Chemistry Reference
In-Depth Information
TABLE 7.14.
(
Continued
)
Reaction
Conditions
% ee
(Confi g.)
Catalyst
R
X
n
S
/
C
Reference
RuBr
2
[(
R
) -
SYNPHOS]
Me
SPh
2
100
MeOH,
30 ° C,
30 atm
H
2
, 24 h
98 (
R
)
248
RuCl
2
[(
R
) - BINAP]
(DMF)n
Me
P(O)
(OMe)
2
1
N/A
MeOH,
25 ° C,
4 atm H
2
,
72 h
98 (
R
)
280
RuBr
2
[(
S
) - MeO -
BIPHEP]
2 - Thienyl
P(O)
(OEt)
2
1
100
MeOH, rt,
10 atm
H
2
, 70 h
97 (
R
)
281
RuCl
2
[(S) -
TolBINAP(pica)]
Ph
SiMe
2
t
Bu
0
10,000
EtOH, rt,
10 atm,
2.5 h
95
273
Ru catalyst, they possess a signifi cant stereodirecting ability in achieving high enanti-
oselectivity. For example, methoxyacetophenone is hydrogenated with a Ru-(
R
) -
XylBINAP/(
R
)-DIPEN complex to provide the corresponding (
R
) - diol with 95% ee.
Hydrogenation of an α , α ′-dialkoxy ketones is catalyzed by the Ru-BINAP system
to give chiral 1-
o
- octadecyl - 3 -
o
-trityl glycerol with over 96% ee [272]. A series of
acyl silanes were also hydrogenated with high selectivities using Ru-TolBINAP(pica)
catalysts [273] .
A halogen atom at an appropriate position in the substrate can also exert great direct-
ing infl uence through interaction with Ru [18b,239a,282]. Hydrogenation of
ortho
-
haloaryl ketones can be catalyzed by the Ru-BINAP system with excellent
enantioselectivities. For example,
ortho
-bromoacetophenone can be converted into the
corresponding chiral alcohol with 96% ee (Eq. 7.40). However, this type of substrates
can be hydrogenated more effectively with the Ru/chiral phosphine/diamine system
[283]. Asymmetric hydrogenation of phenylthioketones has been realized with Ru cata-
lysts. BINAP, MeO - BIPHEP [277] , BDPP [278] , and Me - CnrPHOS [279d] are effi cient
for this transformation.
Br
O
Br
OH
Ru[(S)-BINAP]Cl
2
(DMF)
n
,
S/C
=700
MeOH, 100
o
C, 100 atm H
2
96% ee
(7.40)
Several chiral Ru complexes have been applied successfully for the asymmetric
hydrogenation of α - ,
β - ,
and
γ-diketones. Hydrogenation of an α - diketone,
2,3 -
