115228-55-2Relevant academic research and scientific papers
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
Schoellkopf, Ulrich,Westphalen, Karl-Otto,Schroeder, Juergen,Horn, Klaus
, p. 781 - 786 (2007/10/02)
The lithiated bislactim ether 2a of cyclo(-L-Val-Ala-) reacts with acyl chlorides 3 highly diastereoselectively to yield the compounds 4 with (2S,5S)-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 4e via the intermediates 14 or 15 and16a.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.
