Asymmetric Allylic Alkylation and Hydrogenation with Transition Metal Complexes of Diphosphite…
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phosphochloridites 5c-d, by starting from 2,2′-dihydroxy-
5,5′,6,6′,7,7′,8,8′-octahydro-1,1′-binaphthol. Diphosphite
ligands 2a-b were synthesized stereospecifically accord-
and was used directly without further purification.
Treatment of compound 4 (77.6 mg, 0.67 mmol), 5d
(530.1 mg, 1.48 mmol), and DMAP (17.8 mg, 0.15 mmol)
as described for the synthesis of ligand 2c afforded
ligand 2d, which was purified by flash chromatography
(Rf =0.44, n-hexane:toluene=1:1) to produce a white solid
(211.8 mg, 42% yield). [α]D20 =+147 (c 0.13, CH2Cl2); Mp
109–110°C; 1H NMR (400 MHz, DMSO-d6) δ 7.12 (s, 2H,
Ar), 7.05 (dd, J=17.6, 8.2 Hz, 4H, Ar), 6.88 (d, J=7.4 Hz,
2H, Ar), 4.15 (s, 2H, CH), 2.76 (s, 8H, CH2), 2.58 (s, 4 H,
CH2), 2.10 (d, J=10.6 Hz, 6H, CH2), 1.71 (s, 16H, CH2),
1.46 (s, 6H, CH2) ppm. 13C NMR (100 MHz, DMSO-d6)
δ 146.27, 145.77, 137.25, 134.96, 133.78, 129.82, 129.36,
127.71, 119.33, 119.02, 77.12, 76.92, 32.73, 28.81, 27.67,
27.54, 23.36, 22.45, 22.36, 22.34, 22.23 ppm. 31P NMR
(161 MHz, DMSO-d6) δ 142.59 ppm. HRMS (ESI+): calcd
for C46H50NaO6P2 [M+Na]+783.2975; found: 783.2965.
1
ing to the literature procedures,[33] and their H NMR,
13C NMR, 31P NMR, and HRMS were consistent with the
expectation for them. All of the ligands were stable dur-
ing the purification of neutral silica gel under a nitrogen
atmosphere with reasonable yields.
2.2.1 (1S,2S)‑bis[(R)‑1,1′‑H8‑binaphthyl‑2,2′‑diyl]
phosphite‑cyclohexanediol 2c
To a 100 mL Schlenk flask equipped with a condenser
were added 1.0 g of (R)-H8-binaphthol, 20 mL of tolu-
ene, and 12 mL of PCl3. Under a nitrogen atmosphere the
mixture was refluxed for 20 h. After removal of the excess
PCl3 and toluene, the residue was dissolved in 20 mL of
toluene, and then was transferred to another Schlenk flask,
and toluene was removed in vacuo to obtain the com-
pound (R)-1,1′- H8-binaphthyl-2,2′-diyl-chlorophosphite
5c as a white powder, which was used directly in the fol-
lowing step without further purification. To a stirred solu-
tion of compound 4 (77.5 mg, 0.67 mmol), compound
5c (529.9 mg, 1.48 mmol), and 4-dimethylaminopyri-
dine (DMAP) (17.4 mg, 0.15 mmol) in THF (10 mL) at
−15°C, NEt3 (0.32 mL) was slowly added using a syringe
over 2 min., and the solution was stirred for 0.5 h at
−15°C. The mixture was then stirred at room temperature
for 1 h. THF was distilled off in vacuo, and then toluene
(20 mL) was added. The solid was removed by filtration
through a pad of silica gel, and the solvent was removed
under reduced pressure. The residue was purified by flash
chromatography (Rf =0.47, n-hexane:toluene=1:1), and
furnished ligand 2c as a white foamy solid (231.1 mg,
45% yield). [α]D20 =−137 (c 0.12, CH2Cl2); Mp 95–96°C;
1H NMR (400 MHz, DMSO-d6) δ 7.13 (d, J=8.0 Hz,
2H, Ar), 7.06 (d, J=8.0 Hz, 2H, Ar), 6.98 (d, J=8.0 Hz,
2H, Ar), 6.85 (d, J=8.2 Hz, 2H, Ar), 4.05 (s, 2H, CH),
2.86–2.70 (m, 8H, CH2), 2.69–2.56 (m, 4H, CH2), 2.13
(ddd, J=28.0, 16.8, 8.2 Hz, 6H, CH2), 1.81–1.68 (m,
12H, CH2), 1.63 (s, 2H, CH2), 1.58–1.30 (m, 8H, CH2)
ppm. 13C NMR (101 MHz, DMSO-d6) δ 145.95, 145.45,
136.93, 134.64, 133.46, 129.50, 129.04, 127.39, 119.01,
118.70, 76.80, 76.60, 32.41, 28.49, 27.35, 27.22, 23.04,
22.13, 22.04, 22.02, 21.91 ppm. 31P NMR (162 MHz,
DMSO-d6) δ 144.99 ppm. HRMS (ESI+): calcd for
C46H50NaO6P2 [M+Na]+783.2975; found: 783.2947.
2.3 Representative Procedure for the Pd-Catalyzed
Allylic Alkylation of 1,3-Diphenyl-2-propenyl
acetate 6a
To a flame dried Schlenk tube, [Pd(π-allyl)Cl]2 (0.9 mg,
0.0025 mmol) and ligand 2a (3.7 mg, 0.005 mmol) were
added under nitrogen, followed by addition of mixed sol-
vent (CH2Cl2/THF=1:1) 2 mL. The solution was stirred
at 40°C for 0.5 h. Then 1,3-diphenyl-2-propenyl acetate
6a (0.083 mmol) was added, and the mixture was stirred
for 10 min before the addition of nucleophile (0.25 mmol),
BSA (0.062 mL, 0.25 mmol), and anhydrous NaOAc
(8.2 mg, 0.10 mmol). After being stirred for 12 h at room
temperature, water (10 mL) was added and the mixture
was extracted with CH2Cl2 (3×10 mL). And the combined
organic phase was dried over anhydrous Na2SO4. The sol-
vent was removed under vacuum, and the residue was puri-
fied by flash chromatography using petroleum ether/EtOAc
20:1 (v/v) as eluant to afford the desired product. The enan-
tiomeric excess of the products were determined by HPLC
analysis with a Chiralpak AD-H column (0.46×25 cm).
2.4 Representative Procedure for the Rh-Catalyzed
Asymmetric Hydrogenation
After stirring a solution of [Rh(cod)2]BF4 (0.0025 mmol)
and ligand 2a (0.00275 mmol) in degassed CH2Cl2 (1 mL)
at room temperature for 1 h, a solution of the correspond-
ing substrate (0.25 mmol) in degassed CH2Cl2 (2 mL) was
added. The mixture was transferred via syringe into a stain-
less autoclave that had been previously purged with argon.
The hydrogenation was carried out in the autoclave at room
temperature for 6 h. After releasing H2, the reaction mix-
ture was passed through a short silica gel column to remove
the catalyst. After evaporation of the solvent under reduced
2.2.2 (1S,2S)‑bis[(S)‑1,1′‑H8‑binaphthyl‑2,2′‑diyl]
phosphite‑cyclohexanediol 2d
(S)-1,1′-H8-Binaphthyl-2,2′-diyl-chlorophosphite
5d
was synthesized by the same procedure as that of 5c,
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