Asymmetric Allylic Substitution in Water with a Polymeric Pd Catalyst

π-allylpalladium - asymmetric catalysis - aqueous media - PS-PEG polymer supports

Significance

<P>Asymmetric π-allylic substitution of meso-1,4-diacetoxycycloalkenes was performed with an amphiphilic PS-PEG resin-supported chiral phosphine-palladium complex. Thus, the reaction of cis-1,4-diacetoxycyclopentene (meso-1) with diethyl malonate, dibenzylamine and phenols in water gave the corresponding 1-acetoxy-4-substituted cyclopentenes 2a-i with 90-99% ee in 43-64% yield. Cyclohexenyl ester (meso-4) also underwent etherification with phenol to give 5 in 37% yield (95% ee) and 11% of 6.</P>

Comment

<P>The authors have reported earlier the preparation and utility of the polymeric chiral phosphine-palladium complex used here (J. Am. Chem. Soc. 2001, 123, 2919; Org. Lett. 2004, 6, 281; Org. Lett. 2005, 7, 291; Tetrahedron: Asymmetry 2006, 17, 161; J. Org. Chem. 2006, 71, 8644). The reaction pathway giving high enantiomeric excess of the monosubstituted products includes kinetic resolution steps forming disubstituted 3.</P>