Chemistry Letters Vol.35, No.1 (2006)
111
Table 1. CD data of 1–chiral amine complexes in THF at rta
4
1.2
1.0
0.8
0.6
1
(A)
(B)
4
(a)
3
2
First Cotton effect
Second Cotton effect
[1]
/mM
3
2
0
(c)
(d)
Entry
Diamine
Sign
ꢀ" (ꢁ)
Sign
ꢀ" (ꢁ)
1
2
(1R,2R)-7
9.3
ꢃ
ꢃ
+
ꢃ
ꢃ
b
1.50 (338)
1.98 (338)
1.46 (338)
1.18 (339)
0.30 (340)
b
+
+
ꢃ
+
+
b
3.44 (316)
3.36 (315)
3.13 (316)
2.58 (316)
1.03 (319)
b
2
1
0
1–(1
R, 2R)-7
ε
–2
–4
–6
0.12
9.3
ε
(b)
(e)
0.4
0.2
0
1
0
(f)
3
(1S,2S)-7
(1R,2R)-8
ε
4
9.3
5
0.12
9.3
0.12c
275 300
350
400
0
0.5
1.0
1.5
2.0
Wavelength / nm
Molar ratio of (1
R
, 2 )-7 to 1
R
6
(1R,2R)-9
7
ꢃ
ꢃ
ꢃ
b
1.18 (336)
0.37 (338)
0.52 (339)
b
+
+
+
b
0.65 (314)
0.37 (314)
0.36 (314)
b
Figure 1. (A) CD spectra of 1 with (1R,2R)-7 (a), (1S,2S)-7 (b), (1R,2R)-8
(c), and (1R,2R)-10 (d) (½diamineꢁ=½1ꢁ ¼ 1) in THF at rt. Absorption spec-
tra of 1 with (e) and without (1R,2R)-7 (f) are also shown. ½1ꢁ ¼ 9:3 (a–c, e,
and f) and 7.1 mM (d). Inset photographs show the visible difference of 1
with and without (1R,2R)-7 in THF under UV-light at 365 nm. (B) Plots
of the ICD intensity of the 2nd Cotton effect ( ) and the differential IR
absorbance (ꢀAbs) at 1673 cmꢃ1 of 1 ( ) as a function of the relative
concentration of (1R,2R)-7 to 1 (½1ꢁ ¼ 9:3 mM) in THF. A solid line in
the plot is a fit to the theoretical binding curve.9
8
(1R,2R)-10 7.1
0.12d
9.3
0.12d
9
10
11
a
(S)-11
ꢃ
3.48 (341)
+
8.72 (313)
½Diamineꢁ=½1ꢁ ¼ 1 (Entries 1, 3, 4, 6, 8, and 10) and 4 (Entries 2, 5, 7, 9, and 11);
ꢀ" (Mꢃ1 cmꢃ1) and ꢁ (nm). bCould not be measured because of precipitation of
the complex. cIn THF=CHCl3 ¼ 1=1(v/v). dIn THF=CHCl3 ¼ 1=9 (v/v).
intensity induced by chiral diamines (7, 8, and 10 in Table 1)
showed no change with time, independent of the concentration
of the chiral diamines. These concentration and time dependent
complexations of (1R,2R)-7 with chiral diamines may also
support the cyclic tetramer formation, although further studies
including the solution and solid-state structure determinations
of the acid–base complexes by NMR and X-ray, respectively,
are apparently essential.
In summary, we have synthesized a carboxybiphenol that is
sensitive to the chirality of the chiral diamines, thus showing an
ICD due to an excess single-handed, axially twisted conforma-
tion. The carboxybiphenol has reactive ethynyl groups which
may be used as a versatile building block for the synthesis of
chirality-responsive, ꢀ-conjugated helical polymers.
changes in absorbance at 1673 cmꢃ1 corresponding to the intra-
molecularly hydrogen bonded COOH band with the adjacent OH
group was followed. The absorbance intensity linearly decreased
with the increasing concentration of 7 and almost completely
disappeared at ½1ꢁ ¼ ½7ꢁ, resulting in the formation of the car-
boxylate ions (Figure 1B).9
On the basis of these observations together with the facts
that only the carboxybiphenol 1 is CD active for the chiral di-
amines among the other analogous biphenyl derivatives, but ex-
hibited no CD upon complexation with the chiral monoamines,
we propose a 2:2 cyclic tetramer as a plausible CD active species
as shown in Figure 2A, where each amino group of the chiral
diamine intermolecularly binds to the carboxyl groups of the
different receptors by salt bridges. This tetramer formation
may enable a favorable cisoid conformation of 1 due to the intra-
molecular hydrogen bonds between the adjacent hydroxy groups
of 1, thus generating an excess of one of the axially twisted
conformers, although the exact structure is not presently clear.10
On the other hand, chiral monoamines may simply bind to a
carboxyl group in a 1:1 fashion, so that the 1–monoamine
complexes may exist as both the interconverting cisoid and
transoid forms (Figure 2B), and a such conformational flexibility
may be the reason for no ICD.
As described above, the complexations of 1 with chiral
diamines showing ICDs are dependent on the concentrations
of 1 and the chiral diamines. At a lower concentration of 1
(0.12 mM) in THF, similar intense ICDs were observed immedi-
ately after the addition of (1R,2R)-7 (½7ꢁ=½1ꢁ ¼ 1) to the solution
of 1 (Table 1). However, the ICD intensity was found to be sig-
nificantly time dependent, and steadily decreased with time and
almost completely disappeared after 1 h. Such a decrease in the
ICD with time became slower with the increasing concentration
of (1R,2R)-7 and was negligibly small at ½7ꢁ=½1ꢁ ꢄ 4. We noted
that at high concentrations of 1 (7.1 or 9.3 mM), the Cotton effect
This work was partially supported by Grant-in-Aid for
Scientific Research from the Japan Society for the Promotion
of Science, Japan.
References and Notes
1
Reviews: a) E. Yashima, K. Maeda, T. Nishimura, Chem. Eur. J. 2004, 10,
43. b) S. Allenmark, Chirality 2003, 15, 409. c) H. Tsukube, S. Shinoda,
Chem. Rev. 2002, 102, 2389. d) J. W. Canary, A. E. Holmes, J. Liu,
Enantiomer 2001, 6, 181.
2
3
a) K. Maeda, K. Morino, Y. Okamoto, T. Sato, E. Yashima, J. Am. Chem. Soc.
2004, 126, 4329. b) E. Yashima, T. Matsushima, Y. Okamoto, J. Am. Chem.
Soc. 1997, 119, 6345.
a) V. Maurizot, C. Dolain, I. Huc, Eur. J. Org. Chem. 2005, 1293. b) T.
Nishimura, K. Maeda, E. Yashima, Chirality 2004, 16, S12. c) Y. Inai, Y.
Ishida, K. Tagawa, A. Takasu, T. Hirabayashi, J. Am. Chem. Soc. 2002,
124, 2466.
4
5
a) K. Mikami, M. Yamanaka, Chem. Rev. 2003, 103, 3369. b) P. J. Walsh,
A. E. Lurain, J. Balsells, Chem. Rev. 2003, 103, 3297.
a) H. Takagi, T. Mizutani, T. Horiguchi, S. Kitagawa, H. Ogoshi, Org.
Biomol. Chem. 2005, 3, 2091. b) R. Eelkema, B. L. Feringa, J. Am. Chem.
Soc. 2005, 127, 13480. c) T. Hayashi, T. Aya, M. Nonoguchi, T. Mizutani,
Y. Hisaeda, S. Kitagawa, H. Ogoshi, Tetrahedron 2002, 58, 2803. d) Y.
Kubo, T. Ohno, J. Yamanaka, S. Tokita, T. Iida, Y. Ishimaru, J. Am. Chem.
Soc. 2001, 123, 12700. e) T. Mizutani, H. Takagi, O. Hara, T. Horiguchi, H.
Ogoshi, Tetrahedron Lett. 1997, 38, 1991.
6
7
8
For details of the synthesis and characterization of 1–4 and the Job plot, see
the Supporting Information.
The optically active compounds used in this study showed no CD above
275 nm.
Mizutani, Ogoshi, and co-workers reported that a 2,20-biphenol bearing
bromo and nitro groups exhibited an ICD in the presence of chiral diamines
and proposed a ternary complex for axial chirality induction. See refs 5a
and 5e.
(A)
(B)
R
N
R
R
R
O–
+H3
O
O-
O–
+
+
+
NH3
O–
NH3
NH3
O
O
O
HO
HO
OH
OH
O–
+H3
OH
OH
OH
HO
O–
O
O–
NH3
+
N
R
NH3 O–
+
O
+
HN
O
O
3
R
R
R
9
Acceptable fits were observed for a 1:1 complexation of 1 and 7 only when
the binding constant (K) was greater than 5:0 ꢅ 104 Mꢃ1, although the K
value was too large to be precisely estimated under the present conditions.
cisoid
transoid
CD inactive
cyclic complex
1−diamines
CD active
1−monoamines
10 The coldspray ionization (CSI) MS measurement of a 1:1 mixture of 1
(9.3 mM) and (1R,2R)-7 in THF operating at ꢃ10 ꢂC showed an ion peak
Figure 2. Possible models for complex formation of 1 with chiral
diamines (A) and monoamines (B) at ½1ꢁ ¼ 9:3 mM.
at m=z 1091, which corresponds to ½ð1 7Þ2 þ Naꢁþ.
ꢆ