Synthesis and optical properties of (S)-Nobin

Article abstract of DOI:10.1134/S1070363209050168

A preparative method of synthesis of optically pure S-2-amino-2'-hydroxy-1, 1'-binaphthyl (S-Nobin), the precoursor in the synthesis of other asymmetric 1,1-binaphthyls applied as the ligands at the creation of the catalysts of asymmetric synthesis, is mo

Full text of DOI:10.1134/S1070363209050168

ISSN 1070-3632, Russian Journal of General Chemistry, 2009, Vol. 79, No. 5, pp. 962–966. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © E.P. Studentsov, O.V. Piskunova, A.N. Skvortsov, N.K. Skvortsov, 2009, published in Zhurnal Obshchei Khimii, 2009, Vol. 79,
No. 5, pp. 790–794.
Synthesis and Optical Properties of (S)-Nobin
a
a
b
a
E. P. Studentsov , O. V. Piskunova , A. N. Skvortsov , and N. K. Skvortsov
a
St. Petersburg State Institute of Technology, Moskovskii pr. 26, St. Petersburg, 190013 Russia
e-mail: srvorn@mail.ru
b
St. Petersburg State Polytechnic University, St. Petersburg, Russia
Received December 25, 2008
Abstract―A preparative method of synthesis of optically pure S-2-amino-2'-hydroxy-1,1'-binaphthyl (S-
Nobin), the precoursor in the synthesis of other asymmetric 1,1-binaphthyls applied as the ligands at the
creation of the catalysts of asymmetric synthesis, is modified. The UV and CD spectra of this compound were
studied in detail and essential dependence of spectral information on the solvent nature was shown.
DOI: 10.1134/S1070363209050168
The class of chiral compounds (R,S)-binaphthyls,
whose optical activity is based on the restricted rotation
of the connected naphthalene rings around С –С'
asymmetric axis is of great interest for the creation of
the catalysts of asymmetric reactions. The R/S
binaphthyls as the ligands in the metal complexes are
abile to transfer the chiral information at the
enantioselective catalysis of different chemical
transformations [1]. In particular, at the asymmetric
synthesis of natural α-amino acids and their derivatives
As a result of the alkaline hydrolysis of menthyl ester
IV to (S)-2-carboxy-2'-methoxy-1,1'-binaphthyl V and
its subsequent transformation according to Curtius
reaction (S)-2-amino-2'-methoxy-1,1'-binaphthyl VI
was obtained in high yield. Demethylation of com-
pound VI with phosphorus tribromide affords (S)-
Nobin VII with the content of the title compound 99%
and with total yield 25% on the initial product I,
therewith, the preparation can be obtained in amount
of tens of grams taking into account the synthetic
accessibility of the intermediates. The physicochemical
characteristics of compound VII correspond to the
1
1
(
S)-Nobin (S-2-amino-2'-hydroxy-1,1'-binaphthyl) is
used, which is in turn the parent compound of others
asymmetric 1,1'-binaphthyls (Binol, Binam and Binap)
2
0
published data [11, 12]: mp. 169–171°C; [α] (–) 118°
D
+
[
2, 3], applied to the catalytic reactions of
(C1, THF); mass-spectrum: 285.25 (100%, М ,
1
hydrogenation, hydrosilylation etc.
С
20
Н
15NO) H NMR spectrum (400 MHz, CDCl
3
), δ,
ppm: 7.94 d (1H, CH-binaphthyl), 7.90–7.77 m (CH-
binaphthyl), 7.40 d (1H, CH-binaphthyl), 7.38–7.33 m
We modified the preparative method of synthesis of
the optically pure (S)-Nobin by an improvement of the
procedures of the synthesis of some known inter-
mediates I–VII, shown in the scheme below [4, 5].
(
1H, CH-binaphthyl), 7.29–7.20
binaphthyl), 7.18–7.74 m (1H, CH-binaphthyl), 7.12 d
1H, CH-binaphthyl), 7.08–7.05 (1H, CH-
m
(3H, CH-
(
m
The central stage is Meyers reaction of the
synthesis of 1,1'-binaphthyls [6–8]. In this case the
nucleophilic substitution was carried out in the
menthyl 1-(–)-menthyloxy-2-naphthylcarboxylate III
by 1-naphthylmagnesium bromide II, that leads to the
synthesis of (S)-2-menthyloxycarbonyl-2'-methoxy-
binaphthyl), 4.88 br (1H, OH), 3.48 br (2H, NH2).
This method of synthesis of (S)-Nobin is definitely
more advantageous than the method of the oxidative
coupling (cross-coupling) of 2-naphtol and 2-naphthyl-
amine in the presence of the Cu(II) or Fe(III) salts and
chiral amines (for example, α-methylbenzylamine) fol-
lowed by the separation of R enantiomers by the
crystallization of complexes with (1S)-(+)-10-cam-
phorsulfonic acid or by affine chromatography, that is
suitable for synthesis of (R)- or (S)-Nobin only in a
small amount [10–12].
1
,1'-binaphthyl IV. High stereospecificity (98%) of the
formation of product IV is reached due to the presence
of two chiral menthyl substituents in compound III
and the appearance of intermediate with the six-
membered ring where magnesium atom is coordinated
with two oxygen atoms of O-menthyl groups [9, 10].
962

SYNTHESIS AND OPTICAL PROPERTIES OF (S)-NOBIN
963
Br
MgBr
O-(−)-Menthyl
COO(−)-Menthyl
OMe
OMe
(a), (b)
+
I
II
III
(
−)-Menthyl
(
−)-Menthyl
MgBr
O
OMe
(c)
2-Methoxynaphthyl
O
COO(−)-Menthyl
O-(−)-Menthyl
IV
OMe
(d)
OMe
(e)
OH
NH2
NH2
COOH
V
VI
VII
2 5
OH, 79%IV; (c) IV, KOH/C H OH, 80°С, 24 h; HCl,
(
a) I, Mg, C
6
H
6
, 1.5 h; (b) II + III, THF, 80°С, 12 h, recryst. from C
2
H
5
9
–
6%V; (d) ClCO Me, (C N, acetone, –15°С, 0.5 h; NaN /H O–CH
20–0°С; recryst. From benzene; 95%VII.
2
2
H
5
)
3
3
2
3
COCH
3 3 2 2
, 1.5 h, –15°С; 92%VI; (e) VI, BBr /CH Cl ,
–
1
–1
In the ultraviolet range the S-Nobin solutions
~80000 M cm . In the absorption spectrum of the
solution in dioxane there are two distinct absorption
bands with the maxima at 230 and 250 nm. In the more
polar solvents the band at 250 nm weakens and is
converted into the small shoulder completely
disappearing in the spectrum of solution in TFE. In the
CD spectrum in this region appears a strong doublet of
two bands with the opposite signs and the
approximately equal rotatory forces. The position of
the doublet changes with the change of solvent, but its
general form remains conservative. By the optical
properties in the range of 220–260 nm this compound
can be easily detected spectroscopically at micromolar
concentrations, including the aqueous solutions
display the absorption spectra and circular dichroism
CD), typical for 2,2'-substituted 1,1'-binaphthyls [13–
5]. A system of three absorption bands is observed
Fig. 1), which corresponds to three basic absorption
(
1
(
bands of β-mono-substituted naphthalene, and they can
be conventionally assigned to three electron transitions
1
1
1
of naphthalene: B , L and L . Significant circular
b
a
b
dichroism occurs in all three regions. Change in the
solvent leads to changes in the band shapes, therewith
in the series dioxane–ethanol–water–trifluoroethanol
(
TFE) the changes are rather similar for all three
bands. (the order of solvents corresponds to the
increase in dipole moments of their molecules).
(
solubility of S-Nobin in water at 25°C is of the order
The most clearly expressed element of the spectrum
is the system of absorption bands in the region 220–
–
1
of magnitude 10 μg ml ).
2
60 nm, which corresponds to the allowed transitions
Nature of the optical activity of chiral binaphthyls
on the band 230–250 nm is well studied [13–15], the
1
B of the naphthyl chromophores [14, 16], ε
b
max
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 5 2009

9
64
STUDENTSOV et al.
to the value of dipole-dipole interaction V multiplied
by the value rDD = R12[d ×d ], where R12 is a vector
connecting the centers of chromophores, d and d are
(
a)
3
2
1
2
4
1
1
1
20
00
1
2
×
10
electric dipole moments of the chromophores
transitions [17]. The sign of the rDD value is related
uniquely to the absolute configuration of the molecule.
At the positive rDD and V values the long-wave transi-
tion obtains positive correction to the rotatory force,
and short-wave transition obtains equal by the absolute
value negative correction. In the case of two isolated
transitions this leads to the appearance in the CD
spectrum of the identical bands of opposite sign.
8
6
4
2
0
0
0
4
1
3
2
0
0
2
00
250
300
350 400 450
λ, nm
b)
The naphthyl chromophore possesses in the region
1
(
of 230–250 nm a strong allowed B transition whose
b
large dipole moment is directed along the long axis of
the molecule (x axis, Fig. 2a). In binaphthyls it is
practically perpendicular to the axis connecting the
centers of chromophores, which creates optimum
conditions for the appearance of rotatory force. It is
presumable that for these transitions d1,2┴R12, and the
angle θ between the vectors d and d is the angle
1
1
50
00
2
1
3
5
0
0
1
4
2
1
2
between the planes of naphthyl rings (Fig. 2b). The
second potential transition of naphthyl chromophore in
this region, which is forbidden for naphthalene but
permitted for its substituted analogs, has a transition
dipole polarized along the y axis. For this transition d
and R are almost parallel; therefore the corresponding
–
50
4
×
10
3
–
100
00
1
2
values of rDD are equal to zero, and the influence of
this transition on the rotatory force is negligible. The
mechanism of the appearance of CD spectrum of
Nobin differs somewhat from that of the spectra of
symmetrical binaphthyls. In symmetrical binaphthyls
2
250
300
350 400 450
λ, nm
Fig. 1. Absorption (a) and circular dichroism (b) spectra of
–)-S-Nobin in various solvents: (1) 1,4-dioxane, (2) 96%
ethanol, (3) water, and (4) 2,2,2-trifluoroetanol.
(
[
13–14] both the naphthyl chromophores are identical,
and two transitions in the CD spectrum are formed due
decisive role in its appearance plays interaction of two
naphthyl chromophores, whose rotation relative to
each other is restricted. The rotatory force of the
chromophore in a small molecule which interacts with
another chromophore is composed of its own rotatory
force, a magneto-electric correction, and a dipole-
dipole correction [17]. Flat naphthyl chromophore
does not possess its own rotatory force. In the spectra
the ratio Δε/ε ~ μ/d ~ 0.001 is observed, where μ and
d are respectively magnetic and electric dipole mo-
ments of transition, μ is relatively small, and mag-
neto-electric component of rotatory force is extremely
small. Therefore it is possible to consider that the
rotatory force of the binaphthyl transitions is caused
only by dipole-dipole component. Contribution to the
rotatory force caused by dipole–dipole interaction in
the first most significant approximation is proportional
1
to the exciton splitting of B transition, the value of
b
this splitting is equal to 2V and depends on θ. The
exciton splitting is small; therefore in the absorption
spectrum of symmetrical binaphthyls one unresolved
peak is observed, and the CD spectrum reflects true
exciton doublet. For Nobin the chromophores and
1
energies of their B transitions are initially different:
b
the transition energy of naphthylamine chromophore is
noticeably smaller, than that of naphthol [3]. For this
reason the doublet in the CD spectrum of Nobin
reflects dipole–dipole interaction of two different
transitions rather than exciton splitting of one
transition.
As shown in Fig. 2b in the Nobin S-enantiomer the
vectors R , d and d form the right-handed triad (or, in
12
1
2
other words, the ends of the vectors d and d form in
1
2
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 5 2009

SYNTHESIS AND OPTICAL PROPERTIES OF (S)-NOBIN
965
(
a)
(b)
×10
1
00
80
y
d
2
3
2
θ
60
40
x
OH
NH
1
R
12
2
2
R
20
0
1
3
d
1
~
2
00
250
300
350 400 450
λ, nm
Fig. 2. (a) Coordinate system of naphthyl chromophore. (b)
The relative alignment of the dipole moments of allowed
transitions (220–260 nm) of (–)-S-Nobin naphthyl
chromophores.
Fig. 3. Changes in the absorption spectrum of (–)-S-Nnobin
in aqueous solution depending on pH: (1) distilled water,
(2) 1.5 M NaOH, and (3) 0.01 M HCl.
the space the element of the right-hand spiral), thus the
value of rDD for S-Nnobin and other S-binaphthols is
positive. Unfortunately, the sign of CD band in this
case is determined also by the sign of V, which is
changed upon going of θ angle through 90° (in bi-
bands, which are conventionally decomposed into two
systems: 240–310 nm and 310–400 nm. A change in
the polarity of solvent also leads to spectral changes in
this region, moreover in the region of 240–310 nm the
solvent affects predominantly the absorption intensity,
and in the region of 310–400 nm, mainly the spectrum
shape. The CD spectrum in this region also is suf-
ficiently conservative, but its interpretation is complex.
In this region transitions appear with the electric
dipoles both parallel and perpendicular to the axis
connecting the chromophores. However, the sym-
metrical doublets of opposite sign are not observed
here, since the influence of these transitions on each
other is not of decisive importance, but the main role
3
naphthyl V ≈ d d cos θ/R ). For the binaphthyls with
1
2
12
rigid connection of 2 and 2' positions the condition θ <
0° is assuredly fulfilled, therewith V > 0 and the
9
positive sign of long-wave band unambiguously
indicates S-configuration. For “nonrigid” binaphthyls
the angle θ theoretically can change over a wide range,
and the sign of V can change; therefore the connection
between the sign of the CD spectrum bands and the
absolute configuration is, generally speaking, not
defined. Nevertheless, the analysis of the spectra of
circular dichroism of 2,2'-disubstituted chiral binaph-
thyls with small substituents [13] shows that in these
compounds the long-wave transition of doublet in the
region of 220–240 nm in the CD spectrum of S-
enantiomers also has a plus sign, and respectively the
average value of angle θ is less than 90° (this
corresponds to the configuration given in Fig. 2b, and
to the traditional image of the formulas of binaphthyls.
Thus, the positive CD sign of the long-wave B-
transition of naphthylamine chromophore (~250 nm)
we observed sufficiently reliably testifies to the S-
configuration of the compound investigated.
plays the dipole–dipole interaction with the strong
1
short-wave B
transition [14]. The common negative
b
sign of these bands coincides with the sign of
analogous exciton bands of symmetrical S-binaphthyls
and on the whole corresponds to the opposite direction
of dipole moments for the B-transition and for the L-
transitions polarized along the chromophore x axis
[16]. The vibronic structure in the observed absorption
spectra typical of the L-transitions is expressed
weakly, and in the CD spectra it is almost imper-
ceptible. This is partly caused by the selection of polar
solvents, partly by the fact that all L-transitions of
Nobin are permitted owing to the complete absence of
symmetry, which decreases the significance of
vibronic sublevels for the formation of the optical
spectrum.
The change in the CD spectrum in the region of B-
transitions with an increase in the polarity of solvent
(
Fig. 1) indicates, taking into account the above stated,
the strong displacement of the long-wave transition
50 nm into the region of short wavelengths rather
than the weakening of its intensity.
In accordance with its chemical structure, S-Nobin
should possess weak amphoteric properties in aqueous
solution. This is completely confirmed by the changes
in the absorption spectra of Nobin at the change in pH
(Fig. 3). In distilled water (pH ~6) the spectrum of
2
1
1
In the region of L and L transitions (280–
a
b
3
60 nm) in the spectra of S-Nobin there are several
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 5 2009

9
66
STUDENTSOV et al.
Nobin is well consistent with the spectra in the aprotic
solvents and corresponds to the neutral form of the
molecule. In 0.01M HCl (pH 2.0) due to the
protonation occurs sharp decrease in the electron-
donor properties of the amino group, and the band of
naphthylamine chromophore it displaces strongly into
the short-wave region, completely merging with the
band of naphthol chromophore. The band at 350 nm
considerably weakens and is displaced into the short-
wave region. Under the alkaline conditions (1.5 M
NaOH) a strong shift of bands occurs to the long-wave
region and an increase in their intensity, in
correspondence with the deprotonation of naphtholic
chromophore. Unfortunately, the observation of the
entire B-band under these conditions is impossible
because of the strong absorption of solvent. Let us note
that in 0.01M NaOH (pH ~11) Nobin has a spectrum
identical with the spectrum in the neutral medium,
hence pK of hydroxy group of Nobin is above 11.
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EXPERIMENTAL
The absorption spectra were taken on a double-
beam scanning spectrophotometer Specord-M40. The
spectra of circular dichroism were obtained on a
dichrograph Mark-V. The dichrograph was calibrated
with the standard aqueous solution of (+)-10-D-
1
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–
1
camphorsulfonic acid (1 mg ml ) in the regions of 190
and 290 nm [18]. For the measurements were used
rectangular quartz cuvettes with the length of optical
path 0.5 cm. The measurements of absorption were
carried out under temperature control at 25°C. In the
spectral region of 200–275 nm the S-Nobin concentra-
1
0. Miyake, J.T., Hatan, S., Shima, R., Ohara, T., and
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–
1
1
996, vol. 61, no. 10, p. 1520.
4
0 g ml . Aqueous solutions of S-Nobin with the
–
1
1
1
1
1
1
1
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concentration 4 g ml were prepared by the dilution of
the solution in ethanol (final content of ethanol in the
aqueous solutions not higher than 2.5 vol %).
In the work were used the commercial reagents
from Aldrich.
ACKNOWLEDGMENTS
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(
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0
0823) and the Program of the President of Russian
Federation for Young Candidates of Sciences (MK-
692.2008.4).
5
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