Merger of Visible Light Induced Oxidation and Enantioselective Alkylation with a Chiral Iridium Catalyst

Abstract

A single chiral octahedral iridium(III) complex is used for visible light activated asymmetric photoredox catalysis. In the presence of a conventional household lamp and under an atmosphere of air, the oxidative coupling of 2-acyl-1-phenylimidazoles with N,N-diaryl-N-(trimethylsilyl)methylamines provides aminoalkylated products in 61-93 % yields with high enantiomeric excess (90-98 % ee). Notably, the iridium center simultaneously serves three distinct functions: as the exclusive source of chirality, as the catalytically active Lewis acid, and as a central part of the photoredox sensitizer. This conceptionally simple reaction Scheme may provide new avenues for the green synthesis of non-racemic chiral molecules.

Asymmetric copper-catalyzed C-N cross-couplings induced by visible light

“…Its application in organic synthesis has therefore expanded rapidly during the past decades (1), most recently in the context of enantioselective photoredox catalysis with transition metals (2,3,4). With several recent noteworthy exceptions, each of which involves the α-functionalization of carbonyl compounds by a chiral iridium catalyst (5,6,7), the metal-catalyzed methods require two catalysts, a transition metal complex that undergoes photoexcitation and serves as a site for redox chemistry, as well as a separate chiral catalyst that effects enantioselective bond formation. Transition metal-free asymmetric photoredox catalysis has also been reported (8,9).…”

Exploiting Octahedral Stereocenters: From Enzyme Inhibition to Asymmetric Photoredox Catalysis

“…At the same time, this iridium enolate represents the key intermediate of the catalytic cycle by reacting with the reductively generated electron-deficient radicals in a stereocontrolled fashion. We subsequently demonstrated that these iridium complexes also catalyze photooxidative enantioselective a-aminoalkylations in air [47] and asymmetric radical/radical couplings [48] that are initiated by photoinduced electron transfer. In both cases, a single catalyst was sufficient for both the photoredox chemistry and the asymmetric catalysis.…”

Direkte asymmetrische Alkylierung von Ketonen: noch immer ein unerreichtes Ziel

“…[53] Als Alkylierungsreagentien wurden Benzyl-und Phenacylbromide sowie a-Silylamine eingesetzt. [53] Als Alkylierungsreagentien wurden Benzyl-und Phenacylbromide sowie a-Silylamine eingesetzt.…”