Zur enantioselektiven Synthese von (2R)-Serin-methylestern oder (2R)-Serinen ausgehend vom Bislactimether von cyclo-(-L-Val-Gly-)

Abstract

The lithiated bis(1actim) ether 8a furnishes with aldehydes and ketones in good yields the addition products 11 with (3R) configuration. The asymmetric inductions at C-3 of 11 (d.e. values) amount to more than 95% with ketones, with aldehydes they are somewhat smaller. With unsymmetrical ketones or aldehydes C-3' also becomes a chiral center. For the (3R)-major diastereomers the "second induction" at C-3' varies from about 4 to about 87% (for benzaldehyde or isobutyraldehyde, respectively), preferably the (3R,3'S) epimers are formed. - Acid hydrolysis of 11 yields (besides methyl L-valinate) the (2R)-serine methyl esters 26. Their e.e. values correspond with the d.e. values of 11. - Dehydratation of 11 furnishes the "Hofmann olefins" 32 and/or the "Saytzeff olefins" 33 which can be transformed in various ways into optically active amino acids.