Chemoselective Synthesis of 3-Bromomethyloxindoles via Visible-Light-Induced Radical Cascade Bromocyclization of Alkenes

A novel visible-light-induced radical cascade bromocyclization of N-arylacrylamides has been accomplished. This reaction overcomes the overbromination at the benzene rings suffered in traditional electrophilic reactions, thus enabling the first highly chemoselective synthesis of valuable 3-bromomethyloxindoles. The combination of pyridine and anhydrous medium is identified as the key factor for the high chemoselectivity in the current photoreaction system, which might work by suppressing the in situ generation of low-concentration Br2 from N-bromosuccinimide. Moreover, the mild reaction conditions ensure the generation of a wide range of the new desired products with excellent functional group tolerance.

Photoinduced radical cascade domino Heck coupling of N-aryl acrylamide with vinyl arenes enabled by palladium catalysis

Here, a redox-neutral palladium-catalyzed photo-induced radical cascade domino Heck reaction of N-aryl acrylamide with vinyl arenes is described. A diverse range of bioactive oxindoles, featuring an all-carbon quaternary center, were synthesized. The reaction is proposed to proceed via an open-shell intermediate and occurs under mild reaction conditions, exhibiting excellent functional group tolerance. Importantly, the synthesized products can be readily transformed into biologically active molecules, including (±)-physostigmine and (±)-physovenine.

Palladium-Catalyzed Decarboxylative O-Allylation of Phenols with γ-Methylidene-δ-valerolactones

A novel Palladium-Catalyzed decarboxylative O-allylation of phenols was developed, in which a γ-methylidene-δ- valerolactone (GMDVs) was found to be an efficient and selective allylation reagent, affording the target allyl phenyl...

Photoinduced arylation of chloroarenes in flow: synthesis of unsymmetrical biaryls

A photoflow cross-coupling reaction of unactivated arenes and aryl chlorides is developed for the synthesis of unsymmetrical biaryl products.

Photoinduced Cross-Coupling of Aryl Iodides with Alkenes

A protocol for photoinduced cross-coupling of aryl iodides having polar π-functional groups or elongated π-conjugation with alkenes has been developed. The radical cascade mechanism involving generation of aryl radicals via C-I bond homolysis of photoexcited aryl iodides and their subsequent addition to alkenes is proposed. The method enables iodide-selective cross-coupling over other halogen leaving groups with functional group compatibility on both arene and alkene motifs.

Photo-induced transition-metal and external photosensitizer-free organic reactions

Photoreactions have become powerful synthetic tools with a broad scope of applications. This review mainly focuses on photoreactions in the absence of transition-metals and photosensitizers, and highlights the mechanisms of such reactions.

Metal-Free, N-Iodosuccinimide-Induced Regioselective Iodophosphoryloxylation of Alkenes with P(O)-OH Bonds

A simple and efficient method for the regioselective iodophosphoryloxylation of alkenes with P(O)-OH bonds has been established by using NIS (N-iodosuccinimide) as the iodination reagent under transition-metal-free conditions. The present protocol is compatible with different functional groups, and suitable for various alkenes and P(O)-OH compounds. A variety of functionalized β-iodo-1-ethyl phosphinic/phosphoric acid esters are obtained in good to excellent yields, which could be further transformed to diversified building blocks for the synthesis of bioactive compounds, pharmaceuticals and functional materials.

Metal-free insertion of sulfur dioxide with aryl iodides under ultraviolet irradiation: direct access to sulfonated cyclic compounds

Metal-free insertion of sulfur dioxide with aryl iodides and silyl enolates or allylic bromide under ultraviolet irradiation at room temperature is accomplished. This protocol provides a convenient route to sulfonated cyclic compounds under mild conditions.

Synthesis of 2-bromomethyl-2,3-dihydrobenzofurans from 2-allylphenols enabled by organocatalytic activation of N-bromosuccinimide

Activation of NBS in acetic acid and a catalytic amount of DBU promotes an intramolecular oxybromination of 2-allylphenols to produce highly aggregated value and densely functionalized 2-bromomethyl-2,3-dihydrobenzofurans.

Photoinduced synthesis of 2-sulfonylacetonitriles with the insertion of sulfur dioxide under ultraviolet irradiation

Metal-free insertion of sulfur dioxide with aryl iodides and 3-azido-2-methylbut-3-en-2-ol under ultraviolet irradiation at room temperature is achieved, giving rise to 2-(arylsulfonyl)acetonitriles in moderate to good yields. Alkyl iodide is also workable under these conditions. This transformation proceeds smoothly under mild conditions with a broad substrate scope. Various functional groups are compatible including amino, ester, halo, and trifluoromethyl groups. No metal catalyst or additive is needed during the reaction process. Mechanistic studies show that under ultraviolet irradiation, an aryl radical is generated in situ from aryl iodide, which undergoes subsequent sulfonylation via the insertion of sulfur dioxide leading to arylsulfonyl radical intermediates. Then the arylsulfonyl radical reacts with 3-azido-2-methylbut-3-en-2-ol giving rise to the corresponding 2-(arylsulfonyl)acetonitrile.

Aromatic Chemistry in the Excited State: Facilitating Metal-Free Substitutions and Cross-Couplings

Transition-metal-catalyzed cross-couplings between aromatic electrophiles and nucleophiles have revolutionized modern chemical syntheses. Nevertheless, transition-metal-free approaches are preferable, considering the various issues caused by metal catalysts. This Minireview summarizes the recent progress in the light-enabled transition-metal-free formation of carbon-carbon and carbon-heteroatom bonds in aromatics, which opens a new avenue in aromatic reactions. From the mechanistic perspective, it classifies different reaction types of aryl electrophiles in an excited state with various nucleophiles. We believe this will provide more rationales for metal-free aromatic substitutions and cross-couplings with light, and guide the development of novel transformations of aromatic compounds facilitated by light.

Synthesis of β-Sulfonyl Amides through a Multicomponent Reaction with the Insertion of Sulfur Dioxide under Visible Light Irradiation

A multicomponent reaction of styrenes, aryldiazonium tetrafluoroborates, sulfur dioxide, nitriles, and water in the presence of a photocatalyst at room temperature is performed. This vicinal aminosulfonylation of styrenes with the insertion of sulfur dioxide under visible light irradiation proceeds efficiently with excellent chemoselectivity, giving rise to the corresponding β-sulfonyl amides in moderate to good yields.

An efficient iodine pentoxide-triggered iodocarbocyclization for the synthesis of iodooxindoles in water

An efficient iodocarbocyclization of alkenes for the synthesis of iodooxindoles has been developed. This reaction proceeds in a chemoselective manner and shows excellent tolerance of various functional groups, including a chemosensitive hydroxymethyl group. Nonmetal inorganic iodine pentoxide was used as both the oxidant and iodine source, making this protocol very practical. On the basis of experimental observations, a plausible electrophilic reaction mechanism was proposed.

Photoinduced Transition-Metal-Free Cross-Coupling of Aryl Halides with H-Phosphonates

Photoinduced transition-metal- and photosensitizer-free cross-coupling of aryl halides (including Ar-Cl, Ar-Br, and Ar-I) with H-phosphonates (including dialkyl phosphonates and diarylphosphine oxides) is reported. Various functional groups were tolerated, including ester, methoxy, dimethoxy, alkyl, phenyl, trifluoromethyl, and heterocyclic compounds. This simple and green strategy provides a practical pathway to synthesize arylphosphine oxides.

Photoinduced synthesis of allylic sulfones using potassium metabisulfite as the source of sulfur dioxide

Synthesis of allylic sulfones through a photoinduced three-component reaction of aryl/alkyl halides, potassium metabisulfite, and allylic bromides under ultraviolet irradiation at room temperature is developed. Diverse allylic sulfones are generated in moderate to good yields.

Metal-catalyzed radical-type transformation of unactivated alkyl halides with C–C bond formation under photoinduced conditions

Recent advances in the metal-catalyzed radical-type transformation of unactivated alkyl halides with C–C bond formation under photoinduced conditions are summarized. Usually, a broad reaction scope is observed including tertiary, secondary, and primary alkyl halides, with good functional group compatibility.

An elimination/Heck coupling/allylation cascade reaction: synthesis of 2,3-dihydrobenzofurans from allenoate adducts

A highly regio- and stereoselective Pd-catalyzed cascade reaction of allenoate adducts has been developed. Various allenoate adducts of phosphine-catalyzed addition of allenoates are found to be efficient substrates for the preparation of 2,3-dihydrobenzofuran. It is the first example of allenoate adducts used as ideal and practical precursors of hard-to-get functionalized 1,3-butadienes for heterocycle synthesis.

Lucas FW, Santos MS, Corrêa AG, Nascimento OR, Jiang H, Paixão MW. Intramolecular radical cyclization approach to access highly substituted indolines and 2,3-dihydrobenzofurans under visible-light

The combination of visible-light and tris(trimethylsilyl)silane promoting intramolecular reductive cyclization protocol for the synthesis of functionalized indolines and 2,3-dihydrobenzofurans has been developed. The transformations occur in the absence of transition metal and additional photocatalyst. In addition, quantum yield (Φ) was determined and electron paramagnetic resonance spectroscopy was performed to better understand the reaction pathway.

The combination of visible-light and tris(trimethylsilyl)silane promoting intramolecular reductive cyclization protocol for the synthesis of functionalized indolines and 2,3-dihydrobenzofurans has been developed.

Photoinduced, Copper-Promoted Regio- and Stereoselective Decarboxylative Alkylation of α,β-Unsaturated Acids with Alkyl Iodides

The first example of UV light-induced, copper-catalyzed regio- and stereoselective decarboxylative coupling of α,β-unsaturated acids with alkyl iodides was reported. Under standard conditions, the 1°, 2°, and 3° alkyl iodides proceeded smoothly with the E-selective alkenes obtained in uniformly good yields and high stereoselectivities.

Rh(iii)-Catalyzed direct C-7 amination of indolines with anthranils

An effective and fascinating method has been developed for direct C-7 amination of indolines under Rh(iii) catalysis with anthranils.

Synthesis of Functionalized 6-Hydroxy-2-oxindole Derivatives by Phenoxide Cyclization

An apparent intramolecular cross-dehydrogenative coupling of N-(3-hydroxy)monoanilide of maleic esters comprising base promoted phenoxide cyclization and subsequent base-mediated aerobic oxidation was developed to synthesize a variety of 2-(6-hydroxy-2-oxoindolin-3-ylidene)acetate derivatives. The isolation of intermediate cyclized products during the large scale reactions and their ready dehydrogenation with 1 equiv of base support this proposed two-step path.