Synthesis of annularly functionalized cyclophanes

Article abstract of DOI:10.1016/S0040-4020(03)00685-9

Friedel-Crafts reaction of m- and p-benzenedicarboxylic acid chlorides with toluene gave diketones. The dicarbonyl dibromides, obtained by NBS bromination of diketones were coupled with various dithiols and dihydroxy benzenes to give cyclophanes incorpora

Full text of DOI:10.1016/S0040-4020(03)00685-9

Tetrahedron 59 (2003) 5365–5371
Synthesis of annularly functionalized cyclophanes
†
Perumal Rajakumar, Muthialu Srisailas and Rajagopal Kanagalatha
*
Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai 600 025, India
Received 31 July 2002; revised 23 April 2003; accepted 29 April 2003
Abstract—Friedel–Crafts reaction of m- and p-benzenedicarboxylic acid chlorides with toluene gave diketones. The dicarbonyl dibromides,
obtained by NBS bromination of diketones were coupled with various dithiols and dihydroxy benzenes to give cyclophanes incorporating
two carbonyl groups. The dicarbonyl dibromide, derived from isophthalic acid chloride was converted into dithiol, which on coupling with
the same dibromide afforded cyclophane incorporating four carbonyl groups. The NaBH4 reduction of the tetraketone cyclophane in
methanol gave the tetraalcohol derivative. q 2003 Elsevier Science Ltd. All rights reserved.
1. Introduction
2. Results and discussion
Cyclophanes1 are an important class of bridged aromatic
compounds, which have received considerable attention in
recent years due to their ability to form host–guest complex
with neutral molecules as well as ionic species. Synthetic
cyclophanes can mimic enzymes and biological systems.2
Intra-annularly functionalized cyclophanes provide a hydro-
philic cavity to the guest molecules.3 Synthesis of
cyclophanes with 1,10-binaphthol4 cationic pyridino-
phanes,5 benzimidazolophanes6 and benzotriazolophanes7
were some of the earlier reports from our laboratory. Herein,
we report the synthesis of cyclophanes possessing carbonyl
units, which are particularly interesting because the
carbonyl groups can be converted into many synthetically
useful functional groups.
Friedel–Crafts reaction of isophthalic and terephthalic acid
chlorides with toluene in the presence of anhydrous AlCl3
gave diketones 14a and 28 in good yield. Two-fold radical
bromination of diketones 1 and 2 with NBS in CCl4 in the
presence of benzoyl peroxide gave dicarbonyl dibromides
34a and 4 in 75 and 62%, respectively (Scheme 1).
In order to check the synthetic applicability of the
dicarbonyl dibromides for the synthesis of cyclophanes,
dibromide 3 was treated with p-xylenyl dithiol. Treatment
of equimolar amounts of dibromide 3 and p-xylenyl dithiol
in EtOH/benzene under high dilution conditions in nitrogen
at rt for 18 h afforded the cyclophane 5a in 63% yield. The
IR spectrum of cyclophane 5a showed a carbonyl stretching
Scheme 1. Preparation of dicarbonyl dibromides. Reagents and conditions: (a) AlCl3, toluene, 08C, 8 h; (b) 2.2 equiv. NBS, CCl4, Bz2O2, 24 h.
Keywords: isophthalic acid; carbonyl cyclophanes; bromination.
*
†
Corresponding author. Tel.: þ91-44-2351269x213; fax: þ91-44-2353309; e-mail: perumalrajakumar@hotmail.com
Present address: Division of Organic Chemistry (Synthesis), National Chemical Laboratory, Pune 411008, India.
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)00685-9

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revealed that the benzene ring of xylenyl moiety is planar as
shown in the ORTEP diagram (Figs. 2 and 3).
Using the same methodology, coupling of m- and o-xylenyl
dithiols with dibromide 3 gave cyclophanes 5b and 5c in 52
and 55% yield, respectively. Cyclophanes 5b and 5c were
characterized by spectroscopic and analytical data
(Scheme 2).
Attention was then focused on the synthesis of cyclophanes
with ethereal linkages by coupling of m-, p- and
o-dihydroxy benzenes with dibromide 3. Treatment of
equimolar amounts of the dibromide 3 with resorcinol in
acetone in the presence of K2CO3 at rt for 120 h gave
cyclophane 6a in excellent yield (82%). The IR spectrum of
the cyclophane 6a showed a band at 1659 cm21 due to a
carbonyl group. The proton NMR spectrum of the
cyclophane 6a showed a singlet at d 5.20 corresponding to
the benzylic protons. Two doublets were observed at d 7.35
and 7.55. The protons of the isophthaloyl group appeared in
the deshielded region. A doublet of doublets at d 8.23, a
triplet at d 7.68 and a singlet at d 7.51 were observed for the
isophthaloyl group. The resorcinol protons appeared in the
upfield region. A doublet of doublets at d 6.55, a triplet at
7.05 and a triplet at 6.40 were observed. The 13C NMR of
the cyclophane 6a showed signals at d 69.64 for benzylic
carbon and at 195.32 for carbonyl carbon in addition to
eleven aromatic carbons. The cyclophane 6a showed
molecular ion peak at m/z 420 in mass spectrum, which
further supports the proposed structure.
Figure 1. Energy minimized structure of cyclophane 5a.
frequency at 1660 cm21. The 1H NMR spectrum of
cyclophane 5a showed two singlets at d 3.60 and 3.69
corresponding to two benzylic methylene groups. All four
hydrogens of the p-xylene moiety resonate as a singlet at d
6.95, which shows that all the xylenyl protons are
equivalent. Two doublets were observed at d 7.30 and
7.74 in the aromatic region along with a multiplet from d
8.02 to 8.22, which corresponds to the protons of the
isophthaloyl group. The 13C NMR spectrum of cyclophane
5a showed two signals at d 35.18 and 35.70 for methylene
carbons. The carbonyl carbon appeared at d 194.84 along
with ten aromatic carbons. In the mass spectrum, cyclo-
phane 5a showed Mþ at m/z 480, which confirmed the
structure of the cyclophane 5a.
Similarly, equimolar amounts of catechol and hydro-
quinone, when treated individually with an equimolar
amount of the dibromide 3, in the presence of K2CO3 in
acetone, gave cyclophanes 6b and 6c in 52 and 48% yield,
respectively, which were characterized by spectroscopic
and analytical data (Scheme 2).
Energy minimization calculation of the cyclophane 5a by
MOPAC method (Fig. 1) showed that the xylenyl benzene
ring is planar and orthogonal with respect to the isophthalic
acid group. The proof of the structure came from X-ray
crystallographic data. XRD studies9 on cyclophane 5a also
Energy minimization calculations on cyclophane 8 (Fig. 4)
and 9 (Fig. 5) by the MOPAC (PM3) method revealed that
the cavity is large enough to accommodate molecules like
durene (Fig. 6) and TCNE (Fig. 7) and hence it is of interest
to synthesize cyclophane 8 and 9 by taking the advantage of
the favorable angular nature of m-terphenyl. The angular
nature and rigidity of the m-terphenyl provide larger non-
collapsible cavity in cyclophane. Hence, coupling of
m-terphenyl dithiol10 with dicarbonyl dibromides might
result in the formation of cyclophanes with a non-
collapsible larger cavity. Reaction of equimolar amounts
of m-terphenyl dithiol with dibromides 3 and 4 individually,
under high dilution conditions gave the cyclophanes 8 and 9
in 48 and 43% yield, respectively (Scheme 3).
Encouraged by the facile synthesis of cyclophanes by
coupling the dithiols with dibromides, focus was oriented in
the direction of synthesis of cyclophanes with four carbonyl
groups. The reduction of such tetracarbonyl cyclophanes
should result in the formation of the corresponding
tetraalcohol, which would be a potential hexadendate
receptor. For example, cyclophane 12 has four OH groups
and two S atoms and energy minimization calculations show
that the molecule can fold up and create a suitable geometry
for octahedral complexation. The dicarbonyl dithiol 10,
Figure 2. ORTEP diagram of cyclophane 5a.

P. Rajakumar et al. / Tetrahedron 59 (2003) 5365–5371
5367
Figure 3. Unit cell packing of crystal structure of cyclophane 5a.
required for the coupling reactions, was prepared from the
dibromide 3. The thiouronium salt, derived from 3 and
thiourea, on hydrolysis with KOH in THF/H2O gave dithiol
10. Coupling of the dicarbonyl dithiol 10 with dibromide 3
under the usual conditions afforded the novel tetracarbonyl
cyclophane 11 in 48% yield. Reduction of the cyclophane
11 with NaBH4 in methanol at 08C for 1 h gave the
tetraalcohol 12 in 45% yield (Scheme 4).
Scheme 2. Synthesis of cyclophanes by coupling of dicarbonyl dibromides with various dithiols and dihydroxy benzenes. Reagents and conditions: (a) p-, m-,
o-xylenyl dithiol, KOH, EtOH, benzene, rt, 18 h; (b) resorcinol/catacol and/hydroquinone, K2CO3, acetone, rt, 120 h.

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P. Rajakumar et al. / Tetrahedron 59 (2003) 5365–5371
Figure 4. Energy minimized structure of cyclophane 8.
Figure 6. Structure of complex of cyclophane 8 with durene.
spectra of the CT complexes of cyclophanes 6a–c with
TCNE show two absorbance maxima at 416 and 398 nm. A
plot of Do/A against 1/Ao was linear. From slope and
intercept, the Ka values were determined using Benesi–
Hildebrand method.11 The Ka was found to be 59, 44 and
47 M21 for CT complexes of cyclophanes 6a-c with TCNE,
respectively.
3. Energy minimization calculations and complexation
studies
Energy minimization calculations based on PM3 by
MOPAC were performed for cyclophanes 8 and 9. The
heat of formation of cyclophanes 8 and 9 are found to be
362.34 and 361.09 kJ, respectively. The cavity sizes of
cyclophane 8 and 9 are approximately 7.5£13 and
˚
8£13.5 A, respectively and can easily form complexes
with small molecules like TCNE, TCNQ, mesitylene and
durene. Steric energies based on MM2 energy minimization
for complexes of cyclophane 8 with TCNE, TCNQ,
mesitylene and durene are 19.27, 2.46, 27.77 and
215.74 kJ which indicates that durene can form the
strongest complex with cyclophane 8.
4. Conclusion
In conclusion, we have developed a simple synthetic route
for cyclophanes incorporating carbonyl units. The main
advantage of carbonyl functionality is that it can be reduced
to alcohol, hence, hydrophilic cavity could be generated and
complexing ability of the cyclophane could be increased. In
fact, we have reduced cyclophane 11 with NaBH4 and the
resulting tetraalcohol has been characterized. Complexation
of cyclophane 11 with various metal ions and other guest
molecules are under investigation.
The heat of formation of cyclophanes 11 and 12 are 212.66
and 250.13 kJ, respectively and energy minimization
calculations by MOPAC (PM3) methods indicate that
cyclophane 12 folds up and creates an favorable cavity for
octahedral complexation.
Complexation studies were carried out in CH3CN/CHCl3
(1:4) for cyclophanes 6a–c with TCNE. The UV–visible
Figure 7. Structure of complex of cyclophane 8 with TCNE.
Figure 5. Energy minimized structure of cyclophane 9.

P. Rajakumar et al. / Tetrahedron 59 (2003) 5365–5371
5369
Scheme 3. Synthesis of cyclophanes with larger cavity. Reagents and conditions: (a) 3/4, KOH, EtOH, benzene, rt, 18 h.
Scheme 4. Synthesis of tetracarbonyl cyclophane and its reduction to tetraalcohol cyclophane. Reagents and conditions: (a) thiourea, THF, 608C, 12 h, 92%;
(b) KOH, THF, H2O, reflux, 12 h, 69%; (c) KOH, EtOH, benzene, rt, 24 h, 48%; (d) NaBH4, MeOH, 08C, 1 h, 45%.
5. Experimental
dibenzoylbenzene (4) were prepared by two fold radical
bromination of 1 and 2 using NBS.
5.1. General
5.1.1. Dibromide 4. Dibromide 4 was obtained by the
radical bromination of 2 with 2 equiv. of NBS using similar
procedures reported earlier.4a Yield 62%; mp 138–1398C
All melting points are uncorrected. The IR spectra were
recorded using Shimadzu FT-IR 8300 Infrared
Spectrometer. The 1H and 13C NMR spectra were recorded
on Jeol GSX 400 NMR Spectrometer at 400 and
100.4 MHz, respectively or on a Varian EM 390 NMR
spectrophotometer at 90 MHz with TMS as internal
standard. The mass spectra were recorded using Jeol mass
spectrometer (EI, 70 eV). THF was freshly distilled from
Na/benzophenone ketyl before use. The xylenyl dithiols
were prepared by the known literature procedure. The
column chromatography was performed using silica gel
(Acme, 100–200 mesh). The organic extracts were dried
using anhydrous sodium sulfate. 1,3-Ditoluoylbenzene (14a)
and 1,4-Ditoluoylbenzene (28) were prepared according to
the literature procedure. 4,400-Bis(bromomethyl)-1,3-
dibenzoylbenzene (34a) and 4,400-Bis(bromomethyl)-1,4-
1
(from CHCl3þhexane); IR (cm21) 1657 (CvO); H NMR
(CDCl3) 4.65 (S, 4H);7.52 (d, 4H, J¼8.3 Hz); 7.80 (d, 4H,
J¼8.3 Hz); 8.10 (S, 4H); 13C NMR (CDCl3) 34.83, 125.56,
127.78, 137.87, 144.89, 197.37. Anal. calcd for
C22H16Br2O2: C, 55; H, 3.42, found: 55.61; H, 3.25.
5.2. General procedure for assembling cyclophanes from
the corresponding dibromides and dithiols
A solution containing equimolar amounts (1 mmol) of the
appropriate dibromide and the dithiol in nitrogen degassed
benzene (200 mL) was added dropwise over 8–10 h to a
well stirred solution of KOH (0.2 g) in 95% ethanol
(600 mL). After the addition, the reaction mixture was

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P. Rajakumar et al. / Tetrahedron 59 (2003) 5365–5371
stirred for an additional 8 h and evaporated to dryness. The
crude product was purified over SiO2 by column chroma-
tography using CHCl3/hexane (1:1).
5.3.2. Cyclophane 6b. Colourless solid; yield 52%; mp
1
191–1938C; IR (cm21) 1658 (CvO); H NMR (CDCl3)
5.22 (s, 4H); 6.82–6.96 (m, 4H); 7.15 (d, 4H, J¼8.3 Hz);
7.58 (s, 1H); 7.76 (d, 4H, J¼8.3 Hz); 8.26 (m, 3H); 13C
NMR (CDCl3) 68.94, 105.19, 111.01, 127.43, 129.61,
129.92, 130.15, 133.55, 135.43, 136.69, 141.41, 158.74,
195.05; m/z 420 (60, Mþ), 364 (74), 347 (41), 312 (47), 256
(32), 223 (31), 119 (100), 91 (53). Anal. calcd for C28H20O4:
C, 79.98; H, 4.79. Found: C, 79.90, H, 4.73.
5.2.1. Cyclophane 5a. Colourless solid; yield 63%; mp
1
214–2158C; IR (cm21) 1660 (CvO); H NMR (CDCl3)
3.60 (s, 4H); 3.69 (s, 4H); 6.95 (s, 4H), 7.30 (d, 4H,
J¼8.3 Hz); 7.74 (d, 4H, J¼8.3 Hz); 8.20–8.22 (m, 4H); 13C
NMR (CDCl3) 35.18, 35.70, 129.08, 130.10, 130.29,
132.16, 133.31, 135.29, 136.73, 137.09, 141.23, 143.86,
194.84; m/z 480 (89, Mþ), 314 (62), 141 (55), 137 (57),
135 (66), 134 (70), 105 (70), 91 (80). Anal. calcd
for C30H24O2S2: C, 74.97; H, 5.03. Found: C, 74.91, H,
5.01.
5.3.3. Cyclophane 6c. Colourless solid; yield 48%; mp
1
194–1958C; IR (cm21) 1653 (CvO); H NMR (CDCl3)
5.16 (s, 4H); 6.67 (s, 4H); 7.19 (d, 4H, J¼8.3 Hz); 7.55 (d,
4H, J¼8.3 Hz); 7.80 (t, 1H, J¼7.8 Hz), 7.92 (d, 1H,
J¼7.8 Hz); 8.27 (s, 1H); 13C NMR (CDCl3) 69.64,
105.19, 110.32, 128.36, 129.87, 131.24, 133.75, 135.41,
136.73, 141.72, 158.54, 195.43; m/z 420 (88, Mþ), 327 (28),
312 (100), 284 (34), 256 (44), 156 (35), 131 (35), 119 (64),
90 (69). Anal. calcd for C28H20O4: C, 79.98; H, 4.79. Found:
C, 79.89; H, 4.66.
5.2.2. Cyclophane 5b. Colourless solid; yield 52%; mp
1
184–1858C; IR (cm21) 1653 (CvO); H NMR (CDCl3)
3.44 (s, 4H); 3.66 (s, 4H); 6.46 (s, 1H); 7.29 (d, 2H,
J¼4 Hz); 7.47 (d, 4H, J¼8.3 Hz); 7.62 (s, 1H); 7.83 (d, 4H,
J¼8.3 Hz); 8.01 (s, 1H); 8.23 (d, 2H, J¼4 Hz); 8.33 (s, 1H);
13C NMR (CDCl3) 35.28, 35.71, 128.21, 129.09, 130.21,
131.22, 132.46, 133.41, 135.29, 136.02, 136.37, 137.09,
141.31, 143.66, 195.38; m/z 480 (91, Mþ), 314 (49), 136
(65), 134 (60), 104 (100), 91 (70), 90 (41). Anal. calcd for
C30H24O2S2: C, 74.97; H, 5.03. Found: C, 74.87, 5.00.
5.4. General procedure for assembling cyclophanes from
m-terphenyl dithiol
A solution containing equimolar amounts (1 mmol) of the
appropriate dibromide and m-terphenyl dithiol in nitrogen
degassed benzene (200 mL) was added dropwise over
8–10 h to a well stirred solution of KOH (0.2 g) in 95%
ethanol (600 mL). After the addition, the reaction mixture
was stirred for an additional 8 h and evaporated to dryness.
The crude product was purified over SiO2 by column
chromatography using CHCl3/hexane (2:1).
5.2.3. Cyclophane 5c. Colourless solid; yield 55%; mp
1
202–2058C; IR (cm21) 1643 (CvO); H NMR (CDCl3)
3.56 (s, 4H); 3.77 (s, 4H); 7.38 (d, 4H, J¼8.3 Hz); 7.72 (d,
4H, J¼8.3 Hz); 8.23 (m, 8H); 13C NMR (CDCl3) 35.13,
35.67, 128.77, 129.23, 131.05, 131.29, 132.14, 133.54,
135.32, 136.73, 137.54, 141.04, 143.66, 195.34; m/z
480 (47, Mþ), 136 (51), 135 (100), 90 (34), 69 (53). Anal.
calcd for C30H24O2S2: C, 74.97; H, 5.03. Found: 74.92,
4.98.
5.4.1. Cyclophane 8. Colourless solid; yield 48%; mp 203–
2048C; IR (cm21) 1656 (CvO); 1H NMR (CDCl3) 3.69 (s,
4H), 3.71 (s, 4H), 7.06–7.97 (m, 24H); 13C NMR (CDCl3)
35.42, 37.27, 119.54, 125.77, 126.03, 126.51, 126.73,
127.31, 128.77, 129.11, 129.45, 129.71, 130.43, 136.96,
137.91, 139.92, 141.22, 143.97, 195.24; m/z 632 (20, Mþ),
376 (54), 312 (47), 256 (41), 223 (17), 119 (100), 91 (35).
Anal. calcd for C42H32O2S2: C, 79.71; H, 5.10. Found: C,
79.84; 4.99.
5.3. General procedure for assembling of cyclophanes
from the corresponding dibromide and dihydroxy
benzenes
To a solution of the appropriate dibromide (1 mmol) and the
respective dihydroxy benzene (1 mmol) in acetone
(600 mL) was added anhydrous K2CO3 (7.0 g) and the
mixture was stirred well at rt for 120 h. The reaction mixture
was then filtered and evaporated to give a residue, which
was extracted with CH2Cl2 (3£100 mL), washed with water
(2£100 mL), then with NaOH (2£100 mL, 10%), again with
water (2£100 mL), finally with brine (200 mL) and dried.
Evaporation of the organic layer afforded the crude product,
which was purified over SiO2 by column chromatography
using CHCl3/hexane (1:1).
5.4.2. Cyclophane 9. Colourless solid; yield 43%; mp 192–
1948C; IR (cm21) 1660 (CvO); 1H NMR (CDCl3) 3.69 (s,
4H), 3.73 (s, 4H), 7.12–8.02 (m, 24H); 13C NMR (CDCl3)
36.75, 37.12, 119.48, 125.74, 126.31, 126.63, 127.37,
128.54, 129.51, 129.65, 129.71, 130.87, 136.72, 138.94,
139.07, 141.52, 143.79, 195.35; m/z 632 (17, Mþ), 376 (45),
320 (23), 312 (56), 256 (63), 223 (27), 119 (100), 91 (54).
Anal. calcd for C42H32O2S2: C, 79.71; H, 5.10. Found: C,
79.62; H, 5.22.
5.3.1. Cyclophane 6a. Colourless solid; yield 82%; mp
1
190–1918C; IR (cm21) 1659 (CvO); H NMR (CDCl3)
5.4.3. Synthesis of dithiol 10. A stirred solution of
dibromide 3 (10 mmol) and thiourea (22 mmol) in THF
(40 mL) was heated at reflux for 12 h. The mixture was
cooled, and the precipitated thiouronium salt was filtered
and dried. The salt was dissolved in H2O/THF (120 mL)
under nitrogen and KOH (1.0 g) was added. The reaction
mixture was refluxed under nitrogen for 12 h, cooled and
carefully quenched with a minimum amount of dil. HCl
(4 M, 40 mL). The solvent was removed in vacuo and
the crude product was purified over SiO2 by column
5.20 (s, 4H); 6.40 (t, 1H, J¼4 Hz), 6.55 (dd, 2H, J¼8.8,
1.95 Hz); 7.05 (t, 1H, J¼7.8 Hz); 7.35 (d, 4H, J¼8.3 Hz);
7.51 (s, 1H); 7.55 (d, 4H, J¼8.3 Hz); 7.68 (t, 1H, J¼7.8 Hz);
8.23 (dd, 2H, J¼8.8, 1.95 Hz); 13C NMR (CDCl3) 69.64,
104.99, 110.41, 127.33, 129.60, 129.99, 130.25, 133.54,
135.11, 136.29, 136.87, 141.71, 158.66, 195.32; m/z 420
(100, Mþ), 392 (24), 256 (9), 197 (20), 165 (14), 156 (23),
119 (25), 90 (30). Anal. calcd for C28H20O4: C, 79.98; H,
4.79. Found: C, 79.85; 4.63.

P. Rajakumar et al. / Tetrahedron 59 (2003) 5365–5371
5371
chromatography using CHCl3/hexane (1:2) to give dithiol
10 as a colourless solid; yield 69%; mp 140–1428C; IR
(cm21) 1660 (CvO); 1H NMR (CDCl3) 1.72 (t, 2H,
J¼8.8 Hz); 3.68 (d, 4H, J¼8.8 Hz); 7.31 (d, 4H, J¼8.3 Hz);
7.48 (s, 1H); 7.65 (d, 4H, J¼8.3 Hz); 7.84 (d, 2H, J¼4 Hz);
8.06 (s, 1H). Anal. calcd for C22H18O2S2 (378.07): C, 69.81;
4.79. Found: C, 69.66; H, 4.82.
authors thank UGC, New Delhi for the financial assistance
(SAP III) to the department, RSIC, IIT Madras for NMR
spectra and Mrs K. Krishnaveni for recording mass spectra.
References
5.4.4. Cyclophane 11. Treatment of equimolar amounts of
dibromide 3 (1 mmol) with dithiol 10 (1 mmol) as described
above for assembling cyclophanes from dithiols, followed
by column purification of the crude product over SiO2 using
CHCl3/hexane (3:1) afforded tetraketone cyclophane 11 as
¨
1. For reviews and some examples, see: (a) Vogtle, F.
Cyclophane Chemistry; Wiley: New York, 1993. (b) In
Cyclophanes; Diederich, F., Ed.; The Royal Society of
Chemistry: Cambridge, 1991. (c) Weber, E. Top. Curr.
Chem. 1994, 172, 1–202. (d) In Inclusion Compounds;
Atwood, J. L., Davies, J. E. D., MacNicol, D. D., Eds.;
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2. (a) Habicher, T.; Diederich, F.; Gramlich, V. Helv. Chim. Acta
1999, 82, 1066–1095. (b) Marti, T.; Peterson, B. R.; Furer, A.;
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Chim. Acta 1998, 81, 109–144. (c) Mattei, P.; Diederich, F.
Helv. Chim. Acta 1997, 80, 1555–1588.
colourless solid; yield 48%; mp 203–2058C; IR (cm21
)
1
1656 (CvO); H NMR (CDCl3) 3.68 (s, 8H); 7.29 (d, 8H,
J¼8.3 Hz); 7.47 (d, 8H, J¼8.3 Hz); 7.78–7.99 (m, 6H);
8.17 (s, 2H); 13C NMR (CDCl3): 35.44, 127.24, 128.94,
129.07, 130.44, 133.37, 136.02, 137.86, 144.03, 195.52; m/z
688 (12, Mþ), 376 (29), 312 (37), 226 (14), 119 (100), 91
(45). Anal. calcd for C44H32O4S2: C, 76.72; H, 4.68. Found:
C, 76.53; H, 4.54.
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J. Org. Chem. 1996, 61, 5090–5102. (b) Hart, H. Pure Appl.
Chem. 1993, 65, 27–34.
5.4.5. Reduction of cyclophane 11. A solution of
cyclophane 11 (0.032 g, 0.5 mmol) in methanol (20 mL)
was treated with NaBH4 (0.040 g, 1 mmol) at 08C for 1 h.
The reaction mixture was stirred at rt for further 6 h, after
which dil. HCl (4 M, 2 mL) was added. The precipitate
formed was filtered off and the filtrate was evaporated to
dryness in vacuo to give a residue, which was purified over
SiO2 using column chromatography using CHCl3/hexane
(3:1) to give cyclophane 12 as colourless solid; yield 45%;
4. (a) Rajakumar, P.; Srisailas, M. Tetrahedron 2001, 57,
9749–9754. (b) Rajakumar, P.; Srisailas, M. Tetrahedron
Lett. 2002, 43, 1909–1913. (c) Rajakumar, P.; Srisailas, M.
Tetrahedron 2003, 59, 5373.
5. Rajakumar, P.; Dhanasekaran, M. Tetrahedron 2002, 58,
1355–1359.
1
6. Rajakumar, P.; Murali, V. Tetrahedron 2000, 56, 7995–7999.
7. Rajakumar, P.; Srisailas, M. Tetrahedron Lett. 1997, 38,
5323–5326.
mp 224–2268C; IR (cm21) 3340 (OH); H NMR (CDCl3)
3.47 (s, 8H); 4.40 (bs, 4H, exchanged with D2O); 7.17–7.78
(m, 24H); 13C NMR (CDCl3) 34.32, 68.02, 117.21, 123.58,
127.05, 129.74, 131.27, 133.25, 134.86, 136.08; m/z 696 (8,
Mþ), 378 (14), 315 (17), 271 (11) 208, (9), 118 (30), 105
(100), 89 (22), 77 (36). Anal. calcd for C44H40O4S2: C,
75.83; H, 5.79. Found: C, 75.68; H, 5.61.
8. Ishiyama, T.; Kizaki, H.; Hayashi, T.; Suzuki, A.; Miyaura, N.
J. Org. Chem. 2001, 63, 4726–4731.
9. XRD studies were carried out by different research group and
crystal parameters will be communicated in due course by the
other authors.
10. Hart, H.; Rajakumar, P. Tetrahedron 1995, 51, 1313–1336.
11. Benesi, H. A.; Hildebrand, J. H. J. Am. Chem. Soc. 1949, 71,
2703–2707.
Acknowledgements
M. S. thanks CSIR, New Delhi for financial assistance. The