Synthesis of dibenzo-fused 10-membered cyclic ethers from isovanillin Via ring-closing metathesis

Article abstract of DOI:10.3987/COM-05-10592

A synthesis of substituted dibenzo-fused 10-membered cyclic ethers is described. 2-Allylbenzyl alcohols and 2-allylphenols derived from isovanillin were coupled by the Mitsunobu reaction to construct intramolecular dienes with ether linkage. The resulting

Full text of DOI:10.3987/COM-05-10592

HETEROCYCLES, Vol. 68, No. 1, 2006
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HETEROCYCLES, Vol. 68, No. 1, 2006, pp. 125 – 136. © The Japan Institute of Heterocyclic Chemistry
Received, 13th October, 2005, Accepted, 2nd December, 2005, Published online, 6th December, 2005. COM-05-10592
SYNTHESIS OF DIBENZO-FUSED 10-MEMBERED CYCLIC
ETHERS FROM ISOVANILLIN VIA RING-CLOSING META-
THESIS
Eng-Chi Wang,a* Yu-Li Lin,a Hsing-Ming Chen,b Sie-Rong Li,a Chizuko
Kabuto,c and Yoshio Takeuchid
aFaculty of Medicinal and Applied Chemistry, Kaohsiung Medical University,
Kaohsiung City, Taiwan 807
bBasic Medical Science Education Center, Fooyin University, Kaohsiung
County, Taiwan 831
cResearch and Analytical Center for Giant Molecules, Graduate School of
Science, Tohoku University, Sendai Japan 980-8578
dFaculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical
University, Toyama Japan 930-0194
Abstract –A synthesis of substituted dibenzo-fused 10-membered cyclic ethers
is described. 2-Allylbenzyl alcohols and 2-allylphenols derived from isovanillin
were coupled by the Mitsunobu reaction to construct intramolecular dienes with
ether linkage. The resulting dienes were subsequently treated with Grubbs’
catalyst to undergo ring-closing metathesis to give the desired cyclic ethers.
INTRODUCTION
Interest in the synthesis of medium macrocyclic ethers has increased because of their occurrence in nature
and their biological activities.1 The cyclic ethers such as seven-membered,2 eight-membered,3 and
nine-membered cyclic ethers4 which were prepared from ring-closing metathesis (RCM) have been
reported in the previous studies. However the synthesis of ten-membered cyclic ethers has paid no
attention. Recently, we have based on RCM and used the powerful catalyst developed by Grubbs5 to
synthesize benzo[b]oxepines,6 benzo[c]oxocines,7 and benzofurans.8 In this our continuing study, we
disclose the synthesis of a series of novel dibenzo-fused 10-membered macrocyclic ethers. The strategy
was started from isovanillin which was transformed it to the requisite aryl benzyl ethers with dienes
functionality by the Mitsunobu reaction.9 Subsequent treatment of these aryl benzyl ethers with Grubbs’
catalyst yielded a series of novel substituted dibenzo-fused 10-membered cyclic ethers in moderate yield,

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HETEROCYCLES, Vol. 68, No. 1, 2006
respectively (Scheme 1). Their structures were assigned rationally by spectral data. In addition the
olefinic double bonds of these giving cyclic ethers (8a-g) were confirmed as cis-configuration by either
1H-NMR spectra or X-Ray crystallography.
OR
OH
O
OH
iii
ii
i
MeO
MeO
MeO
MeO
O
O
O
O
H
H
H
H
3
2
4
1
OR
MeO
5
OH
iv
v
13
O
OMe
OR'
12
1
14
2
4
11
10
a) R = Me
vii
R = Et
3
b)
c)
O
4
vi
OMe
R = i-pr
MeO
9
5
OR'
MeO
RO
8
OR'
6
7
OR
MeO
8
7
OH
a) R = Me, R' = Et; b) R = Me, R' = i-Pr c) R = Et, R '= Me;
a) R' = Me
d) R = Et , R '= Et; e) R = Et, R' = i-Pr ; f) R = i-Pr, R' =
R' = Et
b)
c)
6
Et
R' = i-Pr
g) R = R' = i-Pr
Scheme 1. Reagents and conditions: i) allyl bromide / K2CO3 / acetone, reflux, 8 h, 87%; ii) heated to 180 oC, 3 h, 92%;
iii) RX / K2CO3 / acetone, reflux, 8 h, 80-98%; iv) H2O2 / MeOH/H+, rt, 1.5 h, 71-75%; v) NaBH4 / EtOH, rt, 30 min, 93-98%;
vi) DIAD / TPP, 0 oC to rt, 12 h, 50-57%; vii) 1st generation Grubbs' catalyst / CH2Cl2, 1.5 days, 41-50%
RESULTS AND DISCUSSION
3-Allyloxy-4-methoxybenzaldehyde (2), prepared from isovanillin (1) and allyl bromide, was subjected to
o
the Claisen rearrangement at 180 C to give 2-allyl-3-hydroxy-4-methoxybenzaldehyde (3) in 92 %
yield.10 The resulting compound (3) was reacted with various either alkyl iodide or bromide to undergo
O-alkylation to produce 2-allyl-3-alkoxy-4-methoxybenzaldehydes (4a-c) in 80-98% yield.10 Compounds
(4a-c) were converted into corresponding phenols (5a-c) in yield of 71-75% by Dakin oxidation.6 On the
other hand, compounds (4a-c) were reduced with sodium borohydride to give the corresponding benzyl
alcohols (6a-c) in yield of 93-98% by a reported procedure.7 Subsequently, compounds (5a-c) and (6a-c)
were subjected to the Mitsunobu reaction to undergo intermolecular dehydration to produce the aryl
benzyl ethers with dienes functionality (7a-g) in yield of 50-57%. The structures of 7a-g were confirmed
1
according to their spectral data. For example, the H-NMR spectrum of 7a exhibited one singlet signal
with six protons at δ 3.82 which indicated the overlap of two methoxy groups; one singlet signal with
three protons at δ 3.85 indicating the presence of one another methoxy group; one triplet signal of three

HETEROCYCLES, Vol. 68, No. 1, 2006
127
protons at δ 1.38 with coupling constant J = 6.8 Hz and one quartet signal of two protons at δ 4.02 with J
= 6.8 Hz indicating the presence of one ethoxy group; one singlet signal of two protons at δ 4.90
indicating the presence of benzylic protons and the success of the formation of ether linkage from phenol
and benzyl alcohol via the Mitsunobu reaction. Furthermore two double triplet signals with two protons in
each were observed, one at δ 3.45 with coupling constant J = 6.4, 1.6 Hz, and the other one at δ 3.53 with
coupling constant J = 6.0, 1.6 Hz indicating the presence of two allylic protons. In addition, twenty four
13
carbons found in C-NMR spectrum matched the structure of 7a, C24H30O5. Furthermore, the molecular
ion, m/z 398 (M+) in EI-MS (70 eV) and m/z 398.2090 in the HRMS spectrum were found that is
coincident with the calculated one, 398.2088 for C24H30O5. Subsequent treatment of the dienes (7a-g)
with 1st generation Grubbs’ catalyst furnished the substituted dibenzo-fused 10-membered cyclic ethers
(8a-g) in yield of 41-50%, respectively. The structure of 8a-g was verified based on their spectral data
1
13
1
such as H-NMR, C-NMR, EI-MS, and NOESY spectra. The combination of data from H-NMR and
NOESY spectra enabled us to assign their structures unequivocally. For example, the NOESY
correlations of 8c showed the signal of O-CH2 of ethoxy group at δ 4.03 has two cross peaks; one at δ
3.64 indicating H-8 and the other one at δ 3.86 indicating the methoxy group at C-10. The signal at δ 5.59,
which is the cross peak of H-8, was assigned as H-7. The signal at δ 5.49, which is the cross peak of H-7,
was assigned as H-6. The proton at δ 4.01 was assigned as H-5 for its cross-linking with H-6. The typical
benzylic proton, H-14 at δ 4.94 has two cross peaks; H-1 at δ 6.94 and H-12 at δ 6.73. The signal of H-12
was assigned because of its no cross-linking with methoxy group. Therefore two other aromatic protons,
which were overlapped, could be assigned at δ 6.72. Thus, the assignment of the 1H-NMR spectrum of 8c
was accomplished. Based on the information of NOESY spectrum, the characteristic signals of
dibenzo-fused 10-membered cyclic ethers (8a-g) could be deduced and were summarized in Table 1.
Furthermore, the stereochemistry of dibenzo-fused 10-membered cyclic ether (8a-g) was respectively
certified as cis-configuration on the basis of their olefinic coupling constants (10.0 ~ 10.8 Hz) in 1H-NMR
spectra. In addition the structure of 8c is further confirmed by X-Ray crystallography (Figure 1). The
X-Ray crystal data for 8c revealed that the selected bond length (Ao) between olefinic carbons C(6)-C(7)
is 1.327. The selected bond angles of C(5)-C(6)-H(6), C(5)-C(6)-C(7), C(7)-C(6)-H(6), C(6)-C(7)-C(8),
C(6)-C(7)-H(7), and C(8)-C(7)-H(7) were 116.2o, 127.4o, 116.4o, 127.2o, 116.3o, and 116.4o, respectively.
Thus, the coplanar of H(6)-C(6)-C(7)-H(7) was observed and further confirmed the olefinic double bond
of the structure (8c) as cis-configuration.
On the other hand, the 1H-13C HETCOR spectra provide the further information for the identification of
characteristic carbons at compound (8a-g). For example, in the molecule of 8c, the methyl carbon of

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1
Table 1. The characteristic protons of 10-membered cyclic ethers (8a-g) in H-NMR (CDCl3, 400
MHz) spectra∗
Compds
H-5
H-8
H-6
H-7
H-14
4.01 (d, J = 7.2 Hz) 3.63 (d, J = 8.0 Hz) 5.49(dt, J = 10.4, 8.0 Hz) 5.58 (dt, J = 10.4, 8.0 Hz) 4.94 (s)
4.05 (d, J = 8.0 Hz) 3.99 (d, J = 8.0 Hz) 5.46 (d, J = 10.4, 8.0 Hz) 5.57 (dt, J =10.8, 8.4 Hz) 4.92 (s)
3.99 (d, J = 8.0 Hz) 3.64 (d, J = 8.0 Hz) 5.49 (dt, J = 10.8, 7.8 Hz) 5.59 (dt, J = 10.4, 8.2 Hz) 4.94 (s)
4.01 (d, J = 8.8 Hz) 3.64 (d, J = 8.0 Hz) 5.48 (dt, J = 10.0, 7.8 Hz) 5.57 (dt, J = 10.8, 7.8 Hz) 4.93 (s)
4.05 (d, J = 8.4 Hz) 3.64 (d, J = 8.4 Hz) 5.44 (dt, J = 10.4, 7.6 Hz) 5.56 (dt, J = 10.4, 8.0 Hz) 4.91(s)
4.02 (d, J = 7.2 Hz) 3.66 (d, J = 8.4 Hz) 5.45 (dt, J = 10.4, 7.6 Hz) 5.58 (dt, J = 10.4, 8.2 Hz) 4.92 (s)
4.05 (d, J = 8.0 Hz) 3.65 (d, J = 8.4 Hz) 5.42 (dt, J = 10.8, 7.8 Hz) 5.56 (dt, J = 10.4, 8.0 Hz) 4.91 (s)
8a
8b
8c
8d
8e
8f
8g
*Other chemical shifts are described in EXPERIMENTAL
Figure 1. ORTEP plot of the X-Ray crystal of 8c
ethoxy group was assigned at 15.67 (OCH2CH3) for its linking with the corresponding proton at δ 1.40
(OCH2CH3). Based on the same technique, the other carbons of 8c were assigned as follows: δ 22.44
(C-8), 24.77 (C-5), 55.62 (OCH3), 56.01 (OCH3), 60.86 (OCH3), 69.24 (OCH2CH3), 75.52 (C-14), 109.06
(C-11), 110.08 (C-2), 115.19 (C-12), 125.41 (C-1), 126.48 (C-6), 127.51 (C-7). Thus, the characteristic
carbons of 8a-g could be assigned and compiled in Table 2.
CONCLUSION
We have established a method for the construction of dibenzo-fused 10-membered cyclic ethers from
isovanillin via the Mitsunobu’s reaction and RCM. Furthermore, the olefinic double bond of those
resulting cyclic ethers was identified as cis-configuration. In addition, the assignment of each proton and
typical carbons of those cyclic ethers was achieved by NOSEY and HETCOR spectra, respectively.

HETEROCYCLES, Vol. 68, No. 1, 2006
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13
Table 2. The characteristic carbons of 10-membered cyclic ethers (8a-g) in C-NMR spectra (CDCl3,
100 MHz)
Compds
8a
C-8
C-5
C-14
C-2
C-11
C-12
C-1
C-6
C-7
22.21 24.94 75.73 108.93 109.98 115.55 125.23 126.56 127.36
22.49 25.32 76.27 108.93 110.05 115.96 124.91 126.47 127.37
22.44 24.77 75.52 109.06 110.08 115.19 125.41 126.48 127.52
22.49 24.95 75.82 108.98 110.05 115.45 125.23 126.51 127.45
22.50 25.26 76.24 108.91 110.06 115.73 124.83 126.35 127.39
22.90 24.95 75.96 109.04 110.15 115.34 125.19 126.48 127.44
22.86 25.26 76.31 108.91 110.07 115.55 124.76 126.29 127.38
8b
8c
8d
8e
8f
8g
*Other chemical shifts are described in EXPERIMENTAL
EXPERIMENTAL
1
Melting points (Yanaco micro melting-point apparatus) were uncorrected. H-NMR and 13C-NMR
spectra were obtained on a Varian Gemini-200 or Varian Unity plus 400 Spectrometer. Chemical shifts
were measured in parts per million with respect to TMS. Elemental analyses were recorded on a Heraeus
CHN-O Rapid analyzer. MS spectra were recorded on a Chem/hp/middle spectrometer connected to a
Hewlett Packard series II model gas-liquid chromatograph. HRMS spectra were performed on a JEOL
JMS SX/SX 102A instrument. Silica gel (230-400 mesh) for column chromatography and precoated
silica gel plates (60 F-254) for TLC were purchased from E. Merck Co. UV light (254 nm) was used to
detect spots on TLC plates after development.
Crystal structure analysis of 8c
The crystal structure of compound (8c) has been determined by single-crystal X-Ray diffraction
techniques and refined by full-matrix least-squares procedures to give R value of 0.043. The crystals are
colorless prism, space group P2 /c (#14) with lattice parameters, a = 9.5067(8) Å, b = 6.6759(5) Å, c =
1
29.995(2) Å and Z = 4. A crystal of 0.20 x 0.20 x 0.20 mm was chosen. The data were collected on a
Rigaku AFC8 diffractometer with graphite monochromated Mo (μ) K (0.71070 Å) radiation. The CIF file
has been deposited at the Cambridge Crystallographic Center (CCDC), UK, and received the number as
CCDC 281587.
Starting material and key intermediates: Isovanillin (1) was purchased from TCI, Japan.
3-Allyloxy-4-methoxybenzaldehyde (2), 2-allyl-3-hydroxy-4-methoxybenzaldehyde (3), 3-alkoxy-2-
allyl-4-methoxybenzaldehyde (4), 4-alkoxy-2-allyl-3-methoxyphenols (5a-c), and 4-alkoxy-2-allyl-3-

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methoxybenzyl alcohols (6a-c) were respectively prepared by previous paper.6,7,10
General procedure for the preparation of 3’,4’-dialkoxy-2’-allylbenzyloxy-2-allyl-3,4-dialkoxy-
benzenes (7a-g)
A mixture of dialkoxy-2-allylphenols (5a-c) (7 mmol), dialkoxy-2-allylbenzyl alcohols (6a-c) (7 mmol),
o
and triphenylphosphine (2.2 g, 8.4 mmol) in THF (20 mL) was cooled to 0 C and stirred for few min.
The resulting clear solution was continually stirred at ice bath and added to diisopropyl azodicarboxylate
(1.67 mL, 8.4 mmol) in drops. Then, the resulting solution was allowed to warm to rt and was stirred
continually for 12 h. Subsequently, the reaction mixture was concentrated in vacuo to remove THF. The
giving residue was subjected to silica gel column chromatography (EtOAc: n-hexane = 1: 20) to afford
3’,4’-dialkoxy-2’-allylbenzyloxy-2-allyl-3,4-dialkoxybenzenes (7a-g), respectively.
1-(2’-Allyl-3’-ethoxy-4’-methoxy)benzyloxy-2-allyl-3,4-dimethoxybenzene (7a)
o
7a (1.48 g, 53%) was obtained as light reddish color crystals, mp 59 C (EtOAc + n-hexane), Rf = 0.48
(EtOAc: n-hexane = 1: 5), 1H-NMR (CDCl3, 400 MHz) δ 1.38 (t, J = 6.8 Hz, 3H, OCH2CH3), 3.45 (dt, J
= 6.4, 1.6 Hz, 2H, ArCH2CH=CH2), 3.53 (dt, J = 6.0, 1.6 Hz, 2H, ArCH2CH=CH), 3.82 (s, 6H, OCH3),
3.85 (s, 3H, OCH3), 4.02 (q, J = 6.8 Hz, 2H, OCH2CH3), 4.90 (s, 2H, ArOCH2Ar), 4.94 (m, 4H,
ArCH2CH=CH2), 5.96 (m, 2H, ArCH2CH=CH2), 6.61 (d, J = 8.8 Hz, 1H, ArH), 6.72 (d, J = 8.8 Hz, 1H,
13
ArH), 6.80 (d, J = 8.4 Hz, 1H, ArH), 7.14 (d, J = 8.4 Hz, 1H, ArH); C-NMR (CDCl3, 100 MHz)
δ 15.73, 28.37, 30.32, 55.64, 56.19, 60.89, 68.60, 68.87, 107.02, 110.02, 110.20, 114.59, 114.98, 123.61,
124.15, 128.71, 132.00, 136.82, 137.19, 146.51, 147.38, 148.09, 151.41, 152.59; EI-MS (70eV) m/z (rel.
intensity, %): 398 (M+, 2), 206 (14), 205 (100), 177 (39), 176 (6), 147 (11), 146 (11), 145 (41), 117 (24),
115 (9); HRMS (EI, m/z): Calcd for C24H30O5: 398.2088. Found: 398.2090; Anal. Calcd for C24H30O5: C,
72.34; H, 7.59. Found: C, 72.19; H, 7.68.
1-(2’-Allyl-3’-isopropoxy-4’-methoxy)benzyloxy-2-allyl-3,4-dimethoxybenzene (7b)
o
7b (1.59 g, 55%) was obtained as light yellow color crystals, mp 47 C (EtOAc + n-hexane), Rf = 0.47
(EtOAc: n-hexane = 1: 5), 1H-NMR (CDCl3, 400 MHz) δ 1.28 (t, J = 6.4 Hz, 6H, OCH(CH3)2), 3.45 (dt,
J = 6.0, 1.6 Hz, 2H, ArCH2CH=CH), 3.55 (dt, J = 6.0, 1.6 Hz, 2H, ArCH2CH=CH), 3.81 (s, 3H, OCH3),
3.82 (s, 3H, OCH3), 3.83 (s, 3H, OCH3), 4.52 (sept., J = 6.4 Hz, 1H, OCH(CH3)2), 4.91 (s, 2H,
ArOCH2Ar), 4.94 (m, 4H, ArCH2CH=CH2), 5.94 (m, 2H, ArCH2CH=CH2), 6.60 (d, J = 8.8 Hz, 1H,
ArH), 6.72 (d, J = 8.8 Hz, 1H, ArH), 6.79 (d, J = 8.4 Hz, 1H, ArH), 7.13 (d, J = 8.4 Hz, 1H, ArH);
13C-NMR (CDCl3, 100 MHz) δ 22.57, 28.31, 30.51, 55.47, 56.08, 60.80, 68.55, 74.52, 106.89, 109.84,
110.08, 114.52, 114.98, 123.46, 123.63, 128.77, 132.11, 136.54, 137.10, 144.90, 147.24, 147.96, 151.34,
152.46; EI-MS (70eV) m/z (rel. intensity, %): 412 (M+, 2), 220 (5), 219 (38), 178 (15), 177 (100), 17 (5),

HETEROCYCLES, Vol. 68, No. 1, 2006
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146 (11), 145 (49), 117 (33), 115 (10); HRMS (EI, m/z): Calcd for C25H32O5: 412.2250. Found: 412.2244;
Anal. Calcd for C25H32O5: C, 72.79; H, 7.82. Found: C, 72.65; H, 7.91.
1-(2’-Allyl-3’, 4’-dimethoxy)benzyloxy-2-allyl-3-ethoxy-4-methoxybenzene (7c)
o
7c (1.59 g, 57%) was obtained as light reddish color crystals, mp 39 C (EtOAc + n-hexane), Rf = 0.45
(EtOAc: n-hexane = 1: 5), 1H-NMR (CDCl3, 400 MHz) δ 1.38 (t, J = 7.2 Hz, 3H, OCH2CH3), 3.45 (dt, J
= 6.4, 1.6 Hz, 2H, ArCH2CH=CH), 3.52 (dt, J = 6.0, 1.6 Hz, 2H, ArCH2CH=CH), 3.80 (s, 3H, OCH3),
3.83 (s, 3H, OCH3), 3.87 (s, 3H, OCH3), 4.02 (q, J = 7.2 Hz, 2H, OCH2CH3), 4.91 (s, 2H, ArOCH2Ar),
4.95 (m, 4H, ArCH2CH=CH2), 5.96 (m, 2H, ArCH2CH=CH2), 6.60 (d, J = 8.8 Hz, 1H, ArH), 6.71 (d, J =
8.8 Hz, 1H, ArH), 6.82 (d, J = 8.4 Hz, 1H, ArH), 7.16 (d, J = 8.4 Hz, 1H, ArH); 13C-NMR (CDCl3, 100
MHz) δ 15.68, 28.54, 30.10, 55.59, 56.19, 60.83, 68.47, 68.85, 106.77, 110.06, 110.12, 114.41, 115.03,
123.68, 124.34, 128.74, 131.85, 136.76, 137.18, 147.25, 147.48, 151.40, 152.44; EI-MS (70eV) m/z (rel.
intensity, %): 398 (M+, 8), 192 (14), 191 (100), 176 (7), 161 (11), 160 (37), 159 (7), 145 (5), 121 (4), 91
(4); HRMS (EI, m/z): Calcd for C24H30O5: 398.2088. Found: 398.2091; Anal. Calcd for C24H30O5: C,
72.34; H, 7.59. Found: C, 72.13; H, 7.62.
1-(2’-Allyl-3’-ethoxy-4’-methoxy)benzyloxy-2-allyl-3-ethoxy-4-methoxybenzene (7d)
o
7d (1.48 g, 53%) was obtained as colorless crystals, mp 59 C (EtOAc + n-hexane), Rf = 0.48 (EtOAc:
n-hexane = 1: 5), 1H-NMR (CDCl3, 400 MHz) δ 1.37 (t, J = 7.2 Hz, 3H, OCH2CH3), 1.38 (t, J = 7.2 Hz,
3H, OCH2CH3), 3.46 (d, J = 6.4 Hz, 2H, ArCH2CH=CH), 3.53 (dt, J = 6.0, 1.6 Hz, 2H, ArCH2CH=CH),
3.79 (s, 3H, OCH3), 3.84 (s, 3H, OCH3), 4.02 (q, J = 7.2 Hz, 4H, OCH2CH3), 4.90 (s, 2H, ArOCH2Ar),
4.94 (m, 4H, ArCH2CH=CH2), 5.96 (m, 2H, ArCH2CH=CH2), 6.60 (d, J = 8.8 Hz, 1H, ArH), 6.71 (d, J =
8.8 Hz, 1H, ArH), 6.80 (d, J = 8.4 Hz, 1H, ArH), 7.14 (d, J = 8.4 Hz, 1H, ArH); 13C-NMR (CDCl3, 100
MHz) δ 15.61, 28.49, 30.21, 55.49, 56.08, 68.45, 68.74, 68.75, 106.68, 109.89, 110.02, 114.35, 114.85,
123.57, 124.07, 128.62, 131.87, 136.72, 137.10, 146.37, 147.17, 147.38, 151.34, 152.46; EI-MS (70eV)
m/z (rel. intensity, %): 412 (M+, 8), 206 (15), 205 (100), 178 (13), 177 (50), 147 (14), 146 (15), 145 (33),
144 (10), 117 (29), 115 (12); HRMS (EI, m/z): Calcd for C25H32O5: 412.2244. Found: 412.2247; Anal.
Calcd for C25H32O5: C, 72.79; H, 7.82. Found: C, 72.48; H, 7.90.
1-(2’-Allyl-3’-isopropoxy-4’-methoxy)benzyloxy-2-allyl-3-ethoxy-4-methoxybenzene(7e)
o
7e (1.49 g, 50%) was obtained as colorless crystals, mp 44 C (EtOAc + n-hexane), Rf = 0.51 (EtOAc:
n-hexane = 1: 5), 1H-NMR (CDCl3, 400 MHz) δ 1.28 (d, J = 6.4 Hz, 6H, OCH(CH3)2), 1.38 (t, J = 7.2 Hz,
3H, OCH2CH3), 3.45 (d, J = 6.0 Hz, 2H, ArCH2CH=CH), 3.55 (dt, J = 5.6, 1.6 Hz, 2H, ArCH2CH=CH),
3.80 (s, 3H, OCH3), 3.84 (s, 3H, OCH3), 4.02 (q, J = 7.2 Hz, 2H, OCH2CH3), 4.52 (sept., J = 6.4 Hz, 1H,
OCH(CH3)2), 4.91 (s, 2H, ArOCH2Ar), 4.94 (m, 4H, ArCH2CH=CH2), 5.94 (m, 2H, ArCH2CH=CH2),

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6.59 (d, J = 8.8 Hz, 1H, ArH), 6.71 (d, J = 8.8 Hz, 1H, ArH), 6.79 (d, J = 8.4 Hz, 1H, ArH), 7.13 (d, J =
8.4 Hz, 1H, ArH); 13C-NMR (CDCl3, 100 MHz) δ 15.67, 22.59, 28.56, 30.53, 55.50, 56.16, 68.54, 68.83,
74.55, 106.71, 109.86, 110.07, 114.41, 114.99, 123.64, 128.85, 132.16, 136.57, 137.16, 144.92, 147.20,
147.41, 151.43, 152.47; EI-MS (70eV) m/z (rel. intensity, %): 426 (M+, 3), 220 (5), 219 (36), 178 (13),
177 (100), 147 (6), 146 (11), 145 (45), 117 (31), 115 (9); HRMS (EI, m/z): Calcd for C26H34O5: 426.2401.
Found: 426.2403; Anal. Calcd for C26H34O5: C, 73.21; H, 8.03. Found: C, 73.18; H, 8.07.
1-(2’-Allyl-3’-ethoxy-4’-methoxy)benzyloxy-2-allyl-3-isopropoxy-4-methoxybenzene (7f)
o
7f (1.61 g, 54%) was obtained as light pink crystals, mp 35 C (EtOAc + n-hexane), Rf = 0.49 (EtOAc:
n-hexane = 1: 5), 1H-NMR (CDCl3, 400 MHz) δ 1.27 (d, J = 6.4 Hz, 6H, OCH(CH3)2), 1.38 (t, J = 7.2 Hz,
3H, OCH2 CH3), 3.45 (d, J = 6.0 Hz, 2H, ArCH2CH=CH2), 3.53 (dt, J = 6.0, 1.6 Hz, 2H, CH2=CHCH2Ar),
3.70 (s, 3H, OCH3), 3.85 (s, 3H, OCH3), 4.01 (q, J = 7.2 Hz, 2H, OCH2CH3), 4.53 (sept, J = 6.4 Hz, 1H,
OCHMe2), 4.91 (s, 2H, ArOCH2Ar), 4.94 (m, 4H, 2 x CH2CH=CH2), 5.95 (m, 2H, 2 x CH2CH=CH2),
6.58 (d, J = 8.8 Hz, 1H, ArH), 6.70 (d, J = 8.8 Hz, 1H, ArH), 6.80 (d, J = 8.4 Hz, 1H, ArH), 7.15 (d, J =
8.4 Hz, 1H, ArH); 13C-NMR (CDCl3, 100 MHz) δ 14.13, 15.65, 22.59, 28.88, 30.25, 55.54, 56.09, 68.39,
68.78, 74.57, 106.29, 109.92, 110.00, 114.46, 114.88, 123.90, 124.06, 128.73, 131.86, 136.76, 136.90,
145.78, 146.38, 147.45, 151.55, 152.46; EI-MS (70eV) m/z (rel. intensity, %): 426 (M+, 4), 206 (14), 205
(100), 178 (7), 177 (44), 176 (7), 147 (12), 146 (10), 145 (46), 117 (25), 115 (9), 91 (7); HRMS (EI, m/z):
Calcd for C26H34O5: 426.2401. Found: 426.2403; Anal. Calcd for C26H34O5: C, 73.21; H, 8.03. Found: C,
72.89; H, 7.99.
1-(2’-Allyl-3’-isopropoxy-4’-methoxy)benzyloxy-2-allyl-3-isopropoxy-4-methoxybenzene (7g)
o
7g (1.79 g, 58%) was obtained as light pink crystals, mp 54 C (EtOAc + n-hexane), Rf = 0.67 (EtOAc:
1
n-hexane = 1: 5), H-NMR (CDCl3, 400 MHz) δ 1.27 (d, J = 6.4 Hz, 6H, OCH(CH3)2), 1.28 (d, J = 6.4
Hz, 6H, OCH(CH3)2), 3.45 (dt, J = 6.0, 1.6 Hz, 2H, ArCH2CH=CH2), 3.55 (dt, J = 6.0, 1.6 Hz, 2H,
CH2=CHCH2Ar), 3.78 (s, 3H, OCH3), 3.88 (s, 3H, OCH3), 4.52 (sept, J = 6.0 Hz, 1H, OCHMe2), 4.91 (s,
2H, ArOCH2Ar), 4.94 (m, 4H, 2 x ArCH2CH=CH2), 5.93 (m, 2H, 2 x ArCH2CH=CH2), 6.57 (d, J = 8.8
Hz, 1H, ArH), 6.70 (d, J = 8.8 Hz, 1H, ArH), 6.79 (d, J = 8.4 Hz, 1H, ArH), 7.14 (d, J = 8.4 Hz, 1H,
13
ArH); C-NMR (CDCl3, 100 MHz) δ 22.59, 22.62, 28.93, 30.54, 55.50, 56.12, 68.46, 74.54, 74.62,
106.28, 109.85, 110.00, 114.48, 114.98, 123.63, 123.89, 128.91, 132.10, 136.57, 136.93, 144.88, 145.77,
147.44, 151.60, 152.44; EI-MS (70eV) m/z (rel. intensity, %): 440 (M+, 2), 219 (33), 178 (12), 177 (100),
146 (12), 145 (40), 117 (25), 115 (8); HRMS (EI, m/z): Calcd for C27H36O5: 440.2557. Found: 440.2560;
Anal. Calcd for C27H36O5: C, 73.61; H, 8.24; Found: C, 73.79; H, 8.22.
General procedure for the preparation of 4-alkoxy-5,14-dihydro-8H-13-oxadibenzo[a,f]cyclode-

HETEROCYCLES, Vol. 68, No. 1, 2006
133
cene (8a-g)
Substituted 2’-allylbenzyloxy-2-allylbenzenes (7a-g) (2 mmol) dissolved in CH2Cl2 (40 mL) was added
1st generation Grubbs’ catalyst (80 mg, 0.1 mmol), respectively. The resulting mixture was stirred at rt for
1.5 days. Then, the mixture was concentrated under reduced pressure to remove solvent. The resulting
residue was distilled from micro-distilled apparatus (Eyela Co.) under high vacuum (~0.5 mmHg). The
distillate was subjected to silica gel column chromatography (EtOAc: n-hexane = 1: 25) to give pure
4-alkoxy-5,14-dihydro-8H-13-oxadibenzo[a,f]cyclodecene (8a-g), respectively.
4-Ethoxy-3,9,10-trimethoxy-5,14-dihydro-8H-13-oxadibenzo[a,f]cyclodecene (8a)
o
8a (0.36 g, 48%) was obtained as colorless crystals, mp 128 C (EtOAc + n-hexane), Rf = 0.32 (EtOAc:
n-hexane = 1: 5), 1H-NMR (CDCl3, 400 MHz) δ 1.41 (t, J = 7.0 Hz, 3H, OCH2CH3), 3.63 (d, J = 8.0 Hz,
2H, H-8), 3.83 (s, 3H, 1 x OCH3), 3.84 (s, 6H, 2 x OCH3), 4.00 (q, J = 7.0 Hz, 2H, OCH2CH3), 4.01 (d, J
= 7.2 Hz, 2H, H-5), 4.94 (s, 2H, H-14), 5.49 (dt, 1H, J = 10.4, 8.0 Hz, H-6), 5.58 (dt, 1H, J = 10.4, 8.0 Hz,
H-7), 6.71 (d, J = 8.4 Hz, 1H, H-2), 6.73 (d, J = 8.6 Hz, 1H, H-11), 6.86 (d, J = 8.6 Hz, 1H, H-12), 6.92
13
(d, J = 8.6 Hz, 1H, H-1); C-NMR (CDCl3, 100 MHz) δ 15.60 (OCH2CH3), 22.21 (C-8), 24.94 (C-5),
55.59 (OCH3), 55.92 (OCH3), 61.17 (OCH3), 68.98 (OCH2CH3), 75.73 (C-14), 108.93 (C-2), 109.98
(C-11), 115.55 (C-12), 125.23 (C-1), 126.56 (C-6), 127.36 (C-7), 128.40, 128.56, 133.34, 146.83, 147.00,
149.06, 152.28, 153.27; EI-MS (70eV) m/z (rel. intensity, %): 370 (M+, 5), 204 (33), 203 (100), 202 (18),
191 (14), 190 (11), 175 (34), 143 (25), 115 (12); HRMS (EI, m/z): Calcd for C22H26O5: 370.1775. Found:
370.1777; Anal. Calcd for C22H26O5: C, 71.33; H, 7.07. Found: C, 71.25; H, 7.03.
4-Isopropoxy-3,9,10-trimethoxy-5,14-dihydro-8H-13-oxadibenzo[a,f]cyclodecene (8b)
o
8b (0.32 g, 42%) was obtained as colorless crystals, mp 113 C (EtOAc + n-hexane), Rf = 0.35 (EtOAc:
1
n-hexane = 1: 5), H-NMR (CDCl3, 400 MHz) δ 1.31 (d, J = 6.0 Hz, 6H, OCH(CH3)2), 3.63 (d, J = 8.4
Hz, 2H, H-8), 3.83 (s, 3H, OCH3), 3.84 (s, 6H, 2 x OCH3), 3.99 (d, J = 8.0 Hz, 2H, H-8), 4.05 (d, J = 8.0
Hz, 2H, H-5), 4.42 (sept, J = 6.0 Hz, 1H, OCH(CH3)2), 4.92 (s, 2H, H-14), 5.46 (dt, J = 10.8, 8.0 Hz, 1H,
H-6), 5.57 (d, J = 10.8, 8.4 Hz, 1H, H-7), 6.70 (d, J = 8.0 Hz, 1H, H-2), 6.74 (d, J = 8.8 Hz, 1H, H-11),
13
6.88 (d, J = 8.8 Hz, 1H, H-12), 6.91 (d, J = 8.0 Hz, 1H, H-1); C-NMR (CDCl3, 100 MHz) δ 22.31
(OCH(CH3)2), 22.49 (C-8), 25.32 (C-5), 55.59 (OCH3), 55.97 (OCH3), 61.24 (OCH3), 74.98 (OCH-
(CH3)2), 76.27 (C-14), 108.93 (C-2), 110.05 (C-11), 115.96 (C-12), 124.91 (C-1), 126.47 (C-6), 127.37
(C-7), 128.67, 128.72, 133.61, 145.55, 147.01, 149.19, 152.61, 153.41; EI-MS (70eV) m/z (rel.
intensity, %): 384 (M+, 1), 342 (12), 218 (11), 217 (42), 191 (12), 176 (39), 175 (100), 174 (16), 152 (11),
144 (11), 143 (26), 115 (11); HRMS (EI, m/z): Calcd for C23H28O5: 384.1931. Found: 384.1933; Anal.
Calcd for C23H28O5: C, 71.85; H, 7.34. Found: C, 71.55; H, 7.52.

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9-Ethoxy-3,4,10-trimethoxy-5,14-dihydro-8H-13-oxadibenzo[a,f]cyclodecene (8c)
o
8c (0.37 g, 50%) was obtained as colorless crystals, mp 143 C (EtOAc + n-hexane), Rf = 0.30 (EtOAc:
n-hexane = 1: 5), 1H-NMR (CDCl3, 400 MHz) δ 1.41 (t, J = 7.2 Hz, 3H, OCH2CH3), 3.64 (d, J = 8.0 Hz,
2H, H-8), 3.81 (s, 6H, 2 x OCH3), 3.86 (s, 3H, OCH3), 3.99 (d, J = 8.0 Hz, 2H, H-5), 4.03 (q, J = 7.2 Hz,
2H, OCH2CH3), 4.94 (s, 2H, H-14), 5.49 (dt, J = 10.8, 7.8 Hz,1H, H-6), 5.59 (dt, J = 10.4, 8.2 Hz, 1H,
H-7), 6.72 (d, J = 8.8 Hz, 2H, H-2 and H-11), 6.84 (d, J = 8.8 Hz, 1H, H-12), 6.94 (d, J = 8.0 Hz, 1H,
13
H-1); C-NMR (CDCl3, 100 MHz) δ 15.67 (OCH2CH3), 22.44 (C-8), 24.77 (C-5), 55.62 (OCH3), 56.01
(OCH3), 60.86 (OCH3), 69.24 (OCH2CH3), 75.52 (C-14), 109.06 (C-2), 110.08 (C-11), 115.19 (C-12),
125.41 (C-1), 126.48 (C-6), 127.52 (C-7), 128.53, 128.75, 133.30, 146.24, 147.79, 149.20, 152.25,
153.17; EI-MS (70eV) m/z (rel. intensity, %) 370 (M+, 15), 205 (9), 190 (29), 189 (100), 188 (14), 174
(17), 159 (9.0); HRMS (EI, m/z): Calcd for C22H26O5: 370.1775. Found: 370.1777; Anal. Calcd for
C22H26O5: C, 71.33; H, 7.07. Found: C, 71.59; H, 7.11.
4,9-Diethoxy-3,10dimethoxy-5,14-dihydro-8H-13-oxadibenzo[a,f]cyclodecene (8d)
o
8d (0.31 g, 41%) was obtained as colorless crystals, mp 114 C (EtOAc + n-hexane), Rf = 0.36 (EtOAc:
n-hexane = 1: 5), 1H-NMR (CDCl3, 400 MHz) δ 1.41 (t, J = 7.2 Hz, 3H, OCH2CH3), 3.64 (d, J = 8.0 Hz,
2H, H-8), 3.82 (s, 3H, OCH3), 3.84 (s, 3H, OCH3), 4.00 (q, J = 7.2 Hz, 2H, OCH2CH3), 4.01 (d, J = 8.8
Hz, 2H, H-5), 4.03 (q, J = 7.2 Hz, 2H, OCH2CH3), 4.93 (s, 2H, H-14), 5.48 (dt, J = 10.0, 7.8 Hz, 1H, H-6),
5.57 (dt, J = 10.8, 7.8 Hz, 1H, H-7), 6.71 (d, J = 8.4 Hz, 1H, H-2), 6.72 (d, J = 8.8 Hz, 1H, H-11), 6.85 (d,
J = 8.8 Hz, 1H, H-12), 6.93 (d, J = 8.4 Hz, 1H, H-1); 13C-NMR (CDCl3, 100 MHz) δ 15.63 (OCH2CH3),
15.68 (OCH2CH3), 22.49 (C-8), 24.95 (C-5), 55.64 (OCH3), 56.02 (OCH3), 69.04 (OCH2CH3), 69.29
(OCH2CH3), 75.82 (C-14), 108.98 (C-2), 110.05 (C-11), 115.45 (C-12), 125.23 (C-1), 126.51 (C-6),
127.45 (C-7), 128.65, 128.71, 133.39, 146.21, 146.86, 149.23, 152.43, 153.30; EI-MS (70eV) m/z (rel.
intensity, %) 384 (M+, 22), 207 (12), 205 (14), 204 (32), 203 (100), 202 (21), 190 (9), 176 (11), 175 (23),
143 (18), 115 (8); HRMS (EI, m/z): Calcd for C23H28O5: 384.1931. Found: 384.1934; Anal. Calcd for
C23H28O5: C, 71.85; H, 7.34. Found: C, 71.87; H, 7.34.
9-Ethoxy-4-isopropyl-3,10-dimethoxy-5,14-dihydro-8H-13-oxadibenzo[a,f]cyclodecene (8e)
o
8e (0.37 g, 47%) was obtained as colorless crystals, mp 132 C (EtOAc + n-hexane), Rf = 0.39 (EtOAc:
n-hexane = 1: 5), 1H-NMR (CDCl3, 400 MHz) δ 1.31 (d, J = 6.0 Hz, 6H, OCH(CH3)2), 1.41 (t, J = 7.2 Hz,
3H, OCH2CH3), 3.64 (d, J = 8.4 Hz, 2H, H-8), 3.82 (s, 3H, OCH3), 3.83 (s, 3H, OCH3), 4.03 (q, J = 7.2
Hz, 2H, OCH2CH3), 4.05 (d, J = 8.4 Hz, 2H, H-5), 4.42 (setp, J = 6.0 Hz, 1H, OCH(CH3)2), 4.91 (s, 2H,
H-14), 5.44 (dt, J = 10.4, 7.6 Hz, 1H, H-6), 5.56 (dt, J = 10.4, 8.0 Hz, 1H, H-7), 6.70 (d, J = 8.4 Hz, 1H,
H-2), 6.73 (d, J = 8.8 Hz, 1H, H-11), 6.86 (d, J = 8.8 Hz, 1H, H-12), 6.91 (d, J = 8.4 Hz, 1H, H-1);
13C-NMR (CDCl3, 100 MHz) δ 15.63 (OCH2CH3), 22.45 OCH(CH3)2), 22.50 (C-8), 25.26 (C-5), 55.55

HETEROCYCLES, Vol. 68, No. 1, 2006
135
(OCH3), 55.99 (OCH3), 69.29 (OCH2CH3), 74.96 (OCH(CH3)2), 76.24 (C-14), 108.91 (C-2), 110.06
(C-11), 115.73 (C-12), 124.83 (C-1), 126.35 (C-6), 127.39 (C-7), 128.74, 128.88, 133.58, 145.52, 146.15,
149.28, 152.66, 153.36; EI-MS (70eV) m/z (rel. intensity, %) 398 (M+, 16), 356 (11), 218 (12), 217 (48),
205 (11), 177 (11), 176 (35), 175 (100), 174 (17), 153 (11), 143 (25); HRMS (EI, m/z): Calcd for
C24H30O5: 398.2088. Found: 398.2090; Anal. Calcd for C24H30O5: C, 72.34; H, 7.59. Found: C, 72.10; H,
7.76.
4-Ethoxy-9-isopropyl-3,10-dimethoxy-5,14-dihydro-8H-13-oxadibenzo[a,f]cyclodecene (8f)
o
8f (0.39 g, 49%) was obtained as colorless crystals, mp 124 C (EtOAc + n-hexane), Rf = 0.39 (EtOAc:
n-hexane = 1: 5), 1H-NMR (CDCl3, 400 MHz) δ 1.32 (d, J = 6.4 Hz, 6H, OCH(CH3)2), 1.41 (t, J = 7.2 Hz,
3H, OCH2CH3), 3.66 (d, J = 8.4 Hz, 2H, H-8), 3.81 (s, 3H, OCH3), 3.84 (s, 3H, OCH3), 3.99 (q, J = 7.2
Hz, 2H, OCH2CH3), 4.02 (d, J = 7.2 Hz, 2H, H-5), 4.67 (setp, J = 6.4 Hz, 1H, OCH(CH3)2), 4.92 (s, 2H,
H-14), 5.45 (dt, J = 10.4, 7.6 Hz, 1H, H-6), 5.58 (dt, J = 10.4, 8.2 Hz, 1H, H-7), 6.71 (d, J = 8.0 Hz, 1H,
H-2), 6.72 (d, J = 8.8 Hz, 1H, H-11), 6.84 (d, J = 8.8 Hz, 1H, H-12), 6.93 (d, J = 8.0 Hz, 1H, H-1);
13C-NMR (CDCl3, 100 MHz) δ 15.66 (OCH2CH3), 22.65 (OCH2(CH3)2), 22.90 (C-8), 24.95 (C-5), 55.70
(OCH3), 56.04 (OCH3), 69.12 (OCH2CH3), 75.02 (OCH(CH3)2), 75.96 (C-14), 109.04 (C-2), 110.15
(C-11), 115.34 (C-12), 125.19 (C-1), 126.48 (C-6), 127.44 (C-7), 128.93, 129.14, 133.42, 145.02, 146.87,
149.41, 152.73, 153.32; EI-MS (70eV) m/z (rel. intensity, %): 398 (M+, 15), 356 (13), 217 (10), 204 (30),
203 (100), 202 (19), 190 (13), 177 (14), 176 (16), 175 (41), 153 (13), 143 (24); HRMS (EI, m/z): Calcd
for C24H30O5: 398.2088. Found: 398.2090; Anal. Calcd for C24H30O5: C, 72.34; H, 7.59. Found: C, 72.31;
H, 7.54.
4,9-Diisopropyl-3,10-dimethoxy-5,14-dihydro-8H-13-oxadibenzo[a,f]cyclodecene (8g)
o
8g (0.37 g, 45%) was obtained as colorless crystals, mp 86 C (EtOAc + n-hexane), Rf = 0.48 (EtOAc:
1
n-hexane = 1: 5), H-NMR (CDCl3, 400 MHz) δ 1.31 (d, J = 6.4 Hz, 6H, OCH(CH3)2), 1.32 (d, J = 6.4
Hz, 6H, OCH(CH3)2), 3.65 (d, J = 8.4 Hz, 2H, H-8), 3.81 (s, 3H, OCH3), 3.83 (s, 3H, OCH3), 4.05 (d, J =
8.0 Hz, 2H, H-5), 4.41 (setp, J = 6.4 Hz, 1H, OCH(CH3)2), 4.46 (setp, J = 6.4 Hz, 1H, OCH(CH3)2), 4.91
(s, 2H, H-14), 5.42 (dt, J = 10.8, 7.8 Hz, 1H, H-6), 5.56 (dt, J = 10.4, 8.0 Hz, 1H, H-7), 6.70 (d, J = 8.4
Hz, 1H, H-2), 6.72 (d, J = 8.8 Hz, 1H, H-11), 6.85 (d, J = 8.8 Hz, 1H, H-12), 6.91 (d, J = 8.4 Hz, 1H,
H-1); 13C-NMR (CDCl3, 100 MHz) δ 22.46 (OCH(CH3)2), 22.58 (OCH(CH3)2), 22.86 (C-8), 25.26 (C-5),
55.58 (OCH3), 55.97 (OCH3), 75.00 (2 x OCH(CH3)2), 76.31 (C-14), 108.91 (C-2), 110.07 (C-11), 115.55
(C-12), 124.76 (C-1), 126.29 (C-6), 127.38 (C-7), 128.88, 129.36, 133.58, 144.90, 145.48, 149.40, 152.86,
153.36; EI-MS (70eV) m/z (rel. intensity, %): 412 (M+, 21), 307 (14), 328 (21), 219 (11), 218 (14), 217
(68), 216 (14), 178 (12), 177 (29), 176 (71), 175 (100), 163 (12), 144 (13), 143 (34), 115 (11); HRMS (EI,
m/z): Calcd for C25H32O5: 412.2244. Found: 412.2248; Anal. Calcd for C25H32O5: C, 72.79; H, 7.82.

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Found: C, 72.85; H, 7.93.
ACKNOWLEDGEMENTS
We are grateful to NSC, Taiwan for financial support (NSC 93-2113-M-037-009). We are also thankful to
Professor Hiroki Takahata, Tohoku Pharmaceutical University, Japan for encouragement and to Mr.
Wen-Hsiung Lu, and Mrs. Chi-Jia Wang for taking NMR spectra, to Miss Chia-Jen Tsai for measuring
elemental analysis and to Mr. Min-Yuan Hung for running GC-EI/MS.
REFERENCES
1. T. Yasumoto and M. Murata, Chem. Rev., 1993, 93, 1897.
2. J. O. Hoberg, Tetrahedron, 1998, 54, 12631; and literatures cited therein.
3. I. Kadoda, A. Ohno, K. Matsuda, and Y. Yamamoto, J. Am. Chem. Soc., 2002, 124, 3562.
4. M. T. Crimmins, K. A. Emmitte, and A. L. Choy, Tetrahedron, 2002, 58, 1817.
5. P. Schwab, M. B. France, J. W. Ziller, and R. H. Grubbs, Angew. Chem. Int. Ed. Engl., 1995, 34, 2039;
R. H. Grubbs, S. J. Miller, and G. C. Fu, Acc. Chem. Res., 1995, 28, 446.
6. E. C. Wang, M. K. Hsu, Y. L. Lin, and K. S. Huang, Heterocycles, 2002, 57, 1997.
7. E. C. Wang, C. C. Wang, M. K. Hsu, and K. S. Huang, Heterocycles, 2002, 57, 2021.
8. T. W. Tsai, E. C. Wang, K. S. Huang, S. R. Li, Y. F. Wang, Y. L. Lin, and Y. H. Chen, Heterocycles,
2004, 63, 1771.
9. O. Mitsunobu, Synthesis, 1981, 1.
10. K. S. Huang and E. C. Wang, Tetrahedron Lett., 2001, 42, 6155.