Chemistry Reference
In-Depth Information
OAc
Pd(OAc)
2
, LiOAc, B
Q
9.268
9.280
OAc
re-oxidation
(benzoquinone)
Pd(OAc)
2
co-ordination
OAc
9.281
Pd(0)
(AcO)
2
Pd
AcO
nucleophilic attack
trans to Pd
9.280
OAc
reductive
elimination
(AcO)Pd
(AcO)Pd
9.283
9.282
OAc
OAc
1
3
η
→
η
Scheme 9.76
technical problem associated with the use of benzoquinone: as the starting materials are 1,3-dienes, by
products from the Diels-Alder reaction with benzoquinone may be isolated.
An intramolecular nucleophile, such as an alcohol, may also be used in place of the first acetate
(Scheme 9.77). Treatment of the dienyl alcohol
9.284
with palladium acetate gives the
3
-allyl complex
9.285
by intramolecular nucleophilic attack, which gives the
trans
-acetate
9.287
by reductive elimination.
In the presence of a small amount of lithium chloride, however, ligand exchange at palladium occurs. Now,
the
3
-palladium complex
9.286
does not have an acetate available for intramolecular transfer. Instead,
reductive
elimination
with OAc
O
AcO
OH
no LiCl
9.287
Pd(OAc)
2
trans att
a
ck
by AcO
0.2 eq LiCl
O
O
AcO
2 eq LiCl
PdX
9.284
9.288
9.285
X = OAc
9.286
X = Cl
trans
attack by Cl
O
Cl
9.289
Scheme 9.77
