Planar chirality of twisted trans-azobenzene structure induced by chiral transfer from binaphthyls

Article abstract of DOI:10.1021/jo201578z

The absolute configuration of a binaphthyl-azobenzene dyad 2b, which has a chiral axis and a chiral plane, was determined by comparing the experimental circular dichroism (CD) spectra with the theoretical CD spectra calculated by the time-dependent (TD)-D

Full text of DOI:10.1021/jo201578z

NOTE
pubs.acs.org/joc
Planar Chirality of Twisted trans-Azobenzene Structure Induced by
Chiral Transfer from Binaphthyls
Kazuto Takaishi,*,† Atsuya Muranaka,† Masuki Kawamoto,† and Masanobu Uchiyama*,†,‡
†RIKEN, Hirosawa 2-1, Wako, Saitama 351-0198, Japan
‡Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
S Supporting Information
b
ABSTRACT: The absolute configuration of a binaphthyl-
azobenzene dyad 2b, which has a chiral axis and a chiral plane,
was determined by comparing the experimental circular dichro-
ism (CD) spectra with the theoretical CD spectra calculated by
the time-dependent (TD)-DFT method. The CD signals of the
trans-azobenzene moiety indicated that the two benzene rings
of this moiety are twisted unidirectionally. It is suggested that
these dyads with shorter linkers may be suitable for use as
chiroptical switches.
he cis and trans forms of the azobenzene skeleton can be
easily and reversibly photoisomerized and differ significantly
coupling of 2,20-dihydroxyazobenzene (3) and appropriate
ω-bromo-R-hydroxyalkanes in moderate yields. Usual dimesyla-
tion of 4 gave 5a8 and 5c-e. (aR)-1a and 1c-e were prepared by
tandem etherification of (R)-BINOL (6) and appropriate dimesy-
lates 5. (aR)-2a and 2c-ewere synthesized similarly using benzylated
binol (R)-7.9 In the cyclization to dyads (aR)-1 and (aR)-2, the
yields of (aR)-1d and (aR)-2d were higher than the others. There-
fore, linkers much longer or much shorter than those of (aR)-1d and
(aR)-2d were unfavorable for the cyclization.
T
in length. Therefore, azobenzene structures are widely used as
the photochromic moiety in many types of molecular switches.1
Recently, optically active azobenzene adducts have been re-
ported as potential chiroptical switches.2,3 We have studied the
photoswitching of chiroptical properties, such as circular dichro-
ism (CD) and optical rotation,4 and we reported induced helical
chirality of cis-azobenzene units in axially chiral binaphthyl-
azobenzene dyads,5,6 mainly 1b and 2b (Figure 1). However,
questions remain about (1) the origin of the CD activity of trans-
azobenzene moieties and (2) the effect of linker length between
the binaphthyl and azobenzene moieties on the conformation and
optical properties. The trans-azobenzenes of dyads 1 and 2 are able
to take at least three different configurations. The three (aR)-trans-
forms are shown in Figure 2. The linkers of the left structure, (aR)-
trans-achiral form (hereinafter called (aR)-trans-A form), lie in the
same direction. In contrast, the linkers of the other two structures
are staggered, so that these structures have planar chirality, (aR)-
trans-(pR) form (center) and (aR)-trans-(pS) form (right), respec-
tively. Although inversion of the two benzene rings or the NdN
bond of the azobenzene moiety has been reported,7 we speculated
that the trans-azobenzene moieties of 1 and 2 would be biased
toward the one of the above three configurations due to the cyclic
structure with a chiral binaphthyl. Moreover, we focused on the
influence of linker length, since this might affect the extent of
propagation of chiroptical properties of dyads on photoirradiation.
Perhaps shorter would be better? Herein, we investigated the planar
chirality of the trans-azobenzene moieties, the origin of the CD
activity, and the potential chiroptical switching capabilities of dyads
1aꢀe and 2aꢀe.
Cis-trans reversible photoisomerization of all of these cyclic
dyads occurred and could be detected as changes of absorption at
around 360 nm, which is derived from the allowed πꢀπ* transition
of the trans-azobenzene. As is typical, transfcis isomerization was
induced by 365 nm irradiation, whereas cisftrans isomerization was
induced by 436 nm irradiation. The isomerization ratios of all of
(aR)-1 and -2 were ca. 0.8. Absorption spectra of (aR)-2a and (aR)-
2e after photoirradiation are shown in Figures 3b,c and 3e,f, respec-
tively. Spectral shapes were similar and independent of linker length.
However, there were major differences in the CD spectra at longer
wavelength (400ꢀ600 nm), where only the azobenzene moiety (n-π*)
absorbs, among the compounds (Figures 3a, 3d, and Table 1).10
In general, dyads possessing longer linkers exhibited a low value
of Δε at this region. These CD data indicated that chiral transfer
from the binaphthyl skeleton to the azobenzene moiety is more
favorable in both cis- and trans-azobenzene of dyads with shorter
linkers, that is, (aR)-1aꢀb and -2aꢀb.
First, in the cis-form, the azobenzene moieties have helical
chirality (direction of twisting pattern of the two benzene rings), as
previously reported.5 That is, the negative Cotton effect at longer
wavelength induced by (aR)-binaphthyls after 365 nm irradiation
indicated that helical chirality of cis-azobenzenes was (P). Second, in
(aR)-1b and (aR)-2b are known compounds, as noted above.
Novel azobenzene-binaphthyl dyads were synthesized as shown
in Scheme 1. Compounds 4a8 and 4c-e were prepared by
Received: July 28, 2011
Published: August 03, 2011
r
2011 American Chemical Society
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|

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NOTE
Figure 1. Axially chiral binaphthyl-azobenzene dyads. “aR” means that the axial chirality of binaphthyl is R.
Scheme 1. Synthesis of Azobenzene-binaphthyl Dyads (aR)-1a, 1cꢀe, 2a, and 2cꢀe
(aR)-trans-(pR)-2b is the preferred configuration. Although we
similarly examined the configurations of the other compounds
(Figure S7ꢀS9 in the Supporting Information), in addition to
prediction of NMR, VCD, and [R]D, it was impossible to make a
clear decision as to the predominant structure. However, because CD
of the azobenzene moieties of 1a, 1b and 2a were active, it was
considered that the azobenzene moieties were also unidirectionally
twisted in these compounds. In addition, the CD spectrum of just the
azobenzene moiety, trans-2,20-dimethoxyazobenzene, extracted from
the optimized (aR)-trans-(pR)-2b, was calculated (Figure 6). This
CD spectrum in the 350ꢀ600 nm region was in excellent agreement
with that of (aR)-trans-(pR)-2b. The same tendency was also seen in
the cases of (aR)-trans-A-2b and (aR)-trans-(pS)-2b. Therefore, the
CD signal in this region was derived from the unidirectionally twisted
benzene rings of the azobenzene moiety and was not induced CD
related to the presence of the binaphthyl moiety.14,15 The relationship
between the twisting pattern of the trans-azobenzene moiety judged
from the crystal structures and the Cotton effect are consistent with
those reported by Tamaoki.3b
Figure 2. Configurations of binaphthyl-trans-azobenzene dyads. “aR”
means that the axial chirality of binaphthyl is R. “pR” means that the
planar chirality of azobenzene is R.
the trans-form, it was considered that only one of the three structures
shown in Figure 2 was induced. To confirm this, we calculated the
optimized conformations and their CD spectra of each of the three
configurations of (aR)-1a, -1b, -2a, and -2b. Figure 4 shows the three
optimized geometries and the torsion angles between the two
benzene rings of azobenzene in (aR)-2b obtained by DFT calcula-
tion at the B3LYP/6-31G(d) level.11,12 These structures illustrate
the following two points: (1) In all conformations, the azobenzene
moieties were not fully planar, but their two benzene rings were
twisted. The torsion angles of C(1)ꢀC(2)ꢀC(3)ꢀC(4) were 49.5°
(trans-A-2b), ꢀ125.2° (trans-(pR)-2b), and 137.1° (trans-(pS)-2b),
respectively as if the binaphthyls pulled on each benzene ring.13 (2)
The azobenzene moiety and benzyl groups of binaphthyl at the 3,30-
positions of trans-(pR)-2b did not interact (side view (Figure 4B)),
whereas in trans-(pS)-2b, there is an overlap (side view (Figure 4C)).
Next, by using the optimized geometries, CD signals at 350ꢀ
500 nm were calculated by means of the TD-DFT method
(Figure 5). The Cotton effect patterns of the calculated CD
spectra, compared with the experimental spectra, indicated that
Moreover, we focused on the switching of the optical rotation,16
which can be detected at an unabsorbed wavelength, so that the target
compounds are not degraded during measurements and do not
exhibit hysteresis. The column [R]D in Table 1 shows the values of
(aR)-1 and (aR)-2 during photoirradiation, until the values became
constant. Shorter linkers tended to be associated with larger changes
of [R]D. Actually, [R]D of (R)-1a exhibited the largest change (ca.
1500°), and this compound is a good candidate for a switch based on
dextro-rotation/levo-rotation. In addition, (aR)-1b and (aR)-2a are
candidates for switches based on zero-rotation/dextro-rotation.
Compounds 1cꢀe and 2cꢀe seem to be unsuitable for chiroptical
switches because of their small chiroptical changes. Furthermore, at
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NOTE
Figure 3. (a) CD spectra of (aR)-2a, (b,c) absorption spectra of (aR)-2a, (d) CD spectra of (aR)-2e, and (e,f) absorption spectra of (aR)-2e after
365 nm irradiation (blue, rich in cis-form) and 436 nm irradiation (red, rich in trans-form). Conditions: 1,4-dioxane, 1.0 ꢁ 10ꢀ5 M, 20 °C, light path
length = 10 mm, irradiation 10 mW/cm2, 100 s).
Table 1. CDa Data and [R]Db of (aR)-1aꢀ2e after
Photoirradiation
after 365 nm irradiation
after 436 nm irradiation
CDλ
Δε
[R]D
CDλ
Δε
[R]D
(aR)-1a
(aR)-1b
(aR)-1c
(aR)-1d
(aR)-1e
(aR)-2a
(aR)-2b
(aR)-2c
(aR)-2d
(aR)-2e
425
435
429
433
ꢀ17
ꢀ23
ꢀ16
ꢀ12
0
ꢀ644
ꢀ1318
ꢀ749
ꢀ600
ꢀ63
468
432
429
433
+12
ꢀ10
ꢀ9
ꢀ11
0
+839
+79
ꢀ454
ꢀ559
ꢀ91
+845
+642
ꢀ235
ꢀ511
ꢀ97
435
434
ꢀ8
ꢀ72
472
482
+9
ꢀ19
ꢀ8
ꢀ314
ꢀ507
ꢀ456
ꢀ81
+14
0
435
(432)
ꢀ10
(448)
ꢀ11
0
0
a Conditions: 1,4-dioxane, 1.0 ꢁ 10ꢀ5 M, 20 °C, light path length = 10
mm, irradiation strength = 10 mW/cm2, 100 s. b Conditions: chloro-
form, c = 0.10 g/dL, 20 °C, light path length = 10 cm, irradiation strength
= 10 mW/cm2, 500 s.
298 K, the half-lives of most of these cyclic cis-compounds were
longer than 100 h, which is extraordinary for azobenzene derivatives
(Table S3 in the Supporting Information).
In summary, the absolute configuration of a planar-chiral
binapthyl-trans-azobenzene dyad 2b was determined. The trans-
azobenzene of 2b was twisted unidirectionally. It is likely that the
azobenzene moieties of 1a, 1b, and 2a are also unidirectionally
twisted, though this remains to be confirmed. Huge optical rotation
switching was achieved by dyads with short linkers, suggesting that
asymmetric azobenzenes are good candidates for chiroptical switches,
asymmetric organo catalysts and chiral recognition agents. Further
studies aimed at the synthesis of binaphthyl-azobenzene dyads
connected by extremely short linkers are under way in our laboratory.
Figure 4. Top view and side view of the optimized structures of the
three types of (aR)-trans-2b at the B3LYP/6-31G(d) level. Azobenzene
moieties are shown in orange and binaphthyl skeletons in black.
Hydrogen atoms are not shown.
(30 mL) was stirred for 24 h at 80 °C. The reaction mixture was
poured into the mixed solvent of chloroform and water. The organic
layer was separated and washed successively with 0.1 N hydrochloric
acid solution, water (twice), and brine. After dried over sodium
sulfate, the solvent was evaporated in vacuo to give a residue. The
residue was purified by column chromatography (SiO2; chloro-
form/ethyl acetate = 6/4) to afford 4a (5.61 g, 18.6 mmol, 62%). 4a
is a known compound although synthetic route is difference from
traditional method.8
’ EXPERIMENTAL SECTION
Synthetic Method of 1ꢀ4. 2,20-bis(2-Hydroxyethoxy)azoben-
zene (4a). A suspension of 2,20-dihydroxyazobenzene (6.42 g, 30
mmol), 2-bromo-1-ethanol (10.7 mL, 150 mmol, 5.0 equiv),
and potassium carbonate (20.7 g, 150 mmol, 5.0 equiv) in DMF
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NOTE
Figure 5. (a) Calculated CD of (aR)-trans-A-2b (black), (aR)-trans-(pR)-
2b (green), (aR)-trans-(pS)-2b (blue) (TD-DFT method at the B3LYP/6-
31G(d) level, Gaussian bands with a half-bandwidth of 2500 cmꢀ1), and
experimental CD of (aR)-2b after 436 nm irradiation (1,4-dioxane, 1 ꢁ
10ꢀ5 M, 20 °C). (b) Absorption spectra of (aR)-2b after 436 nm irradiation
(1,4-dioxane, 1 ꢁ 10ꢀ5 M, 20 °C).
Figure 6. (a) Structure of 2,20-dimethoxyazobenzene extracted from
the optimized (aR)-trans-(pR)-2b. (All hydrogen atoms are hidden.) (b)
Calculated CD of 2,20-dimethoxyazobenzene extracted from the optimized
(aR)-trans-(pR)-2b. (TD-DFT method at the B3LYP/6-31G(d) level,
Gaussian bands with a half-bandwidth of 2500 cmꢀ1.)
2,20-bis(4-Hydroxybutoxy)azobenzene (4c). 4c was synthe-
sized in a similar manner to that for 4a with the exception that
4-bromo-1-butanol was used. 67% yield; Red amorphous; IR
(KBr) 3276, 1487, 1467, 1279, 1232, 744 cmꢀ1; 1H NMR (400
MHz, CDCl3, ppm) δ 1.6ꢀ1.9 (m, 4H), 1.9ꢀ2.2 (m, 4H), 2.46
(s, 2H), 3.7ꢀ4.1 (m, 4H), 4.1ꢀ4.4 (m, 4H), 6.5ꢀ7.2 (m, 4H),
7.2ꢀ7.5 (m, 2H), 7.65, 7.68 (two d, J = 8.4 Hz, J = 6.4 Hz, 2H);
13C NMR (100 MHz, CDCl3, ppm) δ 25.6, 26.1, 30.1, 61.9, 69.4,
69.4, 113.9, 113.9, 117.2, 117.4, 120.1, 121.0, 132.1, 132.3, 142.8,
142.8, 156.2, 156.3 (Some peaks overlapped); LR MS (FAB+)
359.2 (M+H)+; HR MS (FAB+) Calcd for C20H27N2O4 (M+H)+:
359.1971. Found: 359.1966.
HR MS (FAB+) Calcd for C28H42N2O4 (M+): 470.3145. Found:
470.3139.
2,20-bis(4-Mesyloxypropoxy)azobenzene (5c). A suspension
of 4c (780 mg, 2.17 mmol), methanesulfonyl chloride (843 μL, 10.9
mmol, 5.0 equiv), and triethylamine (606 μL, 4.35 mmol, 2.0 equiv) in
dichloromethane (40 mL) was stirred for 2 h at r.t. The reaction
mixture was poured into the mixed solvent of chloroform and water.
The organic layer was separated and washed successively with 0.1 N
hydrochloric acid solution, water (twice) and brine. After dried over
sodium sulfate, the solvent was evaporated in vacuo to give a residue.
The residue was purified by column chromatography (SiO2; chloro-
form/ethyl acetate = 7/3) to afford 5c (887 mg, 1.72 mmol, 79%).
Red amorphous; IR (KBr) 1487, 1353, 1279, 1173, 760 cmꢀ1; 1H
NMR (400 MHz, CDCl3, ppm, major isomer) δ 1.9ꢀ2.1 (m, 8H),
2.91 (s, 6H), 4.23 (t, J= 5.6 Hz, 4H), 4.36 (t, J= 5.6, 2H), 7.0ꢀ7.1 (m,
4H),7.40(t,J= 7.2 Hz, 2H), 7.62 (d, J=7.6Hz,2H);13CNMR(100
MHz, CDCl3, ppm) δ 25.3, 26.3, 37.2, 37.3, 68.9, 68.9, 69.9, 70.0,
114.6, 114.6, 117.1, 117.3, 120.9, 121.2, 132.0, 132.2, 143.1, 143.1,
156.3, 156.5; LR MS (FAB+) 515.1 (M + H)+;HRMS(FAB+) Calcd
for C22H31N2O8S2 (M + H)+: 515.1522. Found: 515.1508.
2,20-bis(5-Mesyloxybutoxy)azobenzene (5d). 5d was synthe-
sized in a similar manner to that for 5c with the exception that 4d
was used; 50% yield; Red amorphous; IR (KBr) 1488, 1342,
1279, 1171, 939, 764 cmꢀ1; 1H NMR (400 MHz, CDCl3, major
isomer) δ 1.6ꢀ1.8 (m, 4H), 1.8ꢀ1.9 (m, 4H), 1.9ꢀ2.0 (m, 4H),
2.92 (s, 6H), 4.1ꢀ4.3 (m, 8H), 6.9ꢀ7.1 (m, 4H), 7.3ꢀ7.7 (m,
4H); 13C NMR (100 MHz, CDCl3, ppm, major isomer) δ 22.3,
28.5, 28.8, 37.2, 69.3, 69.9, 114.5, 117.1, 120.9, 132.1, 143.1,
156.4; LR MS (FAB+) 543.2 (M + H)+; HR MS (FAB+) Calcd
for C24H35N2O8S2 (M + H)+: 543.1835. Found: 543.1825.
2,20-bis(5-Hydroxypentoxy)azobenzene (4d). 4d was synthe-
sized in a similar manner to that for 4a with the exception that
5-bromo-1-pentanol was used; 93% yield; Red amorphous; IR (KBr)
3349, 1491, 1474, 1281, 1154, 755, 743 cmꢀ1; 1H NMR (400 MHz,
CDCl3, ppm) δ 1.4ꢀ1.8 (m, 8), 1.8ꢀ2.0 (m, 4H), 3.63 (br s, 4H),
4.19 (t, J = 6.4 Hz, 4H), 7.00 (t, J = 7.6 Hz, 2H), 7.06 (d, J = 8.4 Hz,
2H), 7.38 (t, J = 7.6 Hz, 2H), 7.64 (d, J = 8.4 Hz, 2H); 13C NMR
(100 MHz, CDCl3, ppm, single isomer) δ 22.4, 28.9, 62.7, 69.6,
114.6, 117.3, 120.9, 131.0, 143.2, 156.5; LR MS (FAB+) 387.2
(M+H)+;HRMS(FAB+) Calcd for C22H30N2O4 (M+): 386.2206.
Found: 386.2196.
2,20-bis(8-Hydroxyoctoxy)azobenzene (4e). 4e was synthe-
sized in a similar manner to that for 4a with the exception that
8-bromo-1-octanol was used; 40% yield; Red oil; IR (KBr) 3462,
1
1489, 1470, 1240, 1155, 1047, 759 cmꢀ1; H NMR (400 MHz,
CDCl3, ppm, major isomer) δ 1.2ꢀ1.4 (m, 12H), 1.4ꢀ1.6 (m, 8H),
1.8ꢀ2.1 (m, 4H), 3.55 (t, J = 6.8 Hz, 4H), 4.16 (t, J = 6.4 Hz, 4H),
6.98 (t, J = 7.2 Hz, 2H), 7.05 (d, J = 8.4 Hz, 2H), 7.36 (t, J = 7.2 Hz,
2H), 7.66 (d, J = 8.4 Hz, 2H); 13C NMR (100 MHz, CDCl3, ppm,
major isomer) δ 25.5, 25.9, 29.1, 29.2, 29.2, 29.3, 62.6, 69.7, 114.5,
117.1, 120.6, 131.9, 143.7, 156.5; LR MS (FAB+) 471.3 (M + H)+;
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NOTE
2,20-bis(8-Mesyloxyoctoxy)azobenzene (5e). 5e was synthe-
sized in a similar manner to that for 5c with the exception that 4e
was used; 89% yield; Red oil; IR (KBr) 1488, 1342, 1279, 1171,
765 cmꢀ1; 1H NMR (300 MHz, CDCl3, ppm, single isomer) δ
1.2ꢀ1.5 (m, 12H), 1.54 (quintet, J = 7.5 Hz, 4H), 1.73 (quintet,
J = 6.6 Hz, 4H), 1.90 (quintet, J = 6.9 Hz, 4H), 2.98 (s, 6H),
3.67 (s, 4H), 4.18 (t, J = 6.6 Hz, 4H), 7.00 (t, J = 7.8 Hz, 2H), 7.09
(d, J = 7.8 Hz, 2H), 7.39 (dt, J = 7.8 Hz, 1.5 Hz, 2H), 7.65 (dd, J =
7.8 Hz, 1.5 Hz, 2H); 13C NMR (100 MHz, CDCl3, ppm, single
isomer) δ 25.1, 25.7, 28.8, 28.9, 29.0, 37.0, 52.4, 69.6, 70.1,
114.5, 117.0, 120.6, 132.0, 142.9, 156.5; LR MS (FAB+) 627.3
(M + H)+; HR MS (FAB+) Calcd for C30H47N2O8S2 (M + H)+:
627.2774. Found: 627.2778.
(300 MHz, CDCl3, ppm) δ 0.8ꢀ2.0 (m, 24H), 3.5ꢀ4.2 (m, 8H),
6.5ꢀ8.0 (m, 20H); 13C NMR (100 MHz, CDCl3, ppm) δ 25.1,
25.6, 25.8, 25.9, 28.5, 28.6, 28.7, 28.8, 29.0, 29.0, 29.1, 29.2, 29.2,
29.3, 69.3, 69.5, 69.5, 69.8, 112.9, 114.6, 115.6, 115.8, 117.2, 118.8,
119.7, 120.0, 120.5, 120.7, 123.2, 123.2, 125.4, 125.9, 126.0, 127.6,
127.7, 128.9, 129.0, 129.1, 129.1, 131.5, 131.9, 134.1, 134.2, 143.2,
143.5, 143.8, 154.4, 154.4, 155.5, 156.7; LR MS (FAB+) 721.3 (M +
H)+; HR MS (FAB+) Calcd for C48H52N2O4 (M+): 720.3927.
Found: 720.3923.
(aR)-2a and (aR)-2cꢀe were synthesized in a similar manner
to that for (aR)-1a with the exception that (R)-3,30-dibenzyloxy-
binaphthol 7 was used.
(aR)-3,30-Dibenzyloxybinaphthyl-azobenzene Dyad 2a.
Yield 5%; Red amorphous; IR (KBr) 3060, 1457, 1438, 1245,
1167, 747 cmꢀ1; 1H NMR (300 MHz, CDCl3, ppm) δ 3.7ꢀ4.0
(m, 2H), 4.1ꢀ4.2 (m, 2H), 4.3ꢀ4.4 (m, 2H), 4.4ꢀ4.5 (m, 2H),
5.04, 5.19 (ABq, νAB = 18.0 Hz, JAB = 11.4 Hz; s, 4H), 6.40, 6.48
(two d, J = 7.8 Hz, J = 8.4 Hz, 2H), 6.6ꢀ7.5 (m, 24H), 7.58, 7.75
(two d, J = 8.1 Hz, 8.1 Hz, 2H); 13C NMR (100 MHz, CDCl3,
ppm) δ 68.8, 70.3, 70.5, 71.0, 108.6, 108.7, 113.2, 113.6, 119.7,
120.2, 122.1, 123.8, 124.2, 124.8, 125.0, 125.3, 125.6, 126.0,
126.6, 126.7, 127.3, 127.5, 127.6, 127.7, 127.8, 128.0, 128.3,
128.5, 128.8, 128.9, 130.7, 130.9, 136.5, 136.7, 142.9, 147.2,
151.1, 151.3, 152.4 (Some peaks overlapped); LR MS (FAB+)
764.4 (M)+; HR MS (FAB+) Calcd for C50H40N2O6 (M)+:
764.2886. Found: 764.2913.
General Procedure for the Synthesis of Compounds (aR)-
1a, (aR)-1cꢀe, (aR)-2a and (aR)-2cꢀe. The synthesis of (aR)-1a
is typical.
(aR)-Binaphthyl-azobenzene Dyad 1a. A suspension of (R)-
BINOL (200 mg, 698 μmol) and 5a (320 mg, 698 μmol), and
potassium carbonate (965 mg, 6.98 mmol, 10 equiv) in DMF
(20 mL) was stirred for 24 h at 80 °C. The reaction mixture was
poured into the mixed solvent of chloroform and water. The organic
layer was separated and washed successively with 0.1 N hydrochloric
acid solution, water (twice) and brine. After dried over sodium sulfate,
the solvent was evaporated in vacuo to give a residue. The residue was
purified by column chromatography (SiO2; n-hexane/chloroform/
ethyl acetate = 6/3/1) and GPC to afford (aR)-1a (33 mg, 59.7
μmol, 9%). Red amorphous; IR (KBr) 3056, 1507, 1489, 1241, 1091,
1052, 750 cmꢀ1;1HNMR(400MHz,CDCl3, ppm, major isomer) δ
4.0ꢀ4.2 (m, 4H), 4.2ꢀ4.3 (m, 2H), 4.3ꢀ4.4 (m, 2H), 6.85 (d, J =
8.4 Hz, 2H), 7.0ꢀ7.1 (m, 4H), 7.1ꢀ7.4 (m, 8H), 7.58 (d, J = 8.0 Hz,
2H), 7.79 (d, J = 8.4 Hz, 2H), 7.83 (d, J = 8.4 Hz, 2H); 13C NMR
(100 MHz, CDCl3, ppm) δ 68.0, 68.7, 69.3, 113.7, 115.8, 116.1,
120.1, 121.5, 122.1, 123.6, 123.9, 125.3, 125.4, 126.2, 126.4, 127.9,
127.9, 128.8, 129.3, 129.4, 129.7, 131.0, 134.0, 134.1, 143.4, 144.2,
152.6, 154.4 (Some peaks overlapped.); LR MS (FAB+) 553.2 (M +
H)+; HR MS (FAB+) Calcd for C36H28N2O4 (M)+: 552.2049.
Found: 552.2061.
(aR)-Binaphthyl-azobenzene Dyad 1c. Yield 29%; Red amor-
phous; IR (KBr) 3057, 1507, 1467, 1242, 1085, 1044, 1014,
750 cmꢀ1; 1H NMR (400 MHz, CDCl3, ppm, major isomer) δ
1.3ꢀ1.7 (m, 8H), 3.5ꢀ4.0 (m, 8H), 6.86 (d, J = 8.7 Hz, 2H),
7.0ꢀ7.5 (m, H), 7.45 (dd, J = 8.1 Hz, 1.5 Hz, 2H), 7.67 (d, J = 9.0
Hz, 2H), 7.78 (d, J = 7.8 Hz, 2H); 13C NMR (100 MHz, CDCl3,
ppm, major isomer) δ 25.2, 25.5, 25.9, 26.3, 68.6, 69.0, 69.2, 70.0,
112.9, 115.3, 115.4, 119.6, 120.1, 120.6, 121.0, 123.2, 125.3,
125.9, 126.0, 127.7, 128.6, 129.0, 129.0, 129.1, 131.1, 134.0,
143.3, 144.6, 148.5, 153.9, 154.3 (Some peaks overlapped.); LR
MS (FAB+) 609.3 (M + H)+; HR MS (FAB+) Calcd for
C40H36N2O4 (M+): 608.2675. Found: 608.2683.
(aR)-3,30-Dibenzyloxybinaphthyl-azobenzene Dyad 2c.
Yield 18%; Red amorphous; IR (KBr) 3061, 1507, 1440, 1249,
1
1169, 1116, 746 cmꢀ1; H NMR (300 MHz, CDCl3, ppm) δ
1.2ꢀ1.7 (m, 8H), 3.5ꢀ3.7 (m, 2H), 3.7ꢀ3.8 (m, 4H), 3.8ꢀ3.9
(m, 2H), 5.05, 5.29 (two ABq, νAB = 12.4 Hz, JAB = 11.4 Hz;
νAB = 16.9 Hz, JAB = 11.4 Hz, 4H), 6.5ꢀ8.0 (m, 28H); 13C NMR
(75 MHz, CDCl3, ppm) δ 25.1, 25.2, 26.0, 26.1, 70.1, 70.2, 71.8,
71.9, 77.2, 77.4, 108.3, 116.0, 120.6, 120.7, 121.1, 123.9, 124.9,
125.8, 126.3, 126.4, 127.4, 127.4, 127.8, 128.3, 128.4, 128.5,
129.1, 130.8, 131.1, 136.6, 144.6, 146.6, 151.5, 154.3 (Some
peaks overlapped); LR MS (FAB+) 820.4 (M+); HR MS (FAB+)
Calcd for C54H48N2O6 (M+): 820.3512. Found: 820.3540.
(aR)- 3,30-Dibenzyloxybinaphthyl-azobenzene Dyad 2d.
19%Yield ; Red amorphous; IR (KBr) 3061, 1457, 1440, 1376,
1247, 1168, 1115, 748 cmꢀ1; 1H NMR (400 MHz, CDCl3, ppm)
δ 0.9ꢀ1.6 (m, 12H), 3.5ꢀ4.2 (m, 8H), 5.06, 5.29 (two ABq,
νAB = 5.5 Hz, JAB = 12.0 Hz; νAB = 7.9 Hz, JAB = 12.0 Hz, 4H),
6.6ꢀ6.8 (m, 2H), 6.8ꢀ7.8 (m, 26H); 13C NMR (100 MHz,
CDCl3, ppm) δ 22.1, 22.4, 28.3, 28.5, 29.3, 29.4, 29.4, 69.0, 69.7,
70.3, 70.6, 72.5, 73.0, 108.3, 108.6, 113.1, 114.3, 119.5, 119.7,
120.6, 123.9, 124.0, 124.8, 125.7, 125.9, 126.3, 126.3, 126.4,
126.5, 127.5, 127.6, 127.7, 127.9, 128.4, 128.5, 128.5, 129.2,
129.2, 130.8, 130.7, 130.9, 136.7, 136.8, 143.3, 144.7, 147.0,
147.1, 148.7, 151.6, 151.6, 154.6 (Some peaks overlapped); LR
MS (FAB+) 848.4 (M+); HR MS (FAB+) Calcd for C56H52N2O6
(M+): 848.3825. Found: 848.3802.
(aR)-Binaphthyl-azobenzene Dyad 1d. Yield 34%; Red amor-
phous; IR (KBr) 3056, 1507, 1466, 1274, 1242, 1087, 750 cmꢀ1
;
1H NMR (400 MHz, CDCl3, ppm) δ 1.0ꢀ1.6 (m, 12H), 3.6ꢀ3.7
(m, 2H), 3.7ꢀ3.8 (m, 2H), 3.9ꢀ4.0 (m, 2H), 4.0ꢀ4.1 (m, 2H),
6.7ꢀ7.8 (m, 20H); 13C NMR (100 MHz, CDCl3, ppm) δ 22.0,
22.3, 28.1, 28.5, 28.7, 29.0, 68.7, 68.8, 69.2, 69.5, 113.0, 114.5, 115.4,
115.5, 119.7, 119.7, 120.4, 120.6, 120.6, 120.7, 123.2, 123.3, 125.4,
125.4, 125.9, 126.1, 127.7, 127.7, 128.6, 128.9, 128.9, 129.1, 129.1,
129.1, 131.1, 134.1, 134.2, 143.1, 144.5, 148.7, 154.2, 154.4; LR MS
(FAB+) 636.3 (M+); HR MS (FAB+) Calcd for C42H40N2O4
(M+): 636.2988. Found: 636.2991.
(aR)- 3,30-Dibenzyloxybinaphthyl-azobenzene Dyad 2e.
Yield 12%; Red amorphous; IR (KBr) 3062, 1457, 1440, 1248,
1168, 1115, 747 cmꢀ1; 1H NMR (300 MHz, CDCl3, ppm) δ 0.7ꢀ
2.0 (m, 24H), 3.5ꢀ4.3 (m, 8H), 5.20, 5.27 (two s, 4H), 6.6ꢀ6.8 (m,
2H), 6.8ꢀ8.0 (m, 26H); 13C NMR (75 MHz, CDCl3, ppm) δ 25.1,
25.5, 25.5, 25.7, 28.6, 28.8, 28.9, 29.1, 29.5, 29.7, 68.8, 69.7, 69.9, 70.4,
70.4, 72.8, 72.9, 108.5, 112.8, 114.8, 119.4, 119.5, 120.3, 120.7, 123.8,
123.9, 124.7, 125.8, 126.4, 127.3, 127.4, 127.8, 127.9, 128.4, 128.5,
129.2, 129.3, 130.8, 130.8, 131.3, 131.9, 136.8, 136.9, 143.3, 144.0,
147.2, 147.2, 148.8, 151.6, 151.6, 155.1 (Some peaks overlapped);
(aR)-Binaphthyl-azobenzene Dyad 1e. Yield 10%; Red amor-
phous; IR (KBr) 3057, 1508, 1488, 1242, 1158 749 cmꢀ1; 1H NMR
7627
dx.doi.org/10.1021/jo201578z |J. Org. Chem. 2011, 76, 7623–7628

The Journal of Organic Chemistry
NOTE
LR MS (FAB+) 932.5 (M+);HRMS(FAB+) CalcdforC62H64N2O6
(M+): 932.4764. Found: 932.4799.
(12) It was difficult to evaluate the energy differences because of the
flexibility of the linkers. However, as an illustration, when the energy of
trans-(pR)-2b was used as a benchmark, the energy differences of trans-
A-2b was +1.6 kcal/mol and that of trans-(pS)-2b was +3.0 kcal/mol.
(13) Crystal structures of twisted trans-azobenzene moieties have
been reported, for example: (a) Kennedy, A. R.; Kirkhouse, J. B. A.;
McCarney, K. M.; Puissegur, O.; Smith, W. E.; Staunton, E.; Teat, S. J.;
Cherryman, J. C.; James, R. J. Am. Chem. Soc. 1996, 118, 2131. (b) Krebs,
F. C.; Jørgensen, M. J. Chem. Soc., Perkin Trans. 2 2000, 1935. (c) Halder,
G. J.; Kepert, C. J.; Moubaraki, B.; Murray, K. S.; Cashion, J. D. Science 2002,
298, 1762. (d) Burke, N. J.; Burrows, A. D.; Mahon, M. F.; Warren, J. E.
Cryst. Growth Des. 2006, 6, 546. (e) Kim, J. S.; Lee, S. J.; Jung, J. H.; Hwang,
I.-C.; Singh, N. J.; Kim, S. K.; Lee, S. H.; Kim, H. J.; Keum, C. S.; Lee, J. W.;
Kim, K. S. Chem.—Eur. J. 2007, 13, 3082. (f) Lee, H.; Lee, S. S. Org. Lett.
2009, 11, 1393 and ref 3b.
’ ASSOCIATED CONTENT
S
Supporting Information. UVꢀvis spectra, CD spectra,
b
Computational details, thermodynamic parameters, and 1H NMR
and 13C NMR spectra of various compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*ktakaishi@riken.jp; uchi_yama@riken.jp
(14) The relationships between the dihedral angles, the calculated CDs,
and the energy differences of each trans-2,20-dimethoxyazobenzene are
summarized in Table S1 and Figure S11 in Supporting Information.
(15) Kobayashi, N.; Higashi, R.; Titeca, B. C.; Lamote, F.; Ceulemans,
A. J. Am. Chem. Soc. 1999, 121, 12018.
(16) (a) Wang, Z. Y.; Todd, E. K.; Meng, X. S.; Gao, J. P. J. Am. Chem.
Soc. 2005, 127, 11552. (b) Wigglesworth, T. J.; Sud, D.; Norsten, T. B.;
Lekhi, V. S.; Branda, N. R. J. Am. Chem. Soc. 2005, 127, 7272. (c) Okumura,
T.; Tani, Y.; Miyake, K.; Yokoyama, Y. J. Org. Chem. 2007, 72, 1634.
’ ACKNOWLEDGMENT
This work was supported in part by the Shorai Foundation for
Science and Technology and by a special doctoral fellowship from
RIKEN. We are also grateful to members of the molecular
characterization team at RIKEN for the spectral measurements.
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