From anisole to cyclohex-2-enone

The Birch reduction converts anisole into 1-methoxycyclohexa-1,4-diene, an enol ether. Under mildly acidic conditions (aqueous oxalic acid) the enol ether is hydrolysed to give cyclohex-3-enone, with the double bond unconjugated.

With a stronger acid or base, the double bond migrates into conjugation with the carbonyl, the more stable position, and cyclohex-2-enone is obtained. This sequence, applied to the methyl ethers of oestrogens, made it possible to prepare the 19-norsteroids of oral contraceptives.