Visible-light-induced intramolecular radical cascade of α-bromo-N-benzyl-alkylamides: a new strategy to synthesize tetracyclic N-fused indolo[2,1-a]isoquinolin-6(5H)-ones.

Polycyclic indole scaffolds are ubiquitous in pharmaceuticals and natural products and in materials science. Here, we present a visible-light-initiated intramolecular aryl migration/desulfonylation/cyclization cascade reaction for the synthesis of tetracyclic indolo[2,1-a]isoquinolin-6(5H)-ones. This protocol not only exhibited a wide substrate scope but also provided a mild route to access a variety of tetracyclic N-fused indoles.

Visible-Light-Induced Intermolecular Dearomative Cyclization of Furans: Synthesis of 1-Oxaspiro[4.4]nona-3,6-dien-2-one.

A fac-Ir(ppy)3-catalyzed intermolecular dearomative cyclization of 2-bromo-2-((5-bromofuran-2-yl)methyl)malonate and alkynes affording substituted spirolactones in yields of 19-91% via a 5- exo-dig radical cyclization under visible light is presented. This method provides a new access to the synthesis of spirocycle skeletons applying water as an external oxygen source under mild reaction conditions.

Visible-Light-Induced Radical Cascade Cyclization: Synthesis of the ABCD Ring Cores of Camptothecins.

A new strategy for constructing indolizino[1,2-b]quinolin-9(11H)-ones (ring cores of camptothecins) from readily available isocyanoarenes and N-(alkyl-2-yn-1-yl)pyridin-2(1H)-ones has been developed through a visible-light-induced radical cascade cyclization process. The reaction proceeds under mild conditions with fair to excellent yields. The easy introduction of substituents for both reactants and the broad functional group tolerance of the reaction make it a straightforward route to the cores of the marketed camptothecins and their derivatives.

Visible-Light-Induced Photocatalytic Aerobic Oxidation/Povarov Cyclization Reaction: Synthesis of Substituted Quinoline-Fused Lactones.

A one-step construction of quinoline-fused lactones was achieved by visible-light-induced photocatalytic aerobic oxidation/Povarov cyclization reaction. This method provides a new access to the synthesis of important fused heterocycles under mild reaction conditions.

Phenylene-coated magnetic nanoparticles that boost aqueous asymmetric transfer hydrogenation reactions.

Phenylene-coated organorhodium-functionalized magnetic nanoparticles are developed through co-condensation of chiral 4-(trimethoxysilyl)ethyl)phenylsulfonyl-1,2-diphenylethylene-diamine and 1,4-bis(triethyoxysilyl)benzene onto Fe3O4 followed complexation with [{Cp*RhCl2}2]. This magnetic catalyst exhibits excellent catalytic activity and high enantioselectivity in asymmetric transfer hydrogenation in aqueous medium. Such activity is attributed to the high hydrophobicity and the confined nature of the chiral organorhodium catalyst. The magnetic catalyst can be easily recovered by using a small external magnet and it can be reused for at least 10 times without loss of its catalytic activity. This characteristic makes it an attractive catalyst for environmentally friendly organic syntheses.

Visible-light-induced cascade dearomatization cyclization between alkynes and indole-derived bromides: a facile strategy to synthesize spiroindolenines.

A visible-light-initiated intermolecular dearomatization cyclization cascade reaction between alkynes and indole-derived bromides has been explored. This transformation exhibits a wide substrate scope and significant functional group tolerance, providing an efficient way to access a variety of spiroindolenines under mild conditions.

Sodium Sulfite-Involved Photocatalytic Radical Cascade Cyclization of 2-Isocyanoaryl Thioethers: Access to 2-CF2/CF3-Containing Benzothiazoles.

A visible-light-induced radical cascade cyclization of 2-isocyanoaryl thioethers for the synthesis of 2-CF2/CF3-containing benzothiazoles has been developed. Sodium sulfite can participate in the photocatalytic cycle as a reductant that efficiently transforms Ir4+ into Ir3+ to promote the fluoroalkylation under mild reaction conditions.

Visible-light-induced radical cascade cyclization of oxime esters and aryl isonitriles: synthesis of cyclopenta[b]quinoxalines.

A visible-light-induced radical cascade cyclization of aryl isonitriles and cyclobutanone oxime esters for the synthesis of cyclopenta[b]quinoxalines has been accomplished for the first time. The key to the success of this process was the integration of the in situ-formed nitrile radical followed by the cascade radical isonitrile/nitrile insertion-cyclization. The easy introduction of substituents for both substrates and the high functional group tolerance of the reaction make it an efficient strategy to give various quinoxaline derivatives in moderate to good yields.

Combining Visible-Light-Photoredox and Lewis Acid Catalysis for the Synthesis of Indolizino[1,2-b]quinolin-9(11H)-ones and Irinotecan Precursor.

One-step construction of substituted indolizino[1,2-b]quinolin-9(11H)-ones was achieved by combining visible-light-photoredox and Lewis acid catalysis for an intramolecular Povarov cycloaddition reaction under mild conditions. In this catalytic process, the visible-light-promoted dehydrogenation protocol of tetrahydroquinolines constitutes the key procedure. Moreover, this method can be applied to the formal synthesis of the precursor of irinotecan, which exhibited good anticancer activities.

Visible-Light-Induced Intermolecular Dearomative Cyclization of 2-Bromo-1,3-dicarbonyl Compounds and Alkynes: Synthesis of Spiro[4.5]deca-1,6,9-trien-8-ones.

A visible-light-induced photocatalytic intermolecular dearomative cyclization of 2-bromo-1,3-dicarbonyl compounds and alkynes afforded biologically important spirocarbocycle structures in moderate to good yields via a 5-exo-dig radical cyclization under mild reaction conditions. A 5.0 mmol scale dearomatization reaction proceeded smoothly with 95% yield even when the catalyst loading was reduced to 0.1 mol %, suggesting that this method was suitable for large-scale synthesis.

Synthesis of 3-CF2-Containing Chromones via a Visible-Light-Induced Radical Cascade Reaction of o-Hydroxyaryl Enaminones.

A general and efficient visible-light-induced CF2 radical-based cascade reaction of o-hydroxyaryl enaminones has been described. This protocol afforded the corresponding functionalized 3-CF2-containing chromones in generally good yields under mild reaction conditions. The use of NaHSO3, which has both basicity and reducibility, efficiently suppressed the formation of two byproducts, 4H-chromen-4-one and 3-bromo-4H-chromen-4-one.

Enantio-relay catalysis constructs chiral biaryl alcohols over cascade Suzuki cross-coupling-asymmetric transfer hydrogenation.

The construction of chiral biaryl alcohols using enantio-relay catalysis is a particularly attractive synthetic method in organic synthesis. However, overcoming the intrinsic incompatibility of distinct organometallic complexes and the reaction conditions used are significant challenges in asymmetric catalysis. To overcome these barriers, we have taken advantage of an enantio-relay catalysis strategy and a combined dual-immobilization approach. We report the use of an imidazolium-based organopalladium-functionalized organic-inorganic hybrid silica and ethylene-coated chiral organoruthenium-functionalized magnetic nanoparticles to catalyze a cascade Suzuki cross-coupling-asymmetric transfer hydrogenation reaction to prepare chiral biaryl alcohols in a two-step, one-pot process. As expected, the site-isolated active species, salient imidazolium phase-transfer character and high ethylene-coated hydrophobicity can synergistically boost the catalytic performance. Furthermore, enantio-relay catalysis has the potential to efficiently prepare a variety of chiral biaryl alcohols. Our synthetic strategy is a general method that shows the potential of developing enantio-relay catalysis towards environmentally benign and sustainable organic synthesis.