Transition‐Metal‐Free Synthesis of Enantioenriched Tertiary and Quaternary α‐Chiral Allylsilanes

Abstract

Access to enantioenriched tertiary and quaternary α‐chiral allysilanes without any transition‐metal catalyst is reported. This was achieved by enantioselective allylic displacement of γ‐silylated allylic bromides through Lewis base activation of Grignard reagents by a bidentate chiral NHC ligand. The process afforded both high γ‐regio‐ and enantioselectivity and is compatible with a wide range of silyl groups on the substrates.

Enantioselective Synthesis of α-Chiral Bicyclo[1.1.1]pentanes via Multicomponent Asymmetric Allylic Alkylation

“…Given the ability of chiral copper complexes and N -heterocyclic carbenes (NHCs) , to efficiently catalyze the enantioselective allylic alkylation of Grignard reagents, we envisaged this type of catalysis as a potential platform for a more straightforward access to α-chiral difunctionalized BCPs that would avoid the stoichiometric use of ZnCl 2 and the use of a precious transition metal catalyst (Scheme c). Importantly, while both copper and NHC catalysis have been employed in highly regio- and enantioselective allylic alkylation of primary and secondary Grignard reagents, the direct use of tertiary BCP–Grignard imposes an important selectivity challenge in the regio- and enantioselective formation of the desired branched product, as illustrated with the low selectivities observed in the few cases where the use of a tertiary Grignard reagent, such as t -BuMgBr, has been reported. , We report here the development of a three-component catalytic transition-metal-free enantioselective direct difunctionalization of [1.1.1]­propellane that proceeds through a chiral NHC-catalyzed allylic alkylation of an in situ prepared tertiary BCP–Grignard reagent and provides α-chiral BCPs with high levels of regio- and enantioselectivity.…”