A dendrimer chiroptical switch based on the reversible intramolecular photoreaction of anthracene and benzene rings

Article abstract of DOI:10.1002/asia.201000159

A series of Frechet-type dendrimers with 9-benzyloxymethylanthracene cores were synthesized and characterized. The chiral source for the dendrimers was an (S)-2-methyl-1-butoxy group in the 3-position of the benzene ring. Irradiation at 366 nm of a dilute

Full text of DOI:10.1002/asia.201000159

FULL PAPERS
DOI: 10.1002/asia.201000159
A Dendrimer Chiroptical Switch Based on the Reversible Intramolecular
Photoreaction of Anthracene and Benzene Rings
Wenjie Liu,[a, b] Derong Cao,*[a] Jinan Peng,[a] Hong Zhang,[a, b] and Herbert Meier*[a, c]
Abstract: A series of Frꢀchet-type den-
drimers with 9-benzyloxymethylanthra-
cene cores were synthesized and char-
acterized. The chiral source for the
dendrimers was an (S)-2-methyl-1-
butoxy group in the 3-position of the
benzene ring. Irradiation at 366 nm of
a dilute benzene solution led to the for-
mation of two diastereomers (1:1)
through a quantitative intramolecular
[4p+4p] cycloaddition between the
central anthracene ring and the neigh-
boring benzene ring. The process can
be reversed with 254 nm UV light or
heat. The benzene rings in the den-
drons work as
a
light-harvesting
system. The optical rotation values
measured for the reversible process
showed fatigue resistance. Thus,
a
Keywords: dendrimers · molecular
switches · cycloaddition · chiroptics ·
diastereomers
promising new type of chiroptical
switch has been created that has optical
rotation values as output signals.
Introduction
vert photostationary mixtures of the two chiral diastereo-
mers. In order to obtain novel and feasible chiroptical
switches, a variety of systems, including overcrowded al-
kenes,[4,5,9–11] diarylethenes,[12–16] binaphthyl derivatives,[17–22]
spiro-pyrans,[23–25] fulgides,[26–28] and azobenzenes,[29–34] have
been studied. The chiroptical switching process can be trig-
gered by light, heat, proton or electron transfer, and so
forth.
The development of molecular chiroptical switches for in-
formation storage remains an important area of research,
even though the emphasis in this field is partly shifting to-
wards supramolecular chemistry and nanotechnology. Den-
drimers represent a key stage in the development of macro-
molecular chemistry for a variety of high-end applications
because of their well-defined, unique macromolecular struc-
ture, good solubility, and low intrinsic viscosity.[35] We re-
cently combined the features of dendrimers and molecular
optical switches to create photochromic systems consisting
of anthracene cores and Frꢀchet-type dendrons.[36] The opti-
cal switch was based on the reversible intramolecular
[4p+4p] photocycloaddition between anthracene and a
neighboring benzene ring. Our long-term interest is to de-
velop chiroptical switches based on this system (Figure 1).
The design and construction of chiroptical switches for high-
density information storage and optical devices at the mo-
lecular level is one of the major challenges in materials sci-
ence.[1–7] The use of organic materials for recording optical
data offers the advantage of easy handling and tailoring of
the organic structures by molecular design. A large variety
of physical and chemical properties can easily be tuned by
making small changes to the structure. Feringa and co-work-
ers[8] described the first chiroptical molecular switch with a
system of sterically overcrowded alkenes. It was based on a
rapid, reversible, photochemical interconversion of two in-
trinsically chiral alkene diastereomers with opposite helici-
ties. Various wavelengths of UV light were used to intercon-
[a] Dr. W. Liu, Prof. Dr. D. Cao, J. Peng, H. Zhang, Prof. Dr. H. Meier
School of Chemistry and Chemical Engineering
South China University of Technology
Guangzhou 510640 (China)
Fax : (+86)20-871-10245
E-mail: drcao@scut.edu.cn
[b] Dr. W. Liu, H. Zhang
School of Chemistry and Chemical Engineering
Guangdong Pharmaceutical University
Zhongshan 528458 (China)
[c] Prof. Dr. H. Meier
Institute of Organic Chemistry
University of Mainz
Duesbergweg 10–14, 55099 Mainz (Germany)
E-mail: hmeier@uni-mainz.de
Figure 1. Optical and chiroptical switching of a compound with a chiral
source.
1896
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2010, 5, 1896 – 1901

A major advantage of such switches is their nondestruc-
tive readout, which can easily be monitored by optical rota-
tion.[2] The readout wavelength is remote from the irradia-
tion wavelengths used for the switching process. The work
reported here has three main aspects:
Photocycloaddition and Cycloreversion Reactions
The photochemistry of anthracene and its derivatives has
been the subject of extensive studies.[39–41] Nevertheless, we
recently discovered a new type of intramolecular [4p+4p]
cycloaddition reaction in this area. Anthracenes with an
electron-rich benzene ring attached by a CH2OCH2 chain in
the 9-position undergo this process for long-wavelength irra-
diations, provided that bimolecular photoreactions can be
avoided.[36,42–46]
1. use of the reversible cycloaddion of anthracene and ben-
zene rings by applying different wavelengths;
2. creation of the chiroptical switch by introduction of a
chiral center;
3. use of the light-harvesting effect of a dendritic structure.
Irradiation of a dilute solution of 4b–d in benzene (anhy-
drous; ~10ꢀ3 m) afforded photoproducts 5b–d (Scheme 2) in
quantitative yields. The conversion of 4a was less complete,
and it was therefore excluded from further studies.
Results and Discussion
Synthesis of Chiral Dendrimers with an Anthracene Core
The synthesis of chiral dendrimers Gi (three generations)
with an anthracene core is shown in Scheme 1. 3,5-Dihy-
droxybenzyl alcohol 1 reacted with Frꢀchet-type dendritic
benzyl chlorides, which were prepared according to known
Scheme 2. Photocycloaddition and cycloreversion of 4b–dÐ5b–d.
Light from a medium-pressure mercury lamp was passed
through a cut-off filter (lꢁ350 nm) to leave mainly the
366 nm emission line for the absorption of the anthracene
chromophore in 4b–d. Intramolecular [4p+4p] photocy-
cloaddition gave diastereomers (5S,8S,3’S)-5b–d and
(5R,8R,3’S)-5b–d in 1:1 ratios. The chiral center of 4b–d is
too far away from the reactive centers to lead to diastereo-
ꢀ
selectivity. Additionally, rotation about the b-C Car bond of
4b–d is possible before product formation. The two diaste-
reotopic addition directions are shown in Scheme 2.
Irradiation of 5b–d with l=254 nm led back to 4b–d. The
corresponding thermal process 5b–d!4b–d was achieved
by heating to 608C in quantitative yield.
Scheme 1. Synthesis of model compound 4a and chiral dendrimers 4b–d.
The [4p+4p] cycloaddition 4!5 proceeds with loss of ar-
1
procedures[37,38] to yield 2a–d. The free hydroxy groups of
2a–d then reacted with (S)-(+)-2-methyl-1-bromobutane to
give the optically active compounds 3a–d (56–72%). Under
phase-transfer conditions (chlorobenzene/water, KOH/
nBu4NBr), 3a–d reacted with 9-chloromethylanthracene to
give model compound 4a and dendrimers 4b–d. Yields for
the latter step ranged from 40 to 80%. The low yield of
40% was caused by the large steric bulk of chiral alcohol
3d.
omaticity. The H NMR spectra reflect this change by con-
siderable up-field shifts of many signals (Figure 2a). The
biggest effects were found for 10-H of 4b [d=8.30 ppm],
which becomes 9-H in 5b [d=4.18 ppm], and for the p-H of
the trisubstituted benzene ring of 4b [d=6.81 ppm], which
becomes 8-H in 5b [d=3.42 ppm].
Because of the chiral center C-3’ in 4b and 5b, the gemi-
nal protons of all CH2 groups (a-CH2, b-CH2, g-CH2, H2C-
2’, H2C-4’ in 4b and H2C-2, H2C-4, g-CH2, H2C-2’, H2C-4’ in
Chem. Asian J. 2010, 5, 1896 – 1901
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1897

D. Cao, H. Meier et al.
FULL PAPERS
bration, but does not change the equilibrium. The successful
functioning of the optical switch OS is possible using 366 nm
light, which is selectively absorbed by 4 and generates pure
5.
Chiroptical-Switch Properties
According to the optical switch, the optical rotation values
of solutions of 4b–d in benzene (4.0ꢂ10ꢀ3 m) can be reversi-
bly modulated by light. As illustrated in Figure 4, the optical
rotation value of 4b increases upon irradiation at l=
366 nm. It returns to its initial magnitude upon irradiation at
l=254 nm. Figure 3 shows the results of six cycles without
fatigue. Thus, a new chiroptical molecular switch with opti-
cal rotation values as “signal output” has been created.
Long-term irradiation of 4/5 at l=366 nm does not reveal
any decomposition; however, the fatigue resistance is some-
what lower for irradiation at l=254 nm. Figure 4 depicts the
Figure 2. a) 1H NMR spectra of 4b (upper part, C6D6) and the diastereo-
mers (5S,8S,3’S)-5b and (5R,8R,3’S)-5b (lower part, C6D6); b) AB parts
ꢀ
of the ABC spin pattern of substructure H2C-2’ HC-3’ in 4b (upper
part) and 5b (two lower parts).
5b) were diastereotopic. However, AB spin patterns are
only observed for H2C-2’ and H2C-4’ in 4b and 5b, and for
g-CH2 in 5b. The other CH2 groups are more distant from
the chiral center and give pseudosinglets in the 400 MHz
1H NMR spectra.
The AB part of the ABC spin pattern, which results from
ꢀ
the segment H2C-2’ HC-3’ in 5b, was the only part of the
1H NMR spectrum in which the two diastereomers of 5b ex-
hibit clearly separated signals (Figure 2b). Integration of
these signals gives the 1:1 ratio of the isomers. More signals
of the diastereomeric mixture are split in the 100 MHz
13C NMR spectrum of 5b (see Experimental Section). The
other compounds 4c,d and 5c,d show equivalent behaviour
in the NMR spectrum (for detailed signal assignments, see
Experimental Section.)
An explanation of the photochemical and photophysical
processes is given in Scheme 3. Energy-rich UV light
(254 nm) is predominantly absorbed by the benzene rings in
the periphery P of the dendrons of 4b–d and/or 5b–d (S0!
Sn). Energy transfer (ET) through the dendron D to the
core C then generates the photoreactive S1 states. For struc-
ture 4, ET could clearly be shown by the increase in the
fluorescence intensity.[36] A corresponding demonstration for
5 is more difficult, because 5 is non-fluorescent. The rigid
and spatially close arrangements of the two condensed ben-
zene rings on one side and the two enol ether p-systems on
the other side of 5 are the basis of a Davidov splitting of the
absorption and a corresponding energy-lowered S1 state.
The S1 states of 4 and 5 then lead to a photostationary state,
which is strongly weighted towards 4. ET accelerates equili-
Figure 3. Relationship between the optical rotation values (deg.cm2/10 g)
and switching cycles of 4b and (5S,8S,3’S)-5b/(5R,8R,3’S)-5b triggered by
irradiation: l=366 (c) and 254 nm (a). The irradiation periods for
complete conversion of a 4ꢂ10ꢀ3 m solution in dry benzene in this special
experiment were about 1 min for the cycloaddition and 2 min for the cy-
cloreversion.
Figure 4. UV/Vis absorbance (A) of 4b (c) and (5S,8S,3’S)-5b/
(5R,8R,3’S)-5b (a) in anhydrous dichloromethane solution. Inset: Rel-
ative absorption intensity at 260 nm obtained by alternating irradiation at
366 (c) and 254 nm (g).
Scheme 3. Photochemical and photophysical processes for the optical
switch OS: 4Ð5.
1898
www.chemasianj.org
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2010, 5, 1896 – 1901

A Dendrimer Chiroptical Switch
1H NMR (CDCl3, 400 MHz): d=0.95 (t, 3J=7.2 Hz, 3H, 5’-H), 1.01 (d,
3J=6.8 Hz, 3H, 3’-CH3), 1.25–1.30 (m, 1H, 4’-H), 1.54–1.58 (m, 1H, 4’-
H), 1.83–1.86 (m, 1H, 3’-H), 3.72 (m, 1H, 2’-H), 3.80 (m, 1H, 2’-H), 4.62
(s, 2H, CH2OH), 5.04 (s, 2H, g-CH2), 6.48 (m, 1H, trisubst. benzene),
6.54 (brs, 1H, trisubst. benzene), 6.59 (brs, 1H, trisubst. benzene), 7.31–
7.44 ppm (m, 5H, peripheral phenyl); 13C NMR (CDCl3, 100 MHz): d=
11.1 (C-5’), 16.3 (3’-CH3), 25.9 (C-4’), 34.5 (C-3’), 65.2 (CH2OH), 69.9 (g-
CH2), 72.8 (C-2’), 100.8, 104.9, 105.4 (CH, trisubst. benzene), 127.3, 127.8,
128.4 (CH, phenyl), 136.8 (Cq, phenyl), 143.1, 159.9, 160.6 ppm (Cq, tri-
subst. benzene); MS (APCI): m/z (%)=300.8 ([M+H]+, 100); elemental
analysis: calcd (%) for C19H24O3 (300.4): C 75.97, H 8.05; found: C 76.27,
H 8.11.
UV/Vis absorption spectra of 4b and 5b in CH2Cl2. The typ-
ical anthracene absorption bands at 347, 366, and 385 nm
disappear completely with irradiation of 4b at l=366 nm.
The quantitatively generated photoproduct 5b does not
absorb light at l>300 nm. This behavior provides the basis
for an efficient switching process. The inset in Figure 4
shows the modulation of the absorbance A at 260 nm by al-
ternating irradiation at 366 and 254 nm. It demonstrates the
fatigue resistance associated with the chiroptical switch
shown in Figure 3.
3-[3,5-Bis(benzyloxy)benzyloxy]-5-((3S)-3-methylbutoxy)-benzyl alcohol
(3c): Yield: 312 mg (61%) as a colorless viscous liquid, ½aꢂ2D0 =+7.38 (c=
0.15, CH2Cl2); 1H NMR (CDCl3, 400 MHz): d=0.94 (t, 3H, 5’-H), 1.01
(d, 3J=6.8 Hz, 3H, 3’-CH3), 1.22–1.30 (m, 1H, 4’-H), 1.53–1.58 (m, 1H,
4’-H), 1.83–1.86 (m, 1H, 3’-H), 3.72 (m, 1H, 2’-H), 3.80 (m, 1H, 2’-H),
4.62 (s, 2H, CH2OH), 4.98 (s, 2H, g-CH2), 5.04 (s, 4H, d-CH2), 6.46 (t,
4J=2.0 Hz, 1H, trisubst. benzene, dendron), 6.54 (br. s, 1H, trisubst. ben-
Conclusions
A new kind of chiral dendrimer with anthracene as the core
and Frꢀchet dendrons has been synthesized. The (S)-2-
methyl-1-butyl group attached to the core served as the
chiral source. Irradiation of 4b–d with l=366 nm light gave
rise to a quantitative intramolecular cycloaddition to give
diastereomers (5S,8S,3’S)- and (5R,8R,3’S)-5b–d in a 1:1
ratio. The process was quantitatively reversible upon irradia-
tion with l=254 nm or by heating to 608C. Thus, the optical
rotation values could be modulated by light. A new chiropti-
cal switch was developed on this molecular basis.
4
zene), 6.57 (d, j Jj=2.0 Hz, 2H, trisubst. benzene, dendron), 6.68 (m,
2H, trisubst. benzene), 7.34–7.43 ppm (m, 10H, peripheral phenyl);
13C NMR (CDCl3, 100 MHz): d=11.1 (C-5’), 16.3 (3’- CH3), 25.9 (C-4’),
34.5 (C-3’), 65.2 (CH2OH), 69.9 (g-CH2), 69.9 (d-CH2), 72.8 (C-2’), 100.8,
101.3, 104.9, 105.4, 106.2 (CH, trisubst. benzene), 127.3, 127.8, 128.4 (CH,
phenyl), 136.6 (Cq, phenyl) 139.2, 143.1, 159.8, 159.9, 160.5 ppm (Cq, tri-
subst. benzene); MS (APCI): m/z (%)=512.9 ([M+H]+, 100); elemental
analysis: calcd (%) for C33H36O5 (512.6): C 77.32, H 7.08; found: C 77.21,
H 7.09.
3-{3,5-BisACTHNUTRGNEU[GN 3,5-bis(benzyloxy)benzyloxy]benzyloxy}-5-((3S)-3-methylbu-
toxy)-benzyl alcohol (3d): Yield: 175 mg (56%) as a colorless solid, m.p.:
998C, ½aꢂ2D0 =+8.68 (c=0.15, CH2Cl2); 1H NMR (CDCl3, 400 MHz): d=
0.96 (t, 3J=7.2 Hz, 3H, 5’-H), 1.02 (d, 3J=6.8 Hz, 3H, 3’-CH3), 1.27 (m,
1H, 4’-H), 1.56 (m, 1H, 4’-H) 1.85 (m, 1H, 3’-H), 3.73 (m, 1H, 2’-H),
3.82 (m, 1H, 2’-H), 4.62 (s, 2H, CH2OH), 4.99 (brs, 6H, g-CH2 and d-
CH2), 5.05 (s, 8H, e-CH2), 6.49 (m, 1H, trisubst. benzene), 6.56–6.60 (m,
5H, trisubst. benzene), 6.69–6.71 (m, 6H, trisubst. benzene), 7.34–
7.45 ppm (m, 20H, peripheral phenyl); 13C NMR (CDCl3, 100 MHz): d=
11.1 (C-5’), 16.3 (3’-CH3), 25.9 (C-4’), 34.5 (C-3’), 65.1 (CH2OH), 69.7 (g-
CH2), 69.8 (d-CH2), 69.9 (e-CH2), 72.8 (C-2’), 100.8, 101.5, 104.9, 105.4,
106.2 (CH, trisubst. benzene, partly superimposed), 127.3, 127.8, 128.2
(CH, phenyl), 136.8 (Cq, phenyl), 139.0, 139.2, 143.1, 159.8, 159.9,
160.6 ppm (Cq, trisubst. benzene, partly superimposed); MS (APCI): m/
z(%)=954.5 ([M+NH4]+, 100); elemental analysis: calcd (%) for
C61H60O9 (937.1): C 78.18, H 6.45; found: C 78.32, H 6.47.
Experimental Section
General: The starting compounds 2a–d were prepared according to the
literature.[37, 38] (S)-(+)-2-methyl-1-bromobutane was purchased from Al-
drich and C6D6 was purchased from Alfa Aesar China. The optical rota-
tion values were determined with Autopol IV. UV/Vis spectra were re-
corded over a range of 200–450 nm using a Hitachi UV-3010 spectropho-
tometer. Melting points were measured with a Tektronix X4 apparatus
and are uncorrected. NMR spectra were obtained on a Bruker DRX 400
spectrometer at 400 MHz for 1H NMR and 100 MHz for 13C NMR in
CDCl3 or C6D6 as solvent. Mass spectra were obtained on an Esquire
HCT PLUS instrument. Elemental analyses were performed on a Her-
aeus elemental analyzer.
General Procedure for Preparation of Chiral Compounds 3a–d: Potassi-
um hydroxide (68 mg, 1.0 mmol, 82%), nBu4NBr (25 mg) and (S)-(+)-2-
methyl-1-bromobutane (166 mg, 1.1 mmol) were added to a solution of
2a–d (1.0 mmol) in dimethylformamide (10 mL). The reaction mixture
was heated to 608C and stirred under nitrogen for 24 h. After cooling to
room temperature, the mixture was poured into water and extracted
three times with ethyl acetate (3ꢂ10 mL). The combined organic phases
were dried over anhydrous MgSO4, and the products 3a–d were purified
by column chromatography (40ꢂ3 cm SiO2, petroleum ether/CH2Cl2/
ether 1:2:0.05).
General Procedure for Preparation of Chiral Compounds 4a–d: A mix-
ture of 9-chloromethylanthracene (113 mg, 0.5 mmol), 3 (0.55 mmol), po-
tassium hydroxide (37 mg, 0.55 mmol, 82%), nBu4NBr (25 mg,
0.078 mmol), chlorobenzene (15 mL), and H2O (0.5 mL) was stirred for
2 d at 608C. The solvent was removed under reduced pressure, and the
residue treated with CH2Cl2 and H2O. The isolated water layer was ex-
tracted three times with CH2Cl2 (3ꢂ10 mL). The combined organic
phases were dried with anhydrous MgSO4 and purified by column chro-
matography (50ꢂ3 cm SiO2, petroleum ether/CH2Cl2/ether 1:1:0.03) to
give 4.
3-Methoxy-5-((3S)-3-methylbutoxy)-benzyl alcohol (3a): Yield: 162 mg
(72%) as
a
colorless viscous liquid, ½aꢂ1D5 =+5.38 (c=0.15, CH2Cl2);
9-{[3-Methoxy-5-((3S)-3-methylbutoxy)benzyl
oxy]methyl}anthracene
1H NMR (CDCl3, 400 MHz): d=0.94 (t, 3J=7.2 Hz, 3H, 5’-H), 1.01 (d,
3J=6.8 Hz, 3H, 3’-CH3), 1.22–1.29 (m, 1H, 4’-H), 1.52–1.57 (m, 1H, 4’-
H), 1.84–1.87 (m, 1H, 3’-H), 3.71 (m, 1H, 2’-H), 3.78 (s, 3H, OCH3), 3.80
(m, 1H, 2’-H), 4.60 (s, 2H, CH2OH), 6.38 (m, 1H, trisubst. benzene),
6.50 ppm (m, 2H, trisubst. benzene); 13C NMR (CDCl3, 100 MHz): d=
11.1 (C-5’), 16.3 (3’-CH3), 25.9 (C-4’), 34.5 (C-3’), 55.1 (OCH3), 65.1
(CH2OH), 72.8 (C-2’), 99.9, 104.2, 105.0 (CH, benzene), 143.1, 160.5,
160.8 ppm (Cq, benzene); MS (APCI): m/z (%)=224.8 ([M+H]+, 100);
elemental analysis: calcd (%) for C13H20O3 (224.3): C 69.61, H 8.99;
found: C 69.47, H 9.04.
(4a): Yield: 165 mg (80%) as a light yellow viscous liquid, ½aꢂ1D5 =+3.68
(c=0.15, CH2Cl2); 1H NMR (CDCl3, 400 MHz): d=0.92 (t, 3J=7.2 Hz,
3H, 5’-H), 0.99 (d, 3J=6.8 Hz, 3H, 3’-CH3), 1.24 (m, 1H, 4’-H), 1.54 (m,
1H, 4’-H) 1.84 (m, 1H, 3’-H), 3.67 (m, 1H, 2’-H), 3.75 (s, 3H, OCH3),
3.78 (m, 1H, 2’-H), 4.64 (s, 2H, b-CH2), 5.47 (s, 2H, a-CH2), 6.41 (m,
1H, trisubst. benzene), 6.55 (m, 2H, trisubst. benzene), 7.43–7.52 (m, 4H,
anthracene), 7.99 (m, 2H, anthracene), 8.30 (m, 2H, anthracene),
8.45 ppm (s, 1H, anthracene); 13C NMR (CDCl3, 100 MHz): d=11.3 (C-
5’), 16.6 (3’-CH3), 26.1 (C-4’), 34.7 (C-3’), 55.3 (OCH3), 63.9 (a-CH2), 72.4
(b-CH2), 72.9 (C-2’), 100.5, 105.4, 106.1 (CH, trisubst. benzene), 124.4,
124.9, 126.1, 128.4, 128.7, 129.0, 131.1, 131.4 (CH and Cq, anthracene),
140.8, 160.6, 160.8 ppm (Cq, trisubst. benzene); MS (APCI): m/z(%)=
3-Benzyloxy-5-((3S)-3-methylbutoxy)-benzyl alcohol (3b): Yield: 201 mg
(67%) as
a
colorless viscous liquid, ½aꢂ1D5 =+6.08 (c=0.15, CH2Cl2);
Chem. Asian J. 2010, 5, 1896 – 1901
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1899

D. Cao, H. Meier et al.
FULL PAPERS
414.8 ([M+H]+, 11), 191 (100); elemental analysis: calcd (%) for
C28H30O3 (414.5): C 81.13, H 7.29; found: C 80.74, H 7.03.
pressure mercury lamp equipped with a Duran glass tube. A slow stream
of argon was bubbled for 15 min through the solution, which was main-
tained at 08C. Compounds 4b–d were then irradiated for 60, 50, and 45 s,
respectively. After irradiation, the solvent was removed at 308C, and the
mixture of diastereomers was obtained as a colorless viscous wax.
9-{[3-Benzyloxy-5-((3S)-3-methylbutoxy)benzyl oxy]methyl}anthracene
(4b): Yield: 191 mg (78%) as a colorless solid, m.p.: 838C, ½aꢂ1D5 =+4.08
(c=0.15, CH2Cl2); 1H NMR (C6D6, 400 MHz): d=0.93 (t, 3J=7.2 Hz,
3
7-Benzyloxy-22-((3S)-3-methylbutoxy)-3-oxahexacy-
3H, 5’-H), 1.03 (d, , J=6.8 Hz, 3H, 3’-CH3), 1.24 (m, 1H, 4’-H), 1.57 (m,
clo[7.6.6.25,8.01,5.010,15.016,21]tricosa-6,10,12,14,16,18,20,22-octaene
((5S,8S,3’S)-5b and (5R,8R,3’S)-5b): Yield: quantitative, ½aꢂ1D5 =+6.08 (c=
1H, 4’-H), 1.83 (m, 1H, 3’-H), 3.59 (m, 1H, 2’-H), 3.67 (m, 1H, 2’-H),
4.63 (s, 2H, b-CH2), 4.81 (s, 2H, g-CH2), 5.48 (s, 2H, a-CH2), 6.81 (m,
1H, trisubst. benzene), 6.84 (m, 1H, trisubst. benzene), 6.85 (m, 1H, tri-
subst. benzene), 7.17–7.27 (m, 3H, peripheral phenyl), 7.35–7.47 (m, 6H,
peripheral phenyl and anthracene), 7.92 (m, 2H, anthracene), 8.30 (s,
1H, anthracene), 8,54 ppm (m, 2H, anthracene). 1H NMR (CDCl3,
400 MHz): d=0.92 (t, 3J=7.2 Hz, 3H, 5’-H), 0.98 (d, 3J=6.8 Hz, 3H, 3’-
CH3), 1.23 (m, 1H, 4’-H), 1.53 (m, 1H, 4’-H), 1.83 (m, 1H, 3’-H), 3.66
(m, 1H, 2’-H), 3.75 (m, 1H, 2’-H), 4.64 (s, 2H, b-CH2), 4.98 (s, 2H, g-
CH2), 5.47 (s, 2H, a-CH2), 6.49 (m, 1H, trisubst. benzene), 6.56 (m, 1H,
trisubst. benzene), 6.62 (m, 1H, trisubst. benzene), 6.56 (m, 1H, trisubst.
benzene), 6.62 (m, 1H, trisubst. benzene, 7.30–7.41 (m, 5H, peripheral
phenyl), 7.43–7.50 (m, 4H, anthracene), 8.00 (m, 2H, anthracene), 8.31
(m, 2H, anthracene), 8.46 ppm (s, 1H, anthracene); 13C NMR (CDCl3,
100 MHz): d=11.1 (C-5’), 16.4 (3’-CH3), 26.0 (C-4’), 34.5 (C-3’), 63.7 (a-
CH2), 69.8 (g-CH2), 72.1 (b-CH2), 72.7 (C-2’), 101.1, 105.9, 106.4 (CH, tri-
subst. benzene), 124.3, 124.8, 125.9, 127.4, 127.7, 128.2, 128.4, 128.5, 128.8,
130.9, 131.3, 136.8 (CH and Cq, anthracene and peripheral phenyl), 140.6,
159.9, 160.4 ppm (Cq, trisubst. benzene); MS (APCI): m/z (%)=490.8
([M+H]+, 100); elemental analysis: calcd (%) for C34H34O3 (490.6):
C 83.23, H 6.98; found: C 83.07, H 7.07.
1
0.15, CH2Cl2); H NMR (C6D6, 400 MHz): d=0.90–1.01 (m, 6H, 5ꢃ-H, 3’-
CH3), 1.16–1.23 (m, 1H, 4ꢃ-H), 1.44–1.52 (m, 1H, 4ꢃ-H), 1.62–1.68 (m,
1H, 3ꢃ-H), 2.51/3.22 (AM of AMX, 2J=ꢀ8.8 Hz, 3J=5.2 Hz, 2H, 2’-H),
2.58/3.15 (AM of AMX, 2J=ꢀ9.1 Hz, 3J=5.6 Hz and 5.8 Hz, 2H, 2’-H),
4
3.42 (dt, 3J=10.8 Hz, j J j=2.0 Hz, 1H, 8-H), 3.69/4.20 (AB, 2J=
3
ꢀ11.0 Hz, 2H, g-CH2), 3.98 (s, 2H, 4-H), 4.18 (d, J=10.8 Hz, 9-H), 4.44,
s, 1H, 4.51, s, 1H (6-H, 23-H), 4.76 (s, 2H, 2-H), 7.07–7.37 ppm (m, 13H,
aromat. H); 13C NMR (C6D6, 100 MHz): d=11.1, 11.2 (C-5’), 16.5 (3’-
CH3), 25.9, 26.0 (C-4’), 34.4 (C-3’), 50.9 (C-9), 52.8 (C-8), 56.6 (C-5), 65.3
(C-1), 69.8 (g-C), 70.8 (C-2), 72.1, 72.2 (C-2’), 80.7 (C-4), 105.3, 106.8 (C-
6, C-23), 122.3, 122.4, 124.8, 125.4, 125.5, 128.1, 128.8 (aromat. CH, some
signals are covered by C6D6), 137.1, 144.6, 144.7, 146.3, 146.5 (aromat.
Cq), 162.5 ppm (Cq, C-7, C-22).
7-[3,5-Bis(benzyloxy)benzyloxy]-22-((3S)-3-methylbutoxy) ꢀ3-oxahexacy-
clo[7.6.6.25,8.01,5.010,15.016,21]tricosa-6,10,12,14,16,18,20,22-octaene
((5S,8S,3’S)-5c and (5R,8R,3’S)-5c): Yield: quantitative, ½aꢂ2D0 =+7.38 (c=
1
0.15, CH2Cl2); H NMR (C6D6, 400 MHz): d=0.90–1.00 (m, 6H, 5ꢃ-H, 3ꢃ-
CH3), 1.13–1.23 (m, 1H, 4ꢃ-H), 1.44–1.52 (m, 1H, 4ꢃ-H), 1.56–1.66 (m,
1H, 3ꢃ-H), 2.50/3.12 (2 m, 2J=ꢀ8.8 Hz, 2H, 2’-H), 2.56/3.19 (2 m, 2J=
2
ꢀ8.8 Hz, 2H, 2’-H), 3.44 (m, 1H, 8-H), 3.66/4.20 (AB, J=ꢀ10.8 Hz, 2H,
9-({3-[3,5-Bis(benzyloxy)benzyloxy]-5-((3S)-3-methylbutoxy)benzyloxy}-
methyl)anthracene (4c): Yield: 182 mg (52%) as a colorless solid, m.p.:
1078C, ½aꢂ1D5 =+5.38 (c=0.15, CH2Cl2); 1H NMR (CDCl3, 400 MHz): d=
0.93 (t, 3J=7.2 Hz, 3H, 5ꢃ-H), 0.99 (d, 3J=6.8 Hz, 3H, 3’-CH3), 1.25 (m,
1H, 4ꢃ-H), 1.54 (m, 1H, 4ꢃ-H), 1.84 (m, 1H, 3ꢃ-H), 3.67 (m, 1H, 2’-H),
3.76 (m, 1H, 2’-H), 4.64 (s, 2H, b-CH2), 4.93 (s, 2H, g-CH2), 5.01 (s, 4H,
d-CH2), 5.48 (s, 2H, a-CH2), 6.49 (m, 1H, trisubst. benzene), 6.56–6.60
(m, 3H, trisubst. benzene), 6.67 (m, 2H, trisubst. benzene), 7.31–7.41 (m,
14H, anthracene and peripheral phenyl), 8.00 (m, 2H, anthracene), 8.32
(m, 2H, anthracene), 8.45 ppm (s, 1H, anthracene); 13C NMR (CDCl3,
100 MHz): d=11.1 (C-5’), 16.4 (3’-CH3), 25.9 (C-4’), 34.5 (C-3’), 63.8 (a-
CH2), 69.7 (g-CH2), 69.9 (d-CH2), 72.1 (b-CH2), 72.8 (C-2’), 101.1, 101.4,
106.0, 106.2, 106.4 (CH, trisubst. benzene), 124.2, 124.7, 125.9, 127.3,
127.8, 128.2, 128.4, 128.5, 128.8, 130.9, 131.3, 136.6, (CH and Cq, anthra-
cene and peripheral phenyl), 139.2, 140.6, 159.8, 160.0, 160.5 ppm (Cq, tri-
subst. benzene); MS (APCI): m/z (%)=703.4 ([M+H]+, 19), 720.5
([M+NH4]+, 100); elemental analysis: calcd (%) for C48H46O5 (702.9):
C 82.02, H 6.60; found: C 81.93, H 6.62.
g-CH2), 3.94/3.97 (AB, 2J=ꢀ12.8 Hz, 2H, 4-H), 4.18 (d, 3J=10.8 Hz, 9-
H), 4.42, s, 1H, 4.49, s, 1H, (6-H, 23-H), 4.72 (s, 2H, 2-H), 4.87 (s, 4H, d-
CH2), 6.76 (m, 3H, trisubst. benzene), 7.10–7.39 (m, 18H, aromat. H);
13C NMR (C6D6, 100 MHz): d=11.3, 11.4 (C-5’), 16.4, 16.7 (3’-CH3), 26.2
(C-4’), 34.5, 34.7 (C-3’), 51.1 (C-9), 53.0 (C-8), 56.8 (C-5), 65.5 (C-1), 69.9
(g-C, d-C), 71.0 (C-2), 72.1, 72.2 (C-2’), 80.9 (C-4), 101.6, 101.8, 105.5,
106.5, 107.1, (C-6, C-23 and CH of trisubst. benzene), 122.6, 124.9, 125.1,
125.5, 125.7, (aromat. CH, some signals are covered by C6D6), 137.3,
139.6, 144.8, 146.6, 160.4 (aromat. Cq, partly superimposed), 162.7 (Cq, C-
7, C-22).
7-{3,5-BisACTHNUTRGNEU[GN 3,5-bis(benzyloxy)benzyloxy]benzyloxy}-22-((3S)-3-methylbu-
toxy-3-oxahexacyclo[7.6.6.25,8.01,5.010,15.016,21]tricosa-6,10,12,14,16,18,20,22-
20
octaene ((5S,8S,3’S)-5d and (5R,8R,3’S)-5d): Yield: quantitative, ½aꢂD
+8.68 (c=0.15, CH2Cl2); 1H NMR (C6D6, 400 MHz): d=0.88–1.00 (m,
6H, 5ꢃ-H), 1.12–1.20 (m, 1H, 4ꢃ-H), 1.36–1.50 (m, 1H, 4ꢃ-H), 1.52–1.62
(m, 1H, 3ꢃ-H), 2.47/3.09 (m, 2J=ꢀ8.8 Hz, 2H, 2’-H), 2.54/3.16 (m, 2J=
=
3
4
ꢀ8.8 Hz, 2H, 2’-H), 3.43 (dt, J=10.4 Hz, J=2.0 Hz, 1H, 8-H), 3.63/4.19
(AB, 2J=ꢀ11.0 Hz, 2H, g-CH2), 3.92/3.95 (AB, 2J=ꢀ12.0 Hz, 2H, 4-H),
4.17 (d, 3J=10.4 Hz, 9-H), 4.39 (s, 1H), 4.47 (s, 1H, 6-H, 23-H), 4.70 (s,
2H, 2-H), 4.80 (s, 8H, e-CH2), 4.90 (s, 4H, d-CH2), 6.75–6.80 (m, 3H, tri-
subst. benzene), 6.83–6.87 (m, 6H, trisubst. benzene) 7.08–7.35 ppm (m,
28H, aromat. H); 13C NMR (C6D6, 100 MHz): d=11.2, 11.3 (C-5’), 16.4,
16.7 (3’-CH3), 26.2 (C-4ꢃ), 34.5, 34.7 (C-3ꢃ), 51.1 (C-9), 53.1 (C-8), 56.8
(C-5), 65.6 (C-1), 69.9 (g-C, d-C, e-C), 71.0 (C-2), 71.9, 72.3 (C-2’), 80.9
(C-4), 101.8, 105.6, 105.8, 106.5, 107.1, (C-6, C-23 and CH of trisubst.
benzene), 122.5, 124.0, 125.1, 125.6, 125.8, 126.2, (aromat. CH, some sig-
nals are covered by C6D6), 137.3, 139.8, 139.9, 144.9, 146.5, 146.6, 160.4,
160.6 (aromat.Cq, partly superimposed), 162.7 ppm (2Cq, C-7, C-22).
9-[(3-{3,5-BisACHTUNGTRENNUNG[3,5-bis(benzyloxy)benzyloxy] benzyloxy}-5-((3S)-3-methyl-
butoxy)benzyloxy) methyl]anthracene (4d): Yield: 225 mg (40%) as a
colorless solid, m.p.: 1458C, ½aꢂ1D5 =+6.78 (c=0.15, CH2Cl2); 1H NMR
3
3
(CDCl3, 400 MHz): d=0.93 (t, J=7.2 Hz, 3H, 5ꢃ-H), 0.99 (d, J=6.8 Hz,
3H, 3’-CH3), 1.25 (m, 1H, 4ꢃ-H), 1.54 (m, 1H, 4ꢃ-H), 1.84 (m, 1H, 3ꢃ-H),
3.68 (m, 1H, 2’-H), 3.76 (m, 1H, 2’-H), 4.64 (s, 2H, b-CH2), 4.93 (s, 2H,
g-CH2), 4.96 (s, 4H, d-CH2), 5.03 (s, 8H, e-CH2), 5.48 (s, 2H, a-CH2),
6.51 (m, 1H, trisubst. benzene), 6.55 (m, 1H, trisubst. benzene), 6.58–
6.62 (m, 4H, trisubst. benzene), 6.68 (m, 6H, trisubst. benzene), 7.31–
7.42 (m, 24H, anthracene and peripheral phenyl), 8.00 (m, 2H, anthra-
cene), 8.32 (m, 2H, anthracene), 8.44 ppm (s, 1H, anthracene); 13C NMR
(CDCl3, 100 MHz): d=11.1 (C-5’), 16.3 (3’-CH3), 25.9 (C-4’), 34.5 (C-3’),
63.8 (a-CH2), 69.7 (g-CH2), 69.8 (d-CH2), 69.9 (e-CH2), 72.1 (b-CH2),
72.8 (C-2’), 101.2, 101.4, 101.5, 106.0, 106.2, 106.3 (CH, trisubst. benzene,
partly superimposed), 124.2, 124.7, 125.9, 127.3, 127.8, 128.2, 128.4, 128.8,
130.9, 131.3, 136.6 (CH and Cq, anthracene and peripheral phenyl, partly
superimposed), 139.0, 140.6, 159.9, 160.0, 160.5 ppm (Cq, trisubst. ben-
zene); MS (APCI): m/z(%)=1144.4 ([M+NH4]+), 637.4 (100); elemental
analysis: calcd (%) for C76H70O9 (1127.4): C 80.97, H 6.26; found:
C 80.72, H 6.27.
General Procedure for the Photocycloreversion of 5b–d: Irradiation of
5b–d in anhydrous benzene with a ZDZ-6 A lamp (l=254 nm) led to a
quantitative reverse reaction to generate pure 4b–d. Heating (Tꢁ608C)
in anhydrous benzene gave the same result.
Acknowledgements
General Procedure for the Generation of Photocycloaddition Products
5b–d: Dilute solutions of compounds 4b-d (15–20 mg) in benzene (10–
15 mL, ca. 10ꢀ3 molLꢀ1) were irradiated (l>350 nm) with a medium-
Financial support by the National Natural Science Foundation of China
(20872038) and the Specialized Chinese Research Fund for the Doctoral
Program of Higher Education (20060561024) is gratefully acknowledged.
1900
www.chemasianj.org
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2010, 5, 1896 – 1901

A Dendrimer Chiroptical Switch
[1] B. L. Feringa, N. P. M. Huck, A. M. Schoevaars, Adv. Mater. 1996, 8,
681–684.
[26] Y. Yokoyama, Y. Shimizu, S. Uchida, Y. Yokoyama, Chem.
Commun. 1995, 785–786.
[2] B. L. Feringa, R. A. van Delden, N. Koumura, E. M. Geertsema,
Chem. Rev. 2000, 100, 1789–1861.
[27] Y. Yokoyama, S. Uchida, Y. Yokoyama, Y. Sugawara, Y. Kurita, J.
Am. Chem. Soc. 1996, 118, 3100–3107.
[3] M. Q. Sans, P. Belser, Coord. Chem. Rev. 2002, 229, 59–66.
[4] B. L. Feringa, Acc. Chem. Res. 2001, 34, 504–513.
[5] B. L. Feringa, J. Org. Chem. 2007, 72, 6635–6652.
[6] W. R. Browne, M. M. Pollard, B. D. Lange, A. Meetsma, B. L. Ferin-
ga, J. Am. Chem. Soc. 2006, 128, 12412–12413.
[7] B. L. Feringa, Molecular Switches, Wiley-VCH, Weinheim, 2001.
[8] B. L. Feringa, W. F. Hager, B. de Lange, E. W. Meijer, J. Am. Chem.
Soc. 1991, 113, 5468–5470.
[28] Y. Yokoyama, Chem. Rev. 2000, 100, 1717–1739.
[29] Z. Y. Wang, E. K. Todd, X. P. Meng, J. P. Gao, J. Am. Chem. Soc.
2005, 127, 11552–11553.
[30] M. C. CarreÇo, I. Garcia, I. NfflÇez, E. Merino, M. Ribagorda, S.
Pieraccini, G. P. Spada, J. Am. Chem. Soc. 2007, 129, 7089–7100.
[31] M. Mathews, N. Tamaoki, J. Am. Chem. Soc. 2008, 130, 11409–
11416.
[32] M. J. Kim, S. J. Yoo, D. Y. Kim, Adv. Funct. Mater. 2006, 16, 2089–
2094.
[33] S. Pieraccini, S. Masiero, G. P. Spada, G. Gottarelli, Chem. Commun.
2003, 598–599.
[9] W. F. Jager, J. C. de Jong. B. de Lange, N. P. M. Huck, A. Meetsma,
B. L. Feringa, Angew. Chem. 1995, 107, 346–349; Angew. Chem. Int.
Ed. Engl. 1995, 34, 348–350.
[10] R. A. van Delden, J. H. Hurenkamp, B. L. Feringa, Chem. Eur. J.
2003, 9, 2845–2853.
[34] L. Angiolini, T. Benelli, R. Bozio, A. Daurœ, L. Giorgini, D. Pedron,
Synth. Met. 2003, 139, 743–746.
[11] M. K. J. ter Wiel, B. L. Feringa, Tetrahedron 2009, 65, 4332–4339.
[12] M. Irie, S. Nakamura, J. Org. Chem. 1988, 53, 6136–6138.
[13] T. Yamaguchi, K. Uchida, M. Irie, J. Am. Chem. Soc. 1997, 119,
6066–6071.
[35] S. M. Grayson, Jean M. J. Frꢀchet, Chem. Rev. 2001, 101, 3819–
3868.
[36] D. Cao, S. Dobis, C. M. Gao, S. Hillmann, H. Meier, Chem. Eur. J.
2007, 13, 9317–9323.
[14] M. Irie, Chem. Rev. 2000, 100, 1683–1684.
[15] K. Matsuda, S. Yamamoto, M. Irie, Tetrahedron Lett. 2001, 42,
7291–7293.
[16] T. Hirose, K. Matsuda, M. Irie, J. Org. Chem. 2006, 71, 7499–7508.
[17] K. S. Burnham, G. B. Schuster, J. Am. Chem. Soc. 1998, 120, 12619–
12626.
[18] M. M. Birau, Z. Y. Wang, Tetrahedron Lett. 2000, 41, 4025–4028.
[19] J. Deng, N. H. Song, Q. F. Zhou, Z. X. Su, Org. Lett. 2007, 9, 5393–
5396.
[37] C. J. Hawker, Jean M. J. Frꢀchet, Macromolecules 1990, 23, 4726–
4729.
[38] See also Z. Bo, A. Schäfer, P. Franke, A. D. Schlüter, Org. Lett.
2000, 2, 1645–1648.
[39] H. D. Becker, Chem. Rev. 1993, 93, 145–172.
[40] H. Bouas-Laurent, A. Castellan, J. P. Desvergne, R. Lapouyade,
Chem. Soc. Rev. 2000, 29, 43–55.
[41] H. Bouas-Laurent, A. Castellan, J. P. Desvergne, R. Lapouyade,
Chem. Soc. Rev. 2001, 30, 248–263.
[20] R. A. van Delden, T. Mecca, C. Rosini, B. L. Feringa, Chem. Eur. J.
2004, 10, 61–70.
[42] D. Cao, C. M. Gao, S. Dobis, H. Meier, Synthesis 2007, 13, 1995–
2001.
[21] Y. C. Zhou, D. Q. Zhang, Y. Z. Zhang, Y. L. Tang, D. B. Zhu, J. Org.
Chem. 2005, 70, 6164–6170.
[43] D. Cao, S. Dobis, D. Schollmeyer, H. Meier, Tetrahedron 2003, 59,
5323–5327.
[22] C. Wang, L. Y. Zhu, J. F. Xiang, Y. X. Yu, D. Q. Zhang, Z. G. Shuai,
D. B. Zhu, J. Org. Chem. 2007, 72, 4306–4312.
[44] S. Dobis, D. Schollmeyer, C. M. Gao, D. R. Cao, H. Meier, Eur. J.
Org. Chem. 2007, 2964–2969.
[23] L. Eggers, V. Buss, Angew. Chem. 1997, 109, 885–887; Angew.
Chem. Int. Ed. Engl. 1997, 36, 881–883.
[24] A. Miyashita, A. Iwamoto, T. Kuwayama, H. Shitara, Y. Aoki, M.
Hirano, H. Nohira, Chem. Lett. 1997, 965–966.
[45] D. Cao, S. Dobis, H. Meier, Tetrahedron Lett. 2002, 43, 6853–6855.
[46] D. Cao, H. Meier, Angew. Chem. 2001, 113, 193–195; Angew. Chem.
Int. Ed. 2001, 40, 186–188.
[25] G. Y. Wen, J. Yan, Y. C. Zhou, D. Q. Zhang, L. Q. Mao, D. B. Zhu,
Chem. Commun. 2006, 3016–3018.
Received: February 26, 2010
Published online: June 25, 2010
Chem. Asian J. 2010, 5, 1896 – 1901
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1901