Palladium asymmetric allylic substitutions, phosphine ligands

A new class of chiral amidine-phosphine and -sulfide hydrid ligands with a variety of modifications is used for the palladium mediated allylic substitutions of both acyclic and cyclic compounds [74] (Figure 3.5). High levels of asymmetric induction were achieved for both substrates. 

Qiiial oxazoline ligands c ntinue to be among those most widely used for asymmetric catalysis. The phosphines 61 ate superior to other oxazoline based phosphines for palladium catalysed as rmmetric allylations <990L1745>. New naphthyl substituted oxazoline ligands include the compounds 62 <99JOC1620> and 63 <98T15721>. ... 

In the allylic substitution of racemic 2-propenyl acetates or related substrates with the same substituents at 1 and 3 positions, the jt-allylpalladium intermediate containing a meso type 7r-allyl group is formed from both enantiomers of the allylic substrate. Two jt-allyl carbons at the 1- and 3-positions are diastereotopic on coordination of a chiral phosphine ligand to palladium. The asymmetric induction arises from preferential attack by the nucleophile on either of the two diastereotopic TT-allyl carbon atoms (Scheme 2-28). 

Significant advances have been made in asymmetric nucleophilic additions to -ir-allyl palladium complexes using chiral ligands. Substitution of allylic acetates in the presence of the chiral phosphine hgand 224 (or other chiral phosphine ligands) can occur with very high levels of enantioselection (1.224). The reaction works best with diaryl-substituted allylic acetates. 

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