Chemistry Reference
In-Depth Information
O
O
P
O
O
O
=
a
O
O
P
O
61
Figure 10.13.
Binol - based diphosphite
61
.
O
Ph
N
N
N
O
O
O
P
P
P
O
N
N
N
Fe
Ph
N
O
O
P
O
O
N
62
63
O
Figure 10.14.
Ligands
62
and
63
.
Bis-Phosphacyclic Ligands
Like the asymmetric hydroformylation of styrene, diphos-
phines usually provide lower ee than the related phosphite-containing ligands. However,
recently, the diphospholane ligands
47
-
49
(Fig. 10.9) have also provided excellent regio-
and enantioselectivities (ee's in the range of 82-96%) [8,30]. The best enantioselectivity
was obtained with ligand
49
, which represents the highest ee reported for a Rh catalyst
in vinyl acetate asymmetric hydroformylation [8a,30].
Other Ligands
Only three other type of ligands have been successfully applied in the
asymmetric hydroformylation of vinyl acetate.
The fi rst one is the bis-(diazaphospholodine) ESPHOS
62
(Fig. 10.14) developed by
Cole-Hamilton and coworkers. This ligand provided high regio- and enantioselectivities
(up to 89%) [31] .
The second one is the successful application of the previously mentioned phosphine-
phosphoroamidite ligand
50
(Fig. 10.10). This ligand provided enantioselectivities up to
96% [23] .
Recently, a ferrocene-based phosphonite ligand
63
(Fig. 10.14) was successfully
applied in this process (ee's up to 83%) [32].
10.2.5. Rhodium - Catalyzed Asymmetric Hydroformylation of Allyl Cyanide
The asymmetric hydroformylation of allyl cyanide (Scheme 10.5) has recently focused
the interest of researchers because the iso-aldehyde derivative can be easily transformed
