Chemistry Reference
In-Depth Information
O
CO
2
Et
O
OH
1. CpW(CO)
3
2. H
+
CO
2
Et
CO
2
Et
Cl
CO
2
Et
Cp(OC)
2
W
4.255
4.256
O
O
O
CO
2
Et
1.
n
-C
8
H
17
CHO
2. MgCl
2
,
Δ
1. NO BF
4
2. NaI
O
H
CO
2
Et
H
O
W
n
-C
8
H
17
Cp
NO
I
4.257
4.258
Scheme 4.89
O
O
BF
3
.OEt
2
Cp(OC)
3
W
O
O
O
Cp(OC)
3
W
•
H
O
4.259
4.260
O
O
(NH
4
)
2
Ce(NO
3
)
6
MeOH, CO
O
O
Cp(OC)
3
W
MeO
2
C
O
O
4.261
4.262
Scheme 4.90
4.6 Carboxylation
Carbon dioxide, unlike carbon monoxide, has found little use in transition-metal-catalysed reactions. Nickel
appears to have a particular affinity for CO
2
. In the presence of low-valent nickel, 1,3-dienes
4.263
react
with CO
2
to give nickelalactones
4.264
, which can undergo a number of decomplexation reactions (Scheme
4.91).
101
Bis-dienes
4.265
can undergo a double functionalization reaction with CO
2
and an organozinc
reagent in the presence of a nickel catalyst (Scheme 4.92).
102
One diene moiety becomes carboxylated, the
other can be alkylated or partially reduced, depending upon the zinc reagent employed. Chiral ligands can
also be employed in this reaction.
103
Alkynes and CO
2
can also couple in the presence of low valent nickel to give a nickelalactone
4.268
which
can be treated with acid or reacted with an organozinc reagent (Scheme 4.93).
104
This useful method for the formation of trisubstituted alkenes has been employed in a synthesis of
erythrocarine
4.275
(Scheme 4.94).
105
After stereoselective formation of the trisubstituted alkene
4.272
by
LNi
O
CO
2
, Ni(COD)
2
, TMEDA
O
4.263
4.264
Scheme 4.91
