Enantioselective catalytic processes are promoted by chiral catalysts that can execute a specific mode of catalytic reactivity, channeling the chemical reaction through a certain mechanistic pathway. Here, we show how by simply using visible light we can divert the established ionic reactivity of a chiral allyl–iridium(iii) complex to switch on completely new catalytic functions, enabling mechanistically unrelated radical-based enantioselective pathways. Photoexcitation provides the chiral organometallic intermediate with the ability to activate substrates via an electron-transfer manifold. This redox event unlocks an otherwise inaccessible cross-coupling mechanism, since the resulting iridium(ii) centre can intercept the generated radicals and undergo a reductive elimination to forge a stereogenic centre with high stereoselectivity. This photochemical strategy enables difficult-to-realize enantioselective alkyl–alkyl cross-coupling reactions between allylic alcohols and readily available radical precursors, which are not achievable under thermal activation. [Figure not available: see fulltext.]
Catalytic asymmetric C–C cross-couplings enabled by photoexcitation
Mazzarella D.;
2021
Abstract
Enantioselective catalytic processes are promoted by chiral catalysts that can execute a specific mode of catalytic reactivity, channeling the chemical reaction through a certain mechanistic pathway. Here, we show how by simply using visible light we can divert the established ionic reactivity of a chiral allyl–iridium(iii) complex to switch on completely new catalytic functions, enabling mechanistically unrelated radical-based enantioselective pathways. Photoexcitation provides the chiral organometallic intermediate with the ability to activate substrates via an electron-transfer manifold. This redox event unlocks an otherwise inaccessible cross-coupling mechanism, since the resulting iridium(ii) centre can intercept the generated radicals and undergo a reductive elimination to forge a stereogenic centre with high stereoselectivity. This photochemical strategy enables difficult-to-realize enantioselective alkyl–alkyl cross-coupling reactions between allylic alcohols and readily available radical precursors, which are not achievable under thermal activation. [Figure not available: see fulltext.]File | Dimensione | Formato | |
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