2-Methylcyclohexanone is treated with a peroxy acid. The major product is

The more substituted ring carbon (C2, secondary and bearing the methyl) migrates in preference to the primary $\mathrm{CH}{}_2$ at C6. Oxygen is inserted between C1 and C2. In the lactone, numbering O as 1 and the carbonyl carbon as 2, the carbon attached to O and carrying the methyl is C7. The product is 7-methyloxepan-2-one.