A new and practical method for preparing enantiomerically pure [1,1′-binaphthalene]-2,2′-diol: Resolution of racemic [1,1′-binaphthalene]-2,2′-diol with threo-(1s,2s)-2-amino-1-(4-nitrophenyl)propane-1,3-diol-cyclohexanone condensate

Article abstract of DOI:10.1002/hlca.200390006

An economic and practical method for preparing enantiomerically pure [1,1′-binaphthalene]-2,2′-diols is reported. Thus, a condensate of threo-(1S,2S)-2-amino-1-(4-nitrophenyl)propane-1,3-diol and cyclohexanone (CHANP) was used as a resolving agent. A 2:1:1 mixture of racemic [1,1′-binaphthalene]-2,2′-diol, boric acid, and CHANP was refluxed for several hours in THF or MeCN to give a white precipitate of bis((R)-[1,1′-binaphthalene]-2,2′-diol}boric acid CHANP derivative, from the precipitate, and a filtrate separated from the precipitate, (R)- and (S)-[1,1′-binaphthalene]-2,2′-diol of 100% ee were obtained in ca. 65% yield, respectively.

Full text of DOI:10.1002/hlca.200390006

Helvetica Chimica Acta Vol. 86 (2003)
157
A New and Practical Method for Preparing Enantiomerically Pure
[1,1'-Binaphthalene]-2,2'-diol: Resolution of Racemic [1,1'-Binaphthalene]-
2,2'-diol with threo-(1S,2S)-2-Amino-1-(4-nitrophenyl)propane-1,3-
diolÀCyclohexanone Condensate
by Dejun Liu, Zixing Shan*, Fei Liu, Chunguang Xiao, Guojian Lu, and Jingui Qin
Department of Chemistry, College of Chemistry and Molecular Science, Wuhan University, Wuhan 430072, China
(fax: 027-87647617; e-mail: kenshan@public.wh.hb.cn)
An economic and practical method for preparing enantiomerically pure [1,1'-binaphthalene]-2,2'-diols is
reported. Thus, a condensate of threo-(1S,2S)-2-amino-1-(4-nitrophenyl)propane-1,3-diol and cyclohexanone
(CHANP) was used as a resolving agent. A 2:1:1 mixture of racemic [1,1 '-binaphthalene]-2,2'-diol, boric acid,
and CHANP was refluxed for several hours in THF or MeCN to give a white precipitate of bis{(R)-[1,1'-
binaphthalene]-2,2'-diol}boric acid CHANP derivative, from the precipitate, and a filtrate separated from the
precipitate, (R)- and (S)-[1,1'-binaphthalene]-2,2'-diol of 100% ee were obtained in ca. 65% yield, respectively.
1. Introduction. Artificial chiral-pool compounds, (À)-(S)- and (‡)-(R)-[1,1'-
binaphthalene]-2,2'-diols possessing a C2-symmetric axis are very important chiral
ligands and auxiliaries, and they have been extensively used in stoichiometric and
catalytic asymmetric reactions [1]. For the preparation of the optically active [1,1'-
binaphthalene]-2,2'-diol [2], fractional recrystallization of diastereoisomers, resolution
with enzymes or microorganisms, enantioselective inclusion complexation, and
asymmetric oxidative coupling have become important approaches. However, these
preparations utilize expensive resolving agents or chiral inductors [3 14], or are not
easy to carry out1), or the time required for preparation is long2). From the practical
point of view, they are not all economical.
threo-(1S,2S)-2-Amino-1-(4-nitrophenyl)propane-1,3-diol (ANP), a −chiral waste×
in the production of chloromycetin, is one of the least expensive artificial chiral
materials available. However, application of ANP and its derivatives to the preparation
of optically active [1,1'-binaphthalene]-2,2'-diols has never been reported. In consid-
eration that reactions of 1,1'-biaryl-2,2'-diol, and B(OH)3 or its ester tend to form an
ionic spirocyclic boron complex in the presence of an amine [15][11c], and that we have
been able to prepare conveniently and chemoselectively ketone condensates of ANP
[16], we recently attempted to resolve racemic [1,1'-binaphthalene]-2,2'-diol with ANP
ketone condensates via the formation of an ionic spiro-borate salt and found an
economic, practical preparative method for both enantiomers of [1,1'-binaphthalene]-
1
)
In all methods for preparation of the enantiomerically pure [1,1'-binaphthalene]-2,2'-diol via a
cyclophosphoric acid ester, preparation of diastereoisomers and separation of the enantiomers from the
diastereoisomers must be carried out under anhydrous conditions, and LiAlH4 was required in the later
step.
2
)
In most cases, preparation requires several days; in certain cases, it takes more than ten days.

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Helvetica Chimica Acta Vol. 86 (2003)
2,2'-diol. Here, we report the new procedure for preparation of enantiomerically pure
(À)-(S)- and (‡)-(R)-[1,1'-binaphthalene]-2,2'-diol.
2. Results and Discussion.
2.1. Preparation of Enantiomerically Pure [1,1'-
Binaphthalene]-2,2'-diols via the Formation of an Ionic Spiro-Borate Salt. Previously,
we have observed that [1,1'-biphenyl]-2,2'-diol reacted easily with B(OH)3 to give a
Mulenhoff×s acid with a boron spirocyclic structure, and the acid could be stabilized by
an amine [15]. Similar to [1,1'-biphenyl]-2,2'-diol, [1,1'-binaphthalene]-2,2'-diol should
also be able to form a spiro-borate salt in the presence of an amine. If a spiro-borate salt
can be stereo-selectively produced from one enantiomer of racemic [1,1'-binaphtha-
lene]-2,2'-diol in the presence of a chiral amine, it is possible to separate efficiently both
enantiomers of racemic [1,1'-binaphthalene]-2,2'-diol. Thus, we examined reactions of
racemic [1,1'-binaphthalene]-2,2'-diol, B(OH)3, and ANP ketone condensates. We are
fortunate to observe that ANP-cyclohexanone condensate (CHANP; i.e. 3-(hydroxy-
methyl)-2-(4-nitrophenyl)-1-oxa-4-azaspiro[4.5]decane) could be used as a resolving
agent for racemic [1,1'-binaphthalene]-2,2'-diol under appropriate conditions. For
example, a 2:1:1 mixture of racemic [1,1 '-binaphthalene]-2,2'-diol ((rac-1), B(OH)3
(2), and CHANP (3) was allowed to reflux in THF or MeCN for several hours to give a
white precipitate of bis{(R)-[1,1'-binaphthalene]-2,2'-diol}-boric acid CHANP deriva-
1
tive, which has been characterized by IR, H-NMR, and MS. The precipitate gave
massy, colorless transparent crystals of (R)-1 of 100% ee in ca. 65% yield after
acidification and kinetic crystallization from toluene3). The solution separated from
the precipitate was evaporated, and the residue was recrystallized from toluene to give
(S)-1 of 100% ee in almost the same yield. It can be seen that a kinetic resolution
occurred under the experimental conditions. However, the efficiency of resolution
strongly depended on the reaction conditions; changing the reactant ratio, reaction
medium, and the period of reaction would result in a decrease in yield of the
enantiomerically pure products and even led to failure of resolution. The procedure for
preparing enantiomerically pure [1,1'-binaphthalene]-2,2'-diols from CHANP via the
formation of an ionic boron complex is shown in the Scheme.
2.2. Influence of Reactant Ratio on Resolution. To form a spiro-borate salt from the
reactants 1, 2, and 3, their molar ratio should be 2:1:1. This has been established by our
experiments (Table 1). It can be seen in Table 1 that only the 2:1:1 molar ratio could
provide enantiomerically pure (R)-1 and (S)-1 in high yield (Entries 2 and 3). Under
the experimental conditions, the reaction occurred stereoselectively and furnished a
large amount of white precipitate of diastereoisomeric bis {(R)-[1,1'-binaphthalene]-
2,2'-diol}-boric acid-CHANP derivative. When an excess of the reactant 1 or 3 was
used, enantiomerically pure [1,1'-binaphthalene]-2,2'-diols were obtained in very low
yield; meanwhile, a large amount of rac-1 was recovered. We observed that the amount
of bis{(R)-[1,1'-binaphthalene]-2,2'-diol}-boric acid-CHANP derivative was decreased
with increasing amount of rac-1 used. In Entry 3, 2.11 g of solid bis{(R)-[1,1'-
binaphthalene]-2,2'-diol}-boric acid-CHANP derivative precipitated from the reac-
3
)
Smrcina et al. proposed that the excess enantiomer in a nonracemic [1,1'-binaphthalene]-2,2'-diol could be
enriched via kinetic crystallization in benzene. We found that toluene is a better solvent than benzene for
kinetic crystallization.

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159
Scheme. Resolution of rac-[1,1'-Binaphthalene]-2,2'-diol with threo-(1S,2S)-2-Amino-1-(4-nitrophenyl)propane-
1,3-diolÀCyclohexanone Condensate (CHANP)
Table 1. Influence of Reactant Ratio on Resolutiona)
Entry
Reactant ratio
Product yield [%]
1/2/3
(R)-form
(S)-form
1
2
3
4
5
6
1 : 1 : 1
2: 1 : 1
2: 1 : 1
3 : 1 : 1
4 : 1 : 1
2: 1 : 2
0
0
68.4
64.4
35.7
0
61.5
54.5
18.2
0
3.5
a) All reactions were carried out in 40 ml of THF under reflux for 6 h and the amount of B(OH)3 used was
5 mmol. In Entry 2, the (R)-isomer was obtained after acidification in Et2O of the resulting white precipitate in
the reaction, evaporation of the Et2O solution, washing the residue with petroleum ether, and then recrystallization
from toluene. In the other reactions, the (R)-isomer was obtained after treatment according to the above
procedure, except without washing the residue obtained by evaporation of the Et2O solution with petroleum ether.
tion system; in Entry 4, the reaction gave 1.66 g of precipitate of the derivative
mentioned; and, in Entry 5, no precipitation occurred. The residue obtained after
evaporation was treated with hot toluene to give a large amount of a white precipi-
tate, but this precipitate, could not provide either of the enantiomerically pure

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[1,1'-binaphthalene]-2,2'-diols after treatment. In Entry 6, although 2.4 g of precipitate
was isolated, after treatment of the solid and evaporation, a large amount of rac-1 was
obtained. It is obvious that the use of excess rac-1 and the resolving agent is not
favorable for stereoselective formation of a spiro-borate salt, indicating that excess rac-
1 and resolving agent promote the reaction to form a spiro-borate salt from (S)-1.
2.3. Influence of Reaction Medium on the Resolution. A 2:1:1 mixture of the
reactants 1, 2, and 3 was allowed to reflux for 5 6 h in different solvents. The results are
shown in Table 2. It can be seen that only the reactions performed in THF and MeCN
furnished the desired products in high yield. When benzene or toluene was used as a
reaction medium (Entries 4 and 5), no precipitation of bis{(R)-1,1'-binaphthalene]-
2,2'-diol}boric acid CHANP derivative occurred. In Entry 3, the reaction performed in
70 ml of Et2O gave 3.6 g of white precipitate, which was stirred in a large amount of
Et2O to give an insoluble solid (a mixture of diastereoisomeric spiro-borate salts) and
an etheral solution from which a large amount of rac-1 was obtained after treatment. It
seems that THF and MeCN are suitable solvents for the resolving reaction; a nonpolar
or a less-polar solvent is not favorable for the resolution.
Table 2. Influence of Reaction Medium on Resolutiona)
Entry
Reaction medium
Product yield [%]
(R)-form
(S)-form
1
2
3
4
5
THF
MeCN
Et2O
Benzene
PhMe
64.4
63.0
54.5
59.0
5.6
trace
trace
a) All reactions were carried out in a 2: 1 : 1 molar ratio under reflux for 5 6 h, and the amount of B(OH) 3 used
was 5 mmol. The (R)-isomer in the Entry 2 was obtained after acidification in Et2O for the white precipitate
resulting from the reaction, evaporation of the Et2O solution, and then direct recrystallization from toluene.
2.4. Influence of Reaction Time on the Resolution. A 2:1:1 mixture of the reactants
1, 2 and 3 was allowed to reflux in MeCN and benzene, respectively, the resolution
results are shown in Table 3. We observed that the reactions performed in benzene,
regardless of the reaction time, did not give a precipitate (Entries 4 6); after
evaporation of the solution, a viscous residue was obtained. Although addition of Et2O
led to precipitation, it could not provide enantiomerically pure products from either the
precipitate or the ethereal solution, and only rac-1 was obtained. When the reaction
was performed in MeCN, a long reaction time resulted in decrease of the yield of
enantiomerically pure [1,1'-binaphthalene]-2,2'-diol (Entry 3). The result implies that,
after over 6 h, (S)-1 in the reaction system participated in the salt-forming reaction, and
amount of the spiro-borate salt from the (S)-isomer increased with prolongation of the
reaction time. On the other hand, the reaction for less than 4 h (Entry 1) merely led
to an enantiomerically pure product in low yield, indicating that it probably takes
more than 3 h for the efficient formation of bis{(R)-[1,1'-binaphthalene]-2,2'-diol}boric
acid.

Helvetica Chimica Acta Vol. 86 (2003)
161
Table 3. Influence of Reaction Time on Resolutiona)
Entry
Reaction medium
Reaction time [h]
Product yield [%]
(R)-form
(S)-form
1
2
3
4
5
6
MeCN
MeCN
MeCN
Benzene
Benzene
Benzene
3
6
11
0.5
6
7.0
59.0
21.7
63.0
trace
15
a) All reactions were carried out in a 2: 1 : 1 molar ratio under reflux, and the amount of B(OH) 3 used was
5 mmol. The (R)-isomer was obtained after acidification in Et2O for the white precipitate resulting from the
reaction, evaporation of the Et2O solution, and then direct recrystallization from toluene
2.5. The Diastereoselectivity of the Formation of the Spiro-Borate. In the presence of
CHANP, both enantiomers of rac-1 can stereoselectively react with B(OH)3 to form a
spiro-borate, and they can be isolated as salts. This has been established by our
experiments. We observed that the diastereoselectivity of the reaction depended
mainly upon the medium used. Only in THF or MeCN do (R)-1 and (S)-1 show a large
difference in the rate of formation of the spiro-borate, and only (R)-1 can react at an
appropriate rate and give a white precipitate of bis{(R)-[1,1'-binaphthalene]-2,2'-diol}-
boric acid CHANP derivative under appropriate conditions. The parallel experiments
performed with enantiomerically pure (R)-1 and (S)-1 indicated that the (S)-isomer
did not yield a precipitate of a spiro-borate salt in these solvents within 6 h. We also
observed that the amount of bis{(R)-[1,1'-binaphthalene]-2,2'-diol}boric acid CHANP
derivative precipitated from the reaction mixture is an important measure of resolution
efficiency. It appears that highly stereoselective formation of bis{(R)-[1,1'-binaphtha-
lene]-2,2'-diol}-boric acid-CHANP derivative is the key to efficient resolution of rac-1
with CHANP.
It can be seen from the above discussion that factors affecting the resolution
efficiency are complicated. When resolution was carried out in a 2:1:1 molar ratio in
THF or MeCN for 5 6 h, diastereoisomeric bis{(R)-[1,1'-binaphthalene]-2,2'-diol}-
boric acid CHANP derivative precipitated and enantiomerically pure (R)-1 and (S)-1
were obtained in ca. 65% yield from the precipitate and the mother liquor. However,
the resolutions showed a poor diastereoselectivety when resolution was not performed
in a 2:1:1 molar ratio or carried out in a nonpolar or less polar solvent or for a longer
time.
3. Conclusions. We have developed a novel and practical method for preparing
enantiomerically pure (‡)-(R)- and (À)-(S)-[1,1'-binaphthalene]-2,2'-diols, (R)-1 and
(S)-1, respectively, through the reaction of rac-1, B(OH)3, and threo-(1S,2S)-2-amino-
1-(4-nitrophenyl)propane-1,3-diol-cyclohexanone condensate. Our method is techno-
logically simple and easy to carry out (one-pot reaction, conventional operation
without special conditions). Morever, the time required for the preparation is short
([1,1'-binaphthalene]-2,2'-diol of 100% ee can be obtained within 24 h) and prepara-
tive cost is low. It is perhaps one of the most economical and practical methods for

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Helvetica Chimica Acta Vol. 86 (2003)
preparing enantiomerically pure (‡)-(R)- and (À)-(S)-[1,1'-binaphthalene]-2,2'-diols
at present.
Experimental Part
General. M.p.: VEB Wagetechnik Rapio PHMK05 instrument; not corrected. Optical rotations: WZZ-1S
1
(Shanghai, China) polarimeter. IR Spectra: Testscan Shimadzu FTIR 8000, in KBr. H-NMR Spectra: Varian
Mercury VS 300, d values [ppm] relative to Me4Si. MS: VG ZAB-HF-3F spectrometer.
Reagents. threo-(1S,2S)-2-Amino-1-(4-nitrophenyl)propane-1,3-diol-cyclohexanone condensate was pre-
pared according to the method described in [16]. rac-[1,1'-Binaphthalene]-2,2'-diol (rac-1) was purchased from
Beijing Xizhong chemical factory, and used without special treatment.
Preparation of (‡)-(R)- and (À)-(S)-[1,1'-Binaphthalene]-2,2'-diols ((R)-1 and (S)-1, resp.) of 100% ee. To
a 100-ml round-bottom flask, 2.86 g (10 mmol) of rac-1, 0.31 g (5 mmol) of B(OH)3, 1.46 g (5 mmol) of threo-
(1S,2S)-2-amino-1-(4-nitrophenyl)propane-1,3-diolÀcyclohexanone condensate, and THF (40 ml) were added.
Then, the flask was fitted successively with a 50-ml pressure-equalized additive funnel charged with an
appropriate amount of anh. CaCl2, a reflux condenser, and an oil bubbler with a stopcock. The mixture was
refluxed with magnetic stirring for 6 h to form a large amount of white precipitate. After cooling to ambient
temp., the precipitate was separated by filtration, washed with a small amount of THF, and then dried under
reduced pressure to give 2.21 g of solid bis{(R)-[1,1'-binaphthalene]-2,2'-diol}-boric acid 1-oxa-4-azaspiro[4.5]-
decane derivative as a solvate of THF; the solid was stirred in 30 ml Et2O for 0.5 h at ambient temp., filtered, and
the insoluble solid was collected, dried, and weighed; 2.11 g. M.p. 222 2258. IR (KBr): 3436m (OÀH), 3053m
‡
(ArÀH), 2965 (sh.), 2942m-s, 2873m (CÀH), 2780 2400m-w (NH2 ), 1612m, 1589m-s (CˆCÀC), 1521s
(NO2), 1510 (sh., CˆCÀC), 1462s (CH2), 1360 (sh., CH2), 1339vs (br., NO2 ‡ BÀO), 1268m (CÀN), 1244vs
(ArÀO), 1072vs (BÀO), 1010vvs, 973vs, 909m-s (CÀOÀC or CÀO), 819m-s (PhÀH), 752m-s (napht.-H).
1H-NMR ((D6)DMSO, 300 MHz): 1.30 1.80 (m, 10 H of cyclohexane and CH2(3), CH2(4) of THF); 2.98
(m, NCH); 3.58 (m, CH2O and CH2(2), CH2(5) of THF); 4.66 (d, J ˆ 7.5, ArCHC); 5.03 (t, CH2OH); 6.93
(d, J ˆ 8.7, 4 H of napht.); 7.07 7.34 (m, 12H of napht.); 7.62( d, J ˆ 8.7, HÀC(2), HÀC(6) of Ph); 7.77 7.98
(m, 8 H of napht.); 8.11 (d, J ˆ 8.7, HÀC(3), HÀC(5) of Ph); 9.25 (s, NH2‡). FAB-MS: 580 (17, [M À
‡
‡
C15H20N2O4 (CHANP)] ; 292 (18, [M À C40H25BO4] ), 286 (22, C20H14O2). This solid is hard to dissolve in
H2O, petroleum ether, Et2O, benzene, PhMe, THF, MeCN, MeOH, EtOH, i-PrOH, CHCl3, AcOEt, Me2CO,
etc., except DMSO and DMF. To the solid product, 2m HCl and Et2O were added, and the mixture was stirred
until complete dissolution occurred. The Et2O layer was separated, and the H2O phase was extracted with Et2O.
The org. phases were combined and dried (Na2SO4); the Et2O soln. was evaporated, and the residue was washed
with petroleum ether. Then, an appropriate amount of toluene was added for recrystallization to give 0.98 g of
massy, colorless transparent crystals of (‡)-(R)-1 in 68.5% yield. M.p. 208 2108. [a]2D2 ˆ ‡35.2( c ˆ 1, THF).
100% ee.
The THF mother liquor removed from the solid was evaporated to give a solid residue, which was
essentially the enriched (S)-isomer. The residue was crystallized from toluene to furnish 0.88 g of massy,
transparent crystals of (À)-(S)-1 in 61.5% yield. M.p. 208 2108. [a]2D2 ˆ À35.3 (c ˆ 1, THF). 100% ee.
Financial support by the National Natural Science Foundation of China (29972033) and the Key Science
Research Foundation of Hubei Province (98IP1305) are gratefully acknowledged.
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Received July 14, 2002