10.1002/cctc.202001479
ChemCatChem
FULL PAPER
the case of an immobilized homogeneous catalyst,[32] and c)
relatively easy determination of the mechanism unlike for the case
of heterogeneous catalysts. Although only one type of catalytic
reaction is described in this paper, these unconventional findings
will challenge others to develop solvent-free solid-state reactions
using chiral metal complex catalysts.
was concentrated under reduced pressure. When a solid product began to
appear in the flask, the concentration was stopped. The mixture was
allowed to stand at 0 °C for 12 h. The white crystals were collected by
filtration to give (R)-5ca (1.26 g, 85% yield, >99% ee).
Acknowledgements
Experimental Section
This work was supported in part by JSPS KAKENHI (Grant-in Aid
for Scientific Research (C), no. 16K05764 (T.K.)) and a special
grant from Soft-Path Science and Engineering Research Center
(SPERC) in Iwate University.
Typical procedure for Rh-catalyzed asymmetric 1,4-addition under
liquid-state.
A mixture of [RhOH(cod)]2 (1) (1.99 mg, 4.37 μmol), (R)-2a (6.98 mg, 8.74
μmol), and 2-cyclohexen-1-one (3a) (168 μL, 1.75 mmol) was placed in a
Schlenk tube and was stirred at room temperature for 5 min under argon
atmosphere. To the mixture was added phenylboronic acid (4a) (277 mg,
2.27 mmol) and H2O (41 μL, 2.27 mmol) under argon stream, and then the
mixture was stirred using magnetic stirrer at 30 °C for 1.5 h. After addition
of H2O under air, the resulting mixture was extracted with air-bubbled
EtOAc (5 mL ×3). The combined organic layers were dried over Na2SO4,
filtered, and concentrated under reduced pressure. The crude mixture was
purified by silica-gel column chromatography with hexane/EtOAc = 5/1 to
give (R)-3-phenylcyclohexanone (5aa) as a colorless oil (321 mg, 95%
yield, >99% ee).
Keywords: Organic solvent-free reactions • Heterogeneous
catalysis • Asymmetric catalysis • Gram scale synthesis •
Pharmaceutical intermediate
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A mixture of [RhOH(cod)]2 (1) (1.99 mg, 4.37 μmol), (R)-2b (8.10 mg, 8.74
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were dried over Na2SO4, filtered, and concentrated under reduced
pressure. The crude mixture was purified by silica-gel column
chromatography with hexane/EtOAc = 4/1 to give (R)-4-phenylchroman-2-
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Gram-scale synthesis of (R)-5ca by organic solvent-free rection with
conventional purification.
A 50 mL Schlenk tube was flushed with argon and was charged with
[RhOH(cod)]2 (1) (1.42 mg, 3.12 μmol), (R)-2b (5.78 mg, 6.24 μmol), 6-
methylcoumarin (3c) (1.00 g, 6.24 mmol), phenylboronic acid (4a) (5.33 g,
43.7 mmol) and H2O (0.79 mL, 43.7 mmol). The mixture was stirred using
magnetic stirrer at 40 °C for 48 h. After addition of H2O under air, the
resulting mixture was extracted with air-bubbled EtOAc (5 mL ×3). The
combined organic layers were dried over Na2SO4, filtered, and
concentrated under reduced pressure. The crude mixture was purified by
silica-gel column chromatography with hexane/EtOAc = 4/1 (200 mL/50
mL) to give (R)-6-methyl-4-phenylchroman-2-one (5ca) as a white solid
(1.40 g, 94% yield, >99% ee).
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After the gram-scale reaction, air-bubbled EtOAc (3.0 mL) was added to
the resulting mixture under air. The organic layer was washed with sat.
NaHCO3 aq. (10 mL), and then the water layer was decanted off. The
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was washed with H2O (10 mL), and then the water layer was decanted off.
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7
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