Chemistry Reference
In-Depth Information
β
-hydride
elimination
Cl
n
-Bu
2
n
-BuLi
Cp
2
Zr
Cp
2
Zr
Cl
n
-Bu
5.227
5.228
Cp
2
Zr
-butane
H
Cp
2
Zr
n
-Bu
5
.
2
9
5
.
2
3
0
Scheme 5.65
OH
H
H
1. O
2
2. H
3
O
+
Cp
2
ZrCl
2
,
n
-BuLi
ZrCp
2
H
H
5.232
5.233
OH
5.231
cis
:
trans
22 h, RT, 75:25
RT, then 75 ° C 1:99
Scheme 5.66
H
PhCOCl,
CuCl, LiCl
Et
Et
Ph
ZrCp
2
O
Et
Et
H
Cp
2
ClZr
5.235
5.234
I
2
cyclisation
H
Et
Ph
Et
Ph
O
Et
Et
H
I
5.236
5.237
Scheme 5.67
The metallacycles can also be used for carbon-carbon bond-forming reactions (Scheme 5.67). Transmet-
allation with cuprates, or the use of catalysis by copper(I) salts allows reaction with a variety of electrophiles.
With an acid chloride, reaction occurs at one of the carbon-zirconium bonds of the metallacycle
5.234
.This
leaves the second carbon-zirconium bond of the acylated product
5.235
available for further chemistry by,
for instance, halogenation,
78
or back attack onto the ketone.
79
More elaborate multiple component couplings
can also be achieved (Scheme 5.68).
80
Another approach to using zirconium is to remember that it has only sixteen electrons and can, therefore,
be attacked by electrophiles (Scheme 5.69). Addition of the anion prepared by deprotonation of allyl chloride
results in addition to zirconium, followed by an alkyl migration with loss of chloride, resulting in the formation
