Efficient synthesis of 4-(2′-alkenyl)-2,5-dihydrofurans and 5,6-dihydro-2H-pyrans via the Pd-catalyzed cyclizative coupling reaction of 2,3- or 3,4-allenols with allylic halides

Article abstract of DOI:10.1021/jo0163997

In the absence of a base, palladium(II) catalysts, such as PdCl₂, PdCl₂(CH₃CN)₂, Pd(OAc)₂, and [(π-C₃H₅)PdCl]₂, can catalyze the cyclizative coupling reaction of 2,3- or 3,4-allenols with allylic halides in DMA at room temperature to provide 2,5-dihydrofurans and 5,6-dihydro-2H-pyrans, respectively, in moderate to good yields. Under similar reaction conditions, nonsubstituted 2,3-allenol 1s affords bimolecular cyclizative coupling product 5s as the major product. The scope of the reaction and its mechanism have been studied briefly. On the basis of the experimental results, the transformation was believed to proceed via a divalent palladium-catalyzed pathway.

Full text of DOI:10.1021/jo0163997

Efficien t Syn th esis of 4-(2′-Alk en yl)-2,5-d ih yd r ofu r a n s a n d
5,6-Dih yd r o-2H-p yr a n s via th e P d -Ca ta lyzed Cycliza tive Cou p lin g
Rea ction of 2,3- or 3,4-Allen ols w ith Allylic Ha lid es
Shengming Ma* and Wenzhong Gao
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, P. R. China
masm@pub.sioc.ac.cn
Received December 21, 2001
In the absence of a base, palladium(II) catalysts, such as PdCl2, PdCl2(CH3CN)2, Pd(OAc)2, and
[(π-C3H5)PdCl]2, can catalyze the cyclizative coupling reaction of 2,3- or 3,4-allenols with allylic
halides in DMA at room temperature to provide 2,5-dihydrofurans and 5,6-dihydro-2H-pyrans,
respectively, in moderate to good yields. Under similar reaction conditions, nonsubstituted 2,3-
allenol 1s affords bimolecular cyclizative coupling product 5s as the major product. The scope of
the reaction and its mechanism have been studied briefly. On the basis of the experimental results,
the transformation was believed to proceed via a divalent palladium-catalyzed pathway.
In tr od u ction
Transition metal-catalyzed cyclization of functionalized
allenes bearing a nucleophilic center has attracted much
attention in recent years.11 Particularly, cyclization reac-
tion of allenols catalyzed by Ag(I),10 Hg(II)10 Pd(0),12 Ru-
(III),13 or Au(III)14 has become quite useful methodologies
for the synthesis of three-, five-, or six-membered oxygen-
containing heterocycles. However, Pd-catalyzed coupling-
cyclization reaction of allenols with allylic halides is still
unknown.
2,5-Dihydrofurans and 5,6-dihydro-2H-pyrans, impor-
tant classes of heterocyclic compounds, are useful inter-
mediates for organic synthesis1 and common structural
units in many natural products.2 These compounds are
usually prepared via a RCM reaction,3 Ag(I)-catalyzed
rearrangement-cyclization of 4-hydroxypropargyl es-
ters,4 dehydration of cis-2-alkene-1,4-diols,5 palladium-
catalyzed reaction of cyclic alkynyl carbonates with
electron-deficient alkenes,6 Prins reaction of terminal
alkene and formaldehyde,7 reaction of oxazirconacyclo-
pentenes with propynoates,8 cyclization of allenols upon
the addition of electrophiles,9 and Ag(I)- or Hg(II)-
catalyzed cyclization reaction of allenols.10
During the course of our study on the chemistry of
functionalized allenes,15-17 we have studied the Pd(0)-
catalyzed coupling-cyclization reaction of 2,3-allenols
(9) (a) Beaulieu, P. L.; Morisset, V. M.; Garratt, D. G. Tetrahedron
Lett. 1980, 21, 129. (b) Smadja, W. Chem. Rev. 1983, 83, 263. (c)
Bridges, A. J .; Thomas, R. D. J . Chem. Soc. Chem. Commun. 1984,
694. (d) Whitby, R.; Kocienski, P. Tetrahedron Lett. 1987, 28, 3619.
(e) Marshall, J . A.; Wang, X. J . Org. Chem. 1990, 55, 2995. (f) Marshall,
J . A.; Wang, X. J . Org. Chem. 1991, 56, 4913.
(10) (a) Olsson, L. I.; Claesson, A. Synthesis 1979, 743. (b) Nikam,
S. S.; Chu, K. H.; Wang, K. K. J . Org. Chem. 1986, 51, 745. (c) Gelin,
R.; Gelin, S.; Albrand, M. Bull. Soc. Chim. Fr. 1972, 1946. (d) Chilot,
J .-J .; Doutheau, A.; Gore, J . Tetrahedron Lett. 1982, 23, 4693. (e) Chilot,
J .-J .; Doutheau, A.; Gore, J . Bull. Soc. Chim. Fr. 1984, II-307. (f)
Marshall, J . A.; Sehon, C. A. J . Org. Chem. 1995, 60, 5966. (g)
Marshall, J . A.; Yu, R. H.; Perkins, J . F. J . Org. Chem. 1995, 60, 5550.
(11) For a review on the palladium-catalyzed chemistry of allene,
see: Zimmer, R.; Dinesh, C. U.; Nadanan, E.; Hhan, F. A. Chem. Rev.
2000, 100, 3067.
(12) For the Pd(0)-catalyzed coupling-cyclization reaction of allenols
with aryl or vinyl halides, see: (a) Uemura, K.; Shiraishi, D.; Noziri,
M.; Inoue, Y. Bull. Chem. Soc. J pn. 1999, 72, 1063. (b) Kang, S.-K.;
Baik, T.-G.; Kulak, A. N. Synlett 1999, 324. (c) Kang, S.-K.; Yamaguchi,
T.; Pyun, S.-J .; Lee, Y.-T.; Baik, T.-G. Tetrahedron Lett. 1998, 39, 2127.
(d) Walkup, R. D.; Guan, L.; Kim, Y. S.; Kim, S. W. Tetrahedron Lett.
1995, 36, 3805. (e) Walkup, R. D.; Guan, L.; Mosher, M. D.; Kim, Y.
S.; Kim, S. W. Synlett 1993, 88.
(1) (a) Marshall, J . A.; Pinney, K. G. J . Org. Chem. 1993, 58, 7180.
(b) Marshall, J . A.; Yu, B. J . Org. Chem. 1994, 59, 324. (c) Yamada,
O.; Ogasawara, K. Synlett 1995, 427. (d) Kim, S.; Kim, K. H. J . Chem.
Soc., Perkin Trans. 1 1997, 1095. (e) Paolucci, C.; Musiani, L.;
Venturelli, F.; Fava, A. Synthesis 1997, 1415. (f) Shieh, S. J .; Fan, J .
S.; Chandrasekharam, M.; Liao, F. L.; Wang, S. L.; Liu, R. S.
Organometallics 1997, 16, 3987. (g) Doyle, M. P.; Forbes, D. C.;
Protopopova, M. N.; Stanley, S. A.; Vasbinder, M. M.; Xavier, K. R. J .
Org. Chem. 1997, 62, 7210. (h) Crotti, P.; Bussolo, L. D.; Favero, L.;
Pineschi, M. Tetrahedron 1997, 53, 1417. (i) Bauer, T. Tetrahedron
1997, 53, 4763.
(2) (a) Kupchan, S. M.; Davies, V. H.; Fujita, T.; Cox, M. R.; Restivo,
R. J .; Bryan, R. F. J . Org. Chem. 1973, 38, 1853. (b) Semple, J . E.;
Wang, P. C.; Lysenko, Z.; J oullie, M. M. J . Am. Chem. Soc. 1980, 102,
7505.
(3) Carda, M.; Castillo, E.; Rodriguez, S.; Uriel, S.; Marco, J . A.
Synlett 1999, 1639.
(4) (a) Shigemasa, Y.; Yasui, M.; Ohrai, S.; Sasaki, M.; Sashiwa, H.;
Saimoto, H. J . Org. Chem. 1991, 56, 910. (b) Saimoto, H.; Yasui, M.;
Ohrai, S.; Oikawa, H.; Yokoyama, K.; Shigemasa, Y. Bull. Chem. Soc.
J pn. 1999, 72, 279.
(5) Sato, F.; Kanbara, H.; Tanaka, Y. Tetrahedron Lett. 1984, 25,
5063.
(6) Darcel, C.; Bruneau, C.; Albert, M.; Dixneuf, P. H. Chem.
Commun. 1996, 919.
(7) Talipov, R. F.; Starikov, A. S.; Gorina, I. A.; Akmanova, N. A.;
Safarov, M. G. Zh. Org. Khim. 1993, 29, 1024.
(8) Xi, C.; Kotora, M.; Takahashi, T. Tetrahedron Lett. 1999, 40,
2375.
(13) For the Ru-catalyzed reaction, see: (a) Yoneda, E.; Kaneko, T.;
Zhang, S.-W.; Onitsuka, K.; Takahashi, S. Org. Lett. 2000, 2, 441. (b)
Trost, B. M.; Pinkerton, A. B. J . Am. Chem. Soc. 1999, 121, 10842.
(14) For the Au-catalyzed reaction, see: Hoffmann-Roder, A.; Krause,
N. Org. Lett. 2001, 3, 2537.
(15) For the corresponding reaction of 1,2-allenyl ketones with
organic halides to afford furans, see: (a) Ma, S.; Zhang, J . Chem.
Commun. 2000, 117. (b) Ma, S.; Li, L. Org. Lett. 2000, 2, 941.
10.1021/jo0163997 CCC: $22.00 © 2002 American Chemical Society
Published on Web 07/26/2002
6104
J . Org. Chem. 2002, 67, 6104-6112

Efficient Synthesis of 4-(2′-Alkenyl)-2,5-dihydrofurans
SCHEME 1
SCHEME 2
with aryl or vinyl halides.18 In the absence of an amine,18a
three-membered vinylic oxiranes were formed (Path A,
Scheme 1) while the formation of the corresponding five-
membered 2,5-dihydrofurans (Path B, Scheme 1) was not
observed. Even when R2 was introduced to increase the
steric hindrance at the 2-position of 2,3-allenols, the
formation of five-membered 2,5-dihydrofurans were still
not observed. Due to the substituent-loading capability
(up to 3) of 2,3-allenols, we are interested in the chem-
istry of polysubstituted 2,5-dihydrofuran-formation reac-
tion from 2,3-allenols and organic halides. In a prelimi-
nary communication,19 we described an efficient synthesis
of 2,5-dihydrofuran via the Pd(II)-catalyzed cyclizative
coupling reaction of 2,3-allenols with allylic halides. In
this paper, we wish to present a full account of our
observation of the reactionsthe scope as well as the
mechanism.
mono-O-tetrahydropyran-2-yl derivatives of butyne-1,4-
diols with LiAlH4.24 2,3-Allenol 1q was prepared via the
reaction of 1,2-allenyllithium with pentanal.25 Allenols
with no-substituent on the allene moiety 1r and 1s were
synthesized via the Cu(I)-mediated homologation of
terminal propargylic alcohols.26
The synthesis of 3,4-allenols 2 is outlined in Scheme
3. The synthesis started with an ortho-Claisen rear-
rangement by heating the corresponding propargylic
alcohols with an excess amount of triethyl orthoacetate
or orthopropionate in the presence of a catalytic amount
of propionic acid. The resulting 3,4-allenoates were then
reduced with LiAlH4 to afford 3,4-allenols 2a -h in
moderate to good yields.27
Th e Cycliza tive Cou p lin g Rea ction of 2,3-Allen ols
w ith Allylic Ha lid es. With different allenols in hand,
the stage was set to study the Pd-catalyzed cyclizative
coupling reaction. Our initial work began with the
reaction of 2,3-allenol 1a with allyl bromide 3a in CH3-
CN at room temperature using 5 mol % Pd(II) and 5 mol
% Ag2CO3 as the cocatalyst and K2CO3 (1.2 equiv) as a
base (entries 1-3, Table 1).15b To our disappointment,
no cyclic product was formed. Surprisingly, the expected
five-membered product, 2-methyl-3-butyl-4-allyl-2,5-di-
hydrofuran (4a ), was afforded in 16% yield together with
Resu lts a n d Discu ssion s
Syn t h esis of St a r t in g Ma t er ia ls. A number of
methods have been reported for the synthesis of alle-
nols,20 and all the requisite 2,3-allenols studied in this
paper were prepared through the application of known
or slightly modified procedure (Scheme 2). 2,3-Allenols
1a -c were synthesized via the reduction of allenic
ketones with LiAlH4.21 Allenols 1d -k were prepared via
the Sn(II)- or Cr(II)-mediated coupling reaction of prop-
argylic bromides with aldehydes and ketones.22 Primary
alcohols 1l-n were prepared from the DIBAL-H reduc-
tion of the corresponding allenoates.23 4-Substituted
allenols 1o and 1p were obtained by the ready reductive
elimination of the tetrahydropyranyloxy group from the
(16) For the corresponding Pd(0)-catalyzed coupling-cyclization of
1,2-allenyl carboxylic acids with organic halides to afford â-substituted
butenolides, see: (a) Ma, S.; Shi, Z. J . Org. Chem. 1998, 63, 6387. (b)
Ma, S.; Duan, D.; Shi, Z. Org. Lett. 2000, 2, 1491.
(17) For the hydrohalogenation reaction of electron-deficient allenes,
see: a) Ma, S.; Shi, Z.; Li, L. J . Org. Chem. 1998, 63, 4522. (b) Ma, S.;
Li, L.; Xie, H. J . Org. Chem. 1999, 64, 5325. (c) Ma, S.; Wang, G. Chin.
J . Chem. 1999, 17, 545. (d) Ma, S.; Wei, Q. J . Org. Chem. 1999, 64,
1026. (e) Ma, S.; Wei, Q. Eur. J . Org. Chem. 2000, 1939.
(18) (a) Ma, S.; Zhao, S. J . Am. Chem. Soc. 1999, 121, 7943. (b) Ma,
S.; Zhao, S. J . Am. Chem. Soc. 2001, 123, 5578.
(24) Cowie, J . S.; Landor, P. D.; Landor, S. R. J . Chem. Soc., Perkin
Trans 1 1973, 720.
(25) (a) Clinet, J .-C.; Linstrumelle, G. Synthesis 1981, 875. (b)
Brandsma, L.; Verkuijsse, H. D. Synthesis of Acetylenes, Allenes and
Cumulenes; Amsterdam, Elsevier: 1981.
(19) Ma, S.; Gao, W. Tetrahedron Lett. 2000, 41, 8933.
(20) Schuster, H. F.; Coppla, G. M. Allenes in Organic Synthesis;
Wiley: New York, 1984.
(21) Buono, G. Synthesis 1981, 872.
(22) (a) Mukaiyama, T.; Harada, T. Chem. Lett. 1981, 621. (b) Place,
P.; Verniere, C.; Gore, J . Tetrahedron 1981, 37, 1359.
(23) (a) Marshall, J . A.; Woif, M. A.; Wallace, E. M. J . Org. Chem.
1997, 62, 367. (b) Ma, S.; J iao, N.; Zhao, S.; Hou, H. J . Org. Chem.
2002, 67, 2837.
(26) Crabbe, P.; Nassim, B.; Robert-Lopes, M. Org. Synth. 1985, 63,
203.
(27) (a) Lai, G.; Anderson, W. K. Synth. Commun. 1995, 4087. (b)
Kimura, M.; Tanaka, S.; Tamaru, Y. Bull. Chem. Soc. J pn. 1995, 68,
1689.
J . Org. Chem, Vol. 67, No. 17, 2002 6105

Ma and Gao
SCHEME 3a
tion (entries 6-8, Table 1). Due to its ready availability,
we chose PdCl2 as the catalyst. Formation of a lower yield
of 4a was observed when allyl chloride was used instead
of allyl bromide (compare entry 8 and entry 9, Table 1).
Further study indicated the effect of solvent on the
formation of 2,5-dihydrofuran 4a was obvious and DMA
was found to provide the product in the highest yield
(entries 10-13, Table 1). When the reaction was carried
out in the absence of allylic halides, the bimolecular
cyclizative coupling product 5a was isolated in 11% yield
1
(eq 2).28 The structure of 5a was confirmed by H-1H
NOESY spectra. The reaction in DMA with less than 5
equiv of allyl bromide afforded lower yields of 4a which
was contaminated with a significant amount of 5a (1
equiv: 36% (4a ), 2 equiv: 54% (4a )).
a
DIBAL-H was used instead of LiAlH4.
PdCl2 was found to be effective even at the catalyst
loading as low as 1 mol % and the corresponding reaction
of 1a with 5 equiv of allyl bromide afforded 4a in 65%
yield when the reaction time was prolonged to 35 h (entry
14, Table 1). It was interesting to note that the reaction
proceeded smoothly without a base although one equiv
of hydrogen halide was formed during the reaction. The
addition of K2CO3 (1.2 equiv) did not improve the yield
of the reaction (entry 15, Table 1).
The current transformation could also be catalyzed by
Pd2(dba)3‚CHCl3 (2.5 mol %) albeit slowly (entry 16, Table
1). However, it turned out that Pd(PPh3)4, one of the most
commonly used Pd(0) catalysts, could not promote this
reaction when the reaction was carried out in an inert
atmosphere (entry 17, Table 1). After this Pd(PPh3)4 (5
mol %)-catalyzed system was exposed to air, the reaction
of 2,3-allenol 1a with allyl bromide afforded 4a in 72%
yield within 72 h (entry 18, Table 1).
To investigate the scope of the reaction, the Pd-
catalyzed cyclizative coupling reaction of allyl bromide
3a with a series of 2,3-allenols 1 was carried out under
the standard conditions (eq 3). The results were sum-
marized in Table 2. Primary, secondary, and tertiary
alcohols all afforded the coupling products in good yields.
The cyclizative coupling reaction of 2-substituted 2,3-
allenols 1a -m proceeded smoothly to afford the corre-
sponding 4-(2′-propenyl)-2,5-dihydrofurans 4a-m in mod-
erate to good yields with the 2-position substituent R3
being alkyl, benzyl, 2′-propenyl, methoxy carbonyl, or
phenyl (entries 1-13, Table 2). When we turned to
2-nonsubstituted-4-monosubstituted 2,3-allenols 1n -p
(R3 ) H, R4 ) n-C6H13 or n-C4H9, entries 14-16, Table
2), the yields of the reaction depended on the substituent
at the 1-position of allenols: the more substituted at
1-position, the higher yield of corresponding 4. 4,4-
Disubstituted 2,3-allenol 1q also provided the desired
product 4q in a good yield (entry 17, Table 2).
TABLE 1. P d -Ca ta lyzed Cycliza tive Cou p lin g Rea ction
of 3-(n -Bu tyl)-3,4-p en ta d ien -2-ol (1a ) w ith Allyl Br om id ea
time
(h)
yield 4a
entry
catalyst
solvent
MeCN
MeCN
MeCN
THF
DMF
DMF
DMF
DMF
(%)i
b,c,d
1
2
3
4
5
6
7
8
Pd(OAc)2
25
46
46
1
NR
NR
NR
16
69
67
48
63
51
19
trace
27
74
65
60
67
NR
72
b,d
PdCl2
PdCl2(PhCN)2
b,d
PdCl2(MeCN)2
PdCl2(MeCN)2
Pd(OAc)2
25
17
49.5
14
12
11.5
12
13
12
35
5
[(π-C3H5)PdCl]2
PdCl2
PdCl2
e
9
DMF
10
11
12
13
14
15
16
17
18
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
CH3COOH
DMSO
PhMe
DMA
DMA
DMA
DMA
DMA
DMA
f
g
Pd2(dba)3‚CHCl3
46
17
72
Pd(PPh3)4
Pd(PPh3)4
h
a
The reaction was carried out at room temperature using 1a
(1 mmol), allylic halide 3 (5 mmol), and Pd (0.05 mmol, 5 mol %)
b
in a solvent (6 mL). K2CO3 (120 mol %) and Ag2CO3 (5 mol %)
were added. c The reaction was carriedout at room temperature
d
for 25 h and then at 50-60 °C for 24 h. 2.5 equiv of 3a were
used. e Allyl chloride was used instead of allyl bromide. f 1 mol %
g
h
PdCl2 was used. 120 mol % K2CO3 was added. The reaction
i
system was exposed to air after 17 h in a N2 atmosphere. Isolated
yield based on allenol 1a .
some side products when the reaction was carried in THF
using 5 mol % PdCl2(CH3CN)2 as the catalyst in the
absence of a base (entry 4, Table 1). The yield of 4a was
improved to 69% when DMF was applied as the solvent
(entry 5, Table 1). Several other palladium catalysts
including PdCl2, Pd(OAc)2, and [(π-C3H5)PdCl]2 were
tested and all proved to be effective for this transforma-
(28) For the palladium-catalyzed dimerization reaction of 1,2-allenyl
ketones, see: (a) Hashmi, A. S. K.; Choi, J .-H.; Bats, J . W. J . Prakt.
Chem. 1999, 341, 342. (b) Hashmi, A. S. K.; Rupert, T. L.; Knofel, T.;
Bats, J . W. J . Org. Chem. 1997, 62, 7295.
6106 J . Org. Chem., Vol. 67, No. 17, 2002

Efficient Synthesis of 4-(2′-Alkenyl)-2,5-dihydrofurans
TABLE 2. P d Cl2-Ca ta lyzed Cycliza tive Cou p lin g
Rea ction of 2,3-Allen ols w ith Allylic Br om id ea
SCHEME 5
2,3-allenol 1
time yield
(h)
entry
R1
R2
R3
R4
R5
(%)b
1
2
3
4
5
6
7
8
9
CH3
CH3
CH3
C4H9-n
Ph
C4H9-n
C4H9-n
C4H9-n
Ph
H
C4H9-n
CH3
CH2Ph
C4H9-n
C4H9-n
C3H5
CO2CH3
Ph
Ph
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
(1a ) 18.5 76 (4a )
(1b) 3.5 71 (4b)
(1c) 18.5 61 (4c)
(1d ) 10.5 81 (4d )
H
H
H
H
H
H
H
H
TABLE 3. P d Cl2-Ca ta lyzed Cycliza tive Cou p lin g
Rea ction of 3,4-Allen ols w ith Allyl Br om id ea
(1e) 21
81 (4e)
64 (4f)
(1f)
2
(1g)
7.5 55 (4g)
(1h ) 14.5 68 (4h )
(1i) 14.5 60 (4i)
10 CH3
11 CH3
12
13
14
15 CH3
16 (CH2)5
17 C4H9-n
CH3 Ph
CH3 C4H9-n
H
H
H
CH3
(1j)
(1k ) 23
(1l) 10
(1m )
(1n ) 38
(1o) 12
9
86 (4j)
57 (4k )
63 (4l)
72 (4m )
32 (4n )
57 (4o)
69 (4p )
69 (4q)
H
H
H
CH2Ph
CH3
H
H
H
3,4-allenol 2
time
(h)
yield
(%)b
C6H13-n
C6H13-n
C4H9-n
C4H9-n
(CH2)5
5
entry
R1
CH3 C4H9-n
C4H9-n
CH3 Ph
CH3 C4H9-t
R2
R3
R4
1
2
3
4
5
6
7
8
H
H
H
H
H
(2a )
(2b)
(2c)
(2d )
(2e)
48
24
34
22
20
12
96
24
63 (6a )
61 (6b)
78 (6c)
48 (6d )
87 (6e)
64 (6f)
34 (6g)c
0 (6h )d
(1p )
(1q) 14
7
H
H
H
H
H
H
H
a
The reaction was carried out at room temperature using 1 (1
mmol), allyl bromide 3a (5 mmol), and PdCl2 (0.05 mmol, 5 mol
H
C4H9-n C3H7-i
b
CH3
H
CH3
H
H
H
CH3
C4H9-n
H
CH3 (2f)
H
H
%) in DMA (6 mL). Isolated yield based on 1.
(2g)
(2h )
SCHEME 4
a
The reaction was carried out at room temperature using 2 (1
mmol), allyl bromide 3a (5 mmol), and PdCl2 (0.05 mmol, 5 mol
b
%) in DMA (6 mL). Isolated yield based on 2. c 33% 2g was
d
recovered. 35% 2h was recovered.
The scope of allylic bromides was also screened. We
found that under the standard reaction conditions, the
reaction of 2,3-allenol 1j with 2-substituted allylic bro-
mides 3b-d underwent smoothly to provide the corre-
sponding products 4t-v in good yields (Scheme 5).
However, when 3-phenyl-2-propenyl bromide was used,
the reaction was complicated and no desired cyclic
product was isolated.
Th e Cycliza tive Cou p lin g Rea ction of 3,4-Allen ols
w ith Allyl Br om id e. Subsequently, we wish to expand
the current reaction from 2,3-allenols to 3,4-allenols.
Thus, under the standard conditions successfully applied
for the 2,3-allenols, the reaction of 3,4-allenols 2a -h with
allyl bromide was studied (eq 4, Table 3), and the results
were summarized in Table 3. Being similar to the results
of 2,3-allenols, 3-substituted 3,4-allenols 2a -e underwent
cyclizative coupling reaction smoothly to afford 5,6-
dihydro-2H-pyrans 6a -e in moderate to good yields
(entries 1-5, Table 3). The reaction of 5,5-disubstituted
3,4-allenol 2f provided the desired product 6f in 64% yield
(entry 6, Table 3), while the reaction of 5-monosubsti-
tuted 3,4-allenol 2g afforded 6g in only 34% yield
together with 33% of starting material 2g being recovered
even when the reaction time was prolonged to 96 h (entry
7, Table 3). Nonsubstituted 3,4-allenol 2h failed to
undergo the cyclizative coupling reaction (entry 8, Table
3).
To our surprise, the reaction of nonsubstituted 2,3-
allenols 1r and 1s with allyl bromide did not provide 4r
and 4s as the major product (Scheme 4). Under the
standard conditions, the reaction of 1r afforded the
expected product 4r in unacceptedly low yield (4%)
together with side products. We failed to determine the
structure of the side products due to its high instability.
The reaction of 2,3-allenol 1s provided bimolecular cy-
clizative coupling product 5s (65%) as the major product
which was contaminated by 4% of 4s. The yield of 5s was
improved to 73% when 0.25 equiv of allyl bromide was
used. It should be noted that the yield of 5s dropped to
24% and much longer reaction time was required to
accomplish this transformation when the reaction was
carried out in the absence of allyl bromide. The reaction
mechanism is more complicated than it first appears, and
the role of allyl bromide is not clear.
Mech a n istic Con sid er a tion s. Two different mech-
anisms involving Pd(II) and Pd(0) species were proposed
for the cyclizative coupling reaction of 2,3-allenols with
allylic halides using 2,3-allenol 1 and allyl bromide 3a
J . Org. Chem, Vol. 67, No. 17, 2002 6107

Ma and Gao
SCHEME 6. P d (II)-Ca ta lyzed P a th w a y
SCHEME 8a
SCHEME 7. P d (0)-Ca ta lyzed P a th w a y
a
2.5 mol% Pd2(dba)3 CHCl3 was used instead of PdCl2.
SCHEME 9
as the representative reactants as illustrated in Schemes
6 and 7, respectively.29
In the Pd(II)-catalyzed mechanism (Scheme 6), PdCl2
coordinates with the double bond remote from the hy-
droxyl group in 2,3-allenol 1. Subsequent cyclic oxypal-
ladation affords 2,5-dihydrofuranyl palladium interme-
diate 7, which reacts with allyl bromide 3a to give
â-bromo-â′-(2,5-dihydrofuranyl)palladium(II) chloride in-
termediate 8, followed by dehalopalladation to provide
the final product 4 and regenerate the Pd(II) species.
On the other hand, in the Pd(0)-catalyzed mechanism
(Scheme 7), the oxidative addition reaction of allyl
bromide 3a with Pd(0) forms a π-allyl palladium(II)
intermediate: in Path A, this palladium(II) intermediate
interacts with the double bond remote from the hydroxyl
group in 2,3-allenol 1 and subsequent cyclic oxypallada-
tion affords intermediate 9, which forms product 4 and
regenerates the Pd(0) species via a reductive elimination
reaction; in Path B, the carbopalladation of the π-allyl
palladium(II) species with the allene moiety generates a
new π-allyl palladium(II) intermediate 10, and intramo-
lecular nucleophilic substitution with the hydroxyl group
furnishs 4 and the Pd(0) species.
results summarized in Table 2 and Table 3. To investi-
gate the mechanism of the current transformation, the
following experiments were conducted (Scheme 8).
Based on the experimental facts outlined in Scheme
8, Pd(0)-catalyzed mechanism may be safely excluded
because it predicts wrong regiochemistry in the product
4, while the Pd(II)-catalyzed mechanism may be accepted.
Moreover, it was in accordance with the fact that Pd-
(PPh3)4 could not promote the reaction in an inert
atmosphere (entry 17, Table 1). When the reaction system
was exposed to air, Pd(PPh3)4 was readily oxidized into
Pd(II), which initiated the cyclizative coupling reaction
(entry 18, Table 1). Due to the increase of steric hindrance
of the CdC bond in 3f, the corresponding reaction with
3f afforded the product 4 in relatively lower yields. The
minor regioisomers in each reaction may be formed via
a coordination-directed direct replacement of the chlorine
atom by the corresponding palladium species 7 (Scheme
9).
Both the Pd(II)- and Pd(0)-catalyzed mechanisms
seemed possible and could account for the experimental
(29) For the mechanism of Pd-catalyzed coupling-cyclization reac-
tion of allenic amides with allylic halides, see (a) Karstens, W. F. J .;
Klomp, D.; Rutjes, F. P. J . T.; Hiemstra, H. Tetrahedron 2001, 57, 5123.
(b) Kimura, M.; Tanaka, S.; Tamaru, Y. J . Org. Chem. 1995, 60, 3764.
(c) Kimura, M.; Fukami, K.; Tanaka, S.; Tamaru, Y. J . Org. Chem.
1992, 57, 6377. (d) Prasad, J . S.; Liebeskind, L. S. Tetrahedron Lett.
1988, 29, 4257.
The Pd(II)-catalyzed pathway seemed to be further
supported by the experimental facts that the reactions
6108 J . Org. Chem., Vol. 67, No. 17, 2002

Efficient Synthesis of 4-(2′-Alkenyl)-2,5-dihydrofurans
SCHEME 10
coupling product 5 or the reaction with allyl bromide
affords cyclizative coupling product 4. The key point here
is that the reactivity of the allene moiety is high due to
the absence of any substituent. The effect of the sub-
stituent of allenols was to prevent the palladium(II)
intermediate 7 from interacting with another molecule
of allenol to afford bimolecular cyclizative coupling
product.
Palladium(II) intermediate is apt to react with the
double bond of allene prior to a normal carbon-carbon
double bond.31 In fact, when 4-bromo-1,2-butadiene 3g
was used instead of allyl bromide, as expected, the
reaction of 2,3-allenols 1s provided the cyclizative cou-
pling product 13 as major product together with bimo-
lecular cyclizative coupling product 5s as the minor
product (eq 5).
SCHEME 11
Con clu sion
In summary, we have developed a novel Pd(II)-
catalyzed cyclizative coupling reaction of 2,3- or 3,4-
allenols with allylic halides, which provides an efficient
route to polysubstituted 2,5-dihydrofurans or 5,6-dihydro-
2H-pyrans. The reaction conditions are mild (room tem-
perature), the catalyst (PdCl2) is readily available and
air stable, the starting materials can be easily prepared,
and the yields are from moderate to good. Further
investigation on the chemistry of allenols is being inten-
sively carried out in our laboratory.
of a stoichimetric amount of (π-allyl) palladium chloride
dimer with 1a and 1j were reluctant to undergo the
transformation to provide the expected products (Scheme
10).
Exp er im en ta l Section
Th e Cycliza tive Cou p lin g Rea ction of Allen ols w ith
Allylic Ha lid es: Gen er a l P r oced u r e. A mixture of allenol
1 or 2 (1 mmol), allylic halide 3 (5 mmol), and PdCl2 (5 mol %)
was stirred in DMA (6 mL) at room temperature. When the
reaction was complete as monitored by TLC, ether was added.
The reaction mixture was washed with brine (three times) and
dried over anhydrous sodium sulfate. The product was purified
by column chromatography on silica gel (petroleum ether/
ether).
(1) 3-Bu tyl-2-m eth yl-4-(2′-p r op en yl)-2,5-d ih yd r ofu r a n
(4a ). The reaction of 1a (0.105 g, 0.75 mmol) and 3a (0.460 g,
3.80 mmol) afforded 0.102 g (76%) of 4a : liquid; 1H NMR (300
MHz, CDCl3) δ 5.80-5.60 (m, 1 H), 5.00-4.95 (m, 2 H), 4.88-
4.80 (m, 1 H), 4.60-4.42 (m, 2 H), 2.80 (d, J ) 6.6 Hz, 2 H),
2.25-2.12 (m, 1 H), 2.00-1.85 (m, 1 H), 1.50-1.20 (m, 4 H),
1.23 (d, J ) 6.0 Hz, 3 H), 0.89 (t, J ) 6.8 Hz, 3 H); 13C NMR
(75.4 MHz, CDCl3) δ 136.53, 135.14, 128.97, 115.67, 83.87,
76.13, 30.17, 29.72, 24.51, 22.71, 20.59, 13.85; MS (m/z) 180
(M+, 3.00), 43 (100); IR (neat) 1635, 1250, 1075 cm-1; HRMS
calcd for C12H20O 180.1514. Found 180.1485.
As enclosed from Tables 2 and 3, the substituent of
allenols played a crucial role on the outcome of the
reaction. For example, the reaction of 2-substituted 2,3-
allenol 1a provided desired 2,5-dihydrofuran 4a in 76%
yield (entry 1, Table 2) while nonsubstituted 2,3-allenol
1s afforded bimolecular cyclizative coupling product 5s
as the major product in 65% yield even in the presence
of 5 equiv of allyl bromide (Scheme 4). How did the great
difference occur? We proposed that the bimolecular
cyclizative coupling product 5 was formed via a Pd(II)-
catalyzed mechanism as outlined in Scheme 11.
The transformation starts with a cyclic oxypalladation
of allenol 1 to generate the 4-(2,5-dihydrofuranyl) pal-
ladium intermediate 7, which reacts with the C2-C3
double bond of another molecular allenol 1, subsequent
â-hydroxyl elimination30 provides the bimolecular cy-
clizative coupling product 5 and regenerates the Pd(II)
species. When allyl bromide is involved, the reaction
becomes more complicated. There exist at least two
possible pathways for this reaction: the reaction of 4-(2,5-
dihydrofuranyl) palladium intermediate 7 with another
molecular allenol 1 provides the bimolecular cyclizative
(2) 2,3-Dim eth yl-4-(2′-p r op en yl)-2,5-d ih yd r ofu r a n (4b).
The reaction of 1b (0.098 g, 1.00 mmol) and 3a (0.627 g, 5.18
mmol) afforded 0.098 g (71%) of 4b: liquid; 1H NMR (300 MHz,
CDCl3) δ 5.83-5.60 (m, 1 H), 5.11-4.93 (m, 2 H), 4.81-4.67
(m, 1 H), 4.60-4.41 (m, 2 H), 2.82 (d, J ) 6.4 Hz, 2 H), 1.59 (s,
3 H), 1.23 (d, J ) 6.3 Hz, 3 H); MS (m/z) 138 (M+, 10.72), 43
(30) Ma, S.; Lu, X. J . Organomet. Chem. 1993, 447, 305.
(31) Ma, S.; Negishi, E. J . Am. Chem. Soc. 1995, 117, 6345.
J . Org. Chem, Vol. 67, No. 17, 2002 6109

Ma and Gao
(100); IR (neat) 1629, 1051 cm-1; HRMS calcd for C9H14
138.1045. Found 138.1020.
O
116.80, 91.49, 78.45, 30.73; MS (m/z) 262 (M+, 14.84) 105 (100);
IR (neat) 1634, 1253, 1066 cm-1; HRMS calcd for C19H18
262.1358. Found 262.1345.
O
(3) 3-Ben zyl-2-m eth yl-4-(2′-p r op en yl)-2,5-d ih yd r ofu r a n
(4c). The reaction of 1c (0.143 g, 0.82 mmol) and 3a (0.482 g,
3.98 mmol) afforded 0.107 g (61%) of 4c: liquid; 1H NMR (300
MHz, CDCl3) δ 7.35-7.00 (m, 5 H), 5.86-5.70 (m, 1 H), 5.16-
4.96 (m, 2 H), 4.78-4.45 (m, 3 H), 3.60 (d, J ) 15.4 Hz, 1 H),
3.28 (d, J ) 15.4 Hz, 1 H), 2.93 (d, J ) 6.2 Hz, 2 H), 1.18 (d,
J ) 6.2 Hz, 3 H); 13C NMR (75.4 MHz, CDCl3) δ 138.81, 135.10,
135.05, 131.09, 128.73, 128.71, 126.52, 116.45, 84.00, 76.43,
31.21, 30.13, 20.77; MS (m/z) 214 (M+, 19.84), 213 (100); IR
(10) 2,2-Dim et h yl-3-p h en yl-4-(2′-p r op en yl)-2,5-d ih y-
d r ofu r a n (4j). The reaction of 1j (0.070 g, 0.40 mmol) and 3a
1
(0.262 g, 2.16 mmol) afforded 0.074 g (86%) of 4j: liquid; H
NMR (300 MHz, CDCl3) δ 7.44-7.25 (m, 3 H), 7.21-7.10 (m,
2 H), 5.84-5.64 (m, 1 H), 5.11-4.92 (m, 2 H), 4.63 (s, 2 H),
2.72 (d, J ) 6.0 Hz, 2 H), 1.32 (s, 6 H); 13C NMR (75.4 MHz,
CDCl3) δ 141.97, 135.35, 135.25, 132.43, 129.28, 128.42, 127.51,
116.23, 90.35, 74.46, 30.67, 27.34; MS (m/z) 214 (M+, 12.67),
43 (100); IR (neat) 1635, 1241, 1058 cm-1; HRMS calcd for
(neat) 1635, 1259, 1075 cm-1; HRMS calcd for C15H18
214.1358. Found 214.1375.
O
C
15H18O 214.1358. Found 214.1308.
(4) 2,3-Dibu tyl-4-(2′-p r op en yl)-2,5-d ih yd r ofu r a n (4d ).
The reaction of 1d (0.145 g, 0.80 mmol) and 3a (0.647 g, 5.35
mmol) afforded 0.144 g (81%) of 4d : liquid; 1H NMR (300 MHz,
CDCl3) δ 5.77-5.55 (m, 1 H), 5.06-4.84 (m, 2 H), 4.77-4.62
(m, 1 H), 4.52-4.30 (m, 2 H), 2.73 (d, J ) 6.0 Hz, 2 H), 2.20-
1.98 (m, 1 H), 1.89-1.70 (m, 1 H), 1.67-1.46 (m, 1 H), 1.42-
1.10 (m, 9 H), 0.96-0.66 (m, 6 H); MS (m/z) 222 (M+, 1.74),
165 (100); IR (neat) 1635, 1261, 1058 cm-1; HRMS calcd for
(11) 3-Bu tyl-2,2-d im eth yl-4-(2′-p r op en yl)-2,5-d ih yd r o-
fu r a n (4k ). The reaction of 1k (0.077 g, 0.50 mmol) and 3a
1
(0.302 g, 2.50 mmol) afforded 0.055 g (57%) of 4k : liquid; H
NMR (300 MHz, CDCl3) δ 5.82-5.66 (m, 1 H), 5.10-4.95 (m,
2 H), 4.43 (s, 2 H), 2.80 (d, J ) 6.3 Hz, 2 H), 1.99 (t, J ) 7.3
Hz, 2 H), 1.45-1.28 (m, 4 H), 1.26 (s, 6 H), 0.91 (t, J ) 6.9 Hz,
3 H); 13C NMR (75.4 MHz, CDCl3) δ 139.50, 135.12, 128.67,
115.63, 89.81, 73.94, 31.99, 29.99, 26.99, 24.74, 23.14, 13.88;
MS (m/z) 193 (M+ - 1, 1.54), 179 (100); IR (neat) 1634, 1253,
1056 cm-1; HRMS calcd for C12H19O (M+ - CH3) 179.1436.
Found 179.1421.
(12) 3-Ben zyl-4-(2′-p r op en yl)-2,5-d ih yd r ofu r a n (4l). The
reaction of 1l (0.098 g, 0.61 mmol) and 3a (0.354 g, 2.92 mmol)
afforded 0.077 g (63%) of 4l: liquid; 1H NMR (300 MHz, CDCl3)
δ 7.40-7.05 (m, 5 H), 5.89-5.69 (m, 1 H), 5.20-5.02 (m, 2 H),
4.63 (s, 2 H), 4.52 (d, J ) 4.0 Hz, 2 H), 3.45 (s, 2 H), 2.97 (d,
J ) 6.0 Hz, 2 H); MS (m/z) 200 (M+, 3.04), 91 (100); IR (neat)
1636, 1266, 1061 cm-1; HRMS calcd for C14H16O 200.1201.
Found 200.1154.
C
15H25O (M+ - 1) 221.1905. Found 221.1926.
(5) 3-Bu tyl-2-p h en yl-4-(2′-p r op en yl)-2,5-d ih yd r ofu r a n
(4e). The reaction of 1e (0.173 g, 0.86 mmol) and 3a (0.528 g,
4.36 mmol) afforded 0.168 g (81%) of 4e: liquid; 1H NMR (300
MHz, CDCl3) δ 7.45-7.10 (m, 5 H), 5.88-5.68 (m, 1 H), 5.63
(brs, 1 H), 5.20-4.95 (m, 2 H), 4.78 (dd, J ) 11.6 and 3.5 Hz,
1 H), 4.65 (d, J ) 11.6 Hz, 1 H), 2.90 (d, J ) 6.2 Hz, 2 H),
2.16-1.97 (m, 1 H), 1.75-1.51 (m, 1 H), 1.38-1.05 (m, 4 H),
0.81 (t, J ) 6.6 Hz, 3 H); MS (m/z) 242 (M+, 2.76), 105 (100);
IR (neat) 1634, 1256, 1055 cm-1; HRMS calcd for C17H22
242.1671. Found 242.1718.
O
(6) 2-Bu tyl-3,4-bis(2′-p r op en yl)-2,5-d ih yd r ofu r a n (4f).
The reaction of 1f (0.111 g, 0.67 mmol) and 3a (0.410 g, 3.39
mmol) afforded 0.088 g (64%) of 4f: liquid; 1H NMR (300 MHz,
CDCl3) δ 5.82-5.64 (m, 2 H), 5.12-4.95 (m, 4 H), 4.75 (brs, 1
H), 4.60-4.45 (m, 2 H), 2.93 (dd, J ) 15.5 and 5.9 Hz, 1 H),
2.84 (d, J ) 6.6 Hz, 2 H), 2.65 (dd, J ) 15.5 and 5.9 Hz, 1 H),
1.72-1.55 (m, 1 H), 1.48-1.20 (m, 5 H), 0.88 (t, J ) 7.1 Hz, 3
H); 13C NMR (75.4 MHz, CDCl3) δ 134.80, 134.74, 132.39,
130.69, 115.81, 115.73, 87.70, 76.48, 33.80, 29.52, 29.33, 26.86,
22.73, 14.00; MS (m/z) 205 (M+ - 1, 13.44), 149 (100); IR (neat)
1635, 1037 cm-1; HRMS calcd for C14H22O 206.1671. Found
206.1718.
(13) 2-Hexyl-4-m eth yl-3-(2′-p r op en yl)-2,5-d ih yd r ofu r a n
(4m ). The reaction of 1m (0.170 g, 1.01 mmol) and 3a (0.597
g, 4.93 mmol) afforded 0.152 g (72%) of 4m : liquid; H NMR
1
(300 MHz, CDCl3) δ 5.80-5.63 (m, 1 H), 5.08-4.95 (m, 2 H),
4.75-4.65 (m, 1 H), 4.56-4.40 (m, 2 H), 2.90 (dd, J ) 15.5
and 5.6 Hz, 1 H), 2.64 (dd, J ) 15.5 and 6.0 Hz, 1 H), 1.72-
1.54 (m, 1 H), 1.62 (s, 3 H), 1.45-1.15 (m, 9 H), 0.86 (t, J )
6.7 Hz, 3 H); 13C NMR (75.4 MHz, CDCl3) δ 135.19, 131.41,
129.05, 115.89, 88.04, 78.42, 34.48, 32.13, 29.70, 29.60, 25.05,
22.87, 14.33, 10.07; MS (m/z) 208 (M+, 1.23), 123 (100); IR
(neat) 1638, 1045 cm-1; HRMS calcd for C14H24O 208.1827.
Found 208.1820.
(7) 2-Bu tyl-3-(m eth oxyca r bon yl)-4-(2′-p r op en yl)-2,5-d i-
h yd r ofu r a n (4g). The reaction of 1g (0.104 g, 0.56 mmol) and
3a (0.361 g, 2.98 mmol) afforded 0.069 g (54%) of 4g: liquid;
1H NMR (300 MHz, CDCl3) δ 5.90-5.69 (m, 1 H), 5.18-4.98
(m, 3 H), 4.75-4.54 (m, 2 H), 3.75 (s, 3 H), 3.33 (d, J ) 5.9 Hz,
2 H), 1.90-1.75 (m, 1 H), 1.72-1.50 (m, 1 H), 1.46-1.22 (m, 4
H), 0.97-0.75 (m, 3 H); MS (m/z) 225 (M++1, 13.05), 167 (100);
IR (neat) 1662, 1634, 1259, 1039 cm-1. Anal. Calcd for
(14) 2-Hexyl-3-(2′-p r op en yl)-2,5-d ih yd r ofu r a n (4n ). The
reaction of 1n (0.148 g, 0.96 mmol) and 3a (0.595 g, 4.92 mmol)
afforded 0.060 g (32%) of 4n : liquid; 1H NMR (300 MHz,
CDCl3) δ 5.92-5.76 (m, 1 H), 5.52-5.48 (m, 1 H), 5.15-5.06
(m, 2 H), 4.69 (brs, 1 H), 4.65-4.52 (m, 2 H), 2.81 (dd, J )
16.5 and 6.6 Hz, 1 H), 2.68 (dd, J ) 16.5 and 6.6 Hz, 1 H),
1.70-1.55 (m, 2 H), 1.50-1.20 (m, 8 H), 0.87 (t, J ) 6.6 Hz, 3
H); 13C NMR (75.4 MHz, CDCl3) δ 141.25, 134.97, 120.65,
116.80, 86.88, 74.77, 34.27, 32.10, 31.87, 29.68, 24.86, 22.86,
14.32; MS (m/z) 194 (M+, 8.25), 109 (100); IR (neat) 1639, 1051
cm-1; HRMS calcd for C13H22O 194.1671. Found 194.1660.
(15) 5-Bu tyl-2,2-d im eth yl-4-(2′-p r op en yl)-2,5-d ih yd r o-
fu r a n (4o). The reaction of 1o (0.104 g, 0.68 mmol) and 3a
C
13H20O3: C, 69.61; H, 8.99. Found: C, 69.27; H, 8.92.
(8) 2-Bu tyl-3-p h en yl-4-(2′-p r op en yl)-2,5-d ih yd r ofu r a n
(4h ). The reaction of 1h (0.126 g, 0.62 mmol) and 3a (0.400 g,
3.30 mmol) afforded 0.102 g (68%) of 4h : liquid; 1H NMR (300
MHz, CDCl3) δ 7.46-7.08 (m, 5 H), 5.95-5.74 (m, 1 H), 5.38-
5.21 (m, 1 H), 5.20-4.97 (m, 2 H), 4.82 (dd, J ) 12.4 and 5.5
Hz, 1 H), 4.68 (dd, J ) 12.4 and 3.1 Hz, 1 H), 3.04 (dd, J )
15.6 and 5.8 Hz, 1 H), 2.90 (dd, J ) 15.6 and 5.9 Hz, 1 H),
1.78-1.12 (m, 6 H), 0.82 (t, J ) 6.6 Hz, 3 H); MS (m/z) 242
(M+, 2.02), 185 (100); IR (neat) 1635, 1255, 1062 cm-1; HRMS
calcd for C17H22O 242.1671. Found 242.1703.
(9) 2,3-Dip h en yl-4-(2′-p r op en yl)-2,5-d ih yd r ofu r a n (4i).
The reaction of 1i (0.145 g, 0.65 mmol) and 3a (0.450 g, 3.72
mmol) afforded 0.103 g (60%) of 4i: liquid; 1H NMR (300 MHz,
CDCl3) δ 7.30-7.16 (m, 8 H), 7.10-7.02 (m, 2 H), 6.12-6.07
(m, 1 H), 5.98-5.80 (m, 1 H), 5.25-5.12 (m, 2 H), 5.01 (dd, J
) 12.8 and 5.4 Hz, 1 H), 4.82 (dd, J ) 12.8 and 3.5 Hz, 1 H),
3.13 (dd, J ) 15.6 and 5.9 Hz, 1 H), 3.02 (dd, J ) 15.6 and 5.8
Hz, 1 H); 13C NMR (75.4 MHz, CDCl3) δ 141.77, 136.23, 135.03,
133.93, 133.87, 128.67, 128.54, 128.46, 128.21, 127.60, 127.57,
1
(0.403 g, 3.33 mmol) afforded 0.075 g (57%) of 4o: liquid; H
NMR (300 MHz, CDCl3) δ 5.84-5.68 (m, 1 H), 5.30 (d, J ) 1.6
Hz, 1 H), 5.08-4.96 (m, 2 H), 4.68-4.60 (m, 1 H), 2.69 (dd, J
) 16.6 and 6.5 Hz, 1 H), 2.58 (dd, J ) 16.6 and 7.0 Hz, 1 H),
1.68-1.48 (m, 1 H), 1.40-1.15 (m, 5 H), 1.22 (s, 3H), 1.19 (s,
3 H), 0.87 (t, J ) 6.9 Hz, 3 H); 13C NMR (75.4 MHz, CDCl3) δ
139.38, 134.87, 129.70, 116.31, 86.00, 85.52, 34.25, 31.44,
29.07, 28.22, 26.96, 22.83, 14.01; MS (m/z) 179 (M+ - CH3,
17.12), 84 (100); IR (neat) 1639, 1245, 1081 cm-1; HRMS calcd
for C12H19O (M+ - CH3) 179.1436. Found 179.1410.
(16) 2-Bu t yl-3-(2′-p r op en yl)-1-oxa sp ir o[4.5]d ec-3-en e
(4p ). The reaction of 1p (0.096 g, 0.50 mmol) and 3a (0.313 g,
2.59 mmol) afforded 0.080 g (69%) of 4p : liquid; 1H NMR (300
MHz, CDCl3) δ 5.95-5.74 (m, 1 H), 5.55 (s, 1 H), 5.17-5.00
(m, 2 H), 4.70-4.64 (m, 1 H), 2.77 (dd, J ) 16.6 and 6.7 Hz, 1
6110 J . Org. Chem., Vol. 67, No. 17, 2002

Efficient Synthesis of 4-(2′-Alkenyl)-2,5-dihydrofurans
1
H), 2.66 (dd, J ) 16.6 and 7.0 Hz, 1 H), 1.80-1.20 (m, 16 H),
0.89 (t, J ) 6.7 Hz, 3 H); 13C NMR (75.4 MHz, CDCl3) δ 140.10,
135.03, 127.83, 116.31, 88.12, 85.00, 38.86, 37.96, 34.43, 31.70,
26.98, 25.56, 23.70, 23.62, 22.88, 14.08; MS (m/z) 234 (M+,
12.45), 191 (100); IR (neat) 1639, 1286, 1060 cm-1; HRMS calcd
for C16H26O 234.1984. Found 234.1992.
g, 5.13 mmol) afforded 0.122 g (63%) of 6a : liquid; H NMR
(300 MHz, CDCl3) δ 5.76-5.62 (m, 1 H), 5.05-4.92 (m, 2 H),
3.94 (s, 2 H), 3.67 (dd, J ) 10.8 and 3.9 Hz, 1 H), 3.50 (dd, J
) 10.8 and 3.7 Hz, 1 H), 2.70 (dd, J ) 15.6 and 6.3 Hz, 1 H),
2.60 (dd, J ) 15.6 and 6.3 Hz, 1 H), 2.25-2.05 (m, 2 H), 1.95-
1.80 (m, 1 H), 1.45-1.20 (m, 4 H), 1.04 (d, J ) 6.9 Hz, 3 H),
0.89 (t, J ) 6.8 Hz, 3 H); 13C NMR (75.4 MHz, CDCl3) δ 135.83,
134.86, 126.38, 115.06, 71.10, 68.14, 33.05, 31.44, 30.77, 29.27,
22.88, 16.85, 13.95; MS (m/z) 194 (M+, 8.04), 153 (100); IR
(17) 2-Bu t yl-4-(2′-p r op en yl)-1-oxa sp ir o[4.5]d ec-3-en e
(4q). The reaction of 1q (0.065 g, 0.34 mmol) and 3a (0.226 g,
1.87 mmol) afforded 0.054 g (69%) of 4q: liquid; 1H NMR (300
MHz, CDCl3) δ 5.86-5.72 (m, 1 H), 5.27 (d, J ) 1.5 Hz, 1 H),
5.08-4.96 (m, 2 H), 4.64-4.56 (m, 1 H), 2.62 (d, J ) 6.8 Hz, 2
H), 1.76-1.16 (m, 15 H), 1.12-0.96 (m, 1 H), 0.92-0.78 (m, 3
H); 13C NMR (75.4 MHz, CDCl3) δ 145.97, 135.86, 123.32,
116.47, 88.80, 83.23, 37.42, 36.69, 34.87, 31.33, 27.83, 25.63,
23.11, 22.63, 22.35, 14.36; MS (m/z) 234 (M+, 2.90), 177 (100);
(neat) 1633, 1234, 1143 cm-1; HRMS calcd for C13H22
194.1671. Found 194.1669.
O
(24) 4-Bu tyl-3-p r op en yl-5,6-d ih yd r o-2H-p yr a n (6b). The
reaction of 2b (0.077 g, 0.55 mmol) and 3a (0.336 g, 2.78 mmol)
afforded 0.060 g (61%) of 6b: liquid; 1H NMR (300 MHz,
CDCl3) δ 5.80-5.64 (m, 1 H), 5.10-4.96 (m, 2 H), 3.97 (s, 2
H), 3.76 (t, J ) 6.5 Hz, 2 H), 2.70 (d, J ) 6.1 Hz, 2 H), 2.15-
1.96 (m, 4 H), 1.42-1.24 (m, 4 H), 0.91 (t, J ) 7.0 Hz, 3 H);
13C NMR (75.4 MHz, CDCl3) δ 136.04, 130.01, 126.71, 115.43,
67.96, 65.04, 33.37, 32.25, 30.40, 28.73, 22.96, 14.27; MS (m/
IR (neat) 1639, 1144, 1082 cm-1; HRMS calcd for C16H26
234.1984. Found 234.1973.
O
(18) 2-Bu tyl-4-(2′-p r op en yl)-2,5-d ih yd r ofu r a n (4r ). The
reaction of 1r (0.087 g, 0.69 mmol) and 3a (0.433 g, 3.58 mmol)
afforded only 5 mg (4%) of 4r : liquid; Available data: 1H NMR
(300 MHz, CDCl3) δ 5.96-5.75 (m, 1 H), 5.44 (d, J ) 1.5 Hz,
1 H), 5.16-5.00 (m, 2 H), 4.88-4.76 (m, 1 H), 4.60-4.44 (m, 2
H), 2.82 (d, J ) 6.7 Hz, 2 H), 1.64-1.20 (m, 6 H), 0.90 (t, J )
7.0 Hz, 3 H); 13C NMR (75.4 MHz, CDCl3) δ 138.59, 134.64,
123.81, 116.38, 86.67, 76.30, 35.95, 31.60, 27.37, 22.73, 13.99;
z) 180 (M+, 4.27), 139 (100); IR (neat) 1633, 1261, 1066 cm-1
HRMS calcd for C12H20O 180.1514. Found 180.1486.
;
(25) 5-Meth yl-4-p h en yl-3-p r op en yl-5,6-d ih yd r o-2H-p y-
r a n (6c). The reaction of 2c (0.180 g, 1.03 mmol) and 3a (0.622
1
g, 5.14 mmol) afforded 0.172 g (78%) of 6c: liquid; H NMR
(300 MHz, CDCl3) δ 7.39-7.20 (m, 3 H), 7.16-7.04 (m, 2 H),
5.77-5.52 (m, 1 H), 5.06-4.91 (m, 2 H), 4.19 (d, J ) 15.9 Hz,
1 H), 4.05 (dd, J ) 15.9 and 1.9 Hz, 1 H), 3.90 (dd, J ) 11.0
and 4.1 Hz, 1 H), 3.65 (dd, J ) 11.0 and 4.0 Hz, 1 H), 2.68-
2.39 (m, 3 H), 0.91 (d, J ) 6.9 Hz, 3 H); 13C NMR (75.4 MHz,
CDCl3) δ 140.73, 137.39, 136.42, 129.77, 128.75, 128.33, 126.90,
116.00, 71.43, 68.23, 34.75, 34.51, 17.32; MS (m/z) 214 (M+,
1.71), 173 (100); IR (neat) 1632, 1440, 1130 cm-1; HRMS calcd
for C15H18O 214.1358. Found 214.1357.
MS (m/z) 166 (M+, 0.24), 121 (100); IR (neat) 1641, 1054 cm-1
.
(19) The reaction of 1s (0.133 g, 0.96 mmol) and 3a (0.595
g, 4.92 mmol) afforded 0.007 g (4%) of 4s and 0.081 g (65%) of
5s.
3-(2′-P r op en yl)-1-oxa sp ir o[4.5]d ec-3-en e (4s): liquid; 1H
NMR (300 MHz, CDCl3) δ 5.88-5.75 (m, 1 H), 5.53 (s, 1 H),
5.15-5.00 (m, 2 H), 4.50 (t, J ) 1.0 Hz, 2 H), 2.80 (d, J ) 6.1
Hz, 2 H), 1.70-1.30 (m, 10 H); MS (m/z) 178 (M+, 11.64), 135
(100); IR (neat) 1639, 1050 cm-1; HRMS calcd for C12H18
178.1358. Found 178.1359.
O
(26) 4-ter t-Bu tyl-5-m eth yl-3-p r op en yl-5,6-d ih yd r o-2H-
p yr a n (6d ). The reaction of 2d (0.151 g, 0.98 mmol) and 3a
(0.594 g, 4.91 mmol) afforded 0.092 g (48%) of 6d : liquid; H
1
3-(1-Cycloh exylid en em eth ylvin yl)-1-oxa sp ir o[4.5]d ec-
1
NMR (300 MHz, CDCl3) δ 5.80-5.64 (m, 1 H), 5.04-4.92 (m,
2 H), 3.91 (s, 2 H), 3.56 (dd, J ) 10.3 and 1.6 Hz, 1 H), 3.45
(dd, J ) 10.3 and 2.4 Hz, 1 H), 2.89-2.74 (m, 2 H), 2.15 (q, J
) 6.5 Hz, 1 H), 1.13 (s, 9H), 1.11 (d, J ) 6.6 Hz, 3 H); 13C
NMR (75.4 MHz, CDCl3) δ 142.489, 136.712, 126.570, 116.096,
71.306, 68.864, 35.575, 35.326, 31.337, 31.299, 20.187; MS (m/
z) 194 (M+, 0.54), 153 (100); IR (neat) 1635, 1133 cm-1; HRMS
calcd for C13H22O 194.1671. Found 194.1624.
3-en e (5s): liquid; H NMR (300 MHz, CDCl3) δ 5.74 (t, J )
1.9 Hz, 1 H), 5.69 (s, 1 H), 4.85 (s, 1 H), 4.82 (s, 1 H), 4.69 (d,
J ) 1.9 Hz, 2 H), 2.20-2.06 (m, 4 H), 1.68-1.25 (m, 16 H); 13
C
NMR (75.4 MHz, CDCl3) δ 144.34, 138.91, 137.99, 130.84,
120.11, 114.57, 90.61, 73.22, 37.46, 37.22, 30.20, 28.94, 28.33,
26.92, 25.65, 23.66; MS (m/z) 258 (M+, 51.93), 215 (100); IR
(neat) 1657, 1162, 1035 cm-1; HRMS calcd for C18H26
258.1984. Found 258.1945.
O
(20) 2,2-Dim et h yl-3-p h en yl-4-(2′-p h en yl-2′-p r op en yl)-
2,5-d ih yd r ofu r a n (4t). The reaction of 1j (0.069 g, 0.40 mmol)
and 3b (0.385 g, 1.95 mmol) afforded 0.086 g (74%) of 4t:
liquid; 1H NMR (300 MHz, CDCl3) δ 7.45-6.90 (m, 10 H), 5.33
(s, 1 H), 5.09 (s, 1 H), 4.55 (s, 2 H), 3.16 (s, 2 H), 1.27 (s, 6 H);
MS (m/z) 290 (M+, 42.71), 275 (100); IR (neat) 1624, 1248, 1058
cm-1; HRMS calcd for C21H22O 290.1671. Found 290.1680.
(21) 4-(2′-Br om o-2′-p r op en yl)-2,2-d im et h yl-3-p h en yl-
2,5-d ih yd r ofu r a n (4u ). The reaction of 1j (0.070 g, 0.40
mmol) and 3c (0.412 g, 2.06 mmol) afforded 0.084 g (71%) of
4u : solid, mp 58-58.5 °C (n-Hexane); 1H NMR (300 MHz,
CDCl3) δ 7.45-7.28 (m, 3 H), 7.25-7.10 (m, 2 H), 5.60 (s, 1
H), 5.44 (s, 1 H), 4.66 (s, 2 H), 3.12 (s, 2 H), 1.34 (s, 6 H); MS
(m/z) 293 (M+ - 1(81Br), 6.77), 291 (M+ - 1(79Br), 5.32), 279
(M+ - CH3(81Br), 99.19), 277 (M+ - CH3(79Br), 100); IR (KBr)
1623, 1240, 1057 cm-1. Anal. Calcd for C15H17BrO: C, 61.45;
H, 5.84. Found: C, 61.67; H, 5.89.
(27) 4-Bu t yl-3-p r op en yl-2-isop r op yl-5,6-d ih yd r o-2H -
p yr a n (6e). The reaction of 2e (0.181 g, 0.99 mmol) and 3a
(0.605 g, 5.00 mmol) afforded 0.192 g (87%) of 6e: liquid; H
1
NMR (300 MHz, CDCl3) δ 5.80-5.64 (m, 1 H), 5.08-4.92 (m,
2 H), 3.96-3.88 (m, 2 H), 3.47 (dt, J ) 10.9 and 3.0 Hz, 1 H),
2.91 (dd, J ) 15.5 and 5.7 Hz, 1 H), 2.64 (dd, J ) 15.5 and 7.1
Hz, 1 H), 2.36-2.08 (m, 2 H), 2.05-1.95 (m, 2 H), 1.74 (d, J )
16.2 Hz, 1 H), 1.44-1.20 (m, 4 H), 1.03 (d, J ) 6.9 Hz, 3 H),
0.91 (t, J ) 7.0 Hz, 3 H), 0.74 (d, J ) 6.9 Hz, 3 H); MS (m/z)
222 (M+, 0.11), 179 (100); IR (neat) 1632, 1127, 1097 cm-1
.
Anal. Calcd for C15H26O: C, 81.02; H, 11.79. Found: C, 80.94;
H, 11.67.
(28) 3-P r op en yl-2,2,5-tr im eth yl-5,6-d ih yd r o-2H-p yr a n
(6f). The reaction of 2f (0.125 g, 0.99 mmol) and 3a (0.603 g,
4.98 mmol) afforded 0.106 g (64%) of 6f: liquid; 1H NMR (300
MHz, CDCl3) δ 5.80-5.62 (m, 1 H), 5.26 (d, J ) 1.4 Hz, 1 H),
5.04-4.92 (m, 2 H), 3.70 (dd, J ) 11.2 and 5.1 Hz, 1 H), 3.24
(dd, J ) 11.2 and 7.5 Hz, 1 H), 2.68-2.52 (m, 2 H), 2.28-2.16
(m, 1 H), 1.21 (s, 6 H), 0.86 (d, J ) 7.4 Hz, 3 H); 13C NMR
(75.4 MHz, CDCl3) δ 141.58, 136.87, 126.25, 116.42, 74.61,
65.78, 36.40, 30.15, 26.90, 25.77, 17.64; MS (m/z) 167 (M++1,
1.99), 151 (100); IR (neat) 1638, 1164, 1094 cm-1; HRMS calcd
for C11H18O 166.1358. Found 166.1382.
(29) 2-Bu tyl-3-p r op en yl-5,6-d ih yd r o-2H-p yr a n (6g). The
reaction of 2g (0.082 g, 0.59 mmol) and 3a (0.386 g, 3.19 mmol)
afforded 0.036 g (34%) of 6g (33% of 2g was recovered): liquid;
1H NMR (300 MHz, CDCl3) δ 5.82-5.66 (m, 1 H), 5.58-5.52
(m, 1 H), 5.08-4.98 (m, 2 H), 4.05-3.94 (m, 1 H), 3.90-3.80
(22) 2,2-Dim eth yl-4-(2′-bu tyl-2′-p r op en yl)-3-p h en yl-2,5-
d ih yd r ofu r a n (4v). The reaction of 1j (0.060 g, 0.34 mmol)
and 3d (0.345 g, 1.95 mmol) afforded 0.068 g (73%) of 4v:
liquid; 1H NMR (300 MHz, CDCl3) δ 7.42-7.26 (m, 3 H), 7.15
(d, J ) 7.8 Hz, 2 H), 4.74 (s, 2 H), 4.53 (s, 2 H), 2.66 (s, 2 H),
1.91 (t, J ) 6.7 Hz, 2 H), 1.35 (s, 6 H), 1.30-1.15 (m, 4 H),
0.84 (t, J ) 6.9 Hz, 3 H); MS (m/z) 270 (M+, 12.79), 255 (100);
IR (neat) 1640, 1245, 1060 cm-1; HRMS calcd for C19H26
270.1984. Found 270.1944.
O
(23) 4-Bu tyl-5-m eth yl-3-p r op en yl-5,6-d ih yd r o-2H-p y-
r a n (6a ). The reaction of 2a (0.155 g, 1.01 mmol) and 3a (0.621
J . Org. Chem, Vol. 67, No. 17, 2002 6111

Ma and Gao
(m, 1 H), 3.58-3.50 (m, 1 H), 2.64 (d, J ) 6.6 Hz, 2 H), 2.23-
2.08 (m, 1 H), 2.02-1.90 (m, 1 H), 1.66-1.20 (m, 6 H), 0.88 (t,
J ) 7.1 Hz, 3 H); 13C NMR (75.4 MHz, CDCl3) δ 138.37, 135.91,
120.50, 116.26, 75.45, 61.91, 37.67, 31.83, 27.13, 25.60, 22.71,
14.03; MS (m/z) 180 (M+, 1.78), 123 (100); IR (neat) 1637, 1266,
1041 cm-1; HRMS calcd for C12H20O 180.1514. Found 180.1465.
(30) (E a n d Z)-4-(2′-Bu ten yl)-3-bu tyl-2-m eth yl-2,5-d i-
h yd r ofu r a n (4a a ). The reaction of 1a (0.096 g, 0.69 mmol)
and 3e (0.317 g, 3.50 mmol) afforded 0.084 g (63%) of 4a a (E/Z
) 1) and 4a b (98:2) as a mixture: liquid; 1H NMR (300 MHz,
CDCl3) δ 5.50-5.20 (m, 2 H), 4.82-4.65 (m, 1 H), 4.50-4.32
(m, 2 H), [2.76 (d, J ) 7.3 Hz), 2.67 (d, J ) 6.2 Hz), 2 H], 2.16-
2.01 (m, 1 H), 1.94-1.76 (m, 1 H), 1.63-1.50 (m, 3 H), 1.40-
1.08 (m, 7 H), 0.93-0.75 (m, 3 H); MS (m/z) 193 (M+ - 1,
times) and dried over anhydrous sodium sulfate. The product
was purified by column chromatography on silica gel (petro-
leum ether/ether ) 40:1) to afford 0.007 g (11%) of 5a : liquid;
1H NMR (300 MHz, CDCl3) δ 5.56 (q, J ) 6.8 Hz, 1 H), 5.15
(d, J ) 1.8 Hz, 1 H), 4.99-4.88 (m, 1 H), 4.84 (d, J ) 1.8 Hz,
1 H), 4.65-4.50 (m, 2 H), 2.30-2.17 (m, 3 H), 1.94-1.82 (m, 1
H), 1.68 (d, J ) 6.8 Hz, 3 H), 1.44-1.20 (m, 11 H), 0.95-0.83
(m, 6 H); MS (m/z) 262 (M+, 11.43), 219 (100); IR (neat) 1456,
1060, 1018 cm-1; HRMS calcd for C18H30O 262.2297. Found
262.2303. The stereochemistry of 5a was confirmed by the 1H-
1H NOESY spectra.
Th e Cou p lin g Rea ction of 2,3-Allen ol 1j w ith a Sto-
ich im etr ic Am ou n t of (π-Allyl) P alladiu m Ch lor ide Dim er .
2,2-Dim eth yl-3-p h en yl-2,5-d ih yd r ofu r a n (11). A mixture
of allenol 1j (0.030 g, 0.17 mmol) and (π-allyl) palladium
chloride dimer (0.063 g, 0.17 mmol) was stirred in DMA (1.2
mL) at room temperature for 96 h. Then ether was added. The
reaction mixture was washed with brine (three times) and
dried over anhydrous sodium sulfate. The product was purified
by column chromatography on silica gel (petroleum ether/ether
) 40:1) to afford 0.010 g (33%) of 11 and 4j (11:4j ) 92:8) as
a mixture: liquid; 1H NMR (300 MHz, CDCl3) δ 7.44-7.28 (m,
5 H), 5.98 (s, 1 H), 4.69 (d, J ) 1.8 Hz, 2 H), 1.49 (s, 6 H); MS
(m/z) 174 (M+, 21.46), 159 (100); IR (neat) 1599, 1494, 1069
cm-1; HRMS calcd for C12H14O 174.1045. Found 174.1069. The
following data are discernible for 2,2-dimethyl-3-phenyl-4-(2′-
propenyl)-2,5-dihydrofuran (4j): 5.85-5.65 (m 1 H), 5.10-4.90
(m, 2 H), 2.76-2.70 (m, 2 H).
Th e Cycliza tive Cou p lin g Rea ction of 2,3-Allen ols 1s
w ith 4-Br om o-1,2-bu ta d ien e 3g. 3-(1′-Meth ylen ep r op e-
n yl)-1-oxa sp ir o[4.5]d ec-3-en e (13). A mixture of allenol 1s
(0.042 g, 0.30 mmol), 4-bromo-1,2-butadiene 3g (0.206 g, 1.55
mmol), and PdCl2 (0.003 g, 5 mol %) was stirred in DMA (2
mL) at room temperature for 9 h. Then ether was added. The
reaction mixture was washed with brine (three times) and
dried over anhydrous sodium sulfate. The product was purified
by column chromatography on silica gel (petroleum ether/ether
) 40:1) to afford 0.032 g (55%) of 13 and 5s (13:5s ) 92:8) as
a mixture: liquid; 1H NMR (300 MHz, CDCl3) δ 6.39 (dd, J )
17.3 and 10.8 Hz, 1 H), 5.88 (s, 1 H), 5.44 (dd, J ) 17.3 and
1.4 Hz, 1 H), 5.20 (s, 1 H), 5.11 (dd, J ) 10.8 and 1.4 Hz, 1 H),
4.76 (s, 1 H), 4.70 (d, J ) 2.0 Hz, 2 H), 1.70-1.25 (m, 10 H);
MS (m/z) 190 (M+, 9.42), 147 (100); IR (neat) 1637, 1447, 1062
cm-1; HRMS calcd for C13H18O 190.1358. Found 190.1327. The
following data are discernible for 3-(1-cyclohexylidenemeth-
ylvinyl)-1-oxaspiro[4.5]dec-3-ene (5s): 2.20-2.05 (m, 4 H).
56.40), 55 (100); IR (neat) 1075 cm-1; HRMS calcd for C12H19
O
(M+ - CH3) 179.1436. Found 179.1481. The following data are
discernible for the other stereoisomer, i.e., 3-butyl-2-methyl-
4-(1′-methyl-2′-propenyl)-2,5-dihydrofuran (4a b): 5.83-5.61
(m, 1 H), 5.01-4.87 (m, 2 H), 3.26-3.14 (m, 1 H).
(31) 3-Bu tyl-2-m eth yl-4-(1′-m eth yl-2′-p r op en yl)-2,5-d i-
h yd r ofu r a n (4a b). The reaction of 1a (0.219 g, 1.56 mmol)
and 3f (0.693 g, 7.65 mmol) afforded 0.060 g (21%) of 4a a and
4a b (14:86) as a mixture: liquid; 1H NMR (300 MHz, CDCl3)
δ 5.80-5.65 (m, 1 H), 5.00-4.88 (m, 2 H), 4.82-4.72 (m, 1 H),
4.56-4.36 (m, 2 H), 3.24-3.14 (m, 1 H), 2.18-2.04 (m, 1 H),
1.96-1.82 (m, 1 H), 1.40-1.12 (m, 7 H), 1.05 (dd, J ) 7.1 and
0.7 Hz, 3 H), 0.95-0.75 (m, 3 H); MS (m/z) 194 (M+, 9.12), 55
(100); IR (neat) 1078, 1020 cm-1. The following data are
discernible for the other stereoisomer, i.e., (E and Z)-4-(2′-
butenyl)-3-butyl-2-methyl-2,5-dihydrofuran (4a a ): 5.50-5.20
(m, 2 H), [2.76 (d, J ) 7.3 Hz), 2.68 (d, J ) 6.1 Hz), 2 H].
(32) (E a n d Z)-4-(2′-Bu ten yl)-2,2-Dim eth yl-3-p h en yl-2,5-
d ih yd r ofu r a n (4ja ). The reaction of 1j (0.070 g, 0.40 mmol)
and 3e (0.184 g, 2.03 mmol) afforded 0.063 g (69%) of 4ja and
1
4jb (89:11) as a mixture: liquid; H NMR (300 MHz, CDCl3)
δ 7.44-7.24 (m, 3 H), 7.20-7.08 (m, 2 H), 5.54-5.24 (m, 2 H),
4.63 (t, J ) 1.2 Hz, 2 H), [2.74 (dd, J ) 7.3 and 0.6 Hz), 2.66
(d, J ) 6.2 Hz), 2 H], [1.64 (dt, J ) 4.8 and 1.3 Hz), 1.51 (dt,
J ) 6.7 and 0.8 Hz), 3 H], 1.36-1.24 (m, 6 H); MS (m/z) 228
(M+, 0.44), 213 (100); IR (neat) 1598, 1490, 1181, 1060 cm-1
;
HRMS calcd for C16H20O 228.1514. Found 228.1469. The
following data are discernible for the other stereoisomer, i.e.,
2,2-dimethyl-4-(1′-methyl-2′-propenyl)-3-phenyl-2,5-dihydrofu-
ran (4jb): 5.84-5.73 (m, 1 H), 5.01-4.94 (m, 2 H), 3.06-2.97
(m, 1 H).
(33) 2,2-Dim et h yl-4-(1′-m et h yl-2′-p r op en yl)-3-p h en yl-
2,5-d ih yd r ofu r a n (4jb). The reaction of 1j (0.131 g, 0.75
mmol) and 3f (0.345 g, 3.81 mmol) afforded 0.055 g (34%) of
4ja and 4jb (15:85) as a mixture: liquid; 1H NMR (300 MHz,
CDCl3) δ 7.40-7.28 (m, 3 H), 7.16-7.11 (m, 2 H), 5.84-5.72
(m, 1 H), 5.02-4.94 (m, 2 H), 4.73-4.63 (m, 2 H), 3.05-2.96
(m, 1 H), 1.33 (s, 3 H), 1.30 (s, 3 H), 1.08 (d, J ) 7.1 Hz, 3 H);
MS (m/z) 228 (M+, 21.57), 227 (100); IR (neat) 1249, 1147, 1057
cm-1. The following data are discernible for the other stere-
oisomer, i.e., (E and Z)-4-(2′-butenyl)-2,2-Dimethyl-3-phenyl-
2,5-dihydrofuran (4ja ): 5.53-5.28 (m, 2 H), [2.74 (d, J ) 7.4
Hz), 2.66 (d, J ) 6.2 Hz), 2 H].
Ack n ow led gm en t. We are grateful to National
Natural Science Foundation of China, the Major State
Basic Research and Development Program (Grant No.
2000O77500), and Shanghai Municipal Committee of
Science and Technology for financial support. Sheng-
ming Ma is the recipient of 1999 Qiu Shi Award for
Young Chinese Scientific Workers issued by Hong Kong
Qiu Shi Foundation of Science and Technology (1999-
2003).
Th e Bim olecu la r Cycliza tive Cou p lin g Rea ction of 2,3-
Allen ol 1a . 3-Bu tyl-4-(2′-eth ylid en e-1′-m eth ylen eh exyl)-
2-m eth yl-2,5-d ih yd r ofu r a n (5a ). A mixture of allenol 1a
(0.069 g, 0.49 mmol) and PdCl2 (0.005 g, 5 mol %) was stirred
in DMA (3 mL) at room temperature for 24 h. Then ether was
added. The reaction mixture was washed with brine (three
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra
and some of the representative 13C NMR spectra. This material
is available free of charge via the Internet at http://pubs.acs.org.
J O0163997
6112 J . Org. Chem., Vol. 67, No. 17, 2002