"Birch reduction of monosubstituted benzenes could furnish either of two possible 1,4-cyclohexadienes … Generally, electron-donating groups (D) retard electron transfer and remain on unsaturated carbons. [D=-OH, -OR, -NR2, -SR, -PR2, -alkyl, -CH2OH, -CH2OR, -CO2R, -C(O)R, -CHO] … The reason why groups such as -C(O)R, -CHO, and -CO2R behave as electron-donating groups in this reaction is that they are reduced to -CH2O- … Electron-withdrawing groups (EWG) facilitate electron transfer and reside on saturated carbons.[EWG= -CO2H, -C(O)NH2, -aryl] … The carboxy group generally dominates the regiochemistry of the reduction when other substituents are present. The strong activation effect by the carboxyl group allows reduction to occur when only one equivalent of alcohol is present or even without an alcohol. In these cases, the intermediate dianion persists in solution and can be trapped with electrophilic reagents to generate a quaternary carbon center. … While ester groups are reduced competitively with the aromatic ring under the usual Birch conditions, addition of one or two equivalents of H2O or t-BuOH to NH3 before metal addition preserves the ester moiety."
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George S. Zweifel and Michael H. Nantz, Modern Organic Synthesis (2006), Ch. 5 : Functional Group Transformations: The Chemistry of Carbon-Carbon π-Bonds and Related Reactions
https://en.wikiquote.org/wiki/Birch_reduction
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