DIOP-DiPAMP hybrids

In 1992 Burgess and co-workers prepared DIOP-DiPAMP hybrids to study the matching and mismatching elfects between the chiral backbone and the stereogenic phosphorus atoms. These ligands were prepared by substitution on the optically pure ditosylate also used to prepare DIOP (Scheme 2.36). 

Very few reports of this reaction with P-stereogenic ligands have been published. An early study with DIOP-DiPAMP hybrids 87 led to very poor enantioseleetivities, which have been slightly improved more recently by using ligands 88 and 89. ... 

Subsequently, Burgess79 prepared a series of hybrid ligands (27a-c) (Figure 3) which were chiral not only in the carbon backbone like (R, R)-DIOP 25 but also at phosphorus, like DIPAMP. 

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