The synthesis of several 4-alkylidene-and 4-cycloalkylideneisoxazol-&ones is described and their tautomerism is investigated by 13C NMR,'H NMR, and IR spectroscopy. Through hydrogen shifts involving the exocyclic substituent (2-propylidene, cyclopentylidene, or 24ndanylidene) these compounds can exist in CH, NH, or OH forms (Scheme 11). The CH form is favored in solvents of low polarity (CDC13) and in the absence of special enthalpic ...
