In connection with a search for more practical syntheses of DL-threonine, useful methods of converting the more readily available DL-allothreonine into its epimer were sought. A method of effecting the inversion was discovered and announced in a preliminary communication.3 While that paper was in press a report43 in the recent British literature on the same subject reached this country, and was followed later by a second article.415 We wish to elaborate at this time our previous communication on the method for the interconversion of DL-allothreonine and DL-threonine, which is also the basis of a higher yielding synthesis of the latter.The reaction of a-acylamido-/3-hydroxy compounds with dehydrating agents such as thionyl chloride and phosphorus chlorides to give oxazolines is of general application.6 Accordingly, 2phenyl-5-methyl-4-carbomethoxyoxazoline hydro-
Communications to the Editor 2297 powder is vigorously stirred under 1 liter ofrefluxing anhydrous ether. One mole of the alkoxybenzyl halide dissolved in 1 1. of ether is added over a two to five hour interval. The resulting Grignard reagent is then filtered through glass cotton to remove the finely divided magnesium powder, which if not removed usually reacts with objectionable vigor during the ultimate decomposition with water or dilute acid. The yield is estimated by the usual acidimetric titration.
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