Question

Propose a mechanism for the following reaction:

Short answer

The mechanism of the reaction is given below.

Step-by-step solution

Sigmatropic rearrangement

Sigmatropic reactions fall under the category of pericyclic reactions. The count of pi bonds does not change in this rearrangement. A change is observed in the position of the pi bonds.

These kinds of reactions possess great stereoselectivity.

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Predicting the mechanism of the given reaction

The mechanism of the reaction is shown below.

Mechanism of the given reaction

In the first step, the negative charge on N-methylpyridine-N-oxide attacks the carbonyl carbon of acetic anhydride forming the acetate ion.

In the second step, the acetate ion abstracts the hydrogen and forms an alkene group.

In the third step, an intramolecular rearrangement leads to the formation of the desired pyridine-substituted product.