Cyclohexanone is treated with (i) pyrrolidine, $\mathrm{H}{}^{+}$ cat., remove water; (ii) $\mathrm{CH}{}_3\mathrm{I}$; (iii) aqueous $\mathrm{H}{}_3\mathrm{O}{}^{+}$. The final product is

Step (i) gives the enamine. The nucleophilic enamine beta-carbon (ring carbon 2) is alkylated by $\mathrm{CH}{}_3\mathrm{I}$ to give an iminium salt (Stork enamine alkylation). Aqueous acid hydrolyses the iminium to the ketone, giving 2-methylcyclohexanone and recovering pyrrolidine.