Chemistry Reference
In-Depth Information
CHO
H
OHC
BLA
2a
(20 mol %)
CH
2
Cl
2
, -78°C
H
93% yield, 98% de, 90% ee
H
OHC
H
F
3
CH
2
CO
2
C
BLA
2a
(20 mol %)
Neat, 35°C
H
75% yield, 98% de, 93% ee
CO
2
Me
H
CO
2
Me
H
MeO
2
C
HCl
BLA
2a
(20 mol %
)
CH
2
Cl
2
, -50°C
H
H
OTBS
O
OTBS
93% yield, 99% de, 96% ee
Scheme 3.5.
Ph
3
P(OTMS)(N=C:)
+
TMSCN
Ph
3
P=O
H
O
TMSO
BLA
2b
(10 mol %)
+
TMSCN
R
CN
R
H
Ph
3
P=O
Toluene, 0°C
91-98% yield
90-97% ee
7 examples
OTMS
O
H
BLA
1b
(10 mol %)
+
TMSCN
R
CN
R
CH
3
Ph
3
P=O
Toluene, 0°C
73-95% yield
85-96% ee
6 examples
Scheme 3.6.
Highly enantioselective cyanosilylation of aldehydes and methyl ketones has been
achieved by the Corey group [10,11]. It was found that enantioselectivities were enhanced
by the addition of various phosphine oxides since a more reactive cyanide donor,
R
3
P(OTMS)(N =C:), is generated
in situ
from the phosphine oxide and TMSCN. Further,
it is quite interesting that the absolute stereochemical course of the reaction is predicted
clearly by pretransition state complexes, which were used earlier to explain the excellent
enantioselectivity in D - A reactions (Scheme 3.6 ).
