Chemistry Reference
In-Depth Information
Oxidative Heck reactions can be involved in tandem reactions in which the
substrate for oxidative olefination is formed through catalysed isomeriza-
tion. A very interesting example of this approach was discovered by Wang
and co-workers involving prior copper(II) catalysed isomerization of cyclo-
propene derivatives to give furans (or rather their organocopper derivatives),
which further react with olefins (Scheme 9.117).
355
Another interesting example of the tandem isomerization-oxidative alke-
nylation strategy exploits the dehydrogenative aromatization of cyclohex-
anones. This tandem process, described by Hong and co-workers, is versatile
and regioselective (Scheme 9.118).
356
So far, aromatic substrates constitute the bulk of published examples of
oxidative Heck reaction via CH activation. Recent studies showed that this
restriction is not absolute. Several examples of the use of olefins, although
not common but rather specific ones, have been reported. Thus, Kapur and
co-workers succeeded in observing reactions between dihydropyrans and a
broad range of olefins
357
and Lei and co-workers demonstrated that specific
sp
3
CH bonds can be involved (Scheme 9.119).
358
R
1
R
1
R
1
Pd(OA c)
2
3-cyanopyridine, O
2
mesitylene-t-BuCOOH
110°C
R
3
R
3
NaOH
N
R
2
N
H
R
3
R
2
HO
O
O
O
R
2
Scheme 9.116 Emulation of intermolecular Fujiwara-Moritani reaction via intra-
molecular reaction.
R
'
ROOC
ROOC
COOR
Pd(OAc)
2,
Cu(OAc)
2
MeCN, DMSO, 60°C
+
COOMe
COOMe
RO
R
'
O
Cu(O Ac)
2
COOMe
Cu(O Ac )
2
Pd(0)
Pd(OAc)
2
R
'
R
'
ROOC
ROOC
Pd(OAc)
2
RO
CuO Ac
RO
PdOAc
O
O
Scheme 9.117 Tandem isomerization-oxidative Heck reaction.
O
O
O
Pd(TFA )
2,
Cu(OAc)
2
O
2,
PivOH, 110°C
COOBu
+
59%
Scheme 9.118 Tandem isomerization-dehydrogenative
aromatization-oxidative
alkenylation-lactonization process.
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