Chemistry Reference
In-Depth Information
-
cyanoacetates provided an attractive procedure to access chiral nitrogen-containing
compounds bearing a quaternary carbon center. Ma and others reported the asymmetric
synthesis of pyrazolidine derivatives
159
through the Cu- and Pd-catalyzed asymmetric
one - pot
In particular, the amination of
α
- substituted
β
- keto esters or
α
- substituted
α
- keto esters, aryl
halides, and dibenzyl azodicarboxylate (Scheme 5.49) [66]. On the basis of Jørgensen
and others' work [64], the optically active allene
160
was produced from enantioselective
copper(II)-catalyzed amination of 2-(2
tandem
addition - cyclization
reaction
of
2 - (2
′
,3
′
- dienyl) -
β
′
,3
′
- dienyl) -
β
- keto ester
158
with azodicarboxyl-
ate. Pyrazolidine
159
was constructed from
- allypalladium intermediate, which was
generated via the carbopalladation of allene
160
.
π
O
1) Bisoxazoline
ent
-
135
, Cu(OTf)
2
, CH
2
Cl
2
Cbz
N
N
+
2) K
2
CO
3
, PhI, Pd(PPh
3
)
4
, THF
Cbz
CO
2
Et
98%, (3
R
, 5
R
)-
159
:(3
R
, 5
S
)-
159
= 36:64
158
Ph
Ph
O
O
Cbz
Cbz
N
N
N
N
+
N
N
Cbz
Cbz
Ph
Ph
ent
-
135
CO
2
Et
CO
2
Et
159
O
(3
R
, 5
R
)-
159
(98% ee)
O
158
Ph
(3
R
, 5
S
)-
159
(98% ee)
O
O
PhPdI
Pd
Cbz
N
CO
2
Et
Cbz
N
CO
2
Et
NH
NH
Cbz
Cbz
160
Scheme 5.49.
Jørgensen and others reported the catalytic enantioselective direct amination of
β
-
keto phosphonates catalyzed by chiral zinc(II) complex, giving optically active
- amino
phosphonic acid derivatives in up to 98% ee (Scheme 5.50) [67]. The use of a catalyst,
composed from chiral bisoxazoline ligand
ent
-
135
and Zn(OTf)
2
, gave the best results.
The reaction of
161
with dibenzyl azodicarboxylate afforded the aminated adduct
162
,
which was converted into the oxazolidinylphosphonic acid derivative
163
.
α
O
O
O
OEt
ent
-
135
O
O
Cbz
P
OEt
Ph
OEt
N
N
Zn(OTf)
2
O
NH
P
+
Ph
OEt
NCbz
O
OEt
OEt
CH
2
Cl
2
Cbz
HN
Ph
P
161
Cbz
162
(85%, 92% ee)
163
Scheme 5.50.
