Nucleophile Ringöffnung von α‐Nitrocyclopropancarbonsäure‐arylestern mit sterisch geschützter, aber elektronisch wirksamer Carbonyl‐ und Nitro‐Gruppe. Ein neues Prinzip der α‐Aminosäure‐Synthese (2‐Aminobutansäure‐a4‐Synthon)

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Abstract
Nucleophilic Ring Opening of Aryl α‐Nitrocyclopropanecarboxylates with Sterically Protected but Electronically Effective Carbonyl and Nitro Group. A New Principle of α‐Amino Acid Synthesis (2‐Aminobutanoic Acid a4‐Synthon)The readily available 2,4,6‐tri(tert‐butyl)‐and 2,6‐di(tert‐butyl)‐4‐methoxypahenol esters 2 of α‐nitrocyclo‐propanecarboxaylic acid ring opening with C‐, N‐, O‐, and S‐nucleophiles (cyanide, malonate, azide, anilines, alkoxides, phenoxides, thiolates) in DMF or alcohol solvents (80–95% yield). The products 6–14 are 2‐nitrobutanoates with the newly introduced substituent in the 4‐position. Reduction of the NO2 group with Zn/AcOH/Ac2O gives N‐acetyl‐α‐amino acid esters 16–22 (40–90% yield). Subsequent oxidative cleavage (H2O2/HCOOH) of The p‐methoxy‐phenyl esters 18 and 20 produces free amino acids (65% 23 and 67% 24, respectively). Thus, the nitro ester 2 corresponds to a 2‐aminobutanoic‐acid a4‐synthon, it is a ‘homo‐Michael acceptor’ producing γ‐substituted α‐amino acids.

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