Asymmetric Nucleophilic Substitution Research Articles

ChemInform Abstract: Dynamic Resolution of α‐Halo Carboxylic Acid Derivatives in Asymmetric Nucleophilic Substitution Using Chiral Auxiliaries

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D-Phg-l-Pro Dipeptide-derived prolinol ligands for highly enantioselective Reformatsky reactions

Optically pure N-aminoethyl prolinol derivatives 3a–c have been prepared from the dynamic kinetic resolution of N-(α-bromo-α-phenylacetyl) proline ester 1 in asymmetric nucleophilic substitution and subsequent reduction. The peptide-derived prolinols are tested as chiral ligands in the asymmetric addition of Reformatsky reagent to aromatic aldehydes. Chiral ligand 3c has been shown to be effective to produce enantioenriched β-hydroxy esters 5a–j with up to 98% ee.

Dynamic Kinetic Resolution of α‐Bromo Carboxylic Acid Derivatives in Asymmetric Nucleophilic Substitution with Chiral α‐Amino Esters.

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Dynamic Kinetic Resolution of α‐Chloro Esters in Asymmetric Nucleophilic Substitution Using Diacetone‐D‐glucose as a Chiral Auxiliary.

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Dynamic Kinetic Resolution of α-Bromo Carboxylic Acid Derivatives in Asymmetric Nucleophilic Substitution with Chiral α-Amino Esters

Dynamic kinetic resolution of -bromo carboxylic acid derivatives in nucleophilic substitution with chiral -amino ester nucleophiles in the presence of TBAI and DIEA has been investigated for stereoselective syntheses of 1,1'-iminodicarboxylic acid derivatives. Nucleophilic substitutions with various chiral -amino esters gave iminodiacetates 2-8 with stereoselectivities up to 87 : 13 dr. Also, the reactions of N-(-bromo--phenylacetyl)-L-alanine methyl ester with L-alanine, D-alanine and glycine methyl ester nucleophiles afforded N-carboxyalkyl dipeptide analogues 10-12 up to 90 : 10 dr.�⨀ԀĀ衺�⨀ԀĀऐ돀졽�⨀堘�⨀ꢐ�⨀돐좐�⨀��⨀킐�⨀뤏덐�⨀렏頏࢑�⨀਀࢑�⨀ᢑ�⨀؀ကᢑ�⨀?麆Ѐက䂑�⨀䂑�⨀

Dynamic Resolution of α‐Bromo Tertiary Amides for Stereoselective Preparation of Dipeptide Analogues.

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Dynamic kinetic resolution of α-chloro esters in asymmetric nucleophilic substitution using diacetone- D-glucose as a chiral auxiliary

Diacetone- D-glucose mediated dynamic kinetic resolution of α-chloro-α-aryl esters in nucleophilic substitution reactions has been investigated. Reactions of various amine nucleophiles in the presence of TBAI and DIEA can provide the substitution products 2– 10 up to 97% yield and 97:3 dr. This simple procedure with easy removal of the chiral auxiliary provides a practical protocol for asymmetric syntheses of α-amino acid derivatives up to 97:3 er.

Dynamic Resolution of α-Bromo Tertiary Amides for Stereoselective Preparation of Dipeptide Analogues

Dynamic resolution of -bromo tertiary acetamides in asymmetric nucleophilic substitution reaction is described. Intermolecular substitution of -bromo tertiary acetamides with dibenzylamine in the presence of TBAI and gave the dipeptide analogues 7-10 with high stereoselectivities up to 90 : 10 dr. Also, cyclic dipeptide analogues 20-29 were produced by the intramolecular nucleophilic cyclization of -bromo tertiary acetamides with low stereoselectivities in 84-42% yields.

Asymmetric Nucleophilic Substitution of α‐Bromo Amides via Dynamic Kinetic Resolution for the Preparation of Dipeptide Analogues.

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Asymmetric nucleophilic substitution of α-bromo amides via dynamic kinetic resolution for the preparation of dipeptide analogues

Asymmetric nucleophilic substitution reactions of α-bromo α-aryl acetamides derived from l-amino acids are described. The simple and practical syntheses of dipeptide analogues have been developed with dibenzylamine, TBAI and a base to provide 2a–2n and 4 in 50–98% yields with diastereomeric ratios from 74:26 to >99:1. Mechanistic investigations suggest that α-bromo acetamides are configurationally labile under the reaction condition and the primary pathway of the asymmetric induction is a dynamic kinetic resolution. The semiempirical calculations of two epimeric transition states of 1b found that (αS)-epimer is the faster reacting epimer with the formation of an intermolecular hydrogen bond that facilitates delivery of the amine nucleophile.

First asymmetric nucleophilic displacement reactions on chiral α-substituted aldehyde hydrazones

The first asymmetric nucleophilic substitution reaction on racemic α-substituted aldehydes using enantiomerically pure hydrazines as chiral auxiliaries is presented. The diastereoselectivity of the process is achieved by a dynamic kinetic resolution via the 1:1 epimeric mixture of the substrate hydrazones. The a 2-reactivity (Umpolung) of the α-substituted hydrazones is accomplished by complexation with Lewis acids. Several carbon-, sulfur- and oxygen-nucleophiles were shown to readily undergo substitution of the α-leaving group under these conditions, affording the substitution products with good to excellent chemical yields and with low to moderate diastereoselectivities. Two methods for the cleavage of the chiral auxiliary are described.