Organic Syntheses, Vol. 76, 1
[1,1'-Binaphthalene]-2,2'-diol]
Submitted by Dongwei Cai, David L. Hughes, Thomas R. Verhoeven, and Paul J. Reider
1.
Checked by Rachel van Rijn and Amos B. Smith, III.
1. Procedure
A
500-mL flask, equipped with a
magnetic stirring bar and a
reflux condenser, is charged with
1,1'-bi-2-naphthol (23.0 g, 80 mmol) and
N-benzylcinchonidinium chloride (18.6 g, 44 mmol) (Note
1).
Acetonitrile (300 mL) is added, and the resulting suspension is refluxed for 4 hr, cooled and stirred at room temperature overnight. The mixture is then cooled to 0–5°C, kept at that temperature for 2 hr, and filtered (Note
2). The filtrate is concentrated to dryness, redissolved in
ethyl acetate (300 mL), and washed with
1 N hydrochloric acid (HCl, 2 × 100 mL) (Note
3) and
brine (100 mL). The organic layer is dried over
sodium sulfate (Na2SO4), filtered, and concentrated to a light brown solid [
10.28–10.65 g, mp
205-206°C,
89-93% recovery, 99.0% ee S-enantiomer
[α]21D −27.6
−29.4° (
THF,
c 1)] (Note
4), (Note
5), (Note
6).
The solid complex is washed with
acetonitrile (50 mL). This
acetonitrile solution is discarded because of the low ee (

80% ee of the S-enantiomer is contained). The resulting solid complex (96% ee, R-enantiomer) is transferred to a
250-mL flask.
Methanol (100 mL) is added, and the resulting suspension is refluxed for 24 hr to upgrade the enantiomeric excess to >99% ee. After the mixture is cooled to room temperature, it is filtered and the solid washed with
methanol (20 mL). The solid complex is suspended in a mixture of
ethyl acetate (300 mL) and
1 N HCl (150 mL) and stirred until complete dissolution occurs (0.5 hr). The solution is transferred to a
separatory funnel, and the organic layer is separated and then washed with
1 N HCl (150 mL) and
brine (150 mL). The organic layer is dried over Na
2SO
4, filtered, and concentrated to an off-white crystalline solid [
9.83-10.16 g,
85-88% recovery, mp
206-207°C, >99.8% ee of the R-enantiomer
[α]21D 26.2
30.9° (
THF,
c 1)] (Note
4), (Note
5), (Note
6).
2. Notes
2. The enantiomeric excess of
1,1'-bi-2-naphthol in the filtrate at room temperature is 98.6% and at 0-5°C 99.0%.
4. Numerous chiral HPLC columns have been used for determination of chiral purity of
1,1'-bi-2-naphthol.
2,3 The submitters used
Diacel Chiralpak OP(+) column (4.6 mm × 250 mm) at room temperature for their chiral assay. Typical retention times of
1,1'-bi-2-naphthol are 14 min (R-enantiomer) and 20 min (S-enantiomer) using
methanol as an eluting solvent at 0.5 mL/min. The submitters' detection limit of minor enantiomers is about 0.1%. The checkers used a
Pirkle covalent D-phenylglycine column using
isopropyl alcohol:hexane (5:95) as the eluting solvent at 1.0 mL/min with UV at 312 nm.
5. Enrichment to >99.8% ee is possible by recrystallization from a
tert-butyl methyl ether (MTBE)/hexane mixture:
1.0 g of (S)-1,1'-bi-2-naphthol is dissolved in
MTBE (10 mL), then
hexane is added (20 mL). The resulting solid is stirred at room temperature for 2 hr, then filtered to provide a white crystalline solid (
0.65 g, >99.8% ee, >99 wt% purity).
6. Other physical properties of the products are as follows: IR cm
−1: 3550 (s), 3050 (m), 1610 (m), 1590 (m), 1390 (m), 1180 (s), 1140 (s);
1H NMR (250 MHz, CDCl
3) δ: 5.0 (s, 2 H, OH), 7.16 (d, 2 H, J = 8.3), 7.30 (m, 2 H), 7.38 (m, 4 H), 7.90 (d, 2 H, J = 8.1), 7.99 (d, 2 H, J = 8.9);
13C NMR (62.9 MHz, CDCl
3) δ: 110.8, 117.8, 124.0, 124.2, 127.5, 128.4, 129.5, 131.4, 133.4, 152.8; HRMS (FAB, m-nitrobenzyl alcohol): R enantiomer, m/z 304.1335 [(M+NH
4+); calcd for C
20H
14O
2+NH
4+: 304.1337]; S-enantiomer, m/z 304.1331 [(M+NH
4+); calcd for C
20H
14O
2+NH
4+: 304.1337].
Waste Disposal Information
All toxic materials were disposed of in accordance with "Prudent Practices in the Laboratory"; National Academy Press; Washington, DC, 1995.
3. Discussion
Both enantiomers of
1,1'-bi-2-naphthol are widely used for various applications: 1) chiral inducing agents for catalytic, asymmetric reactions such as the Diels-Alder reaction,
4 ene reaction,
5 6 or as Lewis acids;
7 8 2) enantioselective reduction of ketones;
9 10 3) synthesis of chiral macrocycles
11 12 and other interesting compounds.
13 Previously reported resolutions include: 1) making a cyclic phosphate of binaphthol, then resolution and subsequent reduction to release the pure binaphthol;
14 2 15 16 17 18 2) using enzymatic hydrolysis of the diester of binaphthol;
19 3 and 3) forming inclusion complexes with suitable compounds.
20 21 22 The use of
N-benzylcinchonidinium chloride to make inclusion complexes was reported by Tanaka and co-workers for obtaining one enantiomer of
binaphthol.
23 24 Using
acetonitrile as solvent, in which the inclusion complex has very low solubility, allows for the isolation of both enantiomers with high enantiomeric excess. This simple and efficient procedure represents a much better resolution for
1,1'-bi-2-naphthol.
25
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
1,1'-Bi-2-naphthol: [1,1'-Binaphthalene]-2,2'-diol (8,9); (602-09-5)
N-Benzylcinchonidinium chloride: Cinchonanium, 9-hydroxy-1-(phenylmethyl)-, chloride, (9S)- (10); (69221-14-3)
Acetonitrile: TOXIC (8,9); (75-05-8)
(S)-(-)-1,1'-Bi-2-naphthol: [1,1'-Binaphthalene]-2,2'-diol, (S)-(-)- (8);
[1,1'-Binaphthalene]-2,2'-diol, (S)- (9); (1853-99-2)
(R)-(+)-1,1'-Bi-2-naphthol: [1,1'-Binaphthalene]-2,2'-diol, (R)-(+)- (8);
[1,1'-Binaphthalene]-2,2'-diol, (R)- (9); (18531-94-7)
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