Chemistry Reference
In-Depth Information
CO
2
Me
CO
2
Me
CO
2
Me
MeO
2
C
MeO
2
C
MeO
2
C
I
CPh
3
Fp
Fp
H
6.308
6.313
6.314
Scheme 6.119
Nuc
HBF
4
Nuc
Fp
Nuc
Fp
Fp
OEt
OEt
OEt
H
6
.
1
6.316
6
.
3
Fp
I
Nuc
6.319
Nuc
6.318
Scheme 6.120
Fp
Fp
Fp
Ag
2
O
base
NH
3
HN
HN
6.320
6.321
6.322
Fp
O
HN
N
O
6
.
3
6
3
2
4
Scheme 6.121
Alternatively, the Fp complex
6.321
can be oxidized using a strong inorganic one-electron oxidant, such as
silver(I) or cerium(IV) (Scheme 6.121).
130
This causes the formation of a seventeen-electron radical cation
6.322
. This intermediate, which is formally iron(III), can relieve its electron deficiency to some extent by
CO insertion. The acyl iron complex
6.323
can then be intercepted by a nucleophile such as an amine or an
alcohol. This can be either inter- or intramolecular. The reaction follows a different course if the Fp group is
to an oxygen atom, as in complex
6.325
(Scheme 6.122). The Fp radical cation is a leaving group and is
expelled to create an oxonium ion
6.327
, which can, in turn, be trapped by a nucleophile.
Some remarkable examples of stereocontrol have been reported using the Fp complexes of enediol ethers.
131
1,2-Diethoxyethene can be used as a vinyl dication equivalent (Scheme 6.123). The Fp complex
6.329
of
cis
-
1,2-diethoxyethene reacted with dimethyl copper lithium stereospecifically to give the
syn
adduct
6.330
.Acid
treatment gave the
trans
complex
6.331
with net inversion of the alkene geometry. Addition of the enolate of
cyclohexanone, followed by acidification and decomplexation then gave the vinylated ketone
6.334
, with the
cis
alkene, the result of a second inversion.
