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Asymmetric syntheses via heterocyclic intermediates, XL. Studies on the acylation of lithiated bislactim ethers of cyclo(‐ L ‐Val‐Ala‐) and cyclo(‐ L ‐Val‐Gly‐) Asymmetric synthesis of ( R )‐α‐alkenyl and ( R )‐α‐ethinyl alanine methyl esters by the bislactim ether method
Author(s) -
Schöllkopf Ulrich,
Westphalen KarlOtto,
Schröder Jürgen,
Horn Klaus
Publication year - 1988
Publication title -
liebigs annalen der chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0170-2041
DOI - 10.1002/jlac.198819880813
Subject(s) - chemistry , acylation , adduct , diastereomer , ether , wittig reaction , yield (engineering) , stereochemistry , enol , alanine , medicinal chemistry , chloride , acyl chloride , benzamide , benzoyl chloride , organic chemistry , catalysis , amino acid , biochemistry , materials science , metallurgy
Abstract The lithiated bislactim ether 2a of cyclo(‐ L ‐Val‐Ala‐) reacts with acyl chlorides 3 highly diastereoselectively to yield the compounds 4 . with (2 S ,5 S )‐configuration. With acetyl chloride ( 3a ) the N ‐acetyl compound 7 is formed as a sideproduct. Alternatively, the compounds 4 can be obtained by oxidation of the carbinols 8 . From 4a and b , the olefins 11a and b are obtained by Wittig reaction. These are precursors of methyl ( R )‐α‐alkenyl alanine methyl esters of type 13 . ( R )‐α‐ethinyl alanine methyl ester 17 is obtainable from 4a and 4c via the intermediates 14 or 15 and 16a . The lithiated bislactim ether 2c of cyclo(‐ L ‐Val‐Gly‐) reacts with benzoyl chloride ( 3b ) to give the „bis adduct” 18 . However, 6b is obtained from 2c and the benzamide 19 , though as a 1:1 diastereomeric mixture. Presumably, 6b epimerizes via the enol 21a subsequently to its diastereoselective formation.