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Enantioselective synthesis of (R)-α-amino acids via heterocyclic intermediate-(3S)-2,5-dimethoxy-3-see-butyl-3, 6-dihydropyrazine (5), using L-isoleucine as chiral auxiliaryreagent and glycine as raw meterial, has been studied. The alkylation of compound 5 withbutyllithium affords its lithium derivative (6) according to the cardanion mechanism. Then 6reacts with alkyl halide RX (7) to give the alkylated products (8) with very high diastereo-selectivity. In this reaction, the group R of 7 enters trans to the see-butyl group at C-3, i. e.the (R)-configuration is induced at C-6 of 8. After hydrolysis the (R)-α-amino acid methylesters (9) are obtained.
Enantioselective synthesis of (R) -alpha-amino acids via heterocyclic intermediate- (3S) -2,5-dimethoxy-3-see-butyl-3,6- dihydropyrazine (5) using L-isoleucine as chiral auxiliary reagent and glycine as The raw material has been studied. The alkylation of compound 5 with butyllithium affords its lithium derivative (6) according to the cardanion mechanism. Then 6 facts with alkyl halide RX (7) to give the alkylated products (8) with very high diastereo-selectivity. In this reaction, the group R of 7 is trans-to the see-butyl group at C-3, iethe (R) -configuration is induced at C-6 of 8. After hydrolysis the (R) -alpha-amino acid methylesters (9) are obtained.