A New, Convenient Method of Resolution of Racemic 1,1′-Bi-2-naphthol Using Boric Acid and (R)-(+)-α-Methylbenzylamine

Full text of DOI:10.1021/jo990710r

J . Org. Chem. 1999, 64, 7643-7645
7643
A New , Con ven ien t Meth od of Resolu tion
of Ra cem ic 1,1′-Bi-2-n a p h th ol Usin g Bor ic
Acid a n d (R)-(+)-r-Meth ylben zyla m in e
Mariappan Periasamy,* Lakshmanan Venkatraman,
Sangarappan Sivakumar,
Nangunoori Sampathkumar, and
C. Ramaraj Ramanathan
School of Chemistry, University of Hyderabad,
Central University P.O., Hyderabad 500 046, India
Received April 27, 1999
diols, and amino acid derivatives, it was discovered that
1 forms a 2:1 complex with (S)-proline 3 in methanol.16
Decomposition of the complex gives partially resolved
1 (Scheme 1). The enantiomeric purity of the sample was
further enriched through preparation of a borate complex
using B(OH)3 and TMEDA in CH3CN.16c,d Although this
two-step procedure of resolution of 1 involves inexpensive
reagents, recovery of the water-soluble (S)-proline is
somewhat difficult. Therefore, we have undertaken stud-
ies to explore the development of a convenient resolution
procedure using B(OH)3 and a chiral amine. We wish to
report that the readily accessible chiral R-methylbenzyl-
amine is useful in obtaining both S and R isomers of 1
in >99% ee (52-70% of theoretical yields).
In tr od u ction
The C2-chiral 1,1′-bi-2-naphthol 11 is one of the widely
used chiral auxiliaries in stoichiometric and catalytic
asymmetric synthesis, such as enantioselective reduction
of ketones,2 in various catalytic asymmetric Diels-Alder
reactions,3 ene reactions,4 asymmetric Michael additions,5
hydroformylations,6 alkylations,7 oxidations,8 epoxida-
tions,9 and nitroaldol reactions.10 It has been also used
as a chiral host for optical resolution and chiral shift
reagent for the determination of the optical purity and
absolute configurations of a wide range of chiral com-
pounds.11 In this regard, preparation of enantiomerically
pure 1 is of current interest. There are numerous
methods for the preparation of enantiomerically pure 1
such as enzymatic resolution,12 separation of diastereo-
mers using cinchonidinium derivatives,13 a tartaric acid
amide,14 binaphthyl phosphoric acid,15 and boric acid
derivatives.16,17
Resu lts a n d Discu ssion
We have observed that the (R)-(+)-R-methylbenzyl-
amine, B(OH)3, and racemic 1 give a precipitate on
heating at reflux in CH3CN. Decomposition of the pre-
cipitate with dilute HCl gives the (S)-(-)-1 in >99% ee
(29% yield, 58% of theoretical). The filtrate upon evapo-
ration followed by dilute HCl treatment of the residue
gives the (R)-(+)-1 in 56% ee (53% yield). The use of (S)-
(-)-R-methylbenzylamine gave the (R)-(+)-1 in >99% ee
and (S)-(-)-1 in 52% ee in similar yields.
We have used 1 and boric acid in a 3:2 ratio in these
experiments, since heating of a mixture of these sub-
strates in benzene leads to the formation of a C3-
symmetric propeller 5,16d previously reported in the
reaction of BrBH2‚SMe2 with binaphthol.3e
During our efforts on the preparation of diastereomeric
borate complexes such as 2 using boric acid, racemic
(1) Pu, L. Chem. Rev. 1998, 98, 2405.
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T.; Mano, S.; Horiuchi, T.; Takaya, H. J . Am. Chem. Soc. 1997, 119,
4413.
Unfortunately, recrystallization of the precipitate ob-
tained in Scheme 2 using (()-1, boric acid, and R-meth-
ylbenzylamine did not yield crystals suitable for X-ray
crystal structure analysis. However, the filtrate on
standing yielded crystals suitable for X-ray analysis
(7) Chan, A. S. C.; Zhang, F. Y.; Yip, C. W. J . Am. Chem. Soc. 1997,
119, 9, 4080.
(8) (a) Komatsu, N.; Hashizuma, M.; Sugita, T.; Uemura, S. J . Org.
Chem. 1993, 58, 4529. (b) Reetz, M. T.; Merk, C.; Naberfeld, G.;
Rudolph, J .; Griebenow, N.; Goddard, R. Tetrahedron Lett. 1997, 38,
5273.
(9) Bougauchi, M.; Watanabe, S.; Arai, T.; Sasai, H.; Shibasaki, M.
J . Am. Chem. Soc. 1997, 119, 2329.
(10) Sasai, H.; Suzuki, T.; Arai, T.; Shibasaki, M. J . Am. Chem. Soc.
1992, 114, 4418.
(11) (a) Toda, F.; Mori, K.; Okada, J .; Node, M.; Itoh, A.; Oomine,
K.; Fuji, K. Chem. Lett. 1988, 131. (b) Toda, F.; Mori, K.; Sato, A. Bull.
Chem. Soc. J pn. 1988, 61, 4167.
(12) Kazlauskas, R. J . J . Am. Chem. Soc. 1989, 111, 4953.
(13) (a) Hu, Q. S.; Vitharana, D.; Pu, L. Tetrahedron: Asymmetry
1995, 6, 2123. (b) Tanaka, K.; Okada, T.; Toda, F. Angew. Chem., Int.
Ed. Engl. 1993, 32, 1147. (c) Cai, D.; Hughes, L. D.; Verhoeven, T. R.;
Reider, P. J . Tetrahedron Lett. 1995, 36, 7991.
(14) Toda, F.; Tanaka, K. J . Org. Chem. 1988, 53, 3607.
(15) (a) Gong, B.; Chen, W.; Hu, B. J . Org. Chem. 1991, 56, 423. (b)
J acques, J .; Fouquey, C. Org. Synth. 1988, 67, 1. (c) Kyba, E. P.; Gokel,
G. W.; J ong, F. D.; Koga, K.; Sousa, L. R.; Seiegel, M. G.; Kaplan, L.;
Sogah, G. D. Y.; Cram, D. J . J . Org. Chem. 1977, 42, 4173. (d) Fabri,
C.; Delogu, G.; De Lucchi, O. J . Org. Chem. 1995, 60, 6599.
(16) (a) Periasamy, M. Pure Appl. Chem. 1996, 68, 663 (presented
at the IUPAC International Conference in Organic Synthesis (ICOS
10), Dec 11-16, 1994, Abstract No. SL 36, Bangalore, India). (b)
Periasamy, M.; Prasad, A. S. B.; Kanth, J . V. B.; Reddy, Ch. K.
Tetrahedron: Asymmetry 1995, 6, 341. (c) Venkatraman, L.; Peri-
asamy, M. Tetrahedron: Asymmetry 1996, 7, 2471. (d) Periasamy, M.;
Venkatraman, L.; J ustin Thomas, K. R. J . Org. Chem. 1997, 62, 4302-
4306. (e) Periasamy, M.; Ramanathan, C. R.; Prasad, A. S. B.; Kanth,
J . V. B. Enantiomer 1998, 3, 3.
(17) Shan, Z.; Xiong, Y.; Li, W.; Zhao, D. Tetrahedron: Asymmetry
1998, 9, 3985-3989.
10.1021/jo990710r CCC: $18.00 © 1999 American Chemical Society
Published on Web 09/08/1999

7644 J . Org. Chem., Vol. 64, No. 20, 1999
Notes
(Scheme 2). The data revealed that the crystal obtained
in this way is a Bronsted acid-amine complex 6.19
F igu r e 1. Perspective view of the complex 6.
Clearly, the 1,1′-bi-2-naphthol and boric acid tend to
form a complex of the type 6 in the presence of R-meth-
ylbenzylamine. Therefore, we have carried out the reso-
lution experiments using racemic 1 and boric acid in a
2:1 ratio with different amounts of (R)-(+)-R-methylben-
zylamine in CH3CN. The results are summarized in Table
1.
Sch em e 1
The partially enriched 1 gives better results (Table 1,
entry 3). Moreover, it was observed that when THF was
used as a solvent, the opposite enantiomer was isolated
from the precipitate in 95% ee (Table 1, entry 4). Again,
the results are better when partially enriched 1 was used
(Table 1, entries 5 and 6). Obviously, one of the diaster-
eomers is insoluble in CH3CN and the other is insoluble
in THF.
We have exploited this difference in solubility in CH3-
CN and THF of the diastereomeric complexes to develop
a convenient, practical method of resolution as illustrated
Ta ble 1. Resolu tion of 1,1′-Bi-2-n a p h th ol Usin g B(OH)3
a n d (R)-(+)-r-Meth ylben zyla m in ea
(18) (a) Hay, A. S. J . Org. Chem. 1962, 27, 3320. (b) de J ong, C. R.
H. I. In Organic Synthesis by Oxidation with Metal Compounds; Mijs,
W. J ., de J ong, C. R. H. I., Eds.; Plenum Press Inc.: New York, 1986;
pp 423-443. (c) Nakajima, M.; Miyoshi, I.; Kanayama, K.; Hashimoto,
S. I. J . Org. Chem. 1999, 64, 2264. (d) Vogel, A. I. Text Book of Practical
Organic Chemistry; Longman: Birmingham, AL, 1978.
optically active 1 from
precipitate
yield
(%) % ee
filtrate
1
(R)-(+)-4
(mmol) solvent
yield
(%)
S no. % ee
% ee
(19) Cr ysta l Str u ctu r e An a lysis. The X-ray diffraction measure-
ments were carried out at 293 K on an automated Enraf-Nonious
MACH 3 diffractometer using graphite-monochromated Mo KR (λ )
0.71073 Å) radiation. Intensity data were collected by the ω-scan mode.
The data were reduced using the XTAL program. No absorption
correction was applied. θ range for data collection is 1.63-21.98°.
1
2
3
4
5
6
0
0
15
10
10
5
5
5
CH3CN S, 91
CH3CN S, 81
CH3CN S, 97
40
45
55
24
25
28
R, 61
R, 40
R, 55
S, 20
S, 20
S, 25
50
50
38
70
68
65
S, 30
0
R, 20
R, 34
THF
THF
THF
R, 95
R, 97
R, > 99
Crystal structure data for 6: empirical formula
C152H119B3N4O12;
colorless rectangular prism (0.4 × 0.4 × 0.6 mm); crystal system is
triclinic; space group P1; unit cell dimensions, a ) 17.979(8) Å, b )
19.72(7) Å, c ) 20.96(2) Å; R ) 114.16°, â ) 93.52°, γ ) 96.35°; volume
6691(24) Å3, Z ) 2, Dcalc ) 1.105 Mg/m3, absorption coefficient is 0.069
mm-1, F(000) ) 2340, index ranges 0 e h e 18, -20 e k e 20, -22 e
l e 21, total reflections collected were 16524 out of which 16350 were
independent reflections with R(int) ) 0.0000 and R(σ) ) 0.1137. The
structure was solved by direct methods and refined by a full-matrix
least-squares procedure using the SHELX 86 and SHELX 97 program
packages, respectively. The refinement was carried out using 16350
observed [F > 4σ(F)] reflections and converged to a final R1 ) 0.1743,
wR2 ) 0.4390 and goodness of fit of 1.516 with a largest difference
peak and hole of 1.538 and -0.560 e Å-3, respectively. The structure
of the complex was confirmed from the bond angles and bond lengths.
The bond angles O1-B1-O2 ) 112.578°, O1-B1-O3 ) 118.054°, O1-
B1-O4 ) 100.790°, O2-B1-O3 ) 103.660°, O2-B1-O4 ) 112.190°, and
O3-B1-O4 ) 109.831° showed the existence of boron in tetracoordinate
form. The bond distances between boron B1 and four oxygens, B1-O1
) 1.4849 Å, B1-O2 ) 1.4425 Å, B1-O3 ) 1.4588 Å, and B1-O4 ) 1.5016
Å, supports the “ate” complex nature of boron.
a
All experiments were performed using 1,1′-bi-2-naphthol (10
mmol), B(OH)3 (5 mmol), and (R)-(+)-R-methylbenzylamine as
mentioned. The substrates were taken in the solvent (20 mL), and
the contents were refluxed for 12 h (see the Experimental Section
for workup).
in Scheme 3. In this way, (S)-(-)-1 was obtained in >99%
ee (35% yield, i.e., 70% of theoretical) and (R)-(+)-1 was
obtained in >99% ee (26% yield, i.e., 52% of theoretical).
The recovered (S)-(-)-1 (62% ee, 2% yield) and (R)-
(+)-1 (10% ee, 35% yield) have been recycled to obtain 1
with >99% ee (Table 1 and Scheme 3). The experiment
was also carried out using 50 mmol of racemic 1 and
proportional amounts of other reagents to obtain chiral
1 in >99% ee without significant change in yields. The

Notes
J . Org. Chem., Vol. 64, No. 20, 1999 7645
Sch em e 2
Sch em e 3
chiral amine and all the solvents can be readily recovered
for use again. Therefore, the procedure described here
for the resolution of 1,1′-bi-2-naphthol using inexpensive
reagents should be highly economical.
Exp er im en ta l Section
The racemic 1,1′-bi-2-naphthol was prepared in high yield by
oxidative coupling of â-naphthol using CuCl(OH)-TMEDA cata-
lyst and air in MeOH followed by recrystallization from
chlorobenzene.18a-c It was also prepared using FeCl3 in water
by recrystallization from toulene.18d Chiral resolving agent (R)-
(+)-R-methylbenzylamine with 98%-99% ee was used. Enantio-
meric excesses were calculated from values measured on an
Autopol-II automatic polarimeter. It was also confirmed for
samples of 1,1′-bi-2-naphthol with >99% ee by HPLC analysis
using a CHIRALPAK OP column with MeOH as solvent.
Resolu tion of Ra cem ic 1,1′-Bi-2-n a p h th ol Usin g B(OH)3
a n d (R)-(+)-r-Meth ylben zyla m in e (Sch em e 3). Racemic 1,1′-
bi-2-naphthol 1 (10 mmol, 2.86 g), B(OH)3 (5 mmol, 0.31 g), and
(R)-(+)-R-methylbenzylamine (15 mmol, 1.995 mL) were refluxed
in CH3CN (20 mL) for 12 h. The reaction mixture was cooled to
rt and filtered. To the precipitate 4A was added CH3CN (10 mL)
and the mixture refluxed for 6 h. The contents were brought to
rt and filtered. The precipitate 5A was suspended in a mixture
of EtOAc (25 mL) and dilute HCl (1 N, 20 mL) and stirred until
complete dissolution occurred. The organic layer was collected,
and the aqueous layer was extracted with EtOAc (10 mL × 2).
The organic extracts were combined and washed with saturated
brine, dried over magnesium sulfate, and evaporated to dryness
to obtain (S)-(-)-1, 0.96 g, >99% ee (35% yield, 70% of theoreti-
cal), mp 208-210 °C (lit. 15d mp 209-210 °C). The ee values are
yield, 52% of theoretical), mp 208-210 °C (lit.15d mp 209-210
°C). The ee values are based on [R]25 ) 34.5 (c 1, THF).16d The
D
chiral resolving agent (R)-(+)-R-methylbenzylamine, 4, was
recovered by NaOH treatment of the combined dilute HCl
fractions followed by extraction with diethyl ether (25 mL × 2).
After evaporation of the combined ether layers, the residue was
distilled under reduced pressure to isolate 4 in 90% yield (99%
ee).
Ack n ow led gm en t. Financial support of this work
was provided by UGC and CSIR, New Delhi. We are
also grateful to the UGC for financial support under
Special Assistance Program. We are also thankful to
Gerchem Labs (pvt) Ltd., India, for support of part of
the work described here. A few initial experiments
(Scheme 2) were carried out by M.P. during a visit to
the University of Amsterdam (Oct-Dec 1996), and
thanks are due to the NWO, The Netherlands, Prof. W.
N. Speckamp, and Prof. H. Hiemstra for extending
support and facilities. X-ray analysis was carried out
using the National Single Crystal X-ray facility, School
of Chemistry, University of Hyderabad, funded by DST,
New Delhi.
based on [R]25 ) 34.5 (c 1, THF).16d
D
The filtrate 4B was concentrated. The residue was refluxed
for 6 h in THF (20 mL). The reaction mixture was brought to rt
and filtered. The precipitate 5B was digested in a mixture of
EtOAc (25 mL) and dilute HCl (1 N, 20 mL) followed by workup
as outlined above to obtain the (R)-(+)-1, 0.75 g, >99% ee (26%
J O990710R