Chemistry Reference
In-Depth Information
MeO
2
C
O
O
S
Bu
Br
Bu
Ni(CO)
4
,MeOH
KOAc
21% yield
single
diastereomer
S
O
Me
86
87
88
o
Me
Scheme 10.24
Diastereoselective Ni(0) catalyzed synthesis of cyclopentenones.
n-C
3
H
7
Ph
n-C
3
H
7
1) Ni(cod)
2
,P
n
-Bu
3
2) CSA, THF/H
2
O5:1
40% yield
4:1 d.r.
Ph
CN
t
-Bu
O
O
O
90
H
91
89
Scheme 10.25
Synthesis of cyclopentenones avoiding the use of CO.
-allyl nickel complexes (generated from Ni(cod)
2
, enals, and
trimethylsilylchloride), have been used in the synthesis of annulated cyclopentenones.
48-52
In this variant (Scheme 10.26), the silyloxy substituted nickel
Since 1998, Mackenzie's
-allyl complex reacts with
the alkyne under a carbon monoxide atmosphere and then methanol is added to furnish the
cyclopentenone.
Me
92
O
OH
I
OTMS
Ni(CO)
4
Me
26% yield
CO
Me
Me
CO
2
Me
MeO
2
C
93
66
Scheme 10.26
McKenzies's
allyl complex in the synthesis of cyclopentenones.
π
Interestingly, the synthesis of annulated cyclopentenones via an intramolecular
palladium- or nickel-catalyzed metallo-ene-type cyclization/carbonylation, using carbon
monoxide at atmospheric pressure has been reported by Oppolzer (Scheme 10.27). The
reaction allows the use of various nickel or palladium sources, such as Ni(CO)
3
PPh
3
or Ni(COD)
2
/1,4-bis(diphenylphosphino)butane or Pd(dibenzylidene-acetone)
2
/PPh
3
, with
enynes bearing an allylic halide or acetate moiety, furnishing mono- or bicyclic products.
The formation of cyclopentenones or diene derivatives is highly dependent on the choice
of metals and ligands and on the substitution pattern of the substrate. The mechanism is
similar to that described in Scheme 10.22, affording the cyclopentenones or diene deriva-
tives in good yields.
53-55
An intriguing utilization of this methodology is its application to
the synthesis of natural products such as (
)-hirsutene.
55-58
±
