Chemistry Reference
In-Depth Information
B(OH)
2
Pd(OAc)
2
, Ag
2
O,
BQ, air
N
N
3.150
3.151
Scheme 3.61
Ph
O
B
O
Pd(OAc)
2
, BQ,
Ag
2
CO
3
, K
2
HPO
4
Ph
CO
2
H
CO
2
H
3.152
3.153
Pd(OAc)
2
, Ag
2
CO
3
,
K
2
HPO
4
, NaOAc
Ph
I
Scheme 3.62
Pd(OAc)
2
, KOAc
+
I
3.156
3.154
3.155
Scheme 3.63
H
3
CO
I
Pd(OAc)
2
, K
2
CO
3
,
n
-Bu
4
NBr
CH
3
O
O
H
3
CO
3.157
3.158
Scheme 3.64
oxidant in some cases. The use of an aryl halide, rather than an aryl boronate means that the oxidizing agent
can be omitted (Scheme 3.62).
Intramolecular C-H activation by
1
-organopalladium complexes, often generated
in situ
as reactive inter-
mediates, can lead to surprising, but useful cyclic structures (Schemes 3.63, 3.64).
63
Even benzocyclobutenes
may be formed in this way, despite the ring strain.
64
Benzocyclobutenes are valuable intermediates in synthesis
because they undergo thermal electrocyclic ring opening to
o
-xylylenes, which may be trapped in Diels-Alder
reactions (see Scheme 11.16 for another example),
65
or by electrocyclic ring closure. The alkaloid coralydine
3.166
was synthesized using this chemistry (Scheme 3.65).
66
The ester-substituted benzocyclobutene
3.160
was prepared by CH activation of ester
3.159
. The ester could then be converted to an amine
3.161
by Curtius
rearrangement. Condensation with aldehyde
3.162
gave an imine
3.163
which, upon thermolysis, underwent
4-electron electrocyclic ring opening, followed by electrocyclic 6-electron ring closing of the intermediate
