Isoxazolium enolates derived from α,β‐unsaturated and 1,3‐dicarbonyl compounds. The through‐space effect of the enolate moiety on the chemical shift of α‐protons

The reaction of 4‐phenyl‐3,5‐dihydroxyisoxazole with α,β‐unsaturated cyclic ketones and 1,3‐cyclic diketones was studied. β‐Substituted α,β‐unsaturated ketones give pairs of isomeric isoxazolium enolates. The remarkable influence of the heterocyclic betaine on the proton chemical shifts is discussed. 1,3‐Cyclic diketones reacted spontaneously with 4‐phenyl‐3,5‐dihydroxyisoxazole yielding isoxazolium enolate enols and enol ethers.