Chemistry Reference
In-Depth Information
Gd(O
i
Pr)
3
(
x
mol %)
142
(
2X
mol%)
TMSCN (0.5-1 equiv)
HCN (2 equiv)
Ph
O
R
1
O
P
R
2
Ph
N
O
N
R
2
HO
R
1
NC
O
O
F
CH
3
CH
2
CN
R
1
= Ph, 4-MeO-Ph, Ph(CH
2
)
2
,
CH
3
CH
2
CH
2
, i-p ro pyl, t-Bu,
cyclohexenyl
R
2
=H
Up to 9 2% yield
Up to 9 8% ee
HO
F
142
Ph
Ph
PO
1) Gd(O
i
Pr)
3
(xmol %)-
143
or
144
(1.5X mol %)
TBSCN (2 equiv), DMAP,THF
O
R
1
R
1
O
O
HO
R
2
NC
R
3
R
2
O
X
2) H
+
R
3
R
1
=alkyl
R
2
=alkyl,aryl
R
3
=alkyl,H
HO
Y
Up to 100% yield
Up to 95% ee
143
:X=Y=F
144
:X=CN,Y=H
Scheme 8A.84.
OML
n
Electrophilic trapping
Nucleophilic addition
∗
R
O
O
E
[R
m
ML
n
]
∗
∗
R
L
n
M
O
Radical addition
∗
Radical trapping
R
E = electrophile; L = ligand; M = metal; R = alkyl/aryl group; * = stereogenic center
Scheme 8A.85.
8A.4. CATALYTIC ASYMMETRIC TANDEM CONJUGATE
ADDITION REACTION
Asymmetric tandem transformation was an enormously useful strategy for the construc-
tion of complex molecules from readily available starting materials through multistep
transformations, constructing two or more contiguous stereogenic centers by using a
single catalyst in one pot without the need of isolation of the intermediates. In recent
years, through the use of conjugate additions catalyzed not only by metal complexes but
also by various small organic molecules, considerable efforts have been made in develop-
ing catalytic asymmetric tandem transformations (Scheme 8A.85). According to the
