Alkali metals in liquid ammonia in the presence of an alcohol reduce aromatic systems to 1,4-cyclohexadienes. These can be further elaborated into a host of derivatives. The availability of a wide variety of substituted aromatic compounds, either commercial or via synthesis, makes the Birch reduction an important tool in organic synthesis.
The reduction is initiated by addition of a solvated electron to the aromatic system to generate a radical anion, which is then protonated by an alcohol cosolvent to furnish a pentadienyl radical. … The function of the alcohol in the metal -NH, … is capable of isomerizing the 1,4-cyclohexadiene product…
Birch reduction of substrates containing methoxy or N,N-dimethylamino groups may be contaminated with appreciable amounts of conjugated products. In these cases, it is conceivable that the isomerization occurs during workup.