Asymmetric hydrogenation
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 3, March, 2013
757
conversion on the amount of precatalyst, changes in enanꢀ
tioselectivity in the course of the reaction, while mainꢀ
taining the catalytic activity) suggest a more complicated
mechanism of the reaction than can be suggested based on
the literature data. The studies performed on the catalytic
hydrogenation of various challenging substrates showed
that the use of rhodium complexes for the reduction of
dialkyl ketones is a promising approach, while the iridium
complex exhibited a good activity in the catalytic hydroꢀ
genation of imines.
stirred at room temperature for the required time (see Tables 6
and 7). The reaction products were isolated by preparative colꢀ
umn chromatography using dichloromethane as an eluent.
The work was carried out within the Joint European
Laboratory "Homogeneous Catalysis for the Sustainable
Development" and was financially supported by the Rusꢀ
sian Foundation for Basic Research (Project No. 12ꢀ03ꢀ
3
1326) and the France National Center of Scientific Studꢀ
ies (Joint Grant with RFBR No. 12ꢀ03ꢀ93112). The
authors are also grateful to the French Embassy in Mosꢀ
cow for the fellowship grant.
Experimental
References
All the reactions were carried out under argon using the
Schlenk technique. Solvents were purified by distillation under
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1
3
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25 (for ketones) and Varian ChirasilꢀDEX C (for imines) inꢀ
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Asymmetric hydrogenation of ketones (general procedure).
–
3
A solution containing a precatalyst (6.4•10 mmol), MeONa
–
2
(
3.2•10
mmol, 5 equiv.), and the substrate (3.2 mmol,
5
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(
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stirred at room temperature for a required time (see Tables 1—5).
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matography using dichloromethane as an eluent. Enantiomeriꢀ
cally enriched 1ꢀphenylethanol was obtained by this procedure
8
9
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1
1
t
with [Ir(P,SBu )(COD)Cl] as a precatalyst in 96% yield (ee 61%).
Enantiomeric stability of 1ꢀphenylethanol. A solution conꢀ
t
–3
taining [Rh(P,SBu )(COD)Cl] (6.4•10
mmol), MeONa
mmol, 5 equiv.) and enantiomerically enriched
ꢀphenylethanol (3.2 mmol, 500 equiv., ee 61%) in isopropyl
1
–
2
(
3.2•10
1
(
2
alcohol (2 mL) was poured in a 5ꢀmL glass vial, which was
placed under argon in a steel autoclave equipped with a magnetic
stirrer. The autoclave was filled with hydrogen under the presꢀ
sure of 30 Bar, and the mixture was stirred at room temperature
for 16 h. The reaction products were isolated by preparative
column chromatography using dichloromethane as an eluent.
The yield was 100%, ee 59%.
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1
1
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Asymmetric hydrogenation of imines (general procedure).
–
3
A solution containing a precatalyst (6.4•10
mmol), I2
mmol, 3 equiv.), and a substrate (0.64 mmol,
00 equiv.) in dichloromethane (2 mL) was poured into a 5ꢀmL
–
2
(
1.9•10
1
glass vial, which was placed under argon in a steel autoclave
equipped with a magnetic stirrer. The autoclave was filled with
hydrogen under the pressure of 30 Bar, and the mixture was
Received January 15, 2013;
in revised form February 25, 2013