Medium-sized cyclophanes - Part 85: Benzylation by 8-(bromomethyl)[2.2] metacyclophanes. Through-space electronic interactions of [2.2]metacyclophane benzyl cations

Article abstract of DOI:10.1139/V10-003

TiCl₄-mediated Friedel-Crafts benzylation of benzene with 8-(bromomethyl)[2.2]metacyclophanes to afford 8-benzyl[2.2]metacyclophanes is described. Substituent effect through space on the rate of the benzylation of benzene with a bromomethyl group attached on the opposite aromatic ring was first found in this investigation. Interestingly, the introduction of the substituents at the internal position 16 tends to promote the present benzylation reaction rate 1.8-3.8 times. It was found that the benzyl cation intermediate was stabilized by the the direct through-space cation-π interaction among the opposite benzene ring in the benzylation of [2.2] metacyclophane systems.

Full text of DOI:10.1139/V10-003

458
Medium-sized cyclophanes — Part 85: Benzylation
by 8-(bromomethyl)[2.2]metacyclophanes.
Through-space electronic interactions of
[2.2]metacyclophane benzyl cations
Tomoe Shimizu, Kan Tanaka, Arjun Paudel, and Takehiko Yamato
Abstract: TiCl4-mediated Friedel–Crafts benzylation of benzene with 8-(bromomethyl)[2.2]metacyclophanes to afford
8-benzyl[2.2]metacyclophanes is described. Substituent effect through space on the rate of the benzylation of benzene with
a bromomethyl group attached on the opposite aromatic ring was first found in this investigation. Interestingly, the intro-
duction of the substituents at the internal position 16 tends to promote the present benzylation reaction rate 1.8–3.8 times.
It was found that the benzyl cation intermediate was stabilized by the the direct through-space cation–p interaction among
the opposite benzene ring in the benzylation of [2.2]metacyclophane systems.
Key words: cyclophanes, Friedel–Crafts benzylation, benzyl cation intermediate, through-space electronic interaction.
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Resume : On decrit la reaction de benzylation du benzene par le 8-bromomethyl)[2,2]metacyclophanes par la methode de
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Friedel–Crafts catalysee par le TiCl4. Dans ce travail, on a mis en evidence pour la premiere fois, un effet de substituant
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qui se fait sentir a travers l’espace sur la vitesse de benzylation du benzene en raison d’un groupe bromomethyle attachee
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sur le noyau aromatique oppose. Il est interessant de noter que l’introduction de substituants a la position interne 16 ten-
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dent a accelerer les vitesses de reaction de benzylation par des facteurs allant de 1,8 a 3,8. On a trouve que le cation ben-
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zylique intermediaire est stabilise par une interaction cation-p directe a travers l’espace du noyau benzenique oppose dans
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la benzylation de systemes [2,2]metacyclophanes.
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Mots-cles : cyclophanes, benzylation suivant Friedel–Crafts, cation benzylique intermediaire, interaction electronique a tra-
vers l’espace.
energy, [2.2]MCP is prone to giving transannular reaction
Introduction
products.19–21 These are mostly explained by the initial for-
mation of a cyclodehydrogenation reaction product, 4,5,9,10-
tetrahydropyrene. It has been isolated under the electro-
philic,22–25 radical,26 and photolytic reaction conditions,27 to-
gether with other transformation products derived from
tetrahydropyrene. Sato and co-workers28,29 reported another
type of iodine-induced reaction of [2.2]MCP, which gives
1,2,3,3a,4,5-hexahydropyrene. On the other hand, we have
reported30,31 the iodine-induced transannular cyclization of 8-
methoxy[2.2]MCPs to give 4,5,9,10-tetrahydropyrenes with
remarkable ease and with high selectivity. This novel transan-
nular reaction might be attributed to the presence of the me-
thoxy group at the 8-position, which increases the p-electron
density of the benzene ring. Thus, these transannular reac-
tions were ascribed to the through-space electronic interac-
tion through the intra-annular 8,16-positions. As mentioned
above, although two through-space electronic interactions,
(i) interaction through the intra-annular 8- and 16-positions
and (ii) direct through-space cation–p interaction, are possi-
The geometry of the [2.2]metacyclophane ([2.2]MCP)
skeleton is known in detail from an X-ray structural analy-
sis.2,3 The crystal consists of discrete molecules, each of
which has a center of symmetry. The two halves of the mol-
ecule form a stepped system. It is interesting to note that the
benzene rings are not planar, but have a boat conformation,
with the result that the molecule evidently avoids the steric
interaction of the central carbon atoms C(8) and C(16) and
of the attached hydrogen atoms. The X-ray structural analy-
sis of 8,16-dimethyl[2.2]MCP (2) confirms the increased
strain in molecule 2 as compared with that in the parent hydro-
carbon 1 (Fig.1).4–16
Although substituents at positions 8 and 16 in the
[2.2]MCP system seem to have interesting chemical natures
since they are covered by the opposite aromatic ring, there
are few investigations concerning these problems.17,18 Ow-
ing to electronic interaction between two benzene rings, the
proximity of 8- and 16-positions, and the considerable strain
Received 9 March 2009. Accepted 1 December 2009. Published on the NRC Research Press Web site at canjchem.nrc.ca on 3 April
2010.
For Part 84, see ref. 1.
T. Shimizu, K. Tanaka, A. Paudel, and T. Yamato.1 Department of Applied Chemistry, Faculty of Science and Engineering, Saga
University, Honjo-machi 1, Saga-shi, Saga 840-8502, Japan.
1Corresponding author (e-mail: yamatot@cc.saga-u.ac.jp).
Can. J. Chem. 88: 458–462 (2010)
doi:10.1139/V10-003
Published by NRC Research Press

Shimizu et al.
459
Scheme 1.
Fig. 1. Structure and numbering of [2.2]MCPs.
Scheme 2.
ble in the [2.2]MCP systems, the more favored interaction is
not clear so far. Therefore, it is quite interesting to investi-
gate the through-space electronic interaction on the rate of
the benzylation of bromomethyl groups attached on the op-
posite aromatic ring in the [2.2]MCP systems. We wish to
report the benzylation of benzene using cations derived
from 8-(bromomethyl)[2.2]MCPs.
Table 1. TiCl4-mediated benzylation of benzene with 2.
Reaction
Run temperature (8C)
Product yield
(%)a
Recovery
2a (71)
2a (64)
2b (48)
2c (28)
2c (15)
1
2
3
4
5
25
50
50
25
50
4a (29)
4a (36) [25]
4b (52) [40]
4c (62) [51]
4c (85) [76]
Results and discussion
The preparative route of 8-(bromomethyl)[2.2]MCPs (2a–2c)
is shown in Scheme 1. Bromination of 1a and 1c32–34 with
N-bromosucccinimide (NBS) in the presence of benzoyl per-
oxide under CCl4 reflux for 3 h afforded the desired 8-(bromo-
methyl)[2.2]MCPs (2a and 2c) in good yield. However, in
the case of 1b, 8,16-bis(bromomethyl)[2.2]MCP (3) was
also obtained in 30% yield along with the recovery of the
starting compound 1b in 20% yield in spite of 1.2 equiv of
NBS used. Isolation of the desired pure 2b was unsuccess-
ful. We have instead prepared 8-(bromomethyl)-16-meth-
yl[2.2]MCP (2b) following our previously reported
procedure.35,36
The TiCl4-mediated benzylation of benzene with 8-(bromo-
methyl)-5,13-di-tert-butyl[2.2]MCPs (2) was carried out
under various conditions of Scheme 2. The results are com-
piled in Table 1.
The TiCl4-mediated benzylation of benzene with com-
pound 2a at room temperature (25 8C) for 2 h led to benzy-
lation reaction affording the desired 8-benzyl[2.2]MCP (4a)
Note: [Benzene]/2 = 30 (mol/mol), [TiCl4]/2 = 1.5 (mol/mol).
aThe yields were determined by GLC analysis. Isolated yields
are shown in square brackets.
in 29% yield along with the recovery of the starting com-
pound 2a in 71% yield. The present benzylation reaction
was carried out at 50 8C under the same reaction conditions
as above to increase the yield of 8-benzyl[2.2]MCP (4a) to
36%. Interestingly, in similar benzylation of benzene with
16-methyl and 16-methoxy derivatives, much higher yields
of the benzylation products 4b and 4c resulted in 52% and
85% yields, respectively. The data in Table 1 clearly show
that the substituents at the 16-position affected the yield of
the benzylation product of the 8-bromomethyl group in the
opposite aromatic ring and that electron-donating groups,
such as methyl and methoxy functions, increased the yield of
the benzylation product because of its high electron-donating
ability like normal aromatic benzylation.37 Thus, such sub-
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460
Can. J. Chem. Vol. 88, 2010
Scheme 3.
Fig. 2. Pseudo-first-order plots on benzylation of benzene with 2a–2c.
Table 2. Pseudo-first-order plots and rate constants on ben-
zylation of benzene with 2.
Compounds
R
k ꢀ 105 (sec–1)
6.21 ( 0.21)
10.99 ( 1.65)
23.72 ( 1.14)
Relative rate
2a
2b
2c
H
Me
OMe
1.0
1.8
3.8
stituent effect through space on the rate of the benzylation
of bromomethyl group attached on the opposite aromatic
ring was first found in this investigation.
Fig. 3. Proposed through-space electronic interactions of [2.2]MCP
benzyl cation.
The structures of 4a–4c were determined on the basis of
their elemental analyses and spectral data. The 1H NMR
spectrum of 4a in CDCl3 shows a singlet at d 2.15 ppm for
the methylene protons of the benzyl group at 8-position,
which is in a strongly shielded region of the opposite meta-
bridged benzene ring, and d 3.71 ppm for the internal aro-
matic proton at 16-position. Similar findings were observed
in compounds 4b and 4c.
To study the present through-space electronic interactions
in more detail, we have attempted to evaluate the rate of the
benzylation of benzene with 8-(bromomethyl)[2.2]MCP (2)
in the presence of TiCl4. Pseudo-first-order plots on benzy-
lation of benzene with 2a–2c are shown in Fig. 2.
such as methyl and methoxy groups for the opposite ben-
zene ring could shorten the distance between the benzyl cat-
ion and the opposite benzene ring, whereas the H–p
interaction could make this distance longer. The stabilization
by the direct through-space cation–p interaction is possible
in the benzyl cations derived from 8-(bromome-
thyl)[2.2]MCPs. This result strongly suggests that the benzyl
cation intermediate could be stabilized by the through-space
electronic interaction among the opposite benzene ring as
shown in Fig. 3. As previously mentioned, although two
through-space electronic interactions, (i) interaction through
the intraannular 8,16-posisions and (ii) direct through-space
cation–p interaction, are possible in the [2.2]MCP systems,
the latter interaction might be more favorable in the present
systems.
The TiCl4-mediated benzylation rate constant of 8-(bromo-
methyl)[2.2]MCP 2a with benzene is 6.21 ꢀ 105 s–1 (Table
2). It was also found that the introduction of substituents at
the internal position 16 tends to promote the present benzy-
lation reaction rate 1.8–3.8 times. Thus, the rate of benzyla-
tion of internally substituted 8-(bromomethyl)[2.2]MCPs 2b
and 2c are much larger than that of internally unsubstituted
8-(bromomethyl)[2.2]MCP 2a, which is attributable to the
electron-donating nature of 16-substituents, such as methyl
and methoxy group. Although similar findings were also re-
ported in the TiCl4-catalyzed benzylation of benzene with 4-
substituted benzyl bromide,38 much smaller substituents ef-
fects on the benzylation were observed in the present
[2.2]MCP systems than those of the reported benzylations
of benzene with 4-substituted benzyl bromide (Scheme 3).
This is ascribed to the smaller influence of the nature of a
substituent on the remote aromatic ring by a direct through-
space cation–p interaction than that in 4-substituted benzyl
bromide.
Considering the molecular model, it is concluded that the
conformation of the benzyl cation intermediates in
[2.2]MCPs should also be strongly affected by the size of
the substituents at position 16.
As shown in Fig. 3, the interaction between the benzyl
cation and the opposite benzene ring might be much more
favorable for the 16-substituted [2.2]MCP A than the unsub-
stituted one B. Thus, the steric repulsion of 16-substituents,
Conclusions
We have demonstrated the TiCl4-mediated Friedel–Crafts
benzylation of benzene with 8-(bromomethyl)[2.2]MCPs 2
to afford the corresponding 8-benzyl[2.2]MCPs 4. The ben-
zyl cation intermediate stabilized by the through-space elec-
tronic interaction from the opposite benzene ring was first
demonstrated in the benzylation of [2.2]MCP systems. Fur-
ther studies on the chemical properties of the benzylation
products are now in progress.
Experimental
All melting points were uncorrected. 1H NMR spectra
were recorded on a Nippon Denshi JEOL FT-300 spectrom-
eter. Chemical shifts are reported as d values (ppm) relative
Published by NRC Research Press

Shimizu et al.
461
to internal Me4Si. Mass spectra were obtained on a Nippon
Denshi JIR-AQ2OM mass spectrometer at an ionization en-
ergy of 70 eV using a direct-inlet system through GLC; m/z
values reported include the parent ion peak. Infrared (IR)
spectra were obtained on a Nippon Denshi JIR-AQ2OM
spectrophotometer as KBr disks. Elemental analyses were
performed by Yanaco MT-5. GLC analyses were performed
by Shimadzu gas chromatograph, GC-14A; silicone OV-1,
2 m; programmed temperature rise, 12 8C min–1; carrier gas
nitrogen, 25 mL min–1.
1215, 1180, 990, 730. 1H NMR (CDCl3) d: 0.58 (s, 3H,
Me), 1.28 (s, 18H, t-Bu), 2.76–3.02 (m, 8H, CH2), 3.07 (s,
2H, CH2), 7.06 (s, 2H, Ar-H), 7.12 (s, 2H, Ar-H). MS m/z
(%): 426, 428 (M+). Anal. calcd. for C26H35Br (427.47): C
73.05, H 8.25; found: C 72.93, H 8.21.
5,13-Di-tert-butyl-8,16-
bis(bromomethyl)[2.2]metacyclophane (3)
Colorless prisms (from benzene), mp > 300 8C. IR (KBr,
cm–1) nmax: 3040, 2960, 1585, 1475, 1360, 1225, 1220,
1
1190, 890, 760, 665. H NMR (CDCl3) d: 1.33 (18H, s,
Materials
t-Bu), 2.75–3.11 (m, 8H, CH2), 3.04 (s, 4H, CH2), 7.16 (s,
4H, Ar-H). MS m/z (%): 504, 506, 508 (M+). Anal. calcd.
for C26H34Br2 (506.37): C 61.67, H 6.77; found: C 61.52, H
6.72.
Preparation of 5,13-di-tert-butyl-8-substituted 16-meth-
yl[2.2]metacyclophane (1a–1c)32–34 and 5,13-di-tert-butyl-8-
(bromomethyl)-16-methyl[2.2]metacyclophane (2b)35,36 were
previously described.
Benzylation of benzene with 8-(bromomethyl)-5,13-di-
tert-butyl-16-substituted [2.2]metacyclophane (2)
Bromination of 8-methyl[2.2]metacyclophanes (1) with N-
bromosuccinimide
Typical procedure
Typical procedure
To a solution of 5,13-di-tert-butyl-8-(bromomethyl)-16-
methyl[2.2]metacyclophane (2b; 428 mg, 1.0 mmol) in ben-
zene (2.67 mL, 30 mmol) was added TiCl4 (0.16 mL,
1.5 mmol) at 0 8C. The reaction temperature was raised to
room temperature by removing the ice bath. After the reac-
tion mixture had been stirred at 50 8C for 2 h, it was poured
into ice water and extracted with benzene. The extract was
dried over anhydrous sodium sulfate and concentrated. The
residue was subjected to silica-gel (Wako, C-300; 100 g)
column chromatography using as eluent n-hexane–benzene
(1:1) to give 8-benzyl-5,13-di-tert-butyl-16-methyl[2.2]me-
tacyclophane (4b; 170 mg, 40%) as colorless prisms (from
After a mixture of 5,13-di-tert-butyl-8-methoxy-16-meth-
yl[2.2]metacyclophane (1c; 500 mg, 1.4 mmol), N-bromo-
succinimide (300 mg, 1.7 mmol), and benzoyl peroxide
(50 mg, 0.21 mmol) in carbon tetrachloride (150 mL) had
been refluxed for 3 h, the formed precipitates were filtered
off. The filtrate was washed with 10% sodium hydroxide
and water. The organic layer was dried over sodium sulfate
and evaporated in vacuo to leave a colourless solid, which
was recrystallized from n-hexane to give 5,13-di-tert-butyl-8-
(bromomethyl)-16-methoxy[2.2]metacyclophane (2c; 435 mg,
70%) as colorless prisms, mp 239–240 8C. IR (KBr, cm–1)
nmax: 3040, 2960, 1600, 1475, 1450, 1220, 1200, 1100, 1020,
1
n-hexane), mp 167–168 8C. H NMR (CDCl3) d: 0.62 (s,
1
880, 805, 780, 750. H NMR (CDCl3) d: 1.26 (s, 18H, t-Bu),
3H, Me), 1.27 (s, 9H, t-Bu), 1.35 (s, 9H, t-Bu), 2.39 (s, 2H,
CH2), 2.68–3.00 (m, 8H, CH2), 6.36–6.52 (m, 2H, Ar-H),
6.88–7.04 (m, 3H, Ar-H), 7.13 (s, 2H, Ar-H), 7.18 (s, 2H,
Ar-H). MS m/z (%): 424 (M+). Anal. calcd. for C32H40
(424.68): C 90.51, H 9.49; found: C 90.31, H 9.58.
Benzylation of benzene with 2a and 2c was carried out
using the same procedure as described above and product
yields are compiled in Table 1.
2.85 (s, 3H, OMe), 2.68–3.02 (m, 8H, CH2), 3.08 (s, 2H,
CH2), 7.04 (s, 2H, Ar-H), 7.06 (s, 2H, Ar-H). MS m/z (%):
442, 444 (M+). Anal. calcd. for C26H35BrO (443.47): C
70.42, H 7.96; found: C 70.13, H 7.84.
Bromination of 1a and 1b with N-bromosuccinimide was
carried out using the same procedure as described above to
afford 2a and 2b in 80% and 20% yields, respectively. How-
ever, in the case of 1b, 8,16-bis(bromomethyl)[2.2]MCP (3)
was also obtained in 30% yield along with the recovery of
the starting compound 1b in 20% yield in spite of 1.2 equiv
of N-bromosuccinimide used.
8-Benzyl-5,13-di-tert-butyl[2.2]metacyclophane (4a)
Colorless prisms (from n-hexane), mp 195 8C. IR (KBr,
cm–1) nmax: 2964, 2864, 1594, 1478, 1477, 1454, 1359,
1
1275, 731. H NMR (CDCl3) d: 1.36 (s, 18H, t-Bu), 2.15 (s,
8-(Bromomethyl)-5,13-di-tert-butyl[2.2]metacyclophane
(2a)
2H, CH2), 2.17–3.07 (m, 8H, CH2), 3.71 (s, 1H, Ar-H16),
6.60–7.09 (m, 5H, Ar-H), 7.07 (s, 2H, Ar-H), 7.19 (s, 2H,
Ar-H). MS m/z (%): 410 (M+). Anal. calcd. for C31H38
(410.65): C 90.67, H 9.33; found: C 90.57, H 9.35.
Colorless prisms (from n-hexane), mp 132–133 8C. IR
(KBr, cm–1) nmax: 3100, 2900, 1600, 1485, 1400, 1370,
1230, 1190, 1100, 1010, 950, 920, 890, 860, 820, 760, 730,
1
720, 660. H NMR (CDCl3) d: 1.29 (s, 9H, t-Bu), 1.34 (s,
8-Benzyl-5,13-di-tert-butyl-16-
methoxy[2.2]metacyclophane (4c)
9H, t-Bu), 2.40–3.16 (m, 8H, CH2), 2.83 (s, 2H, CH2), 3.68
(broad s, 1H, Ar-H), 6.92–7.20 (m, 4H, Ar-H). MS m/z (%):
412, 414 (M+). Anal. calcd. for C25H33Br (413.45): C 72.63,
H 8.05; found: C 72.41, H 7.76.
Colorless prisms (from n-hexane), mp 132 8C. IR (KBr,
cm–1) nmax: 2960, 2864, 1600, 1478, 1459, 1361, 1208,
1
1024, 727. H NMR (CDCl3) d: 1.32 (s, 9H, t-Bu), 1.37 (s,
5,13-Di-tert-butyl-8-(bromomethyl)-16-
methyl[2.2]metacyclophane (2b)
9H, t-Bu), 2.35 (s, 2H, CH2), 2.69–2.84 (m, 8H, CH2), 2.90
(s, 3H, OMe), 6.52–7.03 (m, 5H, Ar-H), 7.06 (s, 2H, Ar-H),
7.17 (s, 2H, Ar-H). MS m/z (%): 440 (M+). Anal. calcd. for
C32H40O (440.68): C 87.22, H 9.15; found: C 87.33, H 9.74.
Colorless prisms (from n-hexane), mp 272–275 8C. IR
(KBr, cm–1) nmax: 3020, 2940, 1580, 1445, 1350, 1270,
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Can. J. Chem. Vol. 88, 2010
Am. Chem. Soc. 1970, 92 (12), 3675. doi:10.1021/
ja00715a022.
(16) Lindsay, W. S.; Stokes, P.; Humber, L. G.; Boekelheide, V.
J. Am. Chem. Soc. 1961, 83 (4), 943. doi:10.1021/
ja01465a044.
The reaction rate determination for the benzylation of
benzene with 2 in the presence of TiCl4
Typical procedure
To a solution of 5,13-di-tert-butyl-8-bromomethyl-16-meth-
yl[2.2]metacyclophane (2b; 100 mg, 0.2 mmol) in benzene
(4.2 g, 54 mmol) was added a solution of TiCl4 in CS2
(0.10 mL, 0.14 mmol), which was prepared by dissolving
TiCl4 (2.4 mL, 21.08 mmol) in CS2 (12.6 mL), by syringe
(17) Tashiro, M.; Arimura, T.; Yamato, T. Chem. Pharm. Bull.
(Tokyo) 1983, 31 (1), 370.
(18) Yamato, T.; Fujita, K.; Shinoda, N.; Noda, K.; Nagano, Y.;
Arimura, T.; Tashiro, M. Res. Chem. Intermed. 1996, 22 (9),
871. doi:10.1163/156856796X00539.
(19) Smith, B. H. Bridged Aromatic Compounds; Academic
Press: New York, 1964.
1
at 25 8C. The reaction was monitored by H NMR. The re-
action rate was determined by the following equations:
½1ꢁ
½2ꢁ
MCPꢂCH Br þ benzeneTiCl MCPꢂCH C H
4
(20) Keehn, P. M., Rosenfield, S. M., Eds. Cyclophanes; Aca-
ꢂ!
2
2
6
5
demic Press: New York, 1983; Vols. 1 and 2.
¨
(21) Vogtle, F. Cyclophane Chemistry; Wiley: Chichester, UK,
d½MCPꢂCH2Brꢁ
dt
1993.
¼ k½MCPꢂCH2C6H5ꢁ
(22) Allinger, N. L.; Gordon, B. J.; Hu, S.-E.; Ford, R. A. J. Org.
Chem. 1967, 32 (7), 2272. doi:10.1021/jo01282a040.
(23) Sato, T.; Yamada, E.-i.; Okamura, Y.; Amada, T.; Hata, K.
Bull. Chem. Soc. Jpn. 1965, 38 (6), 1049. doi:10.1246/bcsj.
38.1049.
½MCPꢂCH2Brꢁ0
½3ꢁ
ln
¼ kt
½MCPꢂCH2Brꢁ ꢂ ½MCPꢂCH2C6H5ꢁ
(24) Fujimoto, M.; Sato, T.; Hata, K. Bull. Chem. Soc. Jpn. 1967,
40 (3), 600. doi:10.1246/bcsj.40.600.
References
´
(25) Sato, T.; Wakabayashi (nee Fujimoto), M.; Okamura, Y.;
(1) Shimizu, T.; Hita, K.; Rahman, S.; Yamato, T. J. Chem. Res.
2009, 293. doi:10.3184/030823409X447718.
(2) Brown, C. J. J. Chem. Soc. 1953, 3278. doi:10.1039/
JR9530003278.
(3) Shieh, C.-F.; McNally, D.; Boyd, R. H. Tetrahedron 1969,
25 (17), 3653. doi:10.1016/S0040-4020(01)82898-2.
(4) Hanson, A. W. Acta Crystallogr. 1962, 15 (10), 956. doi:10.
1107/S0365110X62002534.
(5) Keehn, P. M., Rosenfield, S. M., Eds. Cyclophanes; Aca-
demic Press: New York, 1983.
(6) Wilson, D. J.; Boekelheide, V.; Griffin, R. W., Jr. J. Am.
Chem. Soc. 1960, 82 (24), 6302. doi:10.1021/ja01509a028.
(7) Allinger, N. L.; Da Rooge, M. A.; Hermann, R. B. J. Am.
Chem. Soc. 1961, 83 (8), 1974. doi:10.1021/ja01469a046.
(8) Gutowsky, H. S.; Juan, C. J. Chem. Phys. 1962, 37 (1), 120.
doi:10.1063/1.1732932.
(9) Sato, T.; Akabori, S.; Kainosho, M.; Hata, K. Bull. Chem.
Soc. Jpn. 1966, 39 (4), 856. doi:10.1246/bcsj.39.856.
(10) Sato, T.; Akabori, S.; Kainosho, M.; Hata, K. Bull. Chem.
Soc. Jpn. 1968, 41 (1), 218. doi:10.1246/bcsj.41.218.
(11) Fujimoto, M.; Sato, T.; Hata, K. Bull. Chem. Soc. Jpn. 1967,
40 (3), 600. doi:10.1246/bcsj.40.600.
Amada, T.; Hata, K. Bull. Chem. Soc. Jpn. 1967, 40, 2363.
doi:10.1246/bcsj.40.2363.
(26) Sato, T.; Nishiyama, K. J. Chem. Soc. Chem. Commun.
1973, 220. doi:10.1246/bcsj.44.2858.
(27) Sato, T.; Nishiyama, K.; Shimada, S.; Hata, K. Bull. Chem.
Soc. Jpn. 1971, 44 (10), 2858. doi:10.1246/bcsj.44.2858.
(28) Hayashi, S.; Sato, T. Bull. Chem. Soc. Jpn. 1972, 45 (8),
2360. doi:10.1246/bcsj.45.2360.
(29) Sato, T.; Nishiyama, K. J. Org. Chem. 1972, 37 (21), 3254.
doi:10.1021/jo00986a014.
(30) Yamato, T.; Ide, S.; Tokuhisa, K.; Tashiro, M. J. Org. Chem.
1992, 57 (1), 271. doi:10.1021/jo00027a048.
(31) Yamato, T.; Matsumoto, J.; Ide, S.; Tokuhisa, K.; Suehiro,
K.; Tashiro, M. J. Chem. Res. (S) 1992, 420.
(32) Tashiro, M.; Yamato, T. Synthesis 1978, 435. doi:10.1055/s-
1978-24769.
(33) Tashiro, M.; Yamato, T. J. Org. Chem. 1981, 46 (8), 1543.
doi:10.1021/jo00321a005.
(34) Tashiro, M.; Yamato, T. J. Org. Chem. 1981, 46 (22), 4556.
doi:10.1021/jo00335a047.
(35) Tashiro, M.; Yamato, T. Chem. Lett. 1982, 11 (1), 61.
doi:10.1246/cl.1982.61.
(36) Tashiro, M.; Yamato, T. J. Chem. Soc. Perkin Trans. 1 1984,
2165. doi:10.1039/p19840002165.
(37) Olah, G. A. Acc. Chem. Res. 1971, 4 (7), 240. doi:10.1021/
ar50043a002.
(38) Olah, G. A.; Kobayashi, S.; Tashiro, M. J. Am. Chem. Soc.
1972, 94 (21), 7448. doi:10.1021/ja00776a030.
(12) Burri, K.; Jenny, W. Helv. Chim. Acta 1967, 50 (7), 1978.
doi:10.1002/hlca.19670500731.
(13) Allinger, N. L.; Gordon, B. J.; Hu, S.-E.; Ford, R. A. J. Org.
Chem. 1967, 32 (7), 2272. doi:10.1021/jo01282a040.
(14) Flammang, R.; Figeys, H. P.; Martin, R. H. Tetrahedron
1968, 24 (3), 1171. doi:10.1016/0040-4020(68)88065-2.
(15) Blaschke, H.; Ramey, C. E.; Calder, I.; Boekelheide, V. J.
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