Construction\nof Vicinal Quaternary Centers via Ru-Catalyzed\nEnantiospecific Allylic Substitution with Lithium Ester Enolates

The installation\nof vicinal quaternary centers with absolute stereocontrol\nconstitutes a considerable challenge in organic synthesis. Herein,\nwe introduce a novel [Cp*Ru(MeCN)<sub>3</sub>]PF<sub>6</sub>/phenoxythiazoline\ncatalyst system that achieves enantiospecific allylic substitution\nof tertiary carbonates with α,α-disubstituted lithium\nester enolates to give products containing vicinal quaternary centers.\nNoteworthy features include the direct use of nonstabilized ester\nenolates, a class of nucleophiles which has rarely been used in transition\nmetal-catalyzed allylic substitution reactions. The approach is demonstrated\nfor a broad scope of tertiary electrophiles as well as ester enolates\nand accomplishes stereoretentive substitution with excellent conservation\nof ee (89–99%) and branched/linear regioselectivities (up to\n40:1).