An Unusual Friedel–Crafts Reaction and Violation of the Markovnikov Rule in the Formation of an Adamantyl Arene

Yoshihara, Hiroki, Yagi, and Itami utilized an unusual Friedel–Crafts-like alkylation in the synthesis of an adamantane-annulated arene. The precursor was a 3° carbocation, which they proposed undergoes a Wagner–Meerwein shift to a 2° carbocation, which subsequently alkylates a benzene ring. This mechanism was supported by their DFT calculations. However, their choice of the B3LYP functional often finds false transition structures. A more appropriate functional showed that the alkylation occurs via a concerted reaction.