Selektive Umfunktionalisierung der terminalen Amidgruppe offenkettiger Polyamide via 2‐Oxazolin‐5‐one als Zwischenstufen . Vorläufige Mitteilung

Selective Modification of the Terminal Amide Group of Linear Polyamides via 2‐Oxazolin‐5‐ones as Intermediates Treatment of aqueous or alcoholic solutions of diamides of type 2 with HCl leads to the formation of amide‐acids and amide‐esters of type 3 ( Scheme 1 and Table ). It has been shown, that 2‐oxazolin‐5‐ones of type 4 are intermediates of this selective transformation of the disubstituted terminal amide group. The selectivity of the transformation is demonstrated by the reaction sequence shown in Scheme 3 . No selectivity has been observed in the acid‐catalyzed hydrolysis of triamide 9 with a monosubstituted terminal amide group ( Scheme 4 ). Hydrolysis of the optically active dipeptide derivatives (+)‐( L )‐ 13 and (+)‐( L )‐ 15 with HBr in nitromethane at 60–80° yields the pure enantiomer (+)‐( L )‐ 14 and (+)‐( L )‐ 16 , respectively ( Scheme 5 ), i.e. , no racemization takes place under the reaction conditions. These results show the usefulness of the dimethylamide group as a protecting group for carboxylic acids for example in the peptide synthesis.