In the last decade, photoredox catalysis has unlocked unprecedented reactivities in synthetic organic chemistry. Seminal advancements in the field have involved the use of well-studied metal complexes as photoredox catalysts...
Twelve naphthochromenone photocatalysts (PCs) were synthesized on gram scale. They absorb across the UV/Vis range and feature an extremely wide redox window (up to 3.22 eV) that is accessible using simple visible light irradiation sources (CFL or LED). Their excited‐state redox potentials, PC*/PC.− (up to 1.65 V) and PC.+/PC* (up to −1.77 V vs. SCE), are such that these novel PCs can engage in both oxidative and reductive quenching mechanisms with strong thermodynamic requirements. The potential of these bimodal PCs was benchmarked in synthetically relevant photocatalytic processes with extreme thermodynamic requirements. Their ability to efficiently catalyze mechanistically opposite oxidative/reductive photoreactions is a unique feature of these organic photocatalysts, thus representing a decisive advance towards generality, sustainability, and cost efficiency in photocatalysis.
The
first light-driven
method for the α-trifluoromethoxylation
of ketones is reported. Enol carbonates react with
N
-trifluoromethoxy-4-cyano-pyridinium, using the photoredox catalyst
4-CzIPN under 456 nm irradiation, affording the α-trifluoromethoxy
ketones in ≤50% isolated yield and complete chemoselectivity.
As shown by 29 examples, the reaction is general and proceeds very
rapidly under batch (1 h) and flow conditions (2 min). Diverse product
manipulations demonstrate the synthetic potential of the disclosed
method in accessing elusive trifluoromethoxylated bioactive ingredients.
Twelve naphthochromenone photocatalysts (PCs) were synthesized on gram scale. They absorb across the UV/Vis range and feature an extremely wide redox window (up to 3.22 eV) that is accessible using simple visible light irradiation sources (CFL or LED). Their excited‐state redox potentials, PC*/PC.− (up to 1.65 V) and PC.+/PC* (up to −1.77 V vs. SCE), are such that these novel PCs can engage in both oxidative and reductive quenching mechanisms with strong thermodynamic requirements. The potential of these bimodal PCs was benchmarked in synthetically relevant photocatalytic processes with extreme thermodynamic requirements. Their ability to efficiently catalyze mechanistically opposite oxidative/reductive photoreactions is a unique feature of these organic photocatalysts, thus representing a decisive advance towards generality, sustainability, and cost efficiency in photocatalysis.
Photocatalysis has
become a prominent tool in the arsenal
of organic
chemists to develop and (re)imagine transformations. However, only
a handful of versatile organic photocatalysts (PCs) are available,
hampering the discovery of new reactivities. Here, we report the design
and complete physicochemical characterization of 9-aryl dihydroacridines
(9ADA) and 12-aryl dihydrobenzoacridines (12ADBA) as strong reducing
organic PCs. Punctual structural variations modulate their molecular
orbital distributions and unlock locally or charge-transfer (CT) excited
states. The PCs presenting a locally excited state showed better performances
in photoredox defunctionalization processes (yields up to 92%), whereas
the PCs featuring a CT excited state produced promising results in
atom transfer radical polymerization under visible light (up to 1.21 Đ, and 98% I*). Unlike all the PC classes reported
so far, 9ADA and 12ADBA feature a free NH group that enables a catalytic
multisite proton-coupled electron transfer (MS-PCET) mechanism. This
manifold allows the reduction of redox-inert substrates including
aryl, alkyl halides, azides, phosphate and ammonium salts (E
red up to −2.83 vs SCE) under single-photon
excitation. We anticipate that these new PCs will open new mechanistic
manifolds in the field of photocatalysis by allowing access to previously
inaccessible radical intermediates under one-photon excitation.
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