Synthesis of novel cyclophanes containing both benzo[1,2-b:5,4-b']difuran and naphthalene rings

Article abstract of DOI:10.1039/b110312a

Facile routes for the synthesis of novel cyclophanes 1a, b containing both benzo[1,2-b:5,4-b']difuran and naphthalene rings have been developed. Irradiation of 1,5-dibenzoyl-2,4-dialkoxybenzene derivatives 3a, b with a 350 nm mercury lamp followed by dehy

Full text of DOI:10.1039/b110312a

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Synthesis of novel cyclophanes containing both benzo[1,2-b:5,4-bЈ]-
difuran and naphthalene rings
Kwanghee Koh Park,* Hongsan Lim, Sun-Hyuk Kim and Dae Hyun Bae
1
Department of Chemistry, Chungnam National University, Taejon 305-764, South Korea.
E-mail: khkoh@cnu.ac.kr
Received (in Cambridge, UK) 12th November 2001, Accepted 17th December 2001
First published as an Advance Article on the web 11th January 2002
Facile routes for the synthesis of novel cyclophanes 1a, b containing both benzo[1,2-b:5,4-bЈ]difuran and naphthalene
rings have been developed. Irradiation of 1,5-dibenzoyl-2,4-dialkoxybenzene derivatives 3a, b with a 350 nm mercury
lamp followed by dehydration afforded benzo[1,2-b:5,4-bЈ]difuran ring systems 5a, b. The cyclophanes 1a, b were
prepared either from the ether-forming reaction between the preformed benzodifuran ring derivatives 5a, b and 2,7-
dihydroxynaphthalene, or from the photocyclization–dehydration reaction of the macrocycles 6a, b prepared by
reacting 1,5-dibenzoyl-2,4-bis(ω-bromoalkoxy)benzene with 2,7-dihydroxynaphthalene. The cyclophanes 2a, b
containing two benzo[1,2-b:5,4-bЈ]difuran and two naphthalene moieties were obtained as minor products.
between the aromatic groups through π–π, electron donor–
acceptor, or cation–π interactions.
Introduction
The design and synthesis of cyclophanes, macrocycles con-
taining aromatic groups, is a fascinating branch of organic and
supramolecular chemistry.1,2 It is well recognized that cyclo-
phanes have a wide range of applicability in emerging tech-
nology as synthetic receptors in molecular recognition, sensors,
and components of molecular motors.2 However, aromatic
groups contained in the cyclophanes are mostly carbocyclic
rings such as benzene and naphthalene derivatives. Hetero-
aromatic ring-containing cyclophanes are usually limited to
pyrrole- and pyridine-containing systems, presumably due
to difficulties in preparing appropriately tethered heterocyclic
compounds.
In this paper, we describe facile synthetic routes to novel
cyclophanes 1a, b containing both benzo[1,2-b:5,4-bЈ]difuran
and naphthalene rings. A few groups have reported the syn-
thesis of the benzo[1,2-b:5,4-bЈ]difuran nucleus,3–5 but the
benzodifuran ring-containing cyclophanes have not been
reported. One reported synthetic method for the benzodifuran
rings is based on the formation of furan rings via intra-
molecular aldol-type condensation reactions of the appropriate
products, obtained from alkylation of o-acylphenols, with the
corresponding α-halocarbonyl compound.3 This method pro-
vides only limited scope for the synthesis of benzodifuran
derivatives which have specific substituents such as acetyl,
cyano, ethoxycarbonyl and carboxy groups at the 2-position.
The other methods are for the preparation of 2,3,5,6-tetra-
arylbenzo[1,2-b;5,4-bЈ]difuran derivatives either by a photo-
chemical reaction4 or by acid-catalyzed cyclocondensation
of resorcinol with p-(benzyloxy)benzoin.5 It was shown that
o-alkoxybenzophenones can be transformed to benzo[b]furan
rings by photocyclization via intramolecular δ-hydrogen
abstraction followed by dehydration reactions.6–8 Here, we have
extended this methodology for the formation of the appro-
priately tethered benzo[1,2-b:5,4-bЈ]difuran rings and cyclo-
phanes 1a, b. In the process of preparation of 1a, b, we also
Results and discussion
obtained the cyclophanes 2a, b containing two benzo[1,2-b:5,4-
bЈ]difuran and two naphthalene moieties as minor products.
The heteroaromatic ring-containing cyclophanes 1 and 2 are of
particular interest because of the possibilities of trans-annular
excitation energy transfer between the aromatic groups, and co-
operative guest binding by sandwiching the guest molecules
For the synthesis of the cyclophanes 1, we first established
a synthetic route to benzo[1,2-b:5,4-bЈ]difuran derivatives 5,
starting from 1,3-dimethoxybenzene (Scheme 1). Friedel–Crafts
acylation of 1,3-dimethoxybenzene with benzoyl chloride gave
1,5-dibenzoyl-2,4-dihydroxybenzene4 in 35% yield, which was
then reacted with α,ω-dibromoalkanes in a 1 : 5 molar ratio in
310
J. Chem. Soc., Perkin Trans. 1, 2002, 310–314
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b110312a

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Scheme 1 Synthetic route to benzo[1,2-b:5,4-bЈ]difuran derivatives 5.
the presence of K2CO3 to obtain 3a and 3b in 66% and 60%
analysis. The number of 1H and 13C NMR peaks confirmed the
yields, respectively. Irradiation of 1.0 mM benzene9 solutions
of compounds 3a, b with 350 nm mercury lamps, followed by
dehydration of the photoproducts with aq. HCl, without
attempting isolation and separation of the benzodifuranol
derivatives 4a, b, afforded benzodifuran derivatives 5a, b in 40%
yields.
symmetrical nature of the compounds. Based on the symmetry
of the compounds, the expected number of 13C NMR peaks is
the same among the corresponding macrocycles 1, 2, 6, and 7,
which is 23 for the a series and 27 for the b series. The actual
carbon numbers present in the compounds are 46 for 1a and 6a,
54 for 1b and 6b, 92 for 2a and 7a, and 108 for 2b and 7b. The
observed number of peaks in the 13C NMR spectra exactly
match the expected number, except that 1b and 7b have one less
peak, and 2b and 5b have two less peaks than expected because
of overlapping of some alkyl carbons. Of course, the syntheses
of the cyclophanes 1a, b and 2a, b via two alternative routes
constitute further firm evidence of their structures.
Establishment of a facile synthetic route to 2,6-bis(ω-bromo-
alkyl)-3,5-diphenylbenzo[1,2-b:5,4-bЈ]difurans 5a, b prompted
us to utilize these compounds in the preparation of benzo-
difuran ring-containing cyclophanes. The synthetic pathways
for the cyclophanes containing both benzodifuran and naph-
thalene rings, 1a, b, are shown in Scheme 2. The cyclophanes 1a,
b were prepared by two alternative routes: one is from the
connection of the preformed benzodifuran ring with tethered
bromoalkyl groups, 5a, b, with dihydroxynaphthalene through
formation of two ether linkages. The other is the reverse order
of the first one; the aforementioned photocyclization reaction
to form the benzodifuran ring was applied to macrocycles 6a, b,
which were obtained by the ether-forming reaction between
dibromides 3a, b and dihydroxynaphthalene.
The ether-forming reactions of 2,7-dihydroxynaphthalene
with 5a, b provided 1a, b in 34–37% yields, together with
the cyclophanes containing two benzodifuran rings and two
naphthalene rings, 2a, b in 10–13% yields. The reactions of 3a, b
with 2,7-dihydroxynaphthalene gave 6a, b in 33–37% yields
and the [2 ϩ 2] products 7a, b in 11% yields. Photocyclization
reactions of the macrocycles 6a, b and then dehydration
reactions of the photoproducts gave 1a and 1b in 34% and 36%
yields, respectively. These results show that the overall yields
for the cyclophanes 1a, b starting from 3a, b are almost the
same for both routes. This scheme provides facile access to
rather complex molecules such as 1a, b from readily available
and straightforward experimental procedures.
In summary, facile routes for the synthesis of novel types
of cyclophanes 1a, b having both benzo[1,2-b:5,4-bЈ]difuran
and naphthalene rings have been developed. The benzodifuran
moieties were formed by photocyclization–dehydration
reactions of 2,4-dialkoxy substituted 1,5-dibenzoylbenzene
derivatives. The cyclophanes 1a, b were prepared either from
the reaction of the preformed benzodifuran ring derivatives 5a,
b with 2,7-dihydroxynaphthalene or from the photo-reaction of
the macrocycles 6a, b having a 1,5-dibenzoyl-2,4-dialkoxy-
benzene moiety and a naphthalene ring. The cyclophanes 2a, b
containing two benzo[1,2-b:5,4-bЈ]difuran rings and two
naphthalene rings were also obtained as minor products. The
cyclophanes 1 and 2 are of particular interest as aryl sub-
stituted benzo[1,2-b:5,4-bЈ]difuran derivatives have high
fluorescence quantum yields,4 and the close proximity of
naphthyl groups to benzodifuran rings in the cyclophanes may
facilitate the intramolecular excitation energy transfer. Indeed,
the shape of the fluorescence spectra of 1a, b is observed to be
essentially the same as that of 2,7-dimethoxynaphthalene, but
the emission intensity of 1a, b is much greater than that of
2,7-dimethoxynaphthalene.10 This indicates efficient excitation
energy transfer from benzodifuran to naphthyl groups in the
macrocycles. The use of these cyclophanes as fluorescent
receptors and components of photochemical molecular devices
looks promising. The schemes described here can be easily
applied to the syntheses of various other types of benzodifuran
ring-containing cyclophanes having different tethering groups,
different aromatic rings with specific substituents, and other
components rather than naphthalene rings to tune their
physicochemical properties for desired applications.
The cyclophanes 2a, b were also obtained via the photo-
cyclization–dehydration reaction of 7a, b with yields of 10–
14%; in this case, the overall yields from 3a, b to 2a, b are much
higher for the route via 5a, b than for the route via 7a, b. This is
expected as the latter route requires a quadruple photocycliza-
tion step involving simultaneous formation of four furan rings,
while the former route contains a double photocyclization step.
The structures of the compounds prepared in this work were
fully characterized by 1H and 13C NMR spectra and elemental
J. Chem. Soc., Perkin Trans. 1, 2002, 310–314
311

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Scheme 2 Synthesis of the cyclophanes containing both benzodifuran rings and naphthalene rings.
C6H5CO-), 7.52 (tt, J = 8 & 1 Hz, 2H, para Ar-H of two
C6H5CO-), 7.68 (s, 1H, Ar-H ortho to both benzoyl groups),
7.75–7.78 (m, 4H, ortho Ar-H of C6H5CO-); 13C NMR δ 25.45,
27.93, 28.40, 28.65, 28.89, 32.65, 33.97, 68.50, 96.15, 121.02,
128.01, 129.33, 132.33, 133.31, 138.89, 161.27, 195.22.
Experimental
All reagents were purchased from Aldrich Chemical Co. and
used as received. Melting points are uncorrected. H and 13C
1
NMR spectra were obtained at 400 and 100 MHz, respectively,
using tetramethylsilane as an internal standard in CDCl3.
NMR measurements and elemental analyses were performed
at the Central Research Facilities of Chungnam National
University.
1
3b. Yield, 60%; mp 82–83 ЊC; H NMR δ 1.0–1.5 (m, 36H),
1.86 (quintet, J = 7 Hz, 4H), 3.41 (t, J = 7 Hz, 4H, two -CH2-Br),
3.92 (t, J = 6 Hz, 4H, two -CH2O-), 6.45 (s, 1H, Ar-H ortho to
both alkoxy groups), 7.41 (t, J = 8 Hz, 4H, m-H of two
C6H5CO-), 7.52 (tt, J = 8 & 1 Hz, 2H, p-H of two C6H5CO-),
7.68 (s, 1H, Ar-H ortho to both benzoyl groups), 7.75–7.78
(m, 4H, o-H of two C6H5CO-); 13C NMR δ 25.82, 25.92, 28.35,
28.95, 29.37, 29.55, 29.60, 29.67, 29.75, 33.02, 34.24, 68.87,
96.50, 121.34, 128.24, 129.58, 132.54, 133.55, 139.19, 161.56,
195.47.
1,5-Dibenzoyl-2,4-dihydroxybenzene
The reported procedure4 was followed using 1,3-dimethoxy-
benzene (13.8 g, 0.1 mol), benzoyl chloride (30.9 g, 0.22 mol),
and AlCl3 (29.3 g, 0.22 mol) in dichloromethane (250 ml) to
give the title compound (11.2 g, 35%); mp 151–153 ЊC (lit.,4
1
147–149 ЊC); H NMR δ 6.62 (s, 1H, Ar-H ortho to both OH
groups), 7.3–7.7 (m, 10H), 8.01 (s, 1H, Ar-H ortho to both
carbonyl groups), 12.86 (s, 2H, two -OH).
Photocyclization–dehydration reactions of 3a, b to 5a, b
1.0 mM Benzene9 solutions (500 ml) of compounds 3a, b
(0.5 mmol) contained in a Pyrex glass vessel were purged with
nitrogen for 1 h and then irradiated under nitrogen with a
350 nm mercury lamp using a RPR-100 photochemical reactor
(Southern New England Ultraviolet Company). After 4–7 h
of irradiation, the reaction mixture was concentrated and the
residue was dissolved in 5 ml of acetone. The acetone solution
was treated with a few drops of 1 M HCl and stirred for 2 h.
Water was added to the reaction mixture, and extracted with
chloroform. The concentrated organic layer was purified by
silica gel column chromatography eluting with 1 : 1 hexane–
dichloromethane to afford benzodifuran derivatives 5a, b.
1,5-Dibenzoyl-2,4-dialkoxybenzenes 3a, b
A solution of 1,8-dibromooctane (12.8 g, 47.1 mmol) or 1,12-
dibromododecane (15.5 g, 47.1 mmol) in acetone (80 ml) was
added very slowly to the suspension of 1,5-dibenzoyl-2,4-
dihydroxybenzene (3.00 g, 9.42 mmol) and K2CO3 (6.51 g,
47.1 mmol) in acetone (100 ml) at reflux which was continued
for 48 h. K2CO3 was removed by filtration. Water (50 ml) was
added to the concentrated filtrate and extracted with dichloro-
methane. Purification of the organic layer by silica gel column
chromatography (eluent: dichloromethane) gave 3a, b.
1
3a. Yield, 66%; mp 87–88 ЊC; H NMR δ 1.0–1.5 (m, 20H),
1.82 (quintet, J = 7 Hz, 4H), 3.40 (t, J = 7 Hz, 4H, two -CH2-Br),
3.92 (t, J = 6 Hz, 4H, two -CH2O-), 6.46 (s, 1H, Ar-H ortho to
both alkoxy groups), 7.41 (t, J = 8 Hz, 4H, meta Ar-H of two
5a. Yield, 40%; mp 86–87 ЊC; 1H NMR δ 1.25–1.43 (m, 12H,
two -CH2CH2-(CH2)3-CH2CH2Br), 1.75–1.84 (m, 8H, two
-CH2CH2-(CH2)3-CH2CH2Br), 2.84 (t, J = 8 Hz, 4H, two
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1
furan-CH2-(CH2)6Br), 3.36 (t, J = 7 Hz, 4H, two -CH2-Br),
7.32–7.38 (m, 2H, p-H of two C6H5), 7.43–7.49 (m, 8H, o- &
m-H of two C6H5), 7.55 and 7.54 (2s, 2H, H4 & H8 of benzo-
difuran ring); 13C NMR δ 26.70, 27.99, 28.16, 28.36, 28.94,
32.68, 33.92, 93.63, 107.91, 116.97, 125.44, 126.95, 128.76,
129.13, 133.03, 152.04, 155.06. Anal. Calcd. for C36H40Br2O2:
C, 65.07; H, 6.07%. Found: C, 64.81; H, 5.93%.
2b. Yield, 10%; mp 122–124 ЊC; H NMR δ 1.20–1.50 (m,
56H, -(CH2)2(CH2)7(CH2)2O-), 1.73–1.85 (m, 16H, -CH2CH2-
(CH2)7CH2CH2O-), 2.83 (t, J = 7 Hz, 8H, furan-CH2-), 4.03 (t,
J = 7 Hz, 8H, -CH2O-), 6.96 (dd, J = 9 & 2 Hz, 4H, H3 &
H6 of naphthalene ring), 7.01 (d, J = 3 Hz, 4H, H1 & H8 of
naphthalene ring), 7.31–7.36 (m, 4H, p-H of C6H5-), 7.41–7.48
(m, 16H, o- & m-H of C6H5-), 7.54 and 7.55 (2s, 2H, H4 & H8 of
benzodifuran ring), 7.61 (d, J = 9 Hz, 4H, H4 & H5 of naphtha-
lene ring); 13C NMR δ 25.96, 26.81, 28.24, 29.14, 29.24, 29.34,
29.39, 29.43, 67.89, 93.62, 105.98, 107.87, 116.25, 116.64,
124.09, 125.45, 126.88, 128.73, 129.00, 129.17, 133.10, 135.96,
152.04, 155.31, 157.62. Anal. Calcd. for C108H124O8: C, 83.68;
H, 8.06%. Found: C, 83.54; H, 8.19%.
5b. Yield, 39%; mp 41–42 ЊC; 1H NMR δ 1.20–1.44 (m,
28H, two -CH2CH2-(CH2)7-CH2CH2Br), 1.74–1.87 (m, 8H,
two -CH2CH2-(CH2)7-CH2CH2Br), 2.83 (t, J = 8 Hz, 4H, two
furan-CH2-(CH2)10Br), 3.38 (t, J = 7 Hz, 4H, two -CH2-Br),
7.31–7.37 (m, 2H, p-H of two C6H5), 7.42–7.49 (m, 8H, o- &
m-H of two C6H5), 7.55 (s, 2H, H4 & H8 of benzodifuran ring);
13C NMR δ 26.80, 28.10, 28.30, 28.68, 29.20, 29.33, 29.39,
32.77, 33.91, 93.57, 107.84, 116.57, 125.41, 126.85, 128.68,
129.10, 133.06, 152.01, 155.22. Anal. Calcd. for C44H56Br2O2:
C, 68.04; H, 7.27%. Found: C, 67.79; H, 7.13%.
Synthesis of 6a, b and 7a, b
The reaction of 3a (1.00 g, 1.43 mmol) or 3b (1.00 g, 1.23 mmol)
with 2,7-dihydroxynaphthalene (1.2 equiv.) was carried out
in the same manner as the corresponding reaction of 5a, b.
Purification of the reaction mixture by silica gel column
chromatography eluting with 40 : 1 dichloromethane–ethyl
acetate provided 6a, b and 7a, b as separate fractions.
Synthesis of 1a, b and 2a, b from 5a, b
The compound 5a, b (0.30 mmol) was reacted with 2,7-
dihydroxynaphthalene (58 mg, 0.36 mmol) in refluxing acetone
(50 ml) in the presence of K2CO3 (0.42 g, 3.0 mmol) for 48–72 h
and worked-up as described for the synthesis of 3a, b. Silica gel
column chromatography eluting with 1 : 1 hexane–dichloro-
methane afforded 1a, b and 2a, b as separate fractions.
1
6a. Yield, 33%; mp 169 ЊC; H NMR δ 1.15–1.52 (m, 20H),
1.81 (quintet, J = 7 Hz, 4H), 3.93 (t, J = 7 Hz, 4H), 4.12 (t, J =
7 Hz, 4H), 6.50 (s, 1H, Ar-H ortho to both alkoxy groups), 6.98
(dd, J = 9 & 2 Hz, 2H, H3 & H6 of naphthalene ring), 7.05 (d,
J = 2 Hz, 2H, H1 & H8 of naphthalene ring), 7.40 (t, J = 8 Hz,
4H, m-H of two C6H5CO-), 7.51 (t, J = 8 Hz, 2H, p-H of two
C6H5CO-), 7.64 (d, J = 9 Hz, 2H, H4 & H5 of naphthalene ring),
7.66 (s, 1H, Ar-H ortho to both benzoyl groups), 7.76 (d, J =
9 Hz, 4H, o-H of two C6H5CO-); 13C NMR δ 25.02, 25.36,
27.99, 28.23, 28.27, 28.54, 67.72, 68.54, 96.81, 106.56, 116.06,
121.11, 124.13, 128.03, 129.13, 129.38, 132.36, 133.35, 135.79,
138.84, 157.35, 161.29, 195.13.
1a. Yield, 34%; mp 91–92 ЊC; 1H NMR δ 1.25–1.45 (m,
12H, two -(CH2)2(CH2)3(CH2)2O-), 1.70–1.85 (m, 8H, two
furan-CH2CH2(CH2)3CH2CH2O-), 2.88 (t, J = 6 Hz, 4H,
two furan-CH2-), 4.00 (t, J = 7 Hz, 4H, two -CH2O-), 6.95 (dd,
J = 9 & 2 Hz, 2H, H3 & H6 of naphthalene ring), 7.04 (d, J =
2 Hz, 2H, H1 & H8 of naphthalene ring), 7.32–7.38 (m, 2H,
p-H of two C6H5-), 7.43–7.50 (m, 8H, o- & m-H of two C6H5-),
7.58 and 7.63 (2s, 2H, H4 & H8 of benzodifuran ring), 7.61 (d,
J = 9 Hz, 2H, H4 & H5 of naphthalene ring); 13C NMR δ 25.52,
26.37, 27.78, 28.35, 28.58, 29.02, 68.02, 93.93, 106.53, 107.89,
115.98, 117.31, 124.10, 125.55, 126.97, 128.78, 128.94, 129.18,
132.96, 135.94, 152.02, 155.22, 157.39. Anal. Calcd. for
C46H46O4: C, 83.35; H, 6.99%. Found: C, 83.38; H, 6.73%.
1
7a. Yield, 11%; mp 180–181 ЊC; H NMR δ 1.01–1.53 (m,
40H), 1.80 (broad s, 8H), 3.91 (broad s, 8H), 4.04 (broad s,
8H), 6.45 (s, 2H, Ar-H ortho to both alkoxy groups), 6.98 (d, J =
9 Hz, 4H, H3 & H6 of naphthalene rings), 7.04 (s, 4H, H1 & H8
of naphthalene rings), 7.39 (t, J = 7 Hz, 8H, m-H of C6H5CO-),
7.50 (t, J = 7 Hz, 4H, p-H of C6H5CO-), 7.63 (d, J = 9 Hz, 4H,
H4 & H5 of naphthalene rings), 7.67 (s, 2H, Ar-H ortho to both
benzoyl groups), 7.75 (d, J = 7 Hz, 8H, o-H of C6H5CO-); 13C
NMR δ 25.32, 25.79, 28.54, 28.87, 28.91, 29.04, 67.76, 68.50,
96.34, 105.97, 116.18, 121.11, 124.12, 128.03, 129.05, 129.37,
132.35, 133.30, 135.93, 138.91, 157.59, 161.28, 195.20. Anal.
Calcd. for C92H100O12: C, 79.05; H, 7.21%. Found: C, 78.70;
H, 7.31%.
1
2a. Yield, 13%; mp 199–200 ЊC; H NMR δ 1.33–1.50 (m,
24H, -(CH2)2(CH2)3(CH2)2O-), 1.79 (m, 16H, -CH2CH2(CH2)3-
CH2CH2O-), 2.85 (t, J = 7 Hz, 8H, furan-CH2-), 4.01 (t, J = 7
Hz, 8H, -CH2O-), 6.95 (dd, J = 9 & 3 Hz, 4H, H3 & H6 of
naphthalene ring), 7.01 (d, J = 2 Hz, 4H, H1 & H8 of naphtha-
lene ring), 7.31–7.36 (m, 4H, p-H of C6H5-), 7.42–7.49 (m, 16H,
o- & m-H of C6H5-), 7.54 and 7.55 (2s, 2H, H4 & H8 of benzo-
difuran ring), 7.61 (d, J = 9 Hz, 4H, H4 & H5 of naphthalene
ring); 13C NMR δ 25.78, 26.74, 28.13, 28.91, 28.99, 29.03, 67.80,
93.65, 106.00, 107.92, 116.24, 116.75, 124.11, 125.47, 126.94,
128.75, 129.00, 129.16, 133.07, 135.93, 152.05, 155.17, 157.57.
Anal. Calcd. for C92H92O8: C, 83.35; H, 6.99%. Found: C,
83.37; H, 6.91%.
1
6b. Yield, 37%; mp 118–119 ЊC; H NMR δ 1.05–1.52 (m,
36H), 1.84 (quintet, J = 7 Hz, 4H), 3.91 (t, J = 7 Hz, 4H), 4.08 (t,
J = 7 Hz, 4H), 6.46 (s, 1H, Ar-H ortho to both alkoxy groups),
6.98 (dd, J = 9 & 2 Hz, 2H, H3 & H6 of naphthalene ring),
7.03 (d, J = 2 Hz, 2H, H1 & H8 of naphthalene ring), 7.40 (t, J =
8 Hz, 4H, m-H of two C6H5CO-), 7.51 (t, J = 8 Hz, 2H, p-H of
two C6H5CO-), 7.63 (d, J = 9 Hz, 2H, H4 & H5 of naphthalene
ring), 7.66 (s, 1H, Ar-H ortho to both benzoyl groups), 7.74–
7.77 (m, 4H, o-H of two C6H5CO-); 13C NMR δ 25.22, 25.66,
28.33, 28.56, 28.68, 28.75, 29.05, 29.11, 29.13, 29.28, 67.74,
68.50, 96.44, 106.13, 116.15, 121.04, 124.08, 128.02, 129.05,
129.37, 132.36, 133.39, 135.86, 138.87, 157.49, 161.29, 195.20.
1
1b. Yield, 37%; mp 158–159 ЊC; H NMR δ 1.20–1.50 (m,
28H, two -(CH2)2(CH2)7(CH2)2O-), 1.73–1.85 (m, 8H, two
furan-CH2CH2(CH2)7CH2CH2O-), 2.85 (t, J = 7 Hz, 4H, two
furan-CH2-), 4.06 (t, J = 7 Hz, 4H, two -CH2O-), 6.96 (dd,
J = 9 & 2 Hz, 2H, H3 & H6 of naphthalene ring), 7.04 (d, J =
2 Hz, 2H, H1 & H8 of naphthalene ring), 7.32–7.37 (m, 2H,
p-H of two C6H5-), 7.42–7.49 (m, 8H, o- & m-H of two C6H5-),
7.55 and 7.57 (2s, 2H, H4 & H8 of benzodifuran ring), 7.61 (d,
J = 9 Hz, 2H, H4 & H5 of naphthalene ring); 13C NMR δ 25.75,
26.64, 28.03, 28.68, 28.79, 28.96, 29.06, 29.15, 29.28, 67.87,
93.64, 106.28, 107.89, 116.15, 116.82, 124.13, 125.47, 126.91,
128.74, 128.99, 129.17, 133.09, 135.96, 152.04, 155.30, 157.51.
Anal. Calcd. for C54H62O4: C, 83.68; H, 8.06%. Found: C, 83.35;
H, 8.33%.
1
7b. Yield, 11%; mp 146–147 ЊC; H NMR δ 1.01–1.52 (m,
72H), 1.83 (quintet, J = 7 Hz, 8H), 3.90 (t, J = 6 Hz, 8H), 4.05 (t,
J = 7 Hz, 8H), 6.45 (s, 2H, Ar-H ortho to both alkoxy groups),
6.97 (dd, J = 9 & 2 Hz, 4H, H3 & H6 of naphthalene rings), 7.02
(s, 4H, H1 & H8 of naphthalene rings), 7.40 (t, J = 7 Hz, 8H,
m-H of C6H5CO-), 7.51 (t, J = 7 Hz, 4H, p-H of C6H5CO-), 7.62
(d, J = 9 Hz, 4H, H4 & H5 of naphthalene rings), 7.68 (s,
J. Chem. Soc., Perkin Trans. 1, 2002, 310–314
313

View Article Online
4 M. Abdul-Aziz, J. V. Auping and M. A. Meador, J. Org. Chem.,
1995, 60, 1303.
5 H. P. S. Chawla, P. K. Grover, N. Anand, V. P. Kamboj and A. Kar,
J. Med. Chem., 1970, 13, 55.
2H, Ar-H ortho to both benzoyl groups), 7.75 (d, J = 7Hz,
8H, o-H of C6H5CO-); 13C NMR δ 25.46, 25.98, 28.60,
29.01, 29.15, 29.26, 29.38, 29.41, 29.45, 67.87, 68.59, 96.30,
105.97, 116.20, 121.09, 124.09, 128.02, 128.99, 129.35, 132.33,
133.33, 135.93, 138.95, 157.60, 161.31, 195.24. Anal. Calcd. for
C108H132O12: C, 79.96; H, 8.20%. Found: C, 79.86; H, 8.56%.
6 G. R. Lappin and J. S. Zannucci, J. Org. Chem., 1971, 36, 1808;
T. Sumathi and K. K. Balasubramanian, Tetrahedron Lett., 1992,
33, 2213; E. M. Sharshira, M. Okamura, E. Hasegawa and
T. Horaguchi, J. Heterocycl. Chem., 1997, 34, 861.
7 P. J. Wagner, Acc. Chem. Res., 1989, 22, 83.
Photocyclization–dehydration reactions of macrocycles 6a, b and
7a, b
8 K. K. Park, H. Seo, J.-G. Kim and I.-H. Suh, Tetrahedron Lett.,
2000, 41, 1393; K. K. Park, I. K. Han and J. W. Park, J. Org. Chem.,
2001, 66, 6800.
These were carried out in the same way as described for the
reactions of 3a, b. The macrocycles 6a, b provided 1a and 1b
with 34% and 36% yields, and 7a, b gave 2a and 2b in 14% and
10% yields, respectively.
9 Benzene is a toxic solvent and should be handled with appropriate
care.
10 The absorption maxima and molar absorptivity (in MϪ1 cmϪ1 ) of
5a, b in acetonitrile solvent are 273 (ε = 16200), 302 (13000), 308
(12500) and 315 (12700) nm, whereas those of 2,7-dimethoxy-
naphthalene (DMN) are 275 (ε = 3400), 310 (2100), 316 (1700), and
325 (3000) nm. The absorption spectra of 1a,b are almost identical
with 1 : 1 mixtures of 5a, b and DMN, suggesting little interaction
between the aromatic groups in the cyclophanes. The emission
spectra of 5a, b as well as 1 : 1 mixtures of 5a, b and DMN were
observed as a single band with the long wavelength limit of 311 nm:
because of low molar absorptivity of DMN, it appears that the
naphthalene fluorescence contributes little to the spectra of the
mixtures. The shape of emission spectra of 1a,b was virtually
identical to that of DMN showing a peak at 342 nm and a shoulder
at ca. 330 nm, but the emission intensity of 1a,b was 5.4 times
greater than that of DMN at the same concentration. This indicates
that the efficiency of the excitation energy transfer from the
benzodifuran to the naphthalene moiety is almost 100%. The energy
transfer seems to be facilitated by overlapping of the emission band
of the benzodifuran moiety with the 325 nm absorption band of the
naphthalene moiety.
Acknowledgements
This work was supported by a grant from Korea Research
Foundation (2000-015-DP279).
References and notes
1 J. Breitenbach, J. Boosfeld and F. Vögtle, in Comprehensive
Supramolecular Chemistry, Ed. F. Vögtle, Pergamon, New York,
1996, Vol. 2, pp. 29–67.
2 F. Vögtle, Cyclophane Chemistry, Wiley, Chichester, 1993.
3 L. Rene, J.-P. Buisson, R. Royer and D. Averbeck, Eur. J. Med.
Chem., 1977, 12, 31; L. R. Worden, A. W. Burgstahler,
K. D. Kaufman, J. A. Weis and T. K. Schaaf, J. Heterocycl. Chem.,
1969, 6, 191.
314
J. Chem. Soc., Perkin Trans. 1, 2002, 310–314