5‐Substituted (S)‐tetrahydrofuran‐2‐ones (1a,b) and (S)‐pyrrolidin‐2‐ones (1c,d) were transformed in three steps, by treatment with tert‐butoxybis(dimethylamino)methane (Bredereck's reagent), followed by nitrosation and stereoselective catalytic hydrogenation, into the corresponding 5‐substituted (3S,5S)‐3‐acetylaminotetrahydrofuran‐2‐ones (4a,b) and (3S,5S)‐3‐acetylaminopyrrolidin‐2‐ones (4c,d).
A novel simple synthesis of 5‐substituted‐1,2,4‐oxadiazole‐3‐carboxylates 5 from N‐acylglycines 1, which are transformed with DMF in the presence of phosphorus oxychloride into 2‐substituted‐4‐dimethyl‐aminomethyleneoxazol‐5(4H)‐ones 2, followed by opening into 2‐aroylamino‐3‐dimethylamino‐propenoates 3, and nitrosation to give the oximes 4 as intermediates, which cyclize spontaneously into 5‐substituted‐1,2,4‐oxadiazole‐3‐carboxylates 5. The compounds 2 can be transformed into 5 without isolation of 3 and 4.
Alkyl 2‐(substituted cinnamoylamino)‐3‐dimethylaminopropenoates 5, prepared either from glycine (1) and substituted cinnamoyl chlorides 2 via oxazol‐5(4H)‐ones 4, or from cinnamoylglycinate with t‐butoxy‐bisdimethylaminomethane, were transformed by nitrosation into 5‐substituted‐1,2,4‐oxadiazole‐3‐carboxylates 8. The formation of alkyl N‐cinnamoyloxalic acid hydroxyimidic amides 7, which were isolated as intermediates, represent a novel synthesis of N‐acyl substituted hydroxyimidic amides.
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