Chemistry Reference
In-Depth Information
7
Aldol-Type Reactions
Inmaculada Fernández, Noureddine Khiar, Ana Alcudia, Maria Victoria García and
Rocío Recio
7.1
Introduction
The aldol reaction can be considered as one of the most useful synthetic methods
for a C-C bonding process [1], as the configuration of two new asymmetric centers
can be controlled in most cases with high stereoselectivity.
In this sense, titanium complexes with chiral ligands have been shown to be
good reagents for the stereoselective addition of C nucleophiles to carbonyl com-
pounds. The use of these complexes for the chiral modification of enolates is an
interesting approach to enantioselective aldol reactions as the chiral ligands can
be easily recovered, and no additional manipulations on the products are needed.
7.2
Titanium Lewis Acids for Enolate Formation
Natural carbohydrates can be considered as privileged monodentate ligands for
the preparation of chiral titanium reagents. In this sense, titanium complex
3
is
a successful example of a carbohydrate reagent especially valuable in aldol reac-
tions. It was first prepared by Duthaler and coworkers from CpTiCl
3
(
1
) and
diacetone-d-glucose (DAGOH)
2
(Scheme 7.1) [2].
O
HO
O
O
Et
3
N
+
Ti
Ti
O
Et
2
O
or Toluene
O
Cl
Cl
DAGO
ODAG
Cl
Cl
DAGOH
2
1
3
Scheme 7.1
Synthesis of titanium complex
3.
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