Iterative tandem catalysis

Pahnans et al. prepared 5 by the reaction of [RuCl2(p-cymene)]2 and 2-phenyl-2-aminopropionamide in the presence of potassium carbonate. They used 5 in an iterative tandem catalysis for the synthesis of chiral oligoesters. The enzymatic ring opening of 6-methyl-e-caprolactone was combined with ruthenium-catalyzed alcohol racemization to produce optically active oligomers of 6-methyl-e-capro-lactone [23] (Scheme 1.17). 

Scheme 12 Chiral polymers from racemic co-methylated lactones by iterative tandem catalysis [105, 106]...

Iterative Tandem Catalysis Chiral Polymers from Racemic -Methylated Lactones... 

S) -isopropylmorpholine-2,5 -dione immobilized porcine pancreas lipase iterative tandem catalysis indium tin oxide kinetic resolution polymerization large... 

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. 

Ring-Opening of co-Substituted Lactones by Novozym 435 Selectivity Issues and Application to Iterative Tandem Catalysis... 

TTie extension of tandem catalysis to polymer chemistry is, however, not trivial. In order to reach high molecular weight polymers, each reaction has to proceed with almost perfect selectivity and conversion. Obviously, combining different catalytic reactions limits the choice of suitable reactions since they must also be compatible with each other. We recently introduced Iterative Tandem Catalysis (ITC), a novel polymerisation method in which chain growth during polymerisation is effectuated by two or more intrinsically different catalytic processes that are both compatible and complementary. If the catalysts and monomers are carefully selected, ITC is able to produce chiral polymers from racemic monomers, as was shown by us for the ITC of 6-MeCL and the DKR polymerisation of sec-diols and diesters. ... 

Fig. 17 Polymerization of 6-MeCL by iterative tandem catalysis [146]. Reproduced by permission of The Royal Society of Chemistry (RSC)...

As reported by Kanca and co-workers, the enantioselective transesterification polycondensation of racemic AB-type monomers containing a secondary hydroxy group and a methyl ester moiety led to chiral polyesters by iterative tandem catalysis. The concurrent actions of an enantioselective acylation catalyst (such as CALB) and a racemisation catalyst (Ru(Shvo)) resulted in the high conversion of the racemic monomers to enantioenriched polymers. AB-type monomers used were typically methyl 6-hydroxyheptanoate, methyl 8-hydroxynonanoate and methyl 13-hydroxytetradecanoate. The polycondensation at 70 "C in toluene gave a polyester of high yield with a M of around several thousand and an enantiomeric excess higher than 74% [18]. 

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