Reversibly Bound Directing Phosphorus Groups

In contrast to the methodologies previously described, the use of a reversibly bounded directing group has the advantage of needing the requisite auxiliary only in catalytic quantities. Moreover, tedious modification/demodification procedures of substrate and product can be avoided. The precondition for the success of this elaborated approach is that three catalytic processes have to operate in a parallel and timed manner. Main contributions in this respect came from the groups of Breit and Tan within a short period of fascinating competition. 

By this approach, the preference for the formation of the terminal formyla-tion product (with = H) induced with PPhj as ligand could be avoided. Moreover, a diastereomeric ratio of up to 98 2 of the anti-substituted five-membered lactones were noted. In order to ensure an effective competition of the primary substrate alcohols with free isopropanol, the auxiliary had to be applied with a concentration of at least 20 mol% with respect to the substrate. 

In order to enhance the configurational stability of the auxiliary, an additional stereocenter bearing an isopropyl group was incorporated, which should suppress the epimerization of the chiral phosphorus center by the anti arrangement of 

Regiodirecting Effects without the Establishment of Covalent Interactions 

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