Mechanochemical Birch Reductive Alkylation of Polycyclic Aromatic Hydrocarbons

Direct alkylation of unfunctionalized polycyclic aromatic hydrocarbons (PAHs) is crucial for tuning their solubility, processability, and electronic properties. However, classical Friedel–Crafts alkylation often fails to introduce primary or secondary alkyl groups because of carbocation rearrangement and overalkylation. This study reports lithium(0)‐mediated mechanochemical Birch reductive alkylation of PAHs using readily available alkyl fluorides. Vigorous ball milling of Li wire generated highly reactive aromatic anions at room temperature under ambient atmosphere. The process did not require solvents for solubilization, highly reactive but hazardous metals such as sodium(0) and potassium(0), or elevated reaction temperatures under an inert atmosphere. The developed method allows the introduction of diverse primary, secondary, chiral, and functionalized alkyl groups. Furthermore, combining the present method with previously developed mechanochemical cyclodehydrogenation/Birch reductive arylation provides streamlined access to complex functionalized PAHs.