Chemistry Reference
In-Depth Information
9
Hydroformylations, Hydrovinylations, and Hydrocyanations
Mike M.K. Boysen
9.1
Hydroformylation Reactions
Asymmetric hydroformylation is a highly useful process as it creates chiral alde-
hydes from simple alkene precursors, gaseous hydrogen, and carbon monoxide as
inexpensive feedstock [1]. The reaction is catalyzed by rhodium(I) complexes and
leads to the desired, branched chiral product
2
but may also give rise to achiral
unbranched aldehyde
3
as an undesired side product (Scheme 9.1). Therefore, a
chiral catalyst has not only to provide a high level of stereoinduction but also to
exert efficient control over the regioselectivity of this transformation [1, 2].
CHO
CO, H
2
CHO
R
1
R
1
Me
R
1
Rh(I) +
ligand*
+
1
2
3
(undesired)
R
1
= aryl, alkyl
Scheme 9.1
Chiral branched aldehydes and achiral unbranched aldehydes from rhodium-
catalyzed asymmetric hydroformylation reaction of alkenes.
The most common ligands for rhodium(I)-catalyzed hydroformylation reactions
are phosphorus based: the ligand BINAPHOS, which was introduced by Takaya
and Nozaki [3], contains one phosphite and one phosphine as donor sites and was
the first ligand to offer high levels of stereoinduction. With regard to carbohydrate-
based ligands for hydroformylation, the vast majority of these feature either phos-
phite or phosphinite donor sites, as they can be easily installed in a carbohydrate
framework by reacting carbohydrate hydroxy groups with an appropriate chloro-
phosphite or phosphine chloride, respectively. Apart from these ligands, a few
carbohydrate phosphines and carbohydrate-derived P-S-donor ligands have been
reported.
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