Question

3,5-dimethylisoxazole is prepared by reaction of 2,4-pentanedione with hydroxylamine in the presence of catalytic H+. The mechanism involves the following steps:
1) Protonation of the carbonyl oxygen and nucleophilic attack by hydroxylamine form tetrahedral intermediate 1;
2) Proton transfer leads to protonated intermediate 2;
3) Elimination of water leads to protonated oxime 3;
4) Following proton transfer, nucleophilic attack by the oxime oxygen on the carbonyl carbon leads to cyclic intermediate 4;
5) Following proton transfer, elimination of water leads to protonated intermediate 5;
6) Elimination of a proton and electron rearrangement leads to the final product.
Write out the reaction mechanism on a separate sheet of paper, and then draw the structure of protonated oxime 3.

Answer 1

Answer: see the graphic