Chemistry Reference
In-Depth Information
O
TMS
O
t
Bu
t
Bu
O
O
P
O
P
O
O
P
O
HN
O
O
O
O
O
O
O
O
=
=
O
H
O
O
O
O
O
O
P
TMS
t
Bu
t
Bu
O
O
12 1
12 2
O
Me
O
Ph
2
P
O
O
PR
2
Ph
2
P
N
R
i
Pr
P
PA r
2
PR
2
S
S
t
Bu
12 4
R
UCAP
3,5 -Me
2
Ph
12 3
(
S
)-Cy,Cy-oxoProNOP: R = Cy
(
S
)-Cp,C p-oxoProNOP: R = Cp
Ph
2
P
O
O
Re
Ph
2
P
NO
N
N
(OC)
3
Cr
PCp
2
PCp
2
PPh
3
PCp
2
PCp
2
Ph
(
S
Re
,
R
C
)-
12 5
(
S
)-Cp,Cp-IndoNOP
(
S,2S
)-Cr(CO)
3
-C p,Cp- IndoNOP
Figure 7.13.
(
Continued
)
COOMe
[Rh-(
R,R
)-
n
-Pr-DuPhos]
COOMe
NHAc
H
2
NHAc
99.6% ee
NHAc
NHAc
[Rh-(
R,R
)-
n
-Pr-DuPhos]
COOMe
COOMe
H
2
99.4% ee
Scheme 7.1.
Hydrogenation of
E
or
Z
- 2 - (acetamido) cinnamic acid methyl esters.
have high tolerance to these heterocycles. Burk, Zhang, and others have demonstrated
that
-dehydroamino acid derivatives possessing furanyl, pyrroyl, and thiophenyl moi-
eties, and other functional groups can be reduced with DuPhos (Scheme 7.2) [26b,27,101-
104], TangPhos [36a], and Et-KetalPhos [30a] catalysts with no compromise in the
catalytic performance. Some strongly coordinating groups such as pyridyl and quinolyl,
however, may require the assistance of Brønsted acids to protonate the heteroatom
[105,106] . Hydrogenation of pyridine -
N
-oxide was also conducted by Adamczyk to
prepare 2-pyridyl-alanine analogues [107]. In addition to these fi ndings, tandem pro-
cesses involving asymmetric hydrogenation followed by cross-coupling of these sub-
strates have also been reported [103]. A great variety of substituted aromatic α - amino
acid derivatives can be prepared by hydrogenation of halogen- and boronic acid-
substituted β - aryl
-
α-dehydroamino acid derivatives. The resulting amino acids can be
α
