Synthesis of racemic (E)- and (Z)-1-amino-2-phenylcyclopropanecarboxylic acid: (E)- and (Z)-cyclopropylphenylalanine

Both E and Z "cyclopropylogs" of DL-phenylalanine ( Delta super(E)-Phe and Delta super(Z)-Phe) have been prepared by the cyclopropanation of each 4-benzylidene-2-phenyl-5(4H)-oxazolone isomer with diazomethane to form the three-membered ring. Opening of the oxazoline ring to give the benzyl ester followed by debenzoylation using Meerwein's reagent gave the benzyl ester hydrochloride of DL- Delta super(Z)-Phe. Hydrogenation gave the free amino acid in good yield. Isomerization of the (Z)-oxazolone to the E isomer followed by cyclopropanation and methyl ester formation gave N-Bz-DL- Delta super(E)-PheOMe. Debenzoylation and conversion to the N-Boc methyl ester followed. Saponification of the ester followed by Boc removal (HCl) gave DL- Delta super(E)-Phe hydrochloride in good yield.