (50 mL)
was refluxed for 3-4 h. The completion of the reaction was
followed by TLC (eluent 1/3 ethyl acetate/hexane). The mixture
was filtered through Celite, and the filtrate was concentrated
in vacuo. The residue was purified by column chromatography
on silica gel to give acetylenic ketones in 72-85% yield.
Gen er a l P r oced u r e for th e Syn th esis of F u r a n s (3a -
g) a n d 3,3′-Bifu r a n s (4a -g). To a solution of acetylenic
ketone (0.25 mmol) in 2 mL of dry THF, under nitrogen,
palladium catalyst (5-mol %) and triethylamine (0.6 mmol)
were added sequentially. The reaction mixture was stirred at
room temperature until TLC showed complete consumption
of starting material (8-12 h). Concentration of the reaction
mixture and purification of the crude products on silica gel
using hexane afforded the respective furans and bifurans in
good yields (Table 1).
IR (CHCl3) cm-1: 3055, 2986, 2960, 1597, 1488, 1420, 1265,
896, 738, 706; HRMS calcd for C18H24O: 256.1827 found
256.1823.
5,5′-Dioctyl-2,2′-d ip h en yl-3,3′-bifu r a n (4c). Colorless oil.
1H NMR (400 MHz, CDCl3): δ 0.87 (t, 6H, J ) 6.6 Hz), 1.26
(m, 20H), 1.68 (m, 4H), 2.67 (t, 4H, J ) 7.4 Hz), 5.99 (s, 2H,),
7.13 (dd, 2H, J ) 1.6 Hz, 7.2 Hz), 7.21 (dd, 4H, J ) 7.4 Hz, 8.1
Hz), 7.58 (dd, 4H, J ) 1.5 Hz, 8.2 Hz); 13C NMR (100 MHz):
δ 14.19, 22.74, 28.15, 28.26, 29.35, 29.43, 31.62, 31.96, 109.90,
115.28, 124.93, 126.67, 128.34, 131.53, 147.31, 155.85; IR
(CHCl3) cm-1: 3063, 2955, 2927, 1601, 1448, 1265, 917, 765,
692; HRMS calcd for C36H46O2: 510.3497 found 510.3494.
2-P en tyl-5-p h en ylfu r a n (3d ). Colorless oil. 1H NMR (400
MHz, CDCl3): δ 0.89 (t, 3H, J ) 7.2 Hz), 1.35 (m, 4H), 1.67
(m, 2H), 2.65 (t, 2H, J ) 7.6 Hz), 6.03 (d, 1H, J ) 3.1 Hz),
6.52 (d, 1H, J ) 3.1 Hz), 7.17-7.72 (m, 5H); 13C NMR (100
MHz): δ 13.99, 22.42, 27.79, 28.15, 31.40, 105.63, 106.81,
123.32, 126.68, 128.57, 131.29, 152.09, 156.50; IR (CHCl3)
cm-1: 3054, 2988, 2960, 1599, 1486, 1421, 1264, 736, 692;
HRMS calcd for C15H18O: 214.1358 found 214.1354.
5,5′-Dip en tyl-2,2′-d ip h en yl-3,3′-bifu r a n (4d ). Colorless
oil. 1H NMR (400 MHz, CDCl3): δ 0.89 (t, 6H, J ) 7.2 Hz),
1.35 (m, 8H), 1.67 (m, 4H), 2.66 (t, 4H, J ) 7.4 Hz), 5.97 (s,
2H,), 7.12-7.60 (m, 10H); 13C NMR (100 MHz): δ 14.02, 22.41,
27.63, 28.02, 31.35, 109.83, 115.20, 124.84, 126.56, 128.25,
131.45, 147.23, 155.75; IR (CHCl3) cm-1: 3054, 2987, 1600,
1265, 896, 738, 705; HRMS calcd for C36H46O2: 510.3497 found
510.3494.
2-(3-Meth oxyp h en yl-5-(2-th ien yl)fu r a n (3e). Colorless
syrupy liquid, 1H NMR (400 MHz, CDCl3): δ 3.85 (s, 3H), 6.56
(d, 1H, J ) 3.7 Hz), 6.67 (d, 1H, J ) 3.7 Hz), 6.81 (m, 1H),
7.04 (t, 1H, J ) 3.2 Hz), 7.22 (m, 2H), 7.29 (m, 3H) 13C NMR
(100 MHz): δ 55.31, 107.21, 107.49, 109.22, 113.00, 116.40,
122.62, 124.20, 127.68, 129.78, 131.70, 133.71, 149.02, 152.22,
159.93; IR (CHCl3) cm-1: 3072, 2950, 2829, 1598, 1484, 1260,
1218, 1044, 775, 737, 698; HRMS calcd for C15H12O2S: 256.0558
found 256.0555.
2,2′-Bis(3-m eth oxyp h en yl)-5,5′-bis(2-th ien yl)-3,3′-bifu -
r a n (4e). Colorless solid. mp 112-113 °C (from methanol) 1H
NMR (600 MHz, CDCl3): δ 3.67 (s, 6H), 6.56 (s, 2H), 6.74 (ddd,
2H, J ) 0.9 Hz, J ) 1.3 Hz, 10.8 Hz), 7.05 (dd, 2H, J ) 3.6
Hz, 5.0 Hz), 7.16 (t, 2H, J ) 8.1 Hz), 7.24-7.29 (m, 6H), 7.33
(dd, 2H, J ) 1.1 Hz, 3.6 Hz); 13C NMR (100 MHz): δ 55.11,
109.74, 110.22, 113.69, 116.11, 117.75, 123.03, 124.66, 127.28,
129.65, 151.65, 133.24, 148.28, 148.52, 159.61; IR (CHCl3)
cm-1: 3041, 2950, 1601, 1541, 1260, 920, 737. Anal. Calcd for
C30H22O4S2: C, 70.57; H, 4.34. Found: C, 70.43; H, 4.29. HRMS
calcd for C30H22O4S2: 510.0959 found 510.0954.
2-(3-Meth oxyp h en yl)-5-p h en ylfu r a n (3f). White solid,
mp 88-89 °C (from methanol); 1H NMR (300 MHz, CDCl3): δ
3.86 (s, 3H), 6.72 (s, 2H), 6.82 (m, 1H), 7.25-7.32 (m, 4H), 7.39
(t, 2H, J ) 7.4 Hz), 7.71 (dd, 2H, J ) 1.4 Hz, 8.3 Hz); 13C NMR
(100 MHz): δ 55.31, 107.19, 107.55, 109.28, 112.94, 116.40,
123.73, 127.37, 128.89, 129.77, 130.72, 132.06, 153.17, 153.40,
160.00; IR (CHCl3) cm-1: 3057, 2958, 1591, 1488, 1260, 1215,
1021, 737, 688. Anal. Calcd for C17H14O2: C, 81.58; H, 5.63.
Found: C, 81.69; H, 5.69. HRMS calcd for C17H14O2: 250.0993
found 250.0991.
5,5′-Bis(3-m eth oxyph en yl)-2,2′-diph en yl-3,3′-bifu r an (4f).
Colorless solid. mp 124-126 °C (from methanol) 1H NMR (300
MHz, CDCl3): δ 3.86 (s, 6H), 6.71 (s, 2H), 6.83 (m, 2H), 7.16-
7.35 (m, 12H), 7.71 (dd, 4H, J ) 1.7 Hz, 8.2 Hz); 13C NMR (75
MHz): δ 55.37, 109.39, 110.23, 113.35, 116.16, 116.54, 125.21,
127.45, 128.53, 129.86, 130.83, 131.73, 148.78, 152.60, 160.01;
IR (CHCl3) cm-1: 3057, 2996, 2958, 2836, 1598, 1488, 1264,
1218, 1021, 729, 691. Anal. Calcd for C34H26O4: C, 81.90; H,
5.26. Found: C, 81.83; H, 5.32. HRMS calcd for C34H26O4:
498.1831 found 498.1828.
2,5-Dip h en ylfu r a n (3a ). White solid, mp 86-87 °C (from
methanol, lit.6 87-88); 1H NMR (300 MHz, CDCl3): δ 6.74 (s,
2H), 7.26 (dd, 2H, J ) 1.3 Hz, 8.1 Hz), 7.41 (t, 4H, J ) 6.7
Hz), 7.74 (dd, 4H, J ) 1.3 Hz, 8.2 Hz); 13C NMR (100 MHz):
δ 102.22, 123.80, 127.36, 128.71, 130.91, 153.50; IR (CHCl3)
cm-1: 3057, 3029, 1602, 1490, 1255, 910, 815, 692; HRMS calcd
for C16H12O: 220.0888 found 220.0884.
2,2′,5,5′-Tetr a p h en yl-3,3′-bifu r a n (4a ). Colorless solid, mp
190-192 °C (from hexane-benzene); 1H NMR (300 MHz,
CDCl3): δ 6.72 (s, 2H), 7.22 (m, 8H), 7.39 (t, 4H, J ) 7.34 Hz),
7.72 (m, 8H); 13C NMR (100 MHz, CDCl3 and DMSO-d6): δ
109.89, 116.20, 123.87, 125.19, 127.40, 127.65, 128.54, 128.77,
130.47, 130.88, 148.87, 152.79; IR (CHCl3) cm-1: 3054, 3027,
1603, 1421, 1265, 909, 731, 691. Anal. Calcd for C32H22O2: C,
87.64; H, 5.06. Found: C, 87.59; H, 5.10. HRMS calcd for
C
32H22O2: 438.1619 found 438.1617.
2-P h en yl-5-(2-th ien yl)fu r a n (3b). Colorless solid, mp 82-
1
83 °C (from hexane); H NMR (400 MHz, CDCl3): δ 6.57 (d,
1H, J ) 3.6 Hz), 6.69 (d, 1H, J ) 3.5 Hz), 7.04 (dd, 1H, J )
4.6 Hz, 6.4 Hz), 7.23 (m, 2H), 7.20 (d, 1H, J ) 4.3 Hz), 7.37 (t,
2H, J ) 7.6 Hz), 7.70 (dd, 2H, J ) 1.54, 8.60 Hz); 13C NMR
(100 MHz): δ 102.12, 102.20, 122.55, 123.71, 124.14, 127.38,
127.67, 128.69, 130.52, 133.91, 149.13, 152.92; IR IR (CHCl3)
cm-1: 3058, 3010, 1601, 1480, 1258, 910, 759, 691. Anal. Calcd
for C14H10OS: C, 74.31; H, 4.45. Found: C, 74.22; H, 4.37.
HRMS calcd for C14H10OS: 226.0452 found 226.0450.
5,5′-Bis-(2-th ien yl)-2,2′-d ip h en yl-3,3′-bifu r a n (4b). Col-
orless syrupy liquid; 1H NMR (400 MHz, CDCl3): δ 6.56 (s,
2H), 7.07 (dd, 2H, J ) 3.9 Hz, 5.2 Hz), 7.19-7.35 (m, 10H),
7.67 (dd, 4H, J ) 1.5 Hz, 8.6 Hz); 13C NMR (100 MHz): δ
109.66, 115.84, 122.98, 124.56, 125.15, 127.48, 127.77, 128.53,
130.49, 133.35, 148.29, 148.52; IR (CHCl3) cm-1: 3057, 2927,
1598, 1495, 1412, 1264, 1223, 919, 766, 691; HRMS calcd for
C
28H18O2S2: 450.0748 found 450.0744.
2-Octyl-5-p h en ylfu r a n (3c). Colorless oil. 1H NMR (300
MHz, CDCl3): δ 0.86 (t, 3H, J ) 7.25 Hz), 1.28 (m, 10H), 1.65
(m, 2H), 2.66 (t, 2H, J ) 7.5 Hz), 6.03 (d, 1H, J ) 3.0 Hz),
6.52 (d, 1H, J ) 3.1 Hz), 7.19-7.62 (m, 5H); 13C NMR (100
MHz): δ 14.02, 22.65, 28.15, 28.22, 29.23 (2C), 29.35, 31.88,
105.67, 106.83, 123.42, 127.25, 128.58, 131.44, 152.22, 156.52;
2-(4-Meth ylp h en yl)-5-p h en ylfu r a n (3g). Colorless solid,
1
mp 96-98 °C (from hexane); H NMR (400 MHz, CDCl3): δ
2.38 (s, 3H), 6.68 (d, 1H, J ) 3.6 Hz), 6.73 (d, 1H, J ) 3.6 Hz),
7.21 (m, 3H), 7.40 (t, 2H, J ) 7.2 Hz), 7.64-7.76 (m, 4H); 13
C
(26) King, A. O.; Negishi, E. I. J . Org. Chem. 1978, 43, 358-360
(27) Araki, Y.; Konoike, T. Tetrahedron Lett. 1998, 39, 5549-552.
(28) Brandsma, L.; Verkruijsse, H. D. Synthesis of Acetylenes, Allenes
and Cumulenes; Elsevier: Amsterdam, 1981.
NMR (100 MHz): δ 21.26, 106.45, 107.14, 123.60, 123.66,
127.15, 128.07, 128.65, 129.35, 130.82, 137.19, 152.91, 153.55;
IR (KBr) cm-1: 3056, 3030, 2987, 1602, 1263, 1023, 793, 756,

6020 J . Org. Chem., Vol. 66, No. 18, 2001
J eevanandam et al.
691. Anal. Calcd for C17H14O: C, 87.15; H, 6.02. Found: C,
87.10; H, 5.91. HRMS calcd for C17H14O: 234.1044 found
234.1042.
Ack n ow led gm en t. The authors are thankful to the
National Science Council of the Republic of China (NSC-
88-2113-M007-003) and National Tsing Hua University
for their financial support.
5,5′-Bis(4-m eth ylph en yl)-2,2′-diph en yl-3,3′-bifu r an (4g).
Colorless solid. mp 238-240 °C (from hexane/chloroform 9/1)
1H NMR (400 MHz, CDCl3): δ 2.39 (s, 6H), 6.67 (s, 2H), 7.25
(m, 10H), 7.65-7.76 (m, 8H); 13C NMR (100 MHz): δ 21.33,
109.18, 116.22, 123.79, 125.06, 127.20, 127.73, 128.47, 129.43,
130.89, 137.55, 148.33, 152.93; IR (KBr) cm-1: 3061, 3030,
2990, 1601, 1499, 1262, 1140, 932, 813, 768, 692. Anal. Calcd
for C34H26O2: C, 87.52; H, 5.62. Found: C, 87.44; H, 5.53.
HRMS calcd for C34H26O2: 466.1932 found 466.1929.
Su p p or tin g In for m a tion Ava ila ble: Copies of both 1H
and 13C NMR spectra of furans (3b-g), bifurans (4a -g) and
X-ray data of the compound 4f. 1H NMR, IR and HRMS
spectral data of compound 1a -g, 2a -g, and 5. This material
is available free of charge via the Internet at http://pubs.acs.org.
J O010188K