Chemistry Reference
In-Depth Information
R
2
R
1
R
2
R
1
Ni(CO)
4
72
Ni
CO
Br
Br
Ni CO
Br
-3CO
77
79
80
CO
R
2
R
1
R
2
R
1
O
R
1
CO
2
Me
MeOH
CO
O
O
Ni Br
CO
R
2
Ni Br
CO
78
O
81
82
Scheme 10.22
Proposed mechanism.
been prepared in just four steps via this reaction using allyl bromide and 2-butynol as
starting materials.
40
Remarkably, this cyclization is a useful methodology for the one-step
synthesis of several ring-fused systems and spiro cyclopentenones (Scheme 10.23) in good
yields and with total stereocontrol, when cyclic allylic systems and alkynes are used as
starting materials.
41-43
O
Me
H
Ni(CO)
4
Br
MeO
2
C
40% yield
Me
CO
2
Me
MeOH
CO
2
Me
H
66
84
83a
O
Br
Me
Ni(CO)
4
37% yield
Me
CO
2
Me
CO
2
Me
66
MeOH
83b
CO
2
Me
85
Scheme 10.23
Synthesis of fused and spiro cyclopentenones.
In another example, depicted in Scheme 10.24, the chiral acetylenic sulfoxide
86
reacts
with the cyclic allyl halide
87
, to furnish cyclopentenone
88
in low yields and with excellent
diastereoselectivity.
44, 45
An interesting variation of the Ni(0)-catalyzed reaction has been reported using iso-
cyanides (as isoelectronic counterparts to carbon monoxide) to synthesize 1-amino-
2-cyclopentenes, which may be hydrolyzed to the corresponding cyclopentenones
(Scheme 10.25).
46, 47
