English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Many chiral alcohols have successfully been used as a chiral auxiliary for the dynamic resolution of -halo esters in nucleophilic substitution. 1 L-Threonine is a proteinogenic -amino acid that bears a chiral alcohol group. However, so far L-threonine has not been used as a chiral auxiliary for the dynamic resolution of -halo esters. We herein report the first example of L-threonine-mediated dynamic kinetic resolution of -bromo esters in nucleophilic substitution with various amine nucleophiles. Treatment of N-acetyl L-threonine isopropyl ester with racemic -bromo phenylacetic acid in the presence of dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP) provided -bromo ester (RS)-1 in 70% yield with about 50:50 diastereomeric ratio (dr). When the mixture of (S)-1 and (R)-1 was treated with p-anisidine (1.2 equiv), tetrabutylammonium iodide (TBAI, 1.0 equiv) and diisopropylethylamine (DIEA, 1.0 equiv) in CH2Cl2 at room temperature for 12 h, amino ester 8a was produced in 63% yield with 84:16 dr as shown in Table 1, entry 1. Also, six different N-protection groups of L-threonine were examined for the substitution with p-anisidine as shown in entries 2-7. The reactions of 2, 3, 4, and 7 bearing N-pivaloyl, N-Boc, Nbenzoyl, and N,N-dibenzyl groups gave slightly better drs ranging from 88:12 to 86:14, while the reactions of 5 and 6 bearing N-p-methoxybenzoyl and N-2-pyridinylcarbonyl groups gave lower drs compared to the reaction of 1. The dr and yield of the substitutions in Table 1 imply that -bromo carbon center is configurationally labile with respect to the rate of substitution and L-threonine-derived -bromo esters

Dynamic Kinetic Resolution of L-Threonine-derived α-Bromo Esters for Asymmetric Synthesis of α-Amino Esters