Chemistry Reference
In-Depth Information
O
CO
2
Me
Pd(OAc)
2
[
o
-(MeO)
2
C
6
H
3
]
3
P
O
OH
11.279
11.278
Scheme 11.91
SiMe
3
Pd(OAc)
2
[
o
-(MeO)
2
C
6
H
3
]
3
P
CO
2
Me
CO
2
Me
Me
3
Si
Me
11.280
Scheme 11.92
With suitably placed hydroxy and ester functional groups, tandem lactonization can ensue (Scheme 11.91).
The intermolecular coupling of two alkynes with this system is also possible (Scheme 11.92), provided that
only one alkyne is terminal, and the acceptor alkyne is electron poor, otherwise extensive self-coupling of the
alkynes may result.
124
The mechanism may involve terminal palladation of one alkyne, followed by insertion of the second and
protonolysis of the vinyl-palladium bond (Scheme 11.93). The intramolecular reaction will be limited to the
larger reaction sizes, due to the strain inherent in cyclic alkynes of smaller size.
The intramolecular alkyne coupling of diyne
11.281
was used in a synthesis of bryostatin
11.283
to close the
macrocycle
11.282
(Scheme 11.94).
125
This reaction was followed by a gold(I)-catalysed 6-
endo
ring closure
of
11.282
and some routine transformations to complete the synthesis. As so often in macrocyclizations, a
low concentration (0.002 M) was found to be important.
L
2
PdX
2
HX
HX
PdL
n
X
PdL
n
X
insertion
coordination
PdL
n
X
Scheme 11.93
