Chiral Oligomers by Iterative Tandem Catalysis

As, Bart A. C. van; Buijtenen, Jeroen van; Heise, Andreas; Broxterman, Quirinus B.; Verzijl, Gerard K. M.; Palmans, Anja R. A.; Meijer, E. W.

doi:10.1021/ja052347d

Cited by 86 publications

(40 citation statements)

References 16 publications

(6 reference statements)

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“…[16] Recently, Mijer and coworkers used 4c, prepared from 3a and 2-phenyl-2-aminopropionamide in the presence of K 2 CO 3 , in an iterative DKR to produce enantioenriched oligoesters (Scheme 9). [17] The enzymatic ring-opening of 6-methyl-ε-caprolactone was combined with the rutheniumcatalyzed racemization of the resulting alcohol to produce optically active oligomers of 6-methyl-ε-caprolactone. 2,4-Dimethylpentan-3-ol, a sterically hindered hydrogen donor that will not initiate enzymatic ring-opening nor take part in chemical transesterification, was used as an additive.…”

Section: Racemization Catalysts and Reaction Conditions For Dkr Of Almentioning

confidence: 99%

Chemoenzymatic Dynamic Kinetic Resolution of Alcohols and Amines

et al. 2010

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Dynamic kinetic resolution (DKR) is an attractive process for the transformation of racemic mixtures into optically active compounds. For successful DKR, efficient racemization is required while the kinetic resolution is proceeding. This Microreview mainly summarizes the recent developments in the DKR of alcohols and amines, based on metal-catalyzed racemization and enzymatic acylation in a single reaction vessel.

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Section: Racemization Catalysts and Reaction Conditions For Dkr Of Almentioning

confidence: 99%

Chemoenzymatic Dynamic Kinetic Resolution of Alcohols and Amines

et al. 2010

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“…[1] Recently, Novozym435 in tandem catalysis with Ru was successfully employed in the synthesis of chiral polymers. [2] The aldol reaction is one of the most exploited carboncarbon bond forming reactions in organic synthesis, while acetaldehyde or acetone are the most important precursors for two-and three-carbon elongation processes. [3] Despite remarkable progress in homogeneous and heterogenous catalysis including organocatalysis, the aldol reaction of acetaldehyde still remains an interesting challenge, in which it may act either as a nucleophile or electrophile, owing to its unsubstituted a-position, thereby leading to the formation of side products from dehydration, self condensation etc.…”

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Tandem Catalysis by Lipase in a Vinyl Acetate‐Mediated Cross‐Aldol Reaction

2011

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Abstract:The lipase Novozym435 (0.6% w/w) was used in tandem with organocatalysts in a first vinyl/ isopropenyl acetate-mediated aldol reaction. The reaction was facilitated through the lipase-catalyzed in situ generation of acetaldehyde/acetone. The important features of the present methodology include the mild and facile reaction conditions, regenerability of the lipase, comparatively high yields and minimal side product formation.

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“…In situ racemization of the hydroxysubstituted stereocenters from the S to the R configuration allows the polymerization to proceed to high conversion. We recently reported the combination of racemization and enzymatic ring opening of chiral lactones; the two reaction steps were conducted alternating in separate reaction vessels and low-molecular-weight oligomers were obtained (degree of polymerization [3][4][5]. [3] In contrast, our goal here is the combination of DKR with a polymerization process in one pot, thereby building up polymers of significant molecular weight and with high optical purity.…”

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Chiral Polyesters by Dynamic Kinetic Resolution Polymerization

et al. 2006

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Chirality is one of the most intriguing features of natural compounds. It determines, for instance, whether a molecule has a beneficial biological function. Consequently, it is of paramount importance in drug discovery to master asymmetric synthesis. For this reason, a number of methods have been developed in modern organic chemistry to obtain enantiopure compounds from racemic mixtures, for example, chemoenzymatic dynamic kinetic resolution (DKR).[1] In this process, the enzymatic kinetic resolution of a racemic compound is combined with the in situ chemical racemization of the chiral center of the substrate. While the theoretical yield in a normal kinetic resolution process is limited to 50 %, which corresponds to total conversion of the preferred enantiomer, in DKR quantitative substrate conversion and high optical purity (> 99 % ee) can be obtained.Despite the numerous asymmetric methods in organic synthesis, concepts for making chiral synthetic polymers are still limited. One obvious reason is the need for optically pure monomers. Possible sources are naturally occurring optically pure monomers such as l-lactide, which, however, limits the range of available monomer building blocks.An alternative is the direct resolution polymerization from synthetic racemic monomers.[2] While most chemical polymerization catalysts are nonstereoselective and therefore not suited for the direct resolution of racemic monomer mixtures, enzymes can be be employed successfully in kinetic resolution polymerizations. In the recent past we and others have shown this for the ring-opening polymerization (ROP) of chiral caprolactones. [2c-e] This process yields polymers with molecular weights of up to 5000 g mol À1 and with over 98 % ee. However, due to the maximum conversion of 50 % in kinetic resolutions it cannot be applied in the polycondensation of racemic diols and dicarboxylic acid derivatives. The reason is that in a typical polycondensation, significant molecular weights can be realized only at an almost quantitative monomer conversion. We anticipated that for chiral monomers this can be achieved by a process analogous to the DKR of small molecules.Here we report on our investigation of a novel concept for the synthesis of chiral polyesters, a lipase-catalyzed dynamic kinetic resolution polymerization of racemic monomers. As shown in Scheme 1, a mixture of stereoisomers of a secondary diol is enzymatically polymerized with a difunctional acyl donor (dicarboxylic acid derivative). Because of its enantioselectivity the lipase converts only the hydroxy groups at the R-configured centers. In situ racemization of the hydroxysubstituted stereocenters from the S to the R configuration allows the polymerization to proceed to high conversion. We recently reported the combination of racemization and enzymatic ring opening of chiral lactones; the two reaction steps were conducted alternating in separate reaction vessels and low-molecular-weight oligomers were obtained (degree of polymerization 3-5).[3] In contrast, our goal here is the ...

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Chiral Oligomers by Iterative Tandem Catalysis

Cited by 86 publications

References 16 publications

Chemoenzymatic Dynamic Kinetic Resolution of Alcohols and Amines

Chemoenzymatic Dynamic Kinetic Resolution of Alcohols and Amines

Tandem Catalysis by Lipase in a Vinyl Acetate‐Mediated Cross‐Aldol Reaction

Chiral Polyesters by Dynamic Kinetic Resolution Polymerization

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