Exploring the Reactivity of α-Lithiated Aryl Benzyl Ethers: Inhibition of the [1,2]-Wittig Rearrangement and the Mechanistic Proposal Revisited

By carefully controlling the reaction temperature, treatment of aryl benzyl ethers with tBuLi selectively leads to α‐lithiation, generating stable organolithiums that can be directly trapped with a variety of selected electrophiles, before they can undergo the expected [1,2]‐Wittig rearrangement. This rearrangement has been deeply studied, both experimentally and computationally, with aryl α‐lithiated benzyl ethers bearing different substituents at the aryl ring. The obtained results support the competence of a concerted anionic intramolecular addition/elimination sequence and a radical dissociation/recombination sequence for explaining the tendency of migration for aryl groups. The more favored rearrangements are found for substrates with electron‐poor aryl groups that favor the anionic pathway. Wittig cannot win: A full account for the selective α‐lithiation of aryl benzyl ethers is reported. By carefully controlling the reaction temperature, aryl α‐lithiobenzyl ethers are stable enough to be trapped by a wide variety of electrophiles leading to functionalized ethers. The mechanism of the expected [1,2]‐Wittig rearrangement in these α‐oxygen‐substituted organolithiums is discussed based on DFT calculations.