3‐(Dimethylamino)‐2,2‐dimethyl‐2 H ‐azirin als α‐Aminoisobuttersäure(Aib)‐Äquivalent: Cyclische Depsipeptide durch direkte Amid‐Cyclisierung

3‐(Dimethylamino)‐2,2‐dimethyl‐2 H ,‐azirine as an α‐Aminoisobutyric‐Acid (Aib) Equivalent: Cyclic Depsipeptides via Direct Amid Cyclization In MeCN at room temperature, 3‐(dimethylamino)‐2,2‐dimethyl‐2 H ‐azirine ( 1 ) and α‐hydroxycarboxylic acids react to give diamides of type 8 ( Scheme 3 ). Selective cleavage of the terminal N , N ‐dimethylcarboxamide group in MeCN/H 2 O leads to the corresponding carboxylic acids 13 ( Scheme 4 ). In toluene/Ph SH , phenyl thioesters of type 11 are formed (see also Scheme 5 ). Starting with diamides 8 , the formation of morpholin‐2,5‐ diones 10 has been achieved either by direct amide cyclization via intermediate 1,3‐oxazol‐5(4 H )‐ones 9 or via base‐catalyzed cyclization of the phenyl thioesters 11 ( Scheme 3 ). Reaction of carboxylic acids with 1 , followed by selective amide hydrolysis, has been used for the construction of peptides from α‐hydroxy carboxylic acids and repetitive α‐aminoisobutyric‐acid (Aib) units ( Scheme 4 ). Cyclization of 14a, 17a , and 20a with HCI in toluene at 100° gave the 9‐, 12‐, and 15‐membered cyclic depsipeptides 15, 18 , and 21 , respectively.