Amino Acids, 1 8 1 ' 1 . -Preparation and Reactions of 2-Isocyanato-2-alkenoates 2-Isocyanato-2-alkenoates 3 were obtained in good yields by the perrhenate-catalyzed decomposition of 2-azidoalkanoates 1 in the presence of diphosgene (2a) or phosgene (2b). Methyl 2-azidopropionate (lh) reacts to give a mixture of methyl 2-isocyanato-2-propenoate (3h) and methyl 2-chloro-2-isocyanatopropionate (4). The addition product 4 could easily be converted into 3h by elimination of HC1 with triethylamine at 0°C. With benzyl alcohol (5a) and tert-butyl alcohol (5b) the isocyanates 3 react smoothly to give the corresponding Z-or Boc-protected 2,3-didehydroamino acid esters 6 and 7 , respectively. The acrylic acid derivative 3h reacts as dienophile with various dienes to yield the Diels-Alder adducts 8-10.
Amino Acids, 16i11. -Synthesis of N-Acyl-2,3-didehydro-2-amino Acid Esters121 N-Acyl-2,3-didehydro-2-amino acid esters 3, 5, 7-12, with a great variety of N-substituents, are obtained in good yields by the perrhenate-catalyzed decomposition of methyl 2-azido carboxylates 1 in organic solvents in the presence of the corresponding acyl chlorides 2. By using methyl 2-azidoisovalerate (la), the conditions (catalyst, solvent, temperature) for the reaction to give 3a were optimized. The reactivity of acyl chlorides can be strongly enhanced with equimolar amounts of dimethyl formamide, which allows a lowering of the decomposition temperature for this reaction. Under these mild reaction conditions also the unstable N-acyldehydroalanine derivative 5f can be obtained in good yield.
The perrhenate‐catalyzed decomposition of α‐azidocarboxylate esters 1 with phosgene or diphosgene provides a simple approach to 2‐isocyanato‐2alkenoate esters 2. The latter undergo the usual addition reactions at the isocyanate group. In addition, the ester with R = R1 = H undergoes radical polymerization and can be used as a dienophile in Diets–Alder reactions. R, R1, e.g., H, Me, Ph.
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