Construction of Vicinal Quaternary Centers via Ru-Catalyzed Enantiospecific Allylic Substitution with Lithium Ester Enolates

The installation of vicinal quaternary centers with absolute stereocontrol constitutes a considerable challenge in organic synthesis. Herein, we introduce a novel [Cp*Ru(MeCN)₃]PF₆/phenoxythiazoline catalyst system that achieves enantiospecific allylic substitution of tertiary carbonates with α,α-disubstituted lithium ester enolates to give products containing vicinal quaternary centers. Noteworthy features include the direct use of nonstabilized ester enolates, a class of nucleophiles which has rarely been used in transition metal-catalyzed allylic substitution reactions. The approach is demonstrated for a broad scope of tertiary electrophiles as well as ester enolates and accomplishes stereoretentive substitution with excellent conservation of ee (89-99%) and branched/linear regioselectivities (up to 40:1).