Chemistry Reference
In-Depth Information
synthesis of complex natural products, and of chiral ligands continue to be the methods of
choice for asymmetric intermolecular PKRs.
Chiral auxiliary-mediated asymmetric PKRs can be classified into three major types,
depending on the position of the auxiliary Xc (the first two of these types, in turn, can be
performed either in an intermolecular or in an intramolecular fashion):
Type
A
: Chiral auxiliary attached to the alkyne (Scheme 5.5)
O
Xc
R
1
Xc
Co
2
(CO)
8
A
inter
+
*
R
1
R
2
*
R
2
O
Xc
R
1
Xc
Co
2
(CO)
8
*
R
1
A
intra
*
Scheme 5.5
Type
B
: Chiral auxiliary attached to the alkene (Scheme 5.6):
O
Xc
Co
2
(CO)
8
B
inter
+
*
Xc
R
*
R
O
Xc
Co
2
(CO)
8
*
Xc
B
intra
*
Scheme 5.6
Type
C
: Chiral auxiliary located in the enyne chain (Scheme 5.7):
O
R
Co
2
(CO)
8
*
C
intra
R
*
Xc
Xc
Scheme 5.7
