Nickel-catalyzed allylic alkylation with diarylmethane pronucleophiles: Reaction development and mechanistic insights

Abstract

Palladium-catalyzed allylic substitution reactions are among the most efficient methods to construct C-C bonds between sp3-hybridized carbon atoms. In contrast, much less work has been done with nickel catalysts, perhaps because of the different mechanisms of the allylic substitution reactions. Palladium catalysts generally undergo substitution by a "soft"-nucleophile pathway, wherein the nucleophile attacks the allyl group externally. Nickel catalysts are usually paired with "hard" nucleophiles, which attack the metal before C-C bond formation. Introduced herein is a rare nickel-based catalyst which promotes substitution with diarylmethane pronucleophiles by the soft-nucleophile pathway. Preliminary studies on the asymmetric allylic alkylation are promising. Just a softy: Contrary to what would be predicted, organosodium nucleophiles derived from diarylmethane pronucleophiles are shown to behave as soft nucleophiles in nickel-catalyzed allylic substitution reactions. This general reaction is demonstrated to proceed through a double inversion pathway. A promising asymmetric version is presented.