The Birch reduction is a classic organic chemistry transformation that uses an alkali metal in liquid ammonia to reduce benzene rings to 1,4-cyclohexadienes.
The claim states a foundational chemical fact: the Birch reduction of benzene yields 1,4-cyclohexadiene using an alkali metal in liquid ammonia. This is a standard textbook reaction taught widely in organic chemistry and is considered common knowledge requiring no citation.