Chemistry Reference
In-Depth Information
CO
2
Me
Pd(0)
+
OCO
2
Et
MeO
2
C
CO
2
Me
CO
2
Me
9.185
9.186
CO
2
Me
L
2
Pd(0)
O
OEt
CO
2
Me
O
9.185
9.186
CO
2
Me
O
OEt
CO
2
Me
L
2
Pd
O
9.187
L
2
Pd
9.189
L
2
Pd
CO
2
+
EtO
9.188
MeO
2
C
CO
2
Me
MeO
2
C
CO
2
Me
Scheme 9.52
NaH,
Pd(dba)
2
, PPh
3
EtO
2
C
O
t
-Bu
C
O
2
Et
O
AcO
OCO
2
Me
AcO
O
t
-Bu
9.189
9.190
O
Scheme 9.53
In fact, carbonates turn out to be better leaving groups than acetates, and selective reactions can be achieved
(Scheme 9.53). The selective reaction at an allylic carbonate over an allylic acetate in cyclopentene
9.189
was employed in the early stages of a synthesis of strychnine.
70
Further aspects of this synthesis can be found
in Scheme 2.58 and Scheme 4.12.
Vinyl epoxides also constitute a “base-free” system (Scheme 9.54). The alkoxide
9.193
generated by the
palladium-mediated ring opening of epoxide
9.191
acts as the base.
HO
CO
2
Et
O
(Ph
3
P)
4
Pd
CO
2
Et
CO
2
Et
EtO
2
C
9.192
9.191
OEt
OEt
O
O
HO
H
O
PdL
2
O
O
PdL
2
OEt
OEt
9.193
9.194
Scheme 9.54
