Abstract
Several reactions of azlactones were explored in order to find a new method for extending carbon chains utilizing the 4-position of 2-oxazolin-5-one derivatives. Treatment of 4-ethoxymethylene-2-phenyl-2-oxazolin-5-one (I) with phenylethynylmagnesium bromide (IIa) gave a ring opened product, ethyl 2-benzoylamino-5-phenyl-2-penten-4-ynoate (IIIa). The reaction of I with diethyl 3-oxoglutarate (X) in benzene in the presence of sodium hydride afforded ethyl 3-carbethoxy-5-benzoylamino-β-resorcylate (XI), whereas 3-benzoylamino-5-carbethoxy-6-carbethoxymethyl-2H-pyran-2-one (XII) was obtained when this reaction was carried out in methylene dichloride using triethylamine as a catalyst. Analogously, 3-benzoylamino-5-cyano-6-phenyl-2H-pyran-2-one (XIV) was synthesized by the reaction of I with 5-phenylisoxazole (XIII). The reaction of 2-phenyl-2-oxazolin-5-one (XVI) with benzoylacetylene (XVII) in acetic anhydride gave 3-benzoylamino-6-phenyl-2H-pyran-2-one (XVIII).
