PPA-Mediated C–C Bond Formation: A Synthetic Route to Substituted Indeno[2,1-c]quinolin-6(7H)-ones

Triflic Acid-Promoted 1,2-Amino Migration Reactions in α-Arylaminoacrylamides: Access to Substituted β-Aminoamides

A straightforward synthesis of substituted β-aminoamides from α-arylamino-β-hydroxyacrylamides, α-arylamino-β-oxoamides, or their tautomeric mixture has been described. The (E)-enol triflate intermediates are readily generated in situ from these substrates in the presence of triflic anhydride (Tf2O) and triethylamine (Et3N) in a chemoselective manner and undergo triflic acid (TfOH)-promoted cyclization and ring-opening reactions with alcohols to deliver the desired products. The one-pot two-step synthetic protocol features the use of readily available starting materials, mild reaction conditions, high chemoselectivity, operational simplicity, and a wide range of synthetic potential of the products.

Anion Cascade Reactions. Part I: Synthesis of 3-Isoquinuclidones from a Nazarov-like Reagent

A simple and atom-economical one-step protocol is described for the synthesis of biologically valuable 3-isoquinuclidones. The method proceeds from the simple starting materials, α-acyl N-arylcinnamamides, and can be performed under mild conditions in the presence of tBuOK. The key steps of this process are the double Michael addition reaction of a Nazarov-like reagent and the subsequent intramolecular hemiamination. These flexible intermolecular reactions could be performed on a gram scale.

Synthesis of O-Heterocycle Spiro-Fused Cyclopentaquinolinones and Cyclopentaindenes through Visible Light-Induced Radical Cyclization Reactions

Presented herein is an effective and sustainable synthesis of O-heterocycle spiro-fused cyclopentaquinolinone and cyclopentaindene derivatives through light-driven cascade reactions of N-(o-ethynylaryl)acrylamides or 2-(2-(phenylethynyl)benzyl)acrylate with various O-heterocycles. Experimental mechanistic studies revealed that these reactions are initiated by visible light-induced radical formation from O-heterocycle and its regioselective addition onto the acrylamide or acrylate moiety followed by 6-exo-dig and 5-endo-trig cascade radical annulation, which is terminated by single electron oxidation and proton elimination. Compared with previously reported synthetic methods for similar purposes, this newly developed protocol has advantages such as a broad substrate scope, extremely mild reaction conditions, excellent atom-economy, high efficiency, and good compatibility with diverse functional groups. With all of these merits, this method is expected to find wide applications in the related research arena.

4-Aminoalkyl Quinolin-2-one Derivatives via Knorr Cyclisation of ω-Amino-β-Keto Anilides

In a high-yielding and solvent-free procedure N-ethoxycarbonyl protected ω-amino-β-keto anilides undergo Knorr cyclisation in neat polyphosphoric acid to provide straightforward route to 4-aminoalkyl quinolin-2-one derivatives with variable length of the alkyl chain.

Superelectrophiles: Recent Advances

Superelectrophiles are reactive species that often carry multiple positive charges. They have been useful in numerous synthetic methods and they often exhibit highly unusual reactivities. Recent advances in superelectrophile chemistry are discussed in this review.

Tf2O-Mediated Cyclization of α-Acyl-β-(2-aminopyridinyl)acrylamides: Access to N-Substituted 4H-Pyrido[1,2-a]pyrimidin-4-imines

A facile and efficient direct synthesis of N-substituted 4H-pyrido[1,2-a]pyrimidin-4-imines is developed from α-acyl-β-(2-aminopyridinyl)acrylamides mediated by triflic anhydride (Tf₂O) in the presence of 2-chloropyridine. This amide activation protocol features mild reaction conditions, simple execution, excellent yields, and high chemoselectivity, and is also applied to the synthesis of substituted 4H-pyrido[1,2-a]pyrimidin-4-ones via a practical one-pot procedure.

Physicochemical properties of a urea/zinc chloride eutectic mixture and its improved effect on the fast and high yield synthesis of indeno[2,1-c]quinolines

An environmentally friendly and efficient method for the synthesis of indeno[2,1-c]quinolines is developed using a urea/zinc chloride eutectic mixture as a green mildly acidic medium.

A controlled tandem transformation of conjugated enynones with arenes under superelectrophilic activation leading to aryl-substituted dienones and indenes

Under superelectrophilic activation in triflic acid (TfOH) and in the presence of arenes, 1,5-diarylpent-2-en-4-yn-1-ones lead to aryl-substituted indenes with yields up to 97%.

Synthesis of N-aryl 2-quinolinones via intramolecular C(sp2)–H amidation of Knoevenagel products

An efficient synthesis of N-aryl 2-quinolinones via K₂S₂O₈-mediated intramolecular C(sp²)–H amidation of Knoevenagel products was developed.

Tandem halogenation/Michael-initiated ring-closing reaction of α,β-unsaturated nitriles and activated methylene compounds: one-pot diastereoselective synthesis of functionalized cyclopropanes

An efficient one-pot synthetic route to highly substituted cyclopropanes has been developed from readily available α,β-unsaturated nitriles and doubly activated methylene compounds under very mild conditions in a highly diastereoselective manner, which involves halogenation, Michael addition and intramolecular ring-closing reaction sequences.

BF3·Et2O-mediated intramolecular cyclization of unsaturated amides: convenient synthesis of dihydroquinolin-2-one-BF2 complexes

A facile and efficient synthesis of substituted dihydropyridone–BF₂ complexes is developed via intramolecular cyclization of α-acyl acrylamides and α-acyl cinnamamides mediated by BF₃·Et₂O, respectively.