Isomerization of oxime derivatives was researched in detail to find out the methods for the syn-anti isomerization of O-substituted oximes. Based on these findings were developed simple methods for the preparation of aza-heterocycles from both stereoisomers of oximes. Quinolines were synthesized from β-aryl ketone oximes by treatment with trifluoroacetic anhydride and 4-chloranil. γ,δ-Unsaturated O-methoxyacetyloximes were transformed to 2H-dihydropyrroles by reaction with methoxy-acetic acid.