Kinetic dynamic, racemic monomers

Dynamic Kinetic Resolution Polymerization of Racemic Monomers 287... 

Hilker et al (44) combined dynamic kinetic resolution with enzymatic polycondensation reactions to synthesize chiral polyesters from dimethyl adipate and racemic secondary diols. The concept offered an efficient route for the one-pot synthesis of chiral polymers from racemic monomers. Palmans at al (18,43) generalized the approach to Iterative Tandem Catalysis (ITC), in which chain growth during polymerization was effected by two or more intrinsically different catalytic processes that were compatible and complementary. 

In polymer chemistry, one of the most challenging tasks is to efficiently synthesize optically active synthetic polymers. The extraordinary enantioselectivity of lipases offers new perspectives towards these materials, and it is therefore not surprising that some research efforts have focused on the use of lipases to synthesize chiral polymers from racemic monomers. Methodologies like kinetic resolution and even chemoenzymatic dynamic kinetic resolution (DKR) have already been exploited on the industrial scale to afford chiral intermediates for the pharmaceutical and agrochemical industry. Recently, these methodologies have been successfully applied in the synthesis of chiral polymers. 

For the synthesis of an optically active polyester from a racemic monomer, a new method of dynamic kinetic resolution was used. A mixture of stereoisomers of a secondary diol, a,a -dimethyl-l,4-benzenedimethanol, were enzymatically polymerised with dimethyl adipate (Scheme 12.6, [1]) [32]. 

An elegant combination of monomers with the components of a dynamic kinetic resolution (DKR) permitted the conversion of a racemic diol into a polymer consisting of enantioenriched units that could be recovered by polymer hydrolysis [28]. Diol 5 and achiral diester 6 were combined with a well-known system of lipase and ruthenium catalyst (see Chapters 4 and 5 for more on this). The esterification of the free hydroxyl groups is very selective (for the R) configuration) but as the polymerization proceeds, the (S) stereocentres are racemized. Upon 92% conversion of the hydroxy groups and hydrolysis of the polymer, an enantioenriched sample of the diol was obtained that contained essentially none of the (S,S)-isomer. 

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