Chemistry Reference
In-Depth Information
Me
Me
Me
Me
O
Co
2
(CO)
8
O
S
X
O
Isooctane,
60-80 °C, 3-12 h
Me
H
S
X
Me
(Major diastereomer)
32%, 9.5:1 dr (X = O)
34%, 12:1 dr (X = CH
2
)
74%, 9:1 dr (X = CMe
2
)
Me
Me
9a
OH
Me
S
Scheme 5.18
Me
Me
Me
Me
Me
O
Me
S
S
Me
Co
2
(CO)
8
Hexane,
65 °C, 42 h
O
Me
O
Me
Me
Me
Me
H
60%, 1.4:1 dr
Scheme 5.19
5.2.3 Chiral 2-Alkynoate Derivatives
The use of chiral 2-alkynoate derivatives in intramolecular PKRs was first reported in
1999.
24
Under suitable conditions, 8-nonen-2-ynoate derivatives of chiral oxazolidinones
and amines underwent cobalt-mediated bicyclization with acceptable yields, albeit with
poor diastereoselectivities (Table 5.3).
24, 25
Products
11e
and
11f
were converted into chi-
rally substituted cyclopentadienes.
25
Another example of a cyclization of a chiral 2-alkynoyl amide was described by Pericas
and co-workers in 1999.
26
The dicobalt hexacarbonyl complex
12
, generated
in situ
by an aminocarbonylation reaction of the dicobalt hexacarbonyl complex of 1-chloro-
2-phenylethyne, provided the 3-azabicyclo[3.3.0]oct-1(8)-ene-2,7-dione system
13
with
moderate yield and marginal diastereoselectivity by an amine
N
-oxide-promoted
27
in-
tramolecular PKR (Scheme 5.20).
