Various 2-oxygen-substituted 2H-azirine-2-carboxylic acid derivatives were synthesized in high yields under mild conditions from readily available precursors, 2-halo-2H-azirines and OH-reagents having pK(a) values in the range of 3-10. This reaction is the first example of substitution at the azirine carbon atom for which an unusual S(N)2'-S(N)2' cascade mechanism was revealed.