Construction of Vicinal Quaternary Centers via Iridium-Catalyzed Asymmetric Allenylic Alkylation of Racemic Tertiary Alcohols

Enantioselective bond formation between sterically hindered fragments to furnish acyclic products with vicinal quaternary centers is a formidable challenge. We report a solution that involves cocatalysis between a chiral Ir-(phosphoramidite,olefin) complex and La(OTf)(3). This robust catalytic system effects highly enantioconvergent and regioselective alkylation of racemic tertiary alpha-allenyl alcohols with tetrasubstituted silyl ketene acetals. The transformation displays broad functional group tolerance for both reaction components and allows efficient generation of beta-allenyl ester products in good yield and with excellent enantioselectivity. Furthermore, both the allene and ester functionalities were leveraged to upgrade the structural complexity of the products via a series of stereoselective metal-catalyzed functionalization reactions.

Automated summary

A robust catalytic system utilizing chiral Ir-phosphoramidite and La(OTf)(3) enables highly enantioselective alkylation reactions of racemic tertiary alpha-allenyl alcohols with tetrasubstituted silyl ketene acetals. The reaction displays broad functional group tolerance and allows efficient generation of beta-allenyl ester products with excellent enantioselectivity, which can be further upgraded in structural complexity via stereoselective metal-catalyzed functionalization reactions.