Methionin als Vorläufer zur enantioselektiven Synthese α‐verzweigter Vinylglycine und anderer Aminosäuren

Methionine as Precursor for the Enantioselective Synthesis of α‐Branched Vinylglycines and of Other Amino Acids Methionine is converted by previously published methods into the diastereoisomerically pure 3‐thiabutyl‐substituted oxazolidinone ( 7 ) and imidazolidinones 5 and 6 . An X‐ray crystal structure determination of cis ‐3‐benzoyl‐2‐( tert ‐butyl)‐4‐(3‐thiabutyl)oxazolidin‐5‐one ( 7 ) confirms the configurational assignments made by NOE‐NMR measurements. Oxidation to sulfoxides and pyrolytic elimination produce vinyl‐substituted heterocycles (see 19, 21 ). Diastereoselective alkylations of the enolate 14 from the imidazolidinone 5 and of the dienolate 23 from the vinyl derivative 19 give geminally alkyl‐ and/or vinyl‐substituted heterocycles. Some of these products were hydrolyzed to free amino acids, such as ( R )‐2‐methyl‐ ( 25a ) and ( R )‐2‐ethyl‐2‐vinylglycine ( 25b ) ( R )‐2‐methylhomoserine ( 27 ). Raney ‐Ni desulfurization of 5 and oxidative degradation of 19 lead to enantiomerically pure derivatives of α‐aminobutyric acid (see 28 ) and of glycine (see 31 ), respectively.