Chemistry Reference
In-Depth Information
M
O
M=Li
YL i
3
tris(binaphthoxide) (YLB)
O
O
Y
M
O
O
O
M
M=K
YK
3
tris(binaphthoxide) (YPB)
153
O
NHOR
O
(S)-YLB
RO NH
2
+
Ph
Ph
Ph
Ph
R= Me, Bn
91-97% ee
Scheme 8A.94.
Recently, a new method for the synthesis of α , β-azido carbonyl compounds that could
be converted to amino acids was reported by Miller et al. [177]. With organic amine as
catalyst, the conjugate addition of azide ion to enolates was carried out smoothly under
mild conditions, and the product was obtained in 63% ee and 97% yield. When catalyst
155
was used, the improvement in enantioselectivity was noteworthy, as shown in
Scheme 8A.95 .
Tomioka et al. developed a powerful method for constructing chiral β - amino car-
bonyl moieties through the asymmetric conjugate addition of lithium amides to enoates
[178]. The addition reaction of lithium
N
- benzyltrimethylsilylamide to enoates afforded
the desired products with high enantioselectivities and yields in the presence of chiral
ligand
156
(Scheme 8A.96 ).
MacMillan et al. developed an effi cient method for the preparation of amino alde-
hydes through the catalytic asymmetric conjugate addition of nitrogen nucleophiles to
α , β-unsaturated aldehydes [179]. This reaction was mediated by imidazolidinone
110
-
p
TSA in CHCl
3
, and the amino aldehyde product was obtained in 92% ee and 92% yield
(Scheme 8A.97 ).
Very recently, Palomo and coworkers [180] reported a highly enantioselective con-
jugate addition of carbamates to α , β-unsaturated ketones. Using chiral Lewis acid
157
as catalyst, the aza-Michael addition of carbamates to α ′ - hydroxy enones yielded the
desired products with excellent enantioselectivities (Scheme 8A.98 ).
8A.5.3. Conjugate Addition of Phosphorous Nucleophiles
Tedeschi and Enders reported the fi rst asymmetric P-C bond formation. The reactions
were carried out under heterogeneous conditions using KOH/Fe
2
O
3
system [181] . The
optically active β - substituted β-phosphono malonates were obtained in good yields and
high enantioselectivities (Scheme 8A.99 ).
