Organic Syntheses, Vol. 76, 6
Checked by Rachel van Rijn and Amos B. Smith, III.
1. Procedure
B. Preparation of (R)-(+)-BINAP.
3 An oven-dried,
250-mL, single-necked flask, equipped with a magnetic stirring bar, is charged with
[1,2-bis(diphenylphosphino)ethane]nickel(II) chloride] (NiCl2dppe, 1.1 g, 2 mmol). The flask is purged with N
2 (using a vacuum and
nitrogen manifold) and anhydrous
dimethylformamide (DMF, 40 mL) is added via a syringe, followed by
diphenylphosphine (2.0 mL, 12 mmol) at room temperature (Note
7). The resulting dark red solution is heated at 100°C for 30 min. A solution of the chiral
ditriflate of binaphthol (11.0 g, 20 mmol) and
1,4-diazabicyclo[2.2.2]octane (DABCO, 9.0 g, 80 mmol) in anhydrous, degassed DMF (60 mL) (Note
8) is transferred in one portion to the reaction flask via cannula, and the resulting dark green solution is kept at 100°C. Three additional portions of
diphenylphosphine (3 × 2 mL) are added by syringe after 1 hr, 3 hr, and 7 hr. The reaction is heated at 100°C until the ditriflate of
binaphthol is completely consumed (2ndash;3 days) (Note
6). The dark brown solution is cooled to −15

−20°C with an
ice/acetone bath and stirred for 2 hr. The product is filtered, and the solid is washed with
methanol (2 × 20 mL) and dried under vacuum. The isolated product (
9.6 g,
77%) is a white to off-white crystalline compound with a chemical purity of

97 area% (HPLC, 220 nm) containing

1% of the monooxide of BINAP (Note
6), (Note
9), (Note
10), (Note
11).
4
2. Notes
1. Both enantiomers of
1,1'-bi-2-naphthol are available from Aldrich Chemical Company, Inc.
2.
Methylene chloride and pyridine were purchased from Aldrich Chemical Company, Inc. and dried over activated 4 Å molecular sieves.
3.
Triflic anhydride was purchased from Aldrich Chemical Company, Inc. and used without purification.
4. The reaction is complete in 2 hr, but may be run overnight.
5. The spectral properties of the
ditriflate of binaphthol are as follows:
1H NMR (500 MHz, CDCl
3) δ: 7.27 (d, 2 H, J = 8.5), 7.42 (ddd, 2 H, J = 1.1, 6.8, 8.2), 7.59 (ddd, 2 H, J = 1.0, 7.0, 8.1), 7.63 (d, 2 H, J = 9.1), 8.02 (d, 2 H, J = 8.2), 8.15 (d, 2 H, J = 9.1);
13C NMR (125 MHz, CDCl
3) δ: 118.3, 119.4, 123.6, 126.8, 127.4, 128.1, 128.5, 132.1, 132.5, 133.2, 145.5.
6. Conditions for the LC assay were as follows: Zorbax Rx-C
8 column, 4.6 mm × 25 cm, room temperature, 1.50 mL/min, linear gradient,
60% CH3CN/water to 90% CH3CN/water in 20 min, then hold at 90% CH
3CN/water for 5 min; water contained 0.1% H
3PO
4; UV detection at 220 nm. Typical retention times are 1.75 min (DMF), 2.32 min (Ph
2POH), 5.53 min (dppe), 6.42 min (Ph
2PH), 7.73 min (BINAPO, dioxide of BINAP), 8.55 min [Ar(OTf)-ArP(O)Ph
2], 11.69 min (
ditriflate of binaphthol), 14.54 min (monooxide of BINAP), 16.00 min Ar(H)-ArPPh
2, 20.99 min (BINAP); typical LC (area %) at the end of the reaction are
DMF (49%), dppe (1.4%) BINAPO (0.6%), ditriflate of
bi-2-naphthol (0.5%), monooxide of BINAP (4%), Ar(H)-ArPPh
2 (0.9%) and BINAP (36%).
7.
NiCl2dppe, DMF (anhydrous grade) and DABCO were obtained from Aldrich Chemical Company, Inc., and used without further purification.
NiCl2dppe can also be obtained from Strem Chemicals Inc. Diphenylphoshine (DPP) was obtained in an ampoule from Strem Chemicals Inc. When not handled properly, DPP [
31P NMR; (200 MHz, CDCl
3) δ: −40 ppm] is rapidly oxidized to diphenylphoshine oxide [
31P NMR; (200 MHz, CDCl
3) δ: 22 ppm]. DPP was transferred directly from the ampoule to a
Schlenk flask under an inert atmosphere. Its purity was checked by
31P NMR to ensure that it was free of oxidation products.
8. This solution was degassed via vacuum and
nitrogen 3–6 times. Exclusion of air from the reaction is critical to minimize formation of phosphine oxide by-products.
9. Recrystallization of the mother liquor after the first crop was obtained yielded a product with a lower purity.
10. Two impurities were identified as
11. The submitters' isolated
BINAP had
[α]20D +219°, 99% ee, mp
237-238°C (lit ref.
5 [α]20D +217°, 98.4% ee). Other physical properties of
BINAP are as follows: IR cm
−1: 3050 (s), 3010 (s), 1480 (m), 1450 (s), 1310 (m), 1180 (m), 1110 (m), 1090 (m);
1H NMR (500 MHz, CDCl
3) δ: 6.83 (d, 2 H, J = 8.4), 6.91 (ddd, 2 H, J = 1.2, 8.2, 6.9), 7.04-7.18 (m, 20 H), 7.34 (ddd, 2 H, J = 1.1, 6.9, 8.0), 7.46 (ddd, 2 H, J = 2.6, 8.5), 7.83 (d, 2 H, J = 8.2), 7.89 (d, 2 H, J = 8.5);
13C NMR (125 MHz, CDCl
3) δ: 125.7, 126.5, 127.5, 127.7, 128.0, 128.1, 128.4, 130.5, 132.8, 132.9, 133.0, 133.2, 133.4, 133.5, 134.1, 134.2, 134.3, 135.5, 135.6, 137.4, 137.5, 138.0, 145.1, 145.4;
31P NMR (101 MHz, CDCl) δ: −14.9 ppm; HRMS (FAB, m-nitrobenzyl alcohol): m/z 623.2074 [(M+H)
+; calcd for C
44H
32P
2: 623.2058].
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
BINAP are very useful ligands for various catalytic asymmetric reactions.
6 7 8 However, the scarce supply and high cost of
BINAP somewhat limit their wide application. A previously reported synthesis of
BINAP was not easy to scale up because of potentially hazardous conditions (320°C with
HBr evolution), and low overall yield.
9 5 This procedure presents a short and efficient process to chiral BINAP from readily available chiral
1,1'-bi-2-naphthol.
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