Transition-Metal-Free Cascade Approach toward 2-Alkoxy/2-Sulfenylpyridines and Dihydrofuro[2,3-b]pyridines by Trapping In Situ Generated 1,4-Oxazepine

Divergent Synthesis of Unsymmetrical Bis-heteroaryl Ketones via Base-Promoted Cascade Reactions of 1,2-Alkynedione-Derived N-Propargylic β-Enaminones

Herein we disclose a transition-metal-free, one-pot two-step strategy for the synthesis of unsymmetrical bis-heteroaryl ketones. N-propargylic β-enaminones generated by the Michael addition of propargylamines onto heteroaryl 1,2-alkynediones have been utilized as synthetic equivalents of pyridine or pyrrole scaffolds. The use of alcohol as a solvent resulted in the formation of 2-alkoxylated pyridine scaffold, whereas the use of DMSO promoted the formation of a pyrrole motif.

Ferrocenyl conjugated oxazepines/quinolines: multiyne coupling and ring-expanding or rearrangement

Ferrocenyl conjugated oxazepine/quinoline derivatives were presented through the reaction of hexadehydro-Diels-Alder (HDDA) generated arynes with ferrocenyl oxazolines under mild conditions via ring-expanding or rearrangement processes. Water molecule participated in this unexpected rearrangement process to produce quinoline skeletons, and DFT calculations supported a ring-expanding and intramolecular hydrogen migration process for the formation of oxazepine derivatives. Two variants of this chemistry, expanded the reactivity between ferrocenyl conjugated substances and arynes, further providing an innovative approach for the synthesis of ferrocene derivatives.

Metal-Free Cascade Formation of C-C and C-N Bond for the Construction of 3-Cyano-2-Pyridones with Insecticidal Properties

A straightforward and efficient methodology has been developed for the synthesis of 3-cyano-2-pyridones via the C-C and C-N bond formation processes. A total of 51 diverse 3-cyano-2-pyridone derivatives were obtained in moderate to excellent yields. This reaction featured advantages such as a metal-free process, wide functional group tolerance, simple operation, and mild conditions. A plausible mechanism for the reaction was proposed. 3-cyano-2-pyridones as ricinine analogues for insecticidal properties were evaluated, and the compound 3ci (LC50 = 2.206 mg/mL) showed the best insecticidal property.

Base-Promoted Annulative Difluoromethylenation of Enaminones with BrCF2CO2Et toward 2,2-Difluorinated 2,3-Dihydrofurans

A practical method for the synthesis of 2,2-difluorinated 2,3-dihydrofurans has been established via the [4 + 1] annulation of enaminones and BrCF₂CO₂Et with Na₂CO₃ promotion. This new protocol does not employ any transition metal reagent and enables the annulative difluoromethylation by the partial cleavage of the C═C double bond. In addition, the further treatment with hydrochloric acid in one pot leads to β-keto enoic acids (4-oxo-2-butenoic acids) via a formal enaminone C-N carboxylation.

Synthesis of 3-[(4-Nitrophenyl)thio]-Substituted 4-Methylene-1-pyrrolines from N-Propargylic β-Enaminones

A facile and efficient method for the synthesis of 3-[(4-nitrophenyl)thio]-substituted 4-methylene-1-pyrrolines is described. When treated with 4-nitrobenzenesulfenyl chloride in refluxing acetonitrile, N-propargylic β-enaminones produced α-sulfenylated N-propargylic β-enaminones, which, in the presence of sodium hydride or cesium carbonate, underwent nucleophilic cyclization to afford 4-methylene-3-[(4-nitrophenyl)thio]-1-pyrrolines in good to high yields. It was shown for the first time that on N-propargylic β-enaminone systems, α-sulfenylation dominates over the formation of thiirenium ion. This one-pot two-step process was found to be general for a variety of N-propargylic β-enaminones and demonstrated good tolerance to a diversity of aromatic and heteroaromatic groups with electron-withdrawing and electron-donating substituents. This process is also applicable to the cyclization of internal alkyne-tethered N-propargylic β-enaminones. The enrichment of 1-pyrroline core with an aryl sulfide moiety might exhibit potential for the synthesis of molecules of pharmacological interest.

A.E.Favorskii’s scientific legacy in modern organic chemistry: prototropic acetylene – allene isomerization and the acetylene zipper reaction

Alexei Evgrafovich Favorskii was an outstanding organic chemist who left a great scientific legacy as a result of long time and fruitful work. Most of the theoretically and practically important discoveries of A.E.Favorskii were made in the chemistry of acetylene and its derivatives. Nowadays, the reactions discovered by him, which include acetylene – allene isomerization, the Favorskii and retro-Favorskii reactions, the Favorskii rearrangement and the vinylation reaction, are widely used in industry and in laboratory synthesis. This review summarizes the main scientific achievements of A.E.Favorskii, as well as their development in modern organic chemistry. Much consideration is given to acetylene – allene isomerization as a convenient method for the synthesis of methyl-substituted acetylenes and to the acetylene zipper reaction as a synthetic tool for obtaining terminal acetylenes. The review presents examples of the application of these reactions in modern organic synthesis of complex molecules, including natural compounds and their analogues.

The bibliography includes 266 references.

Synthesis of 3-(2-quinolyl) chromones from ynones and quinoline N-oxides via tandem reactions under transition metal- and additive-free conditions

The synthesis of 3-(2-quinolyl) chromones from ynones and quinoline N-oxides via a sequential [3+2] cycloaddition/ring-opening/O-arylation reaction under transition metal- and additive-free conditions is reported.

Metal-Free Method for Direct Synthesis of Functionalized β-Ketoenamines

A new method for direct synthesis of β-ketoenamines was developed by a BF₃·OEt₂-catalyzed cyclization of 1-iodoalkyne and α-keto acid followed by an amine-mediated ring-opening in one pot. Its metal-free conditions allowed the easy synthesis of those products bearing the transition metal-sensitive functional groups. Its three-component process achieved wide range of functionalized products.

A new strategy for the synthesis of pyridines from N-propargylic β-enaminothiones

A new robust method for the synthesis of 2,4,5-trisubstituted pyridines with high efficiency and broad functional group tolerance is described.

A simple, tandem approach to the construction of pyridine derivatives under metal-free conditions: a one-step synthesis of the monoterpene natural product, (−)-actinidine

(−)-Actinidine, along with various diversely substituted pyridines were synthesized from simple starting materials, including natural products, using a mild and metal-free method.

Facile synthesis of 2-(2-aminobenzoyl)benzoic acids via a base-promoted aerobic cascade reaction

A novel base-promoted aerobic cascade reaction for the regiospecific synthesis of 2-(2-aminobenzoyl)benzoic acids under metal-free conditions is developed.

Synthesis of 2-Aminopyridines via a Base-Promoted Cascade Reaction of N-Propargylic β-Enaminones with Formamides

N-Substituted formamides as nucleophiles react with in situ-generated 1,4-oxazepines from N-propargylic β-enaminones followed by spontaneous N-deformylation to deliver densely substituted 2-aminopyridines in good yields (31-88%). The formyl group is found to be a superior traceless activating group of free amines and would ultimately be removed in situ. This reaction proceeds smoothly at room temperature, in the presence of NaOH as sole additive, without protection from the atmosphere and generates H₂O and sodium formate as byproducts.

Base-promoted amide synthesis from aliphatic amines and ynones as acylation agents through C-C bond cleavage

A new protocol for the synthesis of amides via base-promoted cleavage of the C(sp)-C(CO) bond of ynones with aliphatic primary and secondary amines under transition-metal-, ligand-, and oxidant-free conditions has been developed. This method exhibits a wide substrate scope, high functional group tolerance and exclusive chemoselectivity, as well as mild reaction conditions.

Base-promoted C–C bond cleavage for the synthesis of 2,3,4-trisubstituted pyrroles from N-propargyl β-enaminones

The synthesis of 2,3,4-trisubstituted pyrroles via base-promoted C–C bond cleavage reaction of N-propargyl β-enaminones is reported.