Anisole is reduced with Na in liquid $\mathrm{NH}{}_3$ and ethanol, and the crude product is then stirred briefly with cold, dilute aqueous oxalic acid so that no double-bond migration occurs. The major product is

Birch reduction gives 1-methoxycyclohexa-1,4-diene, an enol ether. Mild acid hydrolysis converts the enol ether carbon to C=O, leaving the other double bond at the position originally 1,4 to it, which is the beta,gamma-unsaturated ketone cyclohex-3-en-1-one. Only strong acid with heat would isomerise it to the conjugated cyclohex-2-en-1-one.