Asymmetric esterification

Further work by the Ye group has shown that NHCs derived from pre-catalyst 215 can also promote the asymmetric dimerisation of alkylarylketenes 193 to generate alkylidene P-lactones 216 in good diastereo- and enantio-selectivity [83], The asymmetric [4+2] addition of enones and alkylarylketenes to generate 8-lactones 218 in high ee has also been accomplished [84], as has the asymmetric esterification of alkylarylketenes to give esters 217 using benzhydrol, which is assumed to proceed via a Lewis-base mediated mechanism (Scheme 12.46) [85]. 

Scheme 12.47 Asymmetric esterification of ketenes with 2-phenylphenol...

Preparative-scale fermentation of papaveraldine, the known benzyliso-quinoline alkaloid, with Mucor ramannianus 1839 (sih) has resulted in a stereoselective reduction of the ketone group and the isolation of S-papaverinol and S-papaverinol M-oxide [56]. The structure elucidations of both metabolites were reported to be based primarily on ID and 2D NMR analyses and chemical transformations [56]. The absolute configuration of S-papaverinol has been determined using Horeau s method of asymmetric esterification [56]. The structures of the compounds are shown in Fig. 7. 

Asymmetric esterification. me.vo-Cyclohexanedicarboxylic anhydride (1) undergoes a highly stereoselective esterification with the diphenylboric ester (2) of (R)-2-methoxy-l-phenylethanol in the presence of diphenylboryl triflate to provide,... 

Fig. 28 Schematic illustration of a helicity induction in 30 upon complexation with (R)-39 (a), memory of the induced macromolecular helicity after replacement by achiral 76 (b), and storage of the induced helicity or helicity memory by asymmetric esterification with diazomethane (c)...

Asymmetric esterification of benzoic acid with racemic (l-bromoethyl)benzene was performed with chiral cyclic guanidines as stoechiometric bases4 the ester was obtained with ee below 15%. The chiral guanidines 6 were obtained from a chiral diamine of C2 symmetry which was tranformed first to urea and then to several guanidines through an intermediate chloroformamidinium chloride (Figure 4). 

Lipases are commonly recognized as biocatalysts in hydrolysis and esterification reactions. The primary advantages of the used reactions are in asymmetric hydrolysis of chiral esters, as well as asymmetric esterification of a wide range of substrate... 

In addition to this, there are several reports of asymmetric esterification of racemic alcohols with anhydrides as acyl donors. Examples include various primary and secondary alcohols, bicyclic secondary alcohols of the norbomane type, amino alcohols, and ferrocenes. This is exemplified in eq 9 for 1 -phenylethanol. ... 

Determination of configuration by asymmetric esterification. This method developed by Horeau1-2 for determining the configuration of an optically active secondary alcohol is based upon the CranP-Prelog rule of asymmetric synthesis. 

M., Tong, W, and Vater, E.J. (2004) Process and intermediates for the preparation of (lR,2S,5S)-6,6-dimethyl-3-azabicyclo[3,l,0]hexane-2-carboxylates or salts thereof via asymmetric esterification of caronic anhydride. Patent 2004-US19135, 2004113295, 20040615,... 

Efficient preparation of (R)-a-monobenzoyl glycerol by lipase catalyzed asymmetric esterification optimization and operation in packed bed reactor. Biotechnol. Bioeng., 73, 493-499. doi 10.1002/bit.l084... 

HIGHLY EFFICIENT ASYMMETRIC ESTERIFICATION OF CYCLIC MESO-DICARBOXYLIC ANHYDRIDES CATALYZED BY DIPHENYLBORYL TRIFLATE. 

Chiral A-heterocyclic carbenes (NHC), weU known as potent nucleophihc organocatalysts in numerous transformations such as benzoin condensation and Stetter reaction [22], have also recently been reported to catalyze asymmetric esterification of ketenes [23]. By surveying different alcohols and optimizing the reaction conditions, it was found that the addition of benzhydrol to a range of ketenes was efficiently catalyzed by a catalytic amount of NHC 54 , the later being formed in situ from the precatalyst 54 (12 mol%) and cesium carbonate (10 mol%). Some selected results presented in Scheme 3.24 show that enantioenriched esters 53 could be obtained in up to 95% ee, although both the enantioselectivity and the yield appeared to be highly substrate dependent. 

A. Asymmetric Hydrolysis of Racemic Esters and Asymmetric Esterification or Lactonization of Racemic Alcohols... 

B. Asymmetric Hydrolysis of meso-Diesters and Asymmetric Esterification of meso-D o s... 

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