Functionalized calix[4]resorcinarene cavitands. Versatile platforms for the modular construction of extended molecular switches

Article abstract of DOI:10.1246/bcsj.79.1926

We report the synthesis and investigation of the vase-kite conformational switching of bridged calix[4]resorcinarene-based cavitands bearing iodo or ethynyl substituents on the upper rim of the cavity. These reactive centers make the cavitands versatile p

Full text of DOI:10.1246/bcsj.79.1926

1926 Bull. Chem. Soc. Jpn. Vol. 79, No. 12, 1926–1940 (2006)
ꢀ 2006 The Chemical Society of Japan
Functionalized Calix[4]resorcinarene Cavitands. Versatile Platforms
for the Modular Construction of Extended Molecular Switches
ꢀ
Vladimir A. Azov, Anna Schlegel, and Franc¸ois Diederich
Laboratorium fur Organische Chemie, Department of Chemistry and Applied Biosciences,
¨
ETH Zurich, Honggerberg, HCI, CH-8093 Zurich, Switzerland
¨
¨
Received April 20, 2006; E-mail: diederich@org.chem.ethz.ch
We report the synthesis and investigation of the vase–kite conformational switching of bridged calix[4]resorcinar-
ene-based cavitands bearing iodo or ethynyl substituents on the upper rim of the cavity. These reactive centers make the
cavitands versatile platforms for further modular extension by means of Sonogashira cross-couplings, thereby enabling
the construction of diverse functional architectures that are switchable between two highly restricted conformations and
that undergo geometrically defined expansions/contractions on the multi-nanometer scale. This is illustrated by attach-
ment of oligo(phenyleneethynyl) fragments, bearing terminal donor and acceptor BODIPY (dipyrrometheneboron
difluoride) dyes, to a diiodo-substituted cavitand. The multi-nanometer-sized switching motion between the expanded
1
kite and the contracted vase states, induced by temperature or pH changes, was proven by H NMR spectroscopy and
FRET (fluorescence resonance energy transfer) measurements. The cavitand system, with its modular construction
scheme, holds promise to become a general tool for controlled on/off switching of excimer and exciplex formation,
PET (photoinduced electron-transfer), or other processes and for investigating the distance dependence of the underlying
intermolecular interactions.
The design and preparation of molecular devices capable of
large reversible mechanical movements have become a hot
area of research in recent years.1 These structures, mimicking
natural phenomena, such as muscle contraction/expansion,
bear significant potential for nano-construction, nano-manipu-
lation, design of molecular machines and electron-transfer
devices, and information storage. Large motions between bi-
stable states with considerably different geometries, triggered
electrochemically or in ionic reactions, have led to remark-
able long-range shuffling,2,3 contraction/expansion,4 coiling/
uncoiling,5 and shape-flipping in molecular and supramolecu-
lar systems.6–8 On the other hand, the conformational space of
the contracted and expanded states in most of the reported sys-
tems is quite large, generating substantial uncertainties about
the actual geometric orientation of the moving molecular and
supramolecular components. This observation led to our inter-
est in the development of large-scale molecular switching sys-
tems in which both states adopt precisely defined, rigid geome-
tries.9
such as trifluoroacetic acid (TFA), or ZnII ions. The tempera-
ture dependence of the vase–kite equilibrium is caused by sol-
vation effects:10,14 at low temperatures, solvation of the larger,
solvent-exposed surface favors the kite conformer whereas at
higher temperature, the entropic term TꢀSsolv for solvation
of the larger kite surface becomes unfavorable and the vase
conformation predominates. The driving force for vase ! kite
switching at low pH presumably is the protonation of the
mildly basic quinoxaline N-atoms, which leads to repulsive
Coulombic interactions leading to the opening of the vase con-
formation. The switching process is conveniently monitored
by 1H NMR spectroscopy since the chemical shift of the
methine H-atoms in the octol bowl is highly conformation-
dependent.10 In the vase conformation, the methine protons
appear at ꢀ ꢃ 5:6 ppm whereas they appear in the kite confor-
mation at about ꢀ ꢃ 3:7 ppm.
Extension of the wall components15 increases the distance
between their termini in the kite but not in the vase confor-
mation, leading to molecular switching between geometries
of increasingly different extensions. In a general modular
approach, we chose to prepare cavitands 2 and 3 featuring dif-
ferently sized, rigid oligo(phenyleneethynyl) arms attached to
the two N-arylated diazaphthalimide cavity wall flaps in anti
(2) and syn (3) position (Fig. 2). The rigid attachment of the
rod-like arms ensures that the conformational space in the ex-
tended kite conformation remains highly restricted and the
separation of their termini (R1 and R2 in Fig. 2) well defined.
This way, it should be possible to switch the interplanar dis-
tance of terminal chromophores between ca. 0.8 nm (vase) and
ca. (3:0 þ 2r) nm (kite, with r the distance between the termini
and the arylimide anchor) as illustrated in Fig. 2. Such a mod-
ular system promises to become a general tool for controlled
Quinoxaline-bridged calix[4]resorcinarene cavitand
1
(Fig. 1), introduced by Cram and co-workers,10 adopts two
conformations with profoundly different geometries: a closed
vase conformation (C4v symmetry), with a distance of about
0.8 nm between opposite quinoxaline flaps featuring a hydro-
phobic cavity suitable for guest encapsulation,11 and an open
kite conformation (C2v symmetry) with a flat, extended surface
approximately 1:25 ꢁ 1:8 nm in size. Fully reversible switch-
ing from the vase to the kite conformation occurs upon varia-
tion of temperature10 or pH,12 as well as upon metal ion addi-
tion.13 The vase conformer is prevalent at neutral pH at or
above room temperature, whereas the kite conformer is pre-
dominant at temperatures ꢂ 213 K, or upon addition of acid,
Published on the web December 13, 2006; doi:10.1246/bcsj.79.1926

V. A. Azov et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 12 (2006) 1927
1.8 nm
0.8 nm
N
N
N
N
N
N
O
O
O
O
O
O
N
O
N
N
N
N
N
O
O
O
O
O
O
R
R
R
R
R
R
R
∆T, ∆pH
1.25 nm
R
O
N
N
O
O
N
N
1
Vase (C4v)
Kite (C2v)
R = alkyl chains
Fig. 1. Vase–kite switching of the quinoxaline-bridged calix[4]resorcinarene cavitand 1.
a)
R1
R1
X
X
O
N
O
N
N
N
N
N
O
O
O
O
O
N
N
N
O
N
N
N
R = alkyl legs,
O
O
O
O
O
O
R1, R2: chromophores,
R
R
R
R
R
R
R
R
O
O
X=
N
O
N
O
O
O
O
O
N
N
O
N
O
N
N
N
X
X
2
3
R2
R2
b)
0.8 nm
R1
R2
X
(3.0 +2r) nm
X
N
r
r
N
R2
R1
O
O
X
O
O
X
O
O
N
O
O
N
O
O
N
N
N
N
N
N
N
N
O
N
O
N
O
O
N
N
N
O
N
O
O
O
O
O
O
O
O
N
N
O
3.0 nm
Kite
Vase
Fig. 2. a) Differentially bridged cavitands bearing oligo(phenyleneethynyl) arms with terminal chromophores R1 and R2 in anti
(2) and syn (3) orientation. b) Distances between terminal chromophores (R1 ¼ R2) in the vase and kite conformations of anti-
substituted cavitand 2. Legs are omitted for reasons of clarity.
on/off switching of processes, such as excimer and exciplex
formation, or photoinduced electron-transfer (PET), and for
investigating the distance dependence of the underlying inter-
molecular interactions. This is illustrated by attachment of
terminal donor and acceptor BODIPY (dipyrrometheneboron
difluoride) dyes leading to fluorescence resonance energy
transfer (FRET)16 that is strongly dependent on the conforma-
tional state of the system.9
enes have been reported with different moieties substituting
one or two of the quinoxaline rings in the parent cavitand
structure 1.11c,15,17–19 For the preparation of monoalkynylated
cavitand 4, TMS-protected 4-ethynylaniline 520 was condensed
with 5,6-dichloropyrazine-2,3-dicarboxylic anhydride 6 to
give imide 7 (Scheme 1). Tris-quinoxaline-cavitand 811c was
subsequently bridged with imide 7 under standard conditions
(K2CO3/Me2SO, 20 ꢄC) to yield macrocycle 9 in 62% yield.
Unfortunately, all efforts to deprotect the terminal alkyne (n-
Results and Discussion
Bu4NF, CsF, K2CO3, or borax (Na2B4O7 10H2O) in THF or
MeOH/THF) to form cavitand 4 were unsuccessful and only
polar decomposition products were detected by thin-layer
ꢅ
Synthesis of Monoethynylated Cavitands. A variety of
modifications of the cavity walls in bridged calix[4]resorcinar-

1928 Bull. Chem. Soc. Jpn. Vol. 79, No. 12 (2006)
Modified Calix[4]resorcinarene Cavitands
O
O
Cl
Cl
N
N
Cl
Cl
N
N
a
O
N
SiMe3
H2N
SiMe3
+
O
O
5
7
6
R1
O
N
N
N
N
N
N
N
O
O
O
OH
O
N
N
O
O
O
O
O
OH
O
R
R
R
R
R
b
R
R
R
7
R = n-C6H13
O
N
N
N
N
O
O
O
O
N
N
8
9 R1 = SiMe3
4 R1 = H
Br
O
N
N
N
O
O
O
N
N
O
O
O
O
Cl
Cl
N
N
a
b
R
R
N
Br
H2N
Br
8
6
R
R
O
O
N
N
11
10
O
O
N
N
12
Scheme 1. Synthesis of monofunctionalized cavitands. (a) THF, 30 min, 40 ꢄC; then (COCl)2, Py, 50 ꢄC, 16 h; 71% (6), 88% (10).
(b) K2CO3, Me2SO, 16 h, 62% (9), 80% (12). THF = tetrahydrofuran, Py = pyridine.
chromatography (TLC). We have previously observed, that
this class of cavitands is quite sensitive to nucleophilic attack
(F, HO, MeO), leading to cleavage of the ether bridges be-
tween the quinoxaline moieties and the octol base scaffold to
open the rather strained 9-membered rings. In addition, phthal-
imides and, even more so the diaza derivatives used in this
synthesis, are readily ring-opened in the presence of base un-
der very mild conditions, as we had noted in another report.21
To stabilize the labile imide moiety and also to enhance the
solubility of these derivatives, we prepared a 5,6-dichloropyra-
zine-2,3-dicarboximide 10 with methyl substituents ortho to
the N-aryl bond, starting from a commercial aniline 11. From
We therefore changed from the bromide to the more reac-
tive iodide or, alternatively, directly introduced a terminal
alkyne (Scheme 2). For this purpose, iodide 13 was converted
on one hand into iodoimide 14 and, on the other, via com-
pound 15, into ethynylated imide 16. Bridging cavitand 8 with
the two imides subsequently provided the desired functional-
ized cavitands 17 and 18 in 74 and 88% yield, respectively.
Synthesis of Dialkynylated Cavitands. The anti-di-quin-
oxaline-bridged25 and syn-di-quinoxaline-bridged15b calix[4]-
resorcinarenes 19 and 20 were bridged (K2CO3/Me2SO) with
dichloroimides 14 and 16 to give the terminally diiodinated
(21 and 23) and ethynylated (22 and 24) cavitands, respec-
tively, which are ideal scaffolds for further attachment of
rigid arms, such as oligo(phenyleneethynyl) moieties, by
Sonogashira cross-coupling (Scheme 3).
ꢀ
density functional theory calculations (B3LYP/6-31G ),22 the
torsional angle between the planes of the imide and the N-aryl
ring would change from ca. 0ꢄ in the N-phenylated to ca. 70ꢄ
in the 2,6-dimethylphenylated derivative. In this orientation,
the Burgi–Dunitz approach angle for nucleophilic attack at
¨
the imide carbonyls is sterically disfavored.23
Bridging diol 8 with dichloroimide 10 provided cavitand 12
in 80% yield. 1H NMR studies showed that cavitand 12 under-
went reversible temperature- or pH-triggered vase–kite switch-
ing similar to the tetraquinoxaline derivative 1. On the other
hand, Sonogashira cross-coupling24 of cavitand 12 with 1-
ethynyl-4-nitrobenzene did not proceed cleanly; the product
mixture contained ca. 40% of inseparable starting material
even after prolonged reaction times.
All of the new cavitands undergo the vase–kite switching in
both temperature- and pH-triggered modes. Interestingly, they
displayed a higher preference for the kite conformation than
the parent cavitand 1.14a In variable-temperature (VT) 1H NMR
runs, complete conversion of monosubstituted cavitands 17 and
1
18 into the vase form (all multiplets in the H NMR spectrum
are resolved) occurred at ca. 310 K in CD2Cl2, whereas the
equilibration of disubstituted cavitands 21–24 was only com-
pleted at ca. 330 K in CD2Cl2 (sealed tube). All structures
switched to the kite form at ca. 210 K; at that temperature, in
the NMR spectra no residual vase conformer was observed.

V. A. Azov et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 12 (2006) 1929
O
Cl
Cl
N
N
N
I
a
b
O
14
H2N
I
O
13
Cl
Cl
N
N
c, a
N
H
H2N
SiMe3
O
15
16
R1
O
N
N
N
N
O
OH
O
O
O
N
N
N
N
O
O
O
OH
O
O
O
d
R
R
R
R
R
14 or 16
R
R
R
O
N
N
N
O
O
O
O
N
N
N
N
17 R1 = I
18 R1 =
8
R = n-C6H13
H
Scheme 2. Synthesis of monofunctionalized cavitands for acetylenic scaffolding. (a) Compound 6, THF, 30 min, 40 ꢄC; then
(COCl)2, Py, 50 ꢄC, 16 h; 91% (14), 64% (16). (b) Me3Si–CꢆCH, [Pd(PPh3)4], CuI, piperidine, 16 h; 100%. (c) NaOH, THF/
MeOH 2:1, 3 h; 89%. (d) K2CO3, Me2SO, 16 h; 74% (17), 88% (18).
substitution (1), to monosubstituted (17 and 18), and to disub-
stituted (21–24) cavitands. This trend could arise from two
solvation effects acting into the same direction: (i) The kite
form becomes increasingly stabilized when a larger surface is
favorably solvated. Cram and co-workers explained the prefer-
ence for the kite geometry at low temperatures with better sol-
vation of the larger surface as compared to the vase surface.10
(ii) The methyl groups of the 2,6-dimethylphenyl groups at-
tached to the imide moieties sterically prevent favorable solva-
tion of the vase cavity, hence, destabilizing this conformation.14
N
N
O
O
OH
OH
N
N
N
O
O
O
OH
OH
OH
O
R
R
R
R
R
R
R
R
HO
N
OH
O
O
HO
N
N
19
20
a or b
a or b
R1
R1
1
Low-temperature H NMR spectra of the syn-disubstituted
O
O
cavitand 24 allowed for the first time the clear observation
of the kite1–kite2 equilibration between two non-degenerate
structures (Fig. 3). At 203 K, the resonance of the methine pro-
tons in the octol base is clearly split, and the signals between
3.4 and 3.8 ppm correspond to four protons in different chemi-
cal environments. This splitting is explained by the presence
of the two slowly exchanging kite conformations (Fig. 4). At
253 K, the kite1–kite2 conformational equilibration becomes
fast, which, together with vase–kite equilibration on the NMR
time scale, leads to the disappearance of the methine reso-
nances in the spectrum, due to strong broadening. Finally at
333 K, two resolved triplets around 5.5 ppm are observed for
the two sets of methine protons that are in different chemical
environments in the vase form. The slow exchange of two kite
conformations at 203 K is also visible in the complexity of the
aromatic resonances, i.e., the aromatic proton in the octol base,
that points towards the hexyl legs, appears in the form of three
broad signals around 6.4 ppm. Furthermore at 203 K, two
ethynyl resonances appear near 3.2 ppm with the ratio between
the two kite conformations of 1:2.3. By means of iterative line-
N
N
N
O
N
N
N
O
O
O
O
O
O
N
N
N
N
N
O
O
O
O
O
O
R
R
R
R
3
2
2''
3''
R
R
2
3
R
2'
3'
R
O
O
1
1'
1
1'
N
N
N
O
O
O
N
O
O
O
N
N
N
N
N
O
R1
R1
21 R1 = I
22 R1 =
23 R1 = I
24 R1 =
H
H
R = n-C6H13
Scheme 3. Synthesis of terminally diiodinated and diethyn-
ylated cavitands. (a) Compound 14, K2CO3, Me2SO,
16–36 h; 38% (21), 70% (23). (b) Compound 16, K2CO3,
Me2SO, 16–36 h; 55% (22), 60% (24).
All cavitands completely switched to the kite geometry upon
addition of TFA, and this process was reversible upon addition
of base (K2CO3). A clear trend becomes apparent: the kite
geometry becomes more stable upon changing from no wall

1930 Bull. Chem. Soc. Jpn. Vol. 79, No. 12 (2006)
Modified Calix[4]resorcinarene Cavitands
Fig. 3. 1H NMR spectra (CD2Cl2, sealed tube) of cavitand 24 at 333 K (a), 253 K (b), and 203 K (c), showing the transition from the
vase (a) to two slowly equilibrating, non-degenerate kite conformations. For peak assignments, see Scheme 3. Resonance 4
belongs to the ethyne protons. Resonances at 5.32 ppm belong to residual dichloromethane.
H
O
N
N
H
O
O
N
N
N
N
N
N
N
N
O
O
O
O
O
O
O
N
N
N
O
O
O
O
O
O
O
O
R
R
R
R
R
R
R
R
N
O
O
O
N
N
N
24
N
O
N
O
O
Kite 1
Kite 2
H
N
R = n-C6H13
H
H
O
N
N
N
N
N
O
O
O
O
N
N
N
O
O
O
O
R
R
R
R
N
O
O
N
22
O
H
Fig. 4. Conformational switching of cavitand 24 between two non-degenerate kite conformers. As a contrast, the structure of the
kite conformer of cavitand 22 is also shown.

V. A. Azov et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 12 (2006) 1931
Fig. 5. 1H NMR spectra (CD2Cl2, sealed tube) of cavitand 22 at 333 K (a), 253 K (b), and 203 K (c), showing the transition from the
vase to two degenerate kite conformations. For peak assignment see Scheme 3. Resonance 4 belongs to ethyne protons. Reso-
nances at 5.32 and 7.26 ppm belong to residual dichloromethane and trichloromethane, respectively.
shape calculations (see the Experimental Section for details),
the activation parameters for the kite1–kite2 equilibration of
N
O
N
O
cavitand 24 in CD2Cl2 were estimated. The activation enthal-
¼
O
O
O
O
py ꢀH was 62:7 ꢇ 8 kJ molꢈ1, and the activation entropy
F
F
O
O
R
R
N
N
N
N
O
O
N
N
F
F
N
N
B
N
N
R
R
B
¼
ꢀS ¼ 59:0 ꢇ 16 J molꢈ1 Kꢈ1. The positive activation entropy
3
3
is indicative of the release of a significant amount of surface-
solvating solvent molecules into the bulk solution in the tran-
sition state.
O
N
O
N
25
In contrast, kite1–kite2 equilibration of the more symmetric
anti-diethynylated cavitand 22 leads to two degenerate con-
formers. Accordingly, the 1H NMR spectrum at 203 K is great-
ly simplified, particulary, in the aromatic region where the ar-
omatic proton in the octol base on the side of the legs (around
6.4 ppm) appears as one broad singlet (Fig. 5). Also, the split-
ting pattern of the methine resonances (two different environ-
ments) around 3.6 ppm is much less complex.
Synthesis of a Calix[4]resorcinarene Cavitand Undergo-
ing Multi-Nanometer-Sized Expansion/Contraction Mo-
tions. As mentioned in the Introduction, cavitands, such as
21–24, provide versatile platforms to attach by cross-coupling,
with the help of rigid spacers, different chromophores which
in the contracted vase conformation interact at distances of
0.8 nm and below, while being at a multi-nanometer distance
in the expanded kite conformation. As a first example for such
a giant switching system, we chose the extended structure 259
(Fig. 6) with a donor–acceptor BODIPY (dipyrromethenebo-
ron difluoride) dye pair,26 attached by rigid oligo(phenylene-
ethynyl) spacers to the cavitand scaffold, for monitoring
the switching dynamics by fluorescence resonance energy
transfer (FRET).16 Molecular models, based on X-ray crystal
structure coordinates of bridged calix[4]resorcinarenes in the
Fig. 6. A giant molecular switch (25) with a BODIPY dye
pair for monitoring the contraction/expansion motions by
FRET techniques.
vase and kite geometry,13,15b,27 suggested a change in the
distance between the two boron atoms of the dye pair from
ca. 0.7 nm in the contracted to ca. 7 nm in the expanded state
which, according to theoretical considerations, should allow
convenient detection of different FRET efficiency in the two
states.
The synthesis of cavitand 25 started with the preparation
of the dye-appended oligo(phenyleneethynyl)s (Scheme 4).
Bright red BODIPY dye 26,26b,e selected as a donor fluoro-
phore for the FRET pair, was efficiently prepared in 60% yield
from 2-ethyl-1,3-dimethylpyrrole and 4-iodobenzaldehyde in a
3-step sequence without intermediate purifications. It was sub-
sequently coupled with ethynyl-trimethylsilane to form dye
27.26e Alkyne deprotection of compound 27 demanded optimi-
zation since the dye moiety was not stable in the presence of
basic n-Bu4NF and other desilylating reagents at room tem-
perature. Finally, it was possible to achieve high yields of
compound 2826d,e (longest-wavelength absorption maximum
ꢁabs ¼ 529 nm, emission maximum ꢁem ¼ 542 nm in CHCl3)

1932 Bull. Chem. Soc. Jpn. Vol. 79, No. 12 (2006)
Modified Calix[4]resorcinarene Cavitands
I
F
F
d
N
N
f
F
F
F
F
N
N
N
N
a, b, c
B
B
R
B
I
R
+
N
H
3
CHO
I
SiMe3
2
29
30 R = SiMe3
31 R = H
26
27 R = SiMe3
28 R = H
e
e
I
NH
N
F
N
F
N
d
f
a, b, c
F
+
R
B
R
B
F
I
B
F
F
29
3
N
N
N
CHO
33
32
37 R = SiMe3
34 R = H
35 R = SiMe3
36 R = H
e
e
Scheme 4. Synthesis of the BODIPY dye-spacer conjugates 31 and 34. (a) TFA, CH2Cl2, 20 ꢄC, 2–3 h. (b) DDQ, PhMe, 1 h.
(c) NEt3, 20 ꢄC (10 min), then BF3 OEt2, 75 ꢄC (30–40 min); 60% (26), 75% (32) (yields over three steps). (d) Me3Si–CꢆCH,
ꢅ
[Pd(PPh3)4], CuI, Et(i-Pr)2N, THF, 20 ꢄC, 1–5 d; 97% (27), 99% (35). (e) n-Bu4NF, THF, ꢈ78 ꢄC, 30 min; 89% (28), 96%
(31), 98% (36), 97% (34). (f) [Pd(PPh3)4], CuI, Et(i-Pr)2N, THF, 20 ꢄC, 3–5 d; 74% (30), 77% (37). TFA = CF3CO2H,
DDQ = 2,3-dichloro-5,6-dicyano-p-benzoquinone.
by deprotecting with n-Bu4NF at ꢈ70 ꢄC for 30 min and, then,
F
B
adding 2 equivalents of AcOH to avoid the negative effects of
n-Bu4NF basicity during workup. Sonogashira cross-coupling
of dye 28 with spacer 29,20a followed by alkyne deprotection
of compound 30 afforded the desired spacer–donor dye conju-
gate 31.
F
N
N
O
N
N
N
N
The bronze-red acceptor dye 3226c was obtained in 75%
yield in the 3-step sequence starting with the condensation
of 3-methyl-4,5-dihydro-1H-benzo[g]indole 33 with 4-iodo-
benzaldehyde. A protocol similar to that applied for the prep-
aration of dye derivative 31 afforded the spacer–acceptor dye
O
O
a
a
O
N
N
N
17 + 28
18 + 26
O
O
O
R
R
R = n-C6H13
R
R
O
N
O
O
N
conjugate 34 via intermediates 35, 36 (ꢁabs ¼ 619 nm, ꢁem
¼
38
630 nm), and 37. Compound 34 was only sparingly soluble
(ca. 250 mg mLꢈ1) in common organic solvents (CHCl3,
PhMe). Nevertheless, it could be purified by using flash chro-
matography (FC) with large-scale columns, and subsequent
Sonogashira cross-couplings could be successfully carried out.
In trial runs, before moving to the final assembly of the giant
switch, Sonogashira cross-couplings were performed between
mono-functionalized cavitands and donor dyes (17 and 28;
18 and 26; Scheme 5). Both transformations afforded cavi-
tand-dye conjugate 38 in good yields (56 and 64%, respec-
tively) after purification by flash chromatography (SiO2), fol-
lowed by gel permeation chromatography (GPC) with Biorad
BioBeads SX-1.
The final assembly of switch 25 started with the
Sonogashira cross-coupling of cavitand 21 with the donor
dye derivative 31 (Scheme 6). The product was first purified
by flash chromatography (SiO2), and the resulting mixture of
the mono- and bis-cross-coupled products 39 and 40 was sub-
sequently separated by GPC (CH2Cl2). Since the difference in
elution time between the two products was very short (only 18
Scheme 5. Synthesis of dye-labeled cavitand 38 (a) [Pd-
(PPh3)4], CuI, Et(i-Pr)2N, THF, 35 ꢄC, 3 d; 56% (from 17),
64% (from 18).
seconds at a retention time of ca. 16 min on an analytical col-
umn), several consecutive GPC runs were necessary for com-
plete separation. Cavitands 39 and 40 were obtained in pure
form in 28 and 17% yields, respectively (NMR, MS). Both
products have good solubility in common nonpolar organic
solvents (CHCl3, PhMe).
The second Sonogashira cross-coupling between cavitand
39 and dye derivative 34, which was monitored by analytical
GPC, afforded the target structure 25 with a yield of 49% after
flash chromatography and several GPC runs (CH2Cl2). The
spectral data (NMR, MS, UV–vis, and fluorescence spectros-
copy) were in full agreement with the proposed structure and
also confirmed the high purity of the cavitand 25. In the
high-resolution matrix-assisted laser-desorption-ionization
mass spectrum (HR-MALDI-MS, matrix: 3-hydroxypicolinic

V. A. Azov et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 12 (2006) 1933
F
B
F
B
F
N
F
N
N
N
I
O
N
O
N
O
N
N
N
N
N
N
N
O
O
O
O
O
O
O
O
N
O
N
N
O
N
N
N
N
N
O
O
O
O
O
O
O
a
R
R
R
R
R
R
+
31
R
R
R
R
R
R
O
O
O
O
N
N
N
O
N
O
O
O
O
O
O
O
O
N
N
N
O
N
N
O
N
O
N
N
N
21
39
40
I
I
b
34
N
R = n-C6H13
B
F
N
F
25
Scheme 6. Synthesis of target compound 25. (a) Compound 31 (0.75 equiv), [Pd(PPh3)4], CuI, Et(i-Pr)2N, THF/CHCl3, 35 ꢄC, 2 d,
28% (39), 17% (40). (b) Compound 34 (2.25 equiv), [Pd(PPh3)4], CuI, Et(i-Pr)2N, THF/CHCl3, 35 ꢄC, 2 d; 49%.
Fig. 7. 1H NMR spectra (CD2Cl2, sealed tube) of cavitand 25 at 333 K (a), 253 K (b), and 213 K (c) showing the transition from the
vase to the kite conformation.
acid (3-HPA)), the molecular ion after loss of one F atom
was observed at m=z 2880.2161 ([Mþ ꢈ F], C188H156B2F3-
N14O12þ; calc. 2880.2160) as the base peak. Despite its large
size, target compound 25 displayed good solubility in nonpolar
organic solvents (CHCl3, CH2Cl2). The reversed sequence of
dye addition to cavitand 21 (first compound 34 followed by
compound 31) was inefficient due to the poor solubility of
the intermediate mono-dye-labeled cavitand.
Both bis-dye-labeled cavitands 40 and 25 adopt a contracted
(vase) conformation (1H NMR spectrum fully resolved) above
293 K in trichloromethane and above 323 K in dichlorometh-
ane. Upon lowering the temperature to 213 K or upon addition
of TFA (0.3 M), they both undergo expansion to the kite form
as clearly evidenced by the characteristic large upfield shift
(ꢃ5:6 ! ꢃ3:6 ppm) of the methine protons in the octol scaf-
fold (Fig. 7). The pH-triggered switching was reversible upon
addition of base (K2CO3). Large-scale expansion/contraction
movement of cavitand 25 was also clearly proven by FRET
measurements.9 The UV–vis spectrum in CHCl3 (c ¼ 1:0 ꢁ
10ꢈ5 M), featuring three strong absorption bands (Fig. 8a)
assigned to the oligo(phenyleneethynyl) spacers (ꢁmax 332
nm), the donor dye (529 nm), and the acceptor dye (619
nm), was not affected by the TFA addition (c ¼ 0:27 M). Quite
opposite, the emission spectrum in CHCl3 (c ¼ 0:5 ꢁ 10ꢈ7 M,
ꢁexc ¼ 490 nm, 293 K) changed dramatically upon addition
of TFA: the acceptor fluorescence (ꢁem ¼ 630 nm) vanished

1934 Bull. Chem. Soc. Jpn. Vol. 79, No. 12 (2006)
Modified Calix[4]resorcinarene Cavitands
the way to the design of new dynamic molecular devices
and receptors, such as switchable photoinduced energy/elec-
tron-transfer systems or molecular grippers for nano-mechani-
cal applications. Furthermore, we believe that these expanded
dynamic cavitands can be used as general models for studying
the distance dependence of intermolecular interactions such as
excimer and exciplex formation both in the bulk as well as at
the stage of single molecules. Work in this direction is now
underway.
Experimental
General. Melting points were determined using a Buchi Melt-
¨
ing Point B-540 and are uncorrected. The melting points of the
deeply colored BODIPY derivatives could not be accurately deter-
mined. UV–vis spectra were measured on a Varian Cary 500 Scan
spectrophotometer in CHCl3 solution. Fluorescence spectra were
measured on an Instruments S. A. Fluorolog-3 spectrofluorometer
in CHCl3 solution. IR spectra were measured on a Perkin-Elmer
Spectrum BX FT-IR spectrometer using neat samples. 1H, 13C,
and 19F NMR spectra were recorded with Varian Mercury 300
spectrometers at 300, 75, and 282.5 MHz, respectively. The chem-
1
ical shifts were recorded relative to CDCl3 (ꢀ 7.26, H; ꢀ 77.23,
1
13C) and CD2Cl2 (ꢀ 5.32, H; 53.80, ꢀ 13C). C6F6 was used as a
reference for 19F NMR (ꢀ ꢈ161). For the variable temperature
experiments, the temperature was calibrated with 100% MeOH
(T ꢂ 313 K) or CH2OH–CH2OH (T ꢉ 313 K) reference samples.
Temperature regulation was stable within ꢇ0:5 K between 363
and 243 K, and within ꢇ1:5 K at lower temperatures. FT-ICR-
MALDI-MS were measured on a Ion Spec Ultima FT-ICR-MS
(337 nm N2-laser system) using DHB (2,3-dihydroxybenzoic acid)
or DCTB ({(2E)-3-[4-(tert-butyl)phenyl]-2-methylprop-2-enyl-
idene}malononitrile as a matrix. EI-MS were measured on a VG
Analytical Tribrid, U.S.A. Solvents and reagents were purchased
reagent-grade and used without further purification. Cavitands
8,11c,15b 19,15b,25 20,15b 25,9 39,9 and 409 were prepared according
to literature procedures. All reactions were carried out under Ar or
N2. Flash chromatography (FC) was performed using SiO2 from
Fluka or Merck 230–400 mesh (particle size 40–63 mm). Gel per-
meation chromatography (GPC) was performed using Biorad Bio-
Beads SX-1. Anal. thin-layer chromatography (TLC) was per-
formed using precoated SiO2 glass plates with F-254 fluorescent
indicator, and visualization was performed with UV-light at 254
or 366 nm.
Fig. 8. a) UV–vis spectrum of cavitand 25 in CHCl3 at
20 ꢄC (c ¼ 1:0 ꢁ 10ꢈ5 M). b) Fluorescence spectra of
cavitand 25 in CHCl3 at 20 ꢄC (c ¼ 0:5 ꢁ 10ꢈ7 M) show-
ing the change after addition of TFA (c ¼ 0:27 M).
almost completely, whereas the donor fluorescence (ꢁem
¼
542 nm) doubled in intensity (Fig. 8b). With a separation of
ca. 7 nm between the donor and acceptor dyes in the kite con-
formation, fluorescence resonance energy transfer is much less
efficient than in the vase form with the two dyes in close prox-
imity. This result stays in line with theoretical estimation of
the Forster radius R for the 26–32 donor–acceptor dye pair,
o
¨
which was calculated to be about 4.7 nm for the case of freely
rotatong dyes (dye orientation factor ꢂ2 ¼ 2=3). We are cur-
rently investigating the dynamics of the switching motion of
cavitand 25 in single-molecule studies using confocal fluores-
cence microscopy.28
Conclusion
General Procedure A for the Preparation of N-Arylated
Imides of 5,6-Dichloropyrazine-2,3-dicarboxylic Acid. A mix-
ture of aromatic amine (1 molar amount) and compound 6 (1.05
molar amount) in THF under Ar was heated to 40 ꢄC for 30 min.
After cooling to 20 ꢄC, (COCl)2 (1.2 molar amount) and pyridine
(3 molar amounts) were added. The mixture was stirred for 16 h at
50 ꢄC and, then, filtered through Celite. After evaporation of the
solvent, the residue was purified by FC.
General Procedure B for the Bridging of Tris- and Bis-Quin-
oxaline-Bridged Cavitands 8, 19, and 20. Cavitand and 5,6-
dichloropyrazine-2,3-dicarboximide were dissolved in Me2SO,
and the solution degassed by freeze–pump–thaw cycles. K2CO3
was added, and the mixture stirred at 35 ꢄC for 16–36 h under
Ar. The mixture was diluted with icy H2O and filtered, and the fil-
trate washed once more with H2O and dried over P2O5 overnight.
The crude product was purified by FC.
Calix[4]resorcinarene-derived cavitands 17, 18, and 21–24,
with terminal iodo or ethynyl residues attached to the cavity
walls, are versatile platforms for the construction of large-scale
molecular switches. Modular extension of these termini by
means of Sonogashira cross-couplings enables the construction
of functional architectures, which are switchable between two
highly restricted conformations and can undergo geometrically
defined expansions/contractions on the multi-nanometer scale.
This is illustrated by the assembly of the giant molecular
switch 25 with terminal donor and acceptor BODIPY dyes, at-
tached by rigid oligo(phenyleneethynyl) spacers to the cavi-
tand platform. The switching motion of cavitand 25 between
the expanded kite (ca. 7 nm distance between the two dyes)
and the contracted vase state (ca. 7 nm distance), induced by
1
temperature or pH changes, was shown by H NMR spectros-
copy and FRET measurements. The results of this work pave
General Procedure C for the TMS-Deprotection of Ethynyl-
ated Dye Derivatives. The dye derivative (1 molar amount) was

V. A. Azov et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 12 (2006) 1935
dissolved in THF, ant the solution was cooled to ꢈ70 ꢄC. Then, n-
Bu4NF (1 M solution, 1.2 molar amount) was added, and the mix-
ture stirred for 30 min. AcOH (2 molar amounts) was added, and
the mixture was warmed to 20 ꢄC, filtered through a plug of SiO2.
The solvent was evaporated, and the residue was purified by FC.
2,3-Dichloro-6-[4-(trimethylsilyl)ethynylphenyl]-5H-pyrrolo-
[3,4-b]pyrazine-5,7(6H)-dione (7). Compounds 520b (455 mg,
2.22 mmol) and 6 (510 mg, 2.33 mmol), (COCl)2 (0.238 mL, 2.774
mmol), and pyridine (0.535 mL, 6.66 mmol) were allowed to react
in THF (20 mL) according to General Procedure A. Workup and
purification by FC (SiO2; CH2Cl2/cyclohexane 4/1) yielded com-
pound 7 (612 mg, 71%) as a light yellow solid. Rf ¼ 0:4 (SiO2;
CH2Cl2/cyclohexane 4/1); mp 326–327 ꢄC; IR ꢃ 2957, 2897,
1732, 1720, 1546, 1511, 1499, 1393, 1373, 1320, 1224, 1180,
1143, 1125, 1099, 1019, 994, 956, 870, 848, 838, 801, 757, 740,
(156H)-dione (12). Compounds 8 (210 mg, 0.174 mmol) and 10
(69.9 mg, 0.174 mmol), and K2CO3 (27.7 mg, 0.201 mmol) were
allowed to react in Me2SO (10 mL) according General Procedure
B for 16 h. Workup and purification by FC (SiO2; CH2Cl2/EtOAc,
1%) yielded compound 12 (213 mg, 80%) as a white solid. Rf ¼
0:53 (SiO2; CH2Cl2/EtOAc, 1.2%); mp 380 ꢄC (decomp); IR ꢃ
2926, 2855, 1736, 1578, 1481, 1414, 1399, 1358, 1331, 1259,
1221, 1202, 1158, 1117, 1100, 1065, 912, 897, 857, 839 cmꢈ1
;
1H NMR (CDCl3) ꢀ 0.94 (t, J ¼ 6:6 Hz, 12H), 1.05 (s, 3H),
1.32–1.52 (m, 32H), 2.15 (s, 3H), 2.22–2.32 (m, 8H), 5.53–5.69
(m, 4H), 7.21 (s, 2H), 7.24 (s, 2H), 7.30–7.52 (m, 8H), 7.75–7.80
(m, 2H), 7.85–7.91 (m, 4H), 8.19 (s, 2H), 8.22 (s, 2H); 13C NMR
(CDCl3) ꢀ 14.29, 17.62, 18.19, 22.88, 28.15, 29.58, 32.09,
32.51, 32.63, 32.76, 34.44, 118.78, 119.33, 123.57, 123.85,
124.15, 127.73, 128.04, 128.13, 128.95, 129.05, 129.14, 129.51,
131.38, 132.06, 135.70, 135.92, 136.00, 137.10, 138.50, 139.31,
139.69, 139.78, 139.93, 141.56, 152.24, 152.54, 152.62, 152.71,
152.87þ, 153.01, 158.92, 161.42. HRMS Calcd for C90H85Br-
N9O10 (Mþ þ H): 1530.56028. Found (MALDI, matrix: DCTB):
1530.5613.
1
670, 656, 625 cmꢈ1; H NMR (CDCl3) ꢀ 0.26 (s, 9H), 7.39–7.44
(m, 2H), 7.58–7.63 (m, 2H); 13C NMR (CDCl3) ꢀ 0.09, 96.62,
103.88, 124.34, 126.08, 130.24, 133.08, 143.18, 154.50, 161.09.
HRMS Calcd for C17H14Cl2N3O2Siþ (Mþ þ H): 390.02323.
Found (MALDI, matrix: DCTB): 390.023.
(17s,18S,19r,20R)-17,18,19,20-Tetrahexyl-156-{4-[(trimethyl-
silyl)ethynyl]phenyl}-2,4,6,8,10,12,14,16-octaoxa-155H-3,7,11-
(2,3)-triquinoxalina-15(2,3)-pyrrolo[3,4-b]pyrazina-1,5,9,13-
(1,2,4,5)-tetrabenzenapentacyclo[11.3.1.11;5.15;9.19;13]icosaphan-
155,157(156H)-dione (9). Compounds 8 (110 mg, 0.092 mmol)
and 7 (36 mg, 0.092 mmol), and K2CO3 (15 mg, 0.106 mmol) were
allowed to react in Me2SO (2.5 mL) according to General Proce-
dure B for 16 h. Workup and purification by FC (SiO2; CH2Cl2/
EtOAc, 1–3%) yielded compound 9 (87 mg, 62%) as a slightly
yellowish powder. Rf ¼ 0:5 (SiO2; CH2Cl2/EtOAc, 1.2%); mp
325–335 ꢄC (decomp); IR ꢃ 2954, 2926, 2854, 1797, 1738,
1605, 1571, 1481, 1467, 1413, 1397, 1361, 1332, 1247, 1222,
1203, 1149, 1138, 1118, 1081, 1067, 1020, 961, 912, 899, 861,
2,3-Dichloro-6-(2,6-dimethyl-4-iodophenyl)-5H-pyrrolo[3,4-
b]pyrazine-5,7(6H)-dione (14). Compounds 1329 (0.741 g, 3.0
mmol) and 6 (0.69 g, 3.151 mmol), (COCl)2 (0.31 mL, 3.6 mmol),
and pyridine (1.0 mL, 9.1 mmol) were allowed to react in THF
(40 mL) according to General Procedure A. Workup and purifica-
tion by FC (SiO2; CH2Cl2/cyclohexane 3/1) yielded compound
14 (1.23 g, 91%) as a white solid. Rf ¼ 0:42 (SiO2; CH2Cl2/
cyclohexane 3/1); mp 312–314 ꢄC; IR ꢃ 1789, 1726, 1703,
1567, 1546, 1470, 1445, 1383, 1373, 1315, 1256, 1235, 1222,
1191, 1142, 1114, 1037, 993, 863, 813 cmꢈ1 1H NMR (CDCl3)
;
ꢀ 2.11 (s, 6H), 7.58 (s, 2H); 13C NMR (CDCl3) ꢀ 17.97, 96.80,
128.56, 138.00, 138.75, 143.39, 154.59, 161.01. HRMS Calcd
for C14H9Cl2IN3O2 (Mþ þ H): 447.91165. Found (MALDI,
þ
1
842, 830 cmꢈ1; H NMR (CDCl3) ꢀ 0.3 (s, 9H), 0.93 (t, J ¼ 6:4
matrix: DCTB): 447.9114.
Hz, 12H), 1.31–1.49 (m, 32H), 2.24–2.34 (m, 8H), 5.48 (t,
J ¼ 8:1 Hz, 1H), 5.54–5.62 (m, 3H), 7.09–7.13 (m, 2H), 7.21 (s,
2H), 7.24 (s, 2H), 7.30–7.35 (m, 2H), 7.44–7.50 (m, 2H), 7.51–
7.55 (m, 2H), 7.60–7.64 (m, 2H), 7.80–7.84 (m, 4H), 7.92–
7.95 (m, 2H), 8.14 (s, 2H), 8.17 (s, 2H); 13C NMR (CDCl3) ꢀ
0.14, 14.28, 22.87, 28.12, 29.58, 32.07, 32.61, 34.52, 96.47,
103.98, 118.67, 119.06, 123.56, 123.77, 123.89, 126.06, 127.65,
127.95, 128.94, 129.25, 129.33, 129.42, 130.77, 132.81, 135.56,
135.72, 135.95, 137.05, 139.68, 139.73, 139.84, 141.14, 152.22,
152.35, 152.43, 152.56, 152.77, 152.80, 153.00, 158.78, 161.35.
HRMS Calcd for C93H90N9O10Siþ (Mþ þ H): 1520.65799. Found
(MALDI, matrix: DCTB): 1520.6555.
2,3-Dichloro-6-(4-bromo-2,6-dimethylphenyl)-5H-pyrrolo-
[3,4-b]pyrazine-5,7(6H)-dione (10). Compounds 11 (162.2 mg,
0.811 mmol) and 6 (186.3 mg, 0.851 mmol), (COCl)2 (0.083 mL,
0.973 mmol), and pyridine (0.196 mL, 2.43 mmol) were allowed
to react in THF (10 mL) according to General Procedure A. Work-
up and purification by FC (SiO2; CH2Cl2/cyclohexane 3/1) yield-
ed 10 (285 mg, 88%) as a white solid. Rf ¼ 0:4 (SiO2; CH2Cl2/
cyclohexane 3/1); mp 279–280 ꢄC; IR ꢃ 1791, 1728, 1575, 1546,
1447, 1384, 1372, 1316, 1259, 1224, 1143, 1114, 1037, 991, 874,
864, 814, 748, 612 cmꢈ1; 1H NMR (CDCl3) ꢀ 2.12 (s, 6H), 7.37 (s,
2H); 13C NMR (CDCl3) ꢀ 18.18, 124.46, 127.70, 131.96, 138.75,
143.39, 154.56, 161.04.
2,6-Dimethyl-4-[(trimethylsilyl)ethynyl]aniline (15). Com-
pound 1329 (2.43 g, 9.83 mmol), [Pd(PPh3)4] (0.227 g, 0.197
mmol), and CuI (0.028 g, 0.147 mmol) were mixed in piperidine
(9 mL), and the mixture degassed by freeze–pump–thaw cycles.
Ethynyltrimethylsilane (1.74 mL, 12.3 mmol) was added at 0 ꢄC
under Ar, and the mixture was allowed to warm to 20 ꢄC slowly
and stirred overnight. The formed precipitate was filtered off,
and the solvent evaporated to dryness. FC (SiO2; CH2Cl2/cyclo-
hexane 2/1, then 3/1) yielded compound 15 (2.16 g, 100%) as a
slightly brownish liquid. Rf ¼ 0:3 (SiO2; CH2Cl2/cyclohexane
2/1); bp 110–120 ꢄC (133 Pa); 1H NMR (CDCl3) ꢀ 0.23 (s,
9H), 2.13 (s, 6H), 3.72 (br s, 2H), 7.09 (s, 2H); 13C NMR (CDCl3)
ꢀ 0.39, 17.54, 91.05, 106.67, 111.86, 121.43, 132.29, 143.68.
HRMS Calcd for C13H19NSiþþ (Mþ): 217.12868. Found (EI):
217.1281.
2,3-Dichloro-6-(2,6-dimethyl-4-ethynylphenyl)-5H-pyrrolo-
[3,4-b]pyrazine-5,7(6H)-dione (16). Compound 15 (2.16 g, 9.93
mmol) was dissolved in THF/MeOH 2/1 (30 mL), then 1 M
NaOH (10 mL) was added. The mixture was stirred for 3 h under
Ar and dried with Na2SO4, and the solvent evaporated. Purifica-
tion by FC (SiO2; CH2Cl2/cyclohexane 2/1, then CH2Cl2) fol-
lowed by Kugelrohr distillation in vacuum yielded 2,6-dimethyl-
4-ethynylaniline30 (1.28 g, 89%) as a colorless, readily crystalliz-
ing liquid. Rf ¼ 0:38 (SiO2; CH2Cl2/cyclohexane 2/1); mp 20–
22 ꢄC; bp 120 ꢄC (133 Pa).
(17s,18S,19r,20R)-156-(4-Bromo-2,6-dimethylphenyl)-17,18,-
19,20-tetrahexyl-2,4,6,8,10,12,14,16-octaoxa-155H-3,7,11(2,3)-
triquinoxalina-15(2,3)-pyrrolo[3,4-b]pyrazina-1,5,9,13(1,2,4,5)-
tetrabenzenapentacyclo[11.3.1.11;5.15;9.19;13]icosaphan-155,157-
2,6-Dimethyl-4-ethynylaniline (400 mg, 2.75 mmol), compound
6 (633 mg, 2.89 mmol), (COCl)2 (0.31 mL, 3.6 mmol), and pyri-
dine (1.0 mL, 9.1 mmol) were allowed to react in THF (30 mL)

1936 Bull. Chem. Soc. Jpn. Vol. 79, No. 12 (2006)
Modified Calix[4]resorcinarene Cavitands
according to General Procedure A. Workup and purification by FC
(SiO2; CH2Cl2/cyclohexane 3/1) yielded compound 16 (812 mg,
64%) as a white solid. Rf ¼ 0:6 (SiO2; CH2Cl2/cyclohexane 2/1);
mp 286–287 ꢄC; IR ꢃ 3257, 2924, 1789, 1727, 1597, 1577, 1544,
1475, 1445, 1385, 1374, 1317, 1293, 1237, 1194, 1168, 1142,
1118, 1037, 1009, 993, 892, 883, 838, 814, 749, 730, 718, 678,
(58 mg, 0.42 mmol) were allowed to react in Me2SO (15 mL) ac-
cording to General Procedure B for 36 h. Workup and purification
by FC (SiO2; CH2Cl2/EtOAc, 1 to 2%) yielded compound 21
(122 mg, 38%) as a white solid. Rf ¼ 0:38 (SiO2; CH2Cl2/EtOAc,
1.2%); mp 310–330 ꢄC (decomp); IR ꢃ 2926, 2856, 1797, 1741,
1539, 1481, 1445, 1411, 1358, 1329, 1256, 1234, 1202, 1158,
632, 613 cmꢈ1
;
1H NMR (CDCl3) ꢀ 2.14 (s, 6H), 3.12 (s, 1H),
1116, 1102, 1031, 953, 900, 839, 763, 735, 686 cmꢈ1 1H NMR
;
7.34 (s, 2H); 13C NMR (CDCl3) ꢀ 18.36, 78.71, 82.73, 124.37,
128.98, 132.46, 136.89, 143.32, 154.41, 160.92. HRMS Calcd
(CDCl3) ꢀ 0.91–0.97 (m, 12H), 1.24–1.56 (m, 32H), 1.36 (s, 6H),
2.17 (s, 6H), 2.22–2.38 (m, 8H), 5.60 (t, J ¼ 8:1 Hz, 2H), 5.69 (t,
J ¼ 8:1 Hz, 2H), 7.26–7.34 (m, 8H), 7.65 (br s, 2H), 7.67 (br s,
2H), 7.83–7.88 (m, 4H), 8.23 (s, 4H); 13C NMR (CDCl3) ꢀ 14.25,
17.78, 17.94, 22.89, 28.14, 29.55, 32.06, 32.28, 32.83, 34.47,
34.56, 96.49, 118.65, 123.89, 128.27, 128.77, 129.44, 135.71,
136.84, 137.39, 137.82, 138.15, 139.16, 139.73, 141.38, 151.96,
152.13,þ 152.99, 158.71, 161.27. HRMS Calcd for C96H89I2-
N10O12 (Mþ þ H): 1827.4745. Found (MALDI, matrix: DCTB):
1827.4766.
(17s,18s,19s,20s)-76,156-Bis(4-ethynyl-2,6-dimethylphenyl)-
17,18,19,20-tetrahexyl-2,4,6,8,10,12,14,16-octaoxa-75H,155H-
3,11(2,3)-diquinoxalina-7,15(2,3)-bis(pyrrolo[3,4-b]pyrazina)-
1,5,9,13(1,2,4,5)-tetrabenzenapentacyclo[11.3.1.11;5.15;9.19;13]-
icosaphan-75,77(76H),155,157(156H)-tetrone (22). Compounds
19 (134 mg, 0.124 mmol) and 16 (90 mg, 0.261 mmol), and
K2CO3 (40 mg, 0.286 mmol) were allowed to react in Me2SO (10
mL) according to General Procedure B for 36 h. Workup and pu-
rification by FC (SiO2; CH2Cl2/EtOAc, 1.5%) yielded compound
22 (111 mg, 55%) as a white solid. Rf ¼ 0:52 (SiO2; CH2Cl2/
EtOAc, 1.2%); mp 270–290 ꢄC (decomp); 1H NMR (CDCl3) ꢀ
0.89–0.95 (m, 12H), 1.31–1.54 (m, 38H), 2.19 (s, 6H), 2.22–2.34
(m, 8H), 3.20 (s, 2H), 5.60 (t, J ¼ 8:1 Hz, 2H), 5.69 (t, J ¼ 8:1 Hz,
2H), 7.26 (s, 4H), 7.27–7.32 (m, 4H), 7.40 (br s, 2H), 7.42 (br s,
2H), 7.82–7.87 (m, 4H), 8.22 (s, 4H); 13C NMR (CDCl3) ꢀ 14.29,
18.22, 18.26, 22.88, 28.18, 29.58, 32.08, 32.34, 32.88, 34.38,
34.48, 78.92, 82.76, 118.98, 123.95, 124.47, 128.54, 129.46,
129.64, 132.16, 132.98, 135.90, 136.20, 137.05, 137.59, 139.98,
141.64, 152.23, 15þ2.41, 153.28, 159.05, 161.59. HRMS Calcd
for C100H91N10O12 (Mþ þ H): 1623.68179. Found (MALDI,
matrix: DHB): 1623.6793.
þ
for C16H9Cl2N3O2 (Mþ): 345.00718. Found (EI): 345.0072.
(17s,18S,19r,20R)-17,18,19,20-Tetrahexyl-156-(4-iodo-2,6-di-
methylphenyl)-2,4,6,8,10,12,14,16-octaoxa-155H-3,7,11(2,3)-tri-
quinoxalina-15(2,3)-pyrrolo[3,4-b]pyrazina-1,5,9,13(1,2,4,5)-
tetrabenzenapentacyclo[11.3.1.11;5.15;9.19;13]icosaphan-155,157-
(156H)-dione (17). Compounds 8 (176 mg, 0.146 mmol) and 14
(69 mg, 0.154 mmol), and K2CO3 (24 mg, 0.175 mmol) were al-
lowed to react in Me2SO (10 mL) according to General Procedure
B for 16 h. Workup and purification by FC (SiO2; CH2Cl2/EtOAc,
1%) yielded compound 17 (171 mg, 74%) as a white solid. Rf ¼
0:53 (SiO2; CH2Cl2/EtOAc, 1.2%); mp 330 ꢄC (decomp); IR ꢃ
2925, 2856, 1741, 1569, 1481, 1414, 1399, 1359, 1332, 1255,
1222, 1202, 1159, 1117, 1064, 912, 898, 839, 777, 761, 737,
656, 605 cmꢈ1
;
1H NMR (CDCl3) ꢀ 0.94 (t, J ¼ 6:6 Hz, 12H),
1.02 (s, 3H), 1.32–1.52 (m, 32H), 2.13 (s, 3H), 2.22–2.32 (m,
8H), 5.53–5.69 (m, 4H), 7.21 (s, 2H), 7.24 (s, 2H), 7.30–7.36
(m, 2H), 7.44–7.52 (m, 5H), 7.61 (br s, 1H), 7.75–7.80 (m, 2H),
7.85–7.91 (m, 4H), 8.19 (s, 2H), 8.22 (s, 2H); 13C NMR (CDCl3)
ꢀ 14.41, 17.49, 18.07, 22.98, 28.25, 29.68, 32.18, 32.60, 32.85,
34.52, 96.46, 118.70, 119.25, 123.49, 123.75, 127.64, 127.96,
128.85, 128.94, 129.05, 129.42, 135.59, 135.81, 135.90, 136.98,
137.26, 137.97, 138.42, 139.21, 139.58, 139.67, 139.82, 141.45,
152.10, 152.40, 152.47, 152.57,þ152.73, 152.86, 158.76, 161.23.
HRMS Calcd for C90H85IN9O10 (Mþ þ H): 1578.54641. Found
(MALDI, matrix: DHB): 1578.5478.
(17s,18S,19r,20R)-156-(4-Ethynyl-2,6-dimethylphenyl)-17,18,-
19,20-tetrahexyl-2,4,6,8,10,12,14,16-octaoxa-155H-3,7,11(2,3)-
triquinoxalina-15(2,3)-pyrrolo[3,4-b]pyrazina-1,5,9,13(1,2,4,5)-
tetrabenzenapentacyclo[11.3.1.11;5.15;9.19;13]icosaphan-155,157-
(156H)-dione (18). Compounds 8 (136 mg, 0.113 mmol) and 16
(39 mg, 0.113 mmol), and K2CO3 (18 mg, 0.129 mmol) were al-
lowed to react in Me2SO (5 mL) according to General Procedure
B for 16 h. Workup and purification by FC (SiO2; CH2Cl2/EtOAc,
1.5%) yielded compound 18 (147 mg, 88%) as a white solid. Rf ¼
0:44 (SiO2; CH2Cl2/EtOAc, 1.2%); mp 280–285 ꢄC (decomp);
1H NMR (CDCl3) ꢀ 0.94 (t, J ¼ 6:6 Hz, 12H), 1.04 (s, 3H), 1.32–
1.51 (m, 32H), 2.16 (s, 3H), 2.21–2.31 (m, 8H), 3.18 (s, 1H), 5.46–
5.67 (m, 4H), 7.21 (s, 2H), 7.24 (s, 2H), 7.29–7.35 (m, 2H), 7.38 (br
s, 1H), 7.45–7.52 (m, 5H), 7.75–7.80 (m, 2H), 7.85–7.91 (m, 4H),
8.20 (s, 2H), 8.22 (s, 2H); 13C NMR (CDCl3) ꢀ 14.41, 14.54, 17.80,
18.32, 22.99, 28.24, 29.68, 32.17, 32.60, 32.71, 32.83, 34.54,
78.65, 82.87, 118.69, 119.22, 123.51, 123.77, 124.04, 127.61,
127.94, 128.84, 128.98, 129.07, 129.44, 131.87, 132.59, 135.59,
135.80, 135.87, 136.62, 136.96, 137.42, 139.57, 139.65, 139.81,
141.48, 152.10, 152.37, 152.44, 152.53, 152.73, 152.86, 158.73,
(17R,18S,19S,20R)-116,156-Bis(4-iodo-2,6-dimethylphenyl)-
17,18,19,20-tetrahexyl-2,4,6,8,10,12,14,16-octaoxa-115H,155H-
3,7(2,3)-diquinoxalina-11,15(2,3)-bis(pyrrolo[3,4-b]pyrazina)-
1,5,9,13(1,2,4,5)-tetrabenzenapentacyclo[11.3.1.11;5.15;9.19;13]-
icosaphan-115,117(116H),155,157(156H)-tetrone (23).
Com-
pounds 20 (200 mg, 0.186 mmol) and 14 (182 mg, 0.408 mmol),
and K2CO3 (59 mg, 0.427 mmol) were allowed to react in Me2SO
(10 mL) according to General Procedure B for 16 h. Workup
and purification by FC (SiO2; CH2Cl2/EtOAc, 1 to 2%) yielded
compound 23 (237 mg, 70%) as a white solid. Rf ¼ 0:45 (SiO2;
CH2Cl2/EtOAc, 1.2%); mp 255–260 ꢄC (decomp); IR ꢃ 2926,
2856, 1800, 1738, 1540, 1481, 1442, 1412, 1399, 1359, 1331,
1255, 1232, 1199, 1157, 1115, 1100, 1031, 954, 899, 839, 828,
771, 760, 735, 686 cmꢈ1; 1H NMR (CDCl3) ꢀ 0.93 (t, J ¼ 6:6 Hz,
12H), 1.18 (s, 6H), 1.32–1.52 (m, 32H), 2.04 (s, 6H), 2.22–2.32
(m, 8H), 5.45 (br t, J ¼ 7:5 Hz, 2H), 5.59 (br t, J ¼ 7:5 Hz,
2H), 7.19 (s, 1H), 7.24 (br s, 3H), 7.42–7.61 (m, 8H), 7.87–7.95
(m, 4H), 8.02 (s, 1H), 8.17 (s, 2H), 8.23 (s, 1H); 13C NMR
(CDCl3) ꢀ 14.27, 14.41, 17.64, 17.93, 22.86, 28.06, 29.52, 32.01,
32.05, 32.38, 32.54, 34.56, 34.73, 96.32, 118.19, 118.87, 123.71,
123.86, 124.16, 127.73, 128.92, 129.41, 129.76, 135.36, 135.61,
136.50, 137.05, 137.40, 138.03, 138.58, 139.25, 139.78, 141.47,
141.62, 152.36, 152.39, 152.51, 152.88, 153.15, 15þ8.23, 158.31,
160.86, 161.54. HRMS Calcd for C96H89I2N10O12 (Mþ þ H):
161.31, 171.23. HRMS Calcd for C92H86N9O10 (Mþ þ H):
þ
1476.64977. Found (MALDI, matrix: DCTB): 1476.6500.
(17s,18s,19s,20s)-76,156-Bis(4-iodo-2,6-dimethylphenyl)-17,-
18,19,20-tetrahexyl-2,4,6,8,10,12,14,16-octaoxa-75H,155H-3,11-
(2,3)-diquinoxalina-7,15(2,3)-bis(pyrrolo[3,4-b]pyrazina)-1,5,-
9,13(1,2,4,5)-tetrabenzenapentacyclo[11.3.1.11;5.15;9.19;13]icosa-
phan-75,77(76H),155,157(156H)-tetrone (21). Compounds 19
(189 mg, 0.175 mmol) and 14 (165 mg, 0.368 mmol), and K2CO3

V. A. Azov et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 12 (2006) 1937
1827.47508. Found (MALDI, matrix: DCTB): 1827.4766.
6.8 mmol) and ethynyltrimethylsilane (0.24 mL, 1.7 mmol) were
added, and the bright red mixture was stirred under Ar overnight.
The mixture was filtered through Celite and the solvent was
evaporated. FC (SiO2; CH2Cl2/cyclohexane 1/1) gave compound
27 (524 mg, 97%) as a bright red solid. Rf ¼ 0:46 (SiO2; CH2Cl2/
cyclohexane 1/1); mp 244–246 ꢄC; IR ꢃ 2961, 2932, 2872, 2166,
1535, 1475, 1404, 1383, 1360, 1314, 1271, 1260, 1249, 1184,
1158, 1114, 1091, 1050, 974, 864, 840, 760, 709, 654 cmꢈ1; UV–
vis ꢁ 529 (" 75300 Mꢈ1 cmꢈ1) nm; Fluorescence (ꢁexc 490 nm)
ꢁem 543 nm; 1H NMR (CDCl3) ꢀ 0.29 (s, 9H), 0.98 (t, J ¼ 7:8
Hz, 6H), 1.30 (s, 6H), 2.30 (q, J ¼ 7:8 Hz, 4H), 2.53 (s, 6H),
7.22–7.26 (m, 2H), 7.58–7.62 (m, 2H); 13C NMR (CDCl3) ꢀ
0.26, 12.21, 12.84, 14.92, 17.37, 95.74, 104.49, 123.76, 128.47,
130.58, 132.71, 132.99, 136.15, 138.27, 139.26, 154.04; 19F NMR
(CDCl3) ꢀ ꢈ145:2 (q, J ¼ 32:5 Hz). HRMS Calcd for C28H35-
BF2N2Siþ (Mþ): 476.26306. Found (MALDI, matrix: DHB):
476.2613.
(17R,18S,19S,20R)-116,156-Bis(4-ethynyl-2,6-dimethylphen-
yl)-17,18,19,20-tetrahexyl-2,4,6,8,10,12,14,16-octaoxa-115H,-
155H-3,7(2,3)-diquinoxalina-11,15(2,3)-bis(pyrrolo[3,4-b]pyra-
zina)-1,5,9,13(1,2,4,5)-tetrabenzenapentacyclo[11.3.1.11;5.-
15;9.19;13]icosaphan-115,117(116H),155,157(156H)-tetrone (24).
Compounds 20 (80 mg, 0.074 mmol) and 16 (52 mg, 0.149 mmol),
and K2CO3 (22 mg, 0.159 mmol) were allowed to react in Me2SO
(5 mL) according to General Procedure B for 16 h. Workup and
purification by FC (SiO2; CH2Cl2/EtOAc, 1%) yielded compound
24 (72 mg, 60%) as a white solid. Rf ¼ 0:5 (SiO2; CH2Cl2/
EtOAc, 1.2%); mp 280–290 ꢄC (decomp); IR ꢃ 2924, 2855,
1737, 1576, 1481, 1441, 1413, 1365, 1331, 1263, 1228, 1217,
1201, 1154, 1100, 1064, 1034, 953, 899, 839, 772, 727, 689,
644 cmꢈ1
;
1H NMR (CDCl3) ꢀ 0.93 (t, J ¼ 6:6 Hz, 12H), 1.24
(s, 6H), 1.32–1.52 (m, 32H), 2.07 (s, 6H), 2.22–2.32 (m, 8H),
3.16 (s, 2H), 5.46 (br t, J ¼ 7:5 Hz, 2H), 5.59 (br t, J ¼ 7:5 Hz,
2H), 7.19–7.24 (m, 6H), 7.40 (br s, 2H), 7.41–7.61 (m, 4H),
7.88–7.96 (m, 4H), 8.04 (s, 1H), 8.18 (br s, 2H), 8.23 (s, 1H);
13C NMR (CDCl3) ꢀ 14.28, 17.86, 18.17, 22.86, 28.07, 29.53,
32.03, 32.06, 32.39, 32.57, 34.58, 34.74, 78.59, 82.86, 118.19,
118.90, 119.03, 123.70, 123.88, 124.06, 124.15, 127.71, 128.99,
129.44, 129.50, 129.76, 131.96, 132.62, 135.38, 135.62, 136.50,
136.82, 137.05, 137.42, 139.79, 141.51, 141.70, 152.36, 152.41,
{3-Ethyl-5-[(4-ethyl-3,5-dimethyl-2H-pyrrol-2-ylidene-ꢀN)-
(4-ethynylphenyl)methyl]-2,4-dimethyl-1H-pyrrolato-ꢀN}(di-
fluoro)boron (28).26d,e Compound 27 (455 mg, 0.95 mmol), n-
Bu4NF (1.15 mL, 1.15 mmol), and AcOH (0.12 mL) were allowed
to react in THF (12.5 mL) according to General Procedure C.
Workup and purification by FC (SiO2; CH2Cl2/cyclohexane 1/1)
afforded compound 28 (345 mg, 89%) as a bright red solid. Rf ¼
0:43 (SiO2; CH2Cl2/cyclohexane 1/1); mp 248–250 ꢄC; IR ꢃ
3265, 2962, 2925, 2870, 1532, 1475, 1403, 1385, 1371, 1314,
1273, 1260, 1183, 1158, 1115, 1072, 1035, 974, 867, 842, 762,
705, 657 cmꢈ1; UV–vis ꢁ 529 (" 74400 Mꢈ1 cmꢈ1) nm; Fluo-
rescence (ꢁexc 490 nm) ꢁem 543 nm; 1H NMR (CDCl3) ꢀ 0.98
(t, J ¼ 7:5 Hz, 6H), 1.30 (s, 6H), 2.30 (q, J ¼ 7:5 Hz, 4H), 2.53
(s, 6H), 3.18 (s, 1H), 7.25–7.29 (m, 2H), 7.60–7.64 (m, 2H);
13C NMR (CDCl3) ꢀ 12.20, 12.86, 14.93, 17.38, 83.21, 122.78,
128.61, 130.57, 132.86, 133.06, 136.54, 138.27, 139.08, 154.138;
19F NMR (CDCl3) ꢀ ꢈ145:2 (q, J ¼ 32:5 Hz). HRMS Calcd for
152.52, 152.90, 153.18, 158.23, 158.31, 160.93, 161.67. HRMS
(Mþ þ H): 1623.68179. Found
þ
Calcd for
(MALDI, matrix: DCTB): 1623.6792.
C100H91N10O12
{3-Ethyl-5-[(4-ethyl-3,5-dimethyl-2H-pyrrol-2-ylidene-ꢀN)-
(4-iodophenyl)methyl]-2,4-dimethyl-1H-pyrrolato-ꢀN}(difluo-
ro)boron (26).26b,e 2,4-Dimethyl-3-ethylpyrrole (592 mg, 4.81
mmol) and 4-iodobenzaldehyde (536 mg, 2.31 mmol) were dis-
solved in CH2Cl2 (140 mL) and the solution was degassed by
freeze–pump–thaw cycles, then trifluoroacetic acid (0.018 mL,
0.23 mmol) was added. After stirring for 3 h, the mixture was
washed with saturated aq NaHCO3 solution, H2O, and saturated
aq NaCl solution, and then dried with Na2SO4, and the solvent
was evaporated. The solid residue was dissolved in PhMe (70
mL), and a suspension of DDQ (524 mg, 2.31 mmol) in PhMe
(70 mL) was added. The mixture was stirred for 1 h at 20 ꢄC,
and, then, Et3N (1.3 mL, 9.2 mmol) was added. After 10 min,
þ
C25H27BF2N2 (Mþ): 404.22353. Found (MALDI, matrix:
DHB): 404.2224.
{3-Ethyl-5-[(4-ethyl-3,5-dimethyl-2H-pyrrol-2-ylidene-ꢀN)-
(4-{[4-({4-[(trimethylsilyl)ethynyl]phenyl}ethynyl)phenyl]eth-
ynyl}phenyl)methyl]-2,4-dimethyl-1H-pyrrolato-ꢀN}(difluoro)-
boron (30).
Compounds 28 (238 mg, 0.59 mmol) and 2920a
BF3 Et2O (2.3 mL, 18.5 mmol) was added, and the mixture heated
(243 mg, 0.606 mol), [Pd(PPh3)4] (27 mg, 0.024 mmol), and CuI
(4.5 mg, 0.024 mmL) were mixed in dry THF (24 mL), and the
mixture was degassed by freeze–pump–thaw cycles. Et(i-Pr)2N
(0.60 mL, 3.53 mmol) was added, and the bright red mixture
was stirred under Ar for 3 d. The mixture was filtered through Cel-
ite, and the solvent was evaporated. FC (SiO2; CH2Cl2/cyclohex-
ane 1/1) gave compound 30 (304 mg, 74%) as a bright red solid.
Rf ¼ 0:49 (SiO2; CH2Cl2/cyclohexane 1/1); mp 270–275 ꢄC (de-
comp); IR ꢃ 2959, 2920, 2863, 2155, 1534, 1474, 1405, 1372,
1319, 1264, 1249, 1189, 1160, 1115, 1069, 1051, 978, 862, 838,
760, 708, 649 cmꢈ1; UV–vis ꢁ 336 (" 70700 Mꢈ1 cmꢈ1), 529 ("
74200 Mꢈ1 cmꢈ1) nm; Fluorescence (ꢁexc 490 nm) ꢁem 544 nm;
1H NMR (CDCl3) ꢀ 0.27 (s, 9H), 0.99 (t, J ¼ 7:5 Hz, 6H), 1.34
(s, 6H), 2.31 (q, J ¼ 7:5 Hz, 4H), 2.54 (s, 6H), 7.29–7.32 (m, 2H),
7.46 (s, 4H), 7.50–7.57 (m, 4H), 7.65–7.68 (m, 2H); 13C NMR
(CDCl3) ꢀ 0.27, 12.23, 12.87, 14.95, 17.40, 90.46, 90.90, 91.05,
91.30, 96.70, 104.69, 122.98, 123.08, 123.30, 123.70, 128.68,
130.63, 131.52, 131.72, 132.04, 132.34, 133.05, 136.16, 138.28,
139.24, 154.11; 19F NMR (CDCl3) ꢀ ꢈ145:2 (q, J ¼ 32:5 Hz).
HRMS Calcd for C44H43BF2N2Siþ (Mþ): 676.32566. Found
(MALDI, matrix: DHB): 676.3251.
ꢅ
at 75 ꢄC for 40 min. It was then cooled to 20 ꢄC, and filtered
through a plug of SiO2, and the solvent was evaporated. FC (SiO2;
PhMe/cyclohexane, 2/1) yielded compound 26 (700 mg, 60%) as
a dark purple solid. Rf ¼ 0:43 (SiO2; CH2Cl2/cyclohexane 1/1);
mp 285–290 ꢄC; IR ꢃ 2960, 2925, 2868, 1532, 1471, 1403, 1385,
1370, 1314, 1272, 1259, 1181, 1157, 1113, 1062, 1035, 1009, 971,
865, 827, 751, 730, 698, 656 cmꢈ1; UV–vis ꢁ 529 (" 77500
M
ꢈ1 cmꢈ1) nm; Fluorescence (ꢁexc 490 nm) ꢁem 543 nm; 1H NMR
(CDCl3) ꢀ 0.80 (t, J ¼ 7:5 Hz, 6H), 1.12 (s, 6H), 2.05 (q, J ¼ 7:5
Hz, 4H), 2.56 (s, 6H), 6.24–6.28 (m, 2H), 7.37–7.41 (m, 2H);
13C NMR (CDCl3) ꢀ 11.85, 12.65, 14.73, 17.23, 94.23, 130.32,
130.71, 132.75, 135.60, 137.52, 137.98, 138.82, 154.22; 19F NMR
(CDCl3) ꢀ ꢈ142:8 (q, J ¼ 32:5 Hz). HRMS Calcd for C23H26-
þ
BF2IN2 (Mþ): 506.12018. Found (MALDI, matrix: DHB):
506.1204.
{3-Ethyl-5-[(4-ethyl-3,5-dimethyl-2H-pyrrol-2-ylidene-ꢀN)-
{4-[(trimethylsilyl)ethynyl]phenyl}methyl]-2,4-dimethyl-1H-
pyrrolato-ꢀN}(difluoro)boron (27).26e Compound 26 (572 mg,
1.13 mmol), [Pd(PPh3)4] (65 mg, 0.057 mmol), and CuI (11 mg,
0.057 mmL) were mixed in dry THF (24 mL), and the mixture
was degassed by freeze–pump–thaw cycles. Et(i-Pr)2N (1.16 mL,
(3-Ethyl-5-{(4-ethyl-3,5-dimethyl-2H-pyrrol-2-ylidene-ꢀN)-

1938 Bull. Chem. Soc. Jpn. Vol. 79, No. 12 (2006)
Modified Calix[4]resorcinarene Cavitands
[4-({4-[(4-ethynylphenyl)ethynyl]phenyl}ethynyl)phenyl]meth-
yl}-2,4-dimethyl-1H-pyrrolato-ꢀN)(difluoro)boron (31). Com-
pound 30 (270 mg, 0.40 mmol), n-Bu4NF (0.48 mL, 0.48 mmol),
and AcOH (0.05 mL) were allowed to react in THF (8 mL) accord-
ing to General Procedure C. Workup and purification by FC
(SiO2; CH2Cl2/cyclohexane 1/1) afforded compound 31 (232 mg,
96%) as a bright red solid. Rf ¼ 0:45 (SiO2; CH2Cl2/cyclohexane
1/1); mp > 300 ꢄC (decomp); IR ꢃ 3259, 2959, 2925, 2863, 1534,
1473, 1405, 1372, 1312, 1264, 1188, 1159, 1114, 1061, 1041, 975,
834, 760, 703 cmꢈ1; UV–vis ꢁ 334 (" 68100 Mꢈ1 cmꢈ1), 529 ("
76000 Mꢈ1 cmꢈ1) nm; Fluorescence (ꢁexc 490 nm) ꢁem 544 nm;
1H NMR (CDCl3) ꢀ 0.99 (t, J ¼ 7:5 Hz, 6H), 1.34 (s, 6H), 2.31
(q, J ¼ 7:5 Hz, 4H), 2.54 (s, 6H), 3.19 (s, 1H), 7.29–7.32 (m, 2H),
7.49 (s, 4H), 7.51–7.57 (m, 4H), 7.65–7.68 (m, 2H); 13C NMR
(CDCl3) ꢀ 12.10, 12.74, 14.82, 17.28, 79.35, 83.40, 90.46, 90.96,
91.11, 91.15, 122.38, 123.15, 123.32, 123.64, 123.79, 128.81,
130.74, 131.71, 131.83, 131.86, 132.33, 132.46, 133.17, 136.31,
138.41, 139.37, 154.28. 19F NMR (CDCl3) ꢀ ꢈ145:2 (q, J ¼ 32:5
1366, 1326, 1305, 1275, 1248, 1229, 1190, 1157, 1082, 1048,
1016, 963, 860, 839, 824, 772, 753, 731, 708, 640 cmꢈ1; UV–
vis ꢁ 618 (" 116000 Mꢈ1 cmꢈ1) nm; Fluorescence (ꢁexc 590 nm)
1
ꢁem 629 nm; H NMR (CDCl3) ꢀ 0.31 (s, 9H), 1.37 (s, 6H), 2.53
(br t, J ¼ 7 Hz, 4H), 2.88 (br t, J ¼ 7 Hz, 4H), 7.23–7.45 (m,
8H), 7.63–7.69 (m, 2H), 8.80 (br d, J ¼ 7:8 Hz, 2H); 13C NMR
(CDCl3) ꢀ 0.29, 12.69, 20.76, 30.80, 96.01, 104.48, 124.02,
127.44, 128.18, 128.46, 128.73 (t, J ¼ 11 Hz), 128.95, 129.55,
132.22, 132.82, 133.79, 135.99, 136.51, 138.89, 140.76, 150.94;
19F NMR (CDCl3) ꢀ ꢈ134:5 (q, J ¼ 34 Hz). HRMS Calcd for
C38H35BF2N2Siþ (Mþ): 596.26306. Found (MALDI, matrix:
DCTB): 596.2619.
Difluoro{3-methyl-2-[(3-methyl-4,5-dihydro-2H-benzo[g]-
indol-2-ylidene-ꢀN){4-[(trimethylsilyl)ethynyl]phenyl}methyl]-
4,5-dihydro-1H-benzo[g]indolato-ꢀN}boron (36). Compound
35 (143 mg, 0.24 mmol), n-Bu4NF (0.29 mL, 0.29 mmol), and
AcOH (0.036 mL) were allowed to react in THF (5 mL) according
to General Procedure C. Workup and purification by FC (SiO2;
CH2Cl2/cyclohexane gradient 50 ! 40%) afforded compound
36 (124 mg, 98%) as a dark copper-red solid. Rf ¼ 0:33 (SiO2;
CH2Cl2/cyclohexane 3/2); mp 280–300 ꢄC (decomp); IR ꢃ 3288,
2931, 2832, 1553, 1519, 1464, 1431, 1398, 1386, 1366, 1341,
1325, 1309, 1275, 1229, 1191, 1155, 1082, 1045, 1016, 962, 945,
842, 822, 771, 751, 727, 713, 667, 643, 617 cmꢈ1; UV–vis ꢁ 618
(" 115000 Mꢈ1 cmꢈ1) nm; Fluorescence (ꢁexc 590 nm) ꢁem 629
þ
Hz). HRMS Calcd for C41H35BF2N2 (Mþ): 604.28613. Found
(MALDI, matrix: DHB): 676.2864.
Difluoro{2-[(4-iodophenyl)(3-methyl-4,5-dihydro-2H-benzo-
[g]indol-2-ylidene-ꢀN)methyl]-3-methyl-4,5-dihydro-1H-benzo-
[g]indolato-ꢀN}boron (32).26c Compound 3326c (182 mg, 1.0
mmol) and 4-iodobenzaldehyde (0.112 mg, 0.48 mmol) were dis-
solved in CH2Cl2 (35 mL) and degassed by freeze–pump–thaw cy-
cles, then trifluoroacetic acid (0.004 mL, 0.048 mmol) was added.
After stirring for 2 h, the mixture was washed with saturated aq
NaHCO3 solution, H2O, and saturated aq NaCl solution, and then
dried with Na2SO4. After the solvent was evaporated, the solid
residue was dissolved in PhMe (20 mL), and a suspension of
DDQ (0.113 mg, 0.48 mmol) in PhMe (20 mL) was added. The
mixture was stirred for 30 min at 20 ꢄC, then Et3N (0.28 mL, 2.0
1
nm; H NMR (CDCl3) ꢀ 1.37 (s, 6H), 2.54 (br t, J ¼ 7 Hz, 4H),
2.88 (br t, J ¼ 7 Hz, 4H), 3.22 (s, 1H), 7.23–7.45 (m, 8H), 7.65–
7.69 (m, 2H), 8.81 (br d, J ¼ 7:8 Hz, 2H); 13C NMR (CDCl3) ꢀ
12.65, 20.75, 30.79, 78.80, 83.19, 123.03, 127.44, 128.18, 128.43,
128.73 (t, J ¼ 11 Hz), 129.07, 129.57, 132.26, 132.96, 133.75,
135.95, 136.87, 138.67, 140.77, 150.98; 19F NMR (CDCl3) ꢀ
þ
ꢈ134:5 (q, J ¼ 34 Hz). HRMS Calcd for C35H27BF2N2 (Mþ):
mmol) was added. After 10 min, BF3 Et2O (0.50 mL, 4.0 mmol)
524.2230. Found (MALDI, matrix: DCTB): 524.22353.
ꢅ
was added, and the mixture heated at 75 ꢄC for 30 min. It was then
cooled to 20 ꢄC, and filtered through a plug of SiO2, and the
solvent was evaporated. FC (SiO2; PhMe/cyclohexane, gradient
30 ! 0%) yielded compound 32 (226 mg, 75%) as a dark cop-
per-red solid. Rf ¼ 0:49 (SiO2; CH2Cl2/cyclohexane 1/1); mp
310–315 ꢄC (decomp); IR ꢃ 2927, 1550, 1523, 1466, 1432, 1398,
1387, 1367, 1327, 1274, 1230, 1191, 1157, 1113, 1082, 1056,
1048, 1032, 1017, 1007, 962, 944, 911, 870, 820, 767, 750, 730,
719, 708, 699, 678, 625, 616 cmꢈ1; UV–vis ꢁ 619 (" 127000
Difluoro{3-methyl-2-[(3-methyl-4,5-dihydro-2H-benzo[g]-
indol-2-ylidene-ꢀN)(4-{[4-({4-[(trimethylsilyl)ethynyl]phenyl}-
ethynyl)phenyl]ethynyl}phenyl)methyl]-4,5-dihydro-1H-benzo-
[g]indolato-ꢀN}boron (37).
Compounds 36 (139 mg, 0.265
mmol) and 2920a (147 mg, 0.367 mol), [Pd(PPh3)4] (15 mg, 0.013
mmol), and CuI (2.5 mg, 0.013 mmL) were mixed in dry THF
(7.5 mL), and the mixture was degassed by freeze–pump–thaw cy-
cles. Et(i-Pr)2N (0.27 mL, 1.59 mmol) was added, and the dark
blue mixture was stirred under Ar for 5 d. The mixture was fil-
tered through Celite, and the solvent was evaporated. FC (SiO2;
CH2Cl2/cyclohexane 2/3) gave compound 37 (162.5 mg, 77%)
as a dark copper-red solid. Rf ¼ 0:38 (SiO2; CH2Cl2/cyclohexane
2/3); mp > 300 ꢄC (decomp); IR ꢃ 2936, 2832, 2153, 1552, 1524,
1463, 1435, 1422, 1400, 1366, 1326, 1306, 1275, 1248, 1230,
1194, 1157, 1082, 1034, 1015, 965, 944, 863, 833, 768, 748,
721, 706, 668, 641 cmꢈ1; UV–vis ꢁ 322 (" 105000 Mꢈ1 cmꢈ1),
618 (" 138000 Mꢈ1 cmꢈ1) nm; Fluorescence (ꢁexc 590 nm) ꢁem
M
ꢈ1 cmꢈ1) nm; Fluorescence (ꢁexc 590 nm) ꢁem 630 nm; 1H NMR
(CDCl3) ꢀ 1.39 (s, 6H), 2.54 (br t, J ¼ 7 Hz, 4H), 2.88 (br t,
J ¼ 7 Hz, 4H), 7.23–7.44 (m, 8H), 7.87–7.90 (m, 2H), 8.79
(br d, J ¼ 7:8 Hz, 2H); 13C NMR (CDCl3) ꢀ 12.75, 20.77,
30.80, 127.46, 128.20, 128.42, 128.75, 129.61, 130.84, 132.31,
133.80, 135.91, 138.44, 140.79, 151.03; 19F NMR (CDCl3) ꢀ
ꢈ134:5 (q, J ¼ 34 Hz).
Difluoro{3-methyl-2-[(3-methyl-4,5-dihydro-2H-benzo[g]-
indol-2-ylidene-ꢀN){4-[(trimethylsilyl)ethynyl]phenyl}methyl]-
4,5-dihydro-1H-benzo[g]indolato-ꢀN}boron (35). Compound
32 (196 mg, 0.313 mmol), [Pd(PPh3)4] (18 mg, 0.016 mmol), and
CuI (3 mg, 0.016 mmL) were mixed in dry THF (10 mL), and
the mixture was degassed by freeze–pump–thaw cycles. Et(i-Pr)2N
(0.32 mL, 1.88 mmol) and ethynyltrimethylsilane (0.088 mL, 0.63
mmol) were added, and the dark green mixture was stirred under
Ar for 5 d. The mixture was filtered through Celite, and the solvent
was evaporated. FC (SiO2; CH2Cl2/cyclohexane 1/1) gave com-
pound 35 (185 mg, 99%) as a dark copper-red solid. Rf ¼ 0:42
(SiO2; CH2Cl2/cyclohexane 3/2); mp 255–270 ꢄC (decomp); IR
ꢃ 2934, 2889, 2832, 2154, 1552, 1524, 1466, 1434, 1400, 1386,
1
629 nm; H NMR (CDCl3) ꢀ 0.27 (s, 9H), 1.41 (s, 6H), 2.54 (br
t, J ¼ 7 Hz, 4H), 2.89 (br t, J ¼ 7 Hz, 4H), 7.24–7.33 (m, 4H),
7.38–7.49 (m, 8H), 7.52–7.59 (m, 4H), 7.70–7.73 (m, 2H), 8.82
(br d, J ¼ 7:8 Hz, 2H); 13C NMR (CDCl3) ꢀ 0.28, 12.70, 20.77,
30.80, 90.67, 90.90, 91.05, 91.35, 96.72, 104.70, 122.95, 123.09,
123.35, 123.96, 127.45, 128.20, 128.46, 128.74 (t, J ¼ 11 Hz),
129.15, 129.57, 131.53, 131.75, 132.06, 132.26, 132.24, 133.82,
135.98, 136.50, 138.86, 140.77, 150.97; 19F NMR (CDCl3) ꢀ
ꢈ134:5 (q, J ¼ 33:5 Hz). HRMS Calcd for C54H43BF2N2Si
(Mþ): 796.32566. Found (MALDI, matrix: DCTB): 796.3238.
(2-{[4-({4-[(4-Ethynylphenyl)ethynyl]phenyl}ethynyl)phenyl]-
(3-methyl-4,5-dihydro-2H-benzo[g]indol-2-ylidene-ꢀN)methyl}-

V. A. Azov et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 12 (2006) 1939
3-methyl-4,5-dihydro-1H-benzo[g]indolato-ꢀN)(difluoro)boron
(34). Compound 37 (155 mg, 0.195 mmol), n-Bu4NF (0.235 mL,
0.235 mmol), and AcOH (0.03 mL) were allowed to react in THF
(30 mL) according to General Procedure C. Crude FC (SiO2;
CH2Cl2), followed by trituration with CHCl3 (5 mL) and THF
(2 mL), gave compound 34 (138 mg, 97%) as a dark copper-red
solid. The compound is poorly soluble in most common organic
solvents. Rf ¼ 0:35 (SiO2; CH2Cl2/cyclohexane 1/1); mp > 300
ꢄC (decomp); IR ꢃ 3283, 2944, 2832, 1551, 1517, 1465, 1430,
1423, 1386, 1365, 1339, 1321, 1302, 1274, 1228, 1187, 1154,
1082, 1059, 1040, 1016, 963, 945, 904, 841, 833, 822, 775, 758,
751, 731, 715, 707, 646 cmꢈ1; UV–vis ꢁ 320 (" 77400 Mꢈ1 cmꢈ1),
571 (" 21600 Mꢈ1 cmꢈ1), 618 (" 103000 Mꢈ1 cmꢈ1) nm; Fluores-
cence (ꢁexc 590 nm) ꢁem 628 nm; 1H NMR (CDCl3) ꢀ 1.41 (s,
6H), 2.54 (br t, J ¼ 7 Hz, 4H), 2.89 (br t, J ¼ 7 Hz, 4H), 3.19
(s, 1H), 7.24–7.33 (m, 4H), 7.39–7.45 (m, 4H), 7.49 (s, 4H),
7.52–7.59 (m, 4H), 7.70–7.73 (m, 2H), 8.82 (br d, J ¼ 7:8 Hz,
2H); 13C NMR (125 MHz, CDCl3) ꢀ 12.58, 20.70, 30.74, 91.17,
127.58, 128.30, 128.45, 128.60, 128.80, 128.89, 129.26, 129.30,
129.69, 131.74, 131.87, 131.91, 132.36, 132.39, 132.55, 132.57,
140.91, 140.93; 19F NMR (CDCl3) ꢀ ꢈ134:5 (q, J ¼ 33:5 Hz).
152.87, 154.19, 158.75, 161.38; 19F NMR (CDCl3) ꢀ ꢈ145:2 (q,
J ¼ 32:5 Hz). HRMS Calcd for C115H110BFN11O10 (Mþ ꢈ F):
þ
1834.85087. Found (MALDI, matrix: DHB): 1834.8514.
Determination of the Activation Parameters for Kite1–
Kite2 Switching of Cavitand 24. Fitting of NMR spectra was
performed with the gNMR v3.6 for Macintosh program (Cherwell
Scientific Publishing, Ltd., Oxford, UK). For the lineshape fitting
of the kite1–kite2 equilibrium of cavitand 24, enyne protons were
used in a two-site exchange model. Determination of activation
enthalpy and entropy was performed using the method described
by Sandstrom:31
¨
¼
¼
logðk=TÞ ¼ ꢈꢀH =aT þ ꢀS =a þ 10:319;
ð1Þ
where k [Hz] is an exchange constant obtained from spectral fit-
ting, T the temperature in Kelvin, and a ¼ 1:914 ꢁ 10ꢈ2 for ꢀH
¼
in kJ molꢈ1 and ꢀS =a in kJ molꢈ1 Kꢈ1. According to Eq. 1, a
¼
¼
plot of logðk=TÞ vs 1=T (Eyring plot) has a slope of (ꢈꢀH =a)
¼
and an intercept at 1=T ¼ 0 of (ꢀS =a þ 10:319).
Support by the Swiss National Science Foundation, via
the National Research Program ‘‘Supramolecular Functional
Materials’’ and the NCCR ‘‘Nanoscale Science’’ is gratefully
acknowledged. We thank Dr. C. Thilgen (ETH) for help with
the nomenclature.
þ
HRMS Calcd for C51H35BF2N2 (Mþ): 724.28613. Found
(MALDI, matrix: DCTB): 724.2845.
{3-Ethyl-5-[(4-ethyl-3,5-dimethyl-2H-pyrrol-2-ylidene-ꢀN)-
(4-{[4-((17s,18S,19r,20R)-17,18,19,20-tetrahexyl-155,157(156H)-
dioxo-2,4,6,8,10,12,14,16-octaoxa-155H-3,7,11(2,3)-triquinoxa-
lina-15(2,3)-pyrrolo[3,4-b]pyrazina-1,5,9,13(1,2,4,5)-tetraben-
zenapentacyclo[11.3.1.11;5.15;9.19;13]icosaphan-156-yl)-3,5-di-
methylphenyl]ethynyl}phenyl)methyl]-2,4-dimethyl-1H-pyrro-
lato-ꢀN}(difluoro)boron (38). Method A: Compounds 17
(30 mg, 0.019 mmol) and 28 (8.5 mg, 0.021 mmol), [Pd(PPh3)4]
(1.2 mg, 0.001 mmol), and CuI (0.2 mg, 0.001 mmol) were mixed
in dry THF (0.6 mL), and the mixture was degassed by freeze–
pump–thaw cycles. Et(i-Pr)2N (0.02 mL, 0.12 mmol) was added,
and the bright red mixture degassed again and left to stir under
Ar for 3 d. The solvent was evaporated, and FC (SiO2; CH2Cl2/
EtOAc gradient 0 ! 2%), followed by GPC (CH2Cl2) afforded
compound 38 (20 mg, 56%).
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1.07 (s, 3H), 1.32–1.52 (m, 38H), 2.20 (s, 3H), 2.22–2.38 (m,
12H), 2.56 (s, 6H), 5.52–5.69 (m, 4H), 7.21–7.39 (m, 9H), 7.46–
7.51 (m, 5H), 7.69–7.72 (m, 2H), 7.76–7.82 (m, 2H), 7.85–7.93
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123.78, 124.81, 127.63, 127.97, 128.79, 128.89, 129.02, 129.20,
129.40, 130.65, 131.39, 132.04, 132.42, 133.11, 135.60, 135.81,
135.89, 136.36, 136.70, 136.97, 137.54, 138.27, 139.19, 139.60,
139.67, 139.83, 141.50, 152.12, 152.41, 152.48, 152.57, 152.73,
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