SYNTHESIS OF (3R, 6R)-3,6-DIALKYLPIPERAZIN-2,5-DIONE AND (3S, 6S)-3,6-DIALKYLPIPERAZIN-2,5-DIONE DERIVATIVES AS USEFUL INTERMEDIATES TO BOTH (R)-ALPHA-AMINO-ACID AND (S)-ALPHA-AMINO-ACIDS

The alkylation of 2 leads to a diastereomeric mixture where 4 is generally present in greater amounts than 3. The successive alkylation of 4 affords exclusively the cis derivative 7, while a cis/trans mixture is obtained from isomer 3. In alkaline solution, the trans isomer 6 suffers a total conversion into a 1:1 mixture of the cis isomers 5 and 7 easily separated by silica gel chromatography. The configurations of the introduced stereogenic centers at C-3 and C-6 have been assigned on the basis of H-1-NMR spectroscopic data. Cleavage of heterocyclic ring of 5 and 7 leads to the corresponding (R)- and (S)-alpha-aminoacids respectively. Therefore, the substrate 2 appears a very useful chiral template to synthetize enantiomerically pure alpha-amino acids.