Catalyst-directing groups

A new chiral variant of the o-DPPB catalyst-directing group, the or-f/zo-diphenylphosphanylferrocene-carboxylalc (o-DPPF) has been developed. Employing this chiral directing group, a desymmetrizing hydroformylation of... 

Scheme 3. Design of a catalyst-directing group for the control of diastereoselectivity upon hydroformylation of acyclic methallylic alcohols.

As an ideal catalyst-directing group for that particular problem the ortho-diphenyl-phosphino benzoate system (o-DPPB) was introduced [10]. 

Support for the role of the o-DPPB substituent as a catalyst-directing group was provided in a control experiment with the benzoate 7. Thus, exchanging the phosphorus of the o-DPPB group with a CH moiety, itself not able to coordinate to the catalytically active rhodium center, caused a complete loss of stereoselectivity in the hydroformylation reaction [10]. 

Interestingly, the same concept involving a catalyst-directing group allowed also to make efficient use of 1,3 asymmetric induction. This, of course, is a much more difficult situation, since additional degrees of freedom have to be controlled in the course of the stereo-... 

In these cases, the interplay of a preferred substrate conformation as well as catalyst delivery via the catalyst-directing group form the basis for the diastereoselectivity observed... 

FIGURE 10 Schematic representation of the concepts of covalent and supramolecular catalyst-directing group (42,43). 

Alternatively, C—H bond activation of otherwise unreactive bonds with high BDE values can be achieved kinetically through the use of catalyst directing groups. 

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