Synthesis of macrocyclic bis(phenylbenzoxazole) derivatives via tandem Claisen rearrangement and their fluorescence behavior

Article abstract of DOI:10.1002/jhet.5570380617

Novel macrocyclic bis(phenylbenzoxazole) derivatives were easily synthesized from macrocyclic isobutenyl bis(amide-ether)s by tandem Claisen rearrangement and subsequent intramolecular cyclization of the amide-phenol intermediates. The position of substitution of the oligoethylene glycol moiety on the phenylamido groups of the macrocycles did not have a large effect on the yields of the bis(benzoxazole)s for the meta and para derivatives. The fluorescence quantum yields of most of the macrocyclic bis(benzoxazole)s were lower than those of the corresponding nonmacrocyclic bis(benzoxazole) model compounds. The quantum yields of the para-substituted macrocyclic bis(benzoxazole)s were clearly lower than those of the model compounds and decreased with increasing length of the oligoethylene chain.

Full text of DOI:10.1002/jhet.5570380617

Nov-Dec 2001
Synthesis of Macrocyclic Bis(phenylbenzoxazole) Derivatives via
Tandem Claisen Rearrangement and Their Fluorescence Behavior
1353
Emiko Koyama, Hideo Tokuhisa, Yoshinobu Nagawa,
Gang Yang, and Kazuhisa Hiratani*
Nanoarchitectonics Research Center, National Institute of Advanced Industrial Science and Technology (AIST),
Tsukuba Central 4, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562, Japan
Received August 6, 2001
Novel macrocyclic bis(phenylbenzoxazole) derivatives were easily synthesized from macrocyclic
isobutenyl bis(amide–ether)s by tandem Claisen rearrangement and subsequent intramolecular cyclization of
the amide–phenol intermediates. The position of substitution of the oligoethylene glycol moiety on the
phenylamido groups of the macrocycles did not have a large effect on the yields of the bis(benzoxazole)s for
the meta and para derivatives. The fluorescence quantum yields of most of the macrocyclic bis(benzoxa-
zole)s were lower than those of the corresponding nonmacrocyclic bis(benzoxazole) model compounds. The
quantum yields of the para-substituted macrocyclic bis(benzoxazole)s were clearly lower than those of the
model compounds and decreased with increasing length of the oligoethylene chain.
J. Heterocyclic Chem., 38, 1353 (2001).
Much attention has been paid to benzoxazoles because
of macrocyclic bis(phenylbenzoxazole) derivatives bind-
ing oligoethylene glycol at the ortho, meta, or para posi-
tions of the phenylamido groups of the macrocycles, and
we investigate the effect of positional substitution on the
fluorescence.
they have a number of optical applications; they have been
used as optical luminescents [1], whitening agents [2], and
laser dyes [3]. Benzoxazoles also have other important
uses; for example, they can serve as intermediates for
organic syntheses [4] and as therapeutic materials [5].
The Claisen rearrangement has attracted interest because
of its extensive applications for organic synthesis. The pos-
sibility for tandem Claisen rearrangement, that is, transposi-
tion at two reaction centers, extends the reaction's usefulness
even further [6]. We have recently found that isobutenyl
bis(aryl ether) derivatives are easily converted to com-
pounds having two phenolic hydroxy groups via tandem
Claisen rearrangement [7]. Furthermore, we have demon-
strated that some noncyclic isobutenyl bis(aryl ether)s hav-
ing amide groups at the ortho position 1 are easily converted
to bis(benzoxazole)s 2 by heating and that the reaction pro-
ceeds via tandem Claisen rearrangement (Scheme 1) [8,9].
In this paper, we demonstrate a successful synthetic
application of tandem Claisen rearrangement for a series
The series of macrocyclic bis(amide–ether)s 4a–4i
shown in Scheme 2 was prepared as follows: First, 1,3-
bis(2-amino-4-methylphenoxy)-2-methylenepropane
hydrochloride was prepared by a method involving a pro-
tection–deprotection process: 4-methyl-2-aminophenol
was treated with benzaldehyde to form 4-methyl-2-
iminophenol, which was then etherified with 3-chloro-2-
(chloromethyl)-1-propene in the presence of NaH in dry
dimethylformamide (DMF) and deprotected with 12 N
aqueous HCl in chloroform. Next, macrocyclic
bis(amide–ether)s 4a–4i were prepared: 1,3-bis(2-amino-
4-methylphenoxy)-2-methylenepropane hydrochloride
was treated with o-, m-, or p-acetoxybenzoyl chloride in
the presence of pyridine in dry DMF at 0 for 30 minutes
and 20 °C for 3 hours, and the resulting intermediates were

1354
E. Koyama, H.Tokuhisa, Y. Nagawa, G. Yang, and K. Hiratani
Vol. 38
hydrolyzed in 1 N NaOH aqueous solution for 12 hours at
room temperature. Finally, the bisphenol derivatives were
treated with oligoethylene glycol ditosylate in the presence
of potassium carbonate in dry DMF at 70 °C for 3
days(Scheme 2).
5 was carried out by silica gel column chromatography
(eluent: 5:1 chloroform:ethyl acetate). The results for the
rearrangements are summarized in Table 1.
The ortho-substituted macrocyclic bis(benzoxazole)s
5a–5c were not obtained in satisfactory yields (yields of
The bulk rearrangement of meta- and para-substituted
macrocycles 4d–4i was carried out at 230–240 °C for 5–7
hours under vacuum. The heating of o-substituted macro-
cycles 4a–4c at 240 °C for 7 hours gave the complex mix-
ture of the corresponding 5, the intermediates, and other
decomposed compounds. So, the thermal reaction of
4a–4c was carried out under milder conditions (at 210 °C),
which required more than 2 days to complete. The
rearrangement of ortho-substituted macrocycles 4a–4c
proceeded very slowly compared with the rearrangements
of the meta- and para-substituted macrocycles 4d–4i.
Previously, we studied the rearrangement of nonmacro-
cyclic bis(amide–ether)s 1a–1c, which have methoxy
groups at the ortho, meta, or para positions of the phenyl
groups (Scheme 1) [9]. We observed a large difference in
the rate of the thermal reaction among the nonmacrocyclic
compounds 1a–1c: the rearrangements of the meta and
para compounds 1b and 1c were complete within 24 hours
at 180 °C, whereas the rearrangement of 1a needed heating
at 210 °C for 4 days. We concluded that the rate difference
was caused by the hydrogen-bonding interaction between
the oxygen of the methoxy group at the ortho position and
the OH group in the bis(amide–phenol) generated by the
tandem Claisen rearrangement of 1a, effectively inhibiting
subsequent intramolecular cyclization to the correspond-
ing nonmacrocyclic bis(benzoxazole) 2a. This might also
be the case for the macrocyclic system. The purification of
5a–5c: 16–38%). It is likely that partial decomposition
occurred before the macrocyclic bis(benzoxazole)s were
completely formed, since these macrocycles were heated
at a high temperature (210 °C) for a long time. In contrast,
the rearrangements of the meta- and para-substituted
macrocycles 5d–5i quantitatively gave macrocyclic
bis(benzoxazole) and macrocyclic dihydrobenzofuran as a
simple mixture of two products (Scheme 3). These results
were consistent with the trend of the total yields for the
model compounds 1a–1c (total yield of the 2 + 3 mixture:
ortho, 59%; meta, 99%; para, 99%).

Nov-Dec 2001
Synthesis of Macrocyclic Bis(phenylbenzoxazole) Derivatives
1355
The effect of substituent on the 5:6 product ratio for the
macrocycles was different from that for the nonmacro-
cyclic compounds. As described previously [9], the reac-
tions of the ortho- or para-substituted nonmacrocyclic
compounds 1a and 1c preferentially gave bis(benzoxa-
zole)s 2a and 2c (yields: 43% and 60%) compared with 3a
and 3c (yields: 16% and 39%), whereas the reaction of
meta-substituted 1b gave a drastically decreased ratio of
bis(benzoxazole) 2b (8%) to dihydrobenzofuran 3b (91%).
Interestingly, except for the ortho-substituted macrocycles,
the macrocyclic bis(benzoxazole) derivatives 5d–5i were
preferentially obtained from 4d–4i (61–80%). The 5:6
product ratios for the ortho-substituted macrocycles could
not be determined because the thermal reaction gave com-
plex mixtures. It is noteworthy that the oligoethylene gly-
col chain length had almost no effect on the yield of 5.
We expected the molecular shapes of the macrocyclic
bis(benzoxazole)s, and hence the distances between the
benzoxazole units, to vary with the type of linkage (ortho,
meta, or para) and the length of the oligoethylene glycol
moiety. Thus we investigated the influence of structure on
the fluorescence properties by comparing the emission
spectra and quantum yields of macrocycles 5a–5i with
those of model compounds 2a–2c.
The emission spectra of 2 and 5were measured in CHCl (1
3
–6
× 10 M) at 25 °C. The fluorescence quantum yields were
calculated with quinine sulfate in 1 N H SO as a reference (φ
2
4
= 0.51). Typical emission profiles are shown in Figure 1, and
spectral data and quantum yields are summarized in Table 2.

1356
E. Koyama, H.Tokuhisa, Y. Nagawa, G. Yang, and K. Hiratani
Vol. 38
The emission spectra of all model nonmacrocyclic and
unit contributes to the decrease in the quantum yield. The
results are listed in Table 3.
macrocyclic bis(benzoxazole)s showed structured emission
with a strong fluorescence in the range 354–365 nm upon
excitation at 300 nm (Figure 1, Table 2). Overall, there was
no significant difference in the λ
and λ
values
max(ab)
max(fl)
among the bis(benzoxazole) compounds with different sub-
stituted positions and oligoethylene glycol chain lengths; in
compounds with the same substituted positions, the differ-
ence was especially small or there was no difference at all.
Moreover, we could not confirm a peak for excimer forma-
tion between the two neighboring benzoxazoles in any of
the spectra of the nonmacrocyclic or macrocyclic com-
pounds. These results indicate that substituent position has
little effect on the absorption and emission spectral shapes
in spite of the proximity of the benzoxazoles in the various
compounds. However, some tendencies for the fluores-
cence quantum yields were observed: (1) the quantum
yields of the ortho- or para-substituted nonmacrocyclic 2a
and 2c and macrocyclic bis(benzoxazole)s with triethylene
glycol moieties 5a and 5g were higher than those of the
meta-substituted compounds 2b and 5d; (2) the quantum
yield decreased as the length of the oligoethylene glycol
chain increased, although for the ortho-substituted macro-
cycle the decrease was relatively small, whereas for the
para-substituted macrocycle the decrease was large; (3) the
yields of the macrocycles with the shortest chain, 5a, 5d,
and 5g, were almost the same as those of the corresponding
nonmacrocyclic compounds, although for the para-substi-
In both ortho- and para-substituted macrocycles, the T
values of the macrocycles with the pentaethylene glycol
moiety were smaller than those of the macrocycles with the
1
triethylene glycol moiety, but the decrease in the T values
1
for the ortho-substituted macrocycle due to the increase in
the ethylene glycol chain length was greater than that for
the para-substituted macrocycle. In general, the T values
1
13
of the C nuclei decrease with increasing molecular size
and decreasing molecular flexibility [11]. Thus, the
enhancement of molecular flexibility with increasing chain
length is greater for the para-substituted macrocycle than
for the ortho-substituted macrocycle. We may, therefore,
reasonably conclude that the significant decrease in quan-
tum yield for the para-substituted macrocycle is mainly
caused by the enhancement of the radiationless process due
to the ring. However, the quantum yield of 5g was lower
than that of the model nonmacrocyclic compound 2c,
whereas the quantum yields of 5a and 2a were almost equal
even though the T value of 5g is smaller than the T value
1
1
tuted macrocycle, the difference (φ – φ = 0.15) was
2l
2g
of 5a. That is, the molecular flexibility of 5g is larger than
that of 5a. Because of the close proximity of the two ben-
zoxazole units in the para-substituted macrocycles, reab-
sorption and collisional quenching processes may also be
involved in the quenching mechanism.
rather large.
For the nonmacrocyclic compounds, the difference in
the emission efficiencies of a single benzoxazole is
expected to dominate the difference in the quantum yields,
since the two benzoxazoles are bound at the same position.
Kanegae et al. determined the quantum yields of several
2-phenylbenzoxazole derivatives and reported that the
introduction of an electron-donating group in a resonance
position on the phenyl ring hindered the torsional motion
of the C–C bond between the benzoxazole and the phenyl
ring, resulting in an increase in the quantum yield [10]. In
our case, torsional motion in the nonmacrocyclic bis(ben-
zoxazole)s 2a and 2c, which have methoxy groups at the
ortho and para positions, might be hindered more effec-
tively than in the meta-substituted compound 2b, thereby
increasing the quantum yield. The quantum yields of the
ortho- and para-substituted macrocycles, 5a and 5g are
also higher than that of the meta-substituted macrocycle 5e
with triethylene glycol moiety, but this rule was not fol-
lowed for macrocycles with longer chains, suggesting
In conclusion, we have successfully synthesized new
macrocyclic bis(benzoxazole) derivatives 5a–5i from novel
macrocyclic bis(amide–ether) precursors via tandem
Claisen rearrangement induced by heating under vacuum.
During heating, tandem Claisen rearrangement at the
isobutenyl bis(4-methylphenyl ether) units proceeded read-
ily, followed by intramolecular cyclization between the
newly generated phenol group and amide group, to give the
macrocyclic bis(benzoxazole)s. The fluorescence quantum
yields of the macrocyclic bis(benzoxazole)s (especially the
para-substituted macrocycles) decreased with increasing
length of the oligoethylene glycol chain. We concluded that
the difference in the quantum yields was caused by the dif-
ferent molecular shapes of the macrocycles.
EXPERIMENTAL
Instrumentation.
some other quenching mechanism.
13
C spin–lattice relaxation times (T ) of ortho- and para-
1
substituted macrocycles with tri- and pentaethylene gly-
col moieties, 5a, 5c, 5g, and 5i, were measured to investi-
gate how the molecular flexibility of the benzoxazole
1
13
H and C NMR spectra were recorded on a BrukerAF-500
spectrometer using tetramethylsilane (TMS) as an internal standard

Nov-Dec 2001
Synthesis of Macrocyclic Bis(phenylbenzoxazole) Derivatives
1357
in chloroform-d (CDCl ) or dimethyl-d sulfoxide (DMSO-d ). IR
68.66, 111.94, 115.22, 116.99, 118.70, 119.67, 121.59, 124.15,
3
6
6
spectra were obtained with a JASCO FT/IR 420. High-resolution
mass spectra (HRMS) were recorded by an ESI-TOF mass spec-
trometer (PE Biosystems Mariner). UV and fluorescence spectra
were obtained with JASCO V-550 and FP 750 spectrophotometers,
respectively.
127.61, 129.60, 130.71, 133.37, 139.80, 145.56, 156.34, 163.54;
–1
IR (KBr): 3427, 3313, 1629, 1593, 1543, 1489, 1236 cm
.
1,3-Bis[2-[(3-hyroxybenzoyl)amino]-4-methylphenoxy]-2-meth-
ylenepropane.
This compound was obtained as a colorless solid, yield 52%,
Synthesis of 1,3-Bis(2-amino-4-methylphenoxy)-2-methylene-
propane Hydrochloride.
1
mp 148.6–149.7 °C; H NMR (DMSO-d ): δ 2.24 (s, 6H,
6
CH –Ar), 4.68 (s, 4H, –CH –), 5.34 (s, 2H, CH =), 6.85 (dd, J =
3
2
2
1
To a dispersion of 4-methyl-2-aminophenol (5.0 g, 40.1 mmol)
in MeOH (30 mL) was added benzaldehyde (4.3 g, 40.1 mmol),
and the mixture was stirred for 5 hours at room temperature (rt).
The mixture was filtered, and the solid protected-hydroxyary-
lamine obtained was dried in vacuo. The solid was dissolved in
dry DMF (30 mL), and NaH (60% in oil, 2.0 g, 52.1 mmol) and
3-chloro-2-(chloromethyl)propene (251 g, 20.1 mmol) were
added to the solution. The reaction mixture was stirred overnight
at 70 °C. The solvent was removed under vacuum, and the
8.4, J = 1.5 Hz, 2H, Ar), 6.90 (d, J = 8.4 Hz, 2H, Ar), 6.96 (dd,
2
J
= 8.0, J = 2.5 Hz, 2H, Ar), 7.25 (t, J = 7.9 Hz, 2H, Ar),
1
2
7.32–7.35 (m, 4H, Ar), 7.53 (d, J = 2.0 Hz, 2H, Ar), 9.33 (s, 2H,
13
–NH–), 9.76 (br s, 2H, –OH); C NMR (CDCl ): δ 21.32, 68.44,
3
112.49, 114.18, 114.39, 117.68, 118.53, 125.26, 125.98, 126.75,
129.30, 129.54, 135.99, 140.33, 148.39, 157.51, 164.93; IR
–1
(KBr): 3419, 3282, 1654, 1593, 1540, 1481, 1253 cm
.
1,3-Bis[2-[(4-hyroxybenzoyl)amino]-4-methylphenoxy]-2-meth-
ylenepropane.
residue was dissolved in CHCl and washed with water. After
3
half of the solvent was removed, 12 N HCl was added to the solu-
tion at rt. The precipitate obtained was collected by filtration and
washed three times with acetone.
This compound was obtained as a colorless solid, yield 59%,
1
mp 205.8–206.7 °C; H NMR (DMSO-d ): δ 2.25 (s, 6H,
6
CH –Ar), 4.68 (s, 4H, –CH –), 5.34 (s, 2H, CH =), 6.81 (d, J =
3
2
2
8.7 Hz, 2H, Ar), 6.81 (m, 2H, Ar), 6.91 (dd, J = 8.4 Hz, 2H, Ar),
1,3-Bis(2-amino-4-methylphenoxy)-2-methylenepropane
Hydrochloride.
7.56 (d, J = 1.8 Hz, 2H, Ar), 7.79 (d, J = 8.7 Hz, 2H, Ar), 9.19 (s,
13
2H, –NH–), 10.10 (br s, 2H, –OH); C NMR (CDCl ): δ 20.36,
3
This compound was obtained as a colorless solid, yield 82%;
68.52, 112.45, 125.05, 125.59, 127.09, 129.35, 140.38, 148.21,
1
mp 100.7–102.0 °C; H NMR (DMSO-d ): δ 2.26 (s, 6H, CH –),
160.54, 164.52; IR (KBr): 3430, 3261, 1652, 1604, 1539, 1514,
6
3
–1
4.82 (s, 4H, –CH –), 5.52 (s, 2H, CH =), 7.12–7.13 (m, 4H, Ar),
1252 cm
.
2
2
13
7.23 (s, 2H, Ar), 10.12 (br s, 6H, –NH ); C NMR (DMSO-d ):
3
6
General Procedure for Preparation of Macrocyclic Isobutenyl
Bis(amide–aryl ether)s (4).
δ 20.36, 68.97, 113.68, 116.20, 121.06, 124.47, 129.34, 130.41,
–1
139.51, 149.17; IR (KBr): 3398, 1637, 1508, 1273 cm
.
To a solution of 1,3-bis[2-[(hydroxybenzoyl)amino]-4-
methylphenoxy]-2-methylenepropane (1.99 g, 3.7 mmol) and tri-
ethylene glycol ditosylate (1.70 g, 3.7 mmol) in dry DMF (400
General Procedure for Preparation of 1,3-Bis[2-[(hydroxyben-
zoyl)amino]-4-methylphenoxy]-2-methylenepropane.
To a solution of 1,3-bis(2-amino-4-methylphenoxy)-2-methyl-
enepropane hydrochloride and pyridine in dry DMF at 0 °C was
added a solution of o-, m-, or p-acetoxybenzoyl chloride in dry
DMF. The mixture was stirred at 0 °C for 30 minutes and at rt for
3 hours. The DMF was then removed under vacuum from the
mL) was added K CO (2.2 g, 16 mmol), and the mixture was
heated at 70 °C for3 days. The mixture was evaporated, the
2
3
residue was dissolved in CHCl , and the solution was washed
3
with water. After evaporation of the solvent, the residue was puri-
fied by column chromatography on silica gel (eluent: 4:1
reaction mixture, and the residue was dissolved in CHCl . The
CHCl :ethyl acetate) to give 4.
3
3
solution was washed three times with water and then dried over
Macrocyclic isobutenyl bis(amide–aryl ether) (4a, o-, n = 1).
anhydrous MgSO . After evaporation of the solvent, the residue
4
was purified by silica gel column chromatography (eluent: chlo-
roform) to give 1,3-bis[2-[(acetoxybenzoyl)amino]-4-methylphe-
noxy]-2-methylenepropane. The resulting ester derivative was
hydrolyzed in 1 N NaOH (aq)–methanol solution at room temper-
ature for 12 hours. After the reaction, 1 N HCl aqueous solution
was added to neutralize the mixture and precipitate 1,3-bis[2-
[(hydroxybenzoyl)amino]-4-methylphenoxy]-2-methylene-
propane. The precipitate was collected by filtration, washed with
water, and dried in vacuo.
This compound was obtained as a colorless solid, yield 57%,
1
mp 145.6–146.5 °C; H NMR (CDCl ): δ 2.30 (s, 6H, CH –Ar),
3
3
3.52 (s, 4H, –O–CH –), 3.79 (t, J = 4.9 Hz, 4H, –O–CH –), 4.22
2
2
(t, J = 4.9 Hz, 4H, –O–CH –), 4.84 (s, 4H, –CH –), 5.42 (s, 2H,
2
2
CH =), 6.68 (d, J = 8.3 Hz, 2H, Ar), 6.73 (d, J = 8.3 Hz, 2H, Ar),
2
6.94 (d, J = 8.4 Hz, 2H, Ar), 7.14 (t, J = 7.8 Hz, 2H, Ar), 7.45 (t,
J = 8.3 Hz, 2H, Ar), 8.30 (d, J = 7.8 Hz, 2H, Ar), 8.39 (s, 2H, Ar),
13
10.24 (br s, 2H, –NH–); C NMR (CDCl ): δ 20.98, 68.80,
3
68.87, 69.33, 70.94, 111.94, 113.34, 115.82, 121.94, 122.36,
122.97, 124.16, 128.21, 131.02, 132.62, 132.87, 140.81, 145.57,
156.21, 163.26; IR (KBr): 3341, 1662, 1596, 1542, 1480, 1230
1,3-Bis[2-[(2-hyroxybenzoyl)amino]-4-methylphenoxy]-2-meth-
ylenepropane.
–1
+
cm ; HRESIMS m/z 653.2862 (M + H) , calcd for C
H N O
38 41 2 8
This compound was obtained as a colorless solid, yield 54%,
653.2863.
1
mp 115.9–116.8 °C; H NMR (DMSO-d ): δ 2.25 (s, 6H,
6
Macrocyclic Isobutenyl bis(amide–aryl ether) (4b, o-, n = 2).
CH –Ar), 4.78 (s, 4H, –CH –), 5.51 (s, 2H, CH =), 6.77 (d, J =
3
2
2
8.3 Hz, 2H, Ar), 6.95 (d, J = 8.4 Hz, 2H, Ar), 6.99 (t, J = 7.8 Hz,
2H, Ar), 7.05 (d, J = 8.1 Hz, 2H, Ar), 7.43 (t, J = 8.3 Hz, 2H, Ar),
This compound was obtained as a colorless solid, yield 53%,
1
mp 148.8–149.9 °C; H NMR (CDCl ): δ 2.29 (s, 6H, CH –Ar),
3
3
8.04 (d, J = 8.0 Hz, 2H, Ar), 8.23 (s, 2H, Ar), 10.66 (s, 2H,
3.45–3.50 (m, 4H, –O–CH –), 3.56–3.62 (m, 4H, –O–CH –),
3.89 (t, J = 4.8 Hz, 4H, –O–CH –), 4.29 (t, J = 4.8 Hz, 4H,
2
2
2
13
–NH–), 11.62 (br s, 2H, –OH); C NMR (CDCl ): δ 20.63,
3

1358
E. Koyama, H.Tokuhisa, Y. Nagawa, G. Yang, and K. Hiratani
Vol. 38
–O–CH –), 4.86 (s, 4H, –CH –), 5.40 (s, 2H, CH =), 6.65 (d, J =
8.3 Hz, 2H, Ar), 6.74 (d, J = 8.3 Hz, 2H, Ar), 6.98 (d, J = 8.3 Hz,
2H, Ar), 7.14 (t, J = 7.3 Hz, 2H, Ar), 7.46 (t, J = 8.3 Hz, 2H, Ar),
7.32–7.35 (m, 4H, Ar), 8.27 (s, 2H, Ar), 8.43 (br s, 2H, –NH–);
2
2
2
13
C NMR (CDCl ): δ 21.03, 67.62, 69.51, 69.89, 70.61, 70.65,
3
70.88, 111.90, 112.92, 116.88, 118.15, 119.06, 120.94, 124.23,
127.85, 129.80, 131.58, 136.49, 139.83, 144.96, 159.03, 164.98;
8.29 (d, J = 8.0 Hz, 2H, Ar), 8.39 (s, 2H, Ar), 10.30 (br s, 2H,
13
–1
–NH–); C NMR (CDCl ): δ 21.00, 68.96, 69.15, 69.46, 70.79,
IR (KBr): 3428, 1656, 1586, 1537, 1481, 1287 cm ; HRESIMS
3
+
111.91, 113.39, 121.84, 122.14, 122.94, 124.14, 128.17, 130.93,
132.57, 132.88, 140.94, 145.59, 156.44, 163.21; IR (KBr): 3353,
m/z 741.3382 (M + H) , calcd for C
H
N O 741.3387.
42 49
2 10
Macrocyclic Isobutenyl Bis(amide–aryl ether) (4g, p-, n = 1).
–1
1660, 1596, 1541, 1480, 1232 cm ; HRESIMS m/z 697.3162 (M
+
This compound was obtained as a colorless solid, yield 49%, mp
+ H) , calcd for C
H N O 697.3124.
40 45 2 9
1
193.2–194.7 °C; H NMR (CDCl ): δ 2.34 (s, 6H, CH –Ar), 3.75
3
3
Macrocyclic isobutenyl bis(amide–aryl ether) (4c, o-, n = 3).
(s, 4H, –O–CH –), 3.91 (t, J = 4.6 Hz, 4H, –O–CH –), 4.18 (t, J =
2
2
4.6 Hz, 4H, –O–CH –), 4.70 (s, 4H, –CH –), 5.44 (s, 2H, CH =),
This compound was obtained as a colorless solid, yield 32%,
2
2
2
1
6.79 (d, J = 8.4 Hz, 2H, Ar), 6.85 (d, J = 8.4 Hz, 2H, Ar), 7.00 (d,
J = 8.9 Hz, 4H, Ar), 7.85 (d, J = 8.9 Hz, 4H, Ar), 8.39 (s, 2H, Ar),
mp 137.0–138.1 °C; H NMR (CDCl ): δ 2.29 (s, 6H, CH –Ar),
3
3
3.47–3.50 (m, 8H, –O–CH –), 3.58 (t, J = 5.2 Hz, 4H, –O–CH –),
2
2
13
8.51 (br s, 2H, –NH–); C NMR (CDCl ): δ 21.04, 67.65, 69.29,
3.87 (t, J = 5.2 Hz, 4H, –O–CH –), 4.30 (t, J = 4.9 Hz, 4H,
3
2
69.47, 70.93, 111.26, 114.31, 114.61, 120.66, 123.83, 127.47,
127.91, 128.70, 131.54, 139.40, 144.75, 161.79, 164.48; IR (KBr):
–O–CH –), 4.81 (s, 4H, –CH –), 5.44 (s, 2H, CH =), 6.66 (d, J =
8.3 Hz, 2H, Ar), 6.77 (d, J = 8.4 Hz, 2H, Ar), 7.01 (d, J = 8.3 Hz,
2H, Ar), 7.14 (t, J = 7.5 Hz, 2H, Ar), 7.46 (t, J = 7.7 Hz, 2H, Ar),
2
2
2
–1
3438, 1663, 1605, 1540, 1512, 1481, 1254 cm ; HRESIMS m/z
+
653.2884 (M + H) , calcd for C H N O 653.2863.
8.27 (d, J = 7.8 Hz, 2H, Ar), 8.36 (s, 2H, Ar), 10.25 (br s, 2H,
38 41
2 8
13
–NH–); C NMR (CDCl ): δ 20.98, 69.03, 69.10, 69.36, 70.66,
3
Macrocyclic Isobutenyl Bis(amide–aryl ether) (4h, p-, n = 2).
70.81, 111.84, 113.79, 116.27, 121.93, 122.18, 123.08, 124.16,
128.06, 130.91, 132.45, 132.89, 140.58, 145.64, 156.47, 163.21;
This compound was obtained as a colorless solid, yield 35%,
1
–1
mp 206.0–210.2 °C; H NMR (CDCl ): δ 2.34 (s, 6H, CH –Ar),
IR (KBr): 3359, 1659, 1596, 1540, 1480, 1235 cm ; HRESIMS
3
3
+
3.69–3.74 (m, 8H, –O–CH –), 3.89 (t, J = 4.9 Hz, 4H,
m/z 741.3393 (M + H) , calcd for C H N O 741.3387.
2
42 49
2 10
–O–CH –), 4.15 (t, J = 4.9 Hz, 4H, –O–CH –), 4.71 (s, 4H,
2
2
Macrocyclic Isobutenyl Bis(amide–aryl ether) (4d, m-, n = 1).
–CH –), 5.45 (s, 2H, CH =), 6.80 (d, J = 8.3 Hz, 2H, Ar), 6.85 (d,
2
2
J = 8.3 Hz, 2H, Ar), 6.96 (d, J = 8.4 Hz, 4H, Ar), 7.82 (d, J = 8.4
Hz, 4H, Ar), 8.38 (s, 2H, Ar), 8.48 (br s, 2H, –NH–); C NMR
This compound was obtained as a colorless solid, yield 44%,
13
1
mp 156.3–157.0 °C; H NMR (CDCl ): δ 2.33 (s, 6H, CH –Ar),
3
3
(CDCl ): δ 21.06, 67.78, 69.50, 69.66, 70.84, 70.92, 111.59,
3.72 (s, 4H, –O–CH –), 3.82 (t, J = 4.7 Hz, 4H, –O–CH –), 4.13
3
2
2
114.64, 115.28, 120.80, 123.90, 127.48, 128.00, 128.69, 131.64,
139.61, 144.81, 161.74, 164.61; IR (KBr): 3435, 1662, 1606,
(t, J = 4.7 Hz, 4H, –O–CH –), 4.71 (s, 4H, –CH –), 5.43 (s, 2H,
2
2
CH =), 6.80 (d, J = 8.4 Hz, 2H, Ar), 6.83 (d, J = 8.4 Hz, 2H, Ar),
2
–1
1540, 1511, 1482, 1254 cm ; HRESIMS m/z 697.3144 (M +
7.02 (d, J = 8.0 Hz, 2H, Ar), 7.22 (t, J = 8.1 Hz, 2H, Ar), 7.29 (s,
+
H) , calcd for C
H N O 697.3124.
2H, Ar), 7.32 (d, J = 7.8 Hz, 2H, Ar), 8.23 (s, 2H, Ar), 8.40 (br s,
40 45 2 9
13
2H, –NH–); C NMR (CDCl ): δ 21.05, 67.72, 69.82, 70.17,
3
Macrocyclic Isobutenyl Bis(amide–aryl ether) (4i, p-, n = 3).
71.10, 112.13, 112.83, 116.80, 118.36, 119.30, 120.97, 124.24,
127.94, 129.81, 131.70, 136.57, 139.95, 145.03, 159.00, 165.17;
This compound was obtained as a colorless solid, yield 35%,
1
mp 179.0–180.0 °C; H NMR (CDCl ): δ 2.34 (s, 6H, CH –Ar),
–1
3
3
IR (KBr): 3437, 1671, 1584, 1537, 1475, 1254 cm ; HRESIMS
3.66 (s, 4H, –O–CH –), 3.67–3.69 (m, 4H, –O–CH –), 3.62–3.70
+
2
2
m/z 653.2910 (M + H) , calcd for C
H N O 653.2863.
38 41 2 8
(m, 4H, –O–CH –), 3.87 (t, J = 4.7 Hz, 4H, –O–CH –), 4.14 (t, J
2
2
Macrocyclic Isobutenyl Bis(amide–aryl ether) (4e, m-, n = 2).
= 4.7 Hz, 4H, –O–CH –), 4.72 (s, 4H, –CH –), 5.46 (s, 2H,
2
2
CH =), 6.82 (d, J = 8.4 Hz, 2H, Ar), 6.85 (d, J = 8.4 Hz, 2H, Ar),
2
This compound was obtained as a colorless solid, yield 37%,
6.93 (d, J = 8.8 Hz, 2H, Ar), 7.79 (d, J = 8.9 Hz, 2H, Ar), 8.38 (s,
1
mp 134.5–135.3 °C; H NMR (CDCl ): δ 2.32 (s, 6H,
3
13
2H, Ar), 8.47 (br s, 2H, –NH–); C NMR (CDCl ): δ 21.07,
3
CH –Ar), 3.62–3.70 (m, 8H, –O–CH –), 3.80 (t, J = 4.8 Hz,
3
2
67.73, 69.54, 69.78, 70.74, 70.79, 70.94, 111.78, 114.68, 119.71,
120.77, 123.91, 127.42, 128.10, 128.64, 128.74, 131.71, 144.83,
161.72, 164.63; IR (KBr): 3431, 1654, 1605, 1540, 1513, 1252
4H, –O–CH –), 4.10 (t, J = 4.7 Hz, 4H, –O–CH –), 4.71 (s, 4H,
2
2
–CH –), 5.43 (s, 2H, CH =), 6.79 (d, J = 8.2 Hz, 2H, Ar), 6.82
2
2
(d, J = 8.3 Hz, 2H, Ar), 7.01 (d, J = 8.2 Hz, 2H, Ar), 7.22 (t, J =
–1
+
cm ; HRESIMS m/z 741.3352 (M + H) , calcd for
N O 741.3387.
8.2 Hz, 2H, Ar), 7.30–7.37 (m, 4H, Ar), 8.29 (s, 2H, Ar), 8.44
C
H
13
42 49
2 10
(br s, 2H, –NH–); C NMR (CDCl ): δ 21.04, 67.69, 69.61,
3
70.03, 70.74, 70.87, 112.01, 112.92, 116.89, 118.29, 119.06,
120.94, 124.23, 127.89, 129.79, 131.63, 136.54, 139.92,
144.99, 159.06, 165.07; IR (KBr): 3432, 1674, 1593, 1532,
General Procedure for Preparation of 5a–c by Thermal Reaction
of 4a–c.
Typical Procedure 4a.
–1
+
1481, 1281 cm ; HRESIMS m/z 697.3149 (M + H) , calcd for
N O 697.3124.
C
H
Compound 4a (0.06 g, 0.092 mmol) was heated at 210 °C for 2
days under vacuum. The crude mixture was purified by silica gel
chromatography (eluent: 2:1 chloroform:ethylacetate) to give 5a.
40 45
2 9
Macrocyclic Isobutenyl Bis(amide–aryl ether) (4f, m-, n = 3).
This compound was obtained as a colorless solid, yield 26%,
Macrocyclic Bis(benzoxazole) (5a).
1
mp 104.7–105.2 °C; H NMR (CDCl ): δ 2.32 (s, 6H, CH –Ar),
3
3
This compound was obtained as acolorless solid, yield 20%,
3.62 (s, 4H, –O–CH –), 3.63–3.67 (m, 8H, –O–CH –), 3.79 (t,
2
2
1
mp 227.0–228.5 °C; H NMR (CDCl ): δ 2.40 (s, 6H, CH –Ar),
J = 4.7 Hz, 4H, –O–CH –), 4.10 (t, J = 4.6 Hz, 4H, –O–CH –),
3
3
2
2
3.70 (s, 4H, –CH –), 3.71 (s, 4H, –O–CH –), 3.81 (t, J = 4.4 Hz,
4.72 (s, 4H, –CH –), 5.43 (s, 2H, CH =), 6.79–6.81 (m, 4H, Ar),
2
2
2
2
4H, –O–CH –), 4.19 (t, J = 4.3 Hz, 4H, –O–CH –), 5.00 (s, 2H,
7.01 (d, J = 8.0 Hz, 2H, Ar), 7.23 (t, J = 8.4 Hz, 2H, Ar),
2
2

Nov-Dec 2001
Synthesis of Macrocyclic Bis(phenylbenzoxazole) Derivatives
1359
CH =), 6.88 (s, 2H, Ar), 7.00 (d, J = 8.3 Hz, 2H, Ar), 7.07 (t, J =
Macrocyclic Bis(benzoxazole) (5e).
2
7.6 Hz, 2H, Ar), 7.40 (s, 2H, Ar), 7.45 (dt, J = 7.9 Hz, J = 1.7
1
2
This compound was obtained as a colorless solid, yield 71%,
13
Hz, 2H, Ar), 8.11 (dd, J = 7.7 Hz, J = 1.7 Hz, 2H, Ar);
C
1
2
1
mp 143.5–144.5 °C; H NMR (CDCl ): δ 2.43 (s, 6H, CH –Ar),
3
3
NMR (CDCl ): δ 21.49, 36.15, 69.02, 69.70, 70.86, 113.11,
3
3.62 (s, 4H, –CH –), 3.77 (m, 8H, –CH O–), 3.93 (t, J = 4.7 Hz,
2
2
114.62, 116.99, 117.62, 120.99, 121.87, 126.46, 131.64, 132.53,
134.16, 141.50, 144.82, 148.54, 157.53, 162.70; IR (KBr): 1610,
4H, –O–CH –), 4.10 (t, J = 4.9 Hz, 4H, –O–CH –), 5.18 (s, 2H,
2
2
CH =), 6.92 (s, 2H, Ar), 6.97 (d, J = 7.9 Hz, 2H, Ar), 7.21 (t, J =
2
–1
+
1500, 1258 cm ; HRESIMS m/z 617.2699 (M + H) , calcd for
N O 617.2651.
13
7.9 Hz, 2H, Ar), 7.31 (s, 2H, Ar), 7.33–7.38 (m, 4H, Ar);
C
C
H
38 37
2 6
NMR (CDCl ): δ 21.54, 35.89, 67.75, 69.73, 70.80, 71.08,
3
111.89, 114.99, 117.77, 118.69, 119.80, 121.87, 126.50, 128.09,
129.66, 134.23, 141.86, 145.08, 147.89, 158.85, 162.50; IR
Macrocyclic Bis(benzoxazole) (5b).
This compound was obtained as a colorless solid, yield 38%,
–1
(KBr): 1588, 1554, 1484, 1232 cm ; HRESIMS m/z 661.2935
1
mp 146.1–146.9 °C; H NMR (CDCl ): δ 2.39 (s, 6H, CH –Ar),
3
3
+
(M + H) , calcd for C
H N O 661.2913.
40 41 2 7
3.43–3.45 (m, 4H, –O–CH –), 3.49–3.50 (m, 4H, –O–CH –),
2
2
3.70 (s, 4H, –CH –), 3.78 (t, J = 4.7 Hz, 4H, –O–CH –), 4.18 (t,
Macrocyclic Bis(benzoxazole) (5f).
2
2
J = 4.6 Hz, 4H, –O–CH –), 5.09 (s, 2H, CH =), 6.92 (s, 2H, Ar),
2
2
This compound was obtained as a colorless solid, yield 80%,
6.98 (d, J = 8.3 Hz, 2H, Ar), 7.05 (t, J = 7.8 Hz, 2H, Ar), 7.40 (s,
2H, Ar), 7.43 (t, J = 7.7 Hz, 2H, Ar), 8.03 (dd, J = 7.7 Hz, J =
1
mp 102.5–104.0 °C; H NMR (CDCl ): δ 2.42 (s, 6H, CH –Ar),
3
3
1
2
3.61 (s, 4H, –CH –), 3.72 (s, 4H, –CH O–), 3.75–3.77 (m, 8H,
2
2
13
1.6 Hz, 2H, Ar); C NMR (CDCl ): δ 21.44, 36.14, 68.76,
3
–CH O–), 3.91 (t, J = 4.9 Hz, 4H, –O–CH –), 4.11 (t, J = 5.0 Hz,
2
2
69.48, 70.26, 70.91, 113.16, 114.85, 116.93, 117.69, 120.88,
121.92, 126.55, 128.55, 129.53, 131.45, 132.43, 134.02, 141.71,
144.69, 148.17, 157.52, 162.25; IR (KBr): 1602, 1582, 1533,
4H, –O–CH –), 5.18 (s, 2H, CH =), 6.93 (s, 2H, Ar), 6.95 (d, J =
2
2
8.2 Hz, 2H, Ar), 7.19 (t, J = 8.0 Hz, 2H, Ar), 7.32 (d, J = 7.7 Hz,
13
2H, Ar), 7.34 (d, J = 7.5 Hz, 2H, Ar) , 7.35 (s, 2H, Ar); C NMR
–1
+
1478, 1449, 1266 cm ; HRESIMS m/z 661.2907 (M + H) ,
calcd for C N O 661.2913.
(CDCl ): δ 21.51, 35.85, 67.63, 69.69, 70.79, 70.89, 70.93,
3
H
40 41
2 7
112.05, 114.99, 117.75, 118.52, 119.75, 121.88, 126.51, 128.01,
129.66, 134.23, 141.83, 145.08, 147.87, 158.73, 162.52; IR
Macrocyclic Bis(benzoxazole) (5c).
–1
(KBr): 1585, 1553, 1486, 1455 cm ; HRESIMS m/z 705.3179
This compound was obtained as a colorless solid, yield 16%,
+
(M + H) , calcd for C
H N O 705.3176.
42 43 2 8
1
mp 46.6–48.0 °C; H NMR (CDCl ): δ 2.39 (s, 6H, CH –Ar),
3
3
3.43 (s, 4H, –CH –), 3.48 (t, J = 4.9 Hz, 4H, –O–CH –), 3.59 (t,
Macrocyclic Bis(benzoxazole) (5g).
2
2
J = 4.9 Hz, 4H, –O–CH –), 3.68 (s, 4H, –CH –), 3.81 (t, J = 5.1
2
2
This compound was obtained as a colorless solid, yield 65%,
Hz, 4H, –O–CH –), 4.20 (t, J = 4.9 Hz, 4H, –O–CH –), 5.07 (s,
2
2
1
mp 219.5–221.7 °C; H NMR (CDCl ): δ 2.39 (s, 6H, CH –Ar),
3
3
2H, CH =), 6.94 (s, 2H, Ar), 6.99 (d, J = 8.3 Hz, 2H, Ar), 7.02 (t,
2
3.70 (s, 4H, –CH –), 3.79 (s, 4H, –O–CH –), 3.90 (t, J = 4.6 Hz,
2
2
J = 7.5 Hz, 2H, Ar), 7.39 (s, 2H, Ar), 7.41 (dt, J = 7.9 Hz, J =
1
2
4H, –O–CH –), 4.08 (t, J = 4.5 Hz, 4H, –O–CH –), 5.04 (s, 2H,
2
2
13
1.7 Hz, 2H, Ar), 7.98 (dd, J = 7.8 Hz, J = 1.7 Hz, 2H, Ar);
C
1
2
CH =), 6.75 (d, J = 8.9 Hz, 4H, Ar), 6.87 (s, 2H, Ar), 7.24 (s, 2H,
2
NMR (CDCl ): δ 21.46, 36.25, 68.82, 69.58, 70.52, 70.93,
3
13
Ar), 7.87 (d, J = 8.7 Hz, 4H, Ar); C NMR (CDCl ): δ 21.47,
3
113.36, 114.54, 116.90, 117.75, 120.91, 121.93, 126.62, 131.32,
132.39, 134.00, 141.78, 145.00, 148.05, 157.55, 162.06; IR
37.32, 67.72, 69.53, 71.18, 114.65, 114.81, 117.47, 119.79,
121.76, 126.31, 128.92, 129.25, 133.93, 142.00, 144.70, 147.66,
–1
(KBr): 1602, 1583, 1538, 1480, 1451 cm ; HRESIMS m/z
–1
161.18, 162.91; IR (KBr): 1610, 1500, 1258 cm ; HRESIMS
+
705.3160 (M + H) , calcd for C
H N O 705.3176.
42 43 2 8
+
m/z 617.2567 (M + H) , calcd for C
H N O 617.2651.
38 37 2 6
General Procedure for Preparation of 5d–i by Thermal reaction
of 4d–i.
Macrocyclic Bis(benzoxazole) (5h).
This compound was obtained as a colorless solid, yield 61%,
Typical Procedure 4d.
1
mp 248.2–248.9 °C; H NMR (CDCl ): δ 2.40 (s, 6H,
3
Compound 4d (0.06 g, 0.092 mmol) was heated at 240 °C for 5
hours under vacuum. The crude mixture was purified by gel per-
meation chromatography (GPC, eluent: chloroform) to obtain a
mixture of 5d and 6d, and the product ratio was determined by H
NMR spectrum. Then, the mixture was purified by silica gel
CH –Ar), 3.67 (s, 4H, –CH –), 3.94 (s, 4H, –CH O–), 5.05 (s,
3
2
2
2H, CH =), 6.95 (s, 2H, Ar), 7.01–7.04 (m, 4H, Ar), 7.43–7.45
2
13
(m, 4H, Ar), 7.96 (d, J = 6.3 Hz, 2H, Ar); C NMR (CDCl ):
3
1
δ 21.08, 67.80, 69.52, 69.68, 70.86, 70.94, 111.61, 114.66,
115.04, 115.29, 120.82, 123.93, 127.50, 128.02, 128.71,
131.66, 139.64, 144.84, 161.76, 164.63; IR (KBr): 1611, 1500,
chromatography (eluent: 4:1 chloroform:ethyl acetate) to give 5d.
–1
+
1258 cm ; HRESIMS m/z 661.2908 (M + H) , calcd for
N O 661.2913.
Macrocyclic Bis(benzoxazole) (5d).
C
H
40 41
2 7
This compound was obtained as a colorless solid, yield 72%,
Macrocyclic Bis(benzoxazole) (5i).
1
mp 186.9–187.9 °C; H NMR (CDCl ): δ 2.44 (s, 6H, CH –Ar),
3
3
3.63 (s, 4H, –CH –), 3.82 (s, 4H, –CH O–), 3.92 (t, J = 4.8 Hz,
This compound was obtained as a colorless solid, yield 72%,
2
2
1
4H, –O–CH –), 4.15 (t, J = 4.8 Hz, 4H, –O–CH –), 5.15 (s, 2H,
mp 169.4–171.8 °C; H NMR (CDCl ): δ 2.41 (s, 6H, CH –Ar),
2
2
3
3
CH =), 6.93 (s, 2H, Ar), 7.00 (d, J = 7.8 Hz, 2H, Ar), 7.26 (t, J =
3.65 (s, 4H, –CH –), 3.72 (s, 4H, –O–CH –), 3.74–3.77 (m, 8H,
–O–CH –),3.92 (t, J = 5.2 Hz, 4H, –O–CH –), 4.07 (t, J = 5.0 Hz,
2 2
2
2 2
13
7.8 Hz, 2H, Ar), 7.32 (s, 2H, Ar), 7.44–7.47 (m, 4H, Ar);
C
NMR (CDCl ): δ 21.53, 36.02, 67.64, 69.71, 71.16, 112.31,
4H, –O–CH –), 5.11 (s, 2H, CH =), 6.72 (d, J = 8.9 Hz, 4H, Ar),
3
2 2
114.76, 117.78, 118.34, 119.98, 121.86, 126.57, 128.15, 129.70,
134.23, 141.91, 145.06, 147.89, 158.84, 162.44; IR (KBr): 1587,
6.91 (s, 2H, Ar), 7.27 (s, 2H, Ar), 7.87 (d, J = 8.9 Hz, 4H, Ar);
13
C NMR (CDCl ): δ 21.50, 36.64, 67.64, 69.63, 70.81, 70.95,
3
–1
1556, 1487, 1452, 1289 cm ; HRESIMS m/z 617.2661 (M +
71.04, 114.58, 114.76, 117.46, 119.76, 121.78, 126.16, 128.81,
133.99, 142.06, 145.03, 147.73, 161.07, 162.82; IR (KBr): 1611,
+
H) , calcd for C
H N O 617.2651.
38 37 2 6

1360
E. Koyama, H.Tokuhisa, Y. Nagawa, G. Yang, and K. Hiratani
Vol. 38
–1
+
Lynch, R. A. Reamer, R. P. Volante and P. J. Reider, J. Org. Chem., 58,
3176 (1993); [c] S. B. Advani and J. Sam, J. Pharm. Sci., 57, 1693
(1968); [d] J. M. Kay, P. Smith, D. Heath, and J. A. Will, Cardiovasc.
Res., 10, 200 (1976); [e] J. Badin and B. Tinland, Res. Commun. Chem.
Pathol. Pharmacol., 6, 1099 (1973); [f] D. W. Dunwell, and D. Evans,
J. Med. Chem., 20, 797 (1977); [g] Y. Sato, M. Imai, K. Amano, K.
Iwamatsu, F. Konno, Y. Kurata, S. Sakakibara, M. Hachisu, M. Izumi,
N. Matsuki and H. Saito, J. Med. Chem., 41, 3015 (1998).
[6a] F. Weiss and A. Isard, Bull. Soc. Chim. Fr., 6, 2033 (1967);
[b] B. S. Tyhagarajan, K. K. Balasubramanian and R. B Rao, Chem.
Ind. (London), 401 (1967).
1501, 1257 cm ; HRESIMS m/z 705.3201 (M + H) , calcd for
C
H
N O 705.3176.
42 43
2 8
REFERENCES AND NOTES
Author to whom all correspondence should be addressed.
Fax: +81-298-61-3029. E-mail: k.hiratani@aist.go.jp.
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(1981).
*
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Dryanska and Chr. Ivanov, Synthesis, 37 (1976).
[7a] K. Hiratani, K. Kasuga, M.Goto and H. Uzawa, J. Am.
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Kasuga, H. Sugihara, K. Fujiwara and K. Ohashi, Tetrahedron Lett.,
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