Stereoselective Synthesis of cis- and trans-3,4,5-Trisubstituted-1,3-oxazolidin-2-one Derivatives from 1,2-Amino Alcohol Monoesters and Aziridine-2-carboxylates

New cis-N-alkyl-1,3-oxazolidin-2-ones were prepared in moderate to good yields via phosgenation of erythro-1,2-aminoalcohol monoesters, accompanied by formation of aziridine by-products. On the other hand, their regioisomers trans-N-alkyl-1,3-oxazolidin-2-ones were prepared regio- and stereoselectively in good yields by ring expansion of trans-N-alkyl aziridine-2-carboxylates.