Improved Method for Preparation of 3-(1H-Indol-3-yl)benzofuran-2(3H)-ones

3-(1H-Indol-3-yl)benzofuran-2(3H)-ones were efficiently accessed via polyphosphoric acid-mediated condensation of 3-(2-nitrovinyl)-1H-indoles with phenols.

Lossen rearrangement by Rh(III)-catalyzed C-H activation/annulation of aryl hydroxamates with alkynes: access to quinolone-containing amino acid derivatives

A convenient and robust method for the preparation of new CF₃-containing 2-quinolones has been developed via a Rh(III)-catalyzed C-H activation/Lossen rearrangement/annulation cascade of N-pivaloyloxy-arylamides with internal alkynes bearing an α-CF₃-α-amino acid moiety on the triple bond. This work expands the scope of valuable products that are available through C-H activation/annulation reactions of arylamides in organic synthesis.

Recent Advances in One-Pot Modular Synthesis of 2-Quinolones

It is known that 2-quinolones are broadly applicable chemical structures in medicinal and agrochemical research as well as various functional materials. A number of current publications about their synthesis and their applications emphasize the importance of these small molecules. The early synthetic chemistry originated from the same principle of the classical Friedländer and Knorr procedures for the preparation of quinolines. The analogous processes were developed by applying new synthetic tools such as novel catalysts, the microwave irradiation method, etc., whereas recent innovations in new bond forming reactions have allowed for novel strategies to construct the core structures of 2-quinolones beyond the bond disconnections based on two classical reactions. Over the last few decades, some reviews on structure-based, catalyst-based, and bioactivity-based studies have been released. In this focused review, we extensively surveyed recent examples of one-pot reactions, particularly in view of modular approaches. Thus, the contents are categorized as three major sections (two-, three-, and four-component reactions) according to the number of reagents that ultimately compose atoms of the core structures of 2-quinolones. The collected synthetic methods are discussed from the perspectives of strategy, efficiency, selectivity, and reaction mechanism.

Isolation and synthesis of cryptosanguinolentine (isocryptolepine), a naturally-occurring bioactive indoloquinoline alkaloid

Cryptosanguinolentine (isocryptolepine) is one of the minor naturally-occurring monomeric indoloquinoline alkaloids, isolated from the West African climbing shrub Cryptolepis sanguinolenta. The natural product displays such a simple and unique skeleton, which chemists became interested in well before it was found in Nature. Because of its structure and biological activity, the natural product has been targeted for synthesis on numerous occasions, employing a wide range of different strategies. Hence, discussed here are aspects related to the isolation of isocryptolepine, as well as the various approaches toward its total synthesis.

Step-economical synthesis of 3-amido-2-quinolones by dendritic copper powder-mediated one-pot reaction

The one-pot protocol by the dendritic copper powder-mediated Knoevenagel condensation/annelation is delineated here for the synthesis of 3-amido-2-quinolones. It is practical with moisture tolerance and easy setup, and is compatible with many functional groups under mild conditions. This method was applied for the preparation of the key intermediates of biologically relevant 3-amido-2-quinolones.

Synthesis of 3-substituted quinolin-2(1H)-ones via the cyclization of o-alkynylisocyanobenzenes

A facile synthesis of various functionalized 3-substituted quinolin-2(1H)-ones through Ag(i) nitrate-catalyzed cyclization of o-alkynylisocyanobenzenes is described. The reaction allows rapid and convenient access to 3-substituted quinolin-2(1H)-one scaffolds in moderate to good yields.

Nitrostyrenes as 1,4-CCNO-dipoles: diastereoselective formal [4+1] cycloaddition of indoles

An unusual reactivity of nitrostyrenes in phosphorous acid was discovered, which permits the employment of these readily available synthons as 1,4-CCNO-dipole surrogates in a highly diastereoselective (4+1)-cycloaddition of indoles to afford 4′H-spiro[indole-3,5′-isoxazoles] in a diastereomerically pure form.

Unexpected cyclization of 2-(2-aminophenyl)indoles with nitroalkenes to furnish indolo[3,2-c]quinolines

A novel synthetic route to the indoloquinoline core of the alkaloid isocryptolepine involving an unprecedented PPA-mediated reaction of 2-(2-aminophenyl)indenes with nitroalkenes is discovered.

Dual role of polyphosphoric acid-activated nitroalkanes in oxidative peri-annulations: efficient synthesis of 1,3,6,8-tetraazapyrenes

Electrophilically activated nitroalkanes play a dual role in the novel reaction with diaminoperimidines, promoting their oxidative peri-annulation to access tetraazapyrenes.

Direct reductive coupling of indoles to nitrostyrenes en route to (indol-3-yl)acetamides

A highly efficient one-pot method for the reductive coupling of indoles to nitrostyrenes in PPA doped with PCl₃ was developed. This method allows direct access to primary (indol-3-yl)acetamides, interesting as anti-cancer drug candidates.

Benzimidazoles and benzoxazoles via the nucleophilic addition of anilines to nitroalkanes

PPA-induced umpolung triggers efficient nucleophilic addition of unactivated anilines to nitroalkanes to produce N-hydroxyimidamides. The latter undergo sequential acid-promoted cyclocondensation with ortho-OH or ortho-NHR moieties to afford benzoxazoles and benzimidazoles, respectively.

Nitroalkenes as surrogates for cyanomethylium species in a one-pot synthesis of non-symmetric diarylacetonitriles

Nitroalkenes were used as synthetic equivalents of the cyanomethylium cation in a modular, one-pot synthesis of 2-(3-indolyl)acetonitriles and 2,2-diarylacetonitriles involving electrophilic functionalization of aromatic and heteroaromatic C–H bond.

Metal-free ring expansion of indoles with nitroalkenes: a simple, modular approach to 3-substituted 2-quinolones

3-Substituted 2-quinolones are obtained via a novel metal-free transannulation reaction of 2-nitroolefins with 2-substituted indoles in polyphosphoric acid.

Direct metal-free synthesis of diarylamines from 2-nitropropane via the twofold C–H functionalization of arenes

Synthesis of symmetric diarylamines via a twofold intermolecular electrophilic C–H functionalization of electron-rich arenes by umpolung-activated nitroalkane in polyphosphoric acid is demonstrated.

One-pot synthesis of benzoxazoles via the metal-free ortho-C–H functionalization of phenols with nitroalkanes

PPA-activated nitroalkanes are employed in the design of a one-pot cascade transformation involvingortho-C–H functionalization, by Beckman rearrangement, and condensation to produce benzoxazoles and benzobisoxazoles directly from phenols.