Jürgen Kühlwein

Darstellung und Reaktionen von 2-Isocyanato-2-alkensäureestern (Aminosäuren ; 18)

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 (1h) 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 HCl 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.

Eine neue Synthese von Didehydrodipeptiden und Didehydrotripeptiden (Aminosäuren ; 17)

Esters of N-phthaloyl-protected (R)- or (S)-didehydro dipeptides 5-7 were obtained in good yields by the perrhenate-catalyzed decomposition of 2-azidocarboxylates 1 with N-phthaloyl-protected (R)- or (S)-amino acid chlorides 2 in presence of at least equimolar amounts of N-methyl-2-pyridone (4) as acylation catalyst. Esters of didehydro tripeptides 16 were obtained in a comparable procedure from the optically active amino acid chlorides 2 and 2-(2-azidoacyl)amino acid esters 15, which were prepared from 2-azidocarboxylic acids 12 or the corresponding chlorides 13 with 2-amino acid ester hydrochlorides (S)-14. - As an example, the unprotected (S)-alanly-didehydrovalin 20 was prepared from the didehydro dipeptide 18a without any racemization by hydrolysis of the benzyl ester and subsequent hydrogenolytic removal of the N-phthaloyl group.

Eine einfache Synthese von N-Carboxy-α,β-didehydro-α-aminosäure-anhydriden (4-Alkyliden-2,5-oxazolidindionen) (Aminosäuren ; 10)

α-Azidocarboxylic acids 1 react with phosgene in the presence of catalytic amounts of sodium perrhenate in dimethoxyethane at 85°C to give N-carboxy-α,β-didehydroamino acid anhydrides (4-alkylidene-2.5-oxazolidinediones) 2 in good yields.