Chemistry Reference
In-Depth Information
The palladium - catalyzed cycloaddition reactions of three - membered - ring heterocy-
cles such as oxirane and aziridine
66
with heterocumulenes
67
(Y = C =Z) to form the
fi ve - membered - ring products
68
have been studied (Scheme 5.21) [26]. Larksarp and
Alper reported that asymmetric cycloaddition of vinyloxirane
63
with symmetrical car-
bodiimide using (
S
) - TolBINAP afforded product
69
with 94% ee [26a]. Highly enanti-
oselective cycloadducts were also formed in the reaction of
63
with unsymmetrical
carbodiimide, although two regioisomers were always formed [26b]. Trost and Fandrick
reported the asymmetric cycloaddition of aziridine
70
with isocyanate using chiral ligand
43
[26e] .
Z
YCZ
Z
X
X
Y
PdL
n
Y
67
X
Pd+
Pd+
X
L
L
L
L
66
68
: Y=O, Z=NR or Y=NR
1
, Z=NR
2
X=O or NR
YCZ
A
N
Pd
2
(dba)
3
·CHCl
3
(
S
)-TolBINAP
*
NAr
+
Ar
NCN
Ar
O
O
THF
Ar = 4-ClC
6
H
4
69
(95%, 94% ee)
63
[Pd(C
3
H
5
)Cl]
2
B
N
O
Ligand
43
+
Bn
NCO
NBn
NBn
AcOH
71
(98%, 95% ee)
70
CH
2
Cl
2
Scheme 5.21.
The reactivity of allenylpalladium complexes, which are obtained by oxidative addi-
tion of propargyl alcohol derivatives to palladium(0), is attractive in organic synthesis
[27]. The synthesis of oxazolidinone
73
via the cyclization of propargyl alcohol derivative
72
was studied by Tamaru and others (Scheme 5.22) [27b].
OCONHTs
Pd
2
(dba)
3
·CHCl
3
N
Et
3
N
O
ON
Ts
Ts
THF
O
O
72
73
(73%)
Scheme 5.22.
