Chemistry Reference
In-Depth Information
MX
n
MX
n
MX
n
R
R
R
6.233
6.234
6.244
MX
n
MX
n
R
R
H
H
H
H
H
R
R
6.248
6.247
6.245
6.246
Scheme 6.100
MeO
2
C
MeO
2
C
MeO
2
C
MeO
2
C
Ph
3
PAuCl, AgSbF
6
6.249
6.250
exo-
only
Scheme 6.101
Ph
3
PA u C l ,
AgSbF
6
MeO
2
C
MeO
2
C
MeO
2
C
MeO
2
C
MeO
2
C
MeO
2
C
+
6.251
6.252
6.253
endo-
:
exo-
= 7:1
Scheme 6.102
Ts
Ts
N
Ph
3
PAuCl, AgSbF
6
N
6.255
endo-
only
6.254
Scheme 6.103
Precisely which pathway is followed depends on a balance of structural factors and is influenced by
the choice of catalyst (Schemes 6.101-6.104). In the presence of alcohols, ethers are produced (Scheme
6.105),
117
while, in some cases, the carbocationic intermediates can be trapped by suitably placed aryl groups
in intramolecular Friedel-Crafts reactions (Scheme 6.106).
118
With the right substituents and catalysts, four-membered rings
6.265
may also be produced (Scheme
6.107).
119
If an addition alkene is present, then the cyclopropyl carbene intermediate may be intercepted to ef-
fect cyclopropanation of the second alkene. Cyclopropanation can become the dominant pathway, as in
the platinum-catalysed reaction of enyne
6.266
(Scheme 6.108).
120
Whether this occurs, however, once
