Catalytic Asymmetric Allylic Substitution with Alkynylogous Silyl Enol Ethers En Route to Chiral Allenes

Abstract

Abstract Despite their potential as building blocks of allenes, alkynylogous enol silanes have rarely been employed in organic synthesis. Herein, we establish their utility as nucleophiles in catalytic asymmetric allylic substitution, which results in skipped enallenes bearing two vicinal stereogenic elements (axial and central chirality). This iridium-catalyzed reaction utilizes α-alkynyl silyl enol ethers as alkynylogous nucleophile for reaction with easily accessible racemic branched allylic alcohols and endows tetrasubstituted axially chiral allenones, bearing a δ-stereocenter exclusively as a single regioisomer in moderate to good diastereoselectivity (up to 11:1 dr) and in most cases with high enantioselectivity (up to >99.5:0.5 er). The densely functionalized γ-allylic allenones can be elaborated into useful building blocks, including a highly substituted chiral 2-allyl furan derivative. Through this work, α-alkynyl enol silanes are introduced as alkynylogous nucleophiles in transition metal catalysis.