Asymmetric α-Alkylation With Activated and Unactivated Electrophiles by a Highly Productive and Recyclable Lewis Acid/Imidazolium Catalyst.

Asymmetric alkylation is widely used for the construction of α-stereogenic carbonyl compounds, yet existing catalytic protocols typically suffer from several issues: (1) a limitation to π-activated electrophiles, (2) the need for unsatisfying catalyst loadings, (3) a lack of catalyst recyclability, and (4) sophisticated catalyst structures requiring multi-step syntheses. Herein, an efficiently accessible, air-stable bifunctional Cu(II)/imidazolium catalyst (prepared over four steps without chromatographies in 74% yield) is reported that enables highly enantioselective α-alkylations of 1,3-dicarbonyls with unmet productivity (TON up to 1740). The catalyst exhibits broad electrophile compatibility, efficiently engaging π-activated and non-π-activated alkylation agents. Remarkably, stereoretentive allylation with (E)- and (Z)-configured allylbromides was achieved. The catalyst can be recycled over multiple cycles (10+) without loss of efficiency by a simple protocol. EPR proves formation of a Cu(II)-enolate as resting state, for which detailed DFT calculations show that it is structurally anchored by hydrogen-bonding to the imidazolium C(2)H. This feature is essential for stereodifferentiation of both enolate faces. A continuous mechanistic shift from S