Abstract
A key intermediate, 2-isocyano-3-hydroxybutyrate (III) was isolated from a reaction of isocyanoacetate (I) with acetaldehyde (II) in the presence of Et3N. It was found that III was readily converted into 2-isocyanocrotonate (V) and 2-isocyano-2-(1'-hydroxyethyl)-3-hydroxy-butyrate (VI) which are undesirable compounds for the synthesis of threonine. However, by use of a metal catalyst (e. g. NiCl2 or PdCl2), the isocyano-hydroxy compound (III) was selectively converted into 5-methyl-4-alkoxycarbonyl-2-oxazoline (IV) which is an important precursor of threonine. Furthermore, chemical properties of IV were examined; the results suggested that cis-oxazoline was relatively sensitive to acid, base and heat.
On the basis of these results, the reaction of I with II was carried out using Et3N-PdCl2 as a catalyst to obtain threo-threonine (85% purity) in a good yield (85%).
