Nucleophile Ringöffnung von 1‐Nitro‐1‐cyclopropancarbonsäure‐arylestern mit sterisch geschützter, aber elektronisch wirksamer Carbonyl‐ und Nitrogruppe. Ein neues Prinzip der Aminosäuresynthese

Nucleophilic Ring Opening of Aryl 1‐Nitro‐1‐cyclopropanecarboxylate with Sterically Protected, but Electronically Effective Carbonyl and Nitro Group. A New Principle of Amino Acid Synthesis The readily available [2,6‐di‐(tert‐butyl)‐4‐methoxyphenyl] 1‐nitro‐1‐cyclopropanecarboxylate (4) is ring‐opened by nucleophilic attack of the amino groups of (S)‐α‐amino acid esters (products 20–26). Reduction of the nitro group gives rise to derivatives 27–30 of 2,4‐diaminobutanoic acid which are connected with a second amino acid through the nitrogen in position 4 (2‐substituted 6‐amino‐3‐azaheptanedioic acids). In two cases, these were converted into enantiomerically and diastereomerically pure Freidinger's γ‐lactam dipeptides (31, 32), which have previously been shown to mimic a peptide β‐turn.